Acute Postoperative Pain Management in the Older Patient

Thor Hallingbye; Jacob Martin; Christopher Viscomi

Aging Health. 2011;7(6):813-828.

Future Perspective

Opioids have ruled the pain management field for centuries, and rightfully wear the crown at the top of the WHO pain ladder. However, in the near future their reign will end. This will not be easily accomplished, but it is necessary. Opioids, while marvelous in their acute analgesic potential, carry unacceptable personal and societal risks. Addiction and abuse potential are both personal risks of opioids, but have also created widespread disruption of families, diminished work productivity and caused significant criminal behavior. In addition, respiratory depression, constipation and somnolence are just a few of the many risks associated with opioid use. Finally, over several months, opioids lose effectiveness (tolerance) or even contribute to pain (opioid-induced hyperalgesia). Older adults are just as vulnerable, if not more so, to these hazards. What will supplant opioids? It is likely that interventional pain management strategies, nonpharmacological approaches and medications with fewer risks will take on a greater role in the future. Specific classes of drugs such as NMDA receptors and TRPV1 receptor blockers are being developed and show great potential. Unfortunately, the first generation of these agents is limited by side effects. It is likely that in the next 5–10 years, next generation drugs in these classes will be available, and will supplant opioids as the mainstays of pain management.

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Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.

Table 1. Pain assessment tools.
Tool	Description	Discussion
Visual Analogue Scale	A vertical or horizontal 100-mm line anchored by verbal descriptors such as 'no pain' and 'worst pain possible'. Patients make a mark on the line that represents their pain intensity	Requires abstract thought Difficult to use in cognitively or visually impaired May be less valid in older adults
Numerical Rating Scale	Available in a variety of scale ranges and anchors, such as 0–10, with 0 being 'no pain' and 10 being 'worst pain possible'	Requires abstract thought Valid in cognitively impaired Commonly recommended scale for pain assessment in older adults
Verbal Descriptor Scale	Available in a variety of scale types (e.g., pain thermometer, present pain intensity index and graphic rating scale)	Limited amount of choices Requires some command of language Highly preferred by older adults Low failure rate in cognitively impaired
Faces Pain Scale	Consists of seven faces ranging from neutral face (no pain) to grimacing face (worst pain possible)	Requires abstract thought Difficult to use in cognitively impaired May be less preferred by older adults
Behavioral Pain Scale	Observational assessment tool for nonverbal patients compiled by nurse or physician	Generally takes longer to complete Requires knowledge of how scale is used Better results if observer is very familiar with patient

Table 2. Physiologic changes in the older adult.
System	Older vs younger	Importance
Nervous system	Higher prevalence of cognitive impairment Decreased ability to assess pain if demented/delirious Decreases in neurotransmitters and receptors Decreased pain-transmitting nerve fiber function (Aδ and C)	May be worsened by pain medications Use behavioral scale to assess pain level Decrease in autonomic responsiveness (uncompensated hypotension following spinal or epidural anesthesia) Decreased capacity or speed of pain processing Increased pain threshold to short duration pain stimuli
Cardiovascular system	Decreased cardiac output by 1% per year after 30 years of age High frequency of cardiovascular disease	Higher peak arterial concentrations after intravenous dose of medication Severe consequence of untreated hypotension following spinal or epidural anesthesia
Pulmonary system	Decreased sensitivity to hypoxia/hypercarbia Increased incidence of sleep apnea	Postoperative treatment with oxygen Slow titration of opioids Longer interval between doses
Hepatic system	Decreased metabolism of drugs	Decrease dose, increase interval between doses
Renal system	Decreased GFR	Adjust medication dose according to GFR Cautious use of medications with renal toxicity risk (NSAIDs)

Table 3. Pharmacokinetic changes in older adults.
System	Older vs younger	Importance
*Drug absorption and bioavailability*
Gastric pH	5–10% of older patients have decreased gastric acid secretion Widespread PPI and H2 blocker therapy	Drugs requiring acidic environment are poorly absorbed (i.e., ketoconazole and/or iron salts)
Gastrointestinal motility	Delayed gastric emptying, peristalsis and colonic transit	Delay in time to achieve drug plasma levels Risk of constipation
Intestinal permeability	Probably no change in passive permeability
Gastrointestinal blood flow	Probably diminished flow	Limits absorption of highly permeable drugs
Gut wall drug metabolism	Probably diminished	May lead to higher bioavailability (i.e., morphine)
*Volume of distribution*
Serum protein binding of drugs	10% decrease in albumin concentration Increase in α-1-acid glycoprotein	Higher unbound fraction of some drugs (i.e., fentanyl, propofol, midazolam and/or naproxen) Decreased unbound fraction of some drugs (i.e., lidocaine)
Body fat	Increased 20–40%	Higher volume of distribution for lipophilic drugs (i.e., fentanyl and diazepam)
Body water	Decreased 10–15%	Lower volume of distribution for hydrophilic drugs (i.e., morphine)
*Hepatic metabolism*
Hepatic blood flow	Decreased up to 40%	May affect drugs with flow-limited metabolism (i.e., morphine)
Hepatic mass	Decreased up to 40%	May affect drugs with flow-limited metabolism
Phase I metabolism	Potential decrease in some CYP450 enzymes	May affect drugs with capacity-limited metabolism (i.e., theophylline)
Phase II metabolism	No reduction in hydrolysis, reduction or conjugation	Unaffected
*Renal clearance*
Glomerular filtration rate	Reduction by approximately 1 ml/min/year after middle age Wildly variable depending on comorbidities	May require large reductions in dose of renally excreted drugs with narrow therapeutic index and drugs with active metabolites
Renal mass	Decreased up to 25%

Box 1. Opioid dosing in the opioid-tolerant surgical patient.
Step 1: obtain accurate history of opioid consumption Step 2: convert outpatient oral opioids to equivalent dose of parenteral opioids Step 3: multiply the Step 2 dose by 200–400% to predict daily parenteral opioid needs immediately after surgery Step 4: if an intravenous patient-controlled analgesia device will be used, divide Step 3 calculation by 24 to determine hourly maximum dose of opioid to be delivered by patient-controlled analgesia pump

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Executive Summary

Background

Acute and chronic pain are increasingly prevalent in the aging population of the USA. Treatment of pain is complicated by medical comorbidities and the risk of postoperative delirium and cognitive decline.

Challenges of assessing pain in the older patient

Numerous pain assessment scales have been validated in the older population. In cognitively intact older adults, self-report scales are very reliable. In cognitively impaired older adults, behavioral scales are more valid.

Pain experience in the older adult

Sex and age-related differences in pain experience probably exist, but the clinical significance is unclear. Misconceptions about pain experience expose older adults to the risk of undertreatment.

Physiological changes of aging

Aging produces physiological changes within the body. There is a higher prevalence of cognitive impairment, cardiac dysfunction and hepatic and renal impairment in the older population.

Pharmacokinetics & pharmacodynamics: application to drug dosing in the older adult

There are wide variations in pharmacokinetic and pharmacodynamic changes apparent between older individuals. Increased body fat composition leads to higher volume of distribution for fat-soluble drugs and lower volume of distribution for water-soluble drugs.
Decreased hepatic and renal function is probable, with the effect of renal impairment being more important on drug metabolism and elimination. Pharmacodynamic changes are prevalent in the central nervous and cardiac systems.

Analgesic drug classes

Opioids are the prototypical pain medication. They can be safely used in older adults, but there are risks, including side effects, tolerance and opioid-induced hyperalgesia.
Acetaminophen has significant opioid-sparing ability, is well tolerated and can be administered by multiple routes.
NSAIDs have significant opioid-sparing ability. Nonselective COX inhibitors have side effects that the clinician must be aware of. COX-2 inhibitors may decrease the risk of gastrointestinal side effects.
Gabapentinoids have been shown to decrease perioperative pain and risk for development of chronic incisional pain.
N-methyl-D-aspartate receptor antagonists have significant opioid-sparing ability, but their use can be limited by side effects.

Case presentations

Cases presented to illustrate evidence-based decision-making regarding perioperative analgesia.

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