Discussion
Our patient was likely predisposed to experience severe urinary retention given her complex medical history. The following basic physiology is recognized as the scientific basis of severe urinary retention in the setting of intrathecal opioid administration: the opioids receptors involved in the urodynamic effects are μ and δ. Intrathecal opioids acting on opioid receptors in the spinal cord decrease the parasympathetic firing in the sacral region and decrease the afferent inputs from the bladder to the spinal cord which results in an inhibitory modulating effect on the release of acetylcholine that causes detrusor contraction 6. Some speculate that there is a dose-dependent mechanism by which intrathecal opioids cause side effects like urinary retention 1. Other sources describe a primary dose-independent activation of opioid receptors7. A randomized, double-blind study by Raffaeli et al. concluded that side effects of intrathecal opioid like urinary retention can be considered as a patient-dependent effect of the drug, suggesting the presence of a primary dose-independent excitatory component that might be related to the theory of the bimodal activation of opioid receptors. Our case supports this latter theory because dose reduction did not improve the patient’s severe urinary retention.
The improvement of the patient’s urinary retention was achieved by changing the type of narcotic. This demonstrates how different narcotics may vary in how they affect the μ and δ receptors resulting in unique, narcotic-specific outcomes with respect to pain management and risk of voiding dysfunction.
Conclusion :
Morphine sulfate was successfully identified as the cause of the new-onset urinary retention after turning off the morphine IPP. This patient has a complex medical history including stroke with no residual deficits, diabetic neuropathy, and peripheral vascular disease that may have contributed to her susceptibility to severe urinary retention. The patient’s initial complaint of difficulty urinating and her urodynamic testing findings may reflect the influence of intrathecal opioid administration as opioids are known to decrease bladder function by suppressing detrusor contractility and decreasing the sensation of urge8. Of note, different types of opioids may uniquely affect bladder storage and emptying demonstrated during urodynamics. For instance, drugs like fentanyl are more lipophilic than morphine and thus undergo greater systemic uptake. As a result, there is less rostral spread in the central nervous system and less influence on storage and voiding as demonstrated by multichannel urodynamics. Published research also supports replacing morphine with an alternative narcotic such as sufentanil in a regional anesthetic regimen to mitigate the risk of postoperative urinary retention 9. The data indicate that recovery to normal lower urinary tract function is significantly faster after intrathecal sufentanil than morphine 6,9.
This case report highlights that chronic pain patients with multiple comorbidities affecting the nervous system may be uniquely predisposed to severe urinary retention with IPP use. Intrathecal morphine may be more likely to precipitate urinary retention in such a patient. We believe that patients with a morphine IPP in retention should undergo a trial of an alternative narcotic as a primary management strategy to resolve the urinary retention and maintain the benefit of the IPP.