• Lucie Carrara, Mathieu Nault, Louis Morisson, Nadia Godin, Moulay Idrissi, Annik Fortier, Marie Claude Guertin, Véronique Brulotte, Louis-Philippe Fortier, Olivier Verdonck, and Philippe Richebe.
• From the Department of Anesthesiology and Pain Medicine, Maisonneuve-Rosemont Hospital, CIUSSS de l'Est de l'Ile de Montréal (CEMTL), University of Montréal (LC, MN, LM, NG, MI, VB, LPF, OV, PR) and Department of Biostatistics, Montréal Health Innovations Coordinating Center (MHICC), Montréal, QC, Canada (AF, MCG).
• Eur J Anaesthesiol. 2021 Nov 1; 38 (11): 1168-1179.

BackgroundAlthough ketamine, a NMDA-receptor antagonist, tends to increase the bispectral index (BIS), it remains a widely used analgesic whenever administered in low doses during major surgery.ObjectiveThe objective of this study was to compare the impact of intravenous ketamine (given either as a continuous infusion or as a bolus) on BIS and to compare desflurane administration and postoperative outcomes between the groups.DesignProspective, randomised, parallel-group, open-label study.SettingUniversity hospital, operating room.ParticipantsFifty patients, scheduled for major abdominal surgery.Interventions And Main Outcomes MeasuresPatients were randomised into two groups: ketamine by intravenous continuous infusion - group (KI) and ketamine by i.v. bolus - group (KB). In the KI group, ketamine at a rate of 0.25 mg kg-1 h-1 was commenced at skin incision (T0) and maintained at this rate for the duration of surgery. In group KB, a ketamine bolus of 0.25 mg kg-1was administered at T0 and repeated every hour. The difference in BIS between the groups was compared from T0 onwards. The amount of desflurane administered to keep BIS within the usual recommended range (40-60) was compared, as were the doses of phenylephrine and remifentanil. Postoperative pain and recovery outcomes were also assessed.ResultsAfter T0, the BIS increased significantly from baseline in group KB compared with group KI: the rise in BIS was 20 ± 8 vs. 11 ± 6, respectively (P = 0.0001). The between-group mean difference (95% confidence interval (CI), was 9 (5 to 13). In group KB, desflurane administration significantly increased for the first 15 min after T0: 6.3 ± 1.8 vs. 3.8 ± 1.3 ml (P < 0.0001) with a mean intergroup group difference (95% CI) of 2.4 (1.5 to 3.4) ml. There was no difference in desflurane administration when considering the full hour from T0 to T60 min: 16 ± 9 vs. 15 ± 5 ml (P = 0.63) with a mean intergroup difference (95% CI) of 1 (-3 to 5) ml. After surgery, pain scores, opioid consumption, incidence of nausea and vomiting and recovery scores were similar between groups.ConclusionCompared with a continuous ketamine infusion, a ketamine bolus significantly increased the BIS after T0. In order to keep the BIS below 60, significantly more desflurane was administered from T0 to T15 min in group KB. To prevent such higher desflurane administration and its related atmospheric pollution, our results suggest administering intra-operative intravenous ketamine as an infusion rather than a bolus.Trial RegistrationClinicaltrials.gov registration identifier: NCT03781635.Copyright © 2021 European Society of Anaesthesiology and Intensive Care. Unauthorized reproduction of this article is prohibited.

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