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Atelectasis

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collapse of a portion or all of one or both lungs

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apenea monitor

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a monitor used to alert the anesthetist when the patient has not taken a breath within a set period of time. Detects a change in temperature if the air moving between the endotracheal tube and the breathing circuit as the patient breathes

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blood gas analysis

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measurement of the ph, bicarbonate level and partial pressure of oxygen and carbon dioxide in the blood (most often arterial blood obtained via an intraarterial catheter)

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blood pressure

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BP. The force exerted by flowing blood on vessel walls

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calculated oxygen content

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the total volume of oxygen in the blood including both dissolved and bound forms.

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capnogram

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the graphic representation of CO2 levels generated by a capnograph

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capnograph

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also known as an end-tidal CO2 monitor. A monitoring device that measures the amount of CO2 in the air that is breathed in and out by the patient, by sampling air passing between the endotracheal tube connector and the breathing circuit

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cardiac arrhythmias

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Any pattern of cardiac electrical activity that differs from that of the healthy awake animal

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central venous pressure

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CVP. The blood pressure in a large central vein such as the anterior vena cava. Used to assess blood return to the heart and heart functions

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circulation

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Movement of blood through the body

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diastolic blood pressure

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Arterial blood pressure when the heart is in its resting phase between contractions

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Doppler blood flow detector

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A monitoring device that uses ultrasound frequency to convert the motion of red blood cells in small arteries into an audible "whooshing" sound. Used to monitor pulse rate and if used in conjunction with a sphygmomanometer, systolic blood pressure

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esophageal stethoscope

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a monitoring device used to detect and amplify heart sounds via a catheter placed in the esophagus

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flaccid

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lacking any muscle tone

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icterus

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yellow discoloration of the skin and mucous membrane

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mean arterial pressure

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The average arterial blood pressure.

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monitor

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a piece of electronic equipment that keeps track of the operation of a system continuously and warns of trouble

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oscillometer

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A monitoring device used to measure systolic, mean and diastolic blood pressure by detecting and analyzing pulsations of blood in arteries of an extremity

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oxygenation

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Taking in oxygen and expelling carbon dioxide via respiratory system

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partial pressure of oxygen

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PO2. A measurement of the unbound O2 molecules dissolved in the plasma expressed in millimeters of mercury

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percent oxygen saturation

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SO2, meausres the percentage of the total number of hemoglobin binding sites occupied by oxygen molecules.

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pressure transducer

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An instrument designed to measure fluid pressure that converts the pressure wave form into an electrical signal

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pulmonary thromboembolism

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the presence of one or more blood clot in the lungs

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pulse oximeter

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a monitoring device used to estimate the percent oxygen saturation of hemoglobin by measuring subtle differences in light absorption and the pulse rate by detecting blood pulsations in the small arterioles

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respiration

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the process by which oxygen is supplied to and used by the tissues, and carbon dioxide is eliminated from the tissues

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respirometer

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a monitoring device used to measure the tidal volume and respiratory minute volume

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sphygmomanometer

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a monitoring device consisting of a pressure gauge and cuff used to measure arterial blood pressure

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systolic blood pressure

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Arterial blood pressure during contractions of the venitricals

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tachypnea

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rapid respiratory rate

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ventilation

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the movement of gases into and out of the alveoli

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Monitoring Parameters

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Vital signs, heart rate, heart rhythm, respiratory rate and depth, mucous membrane, capillary refill time, pulse strength, blood pressure, body temperature

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Stages and planes of Anesthesia

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4 stages (I, II, III, IV) Stage 3 broken down into 4 planes From stage 1 through 4 there is a progressive decrease in pain perception, motor coordination, consciousness, reflex responses, muscle tone, and cardiopulmonary function

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Objectives of Surgical Anesthesia

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Patient doesn't move. Patient isn't aware. Patient doesn't feel pain. Patient has no memory of the procedure.

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Monitoring Patient Safety

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Assess vital signs- Physical assessment (touch, hearing, vision) Mechanical instruments - electrocardiogram, blood pressure monitor, capnograph, Doppler blood flow monitor, pulse oximeter

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Vital signs grouping

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Circulation- heart rate and rhythm, pulse strength, CRT, mucous membrane color, blood pressure Oxygenation-mucous membrane color, CRT, hemoglobin saturation, inspired oxygen, arterial blood oxygen Ventilation- Respiratory rate and depth, breath sounds, end-expired carbon dioxide levels, arterial carbon dioxide, blood ph

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Indicators of Circulation Heart rate

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Physical Assessment- Palpation of apical pulse through the thoracic wall; Palpation of the peripheral pulse, Auscultation with stethoscope; more difficult in recumbent, anesthetized animals Mechanical Assessment: ECG machine; blood pressure monitor; intraarterial line and transducer Bradycardia- Depressant effect of most anesthetics; Alpha2-agonists and opioids, excessive anesthesia depth, adverse effects of drugs Tachycardia- Anticholiergics; inadequate anesthetic depth; pain, hypotension, blood loss and shock, hypoxemia and hypercapnea

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Indicators of Circulation : Heart Rhythm

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Assessed along with heart rate Normal sinus rhythm vs. sinus arrhythmia Both can be seen in anesthetized animals First or second degree heart block- use ECG to detect Causes of arrhythmias- drugs, medical states or diseases

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Instruments used to monitor Heart rate and Rhythm

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Esophageal stethoscope: Thin flexible catheter attached to audio monitor or conventional stethoscope; electronically amplifies heart sounds, inserted into esophagus to level of the 5th rib and adjusted for maximum sound

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electrocardiography

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a graphic representation of the electrical activity of the heart. Used to detect arrhythmias, which are common in anesthetized animals. Differentiate normal from abnormal and dangerous from harmless rhythms

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commonly encountered cardiac arrhythmias

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Sinus arrhythmia (SA): Heart rate coordinated with respirations; Decreases during expiration; increases during inspiration; normal in dogs, horses, and cattle; Abnormal in cats Sinus bradycardia: Abnormally slow heart rate; Common during anesthesia; excessive anesthetic depth and drug reactions; Correct with reversal agents or anticholinergics Sinus tachycardia: Abnormally fast heart rate; Inadequate anesthetic depth, drug reactions, surgical stimulation; Treat according to cause.

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A-V Heart Block

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Delay or interruption of electrical impulse conduction through the A-V node. Three types

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Three types of AV heart blocks

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first degree, second degree, and third degree

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First and second degree blocks

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see in normal resting horses commonly seen after administration of alpha2-agonists or with high vagal tone, hyperkalemia or cardiac disease.

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Third degree heart blocks

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indicates a cardiac disease and is not commonly seen in anesthetized patients

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First degree AV heart block

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Prolonged P-R interval

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Second degree AV heart block

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Occasional missing QRS complexes

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Third degree AV heart block

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Atrial and ventricular contractions occur independently Randomly irregular P-R intrevals

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Commonly Encountered Cardiac Arrhythmias

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Premature complexes: complexes that occur too early Supraventricular premature complexes (SPC): one or more normal QRS complexes closely following the previous QRS complex

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Supraventricular Tachycardia

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A series of three or more SPC's in a row. The SPC's in supraventricular tachycardia appear normal

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Ventricular Premature Complexes

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One or more wide, bizarre QRS complexes closely following the previous QRS complex. VPC's early, like SPC's but appear different than a normal QRS complex. Isolated VPC's are common in anesthetized animals

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Ventricular Tachycardia

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A series of three or more VPC's in a row. Ventricular tachycardia is treated with lidocaine if it is severe

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Fibrillation

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Chaotic, uncoordinated small muscle bundle contractions within the artria and ventricles

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Atrial fibrillation

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fine undulating baseline Absence of P waves Tachycardia Normal QRS complexes at irregular intervals

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Ventricular Fibrillation

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Undulating baseline Absence of QRS complexes

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Pulseless Electrical Activity (PEA)

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Cessation of heart contractions and/or palpable pulse in the presence of normal or nearly normal ECG May also be referred to as Electomechanical Dissociation (EMD): associated with cardiac arrest, the mechanical activity of the heart; ECG measures the electrical activity of the heart; Anesthetist must do both physical monitoring and ECG monitoring

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Indicators of Circulation Capillary Refill Time (CRT)

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Rate of color return to oral mucous membrane after application of gentle digital pressure Indicates peripheral tissue blood perfusion >2 seconds is prolonged and indicates poor perfusion May result from epinephrine release, low blood pressure, hypothermia, cardiac failure, excessive anesthetic depth, blood loss, shock Results in reduced temperature of affected parts

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Indicators of Circulation: Blood Pressure

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Forced exerted by flowing blood on arterial walls Evaluates tissue perfusion during anesthesia Factors involved: Heart rate, stroke volume, Vascular resistance, arterial compliance and blood volume Varies throughout cardiac cycle Hypotension vs. hypertension If any of the factors is affected by drugs, disease, surgical stimulation, or hydration status the blood pressure with be altered. Hypotension is common during anesthesia because of the drugs used. The exception is dissociatives

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Systolic pressure

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Produced by contraction of the left ventricle All BP monitoring instruments can measure systolic pressure

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Diastolic pressure

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Pressure that remains in the arteries when the heart is in the resting phase between contractions Not all BP monitoring instruments can measure diastolic pressure

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Mean arterial pressure (MAP)

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Average pressure through the cardiac cycle Best indicator of blood perfusion to internal organs

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Indictors of Circulation: Pulse Strength

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Used as a rough indicator of blood pressure Determined by the difference between systolic and diastolic blood pressure, vessel diameter, and other factors Palpate the peripheral artery: Lingual, dorasal pedal, femoral, carotid, facial, aural, different arteries are appropriate for different species Lowered in anesthetized animals A subjective interpretation By palpating the pulse strength prior to and during anesthesia, the anesthetist can detect a change in the pulse strength that may indicate a drop in blood pressure and therefore a drop in organ perfusion

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Blood pressure Monitors

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Direct and indirect

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Direct pressure monitors

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Reading obtained via indwelling catheter inserted into an artery (facial or aural) and attached to a pressure transducer and monitor Most commonly used in equine practices and research facilities Provides continuous reading throughout the cardiac cycle Most accurate

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Indirect pressure monitors

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Reading is obtained by using an external sensor and cuff Most commonly used in general veterinary practices Noninvasive: cuff is placed over appropriate superficial artery Doppler and oscillometric methods Sphygmomanometer

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Central Venous Pressure

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Blood pressure in a large central vein (anterior vena cava): assess blood return to the heart and heart function, especially right-sided heart failure A direct method of measurement: catheter from the jugular vein into the anterior vena cava; Connected to a water manometer Monitor trends over time rather than single readings: May detect overhydration when administering IV fluids

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Indicators of Oxygenation: Mucous Membrane Color

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Assessed by observing the gingiva: varies from patient to patient, Evaluate prior to each procedure to determine baseline for patient Rough assessment of oxygenation and tissue perfusion Alternate sites: tongue, conjunctiva of lower eyelid, mucous membrane lining of prepuce or vulva Pale mucous membranes: blood loss, anemia, poor capillary perfusion Cyanotic membranes (blue to purple): respiratory arrest, oxygen deprivation, pulmonary disease Affected by: body temperature, vascular resistance, gum disease

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Physiology of Oxygen Transport

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Adequate oxygen necessary for metabolic processes Components of total oxygen content: Free, unbound oxygen molecules dissolved in plasma (minor content); Oxygen chemically bound to hemoglobin in erythrocytes most oxygen is carried by hemoglobin 100% saturation: all available hemoglobin binding sites are filled with oxygen. Because about 98% of the oxygen carried in blood is bound to hemoglobin, the PCV is an important determinant of oxygen available to tissues

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Indicators of Oxygenation: Measuring Blood Oxygen

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Calculated oxygen content Partial Pressure (PaO2) Percent oxygen saturation (percent SaO2)

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Calculated oxygen content

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Measures both bound and dissolved oxygen An accurate measurement expressed as mL/dl

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Partial pressure (PaO2)

answer

measures unbound oxygen dissolved in plasma expressed as mm HG and varies in arterial, capillary, or venous blood Highest in arterial blood; lowest in venous blood

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Percent oxygen saturation (percent SaO2)

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percentage of total number of available hemoglobin binding sites occupied by oxygen molecules varies in arterial, capillary, or venous blood Highest in arterial blood; lowest in venous blood Room air is 21% Average normal hemoglobin is 15g/d When PaO2 = <80mm Hg the percent SO2 begins to drop more rapidly

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Partial Pressure and Oxygen Saturation

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A nonlinear direct relationship: As partial pressure (PaO2) decreases the oxygen saturation (SaO2) also decreases, but not as rapidly Indicates oxygen availability in animals with normal hemoglobin levels

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Measuring Partial Pressure (PaO2) and Oxygen Saturation (SaO2)

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Blood gas analyzers measure partial pressure Pulse oximeters measure oxygen saturation PaO2 and SaO2 are elevated in anesthetized patients breathing pure oxygen Low PaO2 and SaO2 observed during anesthesia can indicate hypoxemia and the need for oxygen supplementation or assisted ventilation

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Pulse oximeter

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Measures the saturation of hemoglobin and the heart rate Red and infrared wavelength light technology with digital readout Also used on nonanesthetized animals in intensive care Acceptable vs. Critical values

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Pulse Oximeter Use

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Two types of probes: transmission or reflective

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transmission probes

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Clothes pin configuration: One jaw light source one jaw sensor Applied over nonpigmented tissue, relatively hairless and thin enough to transmit light- tongue, pinna, toe web, vulvar fold, prepuce, Achilles tendon, lip Light passes through the tissue and is measured by the sensor

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Reflective probes

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Light sources and sensor are located next to each other Placed in hollow organ- esophagus or rectum Light is reflected off tissue and is measured by the sensor

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Low Pulse Oximeter Readings

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Incorrect instrument use Anesthetic agent causes vasoconstriction Inadequate tissue perfusion Inadequate oxygen delivery to patient Inadequate ventilation Inadequate circulation Patients with subnormal PaO2 or SaO2 readings may require supplemental oxygen delivery, ventilation through bagging or use of a ventilator

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Ventilation vs. Respiration

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Ventilation: movement of gas in and out of the alveoli. Respiration: processes by which oxygen is supplied to and used by the tissues and carbon dioxide is eliminated from the tissue. Monitoring parameters and indicators provide the anesthetist with ventilation information.

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Indicators of Ventilation Respiratory Rate (RR)

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Number of breaths per minute (bpm) Monitored visually by watching chest wall movements or movements of reservoir bag. Monitored mechanically with apnea monitor or capnograph Normally decreases during anesthesia Tachypnea: may be caused by hypercapnea, pulmonary disease, or mild surgical stimulus Tachypnea must be differentiated from panting

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Indicators of Ventilation Tidal Volume (Vt)

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The amount of air inhaled during a breath Monitored visually by watching chest wall movements or movements of reservoir bag Monitored mechanically with respirometer

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Hypoventilation

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Subnormal tidal volume or shallow breathing Can lead to atelectasis Reversed by gentle bagging

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Hyperventilation

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elevated tidal volume can result from hypercapnea or surgical stimulation A respirometer is located between the expiratory hose of a circle breathing circuit and the anesthetic machine

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Indicators of Ventilation: Respiratory Character

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The effort required to breathe Monitored visually by watching the chest wall movements. Measure time relationship between inspiration and expiration Monitor by auscultating the chest: listen for harsh noises, whistles or squeaks

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Dyspnea

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labored or difficult breathing. Dyspnea may be caused by a blocked airway, respiratory disease, pressure build-up in the breathing circuit or hypoxemia

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Apnea Monitor

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Monitors respirations Warns anesthetist if patient hasn't taken a breath in a preset time period Detects temperature differences between inspired air (cool) and expired air (warm) Sensor placed between endotracheal tube connector and breathing circuit

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Indicators of Ventilation: Capnograph

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End-tidal carbon dioxide monitor (ETCO2) Main stream capnograph Side stream capnograph A capnograph is noninvasive and continuous monitoring, which provides waveform information (a capnogram) as well as a numerical display

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End-tidal carbon dioxide monitor (ETCO2)

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Measures the carbon dioxide in air that is inhaled and exhaled Value closely mirrors arterial CO2 (PaCO2)

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Mainstream capnograph

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sensor placed directly between the endotracheal tube and breathing circuit

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Sidestream capnograph

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sensor located in a computerized monitor; air is pulled in through a tube attached to the fitting between the endotracheal tube and breathing circuit

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Capnogram

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waveform of carbon dioxide levels passing through the capnograph.

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Capnogram Abnormalities Related to Ventilation or Equipment Problems

answer

Hyperventilation: Gradual decrease in ETCO2 value Hypoventilation: Gradual increase in ETCO2 value Flat line (no waveform): Lack of carbon dioxide reaching sensor or machine malfunction Elevated baseline: Patient is rebreathing carbon dioxide or the sensor is contaminated Rounding of edges of waveform: Leaking cuff or partially kinked endotracheal tube

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Capnogram Abnormalities Unrelated to Ventilation or Equipment Problems

answer

Cardiac arrest: Rapid loss of waveform that returns if CPR is successful Hypotension or sudden decrease in cardiac output: rapid decrease in height of rectangle Hypothermia: Gradual decrease in ETCO2 value (short rectangle) Hyperthermia: Gradual increase in ETCO2 value (tall rectangle) Subtle waveform changes can be caused by high or low gas flow, type of breathing circuit used, amount of dead space, excess moisture in sampling line, or blockage or leak in system.

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Indicators of Ventilation: Blood Gas Analysis

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Blood pH Dissolved oxygen and carbon dioxide gas in arterial blood Dissolved oxygen and carbon dioxide gas in venous blood Indicator of oxygenation, ventilation, acid-base status Influenced by respiratory function: rate, depth and character

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Blood gas analysis

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is most commonly performed in large animal practices Sample collection is difficult because the sample must be from an artery or possibly the lingual vein Handling a sample is labor intense: it must be stored on ice and analyzed within 2 hrs Blood gas analyzers are not commonly found in veterinary practices: the sample may have to be taken to a local reference laboratory or a human hospital laboratory

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Carbon dioxide transport

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20-30% of CO2 joins with hemoglobin in the RBC's 5-10% is dissolved in plasma-measured as PaCo2 The remainder (60-70%) reacts with H2O to form carbonic acid, which quickly converts to bicarbonate & hydrogen ions

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Carbon Dioxide Levels and Acid-Base Status

answer

Anesthetized patients may become mildly acidotic: Higher CO2 levels produce higher hydrogen ion concentration; Blood ph will be lower Correct the underlying cause to correct the acidosis: Compare blood pH and PaCO2 levels to determine if acidosis is metabolic or respiratory

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PaO2

answer

Partial pressure of dissolved oxygen in arterial blood: Should be 5 times the inspired oxygen cocentration

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Hypoxemia

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low levels of oxygen

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Indicators of Body Temperature: Core Body Temperature

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A vital sign regulated by thermoregulation: Controlled by the hypothalamus; Shivering, metabolic rate, and peripheral blood flow keep temperature in the normal range; is not an indicator of circulation, oxygenation or ventilation Monitor every 15-30 minutes during anesthesia: rectal thermometer, esophageal or rectal probe with monitor Anesthesia most often decreases body temperature

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Body Temperature loss during anesthesia

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Influencing factors Shaving and skin preparation Lack of shivering or muscular activities Decreased metabolic rate Opened body cavity and exposed viscera Vasodilation caused by preanesthetic and anesthetic drugs Age: pediatric and geriatric animals are more predisposed Size: small patients lose heat fasater Temperature of IV fluids Use of nonrebreathing systems During anesthesia, the greatest body temperature loss occurs in the first 20 minutes

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Body temperature Loss Complications during Anesthesia

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Prolonged anesthetic recovery Reduced anesthetic dose to maintain surgical anesthesia predispose patient to anesthetic overdose Shivering during recovery will increase oxygen demands CNS depression and heart malfunction

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Minimize or Manage Heat Loss during Anesthesia

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Avoid cold prep, surgery, and treatment rooms Barrier between patient and table top Warm IV fluids Circulating warm water blanket Forced warm air blanket Warm water bottle Infrared heating lamps Warmed fluids for abdominal cavity flush Avoid heating pads

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Hyperthermia During Anesthesia

answer

Influencing factors: Excess external heat administration; Drug induced reactions Most often seen during or just before recovery Management: Cold fluids IV, IP, or rectally; fans; ice or alcohol application; reversal agents; increase flow rate of oxygen in nonrebreathing systems

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Malignant Hyperthermia

answer

Most commonly seen in pigs Genetic defect Clinical signs: Patient becomes hot and stiff; ears turn red; increased carbon dioxide production; taxhyarrythmias Management: Stop anesthesia immediately and administer 100% oxygen; use cooling methods; treat with dantrolene

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Assessment of Anesthetic Depth: Reflexes

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An unconscious response to a stimulus Reflexes evaluated: Swallowing, laryngeal, pedal, palpebral, corneal, pupillary light reflex Reported as present, decreased or absent

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Swallowing Reflex

answer

A normal response to food or saliva in the pharynx Monitored by viewing the ventral neck region Present in light surgical anesthesia Lost in medium surgical anesthesia Returns just before the patient regains consciousness Used to determine when to pull the endotracheal tube

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Laryngeal Reflex

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Epiglottis and vocal cords close immediately when larynx is touched by and object Prevents tracheal aspiration Observed during intubation if animal is in the light plane of anesthesia Makes intubation difficult: Especially in cats, pigs, and small ruminants May cause laryngospasm in cats, pigs, and small ruminants

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Palpebral Reflex

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The blink reflex in response to a light tap on the medial or lateral canthus May be elicited by lightly stroking the hairs of the upper eyelid Present in light anesthesia Often lost during medium anesthesia, although the exact point varies Slow palpebral response in horses indicates adequate surgical anesthetic depth Ruminants tend to have a slightly stronger reflex than horses.

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Pedal Reflex

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Flexion or withdrawal of limb in response to squeezing, twisting, or pinching a digit or pad Used in small animals only Varies from subtle muscle contraction to full withdrawal of limb Varies with depth of anesthesia: Present in light anesthesia; Absent in medium anesthesia Requires a high intensity stimulus Reflexes that are absent in medium anesthesia are also absent in deep or excessive anesthetic depth so they cannot be used as an indicator of anesthetic overdose

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Corneal Reflex

answer

Retraction of eyeball within orbit and/or a blink in response to corneal stimulation Touch the cornea with a drop of sterile saline or artificial tears Most useful in large animals; difficult to elicit in small animals Presents in light and medium anesthesia; absent in deep or excessive anesthesia Used primarily to determine if a LA patient is too deep

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Pupillary light Reflex

answer

Constriction of pupils in response to bright, light shined on one retina. Present in light and medium anesthesia absent in deep anesthesia

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Other indicators of Anesthetic Depth

answer

Spontaneous movement Muscle tone Eye position Pupil size Nystagmus Salivary and lacrimal secretions Heart and respiratory rates Response to surgical stimulation

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Judging Anesthetic Depth

answer

Monitor as many variables as possible No one piece of information is reliable by itself Each animal will respond in its on unique way to anesthesia

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