The Gold Standard in Veterinary General Anesthesia Monitoring

The Importance of General Anaesthesia Charting

First and foremost, an anaesthetic record serves as a witness to the events that occur during the period just before, during and just after anaesthesia administration. It also acts as a legal document. This document can either be recorded electronically or by hand. It is extremely important to maintain an accurate general anaesthesia chart because disciplinary actions will be brought against veterinarians who fail to record accurate charts. This may result in malpractice litigation, especially if something were to go wrong during a procedure.

How to appropriately maintain an Anaesthesia Chart

An anaesthetic record should be accurately labelled and legible. An automated or digital anaesthetic record could be useful in this instance if there is a high-risk surgery occurring where lots of fluid need to be monitored. Any mistakes should not be whited out or scribbled out but rather a single or double line marked through a mistake. This should also be initialled. Pen is also preferred since pencil had the potential to be removed against forms of friction. Depending on legislation for an area, these anaesthetic records should be kept for 3 to 5 years.2 It is understood that in an event where the health of the patient is priority over recording on the anaesthesia chart, listing the chain of events retrospectively is still expected.

How to fill out a general anaesthesia chart

Pre-operative

The general information for the pet should be filled out. This includes the name, breed, age, sex and the owner of the pet. The weight and body condition score should also be noted because this information is essential to determine the amount of anaesthesia a pet should receive. Other indicators to be noted are the temperature, heart rate, respiratory rate, thoracic auscultation and the MM and CRT status. Additionally, the ASA classification should be indicated which indicated the health status of the patient before admitting them for surgery. It also will indicate how drugs and vitals should be monitored during surgery. The procedure that is occurring should also be listed along with the size and site of the IV catheter, whether the ET tube is cuffed or uncuffed and what breathing circuit is to be used. All the pre-anaesthetic medication should be listed with the does (mg/kg) or volume (mL), route and time. The fasting status of the patient should also be noted in the pre-anaesthetic procedure and this should be checked with the client. Even though it is not a legal requirement, an indication of whether the owner consent form has been signed should be noted in case of any legal liabilities. This should especially be considered in high risk surgeries.

During Procedure

It is important to note that monitoring the patient is a priority over checking the equipment and charting. There are five main areas to be monitored during the procedure, these are; the central nervous system, the cardiovascular system, the respiratory system, oxygenation and temperature.3 The IV fluid type and rate can also be monitored on the chart. The constant rate infusion (CRI) rate should also be indicated alongside what drugs are being monitored under the CRI rate to avoid toxic reactions or side effects1 as well as to effectively manage the sedation of the pet.

Central Nervous System

In short, monitoring the reflexes and the muscle tone of the central nervous system allows us to monitor the function of the brain. The jaw tone, palpebral reflex, corneal reflex, pedal reflex, eye position, pupil position, laryngeal reflex and lacrimation status all indicate the status of the central nervous system.3 This should all be recorded on the general anaesthesia chart 15-30 min intervals.

Cardiovascular System

The heart rate, mean blood pressure, systolic and diastolic pressure should all be recorded on a grid on the general anaesthesia chart. The systolic rate is often indicated with a 'V' and diastolic pressure with a 'ʌ'.1 The heart rate is often indicated by an 'X'.1 The colour mucous membrane can also indicate the perfusion. A pink mucous membrane indicates good perfusion and oxygenation. A pale, white or slightly blue coloured mucous membrane all indicate poor perfusion3. A mucous membrane that is muddy coloured indicated poor perfusion and oxygenation.

Respiratory System

The respiratory rate and the end tidal CO2 pressure (mmHg/kPa) should be monitored to check the status of the respiratory system.5 The Respiratory rate can be monitored in the grid alongside the heart rate and blood pressure whereas the end tidal volume can be written below the grid in 15 -30 min intervals. The deeper the pet is under anaesthesia, the higher their respiratory rate becomes.

Oxygenation

To measure the oxygen levels in the patient under anaesthesia, the readings form the pulse oximeter should be indicate in readings of SpO2% every 15-30 min.5 Additionally, the colour of the mucous membrane can indicate oxygenation where a pink tissue indicate good oxygenation and perfusion whereas a muddy colour indicate poor oxygenation and perfusion.

Temperature

Hypothermia is almost inevitable during anaesthesia, however, simple measures can be taken to reduce the amount of heat loss. By recording the temperature every 15-30min, an indication of what needs to be done can be accurately assessed. For example, if body temperature is decreasing, adding more blankets will help reduce heat loss.1 Or, if temperature is too high, reducing external heating devices or increasing O2, adding cool packs can help reduce body temperature.

Stages of Anaesthesia

There are four stages of anaesthesia which can be classified by the animal's response pain, their reflexes, and central nervous system responses. It is important to monitor these stages as plunging an animal too deep into anaesthesia may result in irreversible damage or even death. The ideal stage of anaesthesia is between planes 2 and 3 of stage 3.

Stage 1

Conscious but disorientated, some pain is still tolerated

Stage 2

Unconscious and uninhibited action. Suppression of higher control centres

Stage 3

Progressive depression of respiration, circulation, reflexes and muscle ton. Stage 3 is divided into 4 different planes.

Plane 1: Light Anaesthesia

• respiration is regular
• pupils are constricted
• salivation, lacrimation, pharyngeal and laryngeal reflexes persists (can intubate dogs and horses but not cats)
• muscle tone is present
• reaction to pain causes an increased heart rate, respiration rate and blood pressure

Plane 2: Surgical Anaesthesia

• decrease in tidal volume but increase in respiration rate
• surgical stimulation produces heart rate, blood pressure and respiration rate
• oropharynx reflexes diminished in dogs but not in cats
• deep tracheal reflexes persist
• eye centrally fixed
• muscle tone decreases

Plane 3: Deep surgical anaesthesia

• intercostal muscle lag behind contraction of the diaphragm
• eyeball rotated downwards in ventromedial-direction
• palpebral reflexes are diminished in dogs but slowed in cats
• corneal reflexes diminished in dogs and cats but slowed in horses
• lacrimation, salivation, oropharynx and laryngeal reflexes are diminished
• Deep visceral pain is still felt
• Muscle relaxation is good

Plane 4: Anaesthesia is too deep

• Diaphragmatic breathing and tidal volume is reduced
• Beginning of paralysis of intercostal muscles
• Corneas is dry and dull and pupils are dilated
• Heart rate and blood pressure reduce
• Tracheal tug may be present (the exaggerated movement of the mandible, larynx and trachea) which is often mistaken for anaesthesia decreasing

Stage 4

Period between cardiovascular arrest and collapse and respiratory arrest, This period is determinant on oxygenation status before respiratory arrest and the species under anaesthesia

Post-operative

After the operation, recovery instructions should be listed for the pets. Any post-operative medications, their time administered, dose and route should also be indicated similar to that of the pre-anaesthetic medication. The IV catheter care should also be ticked off which includes removal after recovery and its maintenance and flushing.5,6 Any post-operative fluids or analgesia should be noted. The temperature, heart rate, respiratory rate, the MM and CRT status and pain score can also be monitored during recovery. Any additional important notes should also be indicated.6

References:

[Bryant S. Anaesthesia for Veterinary Technicians. John Wiley & Sons. 2010. 78-85

Pettit, TH. Hospital Administration for Veterinary Staff. Goleta: American Publication Company, Inc. Powers, MJ. 1994.

Powers MJ. Record-keeping in anaesthesia: what the law requires. Br J Anaesth. 1994 Jul;73(1):22-4. doi: 10.1093/bja/73.1.22.

World Small Animal Veterinary Association Congress. The Ins and Outs of Anaesthetic Monitoring for Optimal Patient Outcomes. 2018.

Small Animal Surgery. Anaesthesia Chart. 2021. Available form: http://smallanimalsurgery.com.au/wp-content/uploads/Anaesthetic-chart-fillable-form.pdf Association of Veterinary Anaesthetists. Anaesthesia and Recovery Record. 2021. Available from: https://ava.eu.com/wp-content/uploads/2015/11/AVA-ASA-Hi-Electronic.pdf