Hypotensive anaesthesia techniques in orthognathic surgery

We read with interest the article by Lin et al., “Comparison of different hypotensive anaesthesia techniques in orthognathic surgery with regard to intraoperative blood loss, quality of the surgical field, and postoperative nausea and vomiting”. It provoked a lot of discussion and an audit of our practice. The low incidence of postoperative nausea and vomiting (PONV) was particularly notable. In a group of similar cases of similar age and sex ratio, the incidence of PONV requiring intervention in the post anaesthesia care unit (PACU) was 35%, comparable to the sevoflurane group in the study.

Our patient population would usually require stronger analgesia in addition to non-steroidal anti-inflammatory drugs or a COX-2 inhibitor. We routinely use methadone 0.1 mg/kg intravenous (IV) at induction with paracetamol and parecoxib, but even so 45% required rescue analgesia in the PACU, usually a single dose of either fentanyl or oxycodone IV and 60% required a single dose of oral oxycodone in the first 24 h postoperative.

In the study, the authors make no observations about time to emergence and extubation, which one would expect to be prolonged after surgery exceeding 6 h in duration when using either sevoflurane- or propofol-based anaesthesia. In our region, the routine is for patients undergoing surgery, involving the airway, to be extubated in the operating room under the care of the anaesthesiologist before transfer to the PACU. Hence, we would consider all three of the study techniques to be superseded since the introduction of desflurane and remifentanil. Desflurane is relatively insoluble with a blood–gas partition coefficient of 0.45, similar to nitrous oxide. For comparison, sevoflurane has a blood–gas partition coefficient of 0.65 and the older agent halothane a coefficient of 2.4. This characteristic gives desflurane the quickest emergence time of any of the available vapour anaesthetic agents and allows very rapid changes in depth of anaesthesia.

Remifentanil is remarkable for its evanescence and context-insensitive half-life. This feature combined with a dose-related reduction in cardiac output and peripheral perfusion, makes it an ideal drug for controlled hypotension to produce a ‘dry’ surgical field, especially in combination with an inhalational agent. Supplements with beta-blockers or other agents are rarely needed. Although measured differently, the blood loss and quality of surgical field in our audit were at least comparable to those in the study by Lin et al., and all patients were awake and extubated immediately after the dressings were applied, a critical requirement for any anaesthesia technique for this type of surgery.

Funding

None.

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Dec 14, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Hypotensive anaesthesia techniques in orthognathic surgery
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