Critical Care Nurse. 2008;28: 24-29
Copyright © 2008 by the American Association of Critical-Care Nurses.
Cover Article
CE Article
Treatment of Severe Hypothermia With Intravascular Temperature Modulation
Marie Lasater, RN, MSN, CCRN, CNRN
Marie Lasater is a staff nurse at Barnes Jewish Hospital in St Louis, Missouri.
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To learn more about hypothermia, read "Keeping Cool: A Case for Hypothermia After Cardiopulmonary Resuscitation" by Mary Kay Bader et al in the American Journal of Critical Care, 2007;16:636-640. Available at www.ajcconline.org.
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Financial Disclosures
None reported.
This article has been designated for CE credit. A closed-book, multiple-choice examination follows this article, which tests your knowledge of the following objectives:- Identify the types of patients at risk for hypothermia
- Describe the consequences of rapid rewarming
- Discuss the advantages and disadvantages of the various methods of rewarming
Corresponding author: Marie Lasater, RN, MSN, CCRN, CNRN, 14786 Highway 63, Licking, MO 65542 (e-mail: calhorselover{at}yahoo.com).
Hypothermia can occur not only in persons exposed to extreme cold, but also in the elderly and infirm, and in patients with medical conditions that impair the ability to maintain an adequate body temperature. Stages of hypothermia are classified as mild, moderate, and severe (Table 1
). Treatments for hypothermia have been described since the time of Hippocrates (470-410 BC).2 In the ensuing centuries, hypothermia has continued to occur at significant rates in the winter months and in northern regions, with mortality rates up to 40% when body temperature is less than 34°C.3 Hypothermia can be either primary or secondary. Primary hypothermia occurs in otherwise healthy persons who are inadequately clothed and exposed to severe cold. In secondary hypothermia, another illness predisposes the person to accidental hypothermia.4 The elderly and infirm are at increased risk for secondary hypothermia, and conditions such as ethanol intoxication, diabetes, sepsis, uremia, hypoglycemia, and malnutrition can also impair the ability to maintain an adequate body temperature in a cold environment.5
Rewarming a hypothermic patient is not a casual endeavor, because rewarming too rapidly can precipitate a condition known as "afterdrop." Afterdrop is defined as a precipitous reduction in core temperature due to redistribution of body heat to improperly warmed peripheral tissues, with rapid shunting of cold blood from the periphery to the core as the direct result of vasodilatation.6 Afterdrop can cause a further decrease in core temperature, even after a person with hypothermia is removed from the cold. Rewarming a patient with heating pads or by placing frozen extremities in warm water before thermal stabilization of the body core can cause a bolus of cold, hyperkalemic, acidotic blood to return from the periphery to the heart, resulting in a profound, biochemical injury that leads to severe hypotension and dysrhythmias.1,7 Rewarming the core at a prescribed rate is important, because hypothermia alone may not be fatal if the body temperature is greater than 25°C. Shock and metabolic derangements can also be precipitated by hurried rewarming or by warming the periphery before the core. The following case study describes a novel method of rewarming a patient who had hypothermia.
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Discussion
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Medical publications1,2,6,7,9 consistently report that slow, rather than rapid, rewarming contributes to favorable outcomes for patients. Patients with severe hypothermia must not be exposed to extremes of heat and should be rewarmed as safely as possible at a "successful rate," with the core warmed before the periphery. A review of the literature indicates that patients have been successfully rewarmed at rates from 1°C/h to 2.95°C/h without experiencing permanent organ damage. Rewarming at the fairly rapid rate of 2.95°C/h described by Plaisier10 may be an outlier, because most investigators11–13 recommend a rewarming rate of 1°C/h. Patients who are successfully rewarmed but do not survive to hospital discharge are those with multiple preexisting comorbid diseases.12
| CASE STUDY An 81-year-old man with a history of hypertension, congestive heart failure, and chronic renal insufficiency was noted by his family to be nonresponsive. Paramedics called to the home found the patient’s skin cold and dry; he had a blood pressure of 70 mm Hg by palpation, a heart rate of 49/min, a respiratory rate of 14/min, and an oxygen saturation of 98%. The patient was given 0.5 mg of atropine as an intravenous bolus and fluids intravenously and was transported to the local tertiary care hospital.
When the patient arrived in the emergency department, physical examination revealed a cachectic elderly man with cool dry skin and a score of 11 on the Glasgow Coma Scale. Vital signs were as follows: heart rate, 52/min; respiratory rate, 14/min; blood pressure, 104/69 mm Hg; and body temperature, 26.6°C rectally. Further examination revealed irregularly irregular bradycardia, mild suprapubic tenderness, and decreased deep tendon reflexes. Samples of blood, urine, and sputum were obtained for culture, and empirical antibiotics were started per sepsis protocol. A urinary catheter was placed to monitor core temperature and urine output. Admission laboratory values included a potassium level of 7.6 mmol/L, a creatinine level of 7.2 mg/dL (to convert to micromoles per liter, multiply by 88.4), and a serum urea nitrogen level of 95 mg/dL (to convert to millimoles per liter, multiply by 0.357). An electrocardiogram obtained at admission did not show classic J waves, also called Osborne waves (Figure 1), which are common in hypothermia,9 but did show atrial fibrillation with bradycardia and 160° right axis deviation.
Despite fluid replacement, the patient’s blood pressure declined again, to 70/40 mm Hg, and he was treated with active rewarming, consisting of warmed intravenous fluids and a warming blanket, and antibiotic therapy including ciprofloxacin, vancomycin, and cefepime per sepsis protocol. Hyperkalemia was treated with a 1-g intravenous bolus of calcium chloride, 60 g of sodium polystyrene sulfonate (Kayexalate) per rectum, a 25-mL intravenous bolus of 50% dextrose in water, and 10 units of regular human insulin intravenously. Because of the patient’s profound hypothermia, the resident physician used the ICY catheter (designed for intravascular cooling to maintain mild hypothermia in postoperative neurological patients; Alsius Corporation, Irvine, California) to warm the patient gradually. The ICY catheter was placed via the femoral vein, and intravascular warming was initiated with the goal temperature set at 37.5°C. The patient was warmed initially at a rate of 1.5°C/h until a temperature of 33°C was reached and cardiovascular stability was achieved. At that point he was transferred to the medical intensive care unit, where a goal temperature of 37°C was achieved at a steady rate within 12 hours after admission, at a rate of 0.8°C/h. The patient did not experience cardiovascular afterdrop, and normal sinus rhythm resumed 90 minutes after rewarming was initiated (Figure 2). The patient underwent dialysis the evening of admission and had no further dysrhythmias or hypotension. He was successfully extubated 2 days after admission and maintained normothermia throughout the rest of his hospital stay.
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Figure 1 Osborne waves are common in patients with hypothermia and are thought to be due to severe cooling of the left ventricle. Osborn waves, also known as J waves, are positive deflections occurring at the junction between the QRS complex and the ST segment.8
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In patients who had undergone cardiac bypass, the group with the slowest rewarming, about 1.09°C/h, had better cardiac index and peak velocity, lower blood lactate levels, less afterdrop in core and foot temperatures, and shorter intensive care unit stays than did patients who were rewarmed more rapidly.6,14 In addition to the cardiovascular effects, early research indicates that rewarming that is too rapid has a deleterious effect on the nervous system; specifically, rewarming faster than 1°C every 40 minutes induces secondary damage in the neural axon, an effect not seen with slow rewarming.11
Rewarming Methods
Several methods of rewarming are available. Otherwise healthy patients with core temperatures greater than 32.2°C can be successfully rewarmed via spontaneous or passive rewarming. In passive rewarming, the patient is simply covered with an insulating material and removed from the cold. However, patients with core temperatures less than 32.2°C and patients with unstable cardiovascular conditions, endocrinologic or metabolic insufficiency, or an inadequate rate of rewarming require active rewarming.15 Some of the more commonly used methods for active rewarming are forced air warming and active core rewarming (which includes airway warming, peritoneal dialysis, heated irrigation, and extracorporeal blood rewarming; Table 2).
Forced Air Warming.
Heating blankets that use forced air warming transfer heat efficiently. They have the advantage of being readily available and easy to use in hospitals. However, concerns arise as to the potential for thermal injury to vasoconstricted, hypoperfused tissue, as well as a variable and unpredictable rate of rewarming.16
Active Core Rewarming.
For several reasons, active core rewarming is recognized as the most efficient method of safely rewarming patients who have severe hypothermia. Core organs account for 8% of body weight but contribute 56% of bodily heat production in normothermia and an even greater percentage in hypothermia. When warming efforts are directed to the core, rewarming occurs at a more efficient rate and the risk of rewarming collapse (as occurs when the periphery is warmed first) is minimized.1
Airway Warming.
Airway rewarming is a valuable adjunct to other rewarming methods. Most patients who have severe hypothermia are intubated, so ventilator adjustments can be made to provide humidified, warmed air to preserve heat and humidity ordinarily lost with breathing. Although most ventilators can deliver humidified oxygen at temperatures up to 40°C, the amount of heat delivered by this method is small because of the limited surface area of the lungs for heat exchange. However, patients with hypothermia who are intubated can be assured of adequate oxygenation and airway humidity.17
Heated Irrigation.
Published reports have described patients being successfully rewarmed by use of a variety of heated irrigation methods, ranging from gastric and bladder lavage with warm fluids to peritoneal dialysis and thoracic lavage. In all these methods, rewarming is limited by surface area exposed to the warming solution, infusion flow rate, and dwell time. Thoracic lavage with a median rewarming rate of 2.95°C/h has shown the most promise of these techniques10 but is limited by its complexity; it requires the placement of 2 large-bore thoracostomy tubes. Peritoneal dialysis with dialysate warmed to 40°C to 45°C at a rate of 6 to 10 L/h increases body temperature by 1°C/h to 3°C/h. Gastric and bladder lavage are limited because of the limited surface area involved, but those methods can be used in conjunction with other warming methods.17
Extracorporeal Blood Rewarming.
Extracorporeal blood rewarming is effective and can be accomplished with cardiopulmonary bypass, hemodialysis, arteriovenous rewarming, and venovenous rewarming. All these methods are limited because rewarming too rapidly can result in severe complications such as hemolysis, pulmonary edema, and acute tubular necrosis. Because of the severity of complications, extracorporeal rewarming is not recommended for patients with no evidence of cardiac arrest and asystole.18,19
Intravascular Rewarming.
Intravascular rewarming via a closed-loop indwelling catheter is a novel approach to rewarming that was used successfully at a large tertiary teaching hospital in the Midwest. The ICY catheter (Figure 3) used to rewarm the severely hypothermic patient described in the preceding case study was originally developed to provide core temperature cooling in neurosurgery patients and patients after cardiac arrest. The catheter is part of the CoolGard system developed by Alsius Corporation, which includes a temperature monitor, a temperature control unit, a heat exchange unit, and a roller pump20 (Figure 4). Feedback from a bladder thermister regulates the temperature of sterile saline that is circulated through the closed catheter membranes to facilitate steady achievement and maintenance of desired body temperature. This method has no danger of fluid overload because the warmed saline is fully contained within the catheter lumens. The goal temperature and rate of warming (or cooling) can be accurately dialed in on the system.
Use of Meperidine.
Use of meperidine is contraindicated in all methods of rewarming because it inhibits shivering, which attenuates the rate of rewarming. In addition, shivering provides a physiological benefit in decreasing afterdrop in rewarmed patients.21
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Nursing Implications for Intravascular Rewarming
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Intravascular rewarming involves placement of a central catheter, so sterile technique must be observed when the catheter is placed, and a radiograph should be obtained to verify correct placement. Like all central catheters, the catheter must be replaced after 7 days. Although some intravascular temperature modulation catheters are manufactured for insertion in the subclavian vein, use of the femoral vein approach is essential for rewarming patients with hypothermia, because a hypothermic heart that is being rewarmed is irritable, and placement of a subclavian catheter could predispose patients to lethal dysrhythmias.
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Conclusion
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Patients with profound hypothermia can be safely rewarmed as long as rewarming proceeds at a slow rate, generally no faster than 1°C/h to 2°C/h, with warming of the core before the periphery. Use of intravascular rewarming via a technique such as use of the ICY catheter and CoolGard system is one method of restoring normal core body temperature in patients while avoiding hazardous afterdrop.
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PRIME POINTS
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- How to avoid "afterdrop," a precipitous reduction in core temperature, when rewarming patients.
- Patients with profound hypothermia can be safely rewarmed by using a slow rate and by warming the core before warming the periphery.
- Learn about intravascular rewarming, a method of restoring normal core body temperature while avoiding hazardous afterdrop.
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References
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- McEwan M; Search and Rescue Society of British Columbia. Hypothermia: physiology, signs, symptoms and treatment considerations. http://www.sarbc.org/hypo1.html. Updated October 28, 1995. Accessed August 20, 2008.
- Paton BC. Accidental hypothermia. Pharmacol Ther. 1983;22(3):331–337.[Medline]
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- Al-Senani F, Graffagnino C, Grotta J, et al. A prospective, multicenter pilot study to evaluate the feasibility and safety of using the CoolGard system and Icy catheter following cardiac arrest. Resuscitation. 2004; 62(2):143–150.[Medline]
- Giesbrecht G, Goheen M, Johnston C, Kenny G, Bristow G, Hayward J. Inhibition of shivering increases core temperature afterdrop and attenuates rewarming in hypothermic humans. J Appl Physiol. 1997; 83(5):1630–1634.[Abstract/Free Full Text]
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Discussion
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