Role of naloxone in newborn resuscitation.

OBJECTIVE: Because of questions about the basis for the use of naloxone in resuscitation of the newborn, we wished to evaluate the use of naloxone at our institution and an affiliated hospital. METHODOLOGY: Evaluation of the actual use of naloxone at a university hospital and a community hospital: we document naloxone use by daily survey for a month in one; in the other, we perform a retrospective record review of 1 year's use. RESULTS: The university hospital had 240 births during February, 1998. Naloxone was given twice: once, 7 minutes before delivery to a woman at term who had received opiates about 2 hours previously; and once, intramuscularly, to a premature infant for apnea, before being intubated. The community hospital had 2044 births during fiscal 1998. Twenty-six neonates were identified as having received naloxone. Of the 26, 13 received naloxone without needing ventilatory support; all 13 with respiratory depression had a predisposing perinatal complication. CONCLUSION: The use of naloxone in practice may not conform to the American Academy of Pediatrics' guidelines for use in resuscitation of the newborn. The use of naloxone in resuscitation of the newborn should be reevaluated.

Renal hemodynamics in radiocontrast medium-induced renal dysfunction: A role for dopamine-1 receptors.

BACKGROUND: Radiocontrast medium (RCM) administration induces a transient increase in renal blood flow (RBF), followed by a prolonged vasoconstriction. This vasoconstrictor phase in RBF is accompanied by a decrement in glomerular filtration rate (GFR). Nonselective dopamine (DA) receptor stimulation is known to increase RBF and GFR. Clinical studies, however, fail to demonstrate a renoprotective effect of DA following RCM administration. This lack of renoprotection may relate to nonspecific adrenergic stimulation by DA. The effect of select DA-1 receptor stimulation on renal hemodynamics following RCM administration has not been evaluated. METHODS: This study tests the hypothesis that selective DA-1 receptor stimulation blunts the declines in RBF and GFR that follow RCM injections, independent of changes in baseline RBF and GFR. Experiments were performed in six anesthetized, volume-depleted dogs. RBF was measured by an electromagnetic flow probe around the renal artery and GFR by inulin clearance. After a 60-minute equilibration period, baseline values of RBF, GFR, and arterial pressure were determined. Two separate intrarenal bolus injections of the ionic RCM Renograffin were then given in the presence of saline infusion. After a 60-minute recovery period, intra-arterial infusions of either the selective DA-1 receptor agonist fenoldopam or the selective DA-1 receptor antagonist Schering 23390 were started in random order, and experiments were repeated. RESULTS: Neither agent significantly altered baseline values of arterial pressure, RBF, or GFR rate. Fenoldopam prevented reductions in GFR (-17 +/- 2 Deltaml/min, control vs. 2 +/- 1 Deltaml/min, fenoldopam, P < 0.001). Conversely, GFR was further reduced in the presence of Schering 23390 (-15 +/- 2 Deltaml/min, control vs. -23 +/- 1 Deltaml/min, Schering 23390, P < 0.05). Similarly, the maximal reduction in RBF was blunted with fenoldopam (-71 +/- 12 Deltaml/min, control vs. -3 +/- 2 Deltaml/min, fenoldopam, P < 0. 01), whereas Schering 23390 potentiated maximal RBF reductions following the RCM injection (-85 +/- 11 Deltaml/min, control vs. -119 +/- 14 Deltaml/min, Schering 23390, P < 0.05). The duration of recovery from vasoconstriction was also prolonged in the presence of Schering 23390 (342 +/- 35 seconds, control vs. 762 +/- 56 seconds, Schering 23390, P < 0.0001). CONCLUSION: We conclude that selective DA-1 receptor stimulation protects against RCM-mediated decrements in renal hemodynamics, independent of changes in baseline GFR and RBF. Clinical trials are required to examine whether selective DA-1 receptor stimulation may have a role in prophylaxis against nephropathy development in high-risk patients undergoing procedures that require RCM.

Cardiovascular and renal hemodynamic effects of intravenous infusions of the selective DA1 agonist, fenoldopam, used alone or in combination with dopamine and dobutamine.

Fenoldopam (0.1 and 0.2 microgram/kg/min i.v.) was administered to pentobarbital-anesthetized dogs alone and combined with dopamine (DA) and dobutamine. Renal blood flow, heart rate, and mean arterial pressure were measured. Both dosages of fenoldopam increased renal blood flow without altering blood pressure, similar to the effects of DA (1 and 2 micrograms/kg/min). Administration of fenoldopam with only DA (1 microgram/kg/min) produced further increase in renal blood flow. After administration of phenoxybenzamine (15 mg/kg i.v.), DA produced significant increments in renal blood flow and reductions in renal vascular resistance when compared with experiments without phenoxybenzamine, suggesting even low dosages of DA exert alpha-adrenoceptor agonist activity. Dobutamine (2 and 4 micrograms/kg/min) increased renal blood flow about 37% of that produced by DA. Fenoldopam added to dobutamine produced similar increments in renal blood flow as DA. Fenoldopam did not affect the increase in cardiac contractile force produced by DA and dobutamine. Thus, fenoldopam alone or in combination with DA had no advantage over 2 and 4 micrograms/kg/min DA to further increase renal blood flow. In contrast, fenoldopam with dobutamine produced greater increments in cardiac contractile force than DA and equivalent increases in renal blood flow as DA.