Two recent studies performed by Noble et al. and Nelson et al. concluded there is likely no relationship between OA and false positive or false negative SMS [13, 14]. There has been criticism of the Noble et al. study, which used small opioid doses, raising questions about the study’s validity. The exact opioid dose given to the patients would have been equianalgesic to only 0.5 or 1.0 mg of IV morphine, depending on whether one or two doses were given according to the study protocol. With such a low dose of opioids, it has been argued that no significant analgesia was given and thus no effect on the SMS could be expected [15]. In our study, morphine equivalent doses ranged from 2 mg IV to 24 mg IV, expanding the generalizability of the results and increasing the likelihood of an effect on the SMS. The Nelson et al. study did not define the doses of opioids administered to patients.

In contrast, several conclusions can be drawn from the results of or study. First, OA resulted in a statistically significant increase in the rate of indeterminate SMS, while NOA administration prior to RUQUS does not affect the rate of finding a positive, negative, or indeterminate SMS. Thus, if a patient presents for RUQUS in the evaluation for AC, premedication with NOA offers the best chance at assessing the SMS accurately.

OA administered prior to RUQUS resulted in a statistically significant increase in false-negative results, including for morphine-equivalent dosing ≤ 4 mg. Therefore, a negative exam in a premedicated patient may yield less reliable results than a non-medicated patient. NOA premedication, however, did not significantly increase false-negative results.

Patients who received OA for treatment of their abdominal pain were statistically more likely to be diagnosed with AC. This is likely a result of increased pain needing a higher level of analgesia than NOA can typically provide. However, there is no statistically significant difference in the sensitivity or specificity of the exam between the opioid treatment group versus the control group.

RUQUS examinations performed within 30 min of premedication with OA resulted in a statistically significant increase in false-negative results. No such effect is seen in the NOA treatment group or in patients treated with OA greater than 30 min prior to scan. This result suggests delaying a RUQUS for at least 30 min after administration of OA can help mitigate the risk of an incorrect diagnosis.

There are several limitations to our study. It was conducted using data from a military treatment facility, where the patient population (patient age, racial distribution, occupational exposures, etc.) may not be completely generalizable to the general public. This may explain why our institutional sensitivity and specificity of positive SMS for AC are lower than published (41.4% for the full sample set, versus 83% published, and 91.5% versus 95% [7]) as well as the increased false-negative results after premedication.

Further, this study does not take into account specific additional sonographic findings (e.g. presence of gallstones, pericholecystic fluid, etc.) other than the SMS that might further contribute to final radiologic diagnosis. There may be a discrepancy between which factors are weighed more heavily by radiologists than by emergency physicians. In a recent survey, 100% of emergency radiologists thought opioids administered prior to the assessment of the SMS would have a negative impact. On the contrary, only 10% of emergency medical physicians surveyed thought opioids would have an adverse effect on the SMS [13]. While it is difficult to quantify retrospectively, presumably the 24 cases of missed AC on radiology imaging received proper medical care due to the emergency physician’s high clinical suspicion based on the patient’s symptoms and/or other secondary imaging findings (gallstones, pericholecystic fluid, wall-thickening, etc.). It is important to consider these differing clinical perspectives when examining the factors contributing to the study results.