Obesity and Analgesic Response to Morphine in the ED
Obesity and Analgesic Response to Morphine in the ED
Objective The primary objective of this study was to compare the analgesic response to morphine in non-obese, obese and morbidly obese patients for acute pain.
Methods This was a retrospective cohort study conducted in a tertiary care emergency department in the USA. Consecutive adults who received intravenous morphine 4 mg for pain were included. Patients were categorised into three groups based on body mass index (BMI): non-obese (18.5–29.9 kg/m); obese (30.0–39.9 kg/m); and morbidly obese (≥40 kg/m). Baseline and post-dose pain scores were recorded. Pain was measured on a 0–10 numerical rating scale (0=no pain; 10=worst possible pain). Analgesic response was defined as the difference between the initial pain score and post-dose pain score.
Results 300 patients were included in the study (100 in each group). The median baseline pain scores were 8.5, 8 and 8.5 in the non-obese, obese and morbidly obese groups, respectively (p=0.464). The median analgesic response after morphine administration was 2, 3 and 2 in the non-obese, obese and morbidly obese groups, respectively (p=0.160). In the linear regression analysis (R=0.006), BMI was not predictive of analgesic response (coefficient −0.020; p=0.199).
Conclusions Obesity status did not influence analgesic response to a fixed dose of morphine. This suggests that obese and morbidly obese patients do not require a higher dose of morphine for acute pain reduction compared to non-obese patients.
Pain is the most common complaint for patients seen in the emergency department (ED) and weight-based dosing of opioids is frequently used for more severe pain states. It is estimated that a third of adults are obese, with a body mass index (BMI) of 30 or greater, and nearly 6% of adults have grade 3 obesity (BMI ≥40). Therefore, a large proportion of patients who present to the ED with pain are obese or morbidly obese. Using a weight-based dosing strategy, these patients may receive larger total doses of opioids compared to normal weight individuals. However, this can potentially increase the risk of serious adverse events such as respiratory depression. Morphine is the most common opioid used in this setting. However, the data to support morphine dosing are limited in obese individuals because of the relatively low number of obese patients in studies. This may be because of exclusion criteria preventing enrollment of patients beyond a certain weight. Therefore, there is a need for studies evaluating the analgesic response to morphine, especially in patients with very high BMI, such as the morbidly obese.
Weight-based dosing regimens of morphine assume a proportional relationship between changes in weight and clinical effect. However, there is little evidence to support this assumption. Although somewhat counterintuitive, one study performed in the postoperative period found that obese patients actually required fewer doses of opioids to control their pain when compared to non-obese controls. In another study, obese patients were more prone to critical respiratory events such as respiratory depression and hypoxaemia in the postoperative setting. Therefore, the ideal dosing of opioids such as morphine is unclear, and the optimal balance between efficacy and safety can be challenging in these patients.
In previous studies conducted in the ED, weight has not been shown to be predictive of patient response to morphine. However, those studies included relatively few obese patients and even fewer who were morbidly obese. Therefore, the primary objective of this study was to compare the analgesic response to morphine in non-obese, obese and morbidly obese patients who were treated for acute pain in the ED.
Abstract and Introduction
Abstract
Objective The primary objective of this study was to compare the analgesic response to morphine in non-obese, obese and morbidly obese patients for acute pain.
Methods This was a retrospective cohort study conducted in a tertiary care emergency department in the USA. Consecutive adults who received intravenous morphine 4 mg for pain were included. Patients were categorised into three groups based on body mass index (BMI): non-obese (18.5–29.9 kg/m); obese (30.0–39.9 kg/m); and morbidly obese (≥40 kg/m). Baseline and post-dose pain scores were recorded. Pain was measured on a 0–10 numerical rating scale (0=no pain; 10=worst possible pain). Analgesic response was defined as the difference between the initial pain score and post-dose pain score.
Results 300 patients were included in the study (100 in each group). The median baseline pain scores were 8.5, 8 and 8.5 in the non-obese, obese and morbidly obese groups, respectively (p=0.464). The median analgesic response after morphine administration was 2, 3 and 2 in the non-obese, obese and morbidly obese groups, respectively (p=0.160). In the linear regression analysis (R=0.006), BMI was not predictive of analgesic response (coefficient −0.020; p=0.199).
Conclusions Obesity status did not influence analgesic response to a fixed dose of morphine. This suggests that obese and morbidly obese patients do not require a higher dose of morphine for acute pain reduction compared to non-obese patients.
Introduction
Pain is the most common complaint for patients seen in the emergency department (ED) and weight-based dosing of opioids is frequently used for more severe pain states. It is estimated that a third of adults are obese, with a body mass index (BMI) of 30 or greater, and nearly 6% of adults have grade 3 obesity (BMI ≥40). Therefore, a large proportion of patients who present to the ED with pain are obese or morbidly obese. Using a weight-based dosing strategy, these patients may receive larger total doses of opioids compared to normal weight individuals. However, this can potentially increase the risk of serious adverse events such as respiratory depression. Morphine is the most common opioid used in this setting. However, the data to support morphine dosing are limited in obese individuals because of the relatively low number of obese patients in studies. This may be because of exclusion criteria preventing enrollment of patients beyond a certain weight. Therefore, there is a need for studies evaluating the analgesic response to morphine, especially in patients with very high BMI, such as the morbidly obese.
Weight-based dosing regimens of morphine assume a proportional relationship between changes in weight and clinical effect. However, there is little evidence to support this assumption. Although somewhat counterintuitive, one study performed in the postoperative period found that obese patients actually required fewer doses of opioids to control their pain when compared to non-obese controls. In another study, obese patients were more prone to critical respiratory events such as respiratory depression and hypoxaemia in the postoperative setting. Therefore, the ideal dosing of opioids such as morphine is unclear, and the optimal balance between efficacy and safety can be challenging in these patients.
In previous studies conducted in the ED, weight has not been shown to be predictive of patient response to morphine. However, those studies included relatively few obese patients and even fewer who were morbidly obese. Therefore, the primary objective of this study was to compare the analgesic response to morphine in non-obese, obese and morbidly obese patients who were treated for acute pain in the ED.