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Anesthesia defined:

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The total loss of sensation in a body part or in the whole body generally induced by the administration of a drug that depresses the activity of nervous tissue locally or generally.

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Hypnosis

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Artificially induced sleep or trance resembling sleep from which the patient can be aroused by sufficient stimuli

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Analgesia

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Freedom from or absence of pain

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Nocioception

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Physiological process that results in the conscious perception of pain Physical energy (stimuli) => electrical energy at peripheral nocioceptor (pain detector) Nocioceptors are sensitive to mechanical, thermal and chemical stimulation

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General Anesthesia

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Loss of consciousness in addition to loss of sensation. Ideal: Hypnosis, Hyporeflexia, Muscle relaxation, analgesia Single drug or combination of drugs

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Tranquilization

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Reduced anxiety and relaxation, but still aware of surroundings

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Sedation

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CNS depression and drowsiness Reduced awareness of surroundings Patient conscious, but calm Patient aroused with sufficient stimulation Terms are often interchanged

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Balanced Anesthesia

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Combining several drugs - polypharmacy - to induce anesthesia Reduce concentrations of drugs Usually combination of hypnotic drug, analgesic drug and muscle relaxant Also called "Multimodal Anesthesia

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Surgical Anesthesia

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Stage/plane of general anesthesia that provides unconsciousness, muscle relaxation and analgesia to allow surgery Stage III, plane II

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Routes of Anesthetic Administration

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Intravenous Intramuscular Inhalation Subcutaneous Regional Analgesia Intraperitoneal Rectal Intraosseous Oral Topical

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Indication for Chemical Restraint

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Surgery Radiography Cleaning/Grooming Bandaging, splinting, casting Dental prophylaxis Biopsy Catheterization Capture of exotic, wild or feral animals for therapeutic or diagnostic purposes Examination Control of seizures Behavior modification Euthanasia

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Goals of General Anesthesia

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Enter patient into state of controlled and reversible unconsciousness Absence of pain perception, memory, motor response to stimuli or reflex responses Achieve this state without causing significant adverse effects on patient's organ systems Safe anesthesia is achieved through appropriate selection drugs, careful administration and constant monitoring

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Safety

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Evaluate patient and drug selection Gather information for DVM Observe patient in hospital Understand advantages and disadvantages of anesthetic drugs Know how to safely administer these drugs, possible complications, how to monitor patient under general anesthesia

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Record Keeping

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Controlled Substance Logs Patient Records Surgery Logs

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Patient Records

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Record all drugs given, for example Name Sid Schaming Amount Ex: Propofol 10mg (1mL) Route IV Record procedure Dental prophylaxis

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Surgery Logs

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Record Date Patient identification Procedure Surgeon Anesthetist Anesthetic protocol Health status

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ASA 1 :

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Normal, healthy patient.

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ASA 2 :

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Mild systemic disease.

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ASA 3:

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Severe systemic disease.

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ASA 4 :

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Severe systemic disease that is a constant threat to life.

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ASA 5 :

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Moribund patient not expected to live without the surgery.

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Autonomic Nervous System

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Responsible for involuntary control of heart, glands and smooth muscles of body Divided into Sympathetic and Parasympathetic Anesthetic drugs may be agonists or antagonists to receptor sites

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Sympathetic System Primary neurotransmitter:

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epinephrine and norepinephrine Fight or flight response Helps body cope with emergency situations

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Sympathetic System

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In response to a scary situation animal needs to move fast. Muscle work hard. Oxygen need for muscles bronchodilation Blood need to carry oxygen Increase Heart rate and cardiac output. Vasodilation of muscle vessels. Constriction of others. Mydriasis

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Mydriasis

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- increases peripheral vision

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4 basic receptors

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Alpha - 1 Stimulation causes blood vessels to constrict Alpha - 2 Stimulation inhibits release of NE causing sedation, decreased heart rate and blood pressure Beta - 1 Stimulation causes increased heart rate and contractile force Beta - 2 Stimulation causes smooth muscle relaxation and bronchodilation

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Alpha - 1

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Stimulation causes blood vessels to constrict

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Alpha - 2

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Stimulation inhibits release of NE causing sedation, decreased heart rate and blood pressure

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Beta - 1

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Stimulation causes increased heart rate and contractile force

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Beta - 2

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Stimulation causes smooth muscle relaxation and bronchodilation

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Parasympathetic System

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"Rest and restore" or "Rest & digest" Returns body to resting state after excitement and helps body store up for emergency situations

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Parasympathetic System Neurotransmitter -

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acetylcholine

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Parasympathetic System Neurons known as cholinergic 2 types:

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Nicotinic and muscarinic

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Effects of acetylcholine on specific organs:

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Heart: slows HR Salivary glands: increases salivation Gastrointestinal motility, secretions and blood flow: increases Eyes: cause pupillary constriction Anticholinergic drugs can inhibit this activity

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Role of the Veterinary Anesthetist

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Minimum patient database Proper patient fasting Preinduction patient care All supplies are available All equipment is in working order Preanesthetic medication

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Communication is Important

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Makes clients feel more comfortable and less anxious Clients are more confident in your work Good communication shows you care An informed client can better handle unexpected results

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Minimum Patient Database (MPD)

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Patient history Physical examination and assessment Preanesthetic diagnostic workup

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Confirm the Scheduled Procedure

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Verbally Prevents tragic accidents Anesthetizing the wrong patient Performing an unnecessary procedure. Not performing a scheduled procedure. Know the specifics: Exact location of tumors Exact location Owner's wishes regarding cytology or histology Owner's wishes regarding decisions during the procedure

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Patient History

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Information obtained from the client Know what questions to ask and how to ask them: Yes-no questions Leading questions = bad Open ended questions. In addition to information given freely, determine the following: Duration Severity or volume Frequency Appearance or character

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Patient History—Signalment Species

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Species have unique responses to anesthetic agents Horses and cats—opioids Dosing requirements Recovery—horses Anticholinergics avoided in ruminants Ventilation support—large animals Excess airway secretions—cats and ruminants Exotic animals are handled differently

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Patient History—Signalment Breed

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Differences in anatomy and physiology Sighthounds - sensitive to barbiturates Boxers and giant breeds - sensitive to acepromazine Terriers - resistant to acepromazine Brachiocephalic dogs - difficult to intubate Draft horses - sensitive to sedatives

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Patient History—Signalment Age

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Plays a factor in drug choice Neonates and pediatric patients Geriatric patients

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Patient History—Signalment Sex and reproductive status

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Male or female Intact or neutered Used for breeding? Pregnant Stallions—acepromazine Pregnant cows and ewes—xylazine

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Patient History—Medications

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Current or past May influence effect of anesthetic agents Sympathomimetics Tricyclic antidepressants Antibiotics Monoamine oxidase inhibitors Antihistamines

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Patient History—Allergies/Drug Reactions

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Record in the history to prevent future administration Past adverse reactions to anesthetic agents Cats—prolonged ketamine recovery Dogs—behavioral change after acepromazine sedation

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Patient History—Preventive Care

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Vaccination—date and type Fecal analysis and parasite control Heartworm status—dogs FLeV and FIV testing—cats Tetanus toxoid—horses

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Patient History—Past/Current Illnesses

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Preexisting disease: Anorexia, vomiting, diarrhea, coughing, sneezing, polyuria, polydipsia, tenesmus, dysuria. General signs of illness: Stabilized prior to anesthesia. Change in behavior: CNS disorder Pain Systemic illness. Exercise intolerance: Heart disease Anemia Musculoskeletal pain. Weakness: A nonspecific sign. Fainting or seizures: Often difficult to differentiate. Unexplained bleeding: Bruising Blood in feces or urine Prolonged bleeding after injury. Associated with coagulation disorders

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Sistalic pressure

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Pressure on the arterial wall while the heart is beating.

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Diastalic pressure

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Pressure while the heart is relaxed.

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Other Considerations

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Written estimate. Signed consent form: Legally necessary Informs of risks Owner's daytime phone number Permission to perform CPCR Lists extralabel drugs used

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Physical Examination/Physical Assessment

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Examine the entire patient. Use a consistent technique: Head to tail Organ system

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Patient Identification

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Cage tags Patient identification collars Document external characteristics in medical record

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Body Weight

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Must be accurate for proper dosing: <5 kg use a pediatric scale <1 kg use a gram scale Horses—estimated weight body weight (kg) = heart girth (cm)2 × length (cm) 11880 Weigh animals immediately before anesthetic procedure Compare current weight with previously recorded weight

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Body Condition Score

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Assessment of patient weight to the ideal weight. A numeric assessment: 1-9 scale 4-5 in dogs or 5 in cats is the ideal weight 1 is extreme cachexia; 9 is extreme obesity 1-5 scale 3 is the ideal weight 1 is extreme cachexia; 5 is extreme obesity

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Hydration Assessment

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Skin turgor Placement of eye in orbit Mucous membrane color, refill time, moisture level Heart rate and pulse strength Young and obese patients appear more hydrated Old and cachectic patients appear less hydrated Panting dries the mucous membranes

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Level of Consciousness (LOC)

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To assess brain function Patient's responsiveness to stimuli Healthy patients: alert, responsive, bright or quiet Lethargic (lethargy) Obtunded (obtundity) Stuporous (stupor) Comatose (coma)

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Pain Score

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Assess patient's level of pain To help select preanesthetic and anesthetic agents

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Body Temperature

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Use a rectal thermometer Elevated = inflammation Decreased = numerous systemic disorders What is the normal body temperature in the dog and cat?

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General Condition

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Visual examination from a distance Gait Temperament Anxious or excited? Or ill? Activity level Exercise intolerance Weakness Will affect choice of anesthetic agents and methods of administration

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Exterior Surfaces

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Hair coat Skin Lymph nodes and mammary glands: Visual and manual examination Body openings: Odors and discharges Eyes, ears, nose, oral cavity (throat) EENT

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Pupillary Light Reflex (PLR)

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Normal—pupils are the same size Direct reflex Consensual reflex

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Cardiovascular System Examination—Heart Rate

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Measured as beats per minute (bpm) Auscultation of left chest wall Large animal patients vs. small animal patients Obese animals, panting dogs, purring cats Pediatric patients Exercise or stress of handling

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Cardiovascular System Examination—Heart Rhythm

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Evaluation of the heart rate Normal sinus rhythm (NSR): No rhythm irregularities Sinus arrhythmia (SA): Dogs, horses, ruminants Heart rate is affected by respiration

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First degree atrioventricular (A-V) heart block

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Delayed conduction through the A-V node Detected only on ECG tracing

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Second degree A-V heart block

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Periodic block of conduction through the A-V node Results in skipped heartbeats

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Cardiovascular System Examination—Murmurs

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Listen over each valve: Cranial-most aspect of left axilla—PDA Caused by blood flow turbulence May result in increased patient anesthetic risk

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Cardiovascular System Examination—Pulse

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Pulse palpation points Dogs and cats—femoral artery Large animals—facial artery, ventral tail artery, or auricular artery Pulse deficit

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Cardiovascular System Examination—Mucous Membrane Color

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Mucous membrane color Gingiva at base of tooth Alternate sites Capillary refill time (CRT) Normal = <2 seconds

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Respiratory System Examination—Respiratory Rate

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Measured in breaths per minute (bpm) Evaluated visually Inversely proportional to body size

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Respiratory System Examination—Breathing Character

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Effort: Dyspnea and cyanosis Relative length of inhalation and exhalation Regularity of inhalation and exhalation Inhale - exhale - rest - inhale -exhale -rest

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Abdominal Palpation and Auscultation

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Normal is soft and not painful Abdominal distention Borborygmus—large animals Rumen contraction—ruminants

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Preanesthetic Diagnostic Workup

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No one standardized diagnostic workup fits every patient. Geriatric Elective surgery Sick patient Workup based on age, history, and physical examination Workup based on financial considerations

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Preanesthetic Diagnostic Testsand Procedures

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Complete blood count (CBC) Urinalysis Blood chemistry Blood coagulation screens Electrocardiogram (ECG) Radiography Other

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Physical Status Classification

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Classification is based on an evaluation of the Minimum Patient Database Rates patient anesthetic risk: American Society of Anesthesiologists Class P1 = minimal anesthetic risk Class P5 = extreme anesthetic risk Classes P1 and P2 use standard anesthetic protocol Classes P3 to P5 need special protocols and stabilization

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Class P1 =

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minimal anesthetic risk

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Class P5 =

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extreme anesthetic risk

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Classes P1 and P2 use

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standard anesthetic protocol

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Classes P3 to P5 need

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special protocols and stabilization

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Anesthetic Protocols

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Established by the veterinarian Factors considered: Facilities and equipment Familiarity with agents Nature of the procedure Cost Urgency

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Preinduction Patient Care

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Withholding food Why? If the patient is not fasted? Patient stabilization Sick patients Patients with concurrent conditions Reduces anesthetic risk

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Intravenous (IV) Catheterization

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Reasons for placing an IV catheter: Fluids Emergency Constant rate infusion (CRI) of drugs or anesthetic agents Administration of vesicants Sequential administration of incompatible drugs

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Intravenous Catheters

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Through-the-needle Over-the-needle Most commonly used 16-24 gauge, 3/4- to 2-inch catheter (small animals) 12-16 gauge, 5¼-inch catheter (large animals)

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IV Catheter Placement and Maintenance

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Length Size Location Administration set with injection port Free-flowing fluids Minimal patient and catheter movement Slow administration Saline flush

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Placing an IV Catheter in a Small Animal Patient Equipment:

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Clippers #40 blade Alcohol + gauze Chlorhexidine scrub + gauze Tape Catheters (multiple) "Goopy" square Catheter cap Heparin/Saline flush

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Placing an IV Catheter in a Small Animal Patient

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Clip area over the vein Prepare the area using an aseptic technique Hold off the vein, tense the skin, and position the catheter Advance the catheter assembly through the skin Advance it further to firmly Seat in the vein Advance the catheter over the end of the needle Remove the needle Apply pressure Attach T-port, cap, or set line to the catheter hub Secure the catheter with tape Flush the catheter with saline Twist the tape into a "bow-tie" Crisscross the tape under and around the catheter hub Apply ointment to plastic strip Apply the plastic strip over the site of insertion Secure the catheter with tape Create a tension loop with tape

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Giving an IV Injection Through an IV Administration Set Port

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Prepare medication or induction agent Cleanse injection port with alcohol Insert the needle in the injection port Pinch off the administration set line Give medication at an appropriate rate Release administration set line

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Non-rebreathing system Advantages:

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Less resistance to breathing. Easy to disassemble and can be disinfected or sterilized in a variety of ways. May be light weight. Less likely to cause excessive drag on the mask or tracheal tube, facial distortion or accidental extubation. Quicker mask induction. Changes in vaporizer setting affect the inspired gas concentration immediately.

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Non-rebreathing system Disadvantages:

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More cold dry gases are delivered: Less well preserved moisture and heat within the breathing circuits, Danger of hypothermia. More vapor use due to higher fresh gas flow requirement, so more expensive. More pollution to atmosphere (waste gases).

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Non-rebreathing System: Flow Rates

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Generally, around 200ml/kg/min is used (vs. 50 for rebreathing). Higher than that used for the circle rebreathing systems. System would not be a good choice for large patients due to high flow rates required.

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Oxygen Flush system:

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Only use with circle rebreathing system. 50 L/min oxygen, 45psi bypasses vaporizer to circuit. Used to flush out circle system of anesthetic. NEVER use with a non-rebreathing system

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Pressure Check Machine:

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Connect breathing tubes, rebreathing bag, oxygen supply. Close the pop-off valve and occlude end of breathing tube with your thumb. Set flowmeter to 0.2L(< 1L bag) or 1L (? 1L bag). Press O2 flush until manometer reads at 20 cmH2O. Watch manometer, should rise. Turn off flowmeter, count 10 seconds. If pressure holds, then open pop off valve. Finished. If pressure drops, trouble shoot leak.

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Leaks:

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Most common areas for leaks are: Around the soda lime canister, The rebreathing bag, Tubing: Loose, Cracks, Tubes can be sprayed with soapy water solution to locate leaks.

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Scavenger System:

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System to evacuate waste gases from the anesthesia machine without polluting surgery area. Removes anesthetic agent from the waste gas that has left the circuit via the pop-off valve. Passsive vs. active.

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Active scavenging system:

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Mechanical devices attached to the anesthesia machine that connect to a central vacuum system within the building to remove waste gases. Fairly expensive to install (a reasonable system is around $4000-5000).

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Passive-Without Absorber (What school has):

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The waste gases can be ducted out of the building via: An open window, A pipe passing though an outside wall, An extractor fan vented to the outside air (but not into the building's air-conditioning system). Not acceptable method.

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Charcoal canister:

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Passive scavenger with absorber. Canister should be weighed before first use, and then weighed after each day of use and the weight recorded on the canister. Once the weight has increased by 50 grams from the initial weight, it no longer can absorb waste gas and should be disposed of and replaced with a fresh canister (usually q 8-14 hours). Not the same as a CO2 absorber. Does not absorb nitrous oxide.

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CO2 absorber vs. charcoal canister

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CO2 absorber is to remove CO2 from the anesthetic circuit for patient safety. The charcoal canister prevents waste anesthetic gases (sevo, iso) in the room for employee safety.

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How does a rebreathing system compare to a non-rebreathing system? When is each used and why?

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Less dead space in the non-rebreather.

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What are the different types of scavenging systems?

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Passive ; Active system

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What is the difference between a CO2 absorber and a charcoal canister?

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Charcoal-absorbs the gas. CO2 absorbs carbon dioxide and is a chemical reaction.

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How do you check the machine for leaks? How often?

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Every time you use the machine.

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Review:

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What are the components of the anesthestic machine and what do they do?

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Endotracheal Intubation Benefits

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•Protects airway •Delivery of gases without leakage (safety to employees) •More efficient use of inhalant gases •Can give intermittent breaths to expand lungs during anesthesia •Can breathe for patient in emergency situation

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Risks of intubating

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•Over-inflation of cuff can cause tracheal rupture •Forgetting to deflate cuff before removal can cause damage •Can inflame the larynx ; throat in attempts to intubate •Go too far ; may intubate only one lung •Small tubes can become plugged or kinked, causing airway obstruction

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Anatomic Dead Space

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Portions of the breathing passage that contain air, but in which no gas exchange can occur mouth, nasal passage, pharynx, trachea and bronchi ET tube properly placed and correctly sized for the patient will help decrease this dead space Alveoli are not dead space!

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Cuffed Tubes

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Prevent leakage of waste gas, reducing pollution Reduce the risk of aspiration Reduce amount of gas and O2 needed by preventing leaks. Patient can get too light if not inflated enough.

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Rubber Endotracheal Tube

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Endotracheal Tube Nasal - Oral Inexpensive May absorb disinfectant solutions Drying and cracking with prolonged use Extreme flexibility increases the likelihood of kinking or collapse of the tube

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Vinyl Plastic Endotracheal Tube

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Latex-free_project_101 Less porous than rubber Resists cracking Becomes stiff with age See-through material allows you to visualize any condensation or regurgitated material within tube.

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Murphy Tube

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Has a side hole at the tracheal tip Allows airflow even if against wall of trachea

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Magill tube

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Curved with bevelled tip which facilitates passing the tube through the larynx. Available in a variety of sizes from 3 mm to 40 mm internal diameter Come with or without inflatable cuff Does not have a side hole at the end Uncuffed tube Cuffed tube

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Cole Tube

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COLETUBE Birds, exotics Cuffless tube characterized by a "shoulder" near the distal end Designed with the patient end of the tube smaller than the remainder of the tube. The patient end is close to the diameter of the trachea to preventing leaks and aspiration around the tube

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Before you intubate:

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Test the cuff of the selected tubes to be sure they inflate and do not leak.

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How to Intubate:

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The animal does NOT need to be at a surgical level of anesthetic depth Lubricate the tube end with a SMALL amount of sterile lubricant The animal's mouth is then opened to allow intubation (usually by a partner holding the animal in sternal recumbency) The neck and head of the patient should be extended and held in a straight line A laryngoscope can be used to visualize the epiglottis and the vocal folds Insert the tube over the epiglottis and between the vocal folds (arytenoid cartliages) Be careful not to insert the tube dorsally into the entrance to the esophagus

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How to Intubate

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Determine diameter by Size chart (weight) Palpating trachea (brachycephalics,especially) Select three tube sizes The one you think will fit best A half size large A half size smaller Be sure you have ALL needed materials together to intubate before inducing the patient

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Secure the ET tube

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Secure the ET tube in place using a piece of tie gauze or other similar material tied securely around the tube Behind the animal's head (cats and brachycephalics) Behind maxillary canines and up on top of nose (most other dogs)

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After intubation

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After intubation, tie a knot around the ET tube (should be very snug), then tie a bow around the muzzle or back of the head.

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Intubating too far

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Placing the tube too far down the trachea can lead to intubating 1 bronchus. Leads to inflation of only 1 lung Decreased ventilation ebtube

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Inbating Too Far

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Avoid this by pre-measuring the ET tube Cover "cuff side" with gause to prevent contamination with fur. Measure from thoracic inlet to tip of nose.

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Warning

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Do not move the patient unless the endotracheal tube is first detached from the anesthesia machine. This will prevent trauma to the trachea from the twisting action or movement of the tube. If this is step is not taken, tracheal tears or excessive cough after anesthesia may result.

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LARYNGOSCOPE

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Light Source

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Laryngospasm

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Reflex closure of the laryngeal cartilages resulting in blockage of the airway. To prevent, anesthetist must avoid trauma to the laryngeal area during intubation Especially a problem in cats who are very sensitive to this effect

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Avoiding Laryngospasm

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lidocain Be gentle ; patient when intubating. Traumatizing the larynx will cause more laryngospasm. Use lidocaine to desensitize the larynx. Use a laryngoscope for good visualization.

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To check for proper placement

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•Give a breath when finished and watch for chest movement to ensure proper placement. •Watch the reservoir bag for movements with respiration •Palpate neck - should feel only one firm tube in neck. •Animals cannot cry when properly intubated. •Will often hear cough reflex when placed properly.

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Esophageal intubation

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•May occur if the tube is not seen to pass between the vocal folds. •There may sometimes be difficulty in deciding whether the tube has been correctly placed. •If there is any doubt, the tube should be withdrawn and re-introduced

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Tracheal Trauma and Necrosis

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sweltube Stretching of the tracheal wall may be caused by over-inflation of the cuff. This may lead to Tracheitis pressure necrosis of the tracheal wall tracheal rupture

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Recognizing Esophagheal Intubation

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•Cyanosis due to failure to provide oxygen to lungs •Inability to provide a gas-tight seal when inflating the cuff •Stays too light - will not go to sleep •Able to whine/cry • Respiratory sounds audible around the tube in the mouth •Reservoir bag does not move with breaths

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Under-inflation of the Cuff

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Airway not protected from aspiration Tube slides out Anesthetic leaks into room - we breathe the gas.

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Chewing while Intubated

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Patient must not be allowed to chew or bite at tube Hold mouth closed Place mouth gag Until anesthetic plane deepens or tube is removed If tube is bitten, can damage tube. If bitten through, can result in tube becoming lodged in the trachea.

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Intubation

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epiglottis Soft palate Tube goes in here Soft palate epiglottis

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Coughing

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Animals may cough for a day or two after intubation Irritation of the trachea from the tube Respiratory infection, such as infectious tracheobronchitis Will be made worse if cuff is not deflated or if hose not disconnected before moving animal. Be sure tubes are properly cleaned and rinsed prior to use. Improper rinsing can cause build-up of cleaning product residue on tube Avoid spread of kennel cough.

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Anesthetic Recovery

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When do we pull the ET tube? After swallowing reflex has returned. Even longer in brachycephalics ; animals with respiratory problems How to we pull the ET tube? Deflate the cuff. Untie from patient. Gently remove. What complications can arise during this period and how would you address them? Vomiting, cyanosis, delirium

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When should my tube be pulled?

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bulldog Keep tubes in brachycephalics longer.

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What are the risks?

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Trauma to trachea. Tissue nicrosis. Dead space.

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What is anatomic dead space?

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Space between oxygen and the pets lungs.

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What are the benefits of endotracheal intubation?

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Prevents aspiration amnonia. Delivering meds

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Why do we use cuffed tubes?

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Prevent aspiration. Keep cuff from slipping.

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What are signs of esophageal intubation?

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Able to cry. Cyanosis-haven't noticed for a long time. Smelling Iso. Stays too light. Reservoir bag doesn't move. Audible respiratory sounds.

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How can you prevent laryngospasm?

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Put lidocaine back there. Cats

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How can you confirm correct placement of tube?

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Give breath-watch for chest movement. Watch reservoir bag movement. palpate neck. Animals cannot cry when intubated. Often hear cough reflex when placed properly.

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How can you prevent the animal from chewing through the tube if he/she gets too light during anesthesia?

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Hold mouth closed. Put a gag in. Ask for help. Administer more propofol.

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Man Versus Machine

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"Nothing replaces a human for excellent anesthetic monitoring, no matter how technologically advanced it may be "

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Anesthetic Monitoring

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•During anesthetic maintenance, the anesthetist has 2 important responsibilities •Animal must be monitored closely to ensure that the vital signs (esp. HR and RR) remain within acceptable limits •The anesthetist must maintain the animal at an appropriate anesthetic depth (neither too light nor too deep)

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Why monitor anesthetic?

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Why? •If the animal is too light—will feel pain, may "wake up" and struggle during surgical procedure. •If the animal is too deep—will have prolonged recovery, may have anesthetic overdose leading to death. This type of death is preventable and unacceptable

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Patient Monitoring ; Anesthetic Depth

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•The anesthetist should monitor as many variables as possible and weigh all evidence before judging anesthetic depth of the patient. •Each animal is unique and has an individual response to increasing anesthetic depth •Determination of anesthetic plane by monitoring only one reflex or vital sign will eventually result in disaster.

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Constant Monitoring is Best

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•Variables to be assessed every 5 minutes •Respiration rate, depth, and character •Mucous membrane color and CRT •Heart rate •Pulse strength and rate •Jaw tone, eye position, and palpebral reflex activity •Oxygen flow rate (flowmeter) •IV catheter placement and fluid administration •Body temperature

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Vital Signs

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•Important to observe both vital signs and reflex activity •Vital sign—those variables indicating the response of the animal's homeostatic mechanisms to anesthesia

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Reflex Activity

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•Involuntary response to a stimulus •Gives information on depth of anesthesia

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Cardiac Evaluation

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•Heart Rate and Rhythm •Minimum acceptable heart rate is 60 bpm in the dog, 100 bpm in the cat •Heart rates < 25 in the adult horse are considered abnormal (what is the normal HR in the horse?) •Lower heart rates may be due to excessive anesthetic depth or other problems and DVM should be notified immediately •Cardiac rhythm should be normal sinus rhythm. This means that the SV_ node is setting the pace of the heart. •A common arrhythmia, but of no clinical significance, is __sinus arythmia.

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Heart Rate

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•Changes due to depressant effect of most anesthetics on heart rate and myocardial function. •What drugs may actually increase heart rate? •How may a patient's signalment affect the above reference values?

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Bradycardia

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•An animals heart rate is expected to be somewhat lower under anesthesia than when awake, but if falls below an acceptable level, can be life-threatening. •Alert surgeon if ; 100bpm cat •Alert surgeon if ; 60bpm dog •Reasons for a decreased heart rate can include •Hypothermia •Response to Anesthetic drug (cardiac depression) •Systemic depression •Increased CO2 (inadequate ventilation)

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How Can We Treat Bradycardia?

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•Heart rate can be increased by: •Reversal of anesthetic agents •Lightening plane of anesthesia •Warming the body temperature •Providing adequate oxygenation •Pain stimulation •Administration of positive cardiotropic agents (anti-cholinergic drugs) •Atropine •Glycopyrrolate

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Tachycardia

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•Heart rates can increase due to •Shock •Bleeding •Pain •(Note: SHOCK is in this category. A rapid heart rate does not always indicate a light plane of anesthesia and other monitoring parameters must be assessed prior to increasing anesthetic depth) •Regardless of the reason that tachycardia occurs alert surgeon if: •;180bpm large dog •;200bpm small dog •;220bpm cat •However, keep in mind that there are no "set limits" If you are worried about the patient and feel something is "not right" consult doctor and alert staff

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Cardiac Monitoring •Can be accomplished by:

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•Placing a hand over the chest wall or pulse •Auscultation of the chest wall with a stethoscope •Anesthetic monitoring equipment

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Esophageal Stethoscope

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•Allows auscultation of the heart when the chest is not accessible •Thin, flexible tube attached to either regular stethoscope in place of the stethoscope head, or attached to auditory transmitter •Tube is inserted through the oral cavity into patient's esophagus until at base of heart—correct placement confirmed when audible heart beat detected. •Some esophageal stethoscope probes also contain ECG leads or temperature monitors •Audible heart beat does not mean circulation is adequate Can be attached to stethoscope ear piece, as shown here, or may be attached to amplifier system

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Electrocardiogram

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•Direct visualization of the electrical activity of the heart •Allows interpretation of heart rate and rhythm •Does not tell about heart function (need echocardiogram). Remember electrical activity can continue in the absence of a functioning heart •Multiple methods available—can have wire lead attachments that attach to the patient or leads that are within in esophageal

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Remembering EKG Leads

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•Newspapers are delivered to the front porch; Christmas is at the end of the year •Smoke over Fire •Snow on the Grass •Green and white are always right

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EKG

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•There must be a good contact between the ECG leads and skin •Alcohol provides for good contact but it evaporates rapidly requiring frequent application, and is not as good for long-term monitoring. If you notice an abnormal rhythm, alert staff

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Normal Sinus Rhythm

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•A sinus rhythm is a rhythm which originates in and is controlled by the sinoatrial node. •This rhythm is the normal cardiac rhythm in all domestic animals. •To determine if a rhythm is sinus or not based on the EKG requires the following criteria: •There is a P wave for every QRS complex. •The PR interval is relatively constant especially if the R wave to R wave interval varies. •The P wave is positive in lead II

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QRS Complex

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The QRS complex is the electrocardiographic expression of the electrical activation (depolarization) of the ventricular myocardium.

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T Wave

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The T wave is the electrocardiographic expression of repolarization of the ventricular myocardium (getting ready for next impulse)

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Tamplitude

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•Not all arrhythmias are pathologic •Sinus arrhythmias are phasic and usually associated with respiration •The heart rate increases with inspiration and decreases with expiration due to the influence of vagal tone

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P Wave

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•The P wave is the electrocardiographic representation of electrical activation of the atrial myocardium •The PR interval is the electrocardiographic representation of the delay in electrical activation of the ventricles after sino-atrial nodal discharge.

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Pulse Oximetry

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•Measures the percentage of hemoglobin saturated with oxygen in arterial blood •Also monitors pulse rates •Abbreviated as SpO2 •Works on the principle that hemoglobin absorbs red and infrared light at different wavelengths •Depending on whether the hemoglobin is bound to oxygen (infrared) or deoxygenated (red). •Uses two light-emitting diodes that pulse red and infrared light through perfused tissue several hundred times per second. The amount of light absorbed at each wavelength is measured by sensitive photodetectors. •The absorption data is expressed as a percentage of oxygenated hemoglobin to total hemoglobin.

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Pulse Oximetry •Sensors pick up:

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•Sensors—pick which sensor best to use based on animal, mm color, surgical procedure •Lingual Sensor—looks like a clothespin. Most commonly used on the tongue. The Lingual sensor can also be applied to the pinna of the ear, webbing between toes, vulva or prepuce, or other hairless body region

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Pulse Oximetry--Sensors *

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•Reflective probe—can be used with a protective sleeve and placed inside the rectum or used alone on the underside of the tail. •Universal C-clamp—designed for feet, hocks

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Reliability of the Pulse Ox

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•While this machine is commonly used in practice, primarily due to ease of use and low cost, can be unreliable/subject to mechanical error •Note that when a patient is attached to a breathing circuit and placed on 100% oxygen, the SpO2 reading should be >95%. If the reading drops below 95% the technician should immediately evaluate the patient to determine the reason for the decrease

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Pulse Ox Probes Troubleshooting—Reasons for Decreased SpO2

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•Before checking equipment, listen to heart ensure animal is stable. If not, alert doctor. •Look at anesthesia machine, ensure animal is receiving O2, there is an adequate oxygen supply and that the pop-off valve is open •THEN check pulse ox •Sensor may have slipped from proper position •Tongue/mm may have dried out affecting transmission from the probe •In these situations, repositioning or wetting mm surface should result in return of normal values

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Reasons for Low SpO2

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•If, after troubleshooting machine, the SpO2 still displays a below normal reading, the patient may have had a change in its physiological status •Patient may have impaired gas exchange even if RR is normal. May require hand ventilation •Alert doctor

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Capillary Refill Time

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•Rate of returning color to a mucous membrane after the application of gentle digital pressure. •Reflects the perfusion of tissues with blood •Placement of pressure on the mm compresses blood flow within the capillaries •Release of pressure allows blood flow to return to the area •Capillaries refill with blood and color returns

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•A prolonged CRT (>2 seconds) indicates:

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•A prolonged CRT (>2 seconds) indicates perfusion to the area is not adequate and that tissues to the area have a reduced blood supply. •This may be due to •Vasoconstriction (secondary to shock, hypothermia, excessive anesthetic depth, or drug induced) •Decreased blood pressure. •At the same time, a normal CRT (<2seconds) does NOT mean that perfusion is normal. •Remember an animal can have a normal CRT soon after death

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•Where can we evaluate CRT & mm color?

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•Gingival mucosa •Tongue •Conjunctiva of lower eyelid •Mm of prepuce or vulva •Normal mucus membranes = pink___ •Purple/blue = hypoxic__ •White = __bleeding out_

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Blood Pressure

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•Force exerted by flowing blood on arterial walls •Best measured using blood pressure equipment • can be estimated by palpating a major artery and determining the strength of the pulse •The pulse should be strong and synchronized with the heart beat

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Palpating Pulses •Where can we palpate pulses?

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•Femoral •Carotid •Dorsal pedal •Lingual •Facial •Pulse pressure = the pressure detected by manual palpation is the difference between the systolic and diastolic pressures.

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Blood Pressure •Reflects the

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Blood Pressure •Reflects the adequacy of blood circulation throughout the body •Hypotension under anesthesia may be due to •Excessive anesthetic depth •Excessive vasodilation •Cardiac insufficiency (or preexisting heart ds) •Excessive blood loss and hypovolemia

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Normal Blood Pressure

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•Blood pressure is needed to pump blood through high-resistance vascular beds to the tissues that need it •Normal ranges for diastolic blood pressure (pressure during diastole or filling phase of heart beat) = 50-90 mmHg •Normal ranges for systolic blood pressure (pressure during systole or contraction phase of the heart beat) = 90-160 mmHg •THERE IS A RANGE HOWEVERY 120/80 mmHg IS GENERALLY CONSIDERED TO BE THE NORMAL BP IN CATS AND DOGS.

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The MAP is determined by:

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The MAP is determined by the systolic and diastolic pressure; •Normal mean arterial blood pressure (MAP) ranges from 85-120. •The MAP should be maintained above 70 mmHg at all times under anesthesia. •The mean arterial pressure (MAP) is the major determinant of perfusion pressure to the organs of the body. If the MAP falls below 70, blood flow to internal organs is reduced and tissues may become hypoxic. The kidneys are especially sensitive to this effect.

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Direct Monitoring of Blood Pressure

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•Involves placement of a catheter in an artery, then attaching a transducer to the catheter •Transducer is connected to an oscilloscope that displaces the diastolic, systolic, and MAP as well as a waveform representing pulses •More invasive than indirect (involves arterial catheterization). Especially difficult in cats and small dogs. More $$ equipment •More accurate method than indirect monitoring •In private practice, indirect methods of blood pressure monitoring are more commonly used.

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Indirect Blood Pressure Monitoring is:

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•Less invasive, less technically difficult than direct monitoring •Equipment is used to occlude blood flow through an artery, and then detect the pressure at which some flow resumes (systolic pressure), the pressure at which normal flow is reestablished (diastolic pressure, or the average pressure (MAP)

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Indirect Blood Pressure Monitoring

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•There are three main ways this can be done •The noise made by the returning blood flow may be auscultated with a stethoscope (man; difficult in animals) •A doppler flow probe detects an ultrasound echo from red blood cells passing through the vessel, and thereby determines systolic pressure. •An oscillometer can detect the distention of the limb because of the increased volume of blood pulsing through the artery and limb with each heartbeat. Systolic, diastolic and MAP can be determined by this method

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•A doppler flow probe detects:

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an ultrasound echo from red blood cells passing through the vessel, and thereby determines systolic pressure.

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•An oscillometer can detect:

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the distention of the limb because of the increased volume of blood pulsing through the artery and limb with each heartbeat. Systolic, diastolic and MAP can be determined by this method

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Indirect Blood Pressure--Doppler

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•Doppler •Doppler crystals are placed on the skin over arteries producing an audible pulse beat. The Doppler probe emits a series of high-frequency sound waves. When the sound waves encounter a pulsating artery, the frequency is changed. This is detected by the instrument, which converts the sound into an audible "swishing" noise. •Can be used to assess pulse quality and blood pressure trends. •Addition of a sphygmomanometer and cuff, placed proximally to the doppler crystal enables assessment of systolic blood pressure.

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Ultrasonic Doppler indirect blood pressure measuring device—use

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ultrasound gel •Crystal used with Doppler device. Should be placed over the artery—shave hair from area first for best contact. Concave side placed against animal

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Ultrasonic Doppler •The ultrasonic doppler blood pressure device is considered:

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the most accurate indirect method of blood pressure assessment in small animals. •Doppler can be used in exotic species and neonatal animals to monitor pulse rate by placing the lubed crystal on a well lubed cornea. An audible pulse rate will be obtained

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Using a Doppler BP •Using a BP cuff that is too large or too small will:

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result in a false reading •The width of the cuff should be no more than 40% of the circumference of the leg around which the cuff is to be placed •The sensor probe must be placed with the concave portion of the probe lying on the patient's skin. An artery should be palpated and the arrow on the cuff should be placed over the artery.

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Using a Doppler BP

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•Clip hair from the area the probe will be placed to ensure good contact •Only ultrasound gel should be used on the probe •The probe should ONLY be cleaned with water, NEVER alcohol or disinfectants.

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Indirect Blood Pressure: Oscillometric Technique

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•Consists of a cuff detector unit connected to a computerized monitor. Measures blood pressure by detecting oscillations within the cuff bladder which is placed over an artery (distal limb or tail) •Oscillations are caused by the pulsation of the artery beneath the cuff, which changes the volume of the limb slightly •The device the calculates the systolic mean, and diastolic pressures from these cuff pressure changes.

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Oscillometric Technique

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•More expensive than the Doppler •Work automatically •Allow determination of diastolic and mean in addition to systolic •More accurate in large and medium patients

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