Index of suspicion in the nursery

Abstract

A set of nonidentical twins is born at 24 weeks gestational age by normal spontaneous vaginal delivery to a 25-year-old gravida 3 para 2 female. The infants are appropriate for gestational age, weighing 525 and 520 g. Both twins are intubated in the delivery room, given surfactant via endotracheal tubes, and placed on high-frequency oscillators in the neonatal intensive care unit (NICU). Results of clinical examination on admission to the NICU are normal for both twins. On the fourth day after birth, each infant is started on continuous fentanyl infusions at 3 mcg/kg per hour. Urinary output begins to decline 24 hours after initiation of the fentanyl infusions, with a simultaneous decline in renal function (TableT1). On postnatal day 7, marked abdominal distention is noted in both twins.Renal ultrasonography on both infants reveals bilateral hydronephrosis and very distended, urine-filled bladders extending under the hepatic border (Figs. 1 and 2). Fentanyl infusions are discontinued, and indwelling catheters are inserted, allowing bladder drainage in each infant. After catheterization, both twins experience polyuria and improvement in renal function. Repeat renal ultrasonography on postnatal day 9 demonstrates resolution of hydronephrosis and normal bladder size (Figs. 3 and 4)The association between fentanyl infusion and bladder urinary retention remains unknown. The first step in elucidation begins with the differential diagnosis of urinary tract obstruction and hydronephrosis in neonates. The clinician must rule out transient in utero hydronephrosis, tumors, urologic anomalies, and bladder asphyxia. Renal ultrasonography can be performed to rule out ascites or renal vascular diseases as the cause for acute renal failure. The next step involves understanding the mechanism of bladder retention with fentanyl use.There are numerous possible mechanisms for fentanyl-induced bladder retention. The causative mechanism is relaxation of the detrusor muscle and increased urinary bladder compliance. Mechanisms that have been gleaned from animal studies indicate that morphine and other opiates cause urinary retention by activating mu- and delta-opioid receptors in the spinal cord and midbrain periaqueductal gray (PAG) region. Terris and Merguerian found urinary retention to be induced by an increase in urethral sphincter pressures.These infants presented with deteriorating renal function and acute urinary retention requiring urethral catheter placement. Each patient’s prenatal ultrasonography image was normal, which ruled out posterior uretheral valves. Each patient had normal urine output and displayed normal renal function prior to starting fentanyl infusions. The absence of bladder trabeculation signifies a lack of long-standing outflow obstruction. In these twin infants, infusions of fentanyl resulted in bladder outflow obstruction and bilateral ureteral obstruction. The insertion of indwelling catheters allowed drainage of 30 and 25 mL of urine from each bladder. Cessation of the fentanyl infusions resulted in resolution of acute renal failure and hydronephrosis. Follow-up renal ultrasonography showed resolution of urinary bladder distention and hydronephrosis, which strongly suggests that fentanyl infusions were associated with the bladder obstructions.Utpala and associates reported two cases of preterm infants (unrelated) who had urinary retention and renal failure due to continuous fentanyl infusions, both of whom had mild swelling of the suprapubic area. In the twins in this case, marked bladder distention extended beyond the hepatic border.After confirmation of urinary retention through physical examination and renal ultrasonography, discontinuing the causative agent and helping the body eliminate excess fluid should prove beneficial in reversing urine retention. Discontinuing fentanyl should reverse the process causing the urine retention, and catheter placement provides a conduit for fluid to escape from the bladder.Long-term complications with continued use of fentanyl infusions after the development of anuria remain largely undefined, but they may involve organ damage, loss of function, or the need for transplantation.Neonatal urinary obstruction is rare, but must be considered in infants who are receiving fentanyl infusions. Infants may present with decreased urine output and abdominal distention after initiation of such infusions. Discontinuing fentanyl infusions and inserting indwelling urinary catheters proved beneficial in evacuating the bladders and improving renal function in this case.