We read with great interest the article by Bellgardt et al.1 concerning the survival after long-term isoflurane sedation as opposed to intravenous sedation in critically ill surgical patients. Their excellent study on this important subject deserves applause. However, we have some concerns about the strength of their final conclusion that patients after isoflurane sedation had a lower mortality in hospital and after 365 days. Their study showed that sedation was monitored using the Ramsay score and was considered adequate at a target level of 2 to 4. More importantly, patients ventilated for longer periods had a tracheostomy performed, usually within the first week. We would like to point out some issues that might strengthen the conclusions of this article and that might perhaps be beneficial for further randomised controlled trials dealing with the survival after long-term isoflurane sedation in critically ill patients.
First, Bellgardt et al. did not provide detailed data of depth of sedation. They have chosen the Ramsay score, a subjective sedation score, to monitor the depth of sedation of ventilated patients. A target level of 2 to 4 was thought to be suitable, but they failed to provide specific comparison data of both groups. We think deeper sedation may increase long-term mortality in mechanically ventilated critically ill adults, especially when intravenous sedation is used in critically ill patients.2 Depth of sedation is a key factor affecting mortality. It cannot be excluded that deep sedation of patients in the propofol–midazolam group resulted in a higher mortality. The nature of sedation at level 2 of the Ramsay score is quite different from level 4. In future studies, depth of sedation should be assessed using a sedation score and an objective measure, for instance bispectral index.
Second, there was no detailed description of the tracheostomy procedure. It is well known that early tracheostomy shortens duration of ventilation in critically ill patients.3 Furthermore, there is a potential controversy concerning the association between tracheostomy and in-hospital mortality.4,5 To minimise the impact of this potential confounding factor, detailed data on tracheostomy should have been provided. Finally, we would like to mention the risk of selection bias as treatment allocation was not random, and the risk of provider bias as data from one single centre and collected between 2005 and 2010 were analysed.
In conclusion, whether critically ill patients receiving isoflurane sedation have a lower risk of death in hospital and at 1 year needs to be further ascertained in multicentre randomised controlled trials.
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1. Bellgardt M, Bomberg H, Herzog-Niescery J, et al. Survival after long-term isoflurane sedation as opposed to intravenous sedation in critically ill surgical patients: Retrospective analysis. Eur J Anaesthesiol
2. Shehabi Y, Chan L, Kadiman S, et al. Sedation depth and long-term mortality in mechanically ventilated critically ill adults: a prospective longitudinal multicentre cohort study. Intensive Care Med
3. Griffiths J, Barber VS, Morgan L, et al. Systematic review and meta-analysis of studies of the timing of tracheostomy in adult patients undergoing artificial ventilation. BMJ
4. Koch T, Hecker B, Hecker A, et al. Early tracheostomy decreases ventilation time but has no impact on mortality of intensive care patients: a randomized study. Langenbecks Arch Surg
5. Dunham CM, Cutrona AF, Gruber BS, et al. Early tracheostomy in severe traumatic brain injury: evidence for decreased mechanical ventilation and increased hospital mortality. Int J Burns Trauma