question

Monitor

answer

"to warn"; warns the anesthetist of changes in anesthetic depth and patient condition in enough time to permit intervention before they become dangerous

question

When monitoring, observe specific parameters:

answer

1. vital signs 2. reflexes 3. other indicators of anesthetic depth

question

Vital Signs

answer

refers to variables that indicate the response of the animal's homeostatic mechanisms to anesthesia; heart rate, heart rhythm, respiratory rate and depth, mucous membrane color, capillary refill time, pulse strength, blood pressure and temperature; indicates how well the patient is maintaining basic circulatory and respiratory function during anesthesia and are the best indicators of patient well-being; not reliable signs of anesthetic depth

question

Reflex

answer

an involuntary response to a stimulus; reflexes used in veterinary medicine are palpabreal, corneal, pedal, swallowing and laryngeal reflexes, along with pupillary light reflex (PLR)

question

Other indicators of anesthetic depth:

answer

spontaneous movement, eye position, pupil size, muscle tone, nystagmus, salivary and lacrimal secretions, and response to surgical stimulation

question

ACVA offers recommendations in:

answer

1. assessment of circulation, oxygenation, ventilation, and body temperature 2. monitoring of patients under and recovering from neuromuscular blockade 3. monitoring during the recovery period 4. record-keeping 5. recommendations regarding personnel 6. monitoring sedated patients

question

Anesthetic Monitoring

answer

based on the principle that in the average patient, each monitoring parameter is expected to show a predictable response at any given anesthetic depth

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Flaccid

answer

lacking any muscle tone

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Stage 2 of Anesthesia

answer

excitement stage; vocalization, struggling, and paddling; HR and RR elevated; pupils dilated; marked muscle tone; reflexes are present and may be exaggerated

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Stage 3 of Anesthesia

answer

characterized by progressive muscle relaxation, decreasing HR and RR and loss of reflexes; pupils gradually dilate; tear production decreases, PLR is lost; increase in HR, BP, and RR in response to surgical stimulation during light anesthesia is gradually lost

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Stage 3, Plane 1 of Anesthesia

answer

respiratory pattern becomes regular; involuntary limb movements cease; eyes start to rotate ventrally; pupils may become partially constricted; PLR is diminished; gagging and swallowing reflexes are depressed; pedal and palpabreal reflexes are present, but responses are less brisk than in stage 2; unconscious; will not tolerate surgical procedure; will move and exhibit increased HR, RR, and respiratory depth and BP in response to painful stimuli

question

Stage 3, Plane 2 of Anesthesia

answer

suitable for surgical procedures; surgical stimulation may evoke a mildly increased HR or RR, but patient remains unconscious and immobile; PLR is sluggish; pupil size is moderate; respirations are regular, but shallow; RR, HR, and BP are mildly decreased; skeletal muscle tone is more relaxed; pedal and swallowing reflexes are absent; laryngeal and palpabreal reflexes are diminished; ventromedial eye rotation

question

Stage 3, Plane 3 of Anesthesia

answer

significant depression of circulation and respiration is often present; HR and RR are low and tidal volume (Vt) is decreased; HR notably reduced even in the presence of surgical stimulation; pulse strength may be reduced because of a fall in BP; CRT may be increased to 1.5-2 seconds; PLR is poor; eyeballs are central; pupils are moderately dilated; reflex activity is absent; muscle tone is so relaxed that no resistance occurs when the mouth is opened

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Stage 3, Plane 4 of Anesthesia

answer

period of early anesthetic overdose; characterized by abdominal breathing, which occurs as the thoracic muscles progressively become less active and abdominal muscles are increasingly responsible for ventilation; recognized by a "rocking" motion-abdomen expands and contracts in an attempt to move air into and out of the lungs; fully dilated pupils; all reflexes absent; eyes may be dry due to absence of lacrimal secretions; flaccid muscle tone; cardiovascular system is markedly depressed-dramatic drop in BP and HR; pale mucous membranes; prolonged CRT; in danger of respiratory and cardiac arrest

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Stage 4 of Anesthesia

answer

cessation of respiration, which may be followed by circulatory collapse and death; immediate resuscitation is necessary to save the patient

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Optimum Depth

answer

different for every patient depending on the procedure it is undergoing and the interaction of a complex set of factors

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Objectives of Surgical Anesthesia

answer

-patient does not move -patient is not aware -patient does not feel pain -patient has no memory of the procedure

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Capnograph

answer

also known as end-tidal CO2 monitor; a monitoring device that measures the amount of CO2 in the air by sampling air passing between the endotracheal tube connector and the breathing circuit

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Doppler Blood Flow Detector

answer

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

question

Pulse Oximeter

answer

a monitoring device used to estimate: 1. the percent oxygen saturation of hemoglobin (SPO2) by measuring subtle differences in light absorption, and 2. the pulse rate by detecting blood pulsations in the small arterioles

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Circulation

answer

HR and heart rhythm, pulse strength, CRT, mucous membrane color, and BP

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Oxygenation

answer

mucous membrane color, hemoglobin saturation, measurement of expired oxygen, measurement of arterial blood oxygen (PaO2)

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Ventilation

answer

RR and respiratory depth, breath sounds, end-expired CO2 levels, arterial carbon dioxide (PaCO2), and blood pH

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Oscillimeter

answer

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

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Central Venous Pressure

answer

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 function

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Heart Rate

answer

may be physically assessed by palpation of the apical pulse through the thoracic wall, palpation of a peripheral pulse, or auscultation with a stethoscope, or with the assistance of an esophageal stethoscope; may be measured mechanically with an ECG, a BP monitor, or an intra-arterial line attached to a transducer

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Heart Rate

answer

when assessingwith a stethoscope during anesthesia, the heartbeat can be harder to hear because of a decreased strength of contraction and because the heart will gravitate to the lowest aspect of the thoracic cavity; typically decreased in anesthetized patients

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Heart Rate

answer

alpha-2 agonists and opioids are likely to cause bradycardia; anticholinergics, cyclohexamines can elevate HRs; tachycardia is caused by inadequate anesthetic depth, pain during light surgical anesthesia, hypotension, blood loss, shock, hypoxemia, and hypercapnea

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Heart Rhythm

answer

assessed with HR; normal sinus rhythm (NSR) is most common in dogs, cats, and other small animals; some normal, young, fit dogs have an SA that can be very pronounced and easily mistaken for a cardiac arrhythmia; anesthetist must look for cyclic decrease in rate during expiration and increase in rate during inspiration characteristic of SA

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Heart Rhythm

answer

large animals normally have an NSR, but can have an SA; 1st or 2nd degree block is considered normal in the athletic horse if, when conscious, rhythm returns to SA or NSR after gentle exercise or stimulation; use an ECG to identify abnormal rhythms; cardiac arrhythmias are common during anesthesia; commonly caused by anticholinergics, alpha-2 agonists, barbiturates, and cyclohexamines, but also by hypoxia, hypercarbia, heart disease, and GDV

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Esophageal Stethoscope

answer

permits auscultation of the heart from a distance even when the patient's chest is covered with surgical drapes and conventional auscultation is difficult; consists of a thin, flexible catheter attached to an audio monitor that electrically amplifies the heart sounds

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Esophageal Stethoscope

answer

catheter comes in various sizes to fit small animal patients of varying sizes; there are multiple holes near the patient end covered with a plastic sheath, opposite end has a hole that fits into a sensor and transfers heart sounds to the monitor

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Esophageal Stethoscope

answer

catheter tube is lubricated with a small amount of water or lubricating jelly and patient end is entered through the oral cavity into the patient's esophagus to about the 5th rib level; position of the catheter is changed a little at a time and volume on the monitor is adjusted until heartbeat is audible

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Esophageal Stethoscope

answer

requires relatively little maintenance; catheters must be cleaned with chlorhexidine or other disinfectant after each use

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Cardiac Arrhythmias

answer

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

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Electrocardiography

answer

only a veterinarian can make an ECG diagnosis; technician must be able to differentiate normal from abnormal and dangerous from non-dangerous rhythms; monitors anesthetized patients and guides treatment of cardiac arrest

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Electrocardiography

answer

normal ECG tracing is a graphing representation of the electrical activity of the heart as it travels through the cardiac conduction system and heart muscle; appearance of ECG always has the same general pattern of waveforms, intervals, and segments

question

Path of a Wave of Electrical Activity

answer

-begins in the SA node and travels through the internodal tracts (causes atrial contraction) -conducted to the AV node (slows down to allow ventricles to fill with blood) -travels to the ventricles via the bundle of His, bundle brances, and Purkinje fibers

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P Wave

answer

1st waveform; represents contraction of the atria; normally small, rounded, and positive; "double-humped" in adult large animals; separated from QRS complex by the PR interval

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PR Interval

answer

represents the time required for the impulse to move from the SA node to the Purkinje fibers; in normal animals, range must be from 0.6-0.13 seconds in a dog, 0.05-0.09 seconds in a cat, and 0.22-0.56 seconds in a horse

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QRS Complex

answer

represents contraction of the ventricles and follows the PR interval; largest waveform; pointed (peaked); primarily positive in small animals when lead II is used and negative in large animals when the base apex lead is used

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T Wave

answer

follows the QRS complex; represents repolarization of the ventricles in preparation for the next contraction; variable in appearance, but is normally no more than 1/4 the size of the QRS complex

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Normal Sinus Rhythm (NSR)

answer

a regular rhythm in which the HR is normal and the distance between each heartbeat (QRS complex) is approximately equal; normal in anesthetized dogs, cats, horses, and cattle

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Sinus Arrhythmia (SA)

answer

a cyclic change in the HR coordinated with respirations in which the HR decreases (increased distance between QRS complexes) during expiration and increases during inspiration (decreased distance between QRS complexes); normal in dogs (esp. if young and healthy), horses, and cattle; NOT normal in cats

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Sinus Bradycardia

answer

abnormally slow HR; common during anesthesia; a wide variety of causes (excessive depth, drug reactions, etc.); treatment may include administration of appropriate reversal agents or anticholinergics

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Sinus Tachycardia

answer

abnormally fast HR; less common than bradycardia during anesthesia; variety of causes (inadequate anesthetic depth, drug reactions, surgical stimulation,etc.); treatment depends on the underlying cause

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AV Heart Block

answer

involves a delay or interruption in conduction of the electrical impulse through the AV node; 3 types (1st, 2nd, or 3rd degree); all involve a change in the relationship between the P Wave and QRS complex

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First-Degree AV Block

answer

recognized by a prolonged PR interval; often abnormal, but is seen in normal resting horses

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Second-Degree AV Block

answer

appears as occasional missing QRS complexes; often abnormal, but is seen in normal resting horses as long as no more than one beat is skipped in a row and it resolves with exercise or stimulation

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Third-Degree AV Block

answer

abnormal rhythm in which the atrial and ventricular contractions occur independently; recognized by a complete loss of the normal relationship between the P Waves and QRS complexes; characterized by randomly irregular PR intervals; indicated cardiac disease; infrequently seen in anesthetized patients, but, when present, decreases cardiac output and requires treatment

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Premature Complexes

answer

a complex that occurs too early; if associated with a heartbeat or pulse, it may be referred to as a premature contraction

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Supraventricular Premature Complexes (SPCs)

answer

appear as one or more QRS complexes that closely follow the previous QRS, interupting an otherwise regular rhythm; P waves may or may not be present, but, if present, are almost always different from normal P waves; atrial premature complexes (APCs) are a specific type of SPC

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Supraventricular Tachycardia

answer

a series of 3 or more SPCs in a row; SPCs are abnormal, but may or may not require treatment depending on the frequency

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Ventricular Premature Complexes (VPCs)

answer

appears as an irregular undulating baseline with complete absence of recognizable QRS complexes; associated with cardiac arrest and requires emergency treatment

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Pulseless Electrical Activity (PEA)

answer

the cessation of heart contractions and/or palpable pulses in the presence of a normal or nearly normal ECG and is associated with cardiac arrest

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Capillary Refill Time (CRT)

answer

the rate of return of color to oral mucous membranes after the application of gentle digital pressure; indicative of the perfusion of the peripheral tissues with blood; normal CRT is not always a reliable indicator of adequate circulation

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Capillary Refill Time (CRT)

answer

a prolonged CRT (>2 sec.) indicates that tissues in the area tested have reduced blood perfusion-may be a result of vasoconstriction caused by epinephrine release or of low BP caused by anesthetic drugs, hypothermia, cardiac failure, excessive anesthetic depth, blood loss, or shock; poor perfusion will also result in reduced temperature of the affected part

question

Systolic Blood Pressure

answer

produced by the contraction of the left ventricle as it propels blood through the systemic arteries

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Diastolic Blood Pressure

answer

the pressure that remains in the arteries when the heart is in its resting phase between contractions

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Mean Arterial Pressure (MAP)

answer

the average pressure through the cardiac cycle and is the most important value from the anesthetist's standpoint because it is the best indicator of blood perfusion of the internal organs

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Blood Pressure

answer

the force exerted by flowing blood on arterial walls; the monitoring parameter is used during anesthesia to evaluate tissue perfusion; determined by complex interactions among HR, stroke volume, vascular resistance, arterial compliance, and blood volume

question

MAP can be calculated by:

answer

MAP=Diastolic Pressure+1/3(Systolic Pressure-Diastolic Pressure)

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Hypotension

answer

BP that is below normal limits

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Hypertension

answer

BP that is above normal limits

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Pulse Strength

answer

a physical parameter that can be used as a round indicator of BP; assessed by palpating a peripheral artery; normal pulse should be strong and occur after each apical beat or S1 heart sound; decreases under anesthesia, but should still be palpable; interpretation is subjective and normals vary widely; does not always correlate well with BP because pulse strength is determined by the difference between systolic and diastolic BP, vessel diameter, and other factors that do not always correlate with MAP or tissue perfusion

question

Peripheral arteries used to assess pulse strength are:

answer

-lingual (dogs only) -dorsal -pedal -femoral (small animals and small ruminants only) -carotid -facial (horses only) -aural (large animals only)

question

Pressure Transducer

answer

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

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Direct BP Monitoring

answer

the reading is obtained by means of a catheter inserted into an artery and attached to a pressure transducer; infrequently performed in small animal vet practice; commonly used in equine practice and in research and referral institutions; gives the anesthetist a continuous reading of the BP throughout the cardiac cycle and is more accurate than indirect methods

question

Photoplethysmograph

answer

used to provide indirect BP measurements; uses infrared light to measure changes in volume caused by pulse pressure; instrument is designed for human use and is not commonly used in vet patients, but may be useful for dogs and cats <10 kg; creates a continuous waveform tracing in real time and is able to display systolic, diastolic, and mean pressures

question

Doppler Blood Flow Detector

answer

a monitoring device that consists of an ultrasonic probe and an electric monitor; contains a crystal that emits ultrasonic frequency waves and another crystal that receives the returning echoes; outgoing waves bounce off RBCs traveling inside a pulsating artery and return to the probe where they are sent to an electric monitor for processing

question

Doppler Blood Flow Detector

answer

monitor converts returning sound into a "whooshing" sound audible to the attendant; frequency or pitch of sound changes in proportion to the velocity of the RBCs and the intensity changes in proportion to the number of RBCs detected; can be used to continuously monitor HR and heart rhythm or can be used with a conventional cuff and sphygmomamometer to determine the systolic BP; diastolic pressure and MAP cannot be measured by most Doppler systems

question

Use and Operation of a Doppler System:

answer

-choose a location to place the probe over a peripheral artery -clip a 1-2 cm square patch of hair over the artery, gently cleanse the skin, and apply a generous amount of ultrasonic gel -the concave surface of the probe must be oriented parallel to and precisely over the artery and must make firm, but not excessive contact; acquiring a good signal requires very fine changes in position of the probe -after use, clean the probe by wiping it gently with a gauze sponge and store in a protective case

question

Sphygmomanometer

answer

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

question

Determining BP With a Doppler System:

answer

1. when the cuff is inflated with a rubber bulb, an artery lying beneath the cuff is compressed 2. when the cuff pressure exceeds the systolic BP, blood flow through the artery stops and the sound is no longer audible 3. when the cuff pressure is slowly released, blood flow resumes and is again audible when the cuff pressure equals the systolic BP

question

Determining Systolic Pressure With a Doppler System:

answer

1. fit a cuff to the extremity (cuff should be 30-50% of the circumference of the extremity) 2. place the cuff firmly, but not too tightly, to the site where the probe is positioned 3. after establishing a good Doppler's signal, use the bulb to inflate the cuff until the signal can no longer be heard 4. while reading the manometer, gradually decrease the pressure until the pulsing signal first returns

question

Doppler Monitor Technical Problems and Artifacts:

answer

-monitors underestimate the systolic BP in cats by about 15 mm Hg, but are fairly accurate in dogs and large animals -values are affected by patient position in relationship to the probe and blood flow to the extremity and can be altered by ropes used to tie the patient to the table; several readings should be taken and averaged

question

Doppler Monitor Technical Problems and Artifacts:

answer

-signal is difficult to maintain over time and commonly lost if patient is moved or is shivering, if the probe shifts, or contact pressure isn't right -finding the right location or tightness -use of a cuff that is too narrow will give falsely high readings and a cuff that is too wide will give falsely low readings

question

Oscillimetric Blood Pressure Monitor

answer

oscilllometer; consists of a cuff with an internal pressure-sensing bladder, connected to a computerized monitor; machine inflates and deflates the cuff, and the computer measures the oscillations in intracuff pressure caused by the subtle volume changes of the extremity resulting from pulsations of the artery beneath the cuff

question

Oscillimetric Blood Pressure Monitor

answer

calculates the systolic, mean, and diastolic pressures, and the HR from the pressure changes; work automatically and determine the diastolic pressure and MAP

question

Use and Operation of Oscillometer:

answer

1. cuff is selected and placed in the same locations as a Doppler cuff 2. machine will automatically inflate the cuff at pre-programmed intervals or on demand 3. clean and recharge battery as needed

question

Oscillimeter Technical Problems and Artifacts:

answer

1. relatively accurate in animals over 7 kg, but may have difficulty detecting pulsations in cats and other animals with small superficial arteries 2. tend to underestimate high pressures and overestimate low pressures 3. inaccurate in animals with significant hypotension, arrhythmias, or fast HRs

question

Oscillimeter Technical Problems and Artifacts:

answer

4. systolic pressure measures are generally 10-15 mm Hg lower than those obtained by direct monitoring in dogs 5. may not work if the patient moves, is shivering, or if the cuff slips 6. if cuff is too loose, the machine is unable to measure the pressure; if too tight, the values will be inaccurate

question

Central Venous Pressure (CVP)

answer

the BP in a large central vein (ex: anterior vena cava); value allows the vet to assess blood return to the heart and heart function; helpful in monitoring animals for right-sided heart failure because it can detect increased pressure in the vena cava; useful in preventing overhydration in animals receiving IV fluids because CVP value rises when blood volume is excessive

question

Measuring CVP:

answer

1. directly measured by inserting a long catheter percutaneously into the jugular vein or by cutting down into the jugular vein 2. catheter is advanced into the anterior vena cava and toward the heart so the tip of the catheter lies close to the right atrium 3. catheter is connected to a water manometer to obtain a measurement; pressures over 12-15 cm H2O (during exhalation) are considered elevated

question

Blood Gas Analysis

answer

measurement of the pH, bicarbonate level, and partial pressure of oxygen and carbon dioxide in the blood (most often arterian blood obtained via an intra-arterial catheter)

question

Mucous Membrane Color

answer

most commonly assessed by observing the gingiva; normal color is "bubblegum pink," but varies between patients; assess before each procedure; alternative assessment sites are the tongue, conjunctiva of the lower eyelid, or the mucous membrane lining the prepuce or vulva; not a reliable indicator of tissue perfusion; a crude indicator of oxygenation

question

Pale Mucous Membranes

answer

indicate intra-operative blood loss, anemia from any cause, or poor capillary perfusion (as may occur with vasoconstriction, excessive anesthetic depth, or prolonged anesthesia)

question

Cyanosis

answer

indicates very low blood oxygen concentration (PaO2 of approximately 35-45 mm Hg) in patients with a normal PCV; normal causes are respiratory arrest, oxygen deprivation, and severe pulmonary disease

question

Physiology of Oxygen Transport

answer

tissues must have adequate oxygen at all times to perform metabolic processes; total oxygen content of the blood is carried as free, unbound O2 molecules dissolved in plasma and as oxygen that is chemically bound to the hemoglobin contained in RBCs

question

Physiology of Oxygen Transport

answer

each hemoglobin molecule has 4 oxygen binding sites, each of which can bind 1 molecule of O2; each hemoglobin molecule can carry 4 oxygen molecules if all the binding sites are full; when all available binding sites are occupied with oxygen, the hemoglobin is 100% saturated

question

Physiology of Oxygen Transport

answer

dissolved oxygen in plasma represents a small amount of the total blood oxygen content, where bound oxygen represents the majority

question

Blood oxygen is measured by:

answer

1. calculated oxygen content 2. partial pressure of oxygen (PO2) 3. percent oxygen saturation (SO2)

question

Calculated Oxygen Content

answer

measures the total volume of oxygen in the blood, including dissolved and bound forms, expressed in mL/dL, which accurately measures total oxygen available to the tissues

question

Arterial oxygen is calculated by:

answer

-formula: CaO2=(Hb x 1.39 x SaO2/100) + (PaO2 x 0.003) -Hb=hemoglobin in grams per deciliter (g/dL) -SaO2=oxygen saturation -PaO2=partial pressure of oxygen in arterial blood

question

Partial Pressure of Oxygen (PO2)

answer

measures the unbound O2 molecules dissolved in the plasma and is expressed in mm Hg; differs depending on whether arterial, capillary, or venous blood is measured; oxygen content is the highest after oxygen is picked up by blood in the lungs and is lowest as the blood travels back to the heart before reoxygenation in the lungs

question

Percent Oxygen Saturation (SO2)

answer

measures the percentage of the total number of hemoglobin binding sites occupied by oxygen molecules; oxygen saturation varies depending on whether it is sampled in the arterial blood, capillary blood, or venous blood

question

Partial Pressure of Oxygen in Plasma

answer

dependent almost exclusively on the amount of oxygen in the alveoli and the health of the lungs; decreased inspired oxygen or lung disease will decrease partial pressure; partial pressure influences saturation of the hemoglobin because there must be an adequate level of dissolved oxygen in the blood for oxygen to bind

question

Partial Pressure of Oxygen in Plasma

answer

relationship is relatively predictable in healthy patients; in animals with normal hemoglobin, total oxygen available to the tissue decreases very little at partial pressures above 80 mm Hg (saturation above 95%), where total oxygen available tot the tissues decreases rapidly below this level

question

Partial Pressure of Oxygen in Plasma

answer

when Hg is low, neither parameter is accurate; when Hg is 100% saturated (120 mm Hg), any increase in inspired oxygen will have almost no effect on the oxygen-carrying capacity of the blood and little benefit to the patient

question

Pulse Oximeter

answer

estimates the saturation of hemoglobin (SO2), expressed as a percentage of the total binding sites; readily available, relatively inexpensive, non-invasive, portable, and relatively easy to use; equipped with a probe sensitive to the absorption of light by hemoglobin and to blood pulsations in the small arterioles

question

Pulse Oximeter

answer

determines the oxygen saturation (SPO2) by calculating the difference between levels of oxygenated and deoxygenated hemoglobin based on subtle differences in absorption of light; HR is determined by detecting pulsations in the small arterioles; oxygen saturation should be greater than 95%

question

Use and Operation of the Pulse Oximeter

answer

classified as transmission or reflective; transmission probes must be applied over a non-pigmented tissue bed that is thin enough to allow light transmission through the tissue; reflective probes are placed inside a hollow organ with the light source and sensor in contact with a tissue bed

question

Use and Operation of the Pulse Oximeter

answer

require little maintenance, but handle with care; clean with alcohol or mild disinfectant; cover with plastic sleeve before inserting into rectum or esophagus; do not immerse, scrub, or autoclave

question

Icterus

answer

yellow discoloration of the skin and mucous membranes

question

Things that decrease accuracy or result in signal loss of pulse oximeter:

answer

-tissue pigmentation -motion -excessive pressure -orientation in relation to ambient light -patient conditions (anemia, icterus, vasoconstriction, or edema)

question

If pulse readings are abnormally low, consider:

answer

-Is the instrument working correctly? (probe placement, external light sources, and motion) -Does an agent cause vasoconstriction? (some anesthetic agents cause vasoconstriction and decreased peripheral perfusion which lowers SPO2 values) -Is the tissue under the probe adequately perfused? (perfusion of an extremity may decrease gradually over time and give artifically reduced SPO2 readings)

question

If pulse readings are abnormally low, consider:

answer

-Is adequate oxygen being delivered to the patient? -Is oxygen being transferred from the alveoli to the blood? (may be impeded by inadequate ventilation or pre-existing lung disease -Is circulation adequate? (heart disease, bradycardia, severe arrhythmias, or pulmonary embolism may decrease oxygenation)

question

Ventilation

answer

refers to the movement of gases in and out of the alveoli

question

Respiration

answer

a more general term that means the processes by which oxygen is supplied to and used by the tissues, and carbon dioxide is eliminated from the tissues

question

Respiration Rate

answer

the number of breaths per minute; often monitored by watching the chest wall or by observing movement of the reservoir bag; can be monitored mechanically with an apnea monitor or capnograph; normally decreased during anesthesia

question

Apnea Monitor

answer

generates an audible been with each breath

question

Capnograph

answer

displays a digital readout of the RR in breaths per minute

question

Tachypnea

answer

an increase in RR; must be differentiated from panting; many different causes (hypercapnea, pulmonary disease, or a response to a mild surgical stimulus); may also indicate a progression from moderate to light anesthesia; one of the first signs of arousal from anesthesia; some patients (especially obese dogs) breathe rapidly even at a moderate depth of anesthesia

question

Tidal Volume (Vt)

answer

the amount of air inhaled during a breath; monitored by watching the chest wall or movement of the reservoir bag; generally considered to be 10-15 mL/kg, but decreases by at least 25% in most anesthetized animals because most pre-anesthetic and general anesthetic drugs decrease the contraction of the intercostal muscles on inspiration

question

Tidal Volume (Vt)

answer

anesthetized patients may occasionally have increased Vt; hyperentilation may occur from hypercapnea or surgical stimulation

question

Atelectasis

answer

collapse of a portion or all of one or both lungs; in its early stages, it can be reversed by gentle inflation of the lungs by the anesthetist

question

Respirometer

answer

measures Vt; placed between the expiratory hose of a rebreathing circuit and the anesthetic machine

question

Respiratory Character

answer

refers to the effort required to breathe, the relative length of inhalation and exhalation, and regularity; monitored by watching the chest wall; should be smooth and regular with thoracic and diaphragmatic components in anesthetized animals; normal respiratory sounds are almost inaudible in the dog and cat

question

Apnea Monitor

answer

monitors respiratons and warns the anesthetist when the patient has not taken a breath; the sensor is placed between the endotracheal tube connector and the breathing circuit and detects temperature changes between the cool inspired air and warm expired air in the breathing circuit

question

Apnea Monitor

answer

will sound an alarm when no breath is detected for a preset period of time; sensor increases mechanical dead space; may have difficulty detecting respirations if the patient's Vt is significantly decreased or the patient becomes hypothermic and will sound the alarm

question

Capnograph (End-Tidal CO2 Monitor)

answer

measures the amount of CO2 in the air that is breathed in and out by the patient; non-invasive, continuous, and practical; does not measure blood CO2 directly, but expired CO2 closely mirrors arterial CO2 (PaCO2); end-tidal CO2 is about 2-5 mm Hg less than PaCO2; sensor measures infrared light absorption directly proportional to the CO2 level

question

Capnogram

answer

the graphic representation of CO2 levels generated by a capnograph

question

Mainstream Capnograph

answer

an instrument in which the sensor chamber is placed directly between the endotracheal tube and the breathing circuit; mainstream samplers produce an immediate reading with no delay; the sensor chamber is relatively large, heavy, and heated to prevent condensation--increases dead space

question

Sidestream Capnograph

answer

the sensor chamber is located in the computerized monitor and air is pulled into it through a tube attached to a fitting placed between the endotracheal tube and breathing circuit; the fitting on sidestream samplers are very light-weight and small--relatively little mechanical dead space; 2-3 second delay in the display of CO2 levels; samples 50 to over 400 mL of air from the circuit which may cause a significant loss of gas and false readings when very low oxygen flow rates are used

question

Blood CO2 levels are determined by:

answer

1. the rate of production by the cells 2. the rate of transport to the lungs 3. the rate of elimination from the lungs

question

Carbon Dioxide

answer

produced in the cells as a byproduct of cellular metabolism; after diffusing into venous blood, CO2 is transported from the cells to the lungs where it is eliminated by expiration

question

Baseline (capnogram)

answer

the period during which the CO2 level is 0

question

Appearance of a Normal Capnogram

answer

x-axis displays time, y-axis displays the CO2 level; configuration of the waveform is determined by the levels of CO2 through the machine end of the endotracheal tube; during expiration, CO2 levels abrupthy increases to 40 mm Hg, increases slightly until the end of the expiratory effort, then abruptly decreases back to 0 at the beginning of the inspiratory effort

question

Appearance of a Normal Capnogram

answer

shape of resulting waveform is a modified rectangle; an "end-tidal" monitor because the displayed CO2 value at the end of the expiration is most reflective of arterial CO2 levels

question

Effective interpretation of the capnogram requires evaluation of:

answer

1. the baseline value 2. the ETCO2 value 3. the waveform shape 4. the rate at which changes occur

question

Common capnogram abnormalities:

answer

1. hyperventilation caused by increased RR or Vt , or overzealous mechanical or manual ventilation will cause CO2 to be exhaled more quickly than it is produced (shorter rectangle) 2. hypoventilation caused by decreased RR or Vt, or inadequate mechanical or manual ventilation (taller rectangle) 3. detachment of the endotracheal tube from the sensor fitting, esophageal intubation, a blocked endotracheal tube, or apnea will cause a sudden loss of the waveform (flatline)

question

Common capnogram abnormalities:

answer

4. a malfunctioning exhalation unidirectional valve or exhausted CO2 absorbent will cause the baseline to rise above 0, reflecting rebreathing of CO2 in the inspired air and increased ETCO2 5. a leaky cuff or partially kinked endotracheal tube will cause a sloppy up-stroke and down-stroke (rounded edges of the rectangle)

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Pulmonary Thromboembolism

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the presence of one or more blood clots in the lungs

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Examples of capnogram abnormalities:

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1. cardiac arrest will cause a rapid loss of the waveform because CO2 is no longer circulated to the lungs 2. hypotension or a sudden decrease in the ETCO2 (shorter rectangle) 3. hypothermia will cause a gradual decrease in the ETCO2 because of a decrease in the metabolic rate and CO2 production (shorter rectangle) 4. hyperthermia will cause a gradual increase (taller rectangle)

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CO2 is transported through blood by:

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1. 20-30% is bound to hemoglobin in the RBCs 2. 5-10% is dissolved in plasma and is measurable as PCO2 3. 60-70% reacts with water to form carbonic acid

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PaO2

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partial pressure of dissolved oxygen in arterial blood; should be approximately 5 times the inspired concentration of oxygen

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Thermoregulation

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physiologic process; shivering, metabolic rate, and peripheral blood flow keep the temperature within the normal range; controlled by the hypothalamus of the brain

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Hypothermia contributing factors:

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1. animals are routinely shaved before surgery and cleaned with antiseptic and alcohol solutions 2. anesthetized animal is unable to generate heat by shivering or muscular activity 3. metabolic rate of an anesthetized animal is less than that of a conscious animal 4. during the course of surgery, a body cavity may be opened and the viscera exposed to air at room temperature 5. some pre-anesthetic and general anesthetic agents cause peripheral vasodilation

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Hypothermia contributing factors:

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6. pediatric and geriatric animals are less able to maintain thermoregulation 7. small patients lose heat faster because the body surface area is proportionately greater than the surface area of larger patients 8. administration of IV fluids at room temperature 9. patients placed on non-rebreathing systems constantly breathe fresh gas, which is cold and dry

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Techniques to minimize heat loss:

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1. avoid excessively cold temperatures in the surgery suite or treatment room 2. always place a barrier between patient and tabletops, especially if stainless steel 3. warm IV fluids to 37.5 degrees C (approximately 100 degrees F) 4. place a circulating warm water blanket between the patient and table 5. place the patient on a forced warm-air blanket

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Managing hypothermia:

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1. same techniques used to minimize heat loss 2. place warm water bottles containing 37.5 degrees C (approximately 100 degrees F) water next to the patient; must be checked and reheated on a regular basis 3. place the patient under infrared heating lamps at a distance of 75 cm (30 in)

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Malignant Hyperthermia (MH)

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most commonly seen in pigs; caused by a genetic defect that results in excess muscle metabolism in the presence of some anesthetic drugs; minimize restraint to reduce stress; the only medical treatment is dontrolene, which is typically available only at large veterinary or human hospitals

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Reflexes

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an unconscious response to a stimulus; gradually decrease in response to an increasing depth of anesthesia

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Swallowing Reflex

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a response to the presence of saliva in the larynx; present in light anesthesia, but lost in medium surgical anesthesia and returns during recovery just before the patient regains consciousness; return during recovery is main indicator of when to extubate the patient

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Laryngeal Reflex

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an immediate closure of the eppiglottis and vocal cords when the larynx is touched by any object; may be observed during intubation; can make it difficult to pass the endotracheal tube; strong in cats, pigs, and small ruminants

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Palpebral Reflex

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blink reflex; a blink in response to a light tap on the medial or lateral canthus of the eye; gradually lost as anesthetic depth increases; most animals retain the reflex in light anesthesia and lose it during medium anesthesia; should be absent during optimum and deep levels of anesthesia

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Pedal Reflex

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flexion or withdrawal of the limb in response to vigorous squeezing and twisting or pinching of a digit or pad; only useful in small animals; varies depending on anesthetic depth; present during light anesthesia; absent in optimum and deep anesthesia

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Corneal Reflex

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a retraction of the eyeball within the orbit and/or a blink in response to stimulation of the cornea; test by touching the cornea with a sterile object; retraction of the eye is subtle; should be present in light and medium planes of anesthesia and lost when anesthetic depth is excessive; unreliable in small animals

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Pupillary Light Reflex (PLR)

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a constriction of the pupils in response to a bright light shined on one of the retinas; gradually diminished with increasing anesthetic depth; should be present in light and medium surgical anesthesia, but is lost during deep surgical anesthesia

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Dazzle Reflex

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a blink in response to a bright light shined in the retinas ; same significance as PLR, but is generally lost very early

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Spontaneous Movement

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in an unconscious patient, indicates a very light plane of anesthesia; may manifest as shivering, alternating flexion and extension of the limbs, muscle twitching, or tremors; some drugs may be associated with focal muscle twitching, even in a medium plane of anesthesia

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Muscle Tone

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assessment gives the anesthetist an indication of the degree of skeletal muscle relaxation; tone is "marked" in light anesthesia, "moderate" in medium anesthesia, and "flaccid" in deep anesthesia; unreliable in pediatric patients; jaw tone is not useful in large animal patients

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Jaw Tone

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assessment by attempting to open the jaws from a closed position and estimating the amount of passive resistance; avoid opening the patient's mouth too wide or anesthetist will feel resistance regardless of muscle tone; with increasing depth of anesthesia, the resistance to movement of the jaw will progressively decrease

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Eye Position

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refers to the orientation of the cornea in relation to the palpebral fissure; changes from central to ventromedial and back to central with increasing anesthetic depth; in small animals, eyes are generally central during light anesthesia, ventromedial during medium anesthesia, and central during deep anesthesia

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Eye Position

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some anesthetics do not cause eye rotation even at moderate anesthetic depth; eyes of swine are sunken and unhelpful when trying to determine depth of anesthesia

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Pupil Size

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varies with anesthetic depth; dilated (mydriatic) during stage 2 of anesthesia and are normal or constricted (miotic) during light anesthesia, progressively dilate as anesthetic depth increases, and are widely dilated during deep anesthesia; indicator is influenced by drugs

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Nystagmus

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an oscillation of the eyeballs that is commonly seen in horses during certain planes of anesthesia; fast nystagmus occurs during light anesthesia (including recovery) and gradually slows as the anesthetic depth increases or completely wears off; very slow nystagmus may still be present as a "roving eye" during medium anesthesia; typically associated with an adequate plane of anesthesia for surgery; rarely seen in ruminants and small animals under anesthesia

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Heart and Respiratory Rates

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not reliable indicators of anesthetic depth, but can be used to supplement other data; both values tend to decrease as anesthetic depth increases and increase as anesthetic depth decreases; use caution when interpreting because of other influences; some anesthetic agents or adjuncts increase or decrease HR; high PaCO2 and low PaO2 can also increase RR

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Response to Surgical Stimulation

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do not usually reflect a conscious perception of pain

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ACVA Objectives (monitoring guidelines for record keeping)

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1. maintain a legal record of significant events related to the anesthetic period 2. enhance recognition of significant trends or unusual values for physiologic parameters and to allow assessment of the response to intervention

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To meet objectives, ACVA recommends:

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1. record all drugs administered to each patient in the peri-anesthetic period and in early recovery, noting the dose, time, and route of administration, as well as any adverse reaction to a drug or drug combination 2. record monitored variables on a regular basis (every 5-10 minutes) during anesthesia; minimum variables recorded are HR, RR, oxygenation status, and BP 3. record HR, RR, and temperature in the early recovery phase 4. any untoward events or unusual circumstances should be recorded for legal reasons and for reference should the patient require anesthesia in the future

Chapter 5 Notes: Anesthetic Monitoring – Flashcards

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