Incidence and short-term consequences of delirium in critically ill patients: A prospective observational cohort study☆
Introduction
Patients in the intensive care unit (ICU) are severely ill and need support of one or more organ functions. In the last decade, there is an increasing interest in brain dysfunctions such as delirium. Delirium is a syndrome defined as an acute onset of disturbances in consciousness and changes in cognition with a fluctuating course (American Psychiatric Association, 1994). Three subtypes of delirium can be distinguished (Peterson et al., 2006). A hyperactive delirium subtype with symptoms of hyperalertness, agitation, delusions and hallucinations, a hypoactive subtype in which the patient is hypoalert, lethargic, motorically slow and has inappropriate speech and the alternating or mixed subtype. The latter subtype of delirium is characterised by alternating symptoms of hyperactive and hypoactive delirium. The Richmond Agitation Sedation Scale (RASS) ranging from +4 (heavily agitated) to −5 (coma) in combination with the delirium diagnose (Ely et al., 2003) is used to distinguish between the three delirium subtypes (Pandharipande et al., 2007, Peterson et al., 2006). Only positive RASS scores indicates a hyperactive delirium subtype. Delirious patients who only have RASS scores between 0 and −3 are defined as hypoactive delirious patients. Patients with fluctuating RASS scores, between +4 and −3 in combination with a positive delirium screening, are defined as mixed or alternating subtype. These delirium subtypes have different implications for nurses since the hyperactive subtype is easy to recognize but causes more nursing problems and inconvenience. While patients with the hypoactive subtype are, due to their lethargic state, easy to nurse but therefore also easily missed or misdiagnosed as sedation of depression (American Psychiatric Association, 1994). Meagher and Trzepacz (Meagher et al., 2000, Meagher and Trzepacz, 2000) suggest that the different delirium subtypes in hospitalized patients represent a difference in severity of delirium. They argue that, since the duration of a hyperactive delirium is shorter than the duration of the mixed subtypes, and the length of stay in hospital is also shorter, the hyperactive subtype is less severe than the other subtypes. Whether this difference in severity of delirium is also true for ICU patients is not known.
Delirium in ICU patients is associated with short-term health consequences such as prolonged duration of mechanical ventilation and length of stay and higher mortality rates (Dubois et al., 2001, Ely et al., 2001a, Ouimet et al., 2007). The duration of delirium is associated with prolonged cognitive failure (Girard et al., 2010) and each additional day with delirium is associated with a 10% increase in mortality (Pisani et al., 2009).
The delirium incidence in ICU patients ranges from 11 to 89% (Aldemir et al., 2001, Dubois et al., 2001, Ely et al., 2007, McNicoll et al., 2003, Ouimet et al., 2007). Despite the generally high delirium incidence rate accompanied and the serious health consequences there is lack of evidence for prevention of delirium ICU patients. Preventive measures consisting of a multicomponent intervention strategy (Inouye et al., 1999) and prophylactic haloperidol (Kalisvaart et al., 2005) showed positive effects in older hospitalized patients with a high risk for delirium. The effects of these preventive measures are not determined yet in ICU patients.
The high incidence rate in critically ill patients is associated with the frequent occurrence of important risk factors for delirium (Van Rompaey et al., 2008) in ICU patients. The wide range of delirium incidence rates is likely related to case mix differences over studies. It is likely that overall delirium incidence rates and rates per subtype of delirium differ between (elective) surgical and medical patient groups. As these patient groups differ, e.g. regarding their pathophysiological disease processes, severity of illness, and chance of dying (Knaus et al., 1985) we expect them to also differ in their chances of developing delirium, or chances of developing a specific subtype.
Although the classification of the delirium subtypes according to Peterson et al. (2006) is commonly used in the ICU, little is known about incidence rates of the subtypes per ICU diagnosis group and its effects on delirium duration and short-term consequences.
The aim of this study is threefold. First, to determine the delirium incidence rate overall, per subtype of delirium and per ICU diagnosis group. Second, to determine the delirium duration overall, per subtype and per ICU diagnosis group. Third, to determine differences in short-term consequences between delirious and non-delirious patients, and for the delirium subtypes and to determine the contribution of delirium to these short-term consequences.
Section snippets
Methods
The study was approved by the local Medical Ethical Committee (study number 2007/283), which waived the need for informed consent since no interventions were carried out. The study was registered in the Clinical trial register as NCT00604773.
Results
In total 2116 consecutive patients were screened of which 503 were excluded (Fig. 1). The most common reasons for exclusion were sustained coma (26.8%) and delirium before ICU admission (26.6%).
Discussion
In this study we observed that the overall delirium incidence is approximately a quarter of all ICU patients admitted for at least one day, and half of all ICU patients admitted for two days or longer. Important differences in incidence and subgroup distribution between patient categories exist. The incidence rate was the highest in the neurology group and the lowest in the cardiac- and neurosurgical group. The mixed delirium subtype occurred most frequently and also had the longest duration.
Conclusion
Over a quarter of our ICU population with a length of stay >1 day and half of the ICU patients with a length of stay of ≥2 days developed delirium during their ICU stay. There is an important difference between admission categories concerning the delirium incidence rates and the occurrence of subtypes of delirium. Patients who developed delirium were significantly more likely to suffer from short-term health problems and had a six times higher chance of dying compared to ICU patients who did
Acknowledgements
The authors would like to thank Gabriel Roodbol, delirium expert nurse psychiatry, who carried out all the inter-rater reliability measurements during the study. Many thanks to Henk Westerbaan, Maaike Fenten and Wendy Groetelaers-Kusters, for collecting data during the absence of the first author and processing the data in SPSS. We also would like to thank Sjef van der Velde for his support in gathering the electronic database information. Last, we would like to thank Gareth Parsons (University
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This paper was submitted as an entry for the European Academy of Nursing Science's Rosemary Crow award, sponsored by the International Journal of Nursing Studies. The award is open to current doctoral students or recent graduates of the academy's programme.