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Helfand M, Freeman M. Assessment and Management of Acute Pain in Adult Medical Inpatients: A Systematic Review [Internet]. Washington (DC): Department of Veterans Affairs (US); 2008 Apr.


There is much more evidence about outpatients with chronic pain, post-operative inpatients and patients with cancer than patients within the target population for this report. Throughout this report, we give precedence to the few studies that directly observed medical inpatients. We did not systematically review the literature about chronic pain, post-operative pain, or cancer pain assessment and management, but we invoke evidence from other populations when it is pertinent.

Key Question #1. How do differences in timing and frequency of assessment, severity of pain, and follow-up of pain affect choice of treatment, clinical outcomes, and safety?

Routine standardized pain assessment is usually implemented as part of a broader effort to coordinate pain management, particularly for post-operative patients. Usually, it is not possible to isolate timing and frequency of assessment from other components of these programs, which are discussed below in Key Question #2.

In medical inpatients with acute pain, does routine assessment of pain (for example, as the 5th vital sign) affect choice of treatment, clinical outcomes, and safety (Arrows 1a and 1b)?

We found no evidence that directly linked the timing, frequency, or choice of measure for assessment with the timeliness, choice, or safety of treatment specifically in medical inpatients. In the postoperative setting, routine numerical assessment of pain intensity increased utilization of intravenous analgesics and patient-controlled analgesia26 and improved patient and staff satisfaction with pain management, but had unclear effects on pain severity and length of stay. In the emergency department, the addition of a mandated numeric pain scale to the medical record resulted in a significant increase in the proportion of patients in the ED who received analgesia, from 25% before implementation to 35% after implementation (Appendix E, Summary Table 1).27 However, the extent of use on a medical ward of patient-controlled analgesia, regional analgesia, and specialized procedures is not well-documented, and experience in the postoperative and emergency care should not be generalized to this setting.

Does the choice of assessment measure affect choice of treatment, clinical outcomes, and safety?

As described above, since the 1980’s there has been almost universal agreement that routine assessment of self-reported pain intensity is a better measure than pain assessed by a nurse or physician. This is because providers underestimate the severity of patients’ pain in as many as half of cases. The disparity is greatest (60–68%) among patients with severe pain, and lowest (28–36%) among patients with mild pain.28, 29 Routine assessment is encouraged because many patients, especially those who have cognitive impairment, do not always mention pain unless asked.

To be suitable for routine use as a vital sign, a self-reported pain assessment method must be simple to administer, easy for patients to understand, and responsive to changes in pain over time. Table 1 describes the most commonly used pain assessment measures. In case series, these measures have high internal consistency (Cronbach α 0.85 or greater) and at least fair test-retest reliability (r>0.5) in alert, cognitively intact individuals.17, 23, 30 They are highly correlated with one another in such individuals, subject to patients’ preferences for visual, numerical, or verbal descriptions and their willingness to use them. However, none of these assessment measures is intended to diagnose the cause of pain, and none are perfect across the entire spectrum of etiologies, pain types, comorbid conditions, and patient preferences encountered in a general medical ward.

Table 1. Self-Assessment Pain Measures.

Table 1

Self-Assessment Pain Measures.

The single dimension measures assess pain intensity. A 10-point verbal numeric rating scale (VRS or VNRS) is used widely within the VA health care system. Like all of these measures, the VRS has been evaluated more thoroughly in chronic pain and long-term care settings than in acute care settings, although there is one evaluation in medical inpatients undergoing common procedures.31 That study compared a ten-point (N = 100) and five-point scale in 30 inpatients and found that the five-point scale exhibited better subject discrimination between experiences.

It is important to note the absence of evidence or consensus on what constitutes the minimal clinically important difference (MCID) for acute pain management in the hospital setting. The minimal clinically important difference is “…the smallest difference in score in the domain of interest which patients perceive as beneficial and which would mandate, in the absence of troublesome side effects and excessive cost, a change in the patient’s management.”32 The MCID helps define a clinically significant response. A systematic review of pain intensity measurement found that the MCID was defined consistently across studies in chronic pain patients,33 but this is not the case for acute nonsurgical pain. Determining the MCID for the VRS used in the VA system is a first step in studying and improving inpatient pain management.

Do protocols for assessing pain improve outcomes?

Many algorithms for assessing pain intensity and acting on the information are in use (for an example, see Figure 2.) Most algorithms directly link the intensity of pain to specific therapeutic actions, such as rapid administration of IV opioids.

Figure 2. Inpatient Nursing Acute Pain Algorithm.

Figure 2

Inpatient Nursing Acute Pain Algorithm.

We found no evaluations specifically of the effect of algorithms, preprinted orders, clinical pathways, or other protocols for assessing pain in the target population. In most cases, these algorithms are part of larger, institution-wide strategies to improve pain management. Although routine standardized assessment of self-reported pain severity is the cornerstone of these efforts, it is not possible to separate the effect of the assessment component from that of other components of these programs, such as an acute pain management service. The effect of these programs is addressed in Key Question #2.

With respect to safety, a study in cancer patients found that opioid-related oversedation and other adverse effects increased substantially after implementation of pain assessment on a numerical scale routinely with other vital signs.34 This was the only study we identified that looked specifically at the association of routine use of numerical pain rating and adverse treatment effects. It was a retrospective review of records of patients who had experienced an adverse drug effect at the H. Lee Moffitt Cancer Center and Research Institute before (~1999) versus after (2002) implementation of a numerical pain treatment algorithm (Figure 3). Following implementation of the algorithm, there was a 2-fold increase in the risk of opioid oversedation (RR 2.22, 95% CI 1.07–4.60), corresponding to an incidence from 11.0 per 100,000 inpatient hospital days to 24.5 per 100,000 inpatient hospital days post-NPTA (P < 0.001).

Figure 3. Pain Algorithm evaluated in Vila et al.

Figure 3

Pain Algorithm evaluated in Vila et al.

In the outpatient medical setting, VA has instituted several measures to improve pain management, including routine standardized assessment (or pain as the fifth vital sign), audit and feedback to clinical staff, specialist-level pain consultation services, nurse-level pain services, and palliative care services. A retrospective chart review study35 and a prospective diagnostic test evaluation36 cast doubt on the effectiveness of these interventions and on the accuracy of routine pain assessment, respectively, in the VA outpatient setting.

Are there gaps in quality even when pain is assessed routinely?

We did not identify any studies of the timing or frequency of assessment of pain that focused on medical inpatients. However, evaluations conducted in the emergency room are relevant to medical inpatients, because patients headed for nonsurgical, noncancer wards are less likely to get adequate attention in the emergency room.

Surveys conducted in the late 1990’s37, 38 as well as more recent ones,39 suggest that pain in emergency room patients is underdiagnosed and undertreated. . Potential risk factors for delayed or inadequate analgesia include female sex, less severe pain, and daytime admissions. Instituting routine assessment of pain, usually with an educational component, improved rates of assessment and treatment.40, 41 In a University-based, single-institution, retrospective chart review study comparing outcomes in 521 medical encounters before and 479 after introduction of routine pain assessment of all patients in an emergency department, the addition of a mandated numeric pain scale increased the proportion of patients who received analgesia from 25% before implementation to 35% after implementation (p<0.001).27 The time from triage to administration of analgesia improved on average from 152 to 113 minutes (but p>0.05). The standard triage form was revised to include a verbal numeric pain scale ranging from 0 to 10 in the vital signs section, and pain was measured at the same time as vital signs. The series included patients who presented with renal colic, extremity trauma, headache, ophthalmologic trauma or soft tissue injury (Appendix E, Summary Table 1).27 A retrospective before-after study at a single hospital had similar results.42

Several chart review studies conducted in emergency departments focus on gaps in quality that remain even after institution of system changes. In the Nelson study just described, for example, patients with diagnostic uncertainty were less likely to receive analgesia compared with patients who received no workup (27% v. 34% respectively, p=0.0220). In a large, retrospective series from an Australian ED, patients who had a lower-priority triage score were nine times as likely as others to have a delay in treating pain; advanced age (>80 years) and admission to hospital were also associated with delays.43 Documentation and treatment of pain deteriorates when the ED is busy (Appendix E, Summary Table 2).44.45

Specific Condition

Abdominal Pain

Treating acute abdominal pain has traditionally been delayed until after evaluation by a surgeon, for concern that analgesia may alter the findings of physical examination, leading to misdiagnosis and management errors. A 1996 survey of 131 general surgeons in Iowa determined that 89% preferred to withhold analgesia for patients with acute abdomen until examined by a surgeon.46

In fact, there is good evidence that analgesia for acute abdomen is not only safe but beneficial because it facilitates more accurate diagnosis by localizing physical signs and allowing for more detailed examination by reducing patient stress.47–49 More liberal use of analgesia has become common in practice. In a 2003 survey of ED physicians in 60 hospitals, 98.3% responded that it is the practice of their ED to administer narcotic analgesia to patients with acute abdomen prior to surgical consultation. Only 15.3% indicated that it is their practice to always verbally inform the surgeon prior to dosing the patient, and 49.2% reported the belief that analgesics aid in diagnostic accuracy.50

In a recent, good-quality systematic review and meta-analysis (Ranji et al), opioid administration had a negligible impact on clinical management and operative decision.51 The review included 12 placebo-controlled RCTs of opioid analgesia in children and adults, reporting a total of 15 drug/dose comparisons. The combined findings of 11 comparisons from 9 studies in adults revealed a non-significant increase in changes in the physical examination with opioid administration, with a summary RR of 1.51 (95%CI 0.85 – 2.69). There was significant heterogeneity among the studies, and pain relief reported by the opioid group did not significantly differ from placebo in 3 of the comparisons. Most studies did not distinguish between potentially beneficial changes such as improved localization of tenderness and potentially harmful changes such as changes in peritoneal signs. Only 2 studies (including a study in children) specified that loss of peritoneal signs after analgesia occurred in 5.6% to 18.7% of patients with opioids, compared with 2.6% to 7.7% of those in the control group.

In an analysis of diagnostic accuracy in 4 adult studies, there was no significant change in the rate of incorrect management decisions with opioids compared with placebo (+0.3% absolute increase; 95%CI −4.1% to +4.7%). Analgesia was adequately greater than placebo in these studies, and no significant heterogeneity was found. The frequency of possible unnecessary surgeries was similar between opioid and control groups (7.6% v 7.9%). Meta-analysis showed non-significantly fewer unnecessary surgeries among patients with opioids. The reviewers concluded that opioid administration appears to have negligible impact on clinical management, in that 909 patients would need to receive opioids to result in 1 potential management error.51 A trial intravenous morphine vs. placebo, published too recently to be included in the Ranji review, supported these findings.52

Waiting for a surgical consultant is only one cause of delay in treating abdominal pain. One systematic review51 and one primary study53 examined the timing of assessment and analgesia for acute abdominal pain. Three studies examined the relation of severity of pain, ED crowding, and other factors to timing of assessment and treatment (Appendix E, Summary Table 2).39, 43, 44 Immediate referral to surgery when the patient with acute abdominal pain comes to the ED reduces, but does not eliminate, delay in analgesia. A 2004 study in such a setting examined the factors associated with waiting time from prescription to administration of analgesia among 100 consecutive patients presenting with acute abdomen at a hospital in the UK.53 Despite having direct access to an on-call surgical service, thus eliminating the referral delay and the need to withhold analgesia in the interim, the administration of analgesia to patients in this setting was heterogeneous. Sixty-seven percent of patients received analgesia within 1 hour, and 22% waited 2–14 hours after presentation. The study found that severe pain was more likely to be treated quickly, that females had a longer mean wait time than males (129 min v. 69 min, p=0.09), and patients admitted at night waited less time (mean 76 min) than those during the day (mean 114 min). The timing of analgesia was not associated with clinical diagnosis or patient age. Diclofenac was the most commonly prescribed analgesic (37%), followed by pethidine (26%). No patients received analgesia intravenously, and 80% received analgesia through the intramuscular route. Nearly a fourth of patients reported that the analgesia received was inadequate.

Key Question #2. How do the timing and route of administration of pain interventions compare in effectiveness, adverse effects, and safety in inpatient care settings?

In general, pain in medical inpatients is managed by the primary team, with involvement from an acute pain team on a consultation basis. There are no programs directed mainly at improving pain management in medical inpatients who do not have cancer and are not suffering from a terminal disease. For clinicians, one of the main clinical management questions is when to use pain and palliative care consultants for such patients, and whether they improve outcomes in this setting. Another important question is whether use of PCA and other modalities improve control of pain and satisfaction of patients and staff.

Do acute pain management teams and other institutional initiatives improve effectiveness, adverse effects, and safety in medical inpatients?

Most institution-wide efforts to improve pain assessment and management aim to influence the timing and route of administration of pain interventions. As mentioned earlier, it is usually not possible to isolate the effect of administration of treatments from other elements of multifaceted programs. However, it is worth examining the overall effects of these programs and their effect on how treatments are administered.

Elements of institution-wide interventions vary, but most incorporate a majority of the elements listed in Table 2. 19 For example, the VHA/Institute for Healthcare Improvement (IHI) Pain Management Collaborative, employed system-wide strategies to modify existing pain assessment and management practices within the VHA.16 Seventy teams from 22 VISNs throughout the U.S. participated in the 6-month joint Collaborative, with the following measurable objectives: to reduce the prevalence of severe pain by 25%; increase assessment such that 100% of patients will have their pain assessed; increase by 20% the documentation of plan of care among patients with a pain score >=4; and to provide appropriate pain management education to at least 50% of patients with a pain score of >=4. The strategic goals included: 1) provision of a systemwide VHA standard of care for pain management; 2) assurance that pain assessment is performed in a consistent manner and that pain treatment is prompt and appropriate; 3) the inclusion of patients and families as active participants in pain management; 4) continual monitoring and improvement in outcomes of pain treatment; 5) an interdisciplinary, multi-modal approach to pain management; and 6) assurance that clinicians practicing in the VA health care system are adequately prepared to assess and manage pain effectively.

Table 2. Some elements of institution-wide efforts to improve pain assessment and management.

Table 2

Some elements of institution-wide efforts to improve pain assessment and management.

The VHA/IHI Collaborative used learning sessions, monthly team conference calls, and monitoring of results and sharing of improvement methods via Internet. The learning sessions emphasized reliable and standardized measurement, strategies for interval sampling, and strategies for plotting and analyzing data. Data collection methods were specific to each clinical setting: for inpatients and long-term care settings, at least 2 patients each day were selected randomly; for Emergency Departments, teams could either select time points (e.g. 10AM and 3PM) or to select 2 charts randomly each data for data abstraction; for ambulatory settings, medical records of patients who visited during the month were sampled, excluding patients who were being seen for the first time in primary care. The project did not include a concurrent control group. Three of the 4 objectives were met, and most of the improvements occurred during the first 3 months of the collaboration, and sustained during the next 3 months. The goal of 100% patient assessment was not met, although the frequency of pain assessment increased from 58% to 85% of patients during the collaboration period.

Most primary studies in this review focused on postoperative or cancer pain, and were uncontrolled (see next section.) We identified one controlled trial, published since this review, which included medical inpatients. It found that a multifaceted intervention improved assessment of pain, but did not affect pain intensity or duration.54 The trial enrolled a random sample of 3964 English-speaking, cognitively intact subjects admitted to matched medical/surgical units (3 general medicine, 2 general surgery, 2 specialty surgery, 1 oncology, and 1 mixed oncology/general medicine) at Mount Sinai Hospital in New York. Usual care required that pain be assessed at least once per shift using a 4-point scale. The intervention included, in phases: education, standardized pain assessment using a 1- or 4-item (enhanced) pain scale, audit and feedback of pain scores to nursing staff, and a computerized decision support system to guide analgesic prescribing. The enhanced pain assessment asked patients to rate current pain, worst pain, pain relief, and whether the level of pain was acceptable on 4-pt scales. Patients were interviewed within 48 hrs of admission and then once daily. An enhanced pain assessment that asked inpatients to rate current pain, worst pain, pain relief, and whether the pain level was acceptable on 4-point scales increased the likelihood of pain assessment, improved documentation of pain, and resulted in increased analgesia prescribing.54 The percentage of patients who received at least 1 pain assessment per day increased from 32.1% with the standard pain assessment to 79.3% when the enhanced pain scale was combined with the CSS, and to >80% when combined with audit and feedback.

Although the enhanced pain scale and other interventions improved pain assessment and increased analgesic prescribing, the intervention did not alter severity of pain. The percentage of patients who had 72–96 hours of persistent pain following study enrollment and overall mean pain scores remained relatively constant across both blocks and all phases of the study.

Do acute pain management teams and other institutional initiatives improve effectiveness, adverse effects, and safety in other settings?

In patients with cancer, most programs include one or more of the following components: professional and patient education, instituting regular pain assessment (pain as a vital sign), audit of pain results and feedback to clinical staff, computerized decisional support systems, and specialist-level pain consultation services.55 Techniques for improving assessment and documentation of cancer pain included graphic recording on bedside charts, standardized pain assessment flow sheets, incorporation of both formal education and assessment tools, and institution-wide multidisciplinary programs. A 2007 systematic review identified 10 studies of these interventions; several of them included at least some medical inpatients who did not have cancer. These studies demonstrated that routine pain assessment improved patient and staff satisfaction with pain management and improved documentation, but did not improve overall pain scores or pain severity. 55

There is much more evidence from the post-operative setting. A 2003 systematic review on institutional approaches to pain assessment and management, conducted in Australia by the Department of Public Health and the National Institute of Clinical Studies (NICS) identified 3 comparative studies and 29 before-and-after studies of the effect of institutional pain management programs on treatment and patient outcomes.19 Most of these programs implemented routine numerical pain assessment and some form of a pain management team. Overall, interventions improve pain assessment indicators such as use of pain intensity scales, pain flow sheets, a pain plan of care, and documentation of location and quality of pain, and response to treatment. Interventions also increase administration of scheduled (rather than prn) pain medication, reduce use of the IM route, and increase the use of intravenous analgesia and of PCA.

While pain management teams and other system interventions improved the timeliness and frequency of pain assessment, evidence for improvements in pain outcomes was conflicting. The NICS review included 10 studies on dedicated service strategies.19 These included 9 studies on the introduction of pain management teams, most commonly an Acute Pain Service, and 1 before-and-after study of the introduction of a pain monitoring specialist. Two studies were multi-center studies that compared an intervention group with a control group where standard patient care was maintained (i.e. did not introduce a dedicated pain management service).

The results of the controlled studies suggest that Acute Pain Services in tertiary settings reduce the intensity of pain experienced by patients and improve their functional ability, although these effects were not always determined to be clinically important. The use of a dedicated service strategy increased use of patient-controlled analgesia and IV opioids, while IM administration decreased substantially. Prescribing practices also appeared to be altered in that NSAID and paracetamol use increased significantly. A statistically and clinically important improvement in patient satisfaction with pain management was also observed. Analgesia-related adverse effects, such as nausea, vomiting, sedation, diarrhea, and hypotension, appear to be reduced after the introduction of a dedicated service strategy.

The review also examined multi-level strategies, in which strategies were developed to modify existing pain assessment and management policies, procedures, and practices at all levels of the institution. Most multi-level strategies included staff education and the use of standardized pain assessment methods. The integration of pain assessment as a “5th vital sign” was included in two studies. The effects of multi-level strategies on pain reduction, functional ability, and patient satisfaction were variable. Only one study of a multi-level strategy used a control group. The body of evidence on institutional approaches to pain assessment and management was of limited quality overall.19

In summary, institutional interventions improved pain assessment and documentation and staff awareness of pain, and increased use of analgesics. There was only poor-quality evidence that these programs improved safety. Most importantly, the programs’ effect on patient levels of pain was inconsistent; in the relatively higher-quality studies, programs did not improve pain.

How does coordination with the patient’s primary care physician affect outcomes?

We found no evidence about the value of coordinating care with the patient’s primary care physician.

How does the choice of treatment modality affect effectiveness, adverse effects, and safety in inpatient care settings?

Treatment options for pain management are listed in Table 3 below.1, 17, 20 There is a glaring lack of comparative studies of different agents and methods of administration in the general inpatient setting.

Table 3. Treatments for acute pain.

Table 3

Treatments for acute pain.

Effectiveness and safety of patient-controlled analgesia (PCA)

PCA refers to methods of pain relief that allow a patient to self-administer small doses of an analgesic agent as required. The concept of PCA was introduced in 1970, but the method did not become popular until the 1980’s, when improvements in infusion pump technology made wider use of PCA in post-operative patients feasible. 56

The vast majority of studies on the use of PCA pertained to postoperative pain or acute pain due to exacerbation of chronic medical conditions such as sickle cell crisis or cancer. PCA has also been evaluated in patients with fractures or other traumatic injury (see Appendix E, Summary Table 3).57–60

Early trials of PCA compared it with intermittent, intramuscular opioid injections administered by a nurse. More recent trials compare PCA to epidural analgesia. All of these trials were conducted in the setting of post-anesthesia care units or, subsequently, a (postoperative) surgical ward.

In post-operative patients, regional and epidural analgesia have been compared with intravenous opioids, administered intermittently or by patient-controlled analgesia (PCA). Recent systematic reviews identified surgical conditions in which regional analgesia provides superior pain relief compared with opioids, but could not confirm or deny a relationship between the choice of postoperative analgesic techniques on major mortality or morbidity.61, 62 Other systematic reviews have found that, after surgery, patients using PCA consumed higher amounts of opioids and had better pain control and higher satisfaction than patients treated with prn or scheduled opioid treatments, with no higher incidence of most side effects 63–65 Comparative evidence is generally favorable to regional analgesia for certain surgeries, but overall evidence comparing continuous epidural analgesia and PCA is not conclusive. 66–70

The evidence summarized in these reviews has low applicability to medical inpatients, where the course of pain as well as staffing and monitoring procedures differ from those of the post-anesthesia unit. There is almost no information on the use or safety of PCA in a medical ward setting. A fair-quality, non-blinded RCT compared the effectiveness of morphine delivered by nurses as needed versus by IV-PCA in 86 patients who presented to the ED with a pain score of 7+ due to traumatic injury, most commonly fracture (74% in the PCA group, 53.4% of controls), and found that pain relief and patient satisfaction were similar between the treatment modalities.58 Pain scores and physiological measurements were collected at 0, 5, 15, 30, 45, 60, 90, and 120 minutes. Although the PCA group used more than twice as much morphine than controls (mean total 18.83 mg vs. 7.65; mean usage rate 7.26 mg/h v. 4.03 mg/h), the mean VAS pain scores were the same (4.8) in treatment both groups, and there were no significant differences between groups in the satisfaction questionnaires. An area-under-the-curve analysis of VAS scores confirmed no significant difference between groups. The investigators noted the limitation that nurse behavior might have been influenced by the presence of researchers to optimize delivery of pain relief, given the non-blinded design of the study.

Most of the evidence on the adverse effects of PCA was derived from the experience of patients with postoperative pain or chronic conditions.17, 71–73 The opioid-related side effects from IV PCA are the same as those for intermittent opioid analgesic regimens, and include respiratory depression, sedation, constipation, pruritis, nausea, and vomiting. Patient factors and misuse of the PCA device by family members, however, may lead to the inappropriate use of PCA,71 and cases of oversedation caused by equipment programming mishaps have been reported.73

In patients with acute thoracic pain from traumatic injury, analgesia with IV-morphine PCA was equivalent to morphine administered PRN in one study58 and to nebulized morphine in another study,57 but inferior to epidural analgesia in 2 studies.59, 60 Most patients in these studies had suffered fractures, though the populations varied in the type and severity of the injuries.

The lack of data on the use and safety of PCA in medical patients is concerning, for there are protocols for post-op management but not for medical patients. Pain improves predictably in the post-operative period, making weaning protocols easier to implement. Also, use of PCA is integrated into staff routines and monitoring protocols. None of these characteristics apply to medical inpatients.

Specific Conditions

Renal colic and biliary stone pain

Most evidence about treating renal colic is old and addresses whether to use IM, SC, or IV analgesics. The main findings, discussed in more detail below, are (1) NSAIDs provide effective analgesia for acute renal colic, and act more quickly through the IV route than by IM or PR 2) Opioids provide analgesia that is equivalent to NSAIDs but result in a higher incidence of vomiting and other adverse events, particularly pethidine 3) Hydromorphone provided superior pain relief and led to fewer hospital admissions compared with meperidine in one study. 4) Intramuscular injection of opioids should not be used because it causes more discomfort and complications than subcutaneous injection and relieves pain no faster. Many studies excluded patients who had negative followup investigations for biliary stone or renal calculi, which may limit the applicability of findings to all patients presenting with pain from these suspected causes (see Appendix E, Summary Table 4).

A 1998 systematic review of NSAIDS included 3 trials in renal colic in which the same drug was compared by different routes.74 Two trials compared 50 mg intravenous vs. 100 mg rectal indomethacin.75, 76 The 3rd trial compared IV with IM administration of dipyrone and diclofenac in 6 comparisons: dipyrone 1g or 2g IM + placebo IV; dipyrone 1g or 2g IV + placebo IM; diclofenac 75 mg IM + placebo IV; diclofenac 75 mg IV + placebo IM.77 In all 3 trials, the NSAID acted more quickly through the intravenous route than rectal or intramuscular. The difference was significant, but evident only during the first 10 to 20 minutes.

A 2007 Cochrane review of NSAIDS vs. opioids for acute renal colic found that both NSAIDs and opioids provide effective analgesia in acute renal colic, but opioids, particularly pethidine, result in a higher incidence of vomiting and other adverse events.78 Five different NSAIDS (diclofenac, indomethacin, indoprofen, ketorolac, tenoxicam) and 7 opioids were studied in 20 trials from 9 countries with a total of 1613 participants.78 The intramuscular route was most commonly used for each drug type (10 trials), followed by the intravenous route (7 trials). Patients receiving NSAIDs reported lower pain scores than patients receiving opioids in 10 of 13 studies, though the differences were small. Pooled results on efficacy were not available due to heterogeneity between studies. Patients treated with NSAIDs were significantly less likely to require rescue analgesia (RR 0.75, 95%CI 0.61–0.93). A higher incidence of adverse events occurred with opioids than with NSAIDs in the majority of trials, and pethidine in particular was associated with a higher rate of vomiting. Most studies included only participants with renal calculi confirrmed on subsequent testing and excluded patients with negative results on followup tests. These exclusions may limit the applicability of findings to all patients who present with the clinical picture of renal colic.

A 2007 Cochrane review of hydromorphone in acute and chronic pain79 identified one trial in patients with renal colic,80 and one trial in patients with biliary stone pain.81 In a fair-quality double-blind RCT, patients with renal colic were randomized to receive either 50 mg meperidine or 1 mg hydromorphone IV, and their pain scores were measured on a 10-cm VAS were recorded at t=0, 15, 30, 60, and 120 minutes.80 Patients who received hydromorphone achieved more pain relief, required less rescue medication, underwent fewer IV pyelograms, and avoided hospital admission more frequently than did patients who received meperedine. A poor-quality unblinded trial in 42 patients with biliary stone pain compared subcutaneous injection of 1mL dihydromporphinone with 50 mg indomethacin IV.81 Eight initially enrolled patients were excluded from analysis because follow-up X-ray or ultrasonogram investigations were negative for these patients. Pain was evaluated by VAS at baseline and at 10 and 30 minutes after drug injection. Indomethacin and dihydromorphinone were equally effective at reducing pain in patients with acute attacks of biliary stone pain. VAS scores at 0, 10, and 30 minutes were 71.8, 44.1, and 14.2 in the dihydromorphinone group, compared with 68.5, 32.4, 15.8 in the indomethacin group, and the differences between groups were not statistically significant. No serious side effects were observed with either drug. The lack of patient blinding was a limitation in this study, and the exclusion of patients who were later found to be negative for biliary stone may limit applicability of findings to all patients who present with biliary stone pain.

Phantom Limb Pain

Phantom limb pain is a form of neuropathic pain perceived in the missing limb after amputation that is distinct from pain in the residual portion of the limb or stump, and other non-painful sensation of the missing limb. In trials of perioperative interventions, the prevalence of phantom limb pain after amputation among control subjects ranged from 56–82% at day 7, 39–73% at 6 months, and 27–78% at 12 months.82 A survey in 1980 identified more than 50 different therapies in use for the treatment of phantom limb pain 83, suggesting limited consensus on the effectiveness of treatment.

A good-quality systematic review sought to determine the optimal management of acute and chronic phantom limb pain, and identified 12 controlled trials that reported phantom pain as an outcome (see Appendix E, Summary Table 5).82 The included studies were published between 1985–1997, and the 12 trials included a combined total of 375 male and female patients, ages 47–75. Trials were included if they involved a control group and examined any intervention for PLP, regardless of methodology. Interventions involving treatments before and during the amputation were included, as well as treatments for chronic pain.

Trials were divided into 2 groups based on the timing of intervention (early vs. late): 8 trials of preoperative, intraoperative, and early postoperative interventions at <2 weeks, and 4 trials of late (>2 weeks) postoperative interventions. Among the 8 early intervention trials, 3 used epidural anesthesia, 3 used regional nerve blocks, 1 used intravenous calcitonin, and 1 used transcutaneous electrical nerve stimulation (TENS). Controls in these studies received a placebo consisting of a saline infusion or epidural anesthesia consisting of on-demand opioid analgesia. The 4 trials of late postoperative interventions studied the use of TENS, a crossover study comparing the use of a metal threaded sock (Farabloc) vs. no treatment, vibratory stimulation vs. placebo stimulation, and intravenously infused ketamine vs. saline. Subjects served as their own controls in these studies, and in most of the early treatment studies the control group received active treatment with opioid analgesics. No trials examined commonly recommended oral drugs, such as membrane stabilizers or tricyclic antidepressants.

Among the 8 early intervention trials, 3 trials of preoperative epidural pain relief reported mixed results. Three other trials assessed sciatic or posterior tibial nerve blocks with perineural and intraneural bupivacaine blocks during or immediately after surgery, and found no differences in pain between the intervention and control groups in the postacute period, measured at various timepoints up to 12 months after surgery. In a trial of calcium calcitonin (200 IU) and a trial of early TENS, reduced phantom limb pain was observed in the early postoperative period but not in longer-term followup. In trials of the late postoperative phase, Farabloc, low-frequency TENS applied to the ear, and ketamine provided a modest short-term reduction in phantom limb pain and paresthesia. Another late-treatment trial examined TENS at the site of pain but findings were inconclusive. Several studies were limited by small sample sizes, and high loss rates from dropouts, re-amputations, and mortality.

The review82 concluded that there is little evidence from randomized trials to support any particular treatment of phantom limb pain either in the acute perioperative period or later. Evidence on preemptive epidurals, early regional nerve blocks, and mechanical vibratory stimulation provides inconsistent support for these treatments.

Studies of the effectiveness of other treatments for phantom limb pain were identified in the ANZCA report.17 Early postoperative infusion salmon calcitonin was effective at reducing phantom limb pain compared with placebo, in a double-blind crossover trial (n=21). One week after the first treatment, 90% of patients had pain relief of more than 50%, 76% were completely pain free, and 71% never experienced phantom limb pain again. One year later, 8 (62%) of the 13 surviving patients still had more than 75% phantom limb pain relief.84 In single studies, ketamine,85 oral slow-release morphine,86 IV infusion of morphine,87 and gabapentin88 were also effective in reducing phantom limb pain. Lidocaine had no effect on phantom limb pain, but significantly reduced stump pain in one study.87

The ANZCA report also identified three studies of interventions to prevent phantom limb pain.17 A small observational study found that in 14 patients given a bolus dose of ketamine followed by an infusion, begun preoperatively and continued for 72 hours postoperatively, the incidence of severe phantom limb pain was reduced, compared with no ketamine in 14 historical controls.89 An RCT that compared perioperative intravenous ketamine infusion to saline infusion in 45 patients found the incidence of phantom limb pain at 6 months post-amputation was lower in the ketamine group than the control group (47% v. 71%) but the difference was not statistically significant.90 A review of the efficacy of perioperative epidural analgesia determined that the incidence of severe of phantom limb pain was reduced though not completely abolished 12 months after amputation (NNT = 5.8, 95% CI 3.2–28.6).91 A non-pharmacological treatment for phantom limb pain was effective in a study of sensory discrimination training.92

Overall there is a paucity of evidence to guide specific specific treatment of phantom limb pain. Single studies showed evidence of the effectiveness of various therapies (calcitonin, morphine, ketamine, gabapentin, and sensory discrimination training), and perioperative studies of ketamine and epidural analgesia showed reduced incidence of phantom limb pain, but these studies were limited by small sample size.

Key Question #3. For inpatients with impaired self-report due to any of several factors, including delirium or confusion, pre-existing severe dementia, closed head injury, stroke, and psychosis, how do differences in assessment and management of acute pain affect clinical outcomes or safety?

Cognitive impairment complicates assessment and treatment of pain. Several studies have reported underestimation by providers of pain in cognitively impaired patients.93 Most studies of pain in cognitively impaired individuals were conducted in nursing homes,94 where chronic dementia is the most prevalent cause of cognitive impairment. A large bibliography of articles, guidelines, and quality indicators for pain management in nursing homes is available at

Briefly, most guidelines for the management of pain in patients with cognitive impairment emphasize principles set forth in a 1993 article by Parmelee95 and modified by others96–98:

  1. Assess all patients for cognitive impairment using a Mini-Mental State Examination (MMSE).
  2. Mildly impaired individuals are almost as able as cognitively intact individuals to accurately report their pain.
  3. Impaired patients with communication skills will not neglect reporting of pain when queried specifically.
  4. In moderately and severely impaired individuals, try several different scales. Most moderately and severely impaired individuals can understand at least one pain assessment scale (verbal, horizontal visual, or faces)99,100
  5. Self-report can also be improved by other strategies, such as asking the patient to describe painful events that have been experienced that correspond to different pain intensities. Patients can be prompted by asking about common events that occur in a clinical setting such as needle sticks. 98
  6. Markedly impaired patients report less intense pain and a smaller number of pain complaints than the mildly impaired.
  7. For patients who are impaired and deny pain or do not respond to questions about pain, use an observational assessment tool to screen for pain.

This guidance, intended for use in nursing homes, has limited applicability to the medical inpatient setting, where delirium is a much more common cause of cognitive impairment. Buffum reviewed the sparse literature on assessing and managing pain in delirious patients and identified a long list of research gaps and priorities.97 Except for some surveys of the prevalence of delirium among inpatients (cited in Buffum), we identified no relevant studies of pain assessment or management in patients with delirium.

Most studies of pain and cognitive impairment focus on assessment. There is fair evidence from one prospective cohort study99 that most cognitively impaired individuals can understand at least one self-assessment measure. This study was conducted in a series of 160 consecutive inpatients, recruited from 2 Swiss hospitals and referred for dementia consultation. The investigators administered 4 self-assessment scales (horizontal VAS, vertical VAS, faces pain scale, verbal rating scale) and one observational rating scale (the Doloplus scale, developed to assess pain in older people with communicative disorders).99 Patients were considered to have understood a scale if on both self-assessments the patient was able to explain it use and could correctly indicate which position on the scale corresponded to no pain at all, and which position corresponded to the most severe pain. Comprehension of at least 1 scale was demonstrated by 40% of patients with severe dementia, 90% of patients with moderate dementia, and 97% of patients with mild dementia. The correlation between the self-assessment scales was high (Spearman’s rs = 0.81–0.95, p<0.001). The Doloplus observational rating scale correlated only moderately with self-assessment by the patient (Spearman’s rs = 0.31–0.40, p<0.05), and the strength of the correlations did not increase in patients with moderate to severe pain. The investigators in this study concluded that the majority of hospitalized patients with dementia can reliably use self-assessment pain scales, and that observational scales tend to underestimate pain intensity and should be reserved for patients who have demonstrated that they cannot complete a self-assessment. One limitation of this study is that none of the severely demented patients who could demonstrate appropriate use of the self-assessment scales reported experiencing any pain. This means that, at best, the authors’ conclusions about the usefulness of the self-assessment scales may apply only to distinguishing between some pain and none—that is, the study provides no evidence about the scaling properties of self-assessment scales in severely demented patients.

Another study compared the psychometric properties of 4 established pain scales between moderately impaired (MMSE 13–21, n=42) and cognitively unimpaired (MMSE 22–30, n=33) hospitalized older adults (mean age 76 yrs) with pain at admission.101 Patients participated in the study for 14 days. On days 1–7, participants were visited 3 times per day and asked to rate their current pain on each of 4 scales: 1) a 5-pt verbal rating scale; 2) a 7-pt faces scale; 3) a horizontal 21-point box scale; 4) 2 vertical 21-point box scales. Patients were also asked to make retrospective ratings at the end of the day and at weekly time points, with reference to usual, worst, and least pain levels, using each of the 4 scales for each rating. The study sought to determine the effect of mental status on pain rating; scale redundancy, scale reliability, validity/current pain bias (whether a retrospective pain rating represents the actual pain experienced over a given period of time); and whether retrospective pain ratings (memory of pain) were biased by current pain to indicate greater than the average pain experienced by the patient. The horizontal 21-pt box scale emerged as the best scale with respect to psychometrics and validity, regardless of mental status. Little evidence of response perseveration was found on any of the tests. Pain intensity did not vary with mental status. The cognitively impaired group had difficulty with the ratings of least pain, showing a high level of bias in the extent to which memory of pain was influenced by current pain. The investigators concluded that older, cognitively impaired patients are able to rate pain reliably and validly.

Three recent systematic reviews102–104 and part of a broader guideline for assessing pain in the elderly23 examined studies of observational methods to assess pain in cognitively impaired adults (Table 4). These instruments rely on examiners to observe facial features and behavior in order to guess how much pain a patient has.

Table 4. Pain observation scales. From van Herk et al.

Table 4

Pain observation scales. From van Herk et al.

All three reviews concluded that among the numerous scales of nonverbal behavioral pain indicators that currently exist, none are more reliable or valid than others, and none are convincingly appropriate for use in this population. A total of 13 scales were identified in these reviews. Taking all 3 reviews together, the PACSLAC and PAINAD appeared to have the best psychometric properties. Unfortunately, as van Herk and colleagues note, the value of these measures in decision-making is unclear because cutoff values for these scales have not been established.

It is important to note that there is no gold standard for judging the validity of these measures. Most evaluations reported the psychometric properties of these measures rather than their validity.30 Validity was assessed as agreement with self-report or report of relatives to assess validity; these comparisons are of limited value (if self-report were known to be reliable, there would be little need for using an observational measure.)

Key Question #4. For inpatients with dependencies on tobacco, alcohol, stimulant, marijuana, or opioids, how do differences in assessment and management of acute pain affect clinical outcomes or safety?

Addiction, physical dependence and tolerance are common among inpatients. The ANZCA 2005 report17 suggested the following for managing acute pain in opioid-tolerant patients:

  1. Withdrawal from opioids should be prevented by maintenance of normal preaadmission opioid regimens, or appropriate substitutions with another opioid, or the same opioid via another route. Opioid-tolerant patients are at risk of withdrawal if non-opioid analgesic regimens or tramadol alone are used.
  2. Opioid-tolerant patients report higher pain scores and have a lower incidence of opioid-induced nausea and vomiting.
  3. Ketamine may reduce opioid requirements in opioid-tolerant patients.
  4. Intravenous PCA is a useful modality in opioid-tolerant patients, and larger bolus doses ad a background infusion to replace the usual opioid dose may be needed.
  5. Neuraxial opioids can be used although higher doses may be required, and these doses may be inadequate to prevent withdrawal.
  6. Patient education regarding prescribed opioids and communication with the primary physician are advisable upon discharge.

The ANZCA 2005 report17 makes the following suggestions for the management of acute pain in patients with substance abuse disorder:

  1. Management of pain in these patients should focus on prevention of withdrawal, effective analgesia, and symptomatic treatment of affective disorders and behavioral alterations.
  2. Naltrexone should be stopped at least 24 hours prior to elective surgery, and be replaced by multimodal analgesic regimens.
  3. Patients who have completed naltrexone therapy should be regarded as opioid naïve; in the immediate post-treatment phase they may be opioid-sensitivie.
  4. Maintenance methadone regimens should be continued where possible
  5. Buprenorphine maintenance may be continued; if buprenorphine is ceased prior to surgery, conversion to an alternative opioid is required.
  6. There is no cross-tolerance between CNS stimulants and opioids.

The evidence on which these recommendations are based is weak, being derived from case reports, retrospective studies and expert opinion.17

How do the assessment and management of acute pain differ between patients on pre-existing opioid therapy and patients with opiate addiction?

In 2001, the American Academy of Pain Medicine, the American Pain Society, and the American Society of Addiction Medicine issued a statement 105 agreeing upon the following definitions:

Tolerance: “Tolerance is a state of adaptation in which exposure to a drug induces changes that result in a diminution of one or more of the drug’s effects over time.”

Physical Dependence: “Physical dependence is a state of adaptation that often includes tolerance and is manifested by a drug class specific withdrawal syndrome that can be produced by abrupt cessation, rapid dose reduction, decreasing blood level of the drug, and/or administration of an antagonist.”

Addiction: “Addiction is a primary, chronic, neurobiological disease, with genetic, psychosocial, and environmental factors influencing its development and manifestations. It is characterized by behaviors that include one or more of the following: impaired control over drug use, compulsive use, continued use despite harm, and craving.”

The statement also defined “pseudoaddiction” as “patient behaviors that may occur when pain is undertreated,” including a focus on obtaining medications, illicit drug use and deception and other behaviors that may lead clinicians to label them as being “drug seeking.” It also said “a patient who is physically dependent on opioids may sometimes continue to use them despite resolution of pain only to avoid withdrawal. Such use does not necessarily reflect addiction.”

These definitions are not universally agreed upon, and work to harmonize terminology continues. 106 However, these definitions are consistent with the basic concepts that 1) tolerance and physical dependence are normal responses to opioid therapy, but addiction is not; 2) addictive use of medications is associated with aberrant, destructive behaviors such as “persistent sedation or intoxication due to overuse; increasing functional impairment and other medical complications; psychological manifestations such as irritability, apathy, anxiety, or depression; or adverse legal, economic or social consequences 3) addiction is a multidimensional disease with neurobiological and psychological dimensions. Many guidelines say that a history of addiction to opioids or to alcohol is a relative contraindication for prescribing chronic opioids for nonmalignant pain. Guidance on how a history of addiction should influence inpatient management of acute pain is unclear.

The prevalence of addiction among chronic opioid users was unknown.105 Most studies of the prevalence of addiction among patients with chronic pain have used simplistic or outdated criteria for diagnosing addiction, or did not describe their criteria at all.107 Not surprisingly, estimates of the prevalence of addiction varied wildly, from 0.2% to 50%, depending on the investigators’ definition. The apparent prevalence was much lower in studies that used stricter criteria for addiction based on behaviors that are thought to distinguish it from tolerance and physical dependence, and higher in studies that classified patients as addicted if they exhibited “drug-seeking” behavior. While, as a group, the prevalence studies are weak, they do suggest strongly that when a patient on chronic opioid therapy presents with pain, clinicians should not presume that the patient is addicted, and should never diagnose addiction unless there is reason to belief pain control is adequate.

In the literature, there are several lists of signs and symptoms that may be indicators of addiction (as opposed to tolerance and physical dependence.) We found no studies of whether, in acute care settings, clinicians can distinguish addiction from physical dependence or pseudoaddiction. We also found no studies of the discriminant ability of the individual signs and symptoms of addiction, that is, their ability to identify distinct groups of patients for whom different assessment and treatment strategies are most effective.

On the other hand, several instruments intended to screen chronic opioid users for addiction may be helpful in assessing whether relevant signs, symptoms, and behaviors are present. The Pain Medicine Questionnaire and the SOAPP questionnaire have good psychometric properties.107 The CAGE-AID is a modified CAGE which adapts questions about alcohol to drug use (eg “Have you felt you ought to cut down your drinking or drug use?” “Have you felt bad or guilty about your drinking or drug use?” etc.) It has not been tested extensively. None of these instruments has been shown to improve long-term outcomes of chronic nonmalignant pain management, and none has been evaluated in the setting of acute pain in inpatients.

Guidelines for managing post-operative pain specify that initial dosing should be adjusted for patients who take opioids for chronic nonmalignant pain. For the most part, these guidelines for initial dosing have been generalized to patients who have acute pain from other causes, but we did not find any evidence about effectiveness or safety in the target population for this report.

Cover of Assessment and Management of Acute Pain in Adult Medical Inpatients
Assessment and Management of Acute Pain in Adult Medical Inpatients: A Systematic Review [Internet].
Helfand M, Freeman M.
Washington (DC): Department of Veterans Affairs (US); 2008 Apr.

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