Background:

           -Muscle rigidity has been described as a side-effect of fentanyl, specifically activation of expiratory muscles 

           -Excessive expiratory muscle use acts as “anti-PEEP,” causing lung derecruitment and hypoxemia

           -End-expiratory lung volume (EELV) has been used as a surrogate for lung recruitment

Study:

          -Small, two center, observational study (46 patients with ARDS)

          -50% of  patients had a significant increase in EELV after administration of neuromuscular blockade (NMB)

          -Statistically significant correlation between a higher dosage of fentanyl and a greater increase in EELV after NMB

Takeaways:

          -NMB can improve lung recruitment for a subset of patients with ARDS, particularly in patients with significant expiratory muscle use (this can be seen on your physical exam of your intubated ED boarding patient)

          -Although this was not the main point of this study, consider fentanyl-associated “anti-PEEP,” particularly in patients receiving fentanyl whose hypoxemia and/or ventilator mechanics are disproportionate to their imaging

                    -This can be assessed with NMB (but ensure the patient will have adequate minute ventilation first)

                    -Naloxone has also been shown to reverse fentanyl-associated rigidity, but obviously would induce patient discomfort/withdrawal

*Of note, because this was an observational trial, it is possible that the patients with increased work of breathing were simply given more fentanyl. Regardless, these findings are consistent with previously documented physiologic side effects of fentanyl.

References

Plens GM, Droghi MT, Alcala GC, et al. Expiratory muscle activity counteracts positive end-expiratory pressure and is associated with fentanyl dose in patients with acute respiratory distress syndrome. Am J Respir Crit Care Med. 2024;209(5):563-572.