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9780521704632c18 CUFX213A/Peck 9780521618168 December 28, 2007 13:51
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Antiemetics and related drugsNausea and vomiting has many causes including drugs, motion sickness, fear, preg-
nancy, vestibular disease and migraine. In previous decades anaesthesia was almost
synonymous with vomiting, but with the advent of new anaesthetic agents and more
aggressive treatment the incidence of vomiting has decreased. However, even the
latest agents have failed to eradicate this troublesome symptom encountered in the
peri-operative period.Physiology
The vomiting centre (VC) coordinates vomiting. It has no discrete anatomical site
but may be considered as a collection of effector neurones situated in the medulla.
This collection projects to the vagus and phrenic nerves and also to the spinal motor
neurones supplying the abdominal muscles, which when acting together bring about
the vomiting reflex.
The VC has important input from the chemoreceptor trigger zone (CTZ), which lies
in the area postrema on the floor of the fourth ventricle but is functionally outside the
blood–brain barrier. The CTZ is rich in dopamine (D 2 )receptors and also serotonin
(5-HT) receptors. Acetylcholine (ACh) is important in neural transmission from the
vestibular apparatus. Other input is summarized in Figure18.1.
The treatment of nausea and vomiting is aimed at reducing the afferent sup-
ply to the VC. While the administration of antiemetics forms a vital part of treat-
ment, attention should also be given to minimizing the administration of opioids by
the use of non-steroidal anti-inflammatory drugs and avoiding unnecessary anti-
cholinesterase administration. When propofol is used to maintain anaesthesia for
minor surgery, where the use of opioids is limited, it may reduce the incidence of
post-operative nausea and vomiting (PONV).
The following types of agents have been used:
Dopamine antagonists
Anticholinergics
Antihistamines
5-HT 3 antagonists
Miscellaneous