Analgesia in the ICU


Pain assessment, pain control, pain relief

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Related Conditions

Postoperative pain relief


Catheter/apparatus discomfort/naso/orogastric tubes

Endotracheal intubation/suctioning/chest tubes

Phlebotomy/vascular access

Occupational/respiratory/physical therapy

Routine turning and positioning

1. Description of the problem

Postoperative pain control remains a major issue for clinicians and patients, particularly for sick patients admitted to critical care units. Literature review suggests that ~70% of postoperative patients suffer from moderate to severe pain despite the recognition that adequate pain control enhances recovery and discharge after major illnesses. Recent surveys have also suggested that pain and discomfort in mechanically ventilated patients are predictors for development of post-traumatic stress disorder. Inconsistencies in analgesic prescription and wide variations in monitoring sedation and analgesia are common among critical care patients. There is evidence to suggest that inadequate pain control has deleterious effects and is associated with cardiovascular risks, immunosuppression, neuroendocrine stress, coagulation abnormalities, and delayed gastric emptying. Therefore, it becomes the responsibility of physicians and nurses caring for these patients to critically evaluate their practice regarding pain management and to adopt an optimal pain management strategy that includes analgesia and reduction in painful stimuli and promotes education among healthcare professionals.

Optimizing analgesia in the critical care unit poses several challenges in the presence of altered physiology and trauma, including the need for early extubation and rehabilitation. Opioid-related prolonged sedation and accumulation of metabolites results in delayed recovery. Moreover, in mechanically ventilated and sedated patients, conventional pain assessment tools cannot be used because these patients cannot communicate verbally.

In a recently conducted survey of 44 intensive care units, sedation and analgesia assessments did not routinely occur in patients receiving these therapies. In addition, procedural pain (physical therapy, urinary catheterization, bronchoscopy, wound management, establishing central vein lines, and dialysis cannulas) was poorly treated, and patients requiring these interventions tended to be deeply sedated. Achieving a balance between adequate pain control and the need for early extubation and discharge is the key difference in analgesic control in critical care setting. A mechanistic approach and multimodal analgesic technique has been clearly demonstrated to be the most effective pain management strategy to improve outcome. An analgesia- sedation protocol for trauma patients reduces the number of ventilator days and the length of hospital stay. Where appropriate, it is important to adopt regional anesthetic technique to mitigate the use of sedative analgesics and to improve early rehabilitation. Regional anesthesia will improve overall outcome, particularly respiratory and bowel function. Certain conditions like head injury pose unique challenges that have to be taken into account to modify the sedative-analgesic regimen. In this review we discuss an opioid-based analgesic regimen, non-opioid adjuncts, and regional analgesic techniques and suggest guidelines of care.

Many patients in the critical care unit require analgesia and sedation, particularly those patients who are mechanically ventilated. Failure to recognize the need for analgesia, which can manifest as agitation, stress and cardiovascular instability, might often lead to increasing sedation instead of administering analgesic drugs. Procedural pain may cause significant pain and discomfort in critically ill patients, which can be compounded by pre-existing chronic pain.

The consequences of inadequate pain control are manifold, including detrimental effects on respiratory, cardiovascular, immunological, and endocrine disturbances and sleep deprivation. In addition, poorly treated acute pain can lead to a chronic pain state through a wind-up phenomenon wherein repeated painful stimuli lead to a frequency-dependent increase in the excitability of central neurons and eventually a hyperalgesic state.

Types of pain:

Somatic (localized) – usually responds to opiates

Visceral (cramping) – usually responds to anticholinergics

Neuropathic (burning/shooting) – responds to gabapentinoids and antidepressants

Mixed – requires combination therapy

Chronic – seen commonly in ICU patients postoperatively who are admitted postop but have some underlying chronic pain issues

Pain should be anticipated as a ubiquitous experience of all critically ill patients. Assessment of pain is mainly subjective experience and in critically ill patients the presence of endotracheal tubes and co-administered sedation makes routine assessment tools ineffective for recognition of pain and discomfort. Validated tools are available to assess sedation and analgesia, which may improve outcome. There is an impetus from several organizations, including the Joint Commission on Accreditation of Health Care Organization and the American Pain Society, to consider pain as a fifth vital sign, to improve pain assessment with a positive effect on overall outcome. Although surrogate markers lack reliability and specificity in sedated ill patients, physicians should be aware of these physiological and behavioral markers for patients who are unable to respond to oral commands. Agitation must always be assumed to have pain as a factor in ICU patients, and in most patients a therapeutic trial of analgesics must be tried.

2. Acute Pain Management

Opioid Analgesics

Severe pain in critically ill patients should be treated with opioids. These provide the intensivist with the most rapid and reliable way to deal with critical care pain. Recommended opioids include fentanyl, hydromorphone and morphine, which are all mu-receptor agonists (Table I). The choice of agent should be based on the potency, pharmacokinetics and side effect profile as well as any related organ impairment with the patient, which may guide care. For severe intractable pain, one could start treatment with fentanyl at a dose of 25-100 mcg as a bolus followed by an infusion of 25-200 mcg/hr. Peak effect is 4 minutes, and elimination half-life is 2-5 hr. If fentanyl seems insufficient one can progress to hydromorphone. Bolus dose is 0.2-1 mg, infusion is 0.2-2 mg/hr, peak effect is 20 minutes, and elimination half-life is 2-4 hr. Many units still use morphine, but with the accumulation in renal impairment this is becoming a less-favored ICU drug. Dosage for morphine is 1-4 mg bolus, 1-10 mg/hr infusion, peak effect 30 minutes, and elimination half-life of 2-4 hr.

Table I.n

Drugs frequently used to deal with ICU pain.

Non-opioid Analgesics

Although opioids are the foundation of any analgesic regimen, a multimodal approach is necessary to both minimize adverse opioid side effects and treat opioid resistant subtypes of pain. Several readily available drugs are worth mentioning.

Dexmedetomidine is an alpha-2 adrenergic agonist commonly used for sedation in the critically ill. In addition, it has significant analgesic properties with a demonstrated opioid-sparing effect. Its lack of respiratory depression also makes it a useful adjunct in the ICU setting, though dexmedetomidine-induced bradycardia and hypotension can limit its use in the hemodynamically unstable patient.

Ketamine is a dissociative amnestic that exerts an anti-nociceptive via NMDA antagonism. It is commonly used in the perioperative setting and is particularly useful in opioid-tolerant chronic pain patients. Appropriate dosing for post-operative analgesia is 0.1-0.4 mg/kg/hr in combination with opioid therapy. Recent studies have demonstrated a possible role for ketamine as an analgosedative in the ICU. It is an excellent bronchodilator primarily due to secondary release of endogenous catecholamines, and there is no associated respiratory depression. Ketamine causes dreaming and hallucinations, which can be dysphoric. Patients with pre-existing delirium, PTSD, or psychosis are poor candidates for ketamine therapy.

Gabapentinoids (gabapentin and pregabalin) are mainstays in the treatment of neuropathic pain. They work through binding of the alpha-2-delta subunit of voltage gated calcium channels. Both have been shown to decrease pain scores and opioid consumption in various postsurgical populations. The gabapentinoids are mildly sedating. They are renally excreted and can accumulate in patients with decreased creatinine clearance. Abrupt discontinuation should be avoided as a withdrawal syndrome similar to that of alcohol or benzodiazepines can occur.

Regional Anesthesia

Regional anesthesia in the ICU setting offers both significant benefits and challenges. Peripheral nerve blocks have been demonstrated to decrease opioid consumption and pain scores leading to earlier mobilization. However, in deeply sedated patients it is difficult to identify complications including peripheral nerve injury and potentially catastrophic local anesthetic systemic toxicity (LAST). The American Society of Regional Anesthesia (ASRA) recommends against regional anesthesia in the deeply sedated patient. In addition, in instances of coagulopathy and anticoagulation/antiplatelet therapy, the benefits of a peripheral nerve block must be weighed against the potential for bleeding complications.

Problems with pain identification:

Untreated pain is difficult to differentiate due to lack of communication, and it affects all body systems. There is a synergistic effect of pain on anxiety, depression and sleep. All modalities are unpredictable in the ICU and have unwanted side effect profiles.

3. Diagnosis

Various scoring systems for pain assessment have been validated for the ICU. The most recognized are the Faces Pain Rating Scale and the Visual Analog Scale. Pain questionnaires have also looked at qualitative aspects of pain. Tools such as the Adult Nonverbal Pain Scale, based on the pediatric FLACC scale, and the Critical-Care Pain Observation Tool have been created to better diagnose the sedated or unresponsive patient. These rely on some combinations of physiologic variables and patient behavior.


A principled approach to pain management in the ICU allows for the care of these complex patients to be optimized. The best ICU approach to pain is that of an interdisciplinary model. Due to the complex nature of the origin of a patient’s pain, taking a team-oriented approach leads to inclusion of all modalities of pain relief so that pain treatment is effective.

There are key principles that should guide our treatment of ICU patients:

  • Presume that pain is present, even if there is little supporting evidence.

  • Early recognition is key to effective management. Unopposed pain will escalate, making subsequent treatment more difficult.

  • Avoid continuous sedation and analgesia; it leads to tolerance as well as build-up of these medications.

  • Avoid abrupt withdrawal of pain medications in an effort to extubate patients, leading to acute withdrawal and delirium.

In the ICU, pain originates from repeated episodes of acute or short-term stimulation as well as some degree of chronic or sustained pain. Acute pain can originate from the acute underlying illness, or be iatrogenic from therapies. Chronic pain in the ICU can be from a condition that the patient has brought into the unit or from repeated events occurring on the unit.


Pain subtypes seen in the ICU include neuropathic, somatic, visceral and mixed. The ability of physicians to differentiate these on the ICU can be limited by the patient’s ability to cooperate in a good history and physical. Generally most patients in the ICU experience somatic pain. This is defined as dull or aching and is often well localized. As for treatment, patients respond well to nonsteroidal anti-inflammatory agents (when appropriate) as well as opiate drugs. Visceral pain that is cramping/colicky can arise from ICU ileus or from underlying GI pathology. This pain generally responds well to anticholinergic therapy. Neuropathic pain, which is generally burning/shooting in nature, occurs less commonly on the unit but still responds well to gabapentinoids, antidepressants, and anticonvulsant medications.

Special considerations for nursing and allied health professionals.

Pain produces systemic effects that may add to the severity of the underlying illness of ICU patients. Pain affects all systems of the body, through sympathetic outflow, hormonal regulation, catecholamine release and general stress response. This will result in tachycardia, anxiety, diaphoresis, lacrimation, etc., all leading to a rise in catabolic metabolism leading to increased oxygen requirements, increased myocardial stress, increased bowel motility, altered lung function and also adverse renal function due to activation of the renin angiotensin system (RAS). Untreated pain can lead to immune dysfunction, coagulation problems with increased thromboembolic problems, altered blood sugar levels, cardiac problems (ischemia, ventricular dysfunction, arrhythmias, etc.). Finally, pain will alter sleep patterns, leading to poor recovery, delirium and PTSD.

What's the Evidence?

The current emphasis on evidence-based practice requires that guidelines be developed that combine a scientific basis and expert opinion. If one looks at the Wellness model from the World Health Organization’s treatment of pain after cardiac surgery, we can see that guidelines and protocols lead to effective management of post-cardiac surgery pain. If one looks at the complexity of ICU pain, we need to have organized protocols to help us care for these patients. The examination of published literature reviews and evidence-based guidelines can facilitate the development of institution-specific guidelines.

Looking from an evidence-based perspective, one can put in to practice these guidelines to facilitate treatment:

Clinical pathways:

Pathways provide a consistent and repeatable timeline for planning individualized patient care. The pathway details the precise course of the patient, including multidisciplinary elements. These detail not only treatment pathways but also history, exam, diagnostics and treatment. This incorporates pre-emptive treatment for procedures, as well as management of chronic pain issues.


These differ from protocols as they are a way to verify that clinical pathways or tasks are completed. This is a good way to ensure that pathways or tasks are followed. This also helps prevent errors.

Daily Goals:

By having some way of highlighting daily goals (white board, electronic reminders, etc.), all members of the multidisciplinary team can access the plan and ensure that the patient is being treated from all perspectives.

Final points: Consider referring more complex patients to the hospital pain team. For example, if a patient is on multi-modal therapy from the team and still experiencing severe pain, referral to the pain team can often lead to an increased level of support that would benefit him or her. This is also true once patients have been discharged from the unit; they still need to be looked after by a multimodal rehabilitation team.


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