Chapter 189. Hypothermic Patient Management

Hypothermia is defined as a core body temperature below 35°C. The normal physiologic thermoregulatory responses start to fail once the core body temperature reaches this level, leading to the body's inability to generate enough heat to maintain bodily functions. Hypothermia can be subdivided into primary and secondary hypothermia.1 Primary accidental hypothermia occurs when a previously normal individual is subjected to an environmental stress. Secondary accidental hypothermia occurs when a predisposing factor leads to disruption of temperature homeostasis and increases the individual's susceptibility to lesser environmental stresses (e.g., drug intoxication, trauma, and endocrine disorders). Drug intoxication and trauma are acquired conditions that are highly associated with the development of hypothermia.1

There are multiple reasons why trauma patients are at an increased risk to develop hypothermia. These include extended prehospital time, resuscitation with cold (i.e., ambient air temperature) intravenous fluids, exposure to environmental factors, and physiological characteristics of the trauma itself. Both bleeding and hypoperfusion alter thermoregulation. Hypothermia is an independent contributing factor for increased morbidity and mortality in trauma patients, regardless of the patient's Injury Severity Score (ISS). Hypothermia is associated with an increase in the incidence of coagulopathy, multiple organ failure, length of hospital stay, and mortality.2

Significant emphasis has been placed on the prevention of hypothermia as well as the early recognition and correction of hypothermia in the prehospital setting. It is important to recognize that hypothermia can also progress after the patient arrives in the Emergency Department. Studies in the trauma population have reported a significant percentage of patients to have a decrease in their core body temperature during their stay in the Emergency Department.3–5 This recognition has led to the development of multidisciplinary approaches to maintaining normothermia as the patient moves through the hospital.6 The importance of continuity and communication in dealing with hypothermia cannot be overstated.

Hypothermia can be characterized as mild, moderate, and severe. Mild hypothermia is defined as a core temperature of 32.2 to 35°C or 90 to 95°F. Moderate hypothermia is defined as a core temperature of 28 to 32°C or 82.4 to 90°F. Severe hypothermia is defined as a core temperature of less than 28°C or 82.4°F. The scale can be amended in the trauma patient to 34 to 36°C or 93.2 to 96.8°F for mild hypothermia, 32 to 34°C or 89.6 to 93.2°F for moderate hypothermia, and <32°C or <89.6°F for severe hypothermia.

Mild hypothermia causes the body to increase heat production by shivering and increasing its metabolic rate. The heart rate increases and the patient may become tachypneic. Peripheral vasoconstriction may result in acrocyanosis. Neurologic symptoms may include confusion, dysarthria, and impaired judgment.

Moderate hypothermia is associated with a further decrease in the mental status. This includes lethargy, hallucinations, and loss of the pupillary reflex. The heart rate changes from tachycardia to bradycardia. The cardiac rhythm commonly converts from normal sinus to atrial fibrillation.7 The respiratory pattern becomes depressed, with a decreasing respiratory rate and tidal volume. The patient stops complaining of “feeling cold” and shivers less.

The patient is usually comatose by the time severe hypothermia is present, often with evidence of cardiorespiratory collapse. Ventricular irritability becomes evident. Ventricular fibrillation becomes refractory to conversion below 28°C. Asystole occurs at 20°C. The characteristic electrocardiographic (ECG) finding of an Osborne J wave occurs at approximately 32°C (Figure 189-1). This is a positive deflection between the QRS and the ST segment. It is often best seen in ECG leads aVL, aVF, and the left chest leads.8,9 Respiratory drive is increased during the early stages of hypothermia, but progressive respiratory depression occurs below 33°C, resulting in a decrease in minute ventilation. The ciliary action and the cough reflex are also depressed, predisposing to atelectasis and aspiration.

Metabolic problems associated with hypothermia include hyperglycemia (mild hypothermia), hypoglycemia (moderate and severe hypothermia), and impaired oxygen consumption (severe hypothermia). Oxygen consumption per unit time (VO2) increases dramatically with any fall in body temperature.10 A core temperature decrease of 0.3°C is associated with a 7% increase in VO2. Temperature reductions between 0.3 and 1.2°C have been reported to result in a 92% increase in VO2, with proportional increases in minute ventilation.10 The resultant increase in oxygen utilization may result in anaerobic metabolism, acidosis, and significant cardiopulmonary stress.11

Serum electrolyte changes are often unpredictable in the hypothermic patient. Serum potassium is often slightly increased because of renal tubular dysfunction, acidosis, and the breakdown of liver glycogen. When interpreting blood test results, it is recommended that uncorrected values be used to guide therapy due to the complexities of the acid–base balance associated with hypothermia. These derangements are reversible with rewarming.

Coagulopathy is one of the most clinically significant metabolic derangements seen with hypothermia. Evidence suggests that significantly increased clotting times occur at core temperatures less than 35°C.1,3 Temperatures less than 32°C lead to severe platelet dysfunction despite normal platelet counts.1,3 Cold platelets are known to undergo morphologic changes that affect adherence, including loss of shape, cytoplasmic swelling, and dissolution of cytoplasmic microtubules necessary for normal motility. Cold-induced slowing of the enzymatic reaction rate of thromboxane synthetase results in decreased production of thromboxane A2, a potent vasoconstrictor necessary for normal platelet aggregation.12,13 These derangements are reversible with rewarming. Clotting factor dysfunction is another factor contributing to the coagulopathy in the hypothermic patient. This has been shown to be due to the direct effect of hypothermia on the clotting factors physiochemical activity.14 It is important to remember that clinical tests of coagulation are temperature standardized to 37°C. Fibrometers contain a thermal block that heats the plasma and reagents to 37°C before initiating the assay. Thus, tests of coagulation reflect clotting factor deficiencies, but are corrected for any potential effect of hypothermia on clotting factor function.

The heat deficit of a hypothermic patient can be calculated using the formula Q = mc(t2 − t1), where Q is the heat loss (in kcal), m is the patient's body mass (in kg), c is the specific heat of the body (0.83 kcal/kg/°C), and (t2 − t1) is the change in body temperature (°C). Application of this formula will allow the calculation of the amount of heat (in kcal) that must be transferred to a hypothermic patient to regain normothermia, assuming no additional losses. Knowing that the specific heat of water is 1.0 kcal/kg/°C allows one to calculate the expected rate of rewarming given the particular method used.

Patients presenting with core body temperatures in the ranges of hypothermia must be identified and treated. Hypothermia should be easily identified, since a temperature evaluation is a vital sign checked in every patient that comes to the Emer-gency Department. Treat all patients who present to an Emergency Depart-ment with an awareness of the potential that they can develop hypothermia, especially if they are trauma patients or have an altered mental status. Cover all patients with warm sheets or blankets as soon as their initial evaluation and any necessary procedures are completed.

There are no contraindications to the treatment of accidental hypothermia. There are, however, circumstances in which medically induced therapeutic hypothermia may be of benefit.15–18 Refer to Chapter 188 regarding the details of inducing therapeutic hypothermia. These situations are beyond the scope of this chapter.

Certain components of the initial resuscitation of the hypothermic patient deserve mention. All patients with hypothermia are identified by measurement of core body temperature on admission. Close subsequent monitoring is necessary and required. The following challenges to routine temperature monitoring, and suggested remedies, were noted in a review article.9 Poor peripheral perfusion may result in difficulty assessing the pulse and blood pressure, making the use of Doppler ultrasound necessary. Cutaneous probes for temperature and pulse oximetry have difficulty picking up signals in hypothermic patients. Oral and auricular temperature probes are often inaccurate in the hypothermic patient. Consider using a bladder, esophageal, or rectal temperature probe.

Airway management is often required in patients with moderate and severe hypothermia due to a decreased mental status. Standard orotracheal intubation may be difficult due to jaw muscle rigidity. Neuromuscular blocking agents are not recommended for patients with core body temperatures less than 30°C. The use of topical vasoconstricting agents, smaller endotracheal tubes, and blind orotracheal intubation has been suggested. Fiberoptic guided orotracheal intubation can be utilized if available. Management of ventilated patients must include close monitoring of the endotracheal cuff pressure, as the volume and pressure may increase with patient rewarming. Ventilate patients at rates no greater than 8 to 12 breaths per minute to avoid respiratory alkalosis.9

Management of the circulatory system in those with moderate to severe hypothermia often requires fluid resuscitation, as these patients are volume depleted. Dextrose in the initial resuscitation fluid is not contraindicated. Ringer's lactate solution is not recommended due to concerns about decreased hepatic metabolism of lactate in the hypothermic patient. Dehydration results in hemoconcentration. Therefore, a low hematocrit suggests an underlying anemia and/or blood loss. The heart is susceptible to arrhythmias. Avoid transthoracic central venous catheters and pulmonary artery catheters until rewarming has been achieved. Use intravenous catheters in any of the extremities or the external jugular vein. An alternative is a femoral central line as the catheter and guidewire are not long enough to reach the heart and trigger an arrhythmia.

Treat nonperfusing cardiac rhythms (i.e., ventricular fibrillation, asystole, and junctional ventricular rhythms) using Advanced Cardiac Life Support (ACLS) guidelines. The presence of bradycardia, atrial fibrillation, and other dysrhythmias that do not reduce perfusion do not require pharmacologic support, as these will reverse with rewarming. Defibrillation at core body temperatures less than 30 to 32°C may not be effective. Continue resuscitative efforts in conjunction with rewarming.8,9

Resuscitation drugs are often ineffective at core body temperatures below 30°C. Lidocaine has decreased efficacy at these temperatures.8,9 Procainamide has been suggested to increase ventricular fibrillation.8,9 Bretylium has been demonstrated to be effective in animal studies, though information regarding optimal clinical dosage is not known in this patient group.8,9 Use caution when administering and dosing all resuscitation drugs, due to their decreased metabolism in hypothermic patients, which can lead to toxicity. It is recommended that medications be administered at one-half the normal dose during the resuscitation of a moderately or severely hypothermic patient.9 Avoid vasopressors due to their potential to cause arrhythmias.9 Repeat the resuscitation cycle with every increase in core body temperature of 1 to 2°C until a core temperature of 32°C is achieved.8 Patients should not be pronounced dead until they are warm (>32°C) and dead.9

The administration of fluids or blood products can result in hypothermia or worsen it. Infusion of 1 L of crystalloid solution kept at room temperature (21°C) results in a decrease in core body temperature of 0.3°C.1 When patients are receiving large volumes of resuscitation fluid, active measures to prevent hypothermia must be taken. This is even more important in patients receiving blood products, which are kept at 4.0°C. Transfusion of 1 L of blood products leads to a decrease in core body temperature of 0.54°C.1 A normothermic patient can be rendered hypothermic quickly when subjected to an aggressive fluid resuscitation.

One of the mainstays in the prevention of hypothermia during resuscitation is to use fluid warmers to infuse intravenous fluids. Unfortunately, conventional fluid warmers use a coil/sleeve system in a water bath and pose problems at both slow and rapid infusion rates.19 With a slow infusion rate, there is time for the fluid to reach room temperature in the tubing between the warmer and the patient. With a fast infusion rate, the length of time the fluid is exposed to the water bath is too short to effectively warm the fluid.

These problems have been addressed with two devices, both of which are useful in the Emergency Department. They both warm infused fluid to a temperature of 40°C. The first uses a jacket in which circulating warmed fluid covers the entire length of the intravenous tubing, from the warming device to the patient (Hotline, Sims Level 1, Rockland, MA). This device is more effective than conventional fluid warmers at flow rates between 50 and 6000 mL/h.19 The second device uses an inline heating unit that warms the fluid rapidly and allows for substantially higher infusion rates (Systems 250/500/1000, Sims Level 1, Rockland, MA). This device can infuse crystalloid solutions or blood products at rates up to 2200 mL/min and is extremely useful in the resuscitation of patients in severe hemorrhagic shock.19 Similar devices are available from a variety of manufacturers. Use these devices to administer intravenous fluid to hypothermic patients or to those at risk for developing hypothermia. These devices may be used as components in some of the techniques described below.

Perform passive external warming on all patients who are mildly hypothermic or who have normal body temperatures and are undressed. Cover the patient with sheets and blankets as soon as they have been examined and any necessary procedures have been performed. If available, the use of warm blankets and sheets is preferred over those at room temperature.

Techniques

Remove any wet and/or cold clothing. Dry the patient before applying blankets (Figure 189-2). Blankets and sheets may be kept in a blanket warmer as insulating material cooler than the patient will extract heat. Prevent secondary injury to the patient from blankets and sheets that are too hot. There is no reason for the blankets to be any warmer than normal body temperature for passive external rewarming.

Assessment

An otherwise healthy and normal patient will increase their core body temperature by 0.5 to 2.0°C/h with passive external rewarming. The body attempts to regain normothermia by increasing its metabolic rate. The patient may manifest evidence of increased cardiopulmonary stress and lactic acidosis during this time.1

Complications

Complications occur if attempts are made to place inappropriately heated objects directly on the patient. Under no circumstances should heated intravenous fluid bags be placed in the axilla or groin, or in any other prolonged contact with the skin. This may result in thermal injuries ranging from superficial blistering to full-thickness burns. Blankets and sheets that are too warm will also cause damage to the skin.

Summary

Use passive external rewarming as a sole agent in otherwise healthy patients with normothermia who are undressed, patients with mild hypothermia, and as an adjunct to more aggressive rewarming techniques. Always be aware of the possibility of a patient developing hypothermia during their Emergency Department stay.

Indications

Perform these maneuvers as sole therapy for patients with mild hypothermia, on awake and otherwise stable patients with moderate hypothermia, and in conjunction with more aggressive rewarming techniques.

Contraindications

Do not use active external rewarming as the sole therapy for patients with moderate hypothermia who have altered mental status or hemodynamic instability. Active external rewarming is contraindicated as the sole therapy for patients with severe hypothermia (core temperature < 28°C). There is no significant difference in the rates of rewarming between the different devices used for external rewarming. The use of radiant heaters and heating packs is not currently recommended due to the risk of potential complications and limited efficacy.20,21

Equipment

• Warm blankets
• Forced air rewarming blankets
• Fluid circulating rewarming blankets
• Water bath and associated supplies

Technique

Examine the patient. Determine if the patient is a candidate for active external rewarming. Place a forced air rewarming blanket or a fluid circulating rewarming blanket on the patient (Figure 189-3). Do not place these blankets, particularly the fluid circulating ones, underneath the patient. Placing the blanket under the patient may lead to excessive thermal transfer to areas with decreased blood flow due to pressure and prolonged time of contact. A thin sheet may be placed between a fluid circulating blanket and the skin. This is not necessary with forced air blankets. Warmed blankets and sheets may be placed over the warming blankets.

Active external rewarming can be accomplished by immersion of the patient in a warm water bath (Figure 189-4). This technique is easy, effective, and simple. Immersion therapy of the hypothermic patient is not performed in the Emergency Department for several reasons. The equipment is bulky, not portable, and occupies a fixed space. It is difficult to monitor the patient when immersed. Monitoring leads (e.g., electrocardiography and pulse oximetry) will not adhere to wet skin. The use of electrical monitoring equipment in a water bath should be avoided.

Assessment

Care must be taken to reassess any wounds for recurrent bleeding, any catheters or monitors for placement, and any pressure areas that might be in prolonged contact with the heating elements as the patient is covered with the warming device. With respect to the forced air blankets, check the air source connection to the blanket to make sure that the hot air is not blowing directly onto the patient. A directed flow of hot air onto the patient under the blanket may lead to thermal injury.

Complications

Thermal injuries are associated with active external rewarming. They result from improper use of the devices. Maintain vigilance regarding prevention of a focused delivery of heat to a region of skin, particularly one poorly perfused, to essentially eliminate these burns.

Afterdrop refers to a decrease in core temperature that occurs 15 to 20 minutes after active external rewarming begins.8 This is thought to be due to vasodilatation of the peripheral tissues as they rewarm and a subsequent washout of cooler peripheral blood back to the central areas. Peripheral vasodilatation can lead to hypotension if fluid resuscitation is inadequate or the patient has cardiovascular compromise. Afterdrop can be attenuated by the concomitant use of core rewarming techniques.

Summary

Active external rewarming is useful in treating moderately hypothermic patients who are awake and alert. Warming rates of 1.0 to 2.5°C/h have been reported.9 When these devices are being used, frequent monitoring for potential thermal injuries is required in order to prevent secondary injury. This monitoring is easier when the patient is a cooperative partner who can participate in the process. Active external rewarming, like passive external rewarming, is often used in conjunction with more aggressive techniques or core rewarming. The problem of afterdrop is lessened when active external rewarming is used in conjunction with core warming techniques.

Airway rewarming with warmed and humidified oxygen is safe and easily achieved. It can be applied to any hypothermic patient. However, airway rewarming is never used as a sole means of rewarming.

Indications

The technique of airway rewarming may be used in any patient with hypothermia and in conjunction with other techniques. Any patient receiving supplementary oxygen can receive warmed and humidified oxygen. Its efficacy via endotracheal tube is greater than via mask or nasal prongs.

Contraindications

There are no contraindications to airway rewarming. The more severely hypothermic patient will often need their airway controlled by orotracheal intubation due to a depressed level of consciousness. Intubation for the sole purpose of airway rewarming is contraindicated.

Equipment

• Nasal cannula
• Face mask
• Endotracheal tubes
• Humidifier tank
• Heating circuit
• Oxygen source

Techniques

Consult the Emergency Department Respiratory Therapist. They will gather, set up, administer, and monitor the required equipment. Connect the humidifier tank and heating circuit in line with the oxygen source. Humidify and warm the inhaled oxygen to 40 to 45°C. A rewarming rate of 1.0 to 2.5°C/h has been reported.9

Summary

Airway rewarming can be applied to any hypothermic patient. The oxygen must be humidified to prevent fluid loss from evaporation.

These techniques, based on techniques familiar to most Emergency Physicians, are minimally invasive and can be readily performed with minimal interruption of continued resuscitative efforts.

Indications

These techniques are usually reserved for patients with severe hypothermia. They are rarely used in stable patients and generally reserved for situations where extracorporeal warming is not available.

Contraindications

The only contraindications to these techniques are the contraindications to the placement of a urethral catheter (Chapter 142) and a nasogastric tube (Chapter 58). Do not perform gastric lavage concurrently with cardiac compressions. Gastric and bladder lavage are of limited value in the management of the hypothermic patient. They are generally bypassed in favor of peritoneal lavage, pleural lavage, and extracorporeal warming.

Equipment

• Warmed (40°C) intravenous fluid, normal saline or Ringer's lactate
• 60 mL catheter-tip syringe
• See Chapter 142 for urethral catheterization supplies
• See Chapter 58 for nasogastric intubation supplies

Techniques

Place a Foley catheter (Chapter 142) and/or nasogastric tube (Chapter 58). Confirm proper placement. Instill sterile saline or Ringer's lactate warmed to 40°C. Inject 60 mL aliquots into the tube using the catheter-tip syringe. Instill a total of 300 to 400 mL into the stomach and 200 to 250 mL into the bladder. Do not overdistend the respective organ. Gastric overdistention can result in rupture or aspiration. Bladder overdistention can result in rupture and extravasation of fluid. Clamp the Foley catheter or nasogastric tube. Allow the fluid to dwell within the organ for 5 to 10 minutes. Remove the fluid by gravity drainage from the bladder or suction from the stomach. Repeat the process as necessary until the core body temperature increases.

Complications

Gastric lavage may be complicated by perforation of the stomach by either the nasogastric tube or overdistention. Aspiration is a potential complication with gastric lavage. Refer to Chapters 58 and 60 for a more complete discussion of the complications associated with nasogastric intubation and gastric lavage, respectively. Bladder irrigation is safe as long as the bladder is not overdistended. The small surface area of the bladder makes it an inefficient means of rewarming. Refer to Chapter 142 for a more complete discussion of the complications associated with urethral catheterization. Use only normal saline or Ringer's lactate. Do not use sterile water, as it can result in significant volume and electrolyte shifts.

Summary

Perform gastric or bladder irrigation only if other types of body cavity rewarming are contraindicated. These techniques are easily initiated using standard equipment in an Emergency Department. These organs have relatively small surface areas, making these techniques inefficient. Overdistention can result in serious complications.

This technique is invasive, based on techniques familiar to most Emergency Physicians, and can be readily performed with minimal interruption of resuscitative efforts.

Indications

This technique is usually reserved for patients with severe hypothermia. It is rarely used in stable patients and generally reserved for situations where extracorporeal warming is not available.

Contraindications

Suspicion of injury to a hollow viscus is a contraindication to this technique. The presence of a previous laparotomy scar is a strong relative contraindication. The use of an open peritoneal lavage technique does not mesh well with the continuous infusion of fluid required for this procedure. Other contraindications are those associated with performing a diagnostic peritoneal lavage (Chapter 66).

Equipment

• Warm (40°C) intravenous fluid, normal saline or Ringer's lactate
• Warm (40°C) peritoneal dialysis fluid
• Fluid infuser device, optional
• Peritoneal lavage kits
• See Chapter 66 for peritoneal lavage supplies
• See Chapter 58 for nasogastric tube supplies
• See Chapter 142 for Foley catheter supplies

A commercially available, disposable, single-patient use peritoneal lavage kit is available from numerous manufacturers. The kit includes all the material required to perform a closed or semi-open diagnostic peritoneal lavage except lavage fluid. An example is the Arrow kit (Arrow International, Reading, PA). It contains 10% povidone iodine or chlorhexidine swabs, gauze squares, fenestrated drape, tubing for the administration of intravenous fluid, 1% lidocaine, 5 mL syringes, 22 and 25 gauge needles, an 18 gauge × 2.5 inch introducer needle, an 0.89 mm × 45 cm J-tipped guidewire, an 8 French lavage catheter, and a #11 scalpel blade on a handle. Refer to Chapter 66 for a more complete list of equipment.

Technique

Prepare the patient by placing a nasogastric tube (Chapter 58) and a Foley catheter (Chapter 142). Place two peritoneal lavage catheters, one supraumbilical and one infraumbilical (Figure 189-5). Refer to Chapter 66 for complete details regarding placement of the peritoneal lavage catheters. Confirm the position of the catheters. Clamp the infraumbilical catheter. Infuse warm (40°C) intravenous fluid or peritoneal dialysis fluid through the supraumbilical catheter using the Level 1 infuser or a Hotline fluid warmer. The use of dialysate has the added benefit of potentially correcting some electrolyte abnormalities.8,9 The fluid may be infused manually, but this technique is much less efficient. Infuse 1 to 2 L of fluid. Allow the fluid to bathe the peritoneal cavity for 10 minutes. Remove the clamp on the infraumbilical catheter and allow the fluid to drain from the peritoneal cavity. Repeat the procedure. Up to 10 L/h of fluid may be infused in this fashion.9 An alternative technique is to allow the fluid to flow at a moderate rate and continuously through the supraumbilical catheter, into the peritoneal cavity, and out the infraumbilical catheter. This can be performed manually or with a commercial device developed for this purpose (Veratherm Portable Hyperthermic Perfusion System, Thermal Therapeutic Systems Inc., Pittsburgh, PA).

Complications

The potential complications are primarily associated with the placement of the peritoneal lavage catheter. Refer to Chapter 66 for the details regarding these complications. The infusion and removal of the fluid are safe. Avoid using highly hyperosmolar peritoneal dialysates in patients with persistent hypovolemia or with a questionable perfusion status as this may worsen existing hypovolemia. Do not use sterile water, as it can result in significant volume and electrolyte shifts.

Summary

Peritoneal lavage is the most widely recognized means of body cavity lavage. This is due in part to the familiarity of many Emergency Physicians with the diagnostic peritoneal lavage procedure. It has the advantage of being able to be performed concurrently with chest compressions and other resuscitative efforts. This technique can raise the core body temperature by 1 to 3°C/h.

This technique is invasive, based on techniques familiar to most Emergency Physicians, and can be readily performed with minimal interruption of resuscitative efforts. Pleural lavage can be performed closed (via a tube thoracostomy) or open (via a thoracotomy incision).

Indications

This technique is usually reserved for patients with severe hypothermia. It is rarely used in stable patients and generally reserved for situations where extracorporeal warming is not available.

Contraindications

The presence of a pneumothorax and/or hemothorax is the only contraindication to pleural lavage.

Equipment

• See Chapter 39 for tube thoracostomy supplies
• Warm (40°C) intravenous fluid, normal saline or Ringer's lactate
• Warm (40°C) peritoneal dialysate
• Fluid infuser device, optional

Technique

Place two chest tubes into the same pleural space, either the left or the right side, to perform closed pleural lavage (Figure 189-6). The left side is preferred by those who believe that the heart, aorta, and blood within the aorta will be warmed quicker than with right-sided chest tubes. Refer to Chapter 39 for the full details regarding chest tube placement. Place one tube anteriorly in the second or third intercostal space at the midclavicular line (Figure 189-6). Place the other tube posteriorly in the fifth or sixth intercostal space at the posterior axillary line (Figure 189-6). Secure the tubes to the chest wall with suture and tape. Attach the fluid infuser to the anterior chest tube using a Christmas tree adapter. Apply a pleural drainage device to the posterior chest tube in the usual fashion. Infuse warm (40°C) fluid via the fluid infuser device at a rate of 180 to 550 mL/min.8 Allow the fluid to exit into the pleural drainage device. The fluid will flow into the anterior chest tube, bathe the structures in the hemithorax (i.e., great vessels, heart, lung, and mediastinum), and exit via the posterior chest tube. This can be performed manually or with a commercial device developed for this purpose (Veratherm Portable Hyperthermic Perfusion System, Thermal Therapeutic Systems Inc., Pittsburgh, PA).

Pleural lavage may be performed using an open technique (Figure 189-7). This technique is used when a thoracotomy is indicated for other purposes, such as penetrating trauma or to perform open cardiac massage. Refer to Chapter 42 for full details regarding a thoracotomy. Do not use this technique for the sole purpose of rewarming if other, less invasive or extracorporeal techniques are available. The advantage of open pleural lavage is that it allows direct cardiac rewarming and open cardiac massage.

Complications

The complications are primarily associated with the placement of the chest tube. Refer to Chapter 39 for the full details regarding these complications. Maintain free drainage of the irrigation fluid to avoid increasing the intrathoracic pressure.

Summary

Closed pleural lavage is an effective means of rewarming. It can increase the core body temperature by 1 to 5°C/h. It is very similar in efficacy to peritoneal lavage. Chest tube placement is slightly more challenging than placement of a peritoneal lavage catheter. Free drainage is usually easier to achieve and maintain with a chest tube than with a peritoneal lavage catheter. The two techniques may be employed simultaneously and carried out in conjunction with other resuscitative measures.

Extracorporeal rewarming is the most aggressive, effective, and efficient technique to correct severe hypothermia. It includes the use of hemodialysis, arteriovenous rewarming, venovenous rewarming, continuous venovenous hemofiltration, cardiopulmonary bypass, and extracorporeal membrane oxygenation. The choice between the techniques is made on the basis of available resources and the Emergency Physician's familiarity with each technique. Cardiopulmonary bypass is discussed but should not be performed by anyone who is not a Surgeon familiar with the procedure.

Hemodialysis is readily available in most institutions. It requires the placement of a central venous line. The only contraindications to hemodialysis are those associated with central venous line placement (Chapter 49) and hemodialysis. An advantage of hemodialysis is that associated drug toxicity or significant electrolyte abnormalities can be simultaneously managed as the patient is being rewarmed.

Equipment

• See Chapter 49 for central line equipment
• Dual-lumen percutaneous hemodialysis (Quinton or Mahurkar) catheter
• Dialysis machine
• Dialysis nurse or technician
• Warmed (40°C) dialysis fluid

Technique

Place a hemodialysis catheter into a femoral vein. Refer to Chap-ter 49 for the full details regarding the placement of a double-lumen central venous line. The catheter may be placed into a subclavian vein if femoral vein access is contraindicated. Femoral vein placement decreases the risk of inducing an arrhythmia with the guidewire.9 There is a tendency to have fewer problems related to the positioning of the catheter and achieving appropriate flow rates with femoral catheters. Instruct the hemodialysis technician to set the temperature control on the dialysis machine to deliver a blood temperature of 40°C. Attach the dialysis machine tubing to the lumens of the catheter. Begin hemodialysis.

Complications

The potential complications are primarily associated with the placement of the central venous line. Refer to Chapter 49 for the details regarding these complications. The hemodynamic status of hypotensive patients may become worse upon initiation of hemodialysis, but this technique has been successfully used on such patients.9

Summary

Hemodialysis is available at most institutions and is effective in rewarming a patient. The limitations of this technique include the need to have a dialysis technician or nurse available, the time required to obtain on-call personnel, and the time required to set up the equipment. Hemodialysis is a viable option for the rewarming of a hypothermic patient when other forms of extracorporeal warming are not available.

This technique was initially described in 1992.22,23 The authors described placing one large-bore catheter in the femoral artery and another in a central vein (i.e., femoral, internal jugular, or subclavian). This method allows for rewarming in the Emergency Department without the need for specialized equipment (dialysis or bypass machine) and personnel.

Contraindications

Hypotension or the lack of a blood pressure makes this method moot. Known occlusive arterial disease, particularly in the iliofemoral region, is a relative contraindication.

Equipment

• See Chapter 49 for central line equipment
• Two 8.5 French introducer catheters
• Two 10 French single-lumen arteriovenous hemofiltration catheters
• Sims Level 1 System 250/500/1000 Fluid Rewarmer
• Luer-lock adapter, male-to-male
• Warmed (40°C) saline

Technique

Place two catheters, one in the femoral artery and one in a central vein. Refer to Chapter 49 regarding the placement of a central venous catheter. The placement of the arterial catheter is similar to that of the venous catheter.

The tubing for the Level 1 rapid infuser consists of two intravenous spike-tipped lengths that come together in a Y. The Y then runs to a countercurrent warming chamber and then to the patient. Cut off the spike tip from one of the limbs of the Y and attach the male-to-male Luer-lock adapter. Note that if the rapid fluid infuser is a Sims Level 1 System 500, an additional length of wide-bore intravenous tubing may be needed to bridge the distance between the arterial catheter and the fluid-warmer tubing. This version of the Level 1 may be too tall to allow direct connection of one of the limbs to the arterial catheter. Connect this limb to the arterial catheter. Connect the other arm of the Y to a bag of intravenous fluid with the roller clamp closed.

Allow the system to prime with blood under the patient's arterial pressure. Connect the primed distal end of the tubing to the central venous catheter. The blood will travel via the arterial catheter to the extracorporeal circuit and through the proximal limb of the tubing to the warming chamber of the Level 1 infuser, through the heating elements to the distal tubing, and back to the patient via the venous catheter (Figure 189-8).

The driving force in this circuit is the patient's systemic blood pressure. Low-flow states will limit the efficacy of the system. However, you may use a pressure infusion of intravenous fluid via the other limb of the Y to augment flow. This fluid will be warmed as it reaches the patient, since this other limb of the Y is proximal to the warming element. Systemic anticoagulation is not required, as the tubing for the Level 1 infuser is heparin-bonded. Arteriovenous rewarming is faster and more efficient than venovenous rewarming.33

Complications

The complications outlined in the initial description of the procedure include the inability to achieve vascular access, a small hematoma at the arterial puncture site, and ischemia of the limb distal to the arterial catheter.22 Refer to Chapters 49 and 57 for a full description of the complications that may arise in placing a central venous catheter and arterial catheter, respectively.

Summary

Arteriovenous rewarming is an innovative means by which severely hypothermic patients may be rapidly rewarmed without the resources of a dialysis or bypass pump technician. Flow rates of 225 to 375 mL/min are achieved when the patient's systolic blood pressure is greater than 90 mmHg.22 This technique transfers 94 to 157 kcal/h back to a patient with core temperature of 32°C.22

This technique is rarely utilized by Emergency Physicians due to the lack of a venous roller pump and inexperience with this piece of equipment. The technique is briefly described for the sake of completeness. The venovenous technique has two main advantages over arteriovenous rewarming. First is the lack of arterial cannulation, with its potential for limb ischemia. The second is nonreliance on systemic blood pressure/perfusion to drive the system. Flow may be independently determined and delivered by the roller pump. This may be particularly important in the severely hypothermic patient who presents in full cardiorespiratory arrest. The primary disadvantage of this technique is the requirement of expertise in using the roller pump, though advances in design may obviate this in the future.

Contraindications

Persons not familiar with the function and operation of a venous roller pump should not attempt this technique.

Equipment

• See Chapter 37 for central line equipment
• Two 8.5 French introducer catheters
• Two 10 French single-lumen arteriovenous hemofiltration catheters
• Sims Level 1 System 250/500/1000 Fluid Rewarmer
• Luer-lock adapter, male-to-male
• Venous roller pump
• Warmed (40°C) saline

Technique

The setup for this technique is similar to that for arteriovenous rewarming. Place two catheters, one in the femoral vein and one in another central vein. Refer to Chapter 49 for the details regarding the placement of a central venous catheter. Alternatively, place a dual-lumen hemodialysis catheter.24 However, if the latter course is to be followed, make sure that the “outflow” port of the catheter is upstream and that the “inflow” port is downstream. This helps to reduce the amount of warmed fluid returning from the circuit that is immediately withdrawn by the roller pump. Place the venous roller pump in line with this circuit, usually between the patient and the warming elements. Adjust the flow rate within the tolerances of the particular device being used.

Complications

The primary complication associated with use of venous roller pumps is an air embolus. This usually happens when the roller pump is operated by a person unfamiliar with it. Recent advancements in roller-pump technology have made their operation simpler and safer. Refer to Chapter 49 for a complete description of the complications that may arise due to the placement of a central venous catheter.

Summary

Venovenous rewarming is one step away from cardiopulmonary bypass. Its use in the Emergency Department is limited due to lack of equipment availability and familiarity. It is a viable option if a roller pump is available as well as a Physician familiar with this procedure.

Continuous venovenous hemofiltration (CVVH) machines have become more widely available, making this an attractive means of rewarming. The use of CVVH machines has largely replaced the previously described venovenous rewarming technique. This technique has two main advantages over arteriovenous rewarming. First is the lack of arterial cannulation, with its potential for limb ischemia. The second is nonreliance on systemic blood pressure/perfusion to drive the system. The use of CVVH in the management of moderate-to-severe accidental hypothermia has been shown to be rapid, safe, and effective.23,25

Contraindications

Persons not familiar with the function and operation of a CVVH machine should not attempt this technique.

Equipment

• See Chapter 49 for central line equipment
• Dual-lumen percutaneous hemodialysis (Quinton or Mahurkar) catheter
• CVVH Dialysis machine
• Dialysis nurse or technician, trained ICU nurse
• Warmed (40°C) dialysis fluid

Technique

As with standard hemodialysis techniques, rewarming with CVVH utilizes a single intravenously inserted, dual-lumen catheter placed in a central vein and connected to the CVVH dialysis machine. Some CVVH dialysis machines have a built-in thermostat allowing for temperature control while others depend on circulating already warmed dialysis fluid bags. Passive and/or active external rewarming maneuvers should be used in conjunction to the CVVH technique. Continuous cardiopulmonary monitoring and frequent monitoring of core body temperature should be undertaken.

Complications

Recent advancements in CVVH technology have made their operation simpler and safer, particularly in terms of the prior concern over an air embolism. However, their use should be restricted to individuals familiar with the operation of these devices. Refer to Chapter 49 for a complete description of the complications that may arise due to the placement of a central venous catheter.

Summary

CVVH is one step away from cardiopulmonary bypass. Its use in the Emergency Department is limited due to lack of equipment availability and familiarity. It is a viable option if the equipment is available as well as a Physician familiar with this procedure.

Discussion of this technique is limited to some basic properties of rewarming with cardiopulmonary bypass. This technique should not be attempted by anyone who does not regularly use bypass modalities and without the support of an experienced pump technician. This technique represents the last resort of rewarming techniques. Bypass is usually achieved using femoral-femoral bypass. The cardiopulmonary bypass pump can provide complete hemodynamic and respiratory support during the resuscitation.26–28 Core body temperatures can be raised 1 to 2°C every 3 to 5 minutes with flow rates of 2 to 3 L/min. If available, use heparin-bonded tubing to avoid systemic anticoagulation, which can worsen existing coagulopathies. The limitations of this technique are that it is extremely resource-intensive, not readily available in many institutions, and requires specific expertise with respect to surgical and mechanical techniques.

Although extracorporeal membrane oxygenation (ECMO) technology is a staple in most major Pediatric Intensive Care Units across the world, it continues to be rarely utilized in the adult population. The experience in utilizing ECMO for the management of accidental hypothermia in the adult population is limited to several case reports in the literature.29,30 Similar to cardiopulmonary bypass, ECMO can be utilized in those patients with complete cardiac arrest and hypoxemia. Hypoxemia and asphyxia are recognized as major predictive adverse factor for survival and/or poor neurological outcome in the hypothermic patient.31,32 ECMO provides appropriate support for both cardiac as well as pulmonary functions with the added benefit of allowing for hemodialysis for restoration of electrolyte abnormalities and acid–base imbalances. Further description and discussion of this technique is beyond the scope of this textbook.

There has been much research in the last decade regarding the induction of therapeutic hypothermia. This research has primarily focused on those with brain injury, postcardiac arrest, and stroke. This has resulted in the development of a variety of externally applied and internally applied cooling devices. While not specifically designed to treat hypothermia, they can easily be used to manage the hypothermic patient.34 Refer to Chapter 188 for a discussion of these methods and devices.

The management and prevention of hypothermia in the Emergency Department is a challenging and perpetual task. The resuscitation of a severely hypothermic patient in full cardiorespiratory arrest can push the Emergency Physician and the Emergency Department to the limit of their abilities and resources. The real challenge in dealing with hypothermia lies in recognizing and managing the risk of hypothermia in the “routine” patient who presents every day. It is not possible to overstate the importance of continuity of care and the necessity of good communication as the patient is moved from the Emergency Department to either the Operating Room or the Intensive Care Unit, so that rewarming efforts may continue.