Outline the advantages and limitations of various methods for induction of therapeutic hypothermia. 

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College Answer

Therapeutic hypothermia can be induced by a number of methods. These differ in their ease of use and the rapidity of onset of hypothermia. In all cases, irrespective of the methods used, core temperature should be monitored, as should be invasive arterial pressure, ECG etc. Shivering needs to be suppressed with sedation+/- muscle relaxants.

The various methods are outlined below:

Method

Advantages

Limitations

1.Surface cooling

Circulating cold water
blankets
Forced cold air convective
blankets
Ice packs to axillae, groin
etc

Readily available
Easy to use
Relatively cheap

Slow – takes up to 8 hours to reduce temp to 32-34oC Titration of temperature
can be difficult
Ice packs carry risk of
burns

Alcohol and fans

Cheap

Use of fans not practical in
ICU

Immersion in ice bath

Effective for children
Commercial devices under
development

Limited practical use

Newer devices

Cooling garment / pads /
suits / helmet

Increased efficiency
Cooling up to 3oC / hr

Cost

2. Large volume ice cold IV
fluid – 30 ml/kg crystalloid
cooled to 4oC infused over
30 min

Easy
Cheap
Reduction in temp by
1.6oC
Initial study by Bernard
showed no adverse effects

Contra-indicated in
pulmonary oedema
Needs additional method
to maintain hypothermia

3. Body cavity lavage
Gastric 500 ml / 10 min
Bladder 300 ml / 10 min
Peritoneal

Cheap
Gastric and bladder lavage
use indwelling lines

Time-consuming
Invasive

4. Extra-corporeal circuits

May be part of CRRT

Invasive

5. External heat exchange
control devices via
indwelling central line

Cool by 0.8oC / hr
Will achieve and maintain
target temp

Invasive
Expensive

Discussion

The college has presented an excellent tabulated answer.

Following such an effort, one can do little other than provide references.

One such reference is a 2009 article by Kees Polderman and Herold Ingeborg which goes though cooling methods listing their advantages and limitations. In this article, I was surprised to find a table (Table 2) which is almost identical to the college answer - only more detailed. The table is huge, it spans over two pages, and the article as a whole is an amazing resource. This paper, sadly, is not available as a free full text offering. The table below is a stripped-down surrogate.

Methods of Inducing Therapeutic Hypothermia
METHOD ADVANTAGES DISADVANTAGES
Air cooling by skin exposure

Easy, cheap, and without procedural risk

Cooling rate is around 0.5°C per hour

Not very effective.

And you cannot rewarm them this way.

Air cooling with electric fans

Easy, cheap, and without procedural risk

Cooling rate is around 1.0°C per hour

As you fan the patient, you blow aerosolised pathogens all around your ICU, which is a potential infection risk. And you cannot rewarm them this way.

Evaporative air cooling by skin exposure with alcohol, water, sponge baths etc

Easy, cheap, and without much procedural risk. Cooling rate is around 1.0°C per hour

Labour intensive.

The patient ends up wet - that may be a major problem for patients with wounds.

Alcohol is not benign, it may absorb into eroded skin areas and it may irritate.

Electrical safety becomes a concern with exposed transvenous or epicardial pacing wires. And you cannot rewarm them this way.

Air cooling with an inflatable blanket

Easy, cheap, and without procedural risk

Frequently the ICU will already have one.

Cooling rate is around 0.5°C per hour.

One can change the air temperature, and rewarm the patient in this fashion.

Not any more effective effective than cooling by passive air-skin exposure.

Specially designed air-cooling beds (with an air-pumped inflating mattress)

Without procedural risk, and potentially offering a protection against pressure areas.

Cooling rate is around 1.0°C per hour.

One can change the air temperature, and rewarm the patient in this fashion.

Expensive and noisy.

Not available everywhere

Surface cooling by ice packs

Easy and cheap.

Cooling rate is around 1.0°C per hour

Labour intensive.

Uneven cooling - some areas may have little cooling while other areas may develop frostbite or pressure areas.

Surface cooling by immersion in cold water

Rapid cooling rate: around 8-10°C per hour

Cold water is inexpensive.

It may be possible to rewarm the patient this way by changing the bath temperature.

Impractical for large patients - this technique may only be suitable for infants and children.

The patient ends up wet - that may be a major problem for patients with wounds.

Unusual problems arise with attempting to ventilate a partially submerged patient.

Electrical safety becomes a concern with exposed transvenous or epicardial pacing wires.

Surface cooling by skin contact with circulating cold water in a cooling blanket

Good cooling rate: around 1.5°C per hour

Cold water is inexpensive.

Changing the water temperature can be used to rewarm the patient.

Some systems can be coupled in feedback with a temperature probe for more accurate temperature maintenance

Labour-intensive

Initially, takes some time to reach he desired temperature

Surface cooling by skin contact with circulating cold water in a cooling vest

Rapid cooling rate: around 8-10°C per hour

Cold water is inexpensive.

Changing the water temperature can be used to rewarm the patient.

Some systems can be coupled in feedback with a temperature probe for more accurate temperature maintenance

The cooling blankets may be reusable, but the jackets are not -and these can be expensive.

The jackets may leave marks on the skin, and theoretically could cause pressure areas

Infusion of cold fluids

Easy and cheap.

Good cooling rate: 2.5-3.0°C per hour

A large volume of fluid needs to be infused;

this may result in electrolyte derangement and fluid overload. The patient cannot be rewarmed in this way.

Also, there is little control over the temperature which is achieved in this way.

Lastly, exposure of the myocardium to a jet of cold fluid may result in arrhythmias and asystole.

Peritoneal lavage with cold fluids

Potentially, a good cooling rate

Invasive, requires some surgical expertise. Infused cold fluids will be absorbed to some extent, giving rise to electrolyte abnormalities.

The patient cannot be rewarmed in this way.

Intravascular cooling catheters: baloons filled with cold saline, metal catheters for heat exchange,

Good cooling rate: around 2.0°C per hour

Most of these double as central lines, offering central venous access and central temperature monitoring

Invasive, expensive, and disposable.

Catheter-related thrombosis may be an issue.

Extracorporeal circuit cooling

Rapid cooling rate: around 4-6°C per hour

Convenient if the patient is already on ECMO or CVVHDF; little additional workload.

The patient can also be rewarmed in this way.

Very invasive. Major disadvantage due to the need for anticoagulation.

Antipyretic drugs

Easy and cheap.

Poor cooling rate: 0.1-0.5°C per hour

References

Garcia, Juan A., et al. "The oxygen concentrations delivered by different oxygen therapy systems." CHEST Journal 128.4_MeetingAbstracts (2005): 389S-b.

Abe, Yukiko, et al. "The efficacy of an oxygen mask with reservoir bag in patients with respiratory failure." The Tokai journal of experimental and clinical medicine 35.4 (2010): 144-147.