Study of the respiratory depression during an analgosedation technique combining remifentanil and ketamine in TCI for oocyte retrieval

Abstract

Introduction: Various methods of analgesia/anaesthesia have been validated for oocyte retrieval. In our institution, we administer remifentanil in target controlled infusion-mode (TCI), to maintain a score on the visual analogue scale (VAS) of less than 30mm. However, the incidence of respiratory depression is still significant. Our aim was to assess whether the addition of ketamine could reduce the number of respiratory events. Methods: In this prospective, non-randomized, uncontrolled study, 20 women were divided in two groups of ten: group 1 received ketamine at a target plasma concentration (Cp) of 150 ng/ml and group 2 of 200ng/ml. Our main outcome measure was the incidence of adverse respiratory events in relation to remifentanil and ketamine concentrations. Secondary outcome measures include sedation levels, dosage of ketamine-Cp, the accuracy of the Clements 250 pharmacokinetic model, post-operative side effects, intraoperative pain, the duration of the procedure, the outcome of the procedure and patient satisfaction. Results: In patients who experienced adverse respiratory events, both groups combined, remifentanil-consumption was higher (0.167 ± 0.055 mcg/kg/min versus 0.114 ± 0.059 mcg/kg/min, p-value 0,043) and measured ketamine was lower than the predicted Cp, although insignificant (0,020 ± 0.004 versus 0.024 ± 0.006, p-value 0,23). The difference in the incidence of adverse respiratory events in both groups was not significant (30% of bradypnea in both groups). The Clements 250 pharmacokinetic model predicted the ketamine-Cp accurately (bias of -7,25 and inaccuracy of 24,6). Post-operative side effects, patient satisfaction, the duration of the procedure and intra-operative pain levels were comparable in both groups. Conclusion: The association of subanaesthetic doses of ketamine with remifentanil for oocyte retrieval permitted a reduction of remifentanil consumption and adverse respiratory events, but no prevention. However, their incidence was higher when the predicted ketamine-Cp was not reached, and consequently more remifentanil was needed. Further studies at progressively higher target-Cp of ketamine in association with remifentanil should be conducted, under continuous anaesthetic surveillance