Delirium in the PICU

Introduction: Delirium is a well-documented problem in the adult population however, its importance in the paediatric population has evolved recently with the development and validation of reliable paediatric delirium (PD) assessment tools. Definition: The key feature of delirium is an alteration in both cognition and arousal. The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5)(1), defines delirium as a noticeable change in the patient's neurocognitive baseline with an acute disturbance in attention, awareness, and cognition, and is thought to be a direct result of another medical condition rather than due to an established/evolving neurocognitive disorder. Epidemiology: The overall prevalence of delirium in PICU ranges from 4% to 29%, with a recent multi-institutional PD study assessing 994 children for delirium in 25 different PICUs reporting a prevalence of 25%.(2) Higher rates have been reported in children < 5 years of age.(3) A PD prevalence of 49% was found in a paediatric cardiac ICU population. A prevalence rate of 27% was described in a postoperative paediatric population (delirium incidence of 65% within 5 days after surgery).(3) Pathophysiology: Many hypotheses have been proposed. The neuroinflammatory hypothesis suggests that systemic inflammation leads to endothelial activation, enhanced cytokine activity, and infiltration of leukocytes and cytokines into the central nervous system (CNS), producing local ischemia and neuronal apoptosis. The neurotransmitter hypothesis suggests that dysregulation of neurotransmitters like acetylcholine, dopamine, and gamma aminobutyric acid leads to the development of delirium. The oxidative stress hypothesis suggests that hypoxia coupled with increased cerebral metabolism, leads to the production of reactive oxygen species that cause global CNS dysfunction.(3) Risk factors: Risk factors are divided into predisposing and precipitating factors many of which are modifiable (Table 1).(3) Presentation: PD presents in three major subtypes. Hyperactive delirium is characterized by agitation, restlessness, hypervigilance, and combative behaviour, hypoactive delirium is characterized by lethargy, inattention, and decreased responsiveness and mixed type delirium which exhibits aspects of both hyperactive and hypoactive delirium.(1) Hypoactive and mixed type delirium are common presentations in children followed by hyperactive variety. Hypoactive delirium can be easily missed without appropriate screening and diagnostic tools for assessment.(3) PD screening tools: Various screening tools have been developed to detect PD with their advantages and limitations (Table 2). Treatment: Management of delirium involves a multidisciplinary stepwise approach (Figure 1)(3) including the management of the underlying medical illness, minimizing iatrogenic triggers, and optimizing the PICU environment. Pharmacotherapies are indicated if delirium persists and a child's agitated behaviour is distressful or interferes with medical care. Haloperidol, risperidone, and quetiapine have been used safely in children.(5) Outcome and prevention: PD is associated with increased length of mechanical ventilation, increased hospital stay, higher resource utilization, increased healthcare costs, and increased mortality. PD is a hospital acquired complication which can be prevented by using analgosedation approach with the goal to optimize pain and minimize sedation, minimizing iatrogenic factors, early mobilization, and involvement of family members in daily care.(3) Conclusion: PD is an important underrecognized issue in the PICU which needs to be prevented, detected early using screening tools, and managed using a multidisciplinary team approach.