803CHAPTER 65 Hypoxic Ischemic Encephalopathy is already in a severely biochemically compromised state result ing in increased injury after similar durations of no flow ischemia 28,173 Additional clin[.]
CHAPTER 65 Hypoxic-Ischemic Encephalopathy is already in a severely biochemically compromised state resulting in increased injury after similar durations of no-flow ischemia.28,173 Additional clinical factors may worsen pediatric outcomes after cardiac arrest The relative resistance of the immature myocardium to asphyxia means that it is easier to restore cardiovascular function in younger patients after longer durations of cardiac arrest than would be possible in adults Thus, ROSC rates are high in pediatrics despite a higher occurrence of asystole than adults.15,25,256 Less than half of pediatric arrests are witnessed15,25,256 such that bystander CPR, which is therefore delayed, is not associated with improved outcome15,25,257,258 as it is consistently in adult cardiac arrest.15,25,257,258 Finally, first responders appear to have more difficulty providing guidelinerecommended resuscitation to smaller children compared with adult-sized adolescents.259 Thus, although pediatric intensivists have the apparent luxury of dealing with a somewhat resistant and more resilient brain, with capacity for plasticity, this advantage is often trivial compared with the devastating pathobiology of the asphyxial arrest.194,207,260 Treatment After Cardiac Arrest Adequate understanding of the pathobiology of HIE after cardiac arrest in children is possible given the development of contemporary models of pediatric asphyxial arrest These models will hopefully lead to more etiology-specific evaluation of the postresuscitation syndrome in terms of mechanisms and relevant therapies.193,194 Prospective study of clinical targets for supportive postresuscitation care to optimize outcomes is vital Field Interventions Pediatric cardiac arrests are usually not sudden in onset, as in adults Thus, a window of opportunity exists during which interventions could potentially prevent cardiac arrest and associated poor outcome As discussed, children sustaining isolated respiratory arrest have a mortality rate as low as 25%, whereas patients with cardiac arrests as a result of hypoxemia have a much higher mortality.15,21 Thus, the sooner the recognition and interventions, the better are the chances for a good outcome The AirwayBreathing-Circulation approach to CPR for children remains fundamental, with exceptions for children with certain conditions or situations.261–263 Early activation of emergency medical services (EMS) holds the greatest promise for improving outcomes from prehospital pediatric cardiac arrest Dispatcher (911) instructions to provide bystander CPR are associated with improved outcomes after pediatric out-of-hospital cardiac arrest, with one report demonstrating a stronger association when conventional CPR that included rescue breathing was instructed.264 EMS have developed sophisticated methods for dispatch and transport, but there are logistical limits to the rapidity with which they can provide basic interventions Nationwide, the average response time is well over minutes, greater than the time required for an infant to progress from apnea to cardiac arrest As a result, more advanced, traditionally hospital-based, and investigational interventions must also be administered in the prehospital setting in attempts to optimize outcome The quality of CPR delivered by EMS to younger children (1–11 years old) is inferior to adolescents and adults.259 Toward this end, use of medical simulation has greatly improved both the understanding of the mechanics of quality CPR as well as teaching and training (see Chapters 38 and 39) 803 Supportive Care in the Intensive Care Unit A hypothetical algorithm for the management of infants and children after cardiac arrest is provided in Fig 65.7 Postarrest care centers on multimodal monitoring, organ support, and prevention of secondary injury by actively maintaining ventilation, arterial oxygenation, temperature, and blood pressure goals, along with several other aspects of supportive care to minimize HIE.265 There is an association between hyperoxia and outcome in both in vitro and in vivo models of brain injury, thought to be a result of increased oxidative stress.266,267 In neonates, two systematic reviews showed a mortality benefit to resuscitating infants with room air versus 100% oxygen.268,269 No long-term developmental outcomes were available; however, these and other data resulted in changes in the approach to neonatal resuscitation.270 Although neonates have lower partial pressure of arterial oxygen (Pao2) prior to delivery, findings in adults with cardiac arrest may provide more insight for children Kilgannon and colleagues found that hyperoxia (Pao2 300 mm Hg) and hypoxia (Pao2 ,60 mm Hg) on first arterial blood gas post-ROSC were associated with mortality in adults with cardiac arrest.271 Several subsequent reports appear to confirm the increased risk beginning when Pao2 exceeds 300 mm Hg.271–274 A study in children followed, finding an association of extreme hypoxemia (odds ratio [OR], 1.92; 95% confidence interval [CI], 1.80–2.21 at Pao2 of 23 mm Hg) and hyperoxia (OR, 1.25; 95% CI, 1.17–1.37 at Pao2 of 600 mm Hg) on first arterial blood gas with PICU mortality.275 However, a single-center retrospective analysis found no relationship between hyperoxia or hypoxia within the first 24 hours post-ROSC with mortality.276 Similarly, a multicenter retrospective analysis found that although derangements in oxygenation and ventilation were common, there was no association between blood gas parameters in the first hours post-ROSC and survival with favorable neurologic outcome.277 A prospective multicenter study found that oxygenation was not associated with mortality, but hypocapnia (Paco2 ,30 mm Hg) and hypercapnia (Paco2 50 mm Hg) were associated with mortality after pediatric cardiac arrest.278 However, in a large study from Australia and New Zealand, only hypocapnia (Paco2 ,35 mm Hg) was associated with mortality.279 Pediatric guidelines recommend resuscitation with 100% oxygen with subsequent titration of oxygen saturations to 94% or greater post-ROSC.280,281 Although the optimal cerebral perfusion pattern for neuronal and functional recovery remains to be defined,282–284 blood pressure fluctuations, both high and low, adversely affect outcome In their classic study of the neuropathology of systemic circulatory arrest in immature monkeys, Miller and Myers240 found that systolic blood pressures at or below 50 mm Hg during the reperfusion period had devastating effects on survival and neuropathology This occurred even when the ischemic time was less than the 12-minute minimum that caused brain injury in their model In contrast, Bleyaert and coworkers285 showed that intermittent episodes of hypertension (mean arterial pressure 150–190 mm Hg) induced with norepinephrine during the first 24 hours after 16 minutes of global brain ischemia in monkeys worsened neurologic outcome A beneficial effect of transient hypertension during the immediate postresuscitation period has been suggested,14 hypothesizing that this improves flow in areas with microvascular sludging Safar and colleagues286 suggested that transient hypertension was beneficial after cardiac arrest in dogs However, it was applied as part of a multifaceted treatment protocol, and its specific benefit remains controversial In a multicenter, observational cohort 804 S E C T I O N V I Pediatric Critical Care: Neurologic POSTRESUSCITATION ALGORITHM CPR No ROSC? Consider ECPR Yes Neuromonitoring • Imaging (CT, MRI) • EEG • Brain oxygenation Other • Temperature • ECG • Electrolytes • Toxicology screen Supportive care Investigation and monitoring Neurologic exam grossly normal • Normoxia • Normocarbia • Normotension • Prevent hyperthermia • Treat or prevent seizures • Euglycemia Coma postresuscitation Continue supportive care + targeted temperature management Contraindications for hypothermia* No contraindications for hypothermia Consider controlled normothermia • Target temperature: 36°C • Passive rewarming to target temp if begin