Nitrous oxide – does it still have a place in veterinary anaesthesia?

ABSTRACT

Are you afraid of nitrous oxide? Do you wonder what will happen if you use it? Nitrous oxide has been around for over 200 years, but it is used much less in veterinary anaesthesia nowadays. This article provides a brief review of its history, advantages and disadvantages, and guidelines for safe use. We argue that it is still a useful drug as long as a number of safety precautions are followed.

Multiple Choice Questions

1. In cases where it is not possible to measure inspired oxygen concentrations, the recommended ratio of oxygen and nitrous oxide used in a circle system is:

   1. 2 parts nitrous oxide to 1 part oxygen

   2. 79% nitrous oxide, 21% oxygen

   3. 1 part nitrous oxide to 1 part oxygen

   4. Less than 1 part nitrous oxide to 1 part oxygen

2. Which statement about the recovery period following administration of nitrous oxide is FALSE?

   1. Recovery may be faster because nitrous oxide wears off more quickly than other inhalant anaesthetics.

   2. Oxygen must be delivered for 5-10 minutes after nitrous oxide is turned off to prevent diffusion hypoxia.

   3. Low oxygen flow rates produce a more stable anaesthetic and a smoother recovery.

   4. Nitrous oxide reduces the amount of other volatile anaesthetics required, reducing respiratory and cardiac depression.

3. The use of nitrous oxide is contraindicated in which one of the following clinical scenarios:

   1. 8 year-old Labrador with a closed pyometra

   2. 2 year-old Yorkshire Terrier with an intestinal foreign body

   3. 8 week-old DSH spay

   4. 10 year-old Jack Russell Terrier for a joint tap

4. Health and safety considerations are important if nitrous oxide is used in practice. Which one of the following statements is FALSE?

   1. Workplace exposure must be monitored and kept below 1000 ppm.

   2. All anaesthetic machines must have a working oxygen alarm.

   3. An efficient scavenging system must be in place and serviced annually.

   4. Pregnant women must have a choice to avoid exposure if desired.

5. In the postoperative period, it is important for VNs to monitor for signs of pain or discomfort because:

   1. Nitrous oxide is a good anaesthetic but NOT an analgesic

   2. Nitrous oxide inhibits the action of some opioids

   3. Nitrous oxide is used only for procedures that will be very painful

   4. Nitrous oxide wears off quickly, as does the analgesic effect

6. Why is it best to use both a pulse oximeter and an inspired oxygen analyser when monitoring a patient to which nitrous oxide is administered?

   1. At low flow rates, the amount of each gas taken up by the patient's lungs will be different and could result in hypoxaemia

   2. Nitrous oxide causes increased respiratory depression so oxygen saturation may fall

   3. It is very important to know how much oxygen your patient is receiving while on nitrous oxide to prevent diffusion into gas-filled body cavities

   4. It is only really necessary for higher-risk patients

For the answers to the MCQs, please go to: http://www.bvna.org.uk/publications/veterinary-nursing-journal

Additional information

Notes on contributors

Carol Hoy

Carol Hoy RVN NCert(A&CC)

Carol qualified as a VN in 1988 and worked in a number of first-opinion practices before moving to the Queen Mother Hospital in 2008, where she works as an anaesthesia nurse.

Chris Seymour

Chris Seymour MA VetMB DVA DipECVAA FHEA MRCVS

Chris is part of the Veterinary Anaesthesia and Analgesia service at the Queen Mother Hospital and is particularly interested in safety in anaesthetic practice, intravenous fluid therapy during surgery and in providing the best possible pain management for all their patients.