Thursday, October 11, 2012

Therapeutic Hypothermia: The Ultimate Brain Freeze

In the past few years, convincing data has led to the establishment of therapeutic hypothermia protocols in Emergency Departments for improved neuroprotection of sudden cardiac arrest patients.  In addition, there is some evidence of improved neurologic outcome in children who suffer prolonged submersion injury in cold water, although much of this is based on case reports.  Naturally, researchers are interested in determining whether therapeutic hypothermia is beneficial for those patients who have suffered cardiac arrest secondary to drowning.  The following are 2 articles, one review and one retrospective, highlighting recent findings from the research surrounding this topic.

This robust article covers multiple aspects of brain resuscitation including pre-hospital care, ventilatory strategies, surfactant therapy, hemodynamic support, and therapeutic hypothermia.  The following are the pertinent findings for therapeutic hypothermia:

  • Early therapies fell out of favor after evidence of increased incidence of survival with persistent vegitative state after treatment with deep and sustained hypothermia.
  • More recent evidence supports the use of moderate hypothermia after cardiac arrest (many caveats to this)
  • Mixed evidence regarding the benefit for therapeutic hypothermia for hypoxic ischemic encephalopathy in pediatrics
  • Most of the evidence for the use of therapeutic hypothermia after out of hospital arrest involves Ventricular Fibrillation arrest, which cannot be fully extrapolated to asphyxial cardiac arrest common with drowning incidents
  • Summary statement: There are no high-level evidence studies of therapeutic hypothermia in drowning. Treatment recommendations are made by extrapolation from studies of asphyxia and CA.
    • First, prevent hyperthermia in comatose victims. If hyperthermia occurs, treat it promptly. 
    • Second, consider maintaining a target core temperature of 32–34 °C for 12–72 h.  Cooling should be started as soon as possible, and re-warming should be slow, at a rate no faster than 0.5 °C/h.

This retrospective study analyzed the outcomes of 20 drowning patients treated with therapeutic hypothermia over a 4 year period.  The following were some of the key findings:
  • 20% of these patients survived with favorable neurological outcome (based on cerebral performance category score), and 70% died.  In comparison with other studies, this showed no statistical benefit from therapeutic hypothermia
  • In this study, submersion time did not appear to effect rate of survival vs death/vegetative state.
  • Negative outcomes in this study were related to prolonged ACLS, absence of motor response after 3 days, abnormal brain imaging, and abnormal lack of cortical response to evoked potential testing

While therapeutic hypothermia continues to gain support for use in Ventricular Fibrillation Cardiac Arrest patients, given the different pathophysiology of drowning induced cardiac arrest, evidence to support its standardized use is lacking.