Nausea and Vomiting

Postoperative nausea and vomiting are common complications that result in patient discomfort, prolonged stay in the PACU, and rarely, one of the pulmonary aspiration syndromes. Postoperative nausea and vomiting are multifactorial in etiology.^[160]

A study of 27,626 PACU patients using data from an automated anesthesia record-keeping system determined that the probability of postoperative nausea and vomiting in the PACU can be estimated from three patient-related variables (female gender, odds ratio [OR] = 2.45; smoker, OR = 0.53; and age, OR = 0.995), one operative variable (duration of surgery, OR = 1.005), and three anesthesia-related variables (intraoperative use of opioids, OR = 4.18; use of N₂ O, OR = 2.24; and intravenous anesthesia with propofol, OR = 0.40).^[161]

Propofol-based anesthetics are consistently associated with a lower incidence of postoperative nausea and vomiting than other techniques are, even when potent antiemetics such as ondansetron are combined with inhaled drugs.^{[162] [163] [164] [165]} A literature review of 27 publications found that all but 3 contained evidence implicating nitrous oxide in postoperative nausea and vomiting.^[166] This finding is not meant to imply that nitrous oxide should be abandoned but that its use must be evaluated carefully when attempting to design an anesthetic regimen with a lower incidence of nausea and vomiting.^[167]

The type of surgical procedure has an important influence on the occurrence of nausea and vomiting. Patients undergoing laparoscopic surgery and strabismus surgery are at increased risk for nausea and vomiting. Patients who are menstruating have a higher risk of nausea and vomiting after laparoscopy for tubal ligation that is not prevented by droperidol.^[168]

Drug Therapy for Nausea and Vomiting

On December 5, 2001, the U.S. Food and Drug Administration (FDA) issued a new "black box" warning on droperidol (Akorn Pharmaceuticals, Buffalo Grove, IL) stating that even at low doses, it could cause QT prolongation or torsades de pointes, or both.^[169] The revised warning was based on case reports in which cardiac arrest was alleged to be caused by low-dose droperidol administration during the perioperative period.

The FDA has recommended that all elective surgery patients undergo 12-lead electrocardiographic monitoring before the administration of droperidol to determine whether a prolonged QT_c interval is present and to continue electrocardiographic monitoring for 2 to 3 hours after its administration. This recommendation is impractical for anesthesiologists. Several hospitals have removed the drug from its formulary. More action on this issue may occur, but it is known that droperidol is as safe and effective as ondansetron in adults.^{[170] [171]} Metoclopramide is an effective and safe antiemetic for both prevention and treatment of postoperative nausea and vomiting.^{[172] [173]}

Transdermal scopolamine patches can be very effective in reducing the incidence of nausea associated with epidural narcotics if applied preoperatively. ^[174] Of 100 patients who receive transdermal scopolamine, approximately 17 will not vomit in the postoperative period who

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The serotonin antagonists ondansetron, dolasetron, and granisetron are also useful as first-line drugs.^{[176] [177] [178] [179] [180] [181]} Adding dexamethasone can also reduce the frequency of nausea and vomiting, even when compared with the serotonin antagonist alone.^{[182] [183]} There is little evidence of any clinically relevant toxicity for dexamethasone in otherwise healthy patients. Late efficacy seems to be most pronounced.

Hypothermia and Shivering (also see Chapter 40 )

Surgical patients may be admitted to the PACU with inadvertent hypothermia (i.e., core temperatures <36°C).^[184] Mild perioperative core hypothermia may increase the risk of wound infection, bleeding, cardiac complications, and prolonged PACU stay.^{[185] [186] [187] [188]}

A questionnaire study involving clinical anesthesiologists and physician researchers quantified the most important risk factors for hypothermia: neonates, a low ambient operating room temperature, burn injuries, and general anesthesia with neuraxial anesthesia; geriatric patients, low temperature of the patient before induction, a thin body type, and large blood loss.^[189]

The major adverse effects are patient discomfort, vasoconstriction, and shivering. Full recovery sometimes takes many hours.^[190] Shivering increases the metabolic rate and hence the need to increase cardiac output and minute ventilation. Not all patients who shiver postoperatively are hypothermic, thus suggesting that the mechanism of this event may be related to inadequate descending control of spinal reflexes after inhalation anesthesia.^[191]

Once in the PACU, hypothermic patients should have supplemental oxygen, warm intravenous fluids and blood, and external warming. External warming can be accomplished with thermal blankets or thermal ceilings, which lower oxygen consumption.^[192] Patients in whom shivering develops should receive supplemental oxygen. Although many drugs have been used to treat postanesthetic shivering, meperidine (25 to 30 mg intravenously) is very effective in both stopping the shivering and decreasing oxygen consumption. In some patients a second dose is necessary.^[193] Fentanyl is also effective, but for a shorter interval.^[194]