The Obese Surgical Patient: A Need for a Strong Multimodal Analgesia Approach

Chris Pasero, MS, RN-BC


March 20, 2014

Risk Factors for Postoperative Respiratory Depression

There are 2 main categories of risk factors for postoperative respiratory depression. Patient factors are characteristics inherent to the patient, and iatrogenic factors are practices introduced by the healthcare team that increase the risk (Table 1).[1,2]

Table 1. Risk Factors for Opioid-Induced Respiratory Depression

  • Age > 55 years

  • Obesity (body mass index > 30 kg/m2)

  • Untreated obstructive sleep apnea

  • History of snoring or witnessed apneas

  • Excessive daytime sleepiness

  • Retrognathia

  • Neck circumference > 17.5 inches

  • Preexisting pulmonary/cardiac disease or dysfunction (eg, chronic obstructive pulmonary disease, congestive heart failure)

  • Major organ failure (albumin level < 30 g/L and/or blood urea nitrogen > 30 mg/dL)

  • Dependent functional status (unable to walk 4 blocks or 2 sets of stairs or requiring assistance with ambulation)

  • Smoker (> 20 pack-years)

  • American Society of Anesthesiologists patient status classification 3-5

  • Increased opioid dose requirement

  • Opioid-naive patients who require a high dose of opioid in short period of time (eg, 10 mg intravenous [IV ] morphine or equivalent in the postanesthesia care unit [PACU])

  • Opioid-tolerant patients who are given a significant amount of opioid in addition to their usual amount, such as the patient who takes an opioid analgesic before surgery for persistent pain and receives several IV opioid bolus doses in the PACU followed by high-dose IV patient-controlled analgesia (PCA) for ongoing acute postoperative pain

  • First 24 hours of opioid therapy (eg, first 24 hours after surgery is a high-risk period for surgical patients)

  • Pain is controlled after a period of poor control

  • Prolonged surgery (> 2 hours)

  • Thoracic and other large incisions that may interfere with adequate ventilation

  • Concomitant administration of sedating agents, such as benzodiazepines or antihistamines

  • Use of large single-bolus techniques (eg, single-injection neuraxial morphine)

  • Continuous opioid infusion in opioid- naive patients (eg, IV PCA with basal rate)

  • Naloxone administration: Patients who are given naloxone for clinically significant respiratory depression are at risk for repeated respiratory depression.

All patients are at risk for opioid-induced respiratory depression; the factors listed in this table reflect elevated risk.

Copyright 2011, Chris Pasero. Modified from Pasero C, McCaffery M, eds. Pain Assessment and Pharmacologic Management. St. Louis: Mosby/Elsevier; 2011:516. Used with permission.

The patient in this scenario has 3 conditions that have been identified in research and case reports as risk factors for respiratory depression: obesity, hypertension, and loud snoring. All 3 conditions are in the category of patient risk factors. Some patient risk factors are preventable and within the patient's ability to control. Of interest, control of one risk factor may be linked to control of another. For example, preoperative weight loss may be helpful in reducing the risk for diabetes and improving myocardial function and blood pressure.[3,4] This may ultimately lessen the risk for postoperative complications, such as respiratory depression.[1]

All patients are at risk for postoperative respiratory depression and should be screened on admission for risk factors associated with this complication.[1,5,6] There is no universal screening tool at this time that evaluates all risk factors to formulate an overall risk score; however, some tools are available for the assessment of specific risks. For example, the STOP-Bang questionnaire screens patients for OSA,[7] which has been associated with an increased risk for postoperative respiratory depression.[1,2,5] The STOP-Bang questionnaire asks patients about their history of loud snoring, feeling tired or fatigued during the daytime hours, whether anyone has observed apnea during the patient's sleep, and treatment for high blood pressure; other risks assessed include a BMI > 35 kg/m2, age greater than 50 years, neck circumference > 40 cm, and male sex.[7] All of these characteristics are more common in individuals with OSA. Three or more "yes" answers to these questions are associated with a high risk for OSA.[8] Recent research has shown that a STOP-Bang ≥ 6 has high specificity (85.2%) to identify severe OSA.[8]

Iatrogenic risk factors are medical and nursing practices that introduce harm. Many of these are avoidable. For example, the coadministration of sedating drugs, such as benzodiazepines (eg, alprazolam, diazepam) and some antiemetic (eg, promethazine) and antipruritic drugs (eg, diphenhydramine), with opioids can increase sedation and risk for respiratory depression.[1,2,9] Opioid-only treatment plans and giving high opioid doses within short periods of time are other examples of iatrogenic risk. Giving the lowest effective opioid dose or avoiding opioids altogether is critical to preventing the introduction of iatrogenic risk in the patient in this scenario.[2] Ongoing risk assessment throughout the continuum of care is essential and is the responsibility of every member of the healthcare team because patient status can deteriorate and risk can be introduced. In such cases, adjustments in the method and frequency of monitoring are warranted.[1,2,10,11]


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