Page 182 Guide to Pain Management in Low-Resource Settings

170 Justin Baker et al.

Neuronal pathways from the chemoreceptor cells of the small intestine and activates 5-HT re-
3
trigger zone (CTZ). Th e CTZ is located in the fl oor of ceptors on peripheral vagal fibers and central struc-
the fourth ventricle and lacks a true blood-brain bar- tures. Delayed emesis occurs after the first 24 hours
rier. Th is allows the zone to sense fl uctuations in the of the exposure to the emetogen and persists up to
concentration of certain substances in the blood- 4–6 days. In addition to serotonin, substance P, along
stream. Th e CTZ may also be stimulated by posterior with other neurotransmitters, appears to have an im-
fossa tumors. portant role in the maintenance of acute and delayed
Vestibular pathways from the labyrinth. Vestibu- N/V. Anticipatory N/V is defined as a conditioned
lar pathways may be stimulated by vestibular disease such “learned” response, usually occurring when episodes
as vertigo, middle-ear infections, or motion sickness. of N/V have been inadequately controlled with prior
Cortical pathways in response to sensory or psy- exposures. It occurs before, during, or after the expo-
chogenic stimuli. Cortical stimulation may come from a sure to the emetogen, but not at the time emetogen-
CNS or meningeal tumor, increased intracranial pres- related N/V would be expected to occur. In this situa-
sure, anxiety, or uncontrolled pain. tion, a variety of stimuli such as odor, sight, or sound
provoke emesis.
How are nausea and
vomiting classifi ed? What is the diff erential diagnosis
of nausea and vomiting?
Nausea and vomiting are usually classified as acute,
delayed, refractory, anticipatory, or breakthrough. Michael’s case has helped demonstrate that nausea and
Acute emesis, which appears to be mediated by se- vomiting is often multifactorial. Fig. 2 details the diff er-
rotonin, occurs within 3 to 4 hours after exposure ential diagnosis and etiologies of nausea and vomiting
to an emetogen such as chemotherapy (see Table as well as providing a helpful mnemonic to quickly re-
1). Serotonin is released from the enterochromaffin call the cartoon:

Increased
Metabolic abnormalities: Delayed
e.g. uremia, liver failure, intracranial pressure chemotherapy-induced
hypercalcemia nausea and vomiting

Constipation
Anxiety
Nausea and vomiting
etiology mnemonic

A − Anxiety or anticipatory
V − Vestibular
O − Obstructive
Opioids
M − Medications and metabolic Radiation
A − Infection and inflammatory therapy
T − Toxins

Other drugs−
e.g. antibiotics, NSAIDs Autonomic
dysfunction
Bowel
Peptic ulcer
Fig. 1. Diff erential diagnosis/etiologies of nausea and vomiting (adapted from Dalal et al. [1])
obstruction
disease
and a quick diff erential diagnosis mnemonic.
Fig. 1. Diff erential diagnosis/etiologies of nausea and vomiting (adapted from Dalal et al. [1])
and a quick diff erential diagnosis mnemonic.