Evaluation and Pharmacologic Treatment of Postoperative Pain

Pain after a surgical procedure is inevitable. However, as stated by Haruki Murakami, “Suffering is optional.”

Management of postoperative pain has come a full circle. The Joint Commission recognized the underassessment and undertreatment of pain in 2000 and introduced the concept of pain as the fifth vital sign. However, the emphasis of The Joint Commission on the use of opioids for pain control has been criticized as a contributing factor in the prescription opioid epidemic that the modern world is facing. Enhanced recovery pathways involving multimodal analgesia with emphasis on limiting opioids have become the cornerstone of managing pain in the postoperative setting.

A majority of patients who undergo surgery report inadequate pain control. Causes of ineffective pain control include lack of accurate assessment and patient factors such as fear of adverse effects or addiction from medications. Poorly controlled pain increases the incidence of postoperative complications such as pneumonia, delirium, delayed wound healing, and evolution of acute pain into chronic pain, ^, while optimal pain control improves patient satisfaction and enhances the quality of recovery. ^,

Pain management is an important ethical responsibility of every clinician. Adequate pain control requires finesse to find the delicate balance between minimizing immediate adverse effects and preventing long term dependence on opioids. Many institutions have developed standardized guidelines for perioperative analgesia in the form of enhanced recovery after surgery (ERAS) protocols. The acute pain service is an integral part of most anesthesiology departments, with a focus on providing optimal pain management in the postoperative period. Assessment and management of pain in opioid dependent patients and pain in children are beyond the scope of this chapter and are discussed in Chapters 27 and 28, respectively.

Management of postoperative pain starts with an accurate assessment. Guidelines from the American Pain Society recommend that “ clinicians use a validated pain assessment tool to track responses to postoperative pain treatments and adjust treatment plans accordingly .” Effective pain management takes into account the surgical procedure performed and individual patient factors such as comorbidities and the use of preoperative narcotics. The goal of pain assessment is to determine the analgesic requirements of the patient and if there is a need to change the treatment plan.

Evaluation of pain can be extremely challenging as pain is largely subjective. ^, There are multiple evaluation tools available for postoperative pain assessment. However, most require patient participation, which can be difficult in the immediate postoperative period when the patient is still emerging out of anesthesia.

Comprehensive postoperative pain assessment includes several components. Although severity is the most easily quantifiable measure, attention should be paid to other characteristics of pain, including location, quality, onset, progression, radiation, aggravating and relieving factors, and effects of therapy. Pain symptoms that are at an inappropriate site or of unexpected severity based on the surgical procedure performed should be investigated for causes other than the surgery itself. ^, Unexpectedly high pain can be because of opioid tolerance, anxiety, a new medical problem unrelated to surgery, or a potential complication from the surgery itself.

Evaluation of Pain Using Pain Scales

Numerous self-reported pain scales have been developed to quantify the severity of pain ( Table 25.1 ). Among the most frequently used scales are:

Visual Analog Scale (VAS)
Numeric Rating Scale (NRS)
Verbal Rating Scale (VRS)

TABLE 25.1

Commonly Used Scales for Postoperative Assessment of Pain

Pain Scale	Range	Advantage	Disadvantage
Visual Analog Scale	0–10 (cm) 0–100 (mm)	Sensitive to treatment effect Shows ratio level scoring property	Requires visual motor coordination from the patient
Numeric Rating Scale	0–5(6) 0–10(11) 0–20(21) 0–100(101)	Verbally scored Easy to administer High compliance Sensitive to treatment effect	Lacks ratio level scoring property
Verbal Rating Scale	No pain to most intense pain	Easy to understand Better compliance in elderly	Requires patient familiarity with adjectives Interval between adjectives not equal

Visual Analog Scale

VAS is measured by drawing a 10 cm or 100 mm straight line. This line is anchored at each end by a perpendicular line that represents two extremes of pain—no pain on the left end and most intense pain imaginable on the right end. The patient is asked to make a mark at a point on the line, which represents the patient’s level of perceived pain intensity, and the scale is scored by measuring the distance from the end with no pain to the patient’s mark. The line may be depicted with a horizontal or vertical orientation, though a horizontal line is generally preferred. The VAS has often been recommended as the measure of choice for assessment of pain intensity.

It has been suggested that a single VAS score is probably not the most accurate measure of a patient’s pain but is probably within the range of +/–20 mm. A change of 10 mm out of 100 mm pain VAS is considered the minimal clinically important difference, i.e. the minimal change in a pain VAS score that would indicate a significant change in a patient’s pain intensity, and the VAS of 33 or less signifies acceptable pain control after surgery. ^, VAS is sensitive to treatment effects and shows ratio level scoring properties. ^, The reliability of VAS depends on the patient’s ability to place a mark at the intended spot and requires visual and motor coordination. VAS may be challenging to obtain in patients with cognitive impairment, and freedom of choice provided by VAS could be confusing for some patients.

VAS shows a good correlation with NRS in patients with arthritis. However, its usefulness may be limited in the immediate postoperative period, especially in phase 1 of recovery when the patient may have residual effects of anesthesia, blurred vision, or nausea. Nonetheless, it is a simple, useful, and valid tool to assess and reassess a patient’s pain and response to therapy if the problems intrinsic to the score itself are considered.

Numerical Rating Scale

NRS consists of a numeric scale ranging from 0 to 10, 0 to 20, or 0 to 100. ^, ^, ^, ^, Zero represents no pain, whereas the higher end (10, 20, or 100) represents the most intense pain. NRS can be administered verbally or in a written format. ^, When presented graphically, the numbers are often enclosed in boxes, and the scale is referred to as an 11 or 21-point box scale depending on the number of levels of discrimination offered to the patient. Its advantages include that it is simple, easily understood by the patient, and is easily administered and scored by the caregiver. It is a valid tool with a high compliance rate and good consistency over time, which correlates positively with other measures of pain and shows sensitivity to treatments. ^, The principal limitation of NRS is that it does not have ratio qualities, implying that the difference between two and four and the difference between four and six may not represent equivalent intervals in terms of scaling of the intensity of pain. Its major advantage over VAS is that it can be used in patients with visual impairment by recording verbal responses. One author has described the successful use of a six-point NRS (0-5) during the postoperative period in patients with dementia. The six-point NRS is a simplified version of NRS 11. It was reported to be reliable, valid, and much easier to administer in patients with dementia.

The 100 mm VAS and NRS 11 are the most commonly used scales for postoperative pain assessment. A limitation of both scores is that the definition of worst imaginable pain differs among individuals. This can be taken care of by providing the patient with some context of the worst imaginable pain.

Verbal Rating Scale

The VRS comprises a list of adjectives that describe increasing levels of pain. ^, The most common words used are no pain, mild pain, moderate pain, and severe or intense pain. To simplify the documentation, each adjective is assigned a number. The least intensity (no pain) is assigned the number 0, with subsequent intensity assigned one number higher. ^, The strengths of VRS include its simplicity, ease of administration, and scoring. It is straightforward for patients to comprehend, which is important in the very early postoperative period and is most easily understood by patients with cognitive impairment. ^, VRS has much superior compliance rates in the elderly than other scales. One of the pitfalls of this scale is that the interval between each adjective is not equal. Also, the patient must be familiar with words used to describe the pain and should be able to choose the one that describes his/her pain accurately.

Clinical Evaluation of Pain

Along with self-reporting of pain, patients should be observed for clinical signs of distress that include:

facial expression of pain, such as grimacing;
audible expression of pain, such as moaning or crying;
ambulation in the form of limping or posture, e.g. lying in a fetal position; and
avoidance of activities or specific movements.

Assessment tools such as the behavioral pain scale (BPS) and critical-care pain observation tool (CPOT) can help clinicians assess pain control in patients with cognitive impairment or sedation. ^, The CPOT has four components ^, —facial expression, body movements, resistance to passive flexion, and compliance to the ventilator in intubated patients or vocalization in extubated patients. The scale is scored from zero to eight, with zero being no pain and eight being maximum possible pain ( Table 25.2 ) The BPS has three components—facial expression, upper limb movements, and compliance with mechanical ventilation, scored on a scale of one to four. BPS scores range from three (no pain) to 12 (maximum pain) ( Table 25.3 ).

TABLE 25.2

Critical-Care Pain Observation Tool (CPOT)

Component	Description	Score
Facial expression	No muscular tension observed	Relaxed 0
	Presence of frowning, brow lowering, orbit tightening, and levator contraction	Tense 1
	All of the above facial movements plus eyelid tightly closed	Grimacing 2
Body movements	Does not move at all	Absence of movements 0
	Slow, cautious movements; touching or rubbing the pain site; seeking attention through movements	Protection 1
	Pulling tube, attempting to sit up, moving limbs/thrashing, not following commands, striking at staff, trying to climb out of bed	Restlessness 2
Muscle tension evaluation by passive flexion and extension of upper extremities	No resistance to passive movements	Relaxed 0
	Resistance to passive movements	Tense, rigid 1
	Strong resistance to passive movements, inability to complete them	Very tense, rigid 2
Compliance with ventilator	Alarms not activated, easy ventilation	Tolerating ventilator or movement 0
	Tolerating ventilator or movement	Coughing but tolerating 1
	Asynchrony: blocking ventilation, alarms frequently activated	Fighting ventilator 2

Total zero to eight, with zero being no pain and eight being maximum possible pain.

Adapted from Rijkenberg S, Stilma W, Bosman RJ, van der Meer NJ, van der Voort PHJ. Pain measurement in mechanically ventilated patients after cardiac surgery: comparison of the behavioral pain scale (BPS) and the critical-care pain observation tool (CPOT). J Cardiothorac Vasc Anesth . 2017;31(4):1227–1234.

TABLE 25.3

Behavioral Pain Scale (BPS)

Component	Assessment	Score
Compliance with mechanical ventilation	Tolerating movement	1
	Coughing but tolerating ventilation most of the time	2
	Fighting ventilator	3
	Unable to control ventilation	4
Facial expression	Relaxed	1
	Partially tightened	2
	Fully tightened	3
	Grimacing	4
Upper limb movements	No movement	1
	Partially bent	2
	Fully bent with finger flexion	3
	Permanently retracted	4

BPS scores range from 3 (no pain) to 12 (maximum pain).

Both scales are used routinely in the intensive care unit to assess pain in intubated and sedated patients. Increases in heart rate and blood pressure have been suggested as sympathetic responses to noxious stimuli. However, caution must be used when interpreting changes in these vital signs that may also be influenced by other factors, such as postoperative use of vasopressors and inotropes. Behavioral and physiologic indicators are especially important indices for the assessment of pain in patients who are unable to self-report.

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