Objectives
• Explain the physiology of pain.
• Discuss how to perform a pain assessment in the critically ill patient.
• Identify patient and health care professional barriers to a pain assessment.
• Describe the pharmacological and nonpharmacological interventions for pain management.
• Describe nursing interventions that are essential in the treatment of acute pain.
Be sure to check out the bonus material, including free self-assessment exercises, on the Evolve web site at http://evolve.elsevier.com/Urden/priorities/.
Despite national and international efforts, guidelines, standards of practice, position statements, and many important discoveries in the field of pain management in the past three decades, pain remains a major stressor for patients in critical care settings.1 Because many sources of pain are present in critical care settings, such as acute illness, surgery, trauma, invasive equipment, and nursing and medical interventions,2,3 it is not surprising that more than 50% of critically ill patients experience moderate to severe pain.4–6 In a large, international study involving 5957 critically ill adults, the Thunder Project II sponsored by the American Association of Critical-Care Nurses (AACN), turning, drain removal, wound care, and endotracheal suctioning were described as painful procedures of moderate to severe intensity.5 Despite these findings, pain remains undertreated in most critically ill patients.4,6–9 In the Thunder Project II, less than 20% of critically ill adults received opiates before and during painful procedures.9 Poor treatment of acute pain may lead to the development of serious complications10,11 and chronic pain syndromes,12,13 which may seriously impact the patient’s functioning, quality of life, and well-being.
Importance of Pain Assessment
To detect pain, it must be adequately assessed. Because pain is recognized as a subjective experience,14 the patient’s self-report is the most valid measure for pain. Unfortunately in critical care, many factors alter verbal communication with patients: the administration of sedative agents, mechanical ventilation, and the patient’s change in level of consciousness.2,3,15 Nevertheless, except for being unable to speak, many mechanically ventilated patients can communicate that they are in pain by using head nodding, grimacing, hand motions, or by seeking attention with other movements.4,16
Pain scales have been used with postoperative mechanically ventilated patients who were asked to point on the pain intensity scale to communicate their pain.5,17,18 However, in a study of mechanically ventilated adults with various diagnoses (trauma, surgical, or medical), only one third of mechanically ventilated patients were able to use a pain intensity scale.19 With a greater degree of critical illness, providing a pain intensity self-report becomes more difficult because it requires concentration and energy. When the patient is unable to express himself or herself in any way, observable, clustered behavioral and physiological indicators become unique indices for pain assessment and are part of clinical guidelines and recommendations developed in North America.20–23 Many health care agencies have increased their vigilance regarding patients’ pain and its management, including designating pain assessment as the fifth vital sign, as stated by the American Pain Society.
Definition and Description of Pain
Pain is described as an unpleasant sensory and emotional experience associated with actual or potential tissue damage.14 This definition emphasizes its subjective and multidimensional nature. Its subjective characteristic implies that pain is whatever the person experiencing it says it is and that pain exists whenever he or she says it does.24 This definition implies that the patient is able to self-report. In the critical care context, many patients are unable to self-report.25
Infants represent a unique group of vulnerable patients who cannot self-report their pain and therefore communicate by behaviors. Clinicians must be attuned to infant’s behaviors for pain-related clinical assessment.25 This same principle applies to any nonverbal population, for whom behavioral alterations caused by pain are valuable forms of self-report and should be considered as alternative measures of pain.25 Based on this idea, pain assessment must be designed to conform to the patient’s communication capabilities, and this is consistent with the fact that pain is multidimensional.
Components of Pain
The experience of pain includes sensory, affective, cognitive, behavioral, and physiological components:26,27
Types of Pain
Pain can be acute or chronic, with different sensations related to the origin of the pain.
Acute Pain
Acute pain has a short duration, represents tissue damage from an identifiable cause, and corresponds to the healing process (30 days). Undertreated prolonged acute pain can become chronic pain.12,13
Chronic Pain
Chronic pain persists for longer than 3 to 6 months after the healing process from the original injury.28,29 It develops when the healing process is incomplete or with permanent damage to the nervous system. It has also been associated with a prolonged stress response.27 Acute and chronic types of pain can have a nociceptive or neuropathic origin.30
Nociceptive Pain
Nociceptive pain refers to the nociception mechanism, and can be somatic or visceral. Somatic pain involves superficial tissues, including skin, muscles, joints, and bones; the location is well defined; and it may be described as tender, burning, shooting or throbbing. Visceral pain involves organs including the heart, stomach, and liver; location is diffuse, and it is usually described as aching or cramping.
Neuropathic Pain
Neuropathic or deafferentation pain is described as an abnormal sensory process caused by changes in the excitability of nerve cells.31 These changes are associated with the acute inflammatory process or with nerve damage that can be caused by surgery or an illness process.32–34 The origin of the pain may be peripheral or central.
Pain in Critical Care
Pain in the critical care setting is a subjective and multidimensional experience. Its components are sensory, affective, cognitive, behavioral, and physiological. Pain experienced by critical care patients is mostly acute with multiple origins. An understanding of pain physiology provides the foundation for assessment and treatment.
Physiology of Pain
Nociception
Nociception represents the neural and brain activity that is necessary, but not sufficient, for pain. Pain is the conscious experience that emerges from nociception, especially from brain activity.35 Four processes are involved in nociception:30
These four processes are shown in Figure 8-1 and Figure 8-2, which integrates pain assessment with nociception.
CNS, central nervous system; NS, neospinothalamic pathway; PS, paleospinothalamic pathway. (Copyright Céline Gélinas, School of Nursing, McGill University, Canada.)
Transduction
Transduction refers to mechanical (e.g., surgical incision), thermal (e.g., burn), or chemical (e.g., toxic substance) stimuli that damage tissues. These stimuli activate the liberation of chemical substances, such as prostaglandins, bradykinin, serotonin, histamine, glutamate, and substance P, which stimulate peripheral nociceptive receptors and initiate nociceptive transmission.
Transmission
As a result of transduction, an action potential is produced and transmitted by nociceptive nerve fibers in the spinal cord that reach higher centers of the brain. This is called transmission, and it represents the second process of nociception. The principal nociceptive fibers are the Aδ and C fibers. These fibers synapse with two spinothalamic pathways: neospinothalamic (NS) and paleospinothalamic (PS) pathways. Generally, the Aδ fibers transmit the pain sensation to the brain within the NS pathway, and the C fibers use the PS pathway.36
Through synapsing of nociceptive fibers with motor fibers in the spinal cord, muscle rigidity can appear because of a reflex activity.10 Muscle rigidity can be a behavioral indicator associated with pain. It can contribute to immobility and decrease diaphragmatic excursion. This can lead to hypoventilation and hypoxemia. Hypoxemia can be detected by a pulse oximeter (SpO2) and by oxygen arterial pressure (PaO2) monitoring. A ventilated patient’s interaction with the machine (e.g., activation of alarms, fighting the ventilator) also may indicate the presence of pain.37
Perception
The pain message is transmitted via the spinothalamic pathways to centers in the brain where pain is initially perceived. Pain sensation transmitted by the NS pathway reaches the thalamus, and the pain sensation transmitted by the PS pathway reaches brainstem, hypothalamus, and thalamus.36 Projections to the limbic system and the frontal cortex allow expression of the affective component of pain.38–40 Projections to the sensory cortex located in the parietal lobe allow the patient to describe the sensory characteristics of his or her pain, such as location, intensity, and quality.38–42 The cognitive component of pain involves many parts of the cerebral cortex and is complex. These three components (affective, sensory, and cognitive) represent the subjective interpretation of pain. Parallel to this subjective process, certain facial expressions and body movements are behavioral indicators of pain occurring as a result of pain fiber projections to the motor cortex in the frontal lobe.
Modulation
Modulation is the liberation of endogenous opioids, such as β-endorphins, enkephalins, and dynorphins, by the CNS. Through the descending pathways endogenous opioids inhibit the transmission of pain sensation in the spinal cord and produce analgesia. These substances link to mu (µ) receptors located on nociceptive fibers, inhibiting the liberation of substance P and blocking the transmission of the pain sensation.
Pain Assessment
Pain assessment is a vital part of nursing care. It is a prerequisite for adequate pain control and relief. Pain is a subjective, multidimensional concept that requires complex assessment. Pain assessment has two major components: nonobservable/subjective and observable/objective.
Pain Assessment: The Subjective Component
Pain is an entirely subjective experience.14,47–49 The subjective component of pain assessment refers to the patient’s self-report of pain. Because it is the most valid measure, the patient’s self-report must be obtained whenever possible.21 A simple yes or no (presence versus absence of pain) is considered a valid self-report. Mechanical ventilation should not be a barrier to document patients’ self-reports of pain. Many mechanically ventilated patients can communicate that they have pain or can use pain scales by pointing to numbers or symbols on the scale.4,5,17–19 Before concluding that a patient is unable to self-report, three attempts to ask the patient about pain are recommended.3 Sufficient time should be allowed for the patient to respond with each attempt.
If sedation and cognition levels allow the patient to give more information about pain, a multidimensional assessment can be documented. Multidimensional pain assessment tools, including the sensorial, emotional, and cognitive components, are available (e.g., Brief Pain Inventory,50 Initial Pain Assessment Tool,30 Short-Form McGill Pain Questionnaire51). Because of the administration of sedative and analgesic agents in mechanically ventilated patients, the tool must be short enough to be completed. For instance, the short-form McGill Pain Questionnaire takes 2 to 3 minutes to complete and has been used to assess mechanically ventilated patients who were in stable condition.5,17,18
The patient’s self-report of pain can also be obtained by questioning the patient using the mnemonic PQRSTU:52
• P: provocative and palliative or aggravating factors
• R: region or location, radiation
P: Provocative and Palliative or Aggravating Factors
The P investigates what provokes or causes the pain, and the moderating factors that reduce pain or discomfort.
Q: Quality
The Q in the mnemonic refers to the pain sensation that the patient is experiencing. For instance, the patient may describe the pain as dull, aching, sharp, burning, or stabbing. This information provides the nurse with data regarding the type of pain the patient is experiencing (i.e., somatic or visceral). The differentiation between types of pain may contribute to the determination of cause and management. A patient who has had open-heart surgery may complain of chest pain that is shooting or burning.4 This information can lead the nurse to investigate for cutaneous or bone injuries as a result of a sternotomy. Another patient may describe a sharp thoracic pain that may lead the nurse to consider visceral pain as a result of pulmonary embolism. A verbal description of pain is important because it provides a baseline account, allowing the critical care nurse to monitor changes in the type of pain, which may indicate a change in the underlying pathology.
R: Region or Location, Radiation
R usually is easy for the patient to identify, although visceral pain is more difficult for the patient to localize.30 If the patient has difficulty naming the location or is mechanically ventilated, ask that the patient to point to the location on himself or herself or on a simple anatomic drawing.53
S: Severity and Other Symptoms
S denotes pain severity or intensity. Many visual analog scales are available, as are the descriptive and numeric pain rating scales used in critical care (Figure 8-3). Numeric and descriptive pain rating scales have been used to assess pain in mechanically ventilated patients.5,19,46 The Faces Pain Rating Scale was identified as the easiest pain intensity scale by adults in acute and critical care settings.54,55 To have a faces scale more specific to adults, Gélinas56 developed and validated the Faces Pain Thermometer (FPT) for critically ill patients.
A, Visual analog scale (VAS). B, Numeric Rating Scale (NRS). C, Descriptive Rating Scale (DRS). D, Faces Pain Thermometer. (Copyright Céline Gélinas, School of Nursing, McGill University, Canada.)
Asking the patient to grade the pain on a scale of 0 to 10 is a consistent method and aids the nurse in objectifying the subjective nature of the patient’s pain.
The S in the mnemonic also refers to other symptoms accompanying the pain experience, such as shortness of breath, nausea, and fatigue. Anxiety and fear are common emotions associated with pain.
T: Timing
The T refers to documenting the onset, duration, and frequency of pain. This information can help determine whether the pain is acute or chronic. Duration of pain can indicate the severity of the problem.
U: Understanding
The U in the mnemonic is the patient’s perception of the problem or cognitive experience of pain.
Nurses should start by asking, “Do you have pain?” The use of a simple yes or no question allows the patient to answer verbally or indicate a response by a nod of the head or other signs.3 Pain intensity and location also are necessary for the initial assessment of pain.53
Pain Assessment: The Observable or Objective Component
When the patient’s self-report is impossible to obtain, nurses can rely on observation of behavioral and physiological indicators that are strongly recommended for pain management in nonverbal patients.20–22 Pain-related behaviors have received attention in critical care and were also studied in the AACN Thunder Project II.57 Patients who experienced pain during nociceptive procedures were three to ten times more likely to have increased behavioral responses such as facial expressions, body movement responses, and verbal responses than patients without pain. Similar observations were found in a study of 257 mechanically ventilated adults in critical care. Patients who experienced pain during turning showed more intense facial expressions (e.g., grimacing), muscle rigidity, and ventilator dyssynchrony compared with patients without pain.58
Behavioral indicators are strongly recommended for pain assessment in nonverbal patients,21,25 and several tools have been developed and tested in critically ill adults: Behavioral Pain Scale (BPS),43–45 Critical-Care Pain Observation Tool (CPOT),59 Post Anesthesia Care Unit Behavioral Pain Rating Scale (PACU-BPRS),60 Pain Behavioral Assessment Tool (PBAT),57 and Pain Assessment and Intervention Notation (PAIN) algorithm.46 The BPS and the CPOT are supported by experts as appropriate for use with uncommunicative critically ill adults61,62 and by the clinical practice recommendations of a task force of the American Society for Pain Management Nursing (ASPMN).21 The implementation of pain assessment tools is essential so that health care teams can establish a common language of communication. This facilitates inter-professional collaboration and benefits patients.
Behavioral Pain Scale
The BPS shown in Table 8-1 was mainly tested in mechanically ventilated, unconscious patients.43,45,63,64 Its validity was supported with significantly higher BPS scores during nociceptive procedures (e.g., turning, endotracheal suctioning) compared with rest or nonnociceptive procedures (e.g., central venous catheter dressing change, compression stocking applications, eye care). Most clinicians were satisfied with its ease of use, but some expressed concerns about its relative complexity.45 For instance, scores of 3 and 4 for compliance with the ventilator may be ambiguous, and movements with upper limbs may be confused with muscle tension.61
TABLE 8-1
| ITEM | DESCRIPTION | SCORE |
| Facial expression | Relaxed | 1 |
| Partially tightened (e.g., brow lowering) | 2 | |
| Fully tightened (e.g., eyelid closing) | 3 | |
| Grimacing | 4 | |
| Upper limbs | No movement | 1 |
| Partially bent | 2 | |
| Fully bent with finger flexion | 3 | |
| Permanently retracted | 4 | |
| Compliance with ventilation | Tolerating movement | 1 |
| Coughing but tolerating ventilation for most of the time | 2 | |
| Fighting ventilator | 3 | |
| Unable to control ventilation | 4 | |
| Total | 3 to 12 |
From Payen JF, et al: Assessing pain in the critically ill sedated patients by using a behavioral pain scale, Crit Care Med 29(12):2258, 2001.
Critical-Care Pain Observation Tool
The CPOT shown in Table 8-2 was tested in verbal and nonverbal critically ill adult patients.19,59 Content validity was supported by ICU expert clinicians, including nurses and physicians.65 Validity of the CPOT was supported with significantly higher CPOT scores during a nociceptive procedure (e.g., turning with or without other care) compared with rest or a nonnociceptive procedure (e.g., taking blood pressure). Significant positive associations were also found between the CPOT scores and the patient’s self-report of pain (the gold standard).66 Feasibility of the CPOT was positively evaluated by ICU nurses.67 Nurses agreed that the CPOT was quick enough to be used in the ICU, simple to understand, easy to complete, and helpful for nursing practice. The CPOT identifies patients with severe pain very well. For patients with moderate to severe pain, the cutoff seems to be between 2 and 3, depending on the patient’s condition.68 Head injury patients seemed to react differently to the nociceptive procedure.19 They were less likely to show frowning, brow lowering, and grimacing. Compared with other patients, a higher proportion of head injury patients showed tearing and open eyes when exposed to the nociceptive procedure.58
TABLE 8-2
CRITICAL CARE PAIN OBSERVATION TOOL (CPOT)
| INDICATOR | SCORE | DESCRIPTION | |
| Facial expression | Relaxed, neutral | 0 | No muscle tension observed |
| Tense | 1 | Frowning, brow lowering, orbit tightening, and levator contraction or any other change (e.g., opening eyes or tearing during nociceptive procedures) | |
 |
Grimacing | 2 | All previous facial movements plus eyelids tightly closed (the patient may present with mouth open or biting the endotracheal tube) |
| Body movements | Absence of movements or normal position | 0 | Does not move at all (does not necessarily mean absence of pain) or normal position (movements not aimed toward the pain site or not made for the purpose of protection) |
| Protection | 1 | Slow, cautious movements, touching or rubbing the pain site, seeking attention through movements | |
| Restlessness | 2 | Pulling the tube, attempting to sit up, moving limbs or thrashing, not following commands, striking at staff, trying to climb out of bed | |
| Compliance with the ventilator (mechanically ventilated patients) | Tolerating ventilator or movement | 0 | Alarms not activated, easy ventilation |
| Coughing but tolerating | 1 | Coughing, alarms may be activated but stop spontaneously | |
| Fighting ventilator | 2 | Asynchrony; blocking ventilation, alarms frequently activated | |
| or | |||
| Vocalization (nonventilated patients) | Talking in normal tone or no sound | 0 | Talking in normal tone or no sound |
| Sighing, moaning | 1 | Sighing, moaning | |
| Crying out, sobbing | 2 | Crying out, sobbing | |
| Muscle tension | Relaxed | 0 | No resistance to passive movements |
| Evaluation by passive flexion and extension of upper limbs when patient is at rest or evaluation when patient is being turned | Tense, rigid | 1 | Resistance to passive movements |
| Very tense or rigid | 2 | Strong resistance to passive movements, incapacity to complete them | |
| TOTAL | 0-8 | ||
1 The patient is observed at rest for 1 minute to obtain a baseline value of the CPOT.
6 The patient is given a score for each behavior included in the CPOT.
Modified from Gélinas C, et al: Validation of the Critical-Care Pain Observation Tool in Adult Patients, Am J Crit Care, 15(4):420, 2006. Figure courtesy Caroline Arbour, RN, BSc, PhD-student, McGill University, Canada.
Behaviors represent valid information for pain assessment in the critically ill patient, but they present some limitations. They are impossible to monitor in paralyzed patients receiving neuromuscular blocking agents, and their presence may be blurred by the use of high doses of sedative agents such as propofol or midazolam.19 Minimal behavioral responses to painful procedures were found in unconscious mechanically ventilated ICU adults who were more heavily sedated compared with conscious patients.58 Similar results were found in previous studies in which patients who received a higher dose of midazolam obtained a lower score on the BPS.45,64 In those difficult situations, the only possible clues left for the detection of pain are physiological indicators.
Physiological Indicators
Physiological vital signs as indicators of pain have received little attention in critically ill adults. Although vital sign values generally increase during painful procedures,19,45,58,64 they are not consistently related to the patient’s self-report of pain, nor are they predictive of pain.19,58 None of the monitored vital signs (heart rate, mean arterial pressure [MAP], respiratory rate, transcutaneous oxygen saturation [SpO2], or end-tidal CO2) predicted the presence of pain in ICU patients.58
The ASPMN recommendations emphasize that vital signs should not be considered as primary indicators of pain because they can be attributed to other distress conditions, homeostatic changes, and medications.21 Changes in vital signs should rather be considered a cue to begin further assessment of pain or other stressors.
