Curtis N. Sessler and Katie M. Muzevich

Chapter Outline

PAIN Management in the Intensive Care Unit

Pain is widely experienced in the ICU setting and can result from invasive procedures, surgery, and monitoring devices, as well as more direct stimuli from injury, inflammation, and immobility.⁵⁵ Treating pain is a core component of the caregivers’ responsibility to relieve suffering and offers the physiologic benefits of relieving pain-induced altered glucose control, myocardial ischemia, immune system dysfunction, hypercoagulability, ventilator asynchrony, impaired ventilation, and disrupted sleep.⁵⁵ Mechanisms for these downstream effects include neurohormonal derangements, catecholamine release, and stress response.^55,56

Effective treatment of pain begins with the assumption that pain is widely present and that caregivers should systematically evaluate each patient for the presence of pain and its intensity and characteristics, on a repetitive basis.6,8,9,55 Caregivers tend to underrecognize pain and often fail to preemptively treat pain.^3,57 Accordingly, clinicians should err on the side of presuming pain is present—particularly when considering that it is far more effective to prevent and manage pain at an early stage than after it has become severe. Ideally, pain should be described in regard to location, duration, type, exacerbating and relieving factors, and intensity. Pain is sometimes conceptualized by subtypes, including somatic, visceral, and neuropathic, because manifestations and management can be different.⁵⁵ For example, somatic pain is typically dull and aching, often localized, and responds well to opioids and nonsteroidal anti-inflammatory agents (NSAIDs). In contrast, visceral pain is often cramping and colicky and may respond to anticholinergic therapy, although the burning and shooting neuropathic pain is often best treated with antidepressant and anticonvulsant agents.

Because pain is a subjective interpretation by an individual, the ability of that individual to convey the presence and magnitude of pain is of great value in guiding evaluation and management.⁵⁸ Detailed verbal communication by ICU patients is often limited; however, use of simple tools such as the numerical rating scale or a series of cartoon faces ranging from smiling to crying can facilitate communication by pointing or nodding in the nonverbal but cognitively intact patient.⁵⁹ A simple horizontal 0 to 10 numerical scale with enlarged font was judged to be most feasible and valid in one study of pain intensity rating scales.⁶⁰ Other techniques to enhance the use of self-reporting of pain include adding descriptive words to the numerical scale, carefully explaining the tool and correct use with each encounter, providing glasses and hearing aids if necessary, allowing adequate time for instructions and patient response.⁵⁸ Use of a scale that incorporates descriptive pictures, like the faces scale, can facilitate self-reporting of pain intensity regardless of potential language barriers.

Many ICU patients are cognitively impaired and self-reported pain intensity is not feasible. Accordingly, clinicians must rely upon observed behaviors that have been documented to correlate well with self-reported pain or to be associated with noxious stimuli.54,57,61–63 Investigators have combined behaviors into structured assessment tools. Interestingly, much of the early work in pain assessment for noncommunicative ICU patients was in infants and young children, resulting in the development of the COMFORT scale,⁶⁴ the Face, Legs, Activity, Cry and Consolability (FLACC) observation tool,⁶⁵ and others. Subsequently a variety of pain assessment tools for nonverbal critically ill adults have been developed, validated, and thoroughly reviewed.^58,66,67 In the 2012 SCCM guidelines,⁶ published pain observation tools for adults in the ICU were identified as the Critical-Care Pain Observation Tool (CPOT),⁶⁸ the Behavioral Pain Scale (BPS),⁶⁹ the Behavioral Pain Scale—Nonintubated (BPS-NI),⁷⁰ the Non-Verbal Pain Scale (NVPS),⁷¹ the Pain Behavioral Assessment Tool (PBAT),^54,72 and the Pain Assessment, Intervention, and Notation (PAIN) tool.⁷³ Extensive psychometric testing was performed including examination of scale development, testing of reliability, and testing of validity, feasibility, and scale relevance or impact of implementation in ICU patient outcomes yielding a maximum score of 25 and weighted score of 0 to 20. The CPOT had the highest weighted score of 14.7, followed by the BPS with 12.0,⁶ and these two scales are recommended in the 2012 SCCM guidelines as the most valid and reliable behavioral pain scales for monitoring pain in adult medical, postoperative, and trauma ICU patients who are unable to self-report and in whom motor function is intact and behaviors are observable.⁶ CPOT and BPS are displayed in Tables 19.1 and 19.2. Pain is often accompanied by changes in vital signs, with tachycardia, hypertension, and tachypnea being most common. However, changes in vital signs are inconsistently associated with pain, with many confounding factors that can mask anticipated changes—such as administration of beta blockers, as well as lack of specificity with many other causes of tachycardia, hypertension, and tachypnea.⁷⁴ Accordingly, 2012 SCCM guidelines recommend against the use of vital signs (or observational pain scales that include vital signs) alone for pain assessment in adult ICU patients.⁶ However, it is acknowledged that vital signs may be an important cue to prompt further pain assessment.⁶ Other potentially useful approaches include evaluating pain risk profile, use of surrogate (such as family members) report,⁷⁵ and performance of an analgesic trial.^3,55,58

There are several important tenets for managing pain in the ICU. First, when initiating sedative treatment for mechanically ventilated ICU patients, analgesia should be the first step, followed by the addition of a sedative-anxiolytic agent. This “analgesia first” approach is suggested in the 2012 SCCM guidelines⁶ as well as many expert reviews.^18–23,55 Second, the use of preemptive analgesia should be administered prior to the performance of interventions, such as chest tube removal, that are associated with having a high likelihood of producing pain.⁶ It is more effective to prevent pain or manage it at an earlier and milder stage than after pain has become severe.

Successful pain management in the ICU incorporates pharmacologic and nonpharmacologic treatment.⁹ Parenteral opioids are the primary agents used to treat pain in the ICU setting, but use of selected nonopioid and atypical agents can enhance pain relief and may reduce adverse effects. The major parenteral opioids for continuous infusion in ICU patients—fentanyl, morphine, hydromorphone, and remifentanil (see Table 19.4)⁹—are generally considered to be equivalent in regard to analgesic potential as well as class-based adverse effects such as respiratory depression or reduced level of consciousness. Important differences among agents in regard to lipid solubility, volume of distribution (Vd), half-life, clearance, metabolism, and active metabolites have important effects on onset, peak, and offset of action, potency, and the influence of renal or hepatic dysfunction.⁹ Some of the medication features that can influence opioid selection for a particular patient are noted in Table 19.3. For example, morphine sulfate is metabolized to several active metabolites, including morphine-6-glucuronide, which is as active as the parent compound and accumulates in renal failure, resulting in prolonged effects including analgesia but also somnolence and respiratory depression.⁷⁶ The rapid equilibration of fentanyl from plasma to lipid-rich brain tissue is responsible for its rapid onset of action but its high lipophilicity also contributed to large Vd and delayed offset of action after prolonged infusion. Remifentanil has a small Vd, and rapid clearance with metabolism by esterases, yielding a short half-life and rapid offset of action that is independent of renal and hepatic function.^77,78 Several opioids not listed deserve mention. Meperidine has the potential for neuroexcitatory adverse effects such as seizures⁷⁹ and is not recommended for ICU use.⁶ Methadone can slow the development of tolerance to other opioid agents when coadministered but has unpredictable pharmacokinetics and is not administered by continuous infusion.⁶ Methadone is also a potent precipitating agent for prolonging the rate-corrected QT interval (QTc).^80,81 Although opioids are most effective for pain management in the ICU patient, these agents have a well-documented propensity to produce adverse effects (AEs), which are reviewed, along with comments for each AE, in Table 19.4.^9,55 Comprehensive pain management should include awareness of the likely adverse effects and how best to avoid them and to recognize and manage them.

It is often advantageous to use the lowest effective dose of an opioid analgesic, particularly when intolerable side effects are present. Additionally, there are clinical settings in which a nontraditional approach may be more effective, safer, and better tolerated. Employment of alternative or complementary approaches such as adding nonopioid or atypical analgesic agents, use of epidural or other neuraxial alternatives to parenteral opioid, and use of complementary nonpharmacologic interventions should be considered in selected cases.⁹

Sedation Management

Sedative drugs have formed the cornerstone for patient comfort and tolerance of the ICU environment for decades by calming anxiety, providing amnesia, and controlling agitation. There have been changing paradigms from preferential use of moderate- to long-acting benzodiazepines⁵ and acceptance of prolonged deep sedation a decade ago, to patient-focused sedation with careful monitoring, analgesia first, and more recently to an emphasis on the use of nonbenzodiazepine sedative agents and using the lightest level of sedation possible.⁶ Management of sedation should be preceded by examining individual patient characteristics and effective pain control. It incorporates establishing the goals of sedative therapy, monitoring of the depth of sedation, selecting and administering the best agent(s) for the particular patient, and using protocolized management of sedation that includes structured elements to assure use of the lowest effective dose and lightest level of sedation. Common goals of therapy include relief of anxiety, control of frank agitation, promotion of patient-ventilator synchrony, and elimination of awareness when an NMBA is used. Monitoring of the depth of sedation is now routinely performed in most ICUs and is applied to titrate medications to a targeted level of consciousness and to avoid excessive or prolonged sedation.

Monitoring the depth of sedation is most commonly performed by observing patient behaviors, often after varying levels of stimulation, using a structured sedation scale.43

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