Anesthetic Monitoring BCSE Study Guide

Overview and Clinical Importance

Anesthetic monitoring is the cornerstone of safe anesthesia practice and represents one of the most frequently tested topics in the BCSE Anesthesia domain. The ability to rapidly assess patient status, recognize abnormalities, and intervene appropriately can mean the difference between life and death. Studies have shown that vigilant monitoring with pulse oximetry and capnography can prevent up to 93% of anesthetic-related mishaps.

The American College of Veterinary Anesthesia and Analgesia (ACVAA) guidelines emphasize monitoring four key areas: circulation, oxygenation, ventilation, and temperature. This guide covers all these essential monitoring parameters with clinical applications and species-specific considerations.

High-YieldThe ACVAA recommends that a designated person should be solely dedicated to monitoring the anesthetized patient from induction through recovery. This person should not be performing the surgical procedure.

Stage	Name	Clinical Signs
Stage I	Induction (Voluntary Movement)	Period from drug administration to loss of consciousness. Patient awake, may show excitement, rapid respiration, struggling. All reflexes present.
Stage II	Excitement (Involuntary Movement)	Loss of consciousness with involuntary movement, delirium, vocalization. Irregular breathing, breath-holding possible. Maximum muscle tone, dilated pupils. DANGEROUS STAGE - transition quickly!
Stage III	Surgical Anesthesia	Unconsciousness with progressive loss of reflexes and muscle tone. Divided into 4 planes. Target: Plane 2-3 for most surgeries. Regular breathing, muscle relaxation, absent palpebral reflex.
Stage IV	Overdose (Medullary Paralysis)	EMERGENCY! Extreme CNS depression. Weak/absent pulse, dilated pupils, dry cornea, central eye position, absent corneal reflex. Respiratory arrest followed by cardiovascular collapse. DEATH imminent without intervention.

Plane	Clinical Signs	Use
Plane 1 (Light)	Eye central position, sluggish palpebral reflex present, moderate jaw tone, swallowing reflex may be present, regular respiration	Minor non-painful procedures only. Patient may respond to strong surgical stimulation.
Plane 2 (Medium)	Eye rotates ventromedially, palpebral reflex ABSENT, corneal reflex PRESENT, moderate jaw relaxation, regular breathing	IDEAL for most surgical procedures. Good muscle relaxation without excessive cardiovascular depression.
Plane 3 (Deep)	Eye returns toward center, corneal reflex diminishing, jaw very relaxed, diaphragmatic breathing pattern, decreased respiratory rate	Required for procedures needing profound muscle relaxation (orthopedic, ophthalmic). Requires careful monitoring.
Plane 4 (Very Deep)	Eye central with dilated pupils, corneal reflex ABSENT (DANGER!), complete muscle relaxation, irregular/apneic breathing	TOO DEEP! Approaching Stage IV. Immediate lightening of anesthesia required. Cardiovascular support needed.

Eye Position	Depth Indication	Other Signs
Central, pupil normal	Light anesthesia (Stage III, Plane 1)	Palpebral reflex present, strong jaw tone
Ventromedial rotation (down and toward nose)	Surgical anesthesia (Stage III, Plane 2-3) - IDEAL	Palpebral absent, corneal present, relaxed jaw
Central, pupil dilated	TOO DEEP (Stage III Plane 4 or Stage IV)	Corneal absent/weak, flaccid jaw, dry cornea

Section 1: Anesthetic Depth Assessment

Monitoring anesthetic depth involves evaluating the degree of central nervous system (CNS) depression produced by anesthetic agents. Adequate depth ensures the patient is unconscious, pain-free, and immobile during surgery while avoiding excessive depression that leads to cardiovascular collapse.

The Four Stages of Anesthesia

Classical anesthetic stages were described by Guedel and remain clinically relevant today, particularly with inhalant anesthetics.

High-YieldStage II (Excitement) is dangerous and should be transitioned through quickly. Injectable induction agents help bypass this stage. If a patient becomes stuck in Stage II, increasing anesthetic depth or administering additional induction agent is indicated.

MEMORY AID - "Stages SESD" Mnemonic

S = Stage I (Sedation/Induction), E = Stage II (Excitement), S = Stage III (Surgical), D = Stage IV (Death/Danger). Remember: We want to SKIP through E quickly and STAY in S!

Stage III Planes of Surgical Anesthesia

High-YieldThe CORNEAL REFLEX should ALWAYS be present during surgical anesthesia. Loss of the corneal reflex indicates the patient is TOO DEEP and approaching Stage IV. This is a critical exam point!

Key Reflexes for Depth Assessment

Palpebral Reflex

Test by gently touching the medial or lateral canthus of the eye. A blink response indicates the reflex is present. The lateral palpebral reflex disappears with light anesthesia/heavy sedation, while the medial palpebral reflex disappears at a deeper plane (safe for intubation in dogs/cats when absent).

Corneal Reflex

Test by GENTLY touching the cornea with a moistened cotton swab. Should result in blinking. This reflex should ALWAYS be present during surgical anesthesia! Loss indicates dangerously deep anesthesia. Do NOT test frequently as it can damage the cornea.

Jaw Tone

Assess resistance when opening the mouth. Progressive relaxation occurs with increasing depth. Complete loss indicates deep anesthesia. Note: Breeds with strong masseter muscles (Pit Bulls, Rottweilers) may have persistent jaw tone even at adequate depth.

Pedal (Withdrawal) Reflex

Pinch the web between the toes and observe for limb withdrawal. Absence of this reflex indicates adequate depth for surgery. The hindlimb withdrawal reflex is typically lost before the forelimb reflex.

Swallowing Reflex

Should be absent during anesthesia (allows intubation) and should return during recovery. It is generally safe to extubate after observing the second swallowing reflex during recovery.

MEMORY AID - "Eyes Tell the Depth" Mnemonic

CENTRAL = Light or TOO DEEP (differentiate by other reflexes). VENTROMEDIAL (down and in) = SURGICAL plane (just right!). Remember: Good surgery happens when the eyes go DOWN!

High-YieldWith KETAMINE anesthesia, the palpebral and swallowing reflexes may remain present even at adequate surgical depth. Ketamine also causes NYSTAGMUS, which is normal - do not confuse with light anesthesia!

Eye Position Summary by Depth

Free Image Source: https://commons.wikimedia.org/wiki/Category:Veterinary_ophthalmology

Species	Normal HR (bpm)	Minimum Acceptable HR
Dog (large)	70-120	55-60 bpm
Dog (small)	80-140	70-80 bpm
Cat	120-180	80-100 bpm
Horse	28-44	24-28 bpm
Cattle	40-80	36-40 bpm
Goat/Sheep	70-110	60-70 bpm

Method	Description	Advantages/Disadvantages
Doppler	Ultrasonic flow detector placed over artery. Cuff inflated until sounds disappear, then deflated. First return of sounds = systolic BP.	Advantages: Accurate in small patients, continuous audible pulse. Disadvantages: Only measures systolic (in dogs) or approximates mean (in cats).
Oscillometric	Automated cuff detects arterial wall oscillations. Provides systolic, diastolic, and mean arterial pressure (MAP).	Advantages: Provides MAP, automated readings. Disadvantages: Inaccurate with arrhythmias, motion, vasoconstriction. Less reliable in small patients.
Invasive (Direct)	Arterial catheter connected to pressure transducer. Most accurate method. Common sites: dorsal pedal, auricular.	Advantages: Most accurate, continuous, real-time waveform. Disadvantages: Requires arterial catheterization, risk of hematoma, expensive equipment.

Parameter	Normal Range	Minimum Acceptable	Hypotension Threshold
Systolic BP	100-160 mmHg	90 mmHg	Less than 80 mmHg
Mean Arterial Pressure (MAP)	80-120 mmHg	70 mmHg	Less than 60 mmHg
Diastolic BP	40-80 mmHg	40 mmHg	Less than 40 mmHg

Section 2: Cardiovascular Monitoring

Cardiovascular monitoring ensures adequate tissue perfusion throughout anesthesia. The ACVAA objective for circulation monitoring is to ensure adequate circulatory function. Remember: Blood pressure is NOT equal to blood flow (cardiac output)! Blood pressure can be maintained by increased peripheral resistance even when cardiac output is compromised.

Heart Rate Monitoring

Methods of Heart Rate Assessment

Direct auscultation with stethoscope (precordial or esophageal)
Electrocardiography (ECG) - most accurate for rate AND rhythm
Pulse oximeter - provides pulse rate
Doppler monitor - audible pulse sounds
Palpation of peripheral pulses (femoral, dorsal pedal, lingual)

Normal Heart Rates During Anesthesia

MEMORY AID - "Cats are FAST" Mnemonic

Remember heart rate order by species: CATS (120-180) greater than small DOGS (80-140) greater than large DOGS (70-120) greater than RUMINANTS (40-80) greater than HORSES (28-44). Smaller animals = faster heart rates!

High-YieldAlpha-2 agonists (dexmedetomidine, xylazine) cause PROFOUND BRADYCARDIA that may persist even at adequate anesthetic depth. Do not interpret this as 'too deep' - evaluate other parameters!

Blood Pressure Monitoring

Blood pressure (BP) is the most commonly used clinical parameter to assess tissue perfusion during anesthesia. Hypotension (mean arterial pressure less than 60-70 mmHg) is the most common anesthetic complication and can lead to organ damage.

Blood Pressure Measurement Methods

Free Image Source: https://commons.wikimedia.org/wiki/Category:Sphygmomanometers

High-YieldCuff width should be approximately 40% of limb circumference for accurate readings. Too narrow = falsely HIGH readings. Too wide = falsely LOW readings. Remember: 'Narrow = High, Wide = Low.'

Target Blood Pressure Values

MEMORY AID - "MAP 60-70 Rule"

Mean Arterial Pressure should stay above 60-70 mmHg for adequate organ perfusion. Remember: 'SIXTY is SAFE, SEVENTY is STELLAR.' Below 60 = kidney, brain, and heart injury risk!

Electrocardiography (ECG)

The ECG monitors only the electrical activity of the heart - NOT mechanical function or blood flow. A normal-appearing ECG can be present even when cardiac output is severely compromised (pulseless electrical activity - PEA). However, ECG is essential for detecting arrhythmias and is critical during CPR.

Standard 3-Lead ECG Placement

White (Right Arm - RA): Right forelimb
Black (Left Arm - LA): Left forelimb
Green or Red (Left Leg - LL): Left hindlimb
Lead II (RA to LL) is the standard monitoring lead

MEMORY AID - "White is Right, Smoke over Fire" Mnemonic

WHITE lead goes on RIGHT arm. BLACK (smoke) goes over RED (fire) = Black on LEFT arm, Red/Green on LEFT leg. Lead II runs from right arm to left leg - the 'long diagonal.'

Common Anesthetic Arrhythmias

Free Image Source: https://commons.wikimedia.org/wiki/File:SinusRhythmLabels.svg

High-YieldDuring CPR, an ECG is ESSENTIAL to identify the cardiac rhythm and guide therapy. Asystole, PEA, ventricular fibrillation, and pulseless ventricular tachycardia each require different interventions!

Mucous Membrane and Capillary Refill Time (CRT)

Direct observation of mucous membrane color and CRT provides a rapid, non-invasive assessment of peripheral perfusion and oxygenation.

Capillary Refill Time (CRT): Apply brief pressure to the gingiva, release, and count seconds for color to return. Normal CRT is less than 2 seconds. Prolonged CRT (greater than 2 seconds) indicates poor peripheral perfusion, hypotension, or vasoconstriction.

MEMORY AID - "CRT TWO is TRUE" Mnemonic

CRT should be less than TWO seconds. Greater than 2 = perfusion is NOT TRUE (compromised). Anything longer means blood is not getting to tissues fast enough!

Arrhythmia	Causes During Anesthesia	Clinical Significance
Sinus Bradycardia	Alpha-2 agonists, opioids, deep anesthesia, hypothermia, increased vagal tone	Reduce cardiac output if severe. Treat if HR less than acceptable minimum and BP affected.
Sinus Tachycardia	Light anesthesia, pain, hypovolemia, hyperthermia, anticholinergics, ketamine	Increases myocardial oxygen demand. Address underlying cause.
Ventricular Premature Contractions (VPCs)	Hypoxemia, hypercapnia, catecholamine release, myocardial disease, electrolyte imbalance, GDV	Occasional isolated VPCs common under anesthesia. Treat if frequent (greater than 20/min), multifocal, or causing hypotension.
Second-Degree AV Block	Alpha-2 agonists, increased vagal tone	Common with dexmedetomidine. Usually resolves as drug wears off. Monitor BP.

MM Color	Interpretation
Pink (normal)	Adequate oxygenation and perfusion. This is the target!
Pale/White	Vasoconstriction, anemia, or poor perfusion. Check BP and consider volume status.
Blue/Cyanotic	SEVERE hypoxemia (SpO2 typically less than 75%). EMERGENCY - check airway, provide oxygen, ventilate!
Brick Red/Injected	Hypercapnia (high CO2), vasodilation, or sepsis. May also indicate hyperthermia.
Muddy/Gray	Poor perfusion with concurrent hypoxemia. Often indicates shock or severe cardiovascular depression.

Species	Normal RR (breaths/min)	Minimum Acceptable
Dog	10-30	6-8 breaths/min
Cat	15-30	8-10 breaths/min
Horse	8-16	4-6 breaths/min
Cattle	10-30	6-8 breaths/min

Section 3: Respiratory Monitoring

Respiratory monitoring ensures adequate oxygenation (getting O2 IN) and ventilation (getting CO2 OUT). These are distinct processes! A patient can have adequate oxygenation but inadequate ventilation if breathing 100% oxygen, which masks hypoventilation until CO2 accumulation becomes dangerous.

Respiratory Rate and Pattern

Observe chest excursions or rebreathing bag movement. Note that normal respiratory rate does NOT guarantee adequate ventilation - both rate AND tidal volume matter!

Breathing Pattern Observations:

Rapid, shallow breathing: May indicate light anesthesia, pain, or hyperthermia
Slow, deep breathing: May be normal or indicate moderate depth
Diaphragmatic (abdominal) breathing: Indicates deep anesthesia - intercostal muscles relaxed
Apnea: No breathing - TOO DEEP or respiratory arrest! Requires immediate intervention

High-YieldA respiratory rate less than 6 breaths/min or ETCO2 greater than 60 mmHg generally indicates the need for manual or mechanical ventilation. Do not rely on respiratory rate alone - use capnography!

Pulse Oximetry (SpO2)

Pulse oximetry provides non-invasive, continuous monitoring of arterial oxygen saturation (SpO2). The device uses two wavelengths of light (red and infrared) to measure the percentage of hemoglobin saturated with oxygen.

SpO2 Interpretation

MEMORY AID - "90-60-30 Rule" for Oxygen

SpO2 90% roughly equals PaO2 60 mmHg roughly equals 30% FiO2 minimum. If SpO2 drops below 90%, you are on the STEEP part of the oxygen-hemoglobin dissociation curve - small drops in PaO2 cause LARGE drops in saturation!

Pulse Oximeter Probe Placement Sites

Tongue (most common in small animals during anesthesia)
Lip or cheek (alternative if tongue unavailable)
Ear pinna (especially useful during dental procedures)
Interdigital web (between toes)
Prepuce or vulva (if other sites unavailable)
Rectum (reflectance probe)

Free Image Source: https://commons.wikimedia.org/wiki/Category:Pulse_oximeters

High-YieldPulse oximetry has LIMITATIONS: inaccurate with poor perfusion, motion artifact, anemia, carbon monoxide poisoning, methemoglobinemia, pigmented tissues, and ambient light interference. Most importantly, SpO2 does NOT detect hypoventilation when patient is on supplemental O2!

Capnography (ETCO2 Monitoring)

Capnography measures end-tidal carbon dioxide (ETCO2), providing real-time assessment of ventilation, metabolism, and circulatory status. It is considered the gold standard for ventilation monitoring and is essential for detecting hypoventilation BEFORE hypoxemia develops.

Types of Capnographs

Normal ETCO2 Values

MEMORY AID - "CATS are LOW" Mnemonic

Normal ETCO2 in CATS is LOWER (28-32 mmHg) than in dogs (35-45 mmHg). Remember: C-A-T-S = CO2 Around Thirty-Something (low 30s)!

The Normal Capnogram Waveform

A normal capnogram has a characteristic rectangular shape with four distinct phases:

Free Image Source: https://commons.wikimedia.org/wiki/File:Capnogram.png

ETCO2 Interpretation

High-YieldA SUDDEN DROP in ETCO2 to near-zero during surgery is a RED FLAG for cardiac arrest or catastrophic event. Immediately check pulse, confirm circuit connections, and prepare for CPR. During CPR, ETCO2 greater than 20 mmHg indicates effective chest compressions.

Abnormal Capnogram Waveforms

MEMORY AID - "SHARK FIN = SOMETHING STUCK" Mnemonic

A shark fin capnogram means air is having trouble getting OUT (obstruction). Think: The shark fin's "slant" represents slowed expiratory flow. Check for bronchospasm, kinked tube, or mucus plug!

Free Image Source: Open Anesthesia (Creative Commons): https://www.openanesthesia.org/capnography/

SpO2 Value	Interpretation	Action
95-100%	Normal - adequate oxygenation	Continue monitoring
90-94%	Mild hypoxemia	Assess breathing, check airway, increase O2 if needed
80-89%	Moderate hypoxemia	Check ET tube position, suction if needed, may need ventilation
Less than 80%	Severe hypoxemia - EMERGENCY	Immediate intervention! Check circuit, ventilate with 100% O2, consider CPR

Type	Description	Advantages/Disadvantages
Mainstream	Sensor placed directly in breathing circuit at airway	Advantages: Fast response, no sampling delay. Disadvantages: Heavy sensor on ET tube, may cause drag/kink.
Sidestream	Gas sample aspirated via tubing to remote sensor	Advantages: Lightweight at patient, can use with face mask. Disadvantages: 2-3 second delay, sampling line can clog with moisture.

Species	Normal ETCO2 (mmHg)	Notes
Dog	35-45	Similar to humans
Cat	28-32	LOWER than dogs!
Horse	35-45	Hypoventilation common under anesthesia

Section 4: Temperature Monitoring

Temperature regulation is commonly impaired during anesthesia. Hypothermia is the most common temperature abnormality and occurs due to anesthetic-induced thermoregulatory impairment, heat loss to the environment, and reduced metabolic heat production. Temperature should be monitored at least every 15 minutes during anesthesia.

Normal Body Temperatures

MEMORY AID - "37-38 is GREAT" Mnemonic

Target temperature range for most anesthetized patients is 37-38 degrees Celsius (98.6-100.4 degrees Fahrenheit). Below 37 C = getting cold, action needed. Above 39 C = getting hot, check for problems!

Causes of Perioperative Hypothermia

CNS depression: Anesthetics impair the hypothalamic thermoregulatory center
Peripheral vasodilation: Redistribution of heat from core to periphery
Reduced metabolic rate: Decreased heat production under anesthesia
Environmental heat loss: Cold OR, cold surfaces, wet patient, open body cavities
Cold IV fluids: Room temperature fluids cool the patient internally
Cold inspired gases: Dry anesthetic gases require warming by the patient
High surface area to volume ratio: Small patients and neonates especially vulnerable

High-YieldHYPOTHERMIA IS DANGEROUS: It prolongs anesthetic recovery (cold patients metabolize drugs slower), impairs coagulation, increases infection risk, causes cardiac arrhythmias, and can be life-threatening in severe cases. PREVENTION is better than treatment!

Consequences of Hypothermia

MEMORY AID - "Cold = Slow" Mnemonic

When body temperature goes DOWN, EVERYTHING slows DOWN: heart rate slows, breathing slows, drug metabolism slows, recovery slows, coagulation slows. Cold patients STAY asleep longer and bleed more!

Methods of Temperature Measurement

Rectal thermometer: Intermittent measurement, reflects core temperature with some delay
Esophageal probe: Continuous monitoring, reflects core temperature accurately, ideal position near heart
Infrared auricular (ear): Quick but may be inaccurate, not ideal for anesthesia monitoring
Nasopharyngeal probe: Alternative to esophageal, measures slightly lower than core

Hypothermia Prevention Strategies

Pre-warm patient before induction when possible
Forced air warming devices (most effective) - e.g., Bair Hugger
Circulating warm water blankets (place UNDER patient)
Warm IV fluids (use fluid warmers)
Warm lavage fluids for body cavity procedures
Insulate extremities (bubble wrap, towels, socks)
Minimize surgical prep area and wet contact time
Increase OR ambient temperature (at least 68-72 F)
Use low fresh gas flows with circle systems to retain warmth and humidity

High-YieldELECTRIC HEATING PADS are NOT recommended due to burn risk, especially in anesthetized patients who cannot feel pain or move away! Always use thermostatically controlled devices and NEVER place heating elements directly against skin.

Hyperthermia Considerations

While less common than hypothermia, hyperthermia can occur and is potentially life-threatening.

Causes of Perioperative Hyperthermia

Pre-existing fever (infection, inflammation)
Excessive external warming
Drug reactions (opioid-induced hyperthermia in cats)
MALIGNANT HYPERTHERMIA: Rare but rapidly fatal genetic condition triggered by certain anesthetics

Malignant Hyperthermia (MH)

A life-threatening hypermetabolic crisis triggered by inhalant anesthetics (especially halothane) and succinylcholine. Caused by uncontrolled calcium release from skeletal muscle sarcoplasmic reticulum.

Species susceptibility: PIGS (especially stress-susceptible breeds), dogs (rare), cats (rare), humans

Clinical signs: Rapidly rising temperature (can exceed 43 C/109 F), muscle rigidity, tachycardia, tachypnea, dramatically elevated ETCO2, metabolic acidosis, hyperkalemia

Treatment: STOP TRIGGERING AGENTS immediately, hyperventilate with 100% O2, DANTROLENE (specific antidote), active cooling, treat hyperkalemia and acidosis

MEMORY AID - "MH = Hot Pig" Mnemonic

Malignant Hyperthermia is most common in PIGS. Signs: Massive temperature rise, Huge ETCO2 increase, Hyperthermia, Piglike rigidity (muscle stiffness), Immediate danger of death. Treatment: Dantrolene!

High-YieldThe FIRST sign of malignant hyperthermia is often a RAPID, UNEXPLAINED RISE IN ETCO2 before temperature increases. If ETCO2 rises rapidly with no other explanation, consider MH and be prepared to act!

Anesthetic Depth Assessment

Four stages of anesthesia: I (induction), II (excitement - DANGEROUS), III (surgical), IV (overdose)
Target Stage III, Plane 2-3 for most surgeries
CORNEAL REFLEX should ALWAYS be present - loss = TOO DEEP
Eye position: central (light or too deep), ventromedial (surgical = IDEAL)
Ketamine maintains palpebral/swallowing reflexes - do not misinterpret as light

Cardiovascular Monitoring

Target MAP greater than 60-70 mmHg for adequate organ perfusion
ECG monitors electrical activity ONLY - not blood flow
CRT should be less than 2 seconds; prolonged = poor perfusion
BP cuff width = 40% of limb circumference (narrow = falsely high)
Alpha-2 agonists cause profound bradycardia - expected finding

Respiratory Monitoring

SpO2 should be greater than 95%; less than 90% = HYPOXEMIA
Pulse oximetry does NOT detect hypoventilation on supplemental O2
Normal ETCO2: Dogs 35-45 mmHg, Cats 28-32 mmHg (CATS ARE LOWER!)
Elevated baseline on capnogram = CO2 rebreathing (exhausted absorbent)
Shark fin capnogram = airway obstruction (bronchospasm, kinked tube)
Sudden ETCO2 drop to zero = cardiac arrest, disconnect, or esophageal intubation

Temperature Monitoring

Target temperature 37-38 C; hypothermia is MOST COMMON complication
Hypothermia prolongs drug metabolism - cold patients stay asleep longer
Forced air warming devices are MOST effective
Avoid electric heating pads - burn risk in anesthetized patients
Malignant hyperthermia: PIGS most susceptible; rapid ETCO2 rise is first sign

Phase	Name	Description
Phase I	Inspiratory Baseline	Should be at ZERO (0 mmHg). Represents fresh gas inspiration. Elevated baseline = rebreathing CO2!
Phase II	Expiratory Upstroke	Rapid rise as dead space gas is replaced by alveolar gas. Should be STEEP. Slanted = airway obstruction.
Phase III	Alveolar Plateau	Should be relatively FLAT. The highest point (end) = ETCO2 value. Slanted plateau = uneven lung emptying.
Phase IV (0)	Inspiratory Downstroke	Rapid drop as inspiration of fresh gas begins. Returns to baseline.

ETCO2 Value	Interpretation	Common Causes
Greater than 45-50 mmHg	HYPOVENTILATION (hypercapnia)	Deep anesthesia, opioid depression, airway obstruction, equipment malfunction, increased metabolism (malignant hyperthermia)
Less than 35 mmHg	HYPERVENTILATION (hypocapnia)	Light anesthesia, pain, anxiety, excessive mechanical ventilation, hypothermia, decreased metabolism
Zero or absent	NO CO2 DETECTED	Esophageal intubation, circuit disconnect, cardiac arrest, apnea, equipment failure
Sudden decrease	Decreased pulmonary blood flow	Cardiac arrest, pulmonary embolism, severe hypotension, massive hemorrhage

Waveform Abnormality	Appearance	Cause/Action
Elevated baseline	Baseline does not return to zero between breaths	CO2 REBREATHING: Exhausted soda lime, stuck inspiratory valve, inadequate fresh gas flow (non-rebreathing). Change absorbent, check valves.
Shark fin shape (slanted upstroke and plateau)	Obtuse angle between upstroke and plateau, gradual rise throughout expiration	AIRWAY OBSTRUCTION: Bronchospasm (common in asthmatic cats), kinked ET tube, mucus plug. Assess airway, consider bronchodilator.
Curare cleft (dip in plateau)	Notch or cleft in the alveolar plateau	PATIENT EFFORT: Spontaneous breathing effort against ventilator, inadequate muscle relaxation, pain. Check depth, synchronize ventilation.
Exponential decay	Gradual decrease in ETCO2 over multiple breaths	DECREASING CARDIAC OUTPUT: Hemorrhage, cardiovascular depression, developing shock. Check BP, assess blood loss, support circulation.
No waveform	Flat line at zero	ESOPHAGEAL INTUBATION, complete disconnect, cardiac arrest, or apnea. Reposition ET tube, check connections, assess patient!

Species	Normal Temp (Celsius)	Normal Temp (Fahrenheit)	Hypothermia Threshold
Dog	37.5-39.2	99.5-102.5	Less than 37 C (98.6 F)
Cat	37.0-38.5	98.6-101.3	Less than 36 C (96.8 F)
Horse	37.2-38.2	99.0-100.8	Less than 36 C (96.8 F)
Cattle	38.0-39.3	100.4-102.8	Less than 37 C (98.6 F)

System	Effects of Hypothermia
Cardiovascular	Bradycardia, decreased cardiac output, arrhythmias (especially below 32 C), increased blood viscosity
Respiratory	Decreased respiratory rate, decreased minute ventilation, shift of oxygen-hemoglobin curve (impaired O2 release)
Drug Metabolism	PROLONGED drug metabolism and elimination - reduced MAC, prolonged recovery. Normal drug doses become relative OVERDOSES!
Coagulation	Impaired platelet function, decreased activity of coagulation factors, increased bleeding risk
Immune Function	Impaired immune response, increased surgical site infection risk
Recovery	Prolonged emergence, shivering (increases oxygen demand by up to 400%), discomfort, delayed wound healing

ANESTHETIC MONITORING &ndash; BCSE Study Guide