Modern anaesthesia methods in human hospitals have come a long way from getting a patient drunk or just pinning them down by strong assistants, and thankfully veterinary medicine is just as advanced. As well as modern drugs, techniques and protocols, some vet practices also boast they have ‘advanced monitoring equipment’. What is this equipment? What is it used for?

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Who Monitors Anaesthesia and Why?

Anaesthesia means a “loss of sensation”, in particular the loss of sensation to pain. We use anaesthesia to prevent pain during procedures, like the cut of a scalpel blade during surgery. There are three main types of anaesthesia – local anaesthetics block a very small area like a patch of skin; regional blocks cover a larger area such as a leg; general anaesthesia (GA) causes unconsciousness and prevents sensation of pain body-wide. General anaesthesia is our focus today.

During a general anaesthetic, a patient is at a greater risk of complications

Common complications include feeling pain despite being asleep, going too deep into anaesthesia and lowering their heart rate, starting to wake up, vomiting and aspiration of (breathing in) the vomit, loss of blood pressure, poor circulation and (very rarely) even death. Since the surgeon is busy operating, someone else has to monitor the patient to be on the lookout for warning signs that could indicate an unstable anaesthetic, and take steps to correct them. This will involve taking the patient’s heart rate, respiratory rate and pulse regularly, checking their eye position, gum colour and jaw tone, and more. These parameters should be measured at least every five minutes. Advanced monitoring equipment can assist with some of these measurements, and even measure others a human cannot do alone.

So who monitors everything?

In a veterinary practice there are a number of individuals who may monitor an anaesthetic. Most commonly this will be done by a veterinary nurse. They will have had training before qualifying on how to induce and maintain anaesthetics, as well as how to deal with complications. Veterinary surgeons also learn anaesthesia during their course, but often do not monitor anaesthetics directly. However, while performing procedures such as a surgery, they must be aware of the patient’s status too, warn the person monitoring for any issues (such as bleeding) and be prepared to pause their surgery if the anaesthetic must be adjusted. Finally, an anaesthetic may be monitored by a qualified veterinary anaesthetist. To become an anaesthetist, a veterinary surgeon or veterinary nurse must take an extra course designed to teach them the most up to date and advanced anaesthetic monitoring; and how to deal with the most extreme emergencies.

At the end of the day, though, in law the veterinary surgeon is responsible for the anaesthetic, whoever has been delegated the task of monitoring the patient.

What Advanced Monitoring Equipment is There?

Pulse Oximeter

A pulse oximeter detects the saturation of oxygen in the blood’s haemoglobin. This is a measure of circulation and how effectively the heart is carrying oxygen to a patient’s periphery, such as the tongue, toes or ears. The pulse oximeter is a little device that clips over a peripheral area. It uses light to determine how oxygenated tissue is. In a healthy patient, oxygen saturation should be at least 95%. 

If the oxygen saturation drops during a procedure, it can mean a few things. Firstly, the pulse oximeter may be faulty. The device does not work well on thick tissue, hairy areas or if the contact is poor; so we always check if it is attached properly first or test it on our finger. If it is working and the patient’s oxygen saturation is still low, it could indicate the heart is not pumping blood to the peripheries properly, there isn’t enough oxygen in the blood, or the lungs aren’t taking oxygen in at all. All of these are serious situations that may require emergency intervention. It can also indicate the patient is cold and the vessels have constricted; but either way, the “pulseox” can give us advance warning, before we can detect it with our hands or eyes.

Capnograph

A capnograph is one of the most powerful pieces of equipment a vet practice can have. It detects the concentration of carbon dioxide in exhaled breath from a patient. It works by sampling a small amount of the gas from a patient’s breathing tube. A capnograph samples constantly, providing a line graph trace that can show a patient’s breathing rate and quality; as well as identify a number of problems. A normal trace should show zero CO2 as a patient breathes in, then a swift increase to 35-45mmHg or 5% at the start of exhalation, a long pause at this value as the patient breathes out, and a rapid drop back to zero as exhalation ends. 

If the CO2 is too high, it could indicate a patient is rebreathing in exhaled CO2, the oxygen flow is not enough to push out enough CO2, excess CO2 has not been absorbed by the anaesthetic machine, or the patient is breathing too slowly. If the CO2 is too low, it can indicate their breathing tube has been disconnected or not placed properly, their heart has stopped, they are breathing too fast, or circulation is poor. Many of these situations are emergencies that a capnograph can identify almost instantly, giving time for the anaesthetist to correct the situation before more damage is done.

Blood Pressure Monitor

Blood pressure monitors are important to ensure that the heart is pumping effectively, and the tissues are receiving enough nutrients and oxygen without causing damage. It is another way to measure circulation. There are various ways we can measure blood pressure, including blood pressure cuffs, Doppler probes, and intravenous blood pressure monitors. 

A normal dog or cat’s blood pressure is around 100-160mmHg systolic (the high number) and 60-100mmHg diastolic (the low number) – approximately the same as humans’. During surgery, blood pressure can vary wildly. High blood pressure can indicate the patient’s body is responding to pain and more pain relief or anaesthesia is needed; or the anaesthesia is too light. Low blood pressure can be related to anaesthetic drugs used, blood loss, dehydration, shock, high CO2, and allergic reactions, as well as certain patient positions. We can adjust blood pressure if needed by changing the anaesthesia or surgical technique, or giving drugs. Because many drugs affect blood pressure, this must be accounted for too, but anaesthetics are much much safer now we can monitor the effects of medications on blood pressure in real time!

Electrocardiogram (ECG)

An electrocardiogram detects the electrical activity of the heart by detecting the electrical differences between two probes. The probes are safely attached to a patient with sticky pads in specific places, and the wires lead to the electrocardiogram machine itself. A normal healthy heart has a very specific trace on the electrocardiogram, so any abnormalities can indicate a problem. We can use it to also measure the heart rate and rhythm. It is important that we remember that even if the heart has stopped pumping, there can be electrical activity, so we cannot use ECG on its own. ECG will also not tell us how well the heart is pumping and its effect on circulation.

Abnormalities in ECG traces are called dysrhythmias, and there are a number that can be seen in anaesthetised patients, including extra or skipped beats, failure of parts of the heart to contract, faster or slower contracting, and different parts of the heart not contracting in sync. One of the most serious is ventricular fibrillation where the heart is not contracting with any effect – this requires defibrillation and injections of drugs to get the heart contracting smoothly again. The worst situation could show no electrical activity at all, indicating the heart has completely stopped beating. This would require CPR and chest compressions, or declaring the patient dead. 

These machines sound really complicated…

And maintaining a safe anaesthetic is a complex skill! However, these advanced monitoring systems can give us a valuable head start if something seems to be going wrong, giving us precious time to find and correct the cause. That’s why modern veterinary anaesthesia, in practices where the tools are available, is safer than it has ever been before.

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