What general anesthetic techniques are most likely to minimize postopertive nausea and vomiting?
Clearly, the patient at high risk for PONV should receive an anesthetic designed to minimize this problem. Many of these patients are ambulatory and may have higher gastric volumes and lower gastric pHs as a result of prolonged fasting. This may be obviated by permitting clear fluids until 2–3 hours prior to surgery. Atropine or glycopyrrolate has been shown on occasion to reduce PONV by prevent-ing increased vagal tone. Prophylactic use of atropine or glycopyrrolate, however, may reduce the gastroesophageal barrier pressure.
Avoiding mask ventilation in the patient with an uncom-plicated airway may reduce the risk of insufflating large volumes of anesthetic gas into the stomach before intuba-tion of the trachea. Immediately after securing the airway, orogastric tube decompression will reduce gastric disten-tion. The orogastric tube may be left in situ for passive drainage intraoperatively. Capping or clamping a sump defeats its intended purpose of continuous passive drainage. Constant suction may result in gastric mucosal injury.
Avoidance of nitrous oxide (N2O) may be warranted to help minimize nausea and vomiting. Due to its insolubility, nitrous oxide tends to diffuse into closed air spaces, thereby increasing gaseous volume and/or pressure. Diffusion into the gastric bubble may exacerbate gastric distention pre-disposing the patient to PONV. Passage into the middle ear, especially in combination with Eustachian tube dysfunc-tion, can cause dislodgement of the tympanic graft. After graft placement, sudden discontinuation of N2O causes massive negative inner ear pressure. Graft implosion may occur resulting in PONV and pain.
The use of propofol as an induction agent and possibly a maintenance agent may reduce the risk of PONV. Anxiolytics, such as midazolam, may successfully treat the anxiety of nausea and vomiting.
Total intravenous anesthesia that includes propofol and remifentanil infusions as opposed to balanced anesthesia with a volatile agent produces significantly less PONV.
Many medications and maneuvers have been used to control PONV after surgery. A slow, deliberate transfer from the operating room to the postanesthesia recovery unit (PACU) with care turning corners will help prevent emesis. Administration of supplemental oxygen may also reduce the incidence of PONV. Assuming there are no sur-gical misadventures such as an endolymphatic sac disrup-tion or cerebrospinal fluid leak, the anesthesiologist should consider combination therapy for treatment. Use of dex-amethasone prophylactically as a single dose may be quite helpful. Rescue of symptoms in the PACU may include inexpensive medications such as dimenhydramine or diphenhydramine. The use of transdermal scopolamine may be quite useful as well, assuming the patient does not have glaucoma or bladder outlet obstruction.