Intrathecal (IT) morphine grants effective, durable and safe analgesia after Caesarean
section. The most common adverse effects after IT morphine are widespread pruritus and
postoperative nausea and vomiting (PONV).
Postoperative nausea and vomiting is multifactorial in origin; in addition to general and
pre-existing risk factors, such as elevated gonadotropin and progesterone serum levels,
parturients undergoing Caesarean section are exposed to drug-induced, hemodynamic and
surgical (manipulation of the uterus) stimuli.
Anticholinergic agents, and particularly scopolamine, have long been known to decrease
opioid-related nausea and vomiting, although their narrow therapeutic range and inconvenient
route of administration (typically transdermal) has limited their application.
Anticholinergic agents are thought to act via inhibition of muscarinic receptors in several
regions of the medulla oblongata, which are implicated with nausea and vomiting generation;
in addition to the chemoceptor trigger zone, these receptors are particularly concentrated
in, but not limited to the nucleus tractus solitarius. Cholinergic receptors have been
typically associated with motion sickness, but cholinergic agonists such as neostigmine have
been shown to increase the incidence of PONV, especially when injected intrathecally.
Anticholinergic agents with muscarinic selectivity may be effective in preventing and
treating PONV. Intravenous (IV) administration of scopolamine or atropine, but not
glycopyrrolate, reduces the incidence of PONV. Intuitively, as glycopyrrolate does not cross
the blood-brain barrier, most postoperative anti-emetic effects of anticholinergic drugs
should be mediated by central receptors.
Few studies have specifically evaluated the antiemetic effect of IV atropine after balanced
general or opioid-based regional anesthesia, with conflicting results. Atropine may represent
a valid alternative to scopolamine and its adverse effects; however, its apparent duration of
action is "brief" (minutes to 1 hour) when administered IV.
After we became aware of several observations by Ramaioli and De Amici on the efficacy of
small-dose intrathecal (IT) atropine for the treatment of PONV after IT morphine
administration, we set out to investigate the use of this agent for prophylaxis of PONV in a
high-risk population, such as patients receiving IT morphine for postoperative analgesia
after elective Caesarean section.
