Pain Management in the Intensive Care Unit

Curtis N. Sessler

Kimberly Varney Gill

Kristin Miller

Pain, Analgesia, and Critical Illness

Pain is ubiquitous among critically ill patients, yet the nature of critical illness and intensive care unit (ICU) care presents many unique challenges to effective pain management.¹^,²^,³^,⁴^,⁵^,⁶^,⁷^,⁸^,⁹^,¹⁰ A central responsibility of all ICU clinicians is to provide comfort and mitigate unpleasant sensations including pain as well as anxiety, dyspnea, and other forms of distress.¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷ Experts have provided guidance regarding managing pain in the ICU, often within the paradigm of sedation and analgesia. In this chapter, we focus on the unique aspects of pain and analgesia in the ICU within the context of a comprehensive textbook on pain.¹¹^,¹²^,¹³^,¹⁴^,¹⁷^,¹⁸^,¹⁹^,²⁰

ICUs are filled with patients who have suffered critical illness or injury and the accompanying discomfort. Many patients have undergone surgery or experienced trauma or burns and are likely to have pain as a direct result of tissue injury and related management such as dressing changes and wound care. Other patients have localized inflammation due to infection or have neuropathies or other specific conditions that produce pain. The majority of ICU patients undergo routine care which can contribute to discomfort or frank pain. Such interventions include the presence of indwelling tubes (i.e., nasogastric, endotracheal, bladder, and rectal tubes) or vascular catheters that can induce pain during their insertion and in some cases continue to produce discomfort by their mere presence.³^,⁴^,⁵^,²¹^,²² Even simple tasks that are routinely performed many times each day—such as tracheal suctioning or turning of the patient from side to side—are reported as painful by ICU patients.⁵^,⁹^,²²^,²³

The nature of critical illness and ICU care can complicate various aspects of pain management. For example, the sensation of pain may be intensified by the concomitant anxiety, sleep deprivation, and delirium.²³^,²⁴^,²⁵^,²⁶^,²⁷^,²⁸^,²⁹^,³⁰^,³¹^,³²^,³³ It is clear that all of these conditions are commonplace among critically ill patients. Further, immobility and impaired communication can intensify anxiety and perception of pain. Newer integrated approaches to optimize patient comfort and hasten recover comprehensively address analgesia as well as efforts to reduce anxiety yet avoid oversedation, improve sleep quality, prevent delirium, speed liberation from mechanical ventilation, and enhance rehabilitation and mobility.³⁴^,³⁵^,³⁶^,³⁷^,³⁸^,³⁹^,⁴⁰

Pain is often poorly recognized and quantified, further challenging effective pain management.¹¹^,¹² This can be the result of impaired communication due to a reduced level of consciousness from sedative medications or difficulty with phonation and movement due to oral tubes, physical restraints, or paralysis. Although the presence of pain may be inferred as a result of unexplained autonomic hyperactivity (i.e., tachypnea, tachycardia, or hypertension), these signs have many other causes and thus are nonspecific for pain.¹¹ Clinicians’ evaluation of patients for possible pain include observing behaviors such as grimacing or rigid body positioning, but these are less reliable as sedation deepens.¹¹^,²²^,⁴¹^,⁴²^,⁴³^,⁴⁴^,⁴⁵^,⁴⁶^,⁴⁷^,⁴⁸^,⁴⁹^,⁵⁰^,⁵¹^,⁵²^,⁵³^,⁵⁴^,⁵⁵ Overt agitated behavior, a not infrequent occurrence among critically ill patients, is typically attributed to delirium, particularly due to alcohol or sedative drug withdrawal, but can also be the result of inadequately managed pain.⁵⁶^,⁵⁷^,⁵⁸^,⁵⁹^,⁶⁰^,⁶¹^,⁶²^,⁶³

Pharmacologic management of pain is more complex in the ICU than in many other settings.¹¹^,¹²^,¹³^,¹⁴^,¹⁷^,¹⁸^,¹⁹^,²⁰ The majority of ICU patients have organ dysfunction. In particular, the utilization of many opioid and nonopioid analgesics is impacted by the high prevalence of impaired hepatic metabolism or renal clearance, problems with enteral or transdermal drug administration, and concerns for drug interactions with the extensive list of medications required for many ICU patients.⁶⁴^,⁶⁵^,⁶⁶^,⁶⁷ Recognition and amelioration of adverse effects of analgesics and other medications is often more difficult because of ongoing organ dysfunction and concomitant medical problems as well as the large number of medications utilized. In particular, the high prevalence of impaired gastrointestinal mobility from opioids becomes far more than just the inconvenience and discomfort of constipation and can impact administration of nutrition and enteral medications; can worsen respiratory function; and can lead to additional treatment, tests, and interventions.⁶⁸ These many ICU factors elevate the complexity of pain management.

In the ICU setting, opioid administration is often performed for purposes beyond pure pain management, that of providing comfort and tolerance of the ICU interventions along with sedative drugs—called analgosedation. This approach relies on titration of both sedative-hypnotic and opioid analgesic drugs to improve the patient’s tolerance of mechanical ventilation and other aspects of the ICU environment and routine ICU care. The target is comfort without oversedation and is often best achieved with a balanced approach that allows selection of medications that are preferred for a specific patient (e.g., organ dysfunction or hemodynamic compromise) and can minimize adverse effects of medications by using lower doses and potentially synergistic effects.¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²⁰^,⁶⁹^,⁷⁰^,⁷¹^,⁷²^,⁷³^,⁷⁴ Some clinical trials have demonstrated better outcomes when such an approach is used. Although titration of the opioid component to a pain reduction target remains operative, the overall level of consciousness and patient-ventilator interaction often influences the dosing of both sedative and analgesic infusions. Thus, somewhat uniquely to the ICU setting, “pain management” also encompasses management of “analgosedation” and tolerance of mechanical ventilation and other ICU interventions.

Successful management of pain, provision of comfort, and timely recovery from critical illness are highly dependent on the multiprofessional care team implemented in many ICUs. Pain management in particular relies on the effective partnership between the treating physician, the bedside nurse, and the clinical pharmacist. This includes designing a treatment strategy that is patient focused with consideration of the patient’s unique analgesic needs and factors like organ dysfunction that influence management. Implementation is enhanced through standardized approaches, order sets, guidelines, and other tools plus ongoing communication and review. The comprehensive ICU team also includes physical therapists, nutritionists, respiratory therapists, and others who contribute to missions of comfort and rapid recovery. Further, utilization of expert consults from palliative care or pain management services can make an important difference in selected patients. Accordingly, effective pain management in the ICU brings the advantages, but also challenges, of a team-based approach.³⁴^,³⁵^,³⁶^,³⁷^,³⁸^,³⁹^,⁴⁰

TABLE 114.1 Systemic and Physiologic Consequences of Pain in the Intensive Care Unit

Physiologic System and Effects	Consequences
Immune: cytokines elaboration and leukocyte dysfunction	Decreased ability to fight infection and hemodynamic instability
Cardiovascular: increased adrenergic tone and increased vascular resistance	Increased myocardial oxygen demand, stress, and ischemia; venous stasis
Renal: activation of reninangiotensin-aldosterone axis	Water and sodium retention, anasarca
Endocrine: hormonal imbalance, especially cortisol and insulin	Hyperglycemia
Respiratory: restrictive physiology, hyperventilation, lowered residual capacity	Patient-ventilator asynchrony, atelectasis, hypoxia, increased pneumonia risk
Psychological and neurologic: altered sleep stage and serotonergic imbalance	Depression, fatigue, psychosis, sleep deprivation, anxiety
Hematologic: hypercoagulability and platelet dysfunction	Bleeding, thromboembolic disease

A final consideration as to the unique aspects of pain management in the ICU is that the physiologic consequences of untreated pain may be particularly detrimental in critically ill patients who already have ongoing shock, tissue injury, and organ failure producing a complex state of physiologic disruption.⁷⁵ Pain can cause neurohormonal derangements, catecholamine release, stress response, cytokine production, and other physiologic derangements. These and other pain-induced changes can promote hypercoagulability, altered glucose control, myocardial ischemia, hemodynamic compromise, immune system dysfunction, excessive inflammation, ventilator asynchrony, and disrupted sleep.

There is strong motivation from multiple standpoints to effectively detect and manage pain in a multiprofessional and patient-centered approach. Some of these manifestations are listed in Table 114.1. The core evidence-based recommendations directly related to pain and analgesia from the Society of Critical Care Medicine (SCCM) are displayed in Table 114.2 and form the basis of management.¹¹

TABLE 114.2 2013 SCCM Pain, Agitation, and Delirium Guidelines: Statements and Recommendations for Treatment of Pain in the Intensive Care Unit (ICU)

ICU patients frequently experience pain at rest, with routine ICU care and in association with devices and procedures (B).
Pain should be routinely monitored in all adult ICU patients (+1B).
The Behavioral Pain Scale and the Critical-Care Pain Observational Tool are the most valid behavioral pain scales in medical, postoperative, or trauma (with the exception of brain injury) adult ICU patients who are unable to self-report pain (B).
Vital signs may be used as a cue (+2C) but should not be used alone in the assessment of pain (+2C).
Preemptive analgesia should be used in adult ICU patients prior to procedures (+2C), including chest tube removal (+1C).
First-line therapy: intravenous opioids for nonneuropathic pain (+1C)
Consider nonopioid analgesics as adjunctive therapies to reduce opiates and related side effects (+2C).
Treat neuropathic pain with gabapentin or carbamazepine (+1A).
Thoracic epidural anesthesia/analgesia should be considered for abdominal aortic aneurysm postoperative patients (+1B) or patients with traumatic rib fractures (+2B).
Analgesia-first sedation should be used in mechanically ventilated adult ICU patients (+2B).

NOTE: The quality of evidence for each statement and recommendation was ranked as high (A), moderate (B), or low/very low (C). The strength of recommendations was ranked as strong (1) or weak (2) and either in favor of (+) or against (-) an intervention.

Evaluation and Monitoring of Pain in the Intensive Care Unit

Effective pain management begins with the assumption that pain is common among ICU patients and that caregivers should systematically and repeatedly evaluate each patient for the presence of pain, its intensity, and its characteristics.¹¹^,¹²^,¹³^,¹⁶^,⁴¹ Unfortunately, research confirms that caregivers tend to underrecognize pain and often fail to preemptively treat pain.²¹ Accordingly, clinicians should err on the side of presuming pain is present. Repeated assessment is desirable because conditions change over time and pain management is more effective at an early stage than after pain has become established and more severe.

Ideally, pain should be described in regard to location, duration, type, exacerbating and relieving factors, and intensity. Pain should be also be considered by subtype—including somatic, visceral, and neuropathic—because manifestations and management can be different.¹¹^,⁴¹ For example, somatic pain is typically dull and aching, often localized, and responds well to opioids and nonsteroidal anti-inflammatory drugs (NSAIDs). In contrast, visceral pain is often cramping and colicky and may respond to anticholinergic therapy, whereas the burning and shooting neuropathic pain is often best treated with antidepressant and anticonvulsant agents. Repeated and thorough evaluation helps to determine the cause and to appreciate prior responses to therapy.

Because pain is a subjective interpretation by an individual, the ability of that individual to communicate the presence and magnitude of pain is important in guiding evaluation and management when possible.¹¹^,⁴¹ Many ICUs employ a strategy of daily interruption of sedation, even in unstable sedated patients, and this brief period of greater awareness by the patient presents an opportunity for communication about pain. Although detailed verbal communication about the presence, intensity, and character of pain is ideal, it is often not possible with ICU patients and the use of simple tools can enhance communications of the presence and intensity of pain. These simple tools, such as numerical rating scales and a series of cartoon faces ranging from smiling to crying like the Wong-Baker FACES scale, can facilitate communication via pointing or nodding by the cognitively intact but nonverbal patient.⁴² A simple horizontal 0-to-10 numerical scale with enlarged font was judged to be feasible and valid in one comparison of tools.⁴³ Other techniques to improve the process of self-reporting of pain include adding descriptive words to the numerical scale, explaining the tool and correcting errors with each encounter, providing needed glasses and hearing aids, and ensuring adequate time for instructions and patient response.⁴¹ Use of a scale that incorporates descriptive pictures, like the FACES scale, can help overcome language barriers as well as mild cognitive dysfunction.

Many ICU patients are cognitively impaired, and selfreporting pain is not feasible. For these patients, utilizing a structured evidence-based approach to infer the presence and severity of pain based on observation can be performed. Tools have been developed based on observed behaviors that have been correlated with self-reported pain and/or with responses to noxious stimuli in prior research.⁹^,²¹^,⁴⁴^,⁴⁵^,⁴⁶ Various combinations of behaviors have been assembled into structured assessment tools—most include facial expressions, body position and movement, and patient-ventilator interaction. Contraction of facial muscles associated with grimacing correlates particularly well with noxious stimuli.²² The early work in pain assessment for noncommunicative ICU patients was with infants and young children, resulting in the development of the COMFORT Scale, the FLACC Observation tool, and others.⁴¹^,⁷⁶^,⁷⁷ Subsequently, a variety of pain assessment tools for nonverbal critically ill adults have been developed, validated, and critically reviewed.¹¹^,⁴¹^,⁴⁷^,⁴⁸ Published pain observation tools for adults in the ICU care include the Critical-Care Pain
Observation Tool (CPOT); the Behavioral Pain Scale (BPS); the Behavioral Pain Scale for non-intubated patients (BPS-NI); the Nonverbal Pain Scale (NVPS); the Pain Behavioral Assessment Tool (PBAT); and the Pain Assessment, Intervention, and Notation (PAIN) tool.⁴⁹^,⁵⁰^,⁵¹^,⁵²^,⁵³^,⁵⁴^,⁵⁵ Additionally, the Adaptation to the Intensive Care Environment (ATICE) tool incorporates facial grimacing as one of five components.⁷⁸ Following comprehensive testing of psychometric properties and issues of relevance and implementation, the CPOT (Table 114.3) and BPS (Table 114.4) scales were recommended in the 2013 guidelines as the most valid and reliable behavioral pain scales for monitoring pain in adult medical, postoperative, or trauma ICU patients who are unable to self-report and in whom motor function is intact and behaviors are observable.¹¹ Because these tools all rely on behavioral responses to noxious events, their validity can be influenced by other factors, particularly sedative medications. Specifically, both scores of CPOT and BPS decrease and validity falls with deepening sedation.⁵⁰^,⁵⁵ Given the inexact nature of pain evaluation in noncommunicative patients, investigators continue to explore new ways to detect pain including detection of specific muscles during facial movements like grimacing,²²^,⁷⁹ and various measures of autonomic response to nociceptive stimulation including heart rate variability, pupillary dilatation reflex, and skin conductance.⁸⁰^,⁸¹

TABLE 114.3 The Critical-Care Pain Observation Tool (CPOT)

Indicator

Description

Score

Facial expression

No muscular tension observed

Presence of frowning, brow lowering, orbit tightening, and levator contraction

All of the above facial movements plus eyelid tightly closed

Relaxed, neutral

Tense

Grimacing

Body movements

Does not move at all (does not necessarily mean absence of pain)

Slow, cautious movements, touching or rubbing the pain site, seeking attention through movements

Pulling tube, attempting to sit up, moving limb, thrashing, not following commands, striking at staff, trying to climb out of bed

Absence of movements

Protection

Restlessness

Muscle tension

No resistance to passive movements

Relaxed

Evaluation by passive flexion and extension of upper extremities

Resistance to passive movements

Strong resistance to passive movements, inability to complete them

Tense, rigid

Very tense or rigid

Compliance with the ventilator (intubated patient)

Alarms not activated, easy ventilation

Alarms stop spontaneously

Asynchrony: blocking ventilation, alarms frequently activated

Tolerating ventilator or movement

Coughing but tolerating

Fighting ventilator

-OR-

Vocalization (extubated patient)

Talking in normal tone or no sound

Sighing, moaning

Crying out, sobbing

Talking in normal tone or no sound

Sighing, moaning

Crying out, sobbing

Total, range

0-8

NOTE: Subscale scores are summed with a CPOT score ranging from 0 to 8. In one study, CPOT >3 had sensitivity of 67% and specificity of 83% for self-reported pain in conscious ICU patients.⁵⁵

Republished with permission of American Association of Critical-Care Nurses from Gelinas C, Fillion L, Puntillo KA, et al. Validation of the critical-care pain observation tool in adult patients. Am J Crit Care. 2006;15(4):420-427; permission conveyed through Copyright Clearance Center, Inc. Copyright © 2006 by the American Association of Critical-Care Nurses.

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