Auditing hypotension under general anaesthesia to improve hypotension management

Hi everyone, I’m a veterinary nurse from Overdale Vets in Buckton, Derbyshire. I started quality improvement auditing in July 2023 with the topic around blood pressure monitoring during anaesthesia. I carried out two re-audits on the same topic to reassess and monitor for improvement, completing a full cycle audit. The audit was to assess the patient’s under general anaesthetic, which presented with hypotension.

Specifically looking at the number of patients who were hypotensive, the duration of hypotension, which methods of treatment were used and how effective the treatment was. The target was set to maintain a mean blood pressure of at least 60 to 70 millimetres of mercury. This mean allows for adequate tissue and organ perfusion. The main aim was to maintain adequate blood pressure to improve patients’ anaesthesia.

So to carry out the audit, I looked at a month’s worth of anaesthetic sheets, filtering out any patients which were normotensive or under sedation. I also didn’t include cat castrates or x-ray procedures in the audit. I recorded several different factors relating to blood pressure, including the first blood pressure reading, the time between induction and the first blood pressure, methods used to treat the hypotension, if IV fluids were used and at what rate, and lastly recording whether hypertension was resolved.

Following the first audit, I looked at ways we could improve and it was simply ensuring more patients had their blood pressure recorded and was a key point in the team using and understanding blood pressure during anaesthesia. We made more of a conscious effort to ensure every patient that went into theatre or on the dental table had their blood pressure measured.

The first audit results were quite significant with 53% of patients experiencing hypotension during their procedure. In the further two re-audits, this percentage improved to 27% in December and 26% in August. Therefore, the number of hypotensive patients reduced by half. The audit assessed whether the patient’s hypotension was resolved or not by the end of this anaesthesia.

I found these results surprising and I should have investigated the results more during the recovery period to see if hypotension influenced the patient’s recovery. July’s results showed that 88% of hypotension was not resolved and that’s a very high figure. Thankfully, the work the team put into improving the blood pressure reduces down to 66% in December and then again down to 39% in August.

The first plan was to double check cuff placement and start taking readings from the tail as this is more accurate as it is in line with the heart. We started using surgical fluid rates routinely during Ops with cats receiving 3ml per kilo an hour and dogs receiving 5ml per kilo an hour. This is the recommended fluid rate during surgery to maintain adequate profusion. For the first two audits, twice maintenance was the fluid rate of choice.

However, by the last audit, the surgical rate was mainly used. The treatment plan was to use a multimodal technique, checking the patient’s temperature, assessing if the anaesthetic is too deep. Is the patient painful? Can we use any more analgesia? Which also benefits reducing the anaesthetic gases down. These all have a knock-on effect to each other. And then if none of these methods worked to increase the blood pressure, that’s when we would look at using a fluid bolus.

Fluid boluses were a bit of a scare at first. Everyone was apprehensive to use them as they struggled to work them out and they also didn’t want to overload the patients with the fluids. After spending time working the rates out with the nurses and assessing perfusion parameters, we became more comfortable in using them to treat hypotension. One of the things I found really surprising is how different we all monitor anaesthetics. By introducing this audit, it helps everyone look at the different parameters as a whole rather than each being individual.

For example, too high isoflourane will cause hyperthermia and hypertension or too low temperature can cause hypotension, etc. Other practices can use this order and anesthetise hypotensive patients by following a few simple steps and working out what is causing the hypotension.

The steps I’d say to follow are first check the cough, check what the vet is doing. Is the anesthetic too deep? Is the patient hypothermic? Can multimodal analgesia be used? And then assess if a fluid bolus is required, making sure to assess perfusion parameters at each bolus. Thank you for listening.