Induced hypothermia
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Induced hypothermia (also known as therapeutic hypothermia) is the intentional induction of hypothermia for medical purposes. Such practice has been shown to reduce brain damage in infants and increase survivability in certain cases of cardiac arrest. The method also has applications in cardiac surgery and stroke recovery.
Hypothermia may be a consequence of anesthetic induction drugs and occurs to some extent every time an anesthetic is given. Anesthetic drugs produce two different effects that lead to hypothermia during surgery: they increase the width of blood vessels, vasodilation, allowing blood to flow easily from the body's inner organs or core to the periphery or skin. This allows heat to be easily lost or radiated from the body. The temperature control center situated in the hypothalamus is also affected by drugs causing the normal temperature control limits to be increased, compromising the body's normal cold response system.
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[edit] Pathophysiology
During the cardiac arrest there is inadequate perfusion of the brain. If cerebral perfusion is impaired for too long, neuronal cells begin to suffer hypoxic injury. If unchecked, hypoxic injury eventually leads to cell death. Though successful cardiopulmonary resuscitation may restore cerebral circulation, it is believed that the damage to the neurons is accelerated when oxygen and nutrients are reintroduced to the abnormal cellular environment too rapidly. This may result in reperfusion injury. Also, as brain cells begin to die, they may release various hormones signaling other nearby cells to begin the process of apoptosis (cell death). Hypothermia is thought to reduce the damage to brain cells by reducing the brain's metabolic activity.
[edit] Methods
Induced hypothermia is usually accomplished by a combination of several methods:
- Rapid infusion of ice-cold intravenous fluids
- Cooling of internal organs, such as with nasogastric lavage with ice-cold water
- Evaporative cooling of the body surface
- Intravascular cooling, using specialized vascular catheters
- External cooling with ice packs or special cooling blankets
- Prevention of excess heat generation (fevers, shivering) using medication
[edit] Applications
People have been subjected to deep hypothermic cardiac arrest for aortic surgery for over an hour without gross neurological deficits. The subjects reached complete electrocerebral silence between temperatures of 16 °C and 24 °C[1].
The Arctic Sun medical device is a tool used specifically to induce hypothermia. In May 2008, an incident involving this device received major news coverage, when a female patient in West Virginia suffered cardiac arrest, was pronounced dead, and then was revived using this device. [2]
Induced hypothermia has been shown to improve neurologic outcomes after cardiac arrest. Survival post-arrest has been historically poor, as low as 4 percent in published literature. Patients who are successfully resuscitated after cardiac arrest (stopping of the heart), but remain in a comatose state, have greater chances survival and neurologic recovery if mildly cooled to about 33 degrees Celsius (91 °F). The strongest evidence of its utility is in patients who have arrested due to ventricular fibrillation or ventricular tachycardia, though its use has been expanded to other rhythms[3].
This therapy is increasingly being used in hospital emergency departments, intensive care units[4] and is being studied in pre-hospital care. It has been credited in helping the recovery of the Buffalo Bill's Kevin Everett who suffered a severe neck injury and wasn't expected to walk again.
[edit] Animal experiments
Hydrogen sulfide[5] and [6]-gingerol[6] have been used to induce a suspended animation-like hypothermic state in mice and rats (respectively). However, experiments on sheep[7] and pigs[8] have been unsuccessful, suggesting that application to large mammals may not be feasible.
[edit] See also
[edit] External links
[edit] References
- ^ Hayashida M, Sekiyama H, Orii R, Chinzei M, Ogawa M, Arita H, Hanaoka K, Takamoto S (2007). "Effects of deep hypothermic circulatory arrest with retrograde cerebral perfusion on electroencephalographic bispectral index and suppression ratio". JOURNAL OF CARDIOTHORASIC AND VASCULAR ANAESTHESIA 21 (1): 61–67. doi:. PMID 17289482.
- ^ Son making funeral plans gets call that mom's alive: New apparatus helped stave off brain injury by Zack Pettit, Daily Mail, Tuesday May 20, 2008.
- ^ Hypothermia after Cardiac Arrest Study Group (2002). "Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest". NEW ENGLAND JOURNAL OF MEDICINE 346 (8): 549–556. doi:. PMID 11856793.
- ^ Couzin J (2007). "Medicine. The big chill.". 'Science' 317 (5839): 743–745. doi:. PMID 17690272.
- ^ Blackstone E, Morrison M, Roth MB (2005). "H2S induces a suspended animation-like state in mice". 'Science' 308 (5721): 518. doi:. PMID 15845845.
- ^ Ueki S, Miyoshi M, Shido O, Hasegawa J, Watanabe T (2008). "Systemic administration of [6]-gingerol, a pungent constituent of ginger, induces hypothermia in rats via an inhibitory effect on metabolic rate". EUROPEAN JOURNAL OF PHARMACOLOGY 584: 87. doi:. PMID 18295202.
- ^ Haouzi P, Notet V, Chenuel B, Chalon B, Sponne I, Ogier V, Bihain B (2008). "H2S induced hypometabolism in mice is missing in sedated sheep". REPIRATORY PHYSIOLOGY & NEUROBIOLOGY 160 (1): 109–115. doi:. PMID 17980679.
- ^ Li, Jia; Zhang, Gencheng; Cai, Sally; Redington, Andrew N (January 2008). "Effect of inhaled hydrogen sulfide on metabolic responses in anesthetized, paralyzed, and mechanically ventilated piglets.". Pediatric Critical Care Medicine 9 (1): 110–112. doi:. “H2S does not appear to have hypometabolic effects in ambiently cooled large mammals and conversely appears to act as a hemodynamic and metabolic stimulant.”
