Pain Management in the Critically Ill Patient

Introduction

Pain in the critically ill has been historically poorly understood. Only recently has attention and investigation turned toward the issues of pain assessment and treatment in this patient population. The prevalence of poorly treated pain in the critically ill is considerable and greater than commonly believed among health care physicians. This chapter examines some salient issues as well as the modern, pertinent literature detailing barriers to assessing and treating pain in a critical care setting, as well as some strategies for dealing with this challenging clinical dilemma.

Prevalence of Pain in the Intensive Care Unit (ICU)

Although often unable to communicate because of the severity of their disease process or the presence of impediments such as artificial airways or endotracheal tubes (ETT), patients admitted to the ICU often experience pain and discomfort that goes unrecognized and untreated. Estimates vary based on patient populations, but large proportions of both medical and surgical patients report experiencing pain while in the ICU.

One study of cancer patients found that between 55% and 75% of patients reported experiencing pain, discomfort, anxiety, sleep disturbance, or unsatisfied hunger or thirst. Another study demonstrated that 77% of cardiac surgery ICU patients recalled experiencing pain, with 64% rating the pain as moderate or severe. An often-underappreciated source of pain in the ICU is during routine procedures, such as patient turning, ETT suctioning, chest tube removal, arterial or venous line insertion, or wound care. One prospective cohort study of 400 medical ICU patients found that those patients for whom analgesics were prescribed had a higher concomitant incidence of hemodynamic monitoring, greater use of neuromuscular blocking agents, more mechanical ventilation days, and more prolonged ICU and hospital lengths of stay. Consistent with these findings, patients who received analgesics also had higher Trauma Injury Severity Scores and predicted mortality.

The SUPPORT investigators examined more than 4000 ICU patients over two years. Family members reported moderate to severe pain at least half the time for 50% of conscious patients who died in the hospital. Similarly high rates of moderate to severe pain were found in another study of surgical ICU patients.

One investigation used a questionnaire to collect data on patients’ stressful experiences associated with being in an ICU and on mechanical ventilation. Of those who remembered the ETT, a large proportion were significantly bothered by not being able to speak (68%), pain associated with the ETT (56%), and anxiety regarding the ETT (59%). It is not surprising that this study found that those who did not remember the ETT or ICU were on average more severely ill and subject to a longer duration of mechanical ventilation than the group who remembered these experiences. Given the severity of their disease process, the former group may have been more likely to be chemically paralyzed or heavily sedated.

Despite a high incidence of pain in ICU patients, studies find that it often goes untreated. An observational study in 128 Italian ICUs of 661 postoperative patients found that 36% of patients did not receive any analgesia in the first 48 h of their ICU stay. “Pain control” was listed as the reason for administration in only 54.5% of instances in which an opioid was given.

Barriers to Pain Assessment in the ICU

Given the potential compromise of patients’ physiologic stability and communication skills secondary to underlying disease processes, ICU patients present unique challenges for the assessment and treatment of pain. Indeed, critically ill patients have a much higher risk of enduring untreated pain because they often cannot communicate their level of discomfort because of altered mental status, mechanical ventilation, and sedation ( Box 81.1 ). A clinician’s observation and subjective rating of ICU patient pain often underestimates that patient’s pain. Thus whenever possible, ICU patients should rate their own pain. Patient self-reported pain using a one to ten point numeric rating scale (NRS) has been recommended by critical care societies. ^,

A critically ill patient may be obtunded secondary to the underlying disease process or physiologically compromised by a process such as sepsis or shock. The question of how much pain the patient is experiencing may be difficult to answer in these settings. Many patients may not remember these experiences, and even if these experiences can be recalled, there are limitations to assessing pain retrospectively. The use of proxy assessment for patient symptoms is controversial. Proxies, such as family members or bedside clinicians, may overestimate or underestimate the symptoms experienced by patients. ^, Therefore increased vigilance by physicians and nursing staff and the development and use of alternative means of pain assessment are necessary when patients cannot verbalize pain.

Indirect methods of evaluating pain are used for patients unable to communicate verbally. The behavioral pain scale (BPS) ( Fig. 81.1 ) and the Critical Care Pain Observation Tool (CPOT) are commonly used pain scales used in adult patients, excluding those with brain injuries. ^, The BPS uses a patient’s facial expression, upper extremity movements, and compliance with the ventilator as surrogate indicators of pain, with a score of five or greater indicating unacceptable levels of pain. Similarly, the CPOT evaluates facial expression, body movements, muscle tension, and compliance with the ventilator for intubated patients or vocalization for extubated patients. A CPOT score of three or above indicates significant pain.

Various studies to validate these tools in the critically ill have been published, although other scales, such as the adult Nonverbal Pain Scale (NVPS), and the Faces, Legs, Activity, Cry, and Consolability scale, have also been used in different patient populations.

Pain assessment and treatment can also be systematically improved in ICUs. One study examined the assessment and treatment of pain in two surgical ICUs in a university hospital setting. After the investigators implemented a series of measures to introduce a modified visual analog scale (VAS) similar to an NRS ( Fig. 81.2 ) and educated physicians and nurses on the importance of pain assessment and treatment, pain assessments improved from a rate of 42% to more than 70%. Patients whose pain was controlled (VAS less than 3/10) increased from 59% to greater than 90%. Another study showed that after standardized implementation, the CPOT resulted in a more consistent assessment of pain in critically ill patients and fewer analgesic and sedative agents being administered.

The treatment of pain in critically ill and postoperative pediatric patients is also essential for their comfort, and the use of pain protocols in these regards improves patient comfort. More implementation of such protocols may be helpful in the pediatric critical care population.

Barriers to Pain Treatment in the ICU

The difficulty of treating pain in those hospitalized in the ICU has been documented, and there is a defined lack of high-level evidence for clinical decision making in these regards. Frequent need for rapid drug titration can contribute significantly to interpatient variability in response, which is likely more magnified in critically ill patients. Moreover, there can be significant difficulty in distinguishing adverse drug events from other comorbid medical conditions in ICU patients.

A consensus guideline regarding sedation and analgesia in dying critically ill patients ( Box 81.2 ) recognized the difficulty of pain assessment in this setting as a result of several factors, including communication problems particular to the ICU environment, the severity of the critical illness, the potential presence of multisystem organ failure, the possibility of a decreased level of consciousness resulting from illness and drugs, and difficulty in the interpretation and reporting of clinical signs.