We appreciate the work by Smith et al. regarding omitting fentanyl for day care surgery in favour of sevoflurane anaesthesia only. A few findings are worth mentioning in the study, as follows. The absence of a beneficial role of dexamethasone in postoperative nausea and vomiting (PONV). The addition of dexamethasone to fentanyl, which has an analgesic action too, did not potentiate the analgesic action of fentanyl .
The concern about omitting fentanyl as mentioned by the authors was PONV. The ‘inhaled bolus technique’ used by the authors would have delivered more nitrous oxide, contributing to PONV . The duration and number of times such a bolus of inhalation agent was used was not documented in the study. There was no significant difference in the three groups with regard to PONV when compared with individual groups. Although there was a difference in the proportion of patients experiencing moderate-to-severe vomiting or nausea, all patients in all groups were fully satisfied with the control of PONV (score of 10 in all groups). The principal and statistical comparison of unequal data for PONV (143 patients in the pooled fentanyl group and 73 patients in the no supplement group) needs to be clarified.
The other concern was a decrease in heart rate (HR), mean arterial blood pressure, respiratory rate and oxygen saturation in the fentanyl group. We think that this happened probably because of a coincidence of peak effect of fentanyl and high plasma level of sevoflurane as high-dose sevoflurane induction was used, leading to a greater impact on the cardiovascular and central nervous systems. Patients were induced with 8% sevoflurane with a tidal breathing technique, which would have transferred a significant amount of sevoflurane to the blood and reservoir tissues. It takes some time for equilibrium, and during this time, if peak fentanyl plasma level occurs, then it may have an impact on haemodynamic and respiratory parameters. Decreasing the fresh gas flow without first decreasing the inspired concentration of sevoflurane will prolong the equilibrium in maintenance concentration of sevoflurane. The authors did not mention the time frame as to when the end-tidal concentration of sevoflurane decreased to 1.3–1.5%. In the study tables and graphs, the time frame/gap of fentanyl administration/sevoflurane induction and start of surgery is absent. Although the authors mentioned, in the methods section, noting baseline parameters every minute during the first 5 min of induction, comparison is lacking in the graphs. It would have been more informative if the baseline parameters at fentanyl/sevoflurane administration had been mentioned as a continuous timeframe to see the changes with onset of peak plasma levels of fentanyl and its effects. We think that, rather than totally avoiding the use of fentanyl in day care surgery, we should use a titrated dose of fentanyl, and its administration timing needs to be adjusted according to the timing of potent surgical stimulus.
As mentioned by the authors, three patients required ephedrine or atropine for hypotension or bradycardia, respectively. It appears that such treatment was required after induction and prior to skin incision. Haemodynamic parameters were comparable 20 min after skin incision. The time gap between the administration of drugs (fentanyl and high-dose tidal breath sevoflurane induction) and skin incision is not mentioned. The significant lowering of mean arterial BP and HR in the fentanyl group could be explained by a simultaneous peak level of fentanyl and high plasma levels of sevoflurane as used for inhalational induction (8% sevoflurane). After equilibrium was attained (as sevoflurane was stopped until an end-tidal sevoflurane concentration of 1.3–1.5% was achieved), haemodynamic parameters settled to baseline and were comparable in the groups.
Similarly, the episodes of apnoea and desaturation appear to occur after induction and prior to skin incision, which again can be explained as for the haemodynamic parameters. Opioids decrease the monitored anaesthesia care (MAC) requirement of inhalational agents, but the authors' study resulted in a similar concentration of sevoflurane and sevoflurane consumption [4–7]. The high level of end-tidal carbon dioxide can be explained by nonadjustment of MAC in the fentanyl group .
The authors failed to mention the requirement of ‘inhaled boluses’ required in the three groups, which would have indicated the presence of an inadequate plane of anaesthesia. The omission of fentanyl and giving frequent ‘inhaled boluses’ of inhalational agent probably negate the advantage of balanced anaesthesia.
The authors mentioned that supplementing inhaled anaesthesia with fentanyl had no significant sevoflurane-sparing effect but failed to mention any plan in the methodology to decrease sevoflurane use in the fentanyl group. A 1.3–1.5% end-tidal sevoflurane concentration was planned in all the groups. The authors planned to increase the volatile level when an inadequate plane of anaesthesia was suspected, but no plan for decreasing titration according to MAC was mentioned.
Significant episodes of movements in the inhaled anaesthesia group imply an inadequate plane of anaesthesia and may not be acceptable in delicate surgery in which no movement is acceptable. The authors mentioned the use of alfentanil in the inhaled anaesthesia group when the movement did not settle even after increasing the vapour concentration. There was also undue delay in the start of surgery due to movement, although this was clinically insignificant. This again shows the importance of balanced anaesthesia.
The absence of a significant difference in the analgesic effect of fentanyl may also be due to the administration of high-dose preemptive analgesia (slow-release ibuprofen, 1600 mg) administered by the authors in their study. Multimodal analgesia (preemptive analgesia with high-dose ibuprofen, infiltration of the incision site and postoperative oral analgesic) had a contributory role in preventing the analgesic advantage of fentanyl. It may be more appropriate to conclude that administration of a single bolus of high-dose nonopioid preemptive analgesia may be contributory in decreasing the requirement of opioids intraoperatively and thus its side effects rather than omitting fentanyl in day care surgeries without making a note of the role of preemptive analgesia.
The dose requirement and the time to first analgesia requirement was not mentioned by the authors; this would have been valuable in judging the adequacy of intraoperative analgesic administration. The modality of postoperative (intravenous or oral) analgesic administration was not standardized in the study. The morphine requirements of the patients is not clear. Whether other patients also received morphine or more fentanyl in the postoperative period (one, two and one patient in groups one, two and three, respectively, received systemic opioids), in what doses and at what time was not elaborated in the study.
The dose of fentanyl administered by the authors was related to weight, but it is quite difficult to administer 0.02 ml kg−1 with a 2 ml syringe as mentioned by the authors rather than using a more diluted drug. Although the weight range is not mentioned by the authors, in patients with lower body weight, it is a practical concern to administer the calculated dose of fentanyl.
The nonadjustment of sevoflurane concentration in the fentanyl group (decrease in MAC by opioids) and administration of fentanyl along with high-dose sevoflurane concentrations may be responsible for haemodynamic and respiratory problems. The increase in the incidence of movements in the sevoflurane-alone group and the comparable patient satisfaction with regard to PONV mandates reconsidering using sevoflurane alone in day care surgeries.
Readers should be wary about the conclusions of the study before accepting the technique of sevoflurane anaesthesia alone for day care surgery rather than a balanced anaesthetic technique using multimodal analgesia (including shorter acting opioids).
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