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Targeted temperature management (Hypothermia)

See ((Hypothermia))

 

 

 

Targeted temperature management (TTM) is an active treatment that tries to achieve and maintain a specific body temperature in a person for a specific duration of time in an effort to improve health outcomes during recovery after a period of stopped blood flow to the brain.

 

 

TTM attempts to reduce the risk of tissue injury following lack of blood flow: cardiac arrest or the blockage of an artery by a clot as in the case of a stroke.

 

 

TTM improves survival and brain function following resuscitation from cardiac arrest.

 

 

Efficacy for its use for certain types of cardiac arrest, in which an individual does not regain consciousness.

 

 

Targeted temperature management following traumatic brain injury is of unclear benefit.

 

 

Targeted temperature management prevents brain injury by several methods:  decreases  the brain’s oxygen demand, reduces production of neurotransmitters like glutamate, and  as reduces free radical production.

 

 

Hypothermia has been shown to help moderate intracranial pressure and minimize the harmful effect of a patient’s inflammatory immune responses during reperfusion. 

 

 

Methods to lower body temperature may include, the use of cooling blankets, cooling helmets, cooling catheters, ice packs and ice water lavage.

 

 

TTM indications may include: 

 

 

Cardiac arrest

 

 

Neonatal encephalopathy 

 

 

American Heart Association guidelines support the use of cooling following resuscitation from cardiac arrest.

 

 

There is improved survival and brain function when cooled to to a near-normal temperature of 36 °C (97 °F).

 

 

The cooling is effective because it prevents fever, a common complication seen after cardiac arrest.

 

 

In children, following cardiac arrest, cooling does not appear useful.

 

 

Hypothermia therapy for neonatal encephalopathy has been proven to improve outcomes for newborn infants affected by perinatal hypoxia-ischemia, hypoxic ischemic encephalopathy or birth asphyxia. 

 

 

Whole body or selective head cooling to 33–34 °C (91–93 °F), within six hours of birth and continued for 72 hours, reduces mortality and reduces cerebral palsy and neurological deficits in survivors.

 

 

Adverse effects of hypothermia treatment: infection, bleeding, dysrhythmias and high blood sugar, electrolyte abnormalities – specifically hypokalemia, hypomagnesaemia, and hypophosphatemia, as well as hypovolemia.

 

 

Hypothermia acts as a neuroprotectant focused on the slowing of cellular metabolism resulting from a drop in body temperature. 

 

 

For every one degree Celsius drop in body temperature, cellular metabolism slows by 5–7%.

 

 

It is suggested that hypothermia reduces the harmful effects of ischemia by decreasing the body’s need for oxygen.

 

 

In infants suffering perinatal asphyxia,  it apoptosis is a prominent cause of cell death and dhypothermia therapy for neonatal encephalopathy interrupts the apoptotic pathway. 

 

 

Cell death is indirectly caused by oxygen deprivation.

 

 

Cells need oxygen to create ATP, a molecule used by cells to store energy, and cells need ATP to regulate intracellular ion levels. 

 

 

ATP is used to fuel both the importation of ions necessary for cellular function and the removal of ions that are harmful to cellular function. 

 

 

Without oxygen, cells cannot manufacture the necessary ATP to regulate ion levels and thus cannot prevent the intracellular environment from approaching the ion concentration of the outside environment. 

 

 

Oxygen deprivation itself does not precipitate cell death, but rather without oxygen the cell can not make the ATP it needs to regulate ion concentrations and maintain homeostasis.

 

 

A small drop in temperature encourages cell membrane stability during periods of oxygen deprivation. 

 

 

The drop in body temperature helps prevent an influx of unwanted ions during an ischemic insult by making the cell membrane more impermeable.

 

 

Hypothermia, therefore,  prevents the cascade of reactions set off by oxygen deprivation, and moderates  the disruption of homeostasis caused by a blockage of blood flow minimizes the trauma resultant from ischemic injuries.

 

 

Targeted temperature management also may reduce reperfusion injury, that is, damage caused by oxidative stress when the blood supply is restored to a tissue after a period of ischemia. 

 

 

The  inflammatory immune responses occur during reperfusion cause increased intracranial pressure, which leads to cell injury and in some situations, cell death. 

 

 

Hypothermia moderates intracranial pressure and therefore minimizes the harmful effects of a patient’s inflammatory immune responses during reperfusion. 

 

 

Reperfusion oxidation occurs during reperfusion also increases free radical production. 

 

 

Hypothermia reduces both intracranial pressure and free radical production, this might be yet another mechanism of action for hypothermia’s therapeutic effect.

 

 

N-methyl-D-aspartate (NMDA) receptor activation following brain injuries can lead to calcium entry which triggers neuronal death via the mechanisms of excitotoxicity.

 

 

There are a number of methods to induce hypothermia: These include: cooling catheters, cooling blankets, and application of ice applied around the body and cool intravenous fluids.

 

 

Core body temperature is measured in  the esophagus, rectum, bladder in those who are producing urine, or within the pulmonary artery.

 

 

Temperatures below 30 °C (86 °F) are to be avoided, as adverse events increase significantly.

 

 

Rewarming is done slowly with suggested speeds of 0.1 to 0.5 °C (0.18 to 0.90 °F) per hour.

 

 

Targeted temperature management should be started as soon as possible, and reached before 8 hours.

 

 

Targeted temperature management remains partially effective as long as 6 hours after collapse event.

 

 

When body temperature drops below a threshold—typically around 36 °C (97 °F)—people may begin to shiver.

 

 

Drugs commonly used to prevent and treat shivering in targeted temperature management include acetaminophen, buspirone, opioids including pethidine (meperidine), dexmedetomidine, fentanyl, and/or propofol.

 

 

In shivering that is unable to be controlled with these drugs: general anesthesia and/or paralytic medication like vecuronium are given.

 

 

Rewarming  slowly and steadily avoids harmful spikes in intracranial pressure.

 

 

Cooling catheters are inserted into a femoral vein and cooled saline solution is circulated through either a metal coated tube or a balloon in the catheter. 

 

 

Studies indicated targeted temperature management via catheter is safe and effective.

 

 

Adverse events associated with cooling catheters: bleeding, infection, vascular puncture, and deep vein thrombosis (DVT).

 

 

Transnasal evaporative cooling uses two cannulae, inserted into a persons nasal cavity, to deliver a spray of coolant mist that evaporates directly underneath the brain and base of the skull, and it reduces the temperature throughout the rest of the body.

 

 

Transnasal evaporative cooling can be used at the point of cardiac arrest, during ambulance transport, or within the hospital proper. 

 

 

It has cooling rates of 2.6 °C (4.7 °F) per hour in the brain and 1.6 °C (2.9 °F) per hour for core body temperature reduction.

 

 

Cold water can circulate through a blanket, or torso wraparound vest and leg wraps:  70% of a person’s surface area should be covered with water blankets. 

 

 

Water blankets lower a person’s temperature exclusively by cooling a person’s skin and accordingly require no invasive procedures, and is the most common means of controlling body temperature. 

 

 

Water blanket’s undesirable qualities: susceptible to leaking, which may represent an electrical hazard,  burns, overshooting of temperature, slower induction time versus internal cooling, increased compensatory response, decreased patient access, and discontinuation of cooling for invasive procedures such as the cardiac catheterization.

 

 

Non-invasive head cooling caps and helmets designed to target cooling at the brain are available.

 

 

Head cooling caps are used are in preventing or reducing alopecia in chemotherapy, and for preventing cerebral palsy in babies born with hypoxic ischemic encephalopathy.

 

 

Positive effects of mild hypothermia applied following cardiac arrest have been demonstrated.

 

 

Hypothermia is a highly effective treatment in newborn infants following birth asphyxia. 

 

 

Hypothermia for 72 hours started within 6 hours of birth asphyxia significantly increased the chance of survival without brain damage.

 

 

The use of hypothermia to control intracranial pressure (ICP) after an ischemic stroke is safe and practical.

 

 

A systematic review of randomized controlled trials in traumatic brain injury (TBI) suggests there is no evidence that hypothermia is beneficial.

 

 

Hypothermia had shown no improvements in neurological outcomes or in mortality in neurosurgery.

 

 

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