Risk Factors for Postoperative Nausea, Vomiting and Pruritus

Introduction Neuraxial morphine provides effective and long-lasting analgesia after cesarean section. It is currently considered the gold standard for postoperative pain. However, it is associated with problematic side effects including nausea and vomiting, pruritus, and rarely respiratory depression.

Postoperative nausea and vomiting (PONV) occurs in up to 60-80% of parturients receiving neuraxial opioid administration , and reported incidence of pruritus varies from 30% to 100%.

A wide range of pharmaceutical and non pharmaceutical agents are commonly used in clinical practice for the treatment and prophylaxis of neuraxial morphine induced postoperative nausea, vomiting and pruritus. Antiemetic medications such as droperidol, dexamethasone, metoclopramide and ondansetron, have been studied for their efficacy in preventing PONV . Despite the wide variety of these available drugs, many of them are ineffective and have side effects. Dexamethasone ,for example, although it has been proven as an effective antiemetic in patients receiving epidural morphine, it is ineffective monotherapy in patients receiving intrathecal morphine . In addition it is associated severe perineal pruritus . Common side effects of ondansetron are headache, flushing, dizziness and constipation. Droperidol is associated with undesirable side effects: sedation, hypotension, and extrapy-ramidal reactions . Both droperidol and ondansetron are known to prolong the QTc interval.

To date although pruritus after neuraxial administration of morphine is a common side effect, there is little available effective treatment . Studies have found opioid-induced pruritus to be dose dependent and minimal analgesic doses of opioids are recommended. Several agents from numerous drug families have been employed, although none has proved to be totally effective . Treatment medications include: naloxone, nalbuphine, diphenhydramine and droperidol .

To date there are no studies which have identified risk factors for PONV and pruritus after administration of nauraxial morphine. Attempts have been made to identify which patients are at risk for PONV after general anesthesia .

There are anesthetic, surgical, and individual risk factors are linked to PONV Studies in this field have identified several predicting risk factors for PONV .

Apfel et al established a validated simplified scoring systems to assess risk factors for nausea and vomiting after general anesthesia. His simplified sum score system included four risk factors: female gender, prior history of motion sickness or PONV, nonsmoking, and the use of postoperative opioids .

If none or only one risk factor is present the predicted incidence of PONV may vary between about 10% and 21%, whereas if at least two risk factors are present it increases to between 39% and 78%.

To date research has yet to yield a predictive model for neuraxial morphine induced nausea and vomiting (NMINV). Likewise risk factor for neuraxial itching have yet to be established.

Methods This is a prospective, single center study, which will be conducted at the Rabin Medical Center (Beilinson Campus), Petach Tikva, Israel, a tertiary university hospital. The Institutional Review Board has approved this study.

All women undergoing cesarean section delivery under spinal anesthesia with neuraxial morphine will be enrolled after filling out an informed consent prior to surgery. Women undergo spinal anesthesia with 10-12 mg heavy bupivicaine, 20 ucg fentanyl and 100 ucg morphine. Phenylepherine drip is used at anesthesiologist's discretion. If not treatment dose of ephedrine or phenylepherine are given as required by blood pressure.

All women receive prophylaxis intravenous dexamenthasone 4 mg and prophylactic intravenous ondansetron 4mg, as standard departmental protocol.

Prior to surgery women will be given a questionnaire detailing previous motion sickness, previous history of PONV, emesis during pregnancy, smoking history , itching history, skin atopy and allergies. After surgery details about surgery will be added: intraoperative hypotension, use of phenylepherine, intraoperative nausea and vomiting, exteriorization of uterus, extent of adhesions, need for uterotonic medications, and estimated bleeding.

Parturients will be assessed 1 hour and 24 postoperatively by attending anesthesiologist, PONV incidence will be reported using a three point ordinal scale (0 = none, 1 = nausea, 2 = retching, 3 =vomiting).

Nausea includes any feeling of sickness with an inclination to vomit. Retching includes any reverse movement of the stomach and esophagus without vomiting, including attempting vomiting.

Vomiting is defined as the involuntary, forceful expulsion of one's gastric contents through the mouth and sometimes the nose.

A VNRS (vas numerical rating score) (from 0-10 0= no itching at all , 10= worst itching possible) will be used to measure overall presence and severity of pruritus.

Any severe incidence of VNRS defined above 7 will be noted. All parturients need for postoperative antiemetic and antipruritic medications will be reported.