Commentary
Delirium is a sudden state of confusion and/or disturbance of consciousness and cognition that is believed to result from acute brain dysfunction, including neurochemical disequilibrium. It often occurs in association with a general medical condition, such as various types of shock, sepsis, surgery, anesthesia, or electrolyte imbalance. Studies have shown that delirium is associated with increased mortality in critically ill patients [2]. Most ICUs use a systematic assessment tool for early detection of delirium, such as the Confusion Assessment Method for the ICU (CAM-ICU), the Intensive Care Delirium Screening Checklist (ICDSC), or the DSM-IV TR score system. The CAM-ICU is the most frequently used tool to evaluate for the presence of delirium in critically ill patients; it is scored as positive if the patient manifests both an acute change in mental status and inattention, and has either a RASS greater than 0 or disorganized thinking [3].
The level of evidence regarding delirium prevention is low. Ear plugs, eye masks, educational staff, supportive reorientation, and music have been studied as nonpharmacologic methods for preventing delirium [4]. From a pharmacologic standpoint, the dopamine D2 antagonist haloperidol has been explored as a therapy for both treating and preventing delirium, since the condition is thought to be associated with anticholinergic and excessive dopaminergic mechanisms. A randomized controlled study in 142 patients who received haloperidol 2.5 mg intravenously every 8 hours found that the duration of delirium did not differ between the haloperidol and the placebo groups [5]. The most feared adverse effects of haloperidol, such as akathisia, muscle stiffness, arrhythmia, or QT prolongation, did not occur more frequently in the haloperidol group. Similar results have been reported by Al-Qadheeb et al [6]. Pharmacologic prophylaxis of delirium using atypical antipsychotics such as quetiapine has also been explored, but the level of evidence for this intervention remains very low. Current American College of Critical Care Medicine guidelines recommend nonpharmacologic management and do not firmly recommend any pharmacologic prevention for ICU delirium [7].
Dexmedetomidine is a selective alpha-2 adrenergic receptor agonist that acts at the locus ceruleus, providing sedation and analgesia. Studies assessing the choice of sedation in the ICU found that the use of dexmedetomidine or propofol, compared to benzodiazepines, is associated with a lower rate of delirium occurrence, especially in mechanically ventilated patients [8,9]. Dexmedetomidine offers several potential advantages over other sedative drugs: it has little effect on cognition, has minimal anticholinergic effect, and may restore a natural sleep pattern. While propofol causes hypotension, respiratory depression, and deeper sedation, dexmedetomidine is associated with lighter sedation, a minimal effect on respiratory drive, and a milder hemodynamic effect. In a randomized controlled trial involving post-surgery ICU patients, dexmedetomidine partially restored a normal sleep pattern (eg, increased percentage of stage 2 non-rapid eye movement sleep), prolonged total sleep time, improved sleep efficiency, and increased sleep quality [10]; by improving overall sleep quality, dexmedetomidine potentially may prevent delirium. Another study that randomly assigned 700 ICU patients who underwent noncardiac surgery to dexmedetomidine infusion (0.1 mcg/kg/hr from ICU admission on the day of surgery until the following morning) or placebo reported a significantly reduced incidence of delirium in the dexmedetomidine group [11]. On the other hand, a 2015 Cochrane meta-analysis that included 7 randomized controlled studies did not find a significant risk reduction of delirium with dexmedetomidine [12].
The current study by Skrobik et al was a randomized, placebo-controlled trial that examined the role of nocturnal dexmedetomidine in ICU delirium prevention in 100 ICU patients. Nocturnal administration of low-dose dexmedetomidine led to a statistically significant reduction in delirium incidence compared to placebo (RR of delirium, 0.44, 95% CI 0.23 to 0.82, which is similar to that suggested by previous studies). This study adds additional evidence regarding the use of dexmedetomidine for pharmacologic delirium prevention. It included many mechanically ventilated patients (89% of study population), strengthening the applicability of the result. Mechanical ventilation is a known risk factor for ICU delirium, and therefore this is an important population to study; previous trials largely included patients who were not mechanically ventilated. This study also supports the safety of dexmedetomidine infusion, especially in lower doses in critically ill patients, without significantly increasing the incidence of adverse events (mainly hypotension and bradycardia). The study protocol closely approximated real practice by allowing other analgesics, including opioids, and therefore suggests safety and real world applicability.
There are several confounding issues in this study. The study was blinded, and there was concern that the bedside nurses may have been able to identify the study drug based on the effects on heart rate. In addition, 50% of patients received antipsychotics. While baseline RASS score was significantly different between the 2 groups, patients in the dexmedetomidine group reached a deeper level of sedation during the study. Also, the protocol mandated halving the pre-existing sedative on the night of study drug initiation, which could have led to inadequate sedation in the placebo group. Placebo patients received propofol for a similar duration but at a higher dose compared to dexmedetomidine patients, and midazolam and fentanyl infusion was used in a similar pattern between the groups. The high exclusion rate (71%) limits the ability to generalize the results to all ICU patients.