Monitoring During Anesthesia

Monitoring During Anesthesia


A variety of monitoring equipment is available for determining an animal’s status during anesthesia. The electrocardiogram (ECG), the electroencephalogram, and the electromyogram can be displayed and recorded. Blood pressure (arterial [ABP] or central venous [CVP]), heart sounds and/or peripheral blood flow, arterial and venous pH, lactate, oxygen (O2) and carbon dioxide (CO2) tensions, and arterial or capillary blood O2 saturation (pulse oximetry [SpO2]) can be determined. End-expired samples of respiratory gases can be analyzed for O2/CO2 and inhalant anesthetic concentration. “Point of care” devices are available that permit animal-side evaluation of the hemogram, acid-base values, blood chemistries, and serum enzyme values within minutes of collecting a peripheral blood sample. All the monitoring equipment in the world, however, cannot replace an educated, attentive anesthetist.

General Considerations

The animal’s ability to compensate for anesthetic induced changes are generally depressed by anesthesia

II Perioperative monitoring is a sentinel for abnormal or deteriorating physiology and improves safety during anesthesia:

III Prerequisites for helpful intraoperative monitoring: A trained vigilant anesthetist is the most important. This means:

Basic Principles

Monitor body functions (see Chapter 2 for normal values)

II Monitor more than one body system and more than one variable per body system, when possible

III Use monitoring techniques that are specific, accurate, and complementary

Noninvasive Monitoring Techniques

Information is gathered by observing readily apparent variables (e.g., rate of volume of breathing) and/or employing diagnostic testing (e.g., ECG; pulse oximeter; ABP; capnometry (ETCO2]; transcutaneous (O2, CO2) that does not invade the body

Physiologic Considerations


Monitoring responses to anesthesia and surgical stimulation (Boxes 14-1 and 14-2)

Box 14-1   American College of Veterinary Anesthesiologists Suggestions For Monitoring


Objective: to ensure that a responsible individual is aware of the animal’s status at all times during anesthesia and recovery and is prepared either to intervene when indicated or to alert the veterinarian in charge about changes in the animal’s condition


Box 14-2   Commonly Monitored Parameters and Potential Causes of Abnormal Responses

*Pertains to horses and ruminants only; not useful in pigs, dogs, and cats.

II Monitoring key organ systems: Classic monitoring signs were described in terms of stages and planes of anesthesia. These classic signs use eye position and reaction, muscle relaxation, respiratory rate and pattern, and response to surgical stimulation to determine anesthetic depth (see Fig. 9-1). The signs of anesthesia were developed based on diethyl ether anesthesia but continue to be useful for describing the depressant qualities of anesthesia.

Central nervous system (CNS)

1. Observe reflex activity to monitor degree of CNS depression

a. Eye reflexes: Generally more useful and discriminative in large animals

b. Jaw tone: an indication of overall muscle relaxation. Moderate resistance to fully opening the mouth is present during a moderate surgical plane of anesthesia. More useful in small animals.

c. Anal reflex: dull to absent during a surgical plane of anesthesia (species dependent)

d. Pedal reflex: absent with toe pinch during a surgical plane of anesthesia. Withdrawal indicates a light stage of anesthetic that is likely to be inadequate to perform surgery.

2. Monitor skeletal muscle tone and degree of relaxation

3. Electroencephalography

a. Records and averages brain activity

b. Correlates to depth of anesthesia

(1) The bispectral index (BIS) can be used to monitor anesthesia (Fig. 14-1)

(2) Consciousness is represented by a BIS value of 100. Lower values indicate greater degrees of CNS depression (Fig. 14-2, B)

4. End-tidal concentration of anesthetic gases can be monitored, correlated to anesthetic depth, and compared to known MAC values for a particular inhalant anesthetic (see Fig. 14-2, A, and B)

Ventilation and the respiratory system (see Boxes 14-1 and 14-2; Figs. 14-3 through 14-8)

Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Monitoring During Anesthesia

Full access? Get Clinical Tree

Get Clinical Tree app for offline access