REMIFENTANIL REQUIREMENTS DURING PROPOFOL ANAESTHESIA WITH OR WITHOUT 70% NITROUS OXIDE

remifentanil requirements during propofol anaesthesia with or without 70% nitrous oxide

I Tugtekin, E Barth, C Bernhard, G Fröba, S Schraag

Department of Anaesthesiology, University of Ulm, D-89075 Ulm, Germany

Background and Goal of study: There is a debate whether the use of Nitrous oxide (N₂O) as an additive component of general anaesthesia today is still appropriate, mainly due to its unfavourable side effects and environmental hazards (1). It is likely that by omitting N₂O, the requirements of other general anaesthetics may increase. We tested the hypothesis of a significantly higher Remifentanil (REMI) consumption during Propofol (PROP) anaesthesia in the absence of N₂O.

Materials and Methods: After obtained institutional ethic`s committee approval and written informed consent, 24 unpremedicated patients undergoing elective orthopaedic surgery were studied. They were allocated randomly to receive either 70% N₂O (Group 1) or air (Group 2) together with REMI and PROP both administered by Target Controlled Infusion (TCI). The target PROP blood concentration was kept constant at an individual level where its calculated effect site concentration matched the condition of unresponsiveness, whereas REMI was titrated against intraoperative responses, expressed as increases of EEG BIS values above a target level of 40-50. The relative differences in REMI consumptions and REMI C_target were calculated. Statistical analysis was performed using Mann-Whitney U-test with a significance level of a<0.05.

Results and Discussion: Time adjusted REMI consumption and median REMI C_target (ng ml ^-1) are listed in the table below:

GROUP	Remifentanil consumption (mg h ^-1)	Remifentanil C_target (Median, IQ range)
(1) N₂O	0.59	3.40 (2.55-4.03)
(2) Air	0.67	3.55 (3.21-4.15)
Difference (%)	11.94	4.23
p-value	n.s.	n.s.

Every patient responded with a significant BIS alteration both to increased stimulation and to increases in REMI C_target , supporting the hypothesis that BIS also quantifies analgesia demands during PROP anaesthesia.

Conclusion:

This preliminary study gives no evidence of a major overall contribution of N₂O to reduce the amount of analgesic drugs required during general anaesthesia, when titrated against BIS. In fact, the omittance of N₂O leads only to a minor increase in REMI consumption, which also under economical considerations may allow to avoid N₂O .

References:

[1] James MFM. Curr Opin Anaesthesiol 1999;12:461-6.