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HLT-VET42-09 · Lesson 6 · 26 clock hours · practice

Advanced Anesthesia Monitoring and the Anesthetic Record

Objective. The student will monitor an anesthetized patient under veterinarian supervision, accurately recording all physiologic parameters at required intervals, recognizing indicators of lightening or deepening anesthetic depth, and responding to a simulated complication within scope.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Accurate Anesthesia Monitoring Matters

The anesthetized patient cannot protect itself. It cannot signal pain, cannot breathe on command, and cannot compensate for a dropping blood pressure without support. The veterinary technician serves as the patient's advocate during every moment of anesthesia. Accurate, timely documentation on the anesthetic record is not a clerical task—it is a clinical safety tool that allows the supervising veterinarian to detect trends, adjust the anesthetic plane, and intervene before a small problem becomes a crisis.

The Pre-Anesthetic Machine Check

Before any patient is connected to the anesthesia machine, a standardized machine check must be completed and documented. This protects both patient and team.

Checklist steps (perform in order):

1. Oxygen supply – Confirm the oxygen tank pressure or pipeline supply is adequate. Know the minimum pressure your facility requires before starting a case.

2. Vaporizer – Check that the agent-specific vaporizer is filled to the correct level, the fill port cap is tight, and the dial moves freely and returns to zero.

3. Rebreathing circuit – Inspect all hoses for cracks, proper connections, and a patent Y-piece. Confirm reservoir bag is the correct size for the patient (roughly 60 mL/kg body weight).

4. Pop-off valve – Confirm it opens and closes properly. A stuck-closed pop-off valve can cause fatal barotrauma within seconds.

5. Carbon dioxide absorbent – Check the color indicator. Most absorbents turn violet or white when exhausted; replace if color change exceeds approximately one-half of the canister.

6. Leak test – Occlude the patient end of the circuit, close the pop-off valve, fill the system to approximately 20 cm H₂O with oxygen, and observe the pressure gauge for 30 seconds. A drop of more than a few cm H₂O indicates a leak that must be found and corrected before proceeding.

Document pass/fail for each item. Never skip a step to save time.

Parameters to Monitor and Record

Record all parameters at every five-minute interval from induction to extubation. Late or missing entries on the anesthetic record are a patient-safety failure.

| Parameter | Normal range (dog/cat, general guidance) | What a significant change may indicate |

|---|---|---|

| Heart rate | ~60–140 bpm (varies by species, size, agent) | Bradycardia: deep plane, vagal tone, hypothermia; Tachycardia: light plane, pain, hypoxia |

| Respiratory rate | 8–20 breaths/min | Apnea or very slow rate: too deep, opioid effect |

| SpO₂ | ≥95% (ideally ≥98%) | Values <90% are clinically significant hypoxemia |

| End-tidal CO₂ (EtCO₂) | 35–45 mmHg | High: hypoventilation; Low: hyperventilation or equipment issue |

| Blood pressure (MAP) | ≥60–70 mmHg mean arterial | MAP <60 mmHg = hypotension requiring intervention |

| Temperature | Maintain within normal range for species | Hypothermia common under anesthesia; active warming needed |

| Eye position | Ventromedial rotation = surgical plane | Centered or rotated back toward normal = lightening |

| Jaw tone | Relaxed = adequate depth | Increased tone = lightening |

| Palpebral reflex | Slow or absent at surgical plane | Brisk reflex = lightening; completely absent = may be too deep |

Recognizing Changes in Anesthetic Depth

Lightening (patient becoming less deeply anesthetized): heart rate and blood pressure rise, respiratory rate increases, jaw tone returns, palpebral reflex becomes brisk, eye rotates toward a more central position, and swallowing or chewing movements may appear. Alert the veterinarian immediately; do not increase vaporizer without a direct order.

Deepening (patient going too deep): heart rate falls, blood pressure drops, respiratory rate slows or stops, muscle tone is completely absent, and pupils may become fixed and dilated. Alert the veterinarian immediately; be prepared to reduce or turn off the vaporizer and initiate manual ventilation.

Responding to Simulated Complications Within Scope

Apnea (patient stops breathing):

1. Note the time and immediately alert the supervising veterinarian.

2. Begin manual (bag) ventilation at approximately 8–12 breaths per minute, delivering gentle tidal volumes—watch for chest rise.

3. Document the event, time, duration, and your actions on the anesthetic record.

4. Do not adjust the vaporizer dial without a veterinarian order unless you have a standing protocol authorizing it.

Hypotension cue (MAP <60 mmHg or oscillometric alarm):

1. Verify the reading is real—check cuff placement and recheck.

2. Alert the veterinarian immediately with the specific value.

3. Be prepared to relay fluid therapy rate or other interventions as directed.

4. Document on the anesthetic record.

Safety Reminders

Key terms10

Anesthetic recordA written or electronic document on which physiologic parameters, drug doses, and clinical events are recorded at regular intervals throughout the anesthetic procedure; serves as both a clinical safety tool and a legal medical record.
End-tidal CO₂ (EtCO₂)The concentration of carbon dioxide measured at the end of a patient's exhaled breath, expressed in mmHg; reflects alveolar CO₂ and is used to assess adequacy of ventilation.
SpO₂Peripheral oxygen saturation measured non-invasively by pulse oximetry; reflects the percentage of hemoglobin saturated with oxygen.
Mean arterial pressure (MAP)The average arterial blood pressure during one cardiac cycle; a MAP below approximately 60 mmHg is considered hypotension and is a threshold for clinical intervention in anesthetized patients.
Palpebral reflexThe involuntary blink response elicited by lightly touching the medial or lateral canthus of the eye; used to assess anesthetic depth—a brisk reflex suggests a lighter plane.
Pop-off valve (APL valve)The adjustable pressure-limiting valve on a rebreathing circuit that allows excess gas to escape into the scavenging system; must remain open during spontaneous breathing to prevent dangerous pressure buildup.
Leak testA standardized pre-anesthetic procedure in which the breathing circuit is pressurized to a set level and monitored for pressure drop, confirming the system is airtight before patient connection.
ApneaCessation of breathing; under anesthesia this is an emergency requiring immediate veterinarian notification and manual ventilation support.
Ventromedial eye rotationRotation of the globe downward and toward the nose; commonly observed at a surgical plane of anesthesia in dogs and cats and is one indicator of adequate anesthetic depth.
Scavenging systemThe component of the anesthesia machine that captures waste anesthetic gases exhausted from the pop-off valve and directs them safely away from the breathing zone of personnel.

Worked examples4

1. At the 10-minute mark, the oscillometric monitor reads MAP 55 mmHg. At the 15-minute mark it reads MAP 52 mmHg. What trend is this, what threshold has been crossed, and what are your immediate actions in order?
  1. Step 1 – Identify the trend: MAP has declined from 55 to 52 mmHg across two consecutive 5-minute readings, indicating a downward trend.
  2. Step 2 – Apply the clinical threshold: MAP below approximately 60 mmHg is defined as hypotension in the anesthetized patient; both values are below this threshold.
  3. Step 3 – Verify the reading: Confirm cuff placement is correct (cuff width approximately 40% of limb circumference), recheck the reading if any doubt about artifact.
  4. Step 4 – Alert the supervising veterinarian immediately, stating the parameter, both values, and the time points (e.g., 'MAP was 55 at 10 minutes and is now 52 at 15 minutes').
  5. Step 5 – Document both values, the time of each reading, and the time you notified the veterinarian on the anesthetic record.
  6. Step 6 – Await and carry out the veterinarian's orders (e.g., fluid bolus, vaporizer adjustment); document the intervention and the time it was initiated.
Answer: Both values meet the definition of hypotension (MAP <60 mmHg). The trend is worsening. Immediate actions: verify the reading, alert the veterinarian with specific values and times, document on the anesthetic record, and act on the veterinarian's instructions.
2. During the leak test you pressurize the circuit to 20 cm H₂O with the pop-off valve closed. After 30 seconds the gauge reads 14 cm H₂O. What does this result mean, and what must you do before connecting the patient?
  1. Step 1 – Calculate the pressure drop: 20 − 14 = 6 cm H₂O drop in 30 seconds.
  2. Step 2 – Interpret the result: A drop of more than a few cm H₂O indicates a leak in the circuit; this result (6 cm H₂O drop) fails the leak test.
  3. Step 3 – Do not connect the patient to this circuit.
  4. Step 4 – Systematically inspect all connections—hose junctions, Y-piece, endotracheal tube adapter, vaporizer mount, and canister seal—to locate the leak.
  5. Step 5 – Repair or replace the faulty component and repeat the leak test until the circuit holds pressure within the acceptable limit.
  6. Step 6 – Document the initial failure, the corrective action taken, and the passing retest result on the pre-anesthetic checklist before proceeding.
Answer: The circuit fails the leak test (6 cm H₂O pressure loss in 30 seconds). The patient must not be connected. Find and correct the leak, repeat the test until it passes, and document all findings.
3. You are recording parameters every 5 minutes for a 30-minute case. Your anesthetic record has columns for 0, 5, 10, 15, 20, 25, and 30 minutes. At the 20-minute mark you are distracted and the 20-minute column is blank. How many total interval columns does the record have, and what percentage of the record is complete if one interval is missing?
  1. Step 1 – Count the required recording intervals: 0, 5, 10, 15, 20, 25, 30 minutes = 7 intervals.
  2. Step 2 – Count completed intervals: 7 total − 1 missing = 6 completed intervals.
  3. Step 3 – Calculate percent complete: 6 ÷ 7 = 0.857, or approximately 85.7%.
  4. Step 4 – Apply the pass standard: the competency check requires 90% accuracy on the record, and 85.7% falls below that threshold.
  5. Step 5 – Conclusion: One missed interval causes the record to fall below the 90% pass standard. Consistent recording at every interval without distraction is required.
Answer: The record has 7 required intervals. With one missing, the record is approximately 85.7% complete, which is below the 90% pass threshold. No intervals may be skipped.
4. The patient weighs 15 kg. You need to select the correct reservoir (rebreathing) bag size. Using the general guideline of approximately 60 mL/kg, what bag volume should you choose?
  1. Step 1 – Apply the formula: bag volume (mL) = body weight (kg) × 60 mL/kg.
  2. Step 2 – Calculate: 15 kg × 60 mL/kg = 900 mL.
  3. Step 3 – Match to available bag sizes: common sizes are 0.5 L, 1 L, 2 L, 3 L, 5 L. The calculated value of 900 mL falls between 0.5 L and 1 L; select the 1 L bag as the closest size that meets or exceeds the requirement without being excessively large.
  4. Step 4 – Confirm: A 1 L bag is appropriate for a 15 kg patient; a bag that is too small will not allow adequate tidal volumes and may alarm; a bag that is too large makes visual assessment of breathing difficult.
Answer: 900 mL calculated; select a 1 L reservoir bag for a 15 kg patient.
In class: Complete a pre-anesthetic machine check using the standardized checklist (leak test, oxygen flow, vaporizer, rebreathing circuit, pop-off valve, carbon dioxide absorbent color check) and document results before any procedure begins. · Monitor a live or simulator anesthesia case for 30 minutes, recording heart rate, respiratory rate, SpO2, end-tidal CO2, blood pressure, temperature, eye position, jaw tone, and palpebral reflex every five minutes on the anesthetic record sheet. · Respond to two instructor-introduced simulated complications (e.g., apnea, hypotension cue) by verbalizing the correct immediate action within scope—alerting the veterinarian, initiating manual ventilation for apnea, or adjusting vaporizer—and documenting the event on the anesthetic record.
Materials: Anesthesia machine, rebreathing circuit, pulse oximeter, capnograph, oscillometric blood pressure unit, electronic thermometer, anesthetic record form, instructor-scripted complication cards, Tranquilli et al. Lumb & Jones' Veterinary Anesthesia and Analgesia (reference)
Check: Anesthetic record accuracy check and instructor observation: all parameters recorded at every 5-minute interval, no more than one transcription error, and correct verbal response to both simulated complications; pass = 90% accuracy on record plus correct response to both complications.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Anesthesia and Pain Management
1. A veterinary technician completes the pre-anesthetic machine check and finds that more than half of the CO₂ absorbent granules have changed color. What is the correct action?
Anesthesia and Pain Management
2. During monitoring, the patient's palpebral reflex becomes brisk, jaw tone increases, and heart rate rises from 72 to 98 bpm. These signs together most likely indicate:
Anesthesia and Pain Management
3. An anesthetized dog stops breathing. After confirming apnea, which is the correct immediate sequence of actions within the veterinary technician's scope?
Anesthesia and Pain Management
4. Which SpO₂ value measured by pulse oximetry should prompt immediate notification of the supervising veterinarian as clinically significant hypoxemia?
Anesthesia and Pain Management
5. A technician pressurizes the rebreathing circuit to 20 cm H₂O during the pre-anesthetic leak test. After 30 seconds the gauge reads 19 cm H₂O. How should this result be interpreted?
Anesthesia and Pain Management
6. On the anesthetic record, a technician records parameters at 0, 5, 10, 15, and 30 minutes but misses the 20- and 25-minute intervals in a 30-minute case (7 required intervals). What percentage of intervals was recorded, and does this meet the 90% competency standard?
Anesthesia and Pain Management
7. End-tidal CO₂ rises to 58 mmHg in an anesthetized patient breathing spontaneously. This finding most likely indicates:
Anesthesia and Pain Management
8. Which of the following is the primary reason the pop-off valve on the anesthesia machine must be reopened immediately after completing the leak test?
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