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Anaesthesia & Analgesics

Depending on the investigations or procedures required, your pet may need to be anaesthetised.

Our Anaesthesia Service consists of our team of specialist anaesthetist vets; Dr Kristina Lehnus, Dr Marieke De Vries and Dr Tristan Merlin, along with our Anaesthesia Nurse Practitioner, Jennifer Busby.

Depending on the investigations or procedures required, your pet may need to be anaesthetised. Whilst under sedation or anaesthesia, our patients are monitored closely, and records are taken with the assistance of our anaesthesia team.

We also have ongoing pain scoring through each patient’s stay with us to ensure they are as comfortable as possible.

When surgeries are finished, an ongoing analgesia plan will be discussed between the specialists to determine the best ongoing care for the patient. Analgesia is essential in patient recovery and patients will only be discharged from the hospital following procedures, once we are satisfied any pain can be managed at home.

Why does my pet potentially require sedation or anaesthesia?

Depending on the nature of investigations or procedures required, your pet may need to be anaesthetised or sedated. This involves administering drugs that make the animal “sleepy”, provide differing degrees of pain relief and muscle relaxation to allow the procedure to be performed safely for both staff and animals. Whether sedation or anaesthesia is more suitable for your pet, depends on the type of procedure, the temperament of your pet, concurrent diseases your pet has, how painful a procedure could be and how immobilised and relaxed your pet must be. Each sedation or anaesthetic is specifically prepared for each individual patient. Your pet will monitored by one of our anaesthetists and theatre nurses the entire time, until they are fully recovered. After this, they will receive a lot of TLC from our ward nurses, who will continue to monitor them until they leave the hospital to ensure they are comfortable and progressing as expected.

What happens when my pet has a sedation or anaesthetic?

Your pet will generally be starved for around 12 hours before receiving sedative or anaesthetic medication (specific correspondence is sent to you before your appointment). The reasons for this are outlined below. After their assessment by the anaesthetist, your pet will receive a first dose of calming drugs once in the theatre preparation area of the hospital. Depending on how calm your pet is, he or she will either have a cannula placed in order to administer this dose, or receive an intramuscular injection to allow venous cannula placement. To reduce the risk of infection, a fur must be shaved, and the skin prepared aseptically before this cannula is placed. In some cases, where your pet may be very anxious during vet visits, we may prescribe calming medication for your pet to take the night before and the morning of the appointment.

How sleepy he or she becomes following the first injection of calming drugs, depends on the type of drug and the dose given (see below for the difference between sedation and anaesthesia). If your pet is being sedated, drugs are administered until the desired level of immobilisation and relaxation is achieved. If your pet is being anaesthetised, additional drugs are administered until a tube can be placed in their airway (trachea) to protect the airway and deliver oxygen and, depending on the anaesthetic protocol, anaesthetic gases. During the anaesthetic the animal is not consciously aware of its surroundings, and preparation for the investigation or surgery can commence. Your pet will be kept as warm as possible during the procedure or investigation. Once the procedure or investigation is concluded, drug delivery is stopped, to allow the animal to recover from the effects. Depending on the drugs administered, a reversal agent may be given to speed up the recovery process. If your pet was anaesthetised, we wait until it regains “control” over its airway before removing the breathing tube. Once he or she is awake enough to eat and drink, we will offer food based on their dietary needs we will have discussed with you during their admission to hospital.

Almost inevitably, your pet will remain slightly “sleepy” after it receives a sedation or anaesthetic, even if reversal drugs have been given. You may notice he or she is a bit quieter, and perhaps less interested in food if being discharged on the same day as having a sedation or anaesthetic (for outpatients only).


If your pet is deemed to be “too sleepy” to return home the same day, we will keep them under observation for the night. If your pet has undergone a complex procedure, or is sick, requires additional observation or pain relief, the hospital stay will be longer, and this will be discussed with your consultant during the admission process and subsequent phone calls.

What is the difference between sedation and anaesthesia?

Sedation and anaesthesia can be considered part a continuum, during which the animal is increasingly unaware of its surroundings and what procedure it is undergoing. Sedated animals can still move their limbs, turn their head, blink, and protect their own airway (maintain a patent airway and swallow). Anaesthetised animals do not blink when their eyelids are gently stroked, they cannot swallow, and their muscles are totally relaxed: they require a tube in their airway to protect it from aspiration (regurgitated stomach contents) and to keep the airway unobstructed. This emphasises why it is important your pet does not eat before its anaesthetic or sedation: you will receive specific instructions before you attend for your pet’s appointment.

The deeper sedation becomes, the closer the animal is to being anaesthetised. The same drugs could theoretically be used to sedate or anaesthetise an animal: the difference lies in the drug dose and administration technique used. Anaesthesia and sedation therefore share many possible risks, which your consultant will go through with you while obtaining informed consent for the animal to undergo sedation or anaesthesia. 

What does HSR anaesthesia offer me and my pet?

Whilst sedated or anaesthetised, patients at HSR are monitored closely using state-of-the-art multi-parameter monitors. These give an indication of the blood haemoglobin saturation of oxygen, the carbon dioxide and inhalational anaesthetic gas an animal breathes out each breath, its blood pressure, electrical heart activity and rhythm and body temperature.

At HSR, we use specialist anaesthesia equipment to deliver inhalational anaesthetic gases and oxygen, while syringe drivers and fluid pumps are used to precisely administer injectable drugs. Dedicated anaesthesia workstations with integrated ventilators allow carefully controlled mechanical ventilation of anaesthetised animals while monitoring pressure in delicate airways where required.

Records are taken and interpreted under the supervision of our Anaesthesia team. The team works closely alongside our other specialties within the hospital to develops tailor-made anaesthesia and pain relief plans for patients under the care of all clinical disciplines in the hospital, ensuring first class care for all our patients. Each anaesthetic plan is based on a detailed review of patient medical histories, a pre-anaesthetic examination of the patient and liaison with the specialist requesting a procedure. Based on this, the anaesthetist in charge of your pet creates a protocol, considering his or her needs as well as any challenges potentially arising during an investigation or surgery: ensuring patient safety and comfort are paramount throughout the stay at HSR.


Anaesthetists have significant input into the care of critical care patients requiring intensive care and play an ongoing role in adjusting your pet’s pain relief or advising on how to keep your pet calm in the postoperative period, both as an inpatient or an outpatient at HSR. Your pet will only be allowed to come home, once we and you are confident any remaining pain can be adequately managed at home with you.

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