Plus-Hex CLINICAL believe the patient is stable and the VN is competent to carry out this task; however, the anaesthetist must be available in case the VN requires their assistance. The anaesthetist will provide the VN with a comprehensive list of high and low values for each vital sign, so they know when assistance is required.
Pulse oximetry is a non-invasive method of measuring the O 2 saturation( SpO 2
) of the haemoglobin in arterial blood. A transmittance pulse oximeter is used, with the tongue being the most common site for probe placement. The SpO 2 of a healthy conscious patient should be between 95 % and 99 %. It is important to measure and record the SpO 2 as it will show how efficiently the circulatory system is oxygenating the tissues. An SpO 2 of less than 90 % will indicate hypoxia, which can have acute adverse effects on the internal organs. Hypoxia can be caused by the patient hypoventilating, an insufficient fresh gas flow supply or pulmonary disease, so it is vital to identify the cause and treat it swiftly.
The pulse oximeter will also display the patient ' s pulse rate, which is helpful in situations where it is not possible to measure the heart rate by other means during surgery – for example, when a stethoscope would breach the sterile field [ 34 ]. Fortunately, this patient ' s SpO 2 indicated good saturation throughout the anaesthetic, so no interventions were required.
ECG is another non-invasive form of monitoring, which monitors the electrical output of the heart. In healthy dogs, normal sinus rhythm or sinus arrhythmia are seen most commonly, but other arrhythmias can occur. The ECG should be monitored closely so these can be picked up quickly if they develop [ 35 ]. This patient had normal sinus rhythm throughout the anaesthetic.
A capnograph monitors the concentration of CO 2 in the gases expired by the patient, which is known as end-tidal CO 2
( EtCO 2
). It is possible to monitor EtCO 2 by arterial blood gas analysis; however, this method is invasive and more difficult to use, and so capnography is preferred as it is non-invasive and produces results in real time. A healthy, conscious patient should have an
EtCO 2 between 35 mmHg and 45 mmHg; a value above 50 mmHg suggests poor ventilation and mechanical ventilation may need to be initiated. In addition to monitoring EtCO 2
, the capnography trace should be monitored to ensure it maintains a regular waveform; abnormal or absent waveforms would indicate inadequate ventilation and the need for assistance [ 33 ]. This patient ' s EtCO 2 was maintained in the range of 35 – 45 mmHg throughout the anaesthetic, indicating adequate ventilation.
Patients under anaesthetic cannot thermoregulate, so their temperature should be closely monitored throughout the period of anaesthesia. Hypothermia during both the anaesthetic and the recovery period can be serious, as it depresses the central nervous system, which will prolong drug metabolism and the recovery period. It will also increase wound healing time and infection rates as hypothermia interferes with haemostasis. Therefore, steps should be implemented to reduce the risk of hypothermia.
A healthy, unanaesthetised dog will have a body temperature between 37.5 ° C and 39.2 ° C [ 36 ]. If the body temperature begins to decrease, warming techniques should be initiated. It is also important to monitor the patient ' s body temperature to ensure it does not become hyperthermic. This happens less commonly in anaesthetised patients, but it can occur if a patient is being excessively heated or if it has thick fur or a large amount of body fat. As mentioned previously, the use of a rebreathing circuit and HME filter may increase the temperature of the inspired gases, which can influence the patient ' s body temperature [ 23, 24 ]. The patient ' s body temperature did decrease to below 37.5 ° C, despite the use of a warm air blanket( Bair Hugger, 3M), so active warming was continued into recovery.
A patient ' s BP should be monitored throughout anaesthesia as hypotension is commonly reported in anaesthetised dogs and cats. BP is defined as the pressure exerted by blood on the wall of a blood vessel [ 37 ], and it is composed of systolic and diastolic pressures. Systolic pressure is the pressure created at the end of a cardiac cycle, when the pressure is at its highest, whereas diastolic pressure is the pressure created at the beginning of a cardiac cycle, when the pressure is at its lowest. These values can be used to calculate a mean BP.
BP can be measured either invasively or non-invasively. Invasive BP monitoring is the most accurate technique, but it is also the most challenging as it requires the placement of an arterial catheter. The non-invasive methods of monitoring BP are oscillometry, Doppler and high-definition oscillometry. This patient ' s BP was monitored using an oscillometric machine.
A healthy, unanaesthetised dog will have a mean BP between 70 mmHg and 90 mmHg; however, hypotension is common during anaesthesia because many anaesthetic drugs, particularly the inhaled anaesthetic agents, decrease cardiac contractility and cause vasodilation, resulting in a decrease in arterial BP. Hypotension can result in insufficient blood flow to the major organs, which can lead to organ damage, so it is essential to monitor BP and take swift action if hypotension develops. It is advised that the BP of anaesthetised patients should be kept over 60 mmHg to ensure adequate tissue perfusion [ 37 ]. The patient in this case maintained a normal BP throughout the anaesthetic.
Volume 40( 3) • June 2025
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