The Use of Small-Dose Intravenous Nitroglycerin in a Case of Uterine Inversion

Abstract

Uterine inversion is a rare complication, occurring in 0.04%-0.06% of vaginal deliveries, but one that creates serious risk to the patient [1-3]. It is associated with profuse hemorrhage and life-threatening shock. Relaxation of the uterus may be necessary to facilitate its reinsertion. The anesthesiologist may therefore face the difficult situation of having to provide rapid uterine relaxation, usually with a volatile inhaled anesthetic, in a hypovolemic patient. Nitroglycerin is a vascular smooth muscle relaxant whose actions are mediated by cyclic guanosine 3 prime,5 prime-monophosphate. Nitroglycerin has been successfully used for uterine relaxation in cases of retained placentas [4,5]. We describe a case of uterine inversion in which relaxation of the uterus was accomplished quickly and safely with the use of intravenous nitroglycerin. The dose used was sufficient to relax the uterus but did not result in hypotension [4,5]. Case Report A 31-yr-old primigravida delivered a healthy male infant weighing 3420 g under epidural analgesia. During the third stage of labor, overly vigorous traction on the umbilical cord resulted in a uterine inversion. Since the obstetrician was not immediately able to reinsert the uterus, the patient was transferred emergently from the birthing room to a delivery/operating room. Upon arrival in the operating room, oxygen was supplied via face mask. The initial arterial blood pressure was 60/30 mm Hg, and the heart rate was 140 bpm. The patient had an indwelling 18-gauge intravenous catheter in her right arm. We immediately started a second intravenous infusion using a 16-gauge catheter. A liter of lactated Ringer's solution, 250 mL of 5% albumen, and 500 mL of hetastarch were rapidly infused over 6-8 min. Phenylephrine, 100 micro gram, was also administered intravenously. During this time, the obstetrician applied manual pressure on the exposed uterus to tamponade the bleeding. As a result of these resuscitative measures, arterial blood pressure increased to 100/70 mm Hg. Then, while hemodynamic stability was maintained, the patient was placed in a semirecumbent lithotomy position and 10 mL of 2% 2-chloroprocaine was given through the epidural catheter to obtain perineal analgesia. Aggressive intravenous fluid resuscitation continued, and ketamine 10 mg was given intravenously for sedation. This dose is reported to have no effect on uterine tone [6]. With ongoing fluid resuscitation, nitroglycerin 100 micro gram was injected as an intravenous bolus. Within 60 to 90 s, the uterus relaxed enough to permit the obstetrician to reinsert it. Arterial blood pressure remained at 100/70 mm Hg. Trans-abdominal massage of the uterine fundus and an oxytocin infusion gradually improved uterine tone. The uterus was deemed to be firm approximately five minutes after its replacement. Fluids were given intravenously over the next 30 min including 3500 mL of lactated Ringer's solution, 500 mL of hetastarch, 250 mL of 5% albumin and one unit of packed red blood cells. The patient had an estimated peripartum blood loss of 2.0 L. Her postpartum hemoglobin and hematocrit were 6.3 mg% and 18.5%, respectively. She remained hemodynamically stable and was discharged home, receiving iron therapy, on the third postpartum day. Discussion This case demonstrates the value of small-dose intravenous nitroglycerin, in combination with epidural perineal analgesia, for treatment of a uterine inversion. Nitroglycerin has previously been described in two patients with uterine inversion, neither of whom were given anesthesia [7,8]. The current case differs in that we used epidural analgesia (sacral block) as a component of treatment along with volume resuscitation. Some would criticize the use of a preexisting epidural, because sympathetic blockade may cause hypotension in an individual with an inadequate intravascular volume. However, our patient was given sufficient fluids intravenously and was in the lithotomy position. Thus, it is unlikely that a sacral block would significantly affect arterial blood pressure. Uterine inversion involves the collapse of the fundus into the body of the uterus and may be classified as "incomplete" or "complete," depending on whether the fundus extends beyond the cervix [1]. An inversion may be "acute" or "subacute," depending on whether cervical contraction has occurred [1]. While other factors, such as placenta accreta and the use of parenteral magnesium sulfate, may contribute to the etiology of this problem, complete uterine inversion is almost always the result of overly strong traction on the umbilical cord attached to a fundally implanted placenta [9]. Uterine inversion is usually associated with severe shock. There is some controversy as to whether hypotension is entirely due to hypovolemia or whether there is an associated vagal component due to peritoneal traction [2,3]. Nevertheless, uterine inversion is a life-threatening situation and uterine relaxation is often necessary to aid the obstetrician in replacing the uterus. Uterine inversion therefore presents a unique problem for the anesthesiologist. First, hypovolemia must be treated and an attempt must be made to restore effective hemodynamic stability. Second, perineal anesthesia and/or sedation is often necessary to allow the obstetrician to perform the maneuvers necessary to reinsert the uterus [10]. Finally, if the uterus has already begun to contract, uterine relaxation is required for reinsertion. Intravenous nitroglycerin has been used for uterine relaxation in the extraction of retained placentas [4,5]. Initially, doses as large as 500 micro gram were used but were associated with a high incidence of side effects, most notably hypotension [4]. Doses of 50-100 micro gram have since been used successfully to achieve relaxation without causing hypotension or other unwanted side effects [5]. Even at this reduced dose, nitroglycerin has the advantage of a rapid onset of action (30-40 seconds) in combination with a short-lived effect (approximately one minute) [5]. In the case presented, as in most cases of uterine inversion, time was a critical factor in the patient's treatment, because brisk hemorrhage will continue from the exposed, inverted uterus until it is replaced. While the obstetrician provides manual external pressure on the inverted uterus, rapid intravenous fluids and vasopressors are often required to help maintain arterial blood pressure. Definitive treatment requires reinsertion of the uterus. In the case presented here, the cervix had begun to contract upon removal of the placenta and uterine relaxation was necessary to aid the proper obstetric maneuvers. Terbutaline, ritodrine, magnesium sulfate, and volatile inhaled anesthetics have all been used for this purpose [11-13]. The rapid onset of action of intravenous nitroglycerin creates uterine relaxation in a much shorter time than would otherwise be achieved if an anesthesiologist were relying on the uptake of inhaled anesthetics or an initial dose of 2 g magnesium sulfate. In addition, magnesium sulfate may worsen cardiovascular responses to hemorrhage [14], and the uterine effects of magnesium sulfate, terbutaline, and ritodrine may need to be subsequently reversed [11-13]. In contrast, nitroglycerin's short duration of action allows it to dissipate, obviating the need for reversal. The administration of a small dose of intravenous nitroglycerin in combination with epidural perineal analgesia achieved both adequate uterine relaxation and comfort while maintaining stable hemodynamics, thus avoiding the need for induction of general anesthesia with its attendant risks of aspiration of gastric contents and failed tracheal intubation [15]. The use of nitroglycerin may not always preclude the need to administer large-dose volatile inhaled anesthetics; thus, the anesthesia team should be prepared to induce general anesthesia, using overpressure to speed the uptake of the anesthetic. However, initial administration of nitroglycerin is advantageous and should be seriously considered in cases of subacute uterine inversion. In summary, we present a case of complete subacute uterine inversion after a normal vaginal delivery, in which, after aggressive intravenous fluid administration, a preexisting epidural catheter (placed for labor analgesia) was used for perineal analgesia. Subsequently, small-dose intravenous nitroglycerin was useful in achieving the uterine relaxation required for reinsertion. Thus, the use of intravenous nitroglycerin may be an alternative to general anesthesia in cases of uterine inversion.