16 - Antiemetics

Summary

Introduction

In this chapter I will discuss three groups of interventions that reduce the number of people who experience postoperative nausea or vomiting (PONV). The first group is changing the anaesthetic method to reduce risk. The second group is giving preventative drugs or acupoint P6 stimulation to reduce risk. The third group is drug treatment to shorten the duration or reduce the severity of established nausea or vomiting.

It is obvious that if no one experiences PONV there is no benefit in either changing anaesthetic technique or giving drugs to prevent PONV. It is also obvious that if everyone experiences PONV then everyone has a chance of benefiting from either intervention. The majority of people in a population in which less than 50% have PONV cannot benefit from prophylaxis. It is therefore crucial to know the incidence of PONV to calculate the risks and benefits of antiemetic prophylaxis.

We know the likelihood of reducing PONV for many drugs. We know the likelihood of common minor side effects. We do not know the likelihood of rare serious side effects.

Reducing emetic stimuli

Perioperative emetic stimuli are usually assumed to operate through particular characteristics of: the patient, the surgery and the anaesthetic. Only a few factors, in just a few studies, have been shown to independently predict PONV: sex, history of smoking, motion sickness or PONV, duration of operation, opioid administration [1–3].