drugs be administered to empty the stomach or change gastric acidity or volume
before the administration of an anesthetic?
Studies regarding differences in the resting
gastric volume between the inpatient and ambulatory population have yielded
conflicting results. Whereas some anesthesiol-ogists administer liquid antacids
before the induction of anesthesia, no evidence supports the notion that every
patient must receive a soluble agent (0.3 molar sodium citrate, 30 ml). A
soluble antacid is substituted for the conventional nonabsorbable antacid
containing aluminum, magnesium, or calcium hydroxide to avoid the severe
chemical pneumonitis that may result from aspiration of these particulate
substances. Other pharmacologic agents include the H2-receptor
blockers (ranitidine or famoti-dine), which inhibit gastric acid production and
decrease gastric volume. Mental confusion has been reported after intravenous
administration of cimetidine in geriatric patients. Ranitidine is more potent
and specific and has a longer duration of action than cimetidine.
Metoclopramide increases the tone of the lower esophageal sphincter as well as
facilitating gastric emptying. However, it does not guar-antee a stomach free
of gastric contents. It also possesses anti-emetic properties. Metoclopramide,
in conjunction with an H2-receptor blocker, may be more efficacious.
However, the routine use of any of these drugs in patients without specific
risk factors is not currently recommended.
Diabetes mellitus with evidence of autonomic
dysfunc-tion or gastric atony, documented hiatal hernia, a history of
symptomatic gastroesophageal reflux, pregnancy, signifi-cant obesity, acute
abdomen, or current opioid use or abuse are examples of diseases or conditions
that appear to increase the incidence of aspiration during induction or
emergence from general anesthesia or during heavy sedation. Therefore,
prophylaxis in these situations is recommended. There is no advantage to
administration of triple prophylaxis with H2-receptor antagonists,
soluble antacids, and metoclo-pramide. If prophylaxis with an H2-blocker
is employed, it should be given 1–2 hours preoperatively. Another effective
regimen combines metoclopramide on the morning of sur-gery and a nonparticulate
antacid immediately prior to surgery.
Despite the administration of pharmacologic
agents and imposition of fasting, significant amounts of acidic gastric
contents may still be present. Fortunately, aspiration of gastric material
remains a relatively rare occurrence. If a patient is observed to aspirate and
if symptoms of cough, wheeze, or hypoxemia while breathing room air do not
develop within 2 hours, the development of significant respiratory sequelae is
unlikely. Therefore, reliable and otherwise healthy ambulatory patients can
probably be discharged after several hours of observation in the postanesthesia
care area with the proviso that they immedi-ately contact their physician at
the onset of any symptoms.