Page 1847 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

1316 PART 11: Special Problems in Critical Care

in patients with moderate or severe hypothermia. Patients must have patients but may be considered in combination with other rewarming
adequate physiologic reserve to increase their metabolic rate and gener- methods for the patient with no evidence of perfusion.
ate heat to rewarm themselves. Rewarming rates with passive external Closed thoracic lavage also has been proposed for treatment of hypo-
rewarming in mild hypothermia vary between 0.5°C and 2.0°C per hour. 6 thermia. 39-42 This technique uses a large thoracostomy tube inserted into
■ ACTIVE REWARMING the anterior second or third intercostal space in the midclavicular line.
A second tube is inserted in the posterior axillary line in the fifth or
Active rewarming involves the transfer of exogenous heat to the patient sixth intercostal space. Sterile normal saline heated to 40°C to 42°C
by using external or internal techniques. Indications for active rewarming (104-107.6°F) is infused through the anterior tube and allowed to drain
passively from the posterior tube. This technique may have the advan-
include cardiovascular instability, poikilothermia (<32°C), inadequate
rewarming with other methods, endocrinologic insufficiency, and tage of warming the heart and great vessels. However, clinical experience
is limited. Mediastinal irrigation and myocardial lavage could be con-
traumatic peripheral vasodilation (ie, spinal cord injury). Patients with
endocrinologic diseases may have insufficient glycogen stores or insuf- sidered in patients with severe hypothermia and no spontaneous perfu-
sion. These techniques require expertise for thoracotomy and clinical
ficient endogenous thermogenesis. experience is limited.
■ ACTIVE EXTERNAL REWARMING the surface area available for conductive heat transfer is small. In addi-
Irrigation of the stomach, bladder, or colon has limited utility because
Different methods have been used for active external rewarming tion, gastric lavage may predispose to aspiration and must be discontin-
(AER), including immersion in a 40°C bath, warming blankets, heat- ued during chest compressions. Special double lumen esophageal tubes
ing pads, radiant heat, and forced air rewarming. Indications for or modified Sengstaken tubes have had limited evaluation and use. 43,44
use of these devices remain controversial. Concerns were raised in These techniques are warranted only if no other methods are available
the past regarding AER because vasodilation in the extremities may for rewarming.
facilitate transport of colder peripheral blood to the warmer core, Several methods have been used for extracorporeal blood rewarming.
thereby lowering the core temperature (“afterdrop”), but experience These include hemodialysis, venovenous rewarming with continuous
with AER has not found evidence of afterdrop. Peripheral vasodilation renal replacement techniques, venovenous extracorporeal membrane
may also potentially worsen hypotension. Immersion in a warm water oxygenation (ECMO), and cardiopulmonary bypass (CPB). Hemodialysis
bath can impede monitoring and active resuscitation. Thermal injury uses a two-way flow catheter with percutaneous cannulation of a single
can occur with heating pads, warming blankets, and radiant heat vessel. The femoral vein is preferred over the subclavian vein to avoid
sources. The most practical technique for AER in hospitals is forced myocardial irritation with the guidewire. This technique may be most
air rewarming, which transfers heat convectively and prevents heat appropriate in the patient without severe hemodynamic instability,
loss. These devices are usually readily available from postoperative although it has been used in unstable patients. 45,46 Hemodialysis may be
care units. They enable greater contact of warm air with the patient’s the preferred rewarming method when hypothermia is associated with
body than traditional warming blankets. Successful use of forced air as severe renal dysfunction or intoxication with dialyzable substances. An
the primary rewarming method in patients with severe hypothermia alternative to hemodialysis is continuous venovenous rewarming. This
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with and without cardiac arrest has been reported. Newer resistive technique uses countercurrent fluid warming in the dialysis cartridge
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polymer blankets have been compared to forced air rewarming in with use of a roller pump.
volunteers and postoperative patients but there is no experience in More recently, venovenous ECMO has been utilized for treatment
hypothermia victims. 33,34 of severe hypothermia in patients with cardiovascular instability. 48,49
Warming rates of 1°C to 2.5°C per hour have been reported with Potential advantages include the availability of portable units, limited
AER after accidental hypothermia. 32,35 Circulatory problems may be need for heparinization, percutaneous cannulation that does not inter-
minimized if AER is applied only to the trunk. Truncal AER may be fere with resuscitation, support of pulmonary function and rewarming
combined successfully with other methods of active core rewarming rates similar to CPB.
such as warmed intravenous fluids and heated humidified oxygen. The CPB using standard access through the femoral artery or femoral
advantages of AER are ease of institution, availability, low cost, and vein is the most invasive and labor-intensive technique for rewarming.
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noninvasiveness. It has the advantages of providing complete hemodynamic support
■ ACTIVE CORE REWARMING during rewarming and rapid rewarming rates. Core temperature can
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increase 1°C to 2°C every 3 to 5 minutes with femoral flow rates of 2 to
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Numerous alternatives are available for active core rewarming which is 3 L/min. Unfortunately, CPB may require considerable time to institute
the application of heat to the body core. Airway rewarming using heated and is not available in all institutions. Systemic anticoagulation may be
humidified oxygen is relatively simple to institute and should be a part contraindicated in trauma victims or contribute to hypothermic coagu-
of management of most patients with moderate or severe hypothermia. lopathy. Heparin-bonded tubing, portable circuits, and methods using
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51,52
The delivery of heated oxygen is more effective through an endotracheal venovenous access may overcome some of these problems. These
tube than by mask. Oxygen should be warmed to 40°C to 45°C (104- advances have allowed the institution of CPB in emergency departments
53
113°F) through modification of humidifier devices. A rewarming rate and intensive care units. Long-term outcomes of patients with severe
37
of 1°C to 2.5°C per hour can be expected. Although there are several hypothermia treated with CPB have been favorable. 54
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proposed advantages of airway rewarming that include decreased respi- Another technique for active core rewarming is intravascular warm-
ratory heat loss, increased heat donation to the respiratory tract, and ing with an endovascular temperature control device. These systems are
direct heat transfer to the hypothalamus, brain stem, and medulla, its used most commonly to induce mild hypothermia in patients suffering
efficacy remains equivocal. 38 cardiac arrest. Experience is very limited but potential advantages may
Heated irrigation has been used to transfer heat from fluids to inter- include percutaneous femoral insertion and no use of anticoagula-
nal body areas with a variety of techniques. Peritoneal dialysis or lavage tion. 55,56
Peritoneal dialysis can deliver fluid heated to 40°C to 45°C (104-113°F) ■ FUTURE TECHNIQUES
is probably the most widely recognized method of heated irrigation.
to the peritoneal cavity with flow rates of approximately 6 L/h. Potential Techniques such as the use of very high-temperature intravenous fluids
advantages of this technique are hepatic rewarming, use during chest and diathermy are being explored for the treatment of moderate or
compressions, and the capability to simultaneously provide renal severe hypothermia. Intravenous fluids heated to 65°C (149°F) have
replacement when a dialysate is used. Rewarming rates average 1°C been used in animal studies and resulted in rewarming rates of 2.9°C to
to 3°C per hour. This technique is not routinely advocated for stable 3.7°C per hour with minimal intimal injuries. 57,58
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