Understanding Anesthesiology - The Global Regional Anesthesia ...

Post-operative Nausea and Vomiting
One of the most common problems encountered in the
PACU is post-operative nausea and vomiting (PONV).
PONV is unpleasant for both patient and staff. Moreover,
it places the patient at risk for aspiration of gastric
contents, particularly if airway reflexes are blunted due
to the residual effects of opioids, inhaled agents and
muscle relaxants.
When severe PONV is encountered, it is important to
rule out sinister causes such as myocardial ischemia,
bowel obstruction or raised intracranial pressure. More
commonly, the cause is multifactorial with patient, surgical
and anesthetic factors contributing. The many risk
factors for PONV are outlined in Table 17, the most important
(and statistically-robust) factors highlighted in
bold.
The best approach to PONV is prevention. Attention
should be paid to the most emetogenic anesthetic
drugs which are nitrous oxide and neostigmine. Minimizing
the dose of neostigmine to less than 2 mg appears
to eliminate its emetogenic effect and should be
considered if neuromuscular function allows. The modification
of anesthetic factors (such as avoiding the use
of nitrous oxide) is at least as effective as the administration
of a prophylactic antiemetic agent. Current
guidelines recommend that prophylaxis (ondansetron
and/or dexamethasone) be administered selectively to
moderate or high risk patients. These agents are administered
during anesthesia rather than pre-operatively.
Interestingly, ondansetron is much more effective as a
treatment for PONV than as a preventive, where its
NNT (number needed to treat) is around 5. It is also not
free of side effects such as headache, constipation and
elevated liver enzymes.
In the PACU, PONV is best treated with hydration and
intravenous antiemetics such as ondansetron (if not
used as prophylaxis), prochlorperazine or dimenhydrinate.
PONV may act as a limiting factor to the delivery
of opioid analgesia; patients at high risk of PONV benefit
from opioid-sparing analgesic techniques such as peripheral
nerve blocks or neuraxial analgesia.
Table 17 Risk factors for PONV
PATIENT SURGICAL ANESTHETIC
female laparoscopic peri-operative opioids
history of PONV opthalmic neostigmine
history of motion sickness gynecologic nitrous oxide
non-smoking
age