Lecture 6: Anesthesia Monitoring Equipment (copy)

What are the 6 ACVAA monitoring guidelines?

1. Ensure adequate blood flow (circulation)

2. Ensure adequate arterial blood oxygenation

3. Ensure ventilation is adequately maintained

4. Ensure body temperature does not seriously deviate from normal

5. Maintain legal record of significant events and enhance recognition of trends in monitored parameters

6. Ensure responsible person is aware of patient status at all times during anesthesia and recovery

What diagnostics are involved in basic anesthetic monitoring?

•Anesthetic depth signs

•Heart/Pulse rate, rhythm and pulse quality

•Respiratory rate and effort

•Noninvasive blood pressure (NIBP)

•Temperature

•Mucous membrane color & CRT

•Pulse oximetry (SpO2)

•End tidal carbon dioxide (ETCO2) = capnography

What are the basic anesthetic depth signs?

• Eye position

• Respiratory rate and pattern

• Muscle relaxation→Jaw and rear tone (knowt will not let me use actual word)

• Heart/Pulse rate

• Response to stimulation (procedure)

Which of these has adequate anesthesia and why?

the middle because the eye is rotated

When monitoring depth, how can you evaluate heart/pulse rate and rhythm?

1. Palpate pulses or heart beating

2. Esophageal or regular stethoscope

3. Ultrasonic Doppler device to detect the sound of blood flow in the artery.

4. ECG

5. SpO2-plethysmograph wave

What anesthetic depth information does pulse quality give?

subjective measurement of arterial filling and pressure → some idea of stroke volume and vasoreactivity

What are some sites to evaluate pulse quality for SA and LA?

• femoral pulse

• tongue

• lateral saphenous

• LA: transverse facial artery and jugular vein

What does each part of the ECG represent

P wave: atrial depolarization (contraction)

PR interval: time it takes for the electrical impulse to travel from SA node, through the atria, to the AV node, and into the ventricles, marking the delay before ventricular depolarization (QRS complex) begins

QRS complex: ventricular depolarization

ST segment: plateau when ventricles are contracting

T wave: ventricular repolarization (resetting)

What are the clinical uses for ECG besides HR and rhythm?

electrolye abnormalities

How are small animal (lead II) ECG leads placed?

◦ White lead ➔ Right elbow

◦ Black lead ➔ Left elbow

◦ Red lead ➔ Left stifle or abdomen

How are large animal (lead I or base apex) ECG leads placed?

◦ White lead ➔ Right jugular furrow

◦ Black lead ➔ left axilla region

◦ Red lead ➔ Any site remote from the heart

How are respiratory rate and effort evaluated during anesthetic depth monitoring?

1. Start by observing the patient’s thorax or the movement of reservoir bag

2. Esophageal stethoscope – passed to level of the heart

3. Various breathing frequency monitors can be employed ➔ give off an audible “beep”

4. Respirometer can be used to determine tidal volume (TV) and minute volume

5. Capnograph may also display RR Look at the wave!

What are the 2 main indirect noninvasive methods for obtaining blood pressure?

doppler and oscillometric

How does a doppler measure blood pressure?

use inflatable cuff to occlude blood flow in an artery, as the pressure in the cuff is released the Doppler detects the return of blood flow by reflection of sounds waves from moving RBCs

Where is a blood pressure cuff placed on dogs and cats?

the cuff goes on a limb (forelimb or hindlimb) or the tail base, and the probe is placed distal (further down) to the cuff, over an artery

Why should Doppler reading be kept > 80-90mmHg?

to be sure patient is not hypotensive

How is oscillometric blood pressure measured?

Blood flow through the arteries causes vibrations in arterial wall ➔ translated to air in the blood pressure cuff➔ detected and transduced into electrical signals to produce a reading

What are the advantages and disadvantages of doppler blood pressure?

Advantages:

• Audible pulse rate and rhythm

• Some technical skills required to place, but able to quickly obtain reading

Disadvantages:

• Does not give you all variables, SAP/DAP/MAP

• Not as accurate as direct BP, especially as patient becomes hypotensive

• Accuracy affected by selecting correct cuff size

What are the advantages and disadvantages of oscillometric blood pressure?

Advantages:

• Easy to place on limb

• Some can be set to run automatically

• Determines HR, SAP, MAP, and DAP

Disadvantages:

• Actual pressure reading takes longer than Doppler

• Not as accurate as Doppler method, especially in the following situations (but constant improvement): hypotensive patient, small patients, patient movement, arrhythmias, vasoconstriction

How is temperature monitored during anesthesia?

thermometer or temperature probe positioned in esophagus, intranasally, or in rear (knowt won’t let me use the actual word)

What does MM color and CRT grossly assess during anesthetic monitoring?

patient perfusion

What indirectly estimates % oxygen saturation of Hb and also displays the pulse rate (plethysmograph)?

SpO2

How is SpO2 measured?

Spectrophotoelectric device is applied over non-haired skin with pulsatile blood flow → Red and infrared light are absorbed differently by oxygenated and deoxygenated Hb. This difference is calculated and the % Hb saturation is displayed numerically

What SpO2 value is indicative of severe hypoxemia?

SpO2 of 90% = PaO2 of 60 mmHg

What effects the accuracy of SpO2?

•poor circulation due to vasoconstriction, hypotension, hypothermia

•movement artifact

•pigmentation

•tissue thickness

•anemia

•carbon monoxide and cyanide poisoning ➔ falsely high reading

•methemoglobinemia ➔ reads in the mid 80’s

•ambient light?

What is ETCO2?

inspired and expired CO2 concentration measured by capnography

What is a normal ETCO2?

35-45 mmHg

What is increased ETCO2 indicative of?

hypoventilation, hyperthermia

What is decreased ETCO2 indicative of?

hyperventilation, airway obstruction, hypothermia, decreased cardiac

This is a normal capnograph. What do A-B, B-C, C-D, D, and D-E represent?

A-B: baseline

B-C: expiratory upstroke

C-D: expiratory plateau

D: end-tidal concentration

D-E: inspiration

Which capnography sensor is which?

top: sidestream

bottom: mainstream

How does capnography work?

• CO2 produced in cells → carried to lungs → exhaled

• CO2 molecules absorb infrared light → concentration determined by comparing measure absorbance with know standard

How is capnography a useful monitoring tool?

• RR and estimation of PaCO2

• Diagnose disconnection or leak, V/Q mismatch, alveolar dead space, bronchoconstriction, airway obstruction, decreased cardiac output, return of spontaneous circulation during CPR, rebreathing of CO2

• determine if patient is correctly intubated

What are the normal temperature limits under general anesthesia?

98-102.5

What are the normal HR limits under general anesthesia for dogs, cats, horses, and ruminants?

dogs: 50-160

cats: 100-200

horse: 28-50 (foal up to 80)

ruminants: 48-90 for cows and 60-150 for sheep or goats

What are the normal respiration limits under general anesthesia?

10-20 bpm

What are the normal SpO2 limits under general anesthesia?

95-100%

What are the normal blood pressure limits under general anesthesia?

Hypotension defined as MAP < 60 and SAP < 80 (equine keep MAP > 70)