The mortality rates for critically ill patients vary depending on the population studied. In the USA mortality rates for patients in mixed medical-surgical ICUs are reported as 2.8–6 % in critically ill children compared to 10–30 % in critically ill adults. While international numbers are not readily available, in the USA, over 250,000 children ages 1–19 years each year receive ICU care and approximately 23–40 % of these children (Dahlem et al. 2003; Watson et al. 2002; Angus et al. 2001; Census 2002; Fedora et al. 2005) receive mechanical ventilator support. Of those children receiving mechanical ventilation, approximately 30–50 % were previously healthy (Watson et al. 2002). These numbers differ internationally. Fedora et al. (2005) found that 23 % of children admitted to the PICU in the Czech Republic received mechanical ventilator support. Of those children, the mortality rate was 3.5 %. The origin of respiratory failure was extrapulmonary in 66 % of the patients and only 19 % were chronically ill. The PRISM III scores and length of stay were twofold higher in mechanically ventilated patients than those not receiving mechanical ventilation. In developing nations, malnutrition and immune compromise from HIV influence the outcome of children who are mechanically ventilated.

In an international retrospective cohort study of 36 pediatric intensive care units across seven countries, Farias et al. (2006) identified factors that were associated with survival in pediatric patients receiving mechanical ventilation for more than 12 h. The 15.6 % of children who died had more severe lung disease on admission (higher peak inspiratory pressure and more severe hypoxemia) and higher overall illness severity (PRISM III score) and were more likely to develop acute renal failure. Most of the children were mechanically ventilated for acute, emergent conditions, many of which were from severe infections or injury.

Given the heterogeneity of disease requiring acute mechanical ventilator support, it is useful to evaluate mortality rates of patients receiving mechanical ventilation based on their underlying disease process and degree of lung disease. Acute lung injury (ALI) and its more severe form acute respiratory distress syndrome (ARDS) are severe forms of respiratory failure occurring in 9 % (Dahlem et al. 2003; Watson et al. 2002; Angus et al. 2001) of mechanically ventilated children. ALI is a syndrome comprised of acute onset of severe hypoxia and bilateral lung infiltrates not caused by left heart failure. ALI has mortality rates of 8–18 % in nonimmune compromised patients and 40–80 % in children with underlying immune compromise (Randolph 2009; Zimmerman et al. 2010; Flori et al. 2005; Erickson et al. 2007). In Australia and New Zealand, Erickson et al. (2007) reported that ALI accounted for 30 % of the total PICU deaths. Mortality ranged from 44 to 80 % in patients with ARDS with a history of bone marrow transplantation in multiple studies (Randolph 2009). Factors that had an independent association with mortality were severity of illness, PaO₂/FiO₂ ratio, the presence of a non-pulmonary and non-CNS organ dysfunction, and the presence of CNS dysfunction (Randolph 2009; Flori et al. 2005; Erickson et al. 2007).

Severe asthma accounts for 2–20 % of adult ICU admissions. Nearly one third of adults with status asthmaticus require mechanical ventilation and 10–20 % of them will not survive. In contrast, less than 2 % of pediatric patients hospitalized for an asthma exacerbation require mechanical ventilator support, and mortality is rare (Chiang et al. 2009; Roberts et al. 2002). Bronchiolitis, a diagnosis occurring mostly in infancy, also has airway hyperinflation, mucous plugging, and bronchospasm. Mortality in otherwise healthy infants with bronchiolitis is also an uncommon event.

Although mechanical ventilation can be lifesaving, complications from intubation and mechanical ventilation do occur in infants and children. Rivera and Tibballs (1992) found complications from intubation and mechanical ventilation occurred in 24 % of patients. These complications included infection (2.3 %), air leak (6.8 %), post-extubation stridor (2.4 %), bronchopulmonary dysplasia (2.3 %), and atelectasis (7.8 %). In 2007, Jorgenson et al. (2007) performed endoscopic airway evaluations on 1,435 intubated pediatric patients following extubation to determine the incidence of airway injury following intubation. Airway injuries were classified as minor, moderate, or severe. Ninety percent of patient had airway injury on endoscopic evaluation. Thirty-one percent of patients had vocal cord edema, 8.8 % had ulcerations of the arytenoids, 7.9 % had annular ulcerations in the subglottic region, 2.8 % had subglottic stenosis, 2 % had fibrous nodules on the vocal folds, and 0.45 % had vocal cord paralysis. In a study examining post-extubation complications in infants with bronchiolitis, immediate post-extubation complications including upper airway obstruction were common, and fortunately, long-term complications such as subglottic stenosis were very rare (Gomes Cordeiro et al. 2004).

Neuromuscular dysfunction is a common problem in critically ill patients and is a cause of major long-term morbidity in adults (Hermans et al. 2008). The incidence of neuromuscular dysfunction has been reported in 25–33 % of adult patients receiving mechanical ventilation for greater than 7 days and reaches 70–100 % in those with sepsis and multiorgan dysfunction (Hermans et al. 2008; Williams et al. 2007; Banwell et al. 2003; Hough et al. 2009). Critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) are important causes of muscle weakness in critically ill patients and contribute to failure in weaning from mechanical ventilation (Hermans et al. 2008).

CIP and CIM belong to a spectrum of disorders causing muscle weakness in critically ill patients and can be difficult to differentiate clinically. Typically patients with CIP and CIM present with muscle weakness, muscle atrophy, and decreased or absent deep tendon reflexes. CIP is characteristic of axonal degeneration of motor and sensory fibers and can be differentiated from neuromuscular blockade (NMB) by normal repetitive nerve stimulation (Hermans et al. 2008). CIM is an acute myopathy that requires more specialized EMG testing, with muscle biopsy as the gold standard in differentiating CIM from CIP (Hermans et al. 2008). Both can be measured by nerve conduction studies and EMG. The Medical Research Council Sum Score (MRC) initially developed to evaluate patients with Guillain-Barre’ syndrome is used to evaluate CIP and CIM. The score measures muscle force on a scale from 0 to 5 in three muscle groups, with a maximum score of 60. Patients with a score <48 are diagnosed with CIP/CIM (Hermans et al. 2008).

Williams et al. (2007) reviewed the literature on CIP and CIM in the pediatric intensive care population in 2008 and found 34 cases of CIP/CIM in the literature. All 34 cases received mechanical ventilation, 20 were diagnosed with sepsis and or SIRS, five were diagnosed with asthma, and nine were recipients of solid organ or bone marrow transplantation. Twenty-one had received steroids and 24 had received neuromuscular blocking agents prior to the onset of weakness. Banwell et al. (2003) found a 1.7 % incidence of neuropathy following critical illness in 830 children without underlying neuromuscular disease. Of the 14 children with neuropathy, three patients died and four had repeated failure attempts at extubation. Of the children who underwent muscle biopsy, all showed evidence of acute quadriplegic myopathy. On 3-month follow-up, eight of the nine available survivors had persistent proximal muscle weakness of the upper and lower limbs. Two of those children were unable to walk independently (Banwell et al. 2003). This study identified neuropathy based on clinical exam, which has shown to be insensitive in the diagnosis of CIP and CIM in adults (Hermans et al. 2008) and may underestimate the true incidence of neuropathy following critical illness in children.

The role of corticosteroids and neuromuscular blockade in the development of neuromuscular dysfunction is controversial. CIM has been reported in patients treated with corticosteroids and neuromuscular blocking agents: however, this has not been evident in prospective studies. In a secondary analysis of the ARDS Network RCT of methylprednisolone versus placebo for persistent ARDS, Houghes et al. (2009) found evidence of neuromyopathy in 34 % of those studied, with no significant difference between the methylprednisolone and control groups. A diagnosis of neuromyopathy was significantly associated with prolonged mechanical ventilation.

Critically ill children have been found to suffer from psychological sequelae following their pediatric intensive care stay. Psychological or emotional morbidity includes depression, anxiety, and post-traumatic stress disorder (PTSD). PTSD is a psychological condition that occurs following a traumatic or life-threatening event that triggers feelings of intense helplessness and fear. Patients exhibit symptoms of hyperarousal, intrusive recollections, and avoidance. PTSD and delusional memories have been associated with invasive procedures, duration of sedative use, severity of illness, and hospital length of stay (Rennick and Rashotte 2009; Rennick et al. 2002; Colville et al. 2008; Cichetti and Gamey 1993).