Impact of delirium on weaning from mechanical ventilation in medical patients.

Abstract

We share the concerns expressed by Jeon et al.1 on the prevalence of delirium in intensive care units (ICU) and its role as an independent predictor of negative clinical outcomes among ICU patients. We also know that mechanically ventilated (MV) patients are at a high risk of developing delirium during the ICU stay. In their study, they sought to determine the association between delirium in MV patients and subsequent weaning outcomes in medical patients. The Confusion Assessment Method for the ICU (CAM-ICU)was used to assess the presence of delirium on the day of the first weaning trial. This method presents some operational advantages compared with the psychiatrist's interconsultation, like simple learning and it can be performed at the bedside. It can also be applied repeatedly to all ICU patients because it only requires 2–3min for evaluation. The CAM-ICU was not defined to be applied to MV patients receiving high doses of sedatives and hypnotics nor for critically ill patients with severe metabolic or structural encephalopathies and decreased or fluctuating level of consciousness. Therefore, it could be possible that this method overestimates the diagnosis of delirium. Otherwise, some patients on MV can present a phase of altered mental status when moderate or deep sedation is removed. These patients sometimes meet the criteria for delirium, but they should not be considered as such because the prognosis is not the same. It is likely that the CAM-ICU scale is influenced by the level of consciousness and sedative drugs impregnating.2 In the study by Jeon et al.,1 the authors state that patients without delirium were more successfully extubated than those with delirium. After adjusting for potential confounding factors, delirium was significantly associated with difficult but not prolonged weaning. Some risk factors associated with the development of delirium were not analyzed, such as alcoholism, smoking or prior cognitive impairment. On the other hand, some precipitating factors for delirium were not recorded either: hypoxia,metabolic disorders, drug deprivation, sleep deprivation and use of psychoactive medication (sedatives and opioids). Seymour et al.3 performed a single-center, prospective cohort study in which they measured hourly doses of benzodiazepines and propofol exposure during day and night time. The authors found that greater use of benzodiazepines during the day was associated with reduced odds of successful spontaneous breathing trials, extubation and increased odds of subsequent delirium and coma. Nearly half of the patients received greater doses of sedation at night, a practice associated with failed spontaneous breathing trials. We believe that any study that aims to assess risk factors for delirium should consider the use of sedative medication. It would have been interesting to know how many patients received sedative drugs, what kind of drugs and at what dose provided. It would also have been valuable if information regarding the level of consciousness before and during the assessment of delirium would have been available in this study. The drug of choice is important. While benzodiazepines are associated with an increased risk of delirium, others without GABA-ergic action such as opiates have a lower risk.4 Excessive sedation has been associated with prolonged MV and increased ICU stay. The authors did not take the degree of sedation into account in the assessment of delirium. Therefore, the association between delirium and weaning may have been overestimated in this study.