[Postoperative nausea and vomiting]

Peripheral nerve block for ambulatory surgery and postoperative analgesia

PURPOSE OF REVIEW

With this article we intend to increase the awareness of the efficiency and efficacy of peripheral nerve block as a treatment option for outpatient surgical anesthesia and postoperative home-based analgesia.

RECENT FINDINGS

Current investigations have demonstrated that peripheral nerve block is associated with a superior outcome (reduced pain, nausea and vomiting) and more efficient patient turnover than general anesthesia. Continuous peripheral nerve block and patient controlled peripheral nerve block lead to further improvement in postoperative analgesia and patient satisfaction.

SUMMARY

The recent advances and techniques described indicate that peripheral nerve block is both a valid and frequently a preferred option for ambulatory surgery.

PONV: a problem of inhalational anaesthesia?

Even nowadays every third or fourth patient suffers from postoperative nausea and vomiting (PONV) after general anaesthesia with volatile anaesthetics. There is now strong evidence that volatile anaesthetics are emetogenic and that there are no meaningful differences between halothane, enflurane, isoflurane, sevoflurane, and desflurane in this respect. However, when propofol is substituted for volatile anaesthetics the risk for PONV is reduced by only about one fifth, indicating that there are other even more important causes for PONV following general anaesthesia. A main causative factor might be the use of perioperative opioids, but their impact--relative to other factors including volatile anaesthetics--has never been quantified. Patient-specific risk factors have also been shown to be clinically relevant; they are therefore included in the calculation of simplified risk scores that allow prediction of a patient's risk independent of the type of surgery. Although controversial, the well-known different incidences following certain types of surgery are most likely caused by patient-specific and anaesthesia-related risk factors. There is a common consensus that prophylaxis with anti-emetic strategies is rarely justified when the risk of PONV is low, while it is warranted in case of imminent medical risk associated with vomiting or in a patient with a high risk for PONV. A recently published large multicentre trial of factorial design, IMPACT, has demonstrated that various anti-emetic strategies are associated with a very similar and constant relative reduction rate of about 25-30% and that the main predictor for the efficacy of prophylaxis is the patient's risk for PONV. Interestingly, all anti-emetics (dexamethasone, droperidol and ondansetron) work independently, so that their combined benefit can be derived directly from the single effects. The effectiveness of the anti-emetics was also independent of a variety of risk factors, including volatile anaesthetics. This means that any anti-emetic prophylaxis for PONV induced by volatile anaesthetics is equally effective. Of course, the most logical approach for prevention would be the omission of volatile anaesthetics and nitrous oxide using a total intravenous anaesthesia with propofol. However, since volatile anaesthetics are probably not the most important risk factors, it might be even better--if appropriate--to avoid general anaesthesia by using a regional, opioid-free anaesthesia if PONV is a serious problem.

[Postoperative nausea and vomiting]

Numerous pathophysiological mechanisms are known to cause nausea or vomiting but their role for postoperative nausea and vomiting (PONV) is not quite clear. Volatile anesthetics, nitrous oxide and opioids appear to be the most important causes for PONV. Female gender, non-smoking and a history of motion sickness and PONV are the most important patient specific risk factors. With these risk factors an objective risks assessment is achievable as a good rational basis for a risk dependent antiemetic approach: When the risk is low, moderate, or high, the use of none, a single or a combination of prophylactic antiemetic interventions seems to be justified. Performing a total intravenous anesthesia (Ti.v.A) with propofol is a reasonable prophylactic approach, but does not solve the problem satisfactorily alone if the risk is very high, reducing the risk of PONV only by 30%. This is comparable to the reduction rate of antiemetics, such as serotonin antagonist, dexamethasone and droperidol. It must be stressed that metoclopramide is ineffective. Data from IMPACT indicate that prophylaxis is not very effective if the patients risk is low. At a moderate risk the use of Ti.v.A or an antiemetic is reasonable and only a (very) high risk justifies the combination of several prophylactic antiemetic interventions. For the treatment of PONV an antiemetic should be chosen which has not been used prophylactically. The necessary doses are usually a quarter of those needed for prophylaxis.

A risk adapted approach reduces the overall institutional incidence of postoperative nausea and vomiting

PURPOSE

Routine prophylactic antiemetic treatment of surgical patients appears justified only in case of an increased risk of postoperative nausea and vomiting (PONV). The objective of this investigation was to assess the feasibility and efficacy of a dichotomized risk score adapted management of PONV based on ondansetron prophylaxis and treatment with respect to the overall institutional rate of PONV.

METHODS

After estimating the individual PONV risk by a simplified score, 162 adult patients scheduled for elective surgery received either 4 mg ondansetron intravenously (two to four risk factors = high-risk) or no prophylaxis (zero to one risk factor = low-risk). For antiemetic treatment ondansetron was given intravenously and orally. Incidence of PONV was recorded during the first 24 hr after recovery.

RESULTS

Data from 159 subjects were analyzed with 44 patients classified as low-risk and 115 patients classified as high-risk. Nine low-risk and 58 high-risk patients experienced PONV. The expected institutional PONV incidence of 47% was reduced to 36%. Treatment with ondansetron was necessary in seven low-risk and 37 high-risk patients with a complete response rate of 71% (low-risk) and 43% (high-risk).

CONCLUSION

Providing antiemetic prophylaxis with ondansetron to high-risk patients strictly based on a simplified risk score can reduce the overall institutional rate of PONV. However, classifying patients into two groups while using ondansetron as the single antiemetic in the high-risk group appears to be of limited efficacy as the incidence of PONV in high-risk patients is still double that of low-risk patients.