Comment on De Baerdemaeker et al

Abstract

Dear Editor, We read with great interest the article recently published by De Baerdemaeker et al entitled “The effect of isocapnic hyperventilation on early recovery after remifentanil/sevoflurane anaesthesia in O2/air: A randomised trial”. 1 Volatile anaesthetics are commonly used for general anaesthesia, easy to administer, provides an easily controlled anaesthesia depth and are the only anaesthetic agents whose elimination rate is possible to affect.2,3 The study presents a technique for fast weaning from inhalational anaesthesia by infusion of carbon dioxide into the inspiratory limb of the ventilator combined with controlled hyperventilation. Their results are in line with the findings of several recent studies by our group, published in this journal, on the beneficial effects of this technique on the emergence from inhalational anaesthesia.4-9 The technique is simple enough to be implemented in clinical practice.4,5 The data presented by De Baerdemaeker et al are in accordance with our experience from using this IHV‐method in a randomised study, where it was shown that time to extubation was reduced by 50% in patients subdued to long–term inhalational anaesthesia with sevoflurane 1.3 MACage and fentanyl, compared to a “standard” weaning method.6 However, in the study from De Baerdemaeker et al, the reduction in emergence time was less impressive (30%), which is not a surprising finding considering that a lower dose inhalational agent (1.0 MACage) was combined with a target controlled infusion protocol for remifentanil. We are concerned that there is no record of Bispectral index or Entropy for registering anaesthesia depth before emergence and at extubation. This makes it difficult to interpret the results of the study as we do not know if the groups were comparable in this aspect. Furthermore, there is no information on the total dose of remifentanil or muscle relaxants given in treatment and control groups or if additional opiates were given before extubation. In addition, the remifentanil infusion was terminated only minutes before turning off the vaporiser, which could affect the emergence time. The original IHV‐methods were developed for inhalational anaesthesia supplemented with opioids other than remifentanil.4,5 Finally, when, as in the study by De Baerdemaeker and coworkers, the inhalation agent dosage is reduced and the supplemental intravenous anaesthetic is increased, IHV will have less impact on weaning time, as the intravenous anaesthetic elimination is unaffected by IHV.10 High‐doses of opioid during anaesthesia could also have a negative impact on post‐operative outcome.11 In conclusion, even a few minutes of time‐saving during emergence from anaesthesia is valuable considering the high cost and turn‐over of peri‐operative care.12,13 The modest effect of IHV on emergence in this study is a result of remifentanil infusion in combination with low dose sevoflurane, a very late termination of remifentanil and a tendency towards longer anaesthesia duration in the IHV‐group. Without presentation of anaesthesia depth, pain‐scores, physiological or pharmacological variables in the treatment groups, per –or post‐operatively, the results of the present study should be interpreted with caution. We would like to encourage further research and prospective randomised studies on IHV using this particular method.4,5