Increasing the Effectiveness of Targeted Temperature Management

Abstract

Topic

Targeted temperature management and therapeutic hypothermia are essential components of the multimodal approach to caring for compromised patients after cardiac arrest and severe traumatic brain injury.

Clinical Relevance

The continuously evolving science necessitates summation of individual facets and concepts to enhance knowledge and application for optimally delivering care. Targeted temperature management is a complex therapy that requires fine-tuning the most effective interventions to maintain high-quality targeted temperature management and maximize patient outcomes.

Purpose

To describe the underlying pathophysiology of fever and the importance of manipulating water temperature and of preventing and treating shivering during that process.

Content Covered

This article discusses nursing considerations regarding the care of patients requiring targeted temperature management that are necessary to improve patient outcomes.

Fever is the most devastating complication of any neurological injury, including anoxic brain injury secondary to cardiac arrest. Targeted temperature management (TTM) is the only neuroprotective intervention currently recommended to mitigate the detrimental effects of cerebral ischemia and reperfusion injury.^1,2 Although the most effective TTM protocol remains elusive, the best outcomes have been achieved when temperature is constantly maintained between 32 °C and 36 °C for 24 hours and fever is prevented for at least 72 hours following the return of spontaneous circulation.^3–6 Research comparing intravascular and surface cooling methods indicates a difference in the number of patients who achieved target temperatures, the time to target temperature, and the number of episodes of overcooling.^7,8 With surface cooling, however, temperature deviated more and more patients were ever out of range. Despite these differences, those studies found no difference in the occurrence of death or disability from pyrexia at 3 months.^7,8 Therefore, we do not recommend one method over the other; recommendations could be applied when using either method.

Targeted temperature management is best understood as a multimodal bundle of interventions that involves targeting a set temperature and includes hypothermia, controlled normothermia, and fever control.^1,2 Variability in the delivery of these interventions often leads to low-quality TTM and limits the benefits of TTM, as reported in some studies.^3,9–11 Nurses play a critical role in managing the patient’s temperature across all phases of TTM and must strive to control the patient’s temperature as part of the high-quality care they provide.

Shivering and Fever

When the body cools, several reflexive pathways are triggered to prevent heat loss.^12,13 Heat-loss and heatretention neurons in the preoptic nucleus respond to changes in body (core and peripheral) temperatures by causing vasoconstriction to retain heat and vasodilation to promote heat loss; this process is known as the vasomotor response. These neurons also respond by activating thermogenesis through shivering. The vasoconstriction pathway activates when the body’s core temperature reaches a threshold, typically 36.5 °C; shivering occurs at a threshold of 35.5 °C and persists until body temperature falls below a lower threshold of 34 °C.^8,14 During TTM, as patients receiving therapy pass through the vasoconstrictive and shivering thresholds, 40% of them will shiver.¹⁵ Shivering causes a significant decrease in oxygen tension in brain tissue and cerebral metabolic stress, which can eradicate the neuroprotective effects of TTM and therefore must be prevented.¹⁶ When a patient’s temperature is managed to be maintained at 33 °C, modest deviations from the TTM protocol will keep the temperature within the recommended range of 32 to 36 °C.^17,18 When TTM is ordered to maintain the patient’s temperature at 36 °C, poor compliance with protocols has resulted in less time within that target range, more episodes of fever, and poorer neurological outcomes.^2,10

Continuous monitoring of core tempera- threshold, ture and setting a target temperature are priorities and should be initiated as soon as possible after the return of circulation.

Fever, loosely defined as any core temperature higher than 37.8 °C, can occur any time during TTM and can be a response to hypothermia or related to infection; monitoring laboratory test results and TTM phase will help differentiate shivering from fever.¹⁶ Fever after TTM, which occurs in approximately 50% of patients after cardiac arrest, may be associated with more severe brain injury and is believed to be associated with poor outcomes.^14,19,20 Current recommendations include preventing fever for at least the first 72 hours following the return of circulation.¹⁹

Preventing and Managing Shivering

Vasoconstriction and shivering must be overcome to facilitate cooling. Continuous monitoring of core temperature and setting a target temperature are priorities and should be initiated as soon as possible after the return of circulation.²¹ Core temperature can be monitored by using a temperature-sensing Foley catheter or an esophageal temperature probe.²² Rectal probes should be avoided because lag has been noted with core temperature readings from such probes.^23,24 Patients presenting to the hospital after cardiac arrest with temperatures less than 32 °C should be passively rewarmed to 33 °C, and then a target temperature between 32 °C and 34 °C should be maintained; active rewarming to a target temperature of 36 °C should be avoided.^24,25

Before starting TTM, measures to prevent shivering are initiated and include the application of an external warming blanket or jacket (such as the Bair Hugger System, 3M) set at 40 to 43 °C, and socks on the patient’s hands and feet.^17,26,27 Prophylactic pharmacological measures include acetaminophen, buspirone, and magnesium sulfate, which are initiated upon induction.^1,26 Once TTM begins, a low-dose analgesic, sedative, and neuromuscular blockade are added in a stepwise fashion on the basis of the presence and degree of shivering, with a goal of minimizing sedation and preventing shivering (Table 1).^28,29 These interventions result in threshold reductions between 1 °C and 2.5 °C, and they are maintained until the normothermia phase of TTM is reached.^1,26,28-30

Table 1.

Nonpharmacological and pharmacological interventions for preventing and managing shivering

When to initiate	BSAS score	Intervention	Dose	Intervention goals
Before initiating TTM	0	Antipyretic,buspirone, magnesium	Around the clock; to maintain magnesium level between 3 and 4 mg/dL	Preemptive treatment
Localized shivering limited to neck and thorax, ECG artifact, or felt with palpation	1	Skin counterwarming, analgesia	Previous interventions and continuous dexmedetomi-dine or intermittent dosing of fentanyl	Mild sedation
Shivering of the thorax and intermittent shivering of the upper extremities	2	Analgesia	Previous interventions and consider continuous dex- medetomidine or fentanyl	Moderate sedation
Generalized or sustained shivering (includes all 4 extremities)	3	Sedation	Previous interventions and propofol infusion	Deep sedation
Generalized or sustained shivering (includes all 4 extremities) that has been refractory to all previous treatments	3	Neuromuscular blockade	Previous interventions and bolus and infusion of neuromuscular blockade	Last resort when all other interventions have failed

Abbreviations: BSAS, Bedside Shivering Assessment Scale; ECG, electrocardiogram; TTM, targeted temperature management.

Adapted with permission from Jain A et al.¹

Nurses assess for shivering using the Bedside Shivering Assessment Scale or a comparable tool. To effectively assess shivering, nurses must both observe and palpate the neck, thorax, arms, and legs. A score greater than 1 indicates that further investigation is required (Table 1).^31,32 Nurses can monitor a patient’s response to antishivering interventions by continuously monitoring core temperature, the temperature of water within the cooling device, and the temperature trend indicator on external cooling devices.^19,33

Importance of Water Temperature

Achieving and maintaining temperature goals with minimal variability (≤1 °C) requires meticulous attention to water temperature (Table 2).¹⁷ Cooling devices that use automated temperature feedback systems manipulate core temperature by regulating the temperature of water in the catheter or pads.^34,35 Water temperature generally ranges between 18 °C and 25 °C when a patient’s body temperature is at target, but it will decrease to as low as 10 °C to prevent shivering or fever.^7,35 In addition, the temperature trend indicator on external cooling devices registers changes in temperature (0.25 to >2 °C/h) every 5 minutes. ^36,37 Arrows above the thermoneutral bar indicate heat generation; those below the bar indicate heat loss.³⁸ This indicator provides an excellent trend of temperature variability.

Table 2.

Nursing management of shivering during targeted temperature management

	Phase 1	Phase 2	Phase 3	Phase 4
Goal	Cooling, 0.5 to 1.5 °C/h	Maintain hypothermia	Rewarming, 0.25 °C/h	Controlled normothermia for 24 to 48 hours
	Rapid cooling	No wide fluctuations in temperature	No passive rewarming	Prevent fever
Assessment	Shivering (BSAS) Patient temperature Water temperature	Water temperature of cooling device Shivering (BSAS) Patient temperature and trends	Shivering (BSAS) Patient temperature and trends Water temperature	Patient temperature
Nursing interventions	Document time of initiation Document time when target temperature is achieved Administer antishivering interventions and anti-pyretics before or at the time of initiation Keep room as cool as possible Administer cold saline Apply ice packs Expose patient Begin monitoring temperature with core temperature and second temperature source	Monitor patient temperature from 2 sources Monitor water temperature Administer shivering and sedation scales Assess neuromuscular function using TOF, if paralyzed Assess sedation using BIS monitoring Manage shivering Administer antipyretics on set schedule	Actively rewarm patient using advanced cooling technology Warm the room Monitor patient temperature Administer shivering and sedation scales Assess sedation using BIS monitoring Assess neuromuscular function using TOF Document shivering management Document the time target temperature is achieved	Discontinue shivering management Discontinue paralytics and TOF Discontinue sedatives and analgesics Continue temperature management using advanced technology Notify provider of target reached Administer interventions for temperature >37.5 °C

Abbreviations: BIS, bispectral index; BSAS, Bedside Shivering Assessment Scale; TOF, train-of-four.

Changes in ambient temperature, the temperature of fluids and medications infused during TTM, removal of a warming blanket to assess or turn a patient, and inadequate analgesia or sedation are just a few examples of activities that increase temperature variability and can be anticipated.³⁸ Nursing interventions such as keeping the room door closed, letting fluids reach room temperature before infusion, adjusting the temperature of the Bair Hugger, and titrating analgesics and sedatives are effective strategies that, when implemented in a stepwise fashion, minimize temperature variability and promote favorable neurological recovery.^38,39

As an injury-reduction intervention, however, TTM is also associated with potential risks such as shivering.

Recommendations for Practice

Critical care medicine has come a long way in clarifying the role of TTM as a therapeutic intervention after a brain ischemic event¹⁹: from Aristotle’s theory that the brain is merely a thermostat that regulates body temperature in an effort to cool the heart, to the current use of TTM to rapidly and effectively minimize damage from ischemia.^19,25,40 As an injury-reduction intervention, however, TTM is also associated with potential risks such as shivering.⁴¹ If untreated, shivering can be detrimental to patient outcomes.^41,42 Methods for treating shivering include both nonpharmacological and pharmacological agents.^40,41 Best practice includes initiating treatment prophylactically when beginning TTM. Shivering interventions should be assessed with the help of a shivering scale.^40,41 A tiered protocol for use in preventing and treating shivering is recommended.^19,25,40

In critical care, actions to carefully titrate all therapies, limit side effects, and maximize benefit must be recognized as being paramount to success.⁴³ The importance of continual reexamination of interventions that can affect TTM are critical to optimizing therapy.⁴³ Therefore, nurses at the bedside managing the care of patients receiving cooling therapy have an enormous opportunity. Targeted temperature management is complex, and understanding how to fine-tune multiple therapies aimed at reducing temperature variability and preventing fever ultimately improve neurological outcomes and the patient’s chance of survival.CCN