Intraoperative Patient Monitoring During Surgery

Intraoperative Patient Monitoring During Surgery

Effective intraoperative monitoring is one of the most critical responsibilities a veterinary technician or assistant performs during surgery. The anesthetized patient cannot protect its own airway, regulate its own vital functions, or communicate distress. You are the patient's advocate and early-warning system. Detecting a change in status and reporting it promptly can mean the difference between a routine recovery and a preventable anesthetic death.

Parameters You Monitor and Why

Pulse oximetry (SpO₂) measures the percentage of hemoglobin saturated with oxygen in peripheral blood. Normal SpO₂ in an anesthetized patient is generally ≥95%. Values below 95% signal hypoxemia and require immediate action. The probe is typically placed on the tongue, toe web, lip, or ear.

Capnography (EtCO₂) measures end-tidal carbon dioxide, which reflects how well the patient is ventilating. Normal end-tidal CO₂ in small animal patients is roughly 35–45 mmHg. A rising value may indicate hypoventilation or rebreathing; a sudden drop toward zero often signals apnea, a disconnected circuit, or cardiac arrest.

Non-invasive blood pressure (NIBP) is measured by an oscillometric cuff placed on a limb or tail. Mean arterial pressure (MAP) below 60 mmHg is generally considered hypotension and requires prompt reporting and intervention. Systolic, diastolic, and mean values should all be recorded.

Electrocardiography (ECG) monitors heart rate and rhythm. Normal sinus rhythm at an appropriate rate for the species is expected. You must recognize abnormalities such as bradycardia, tachycardia, or irregular rhythms and report them immediately. Note that ECG tells you about electrical activity only — it does not confirm cardiac output.

Respiratory rate and character can be observed by watching chest wall movement, the rebreathing bag, or capnograph waveform. Any sudden change — too slow, too fast, or absent — is significant.

Temperature is often monitored with a rectal or esophageal probe. Hypothermia (core temperature falling below normal) is a common anesthetic complication, especially in small patients.

Mucous membrane color and capillary refill time (CRT) provide a rapid clinical assessment of perfusion. Pink, moist membranes with CRT under two seconds are normal; pale or cyanotic membranes are emergency findings.

Reading and Recording the Anesthetic Sheet

All parameters must be recorded on the anesthetic monitoring sheet at consistent intervals — typically every five minutes. This paper or electronic record becomes a permanent legal medical record. Every entry must include a timestamp. Incomplete or inaccurate records are both a patient safety risk and a professional liability.

When you record values, write what the monitor actually displays. Do not estimate. If a monitor is alarming, document the alarm time, the value, whom you notified, and what action was taken.

Setting Alarm Thresholds

Before surgery begins, confirm that all monitor alarms are active and set to clinically appropriate limits per your supervisor's or protocol's direction. Silencing an alarm without addressing its cause is a serious error. Alarm fatigue — ignoring alarms because they sound frequently — is a recognized patient safety hazard in both human and veterinary medicine.

Anesthetic Depth Assessment

Beyond machine numbers, you assess anesthetic depth through clinical signs. Light anesthesia may present as increased muscle tone, swallowing, eye movement, or response to surgical stimulus. Excessive depth may show profound cardiovascular and respiratory depression. Depth assessment requires integrating multiple findings — no single sign is definitive. Always report changes in depth to the veterinarian.

Key depth indicators include: palpebral reflex, jaw tone, eye position and pupil size, response to stimulation, and heart and respiratory rate trends.

Fluid Therapy During Surgery

Intravenous crystalloid fluids such as lactated Ringer's solution (LRS) are routinely administered during anesthesia to support blood pressure, replace insensible losses, and maintain venous access. The veterinarian will prescribe the fluid type and rate. A commonly cited intraoperative crystalloid starting point for healthy patients is in the range of 5–10 mL/kg/hr, but the exact rate is always a veterinarian order — never assume or change it without direction.

You calculate the drip rate for a standard gravity IV set using the formula:

Drops per minute = (Volume in mL/hr × Drop factor) ÷ 60

Standard macrodrip veterinary sets commonly deliver 10 or 15 drops per mL; microdrip sets deliver 60 drops per mL. Confirm the drop factor printed on the administration set packaging.

Document cumulative fluid volume at each five-minute interval on the anesthetic record.

Detecting and Reporting Deterioration Events

When an alarm activates, follow this sequence:

1. Look at the patient first — confirm the finding is real and not a monitor artifact.

2. Identify which parameter is abnormal and by how much.

3. Verbally report to the surgeon immediately: state the parameter, the current value, and the normal range. Example: *"SpO₂ has dropped to 88% — normal is above 95%."

4. Document the time, the value, your report, and any response.

5. Follow further instructions from the supervising veterinarian.

You do not independently change anesthetic agent delivery, administer drugs, or alter ventilator settings without a veterinarian's order. Your role is to detect, report, and assist.

Safety Reminders

• Never leave a monitored surgical patient unobserved, even briefly.
• Confirm all equipment is functioning and calibrated before the patient is induced.
• Know the location of emergency drugs and crash cart before surgery begins.
• Scope of practice: detecting and reporting abnormalities is your responsibility; treatment decisions belong to the veterinarian.