A simplified index of the plasma sodium threshold for arginine vasopressin secretion-morning fasting, euhydrated sodium levels.

OBJECTIVE: Human pregnancy results in a reduction in plasma osmolality and thus a reduction in the osmotic threshold for arginine vasopressin secretion. Although the functional characteristics of the osmoregulatory system controlling arginine vasopressin secretion have been carefully defined, determination of the osmotic threshold requires a complex, labor-intensive protocol of an intravenous hypertonic saline infusion. To aid in studies of osmotic threshold resetting in pregnancy, we sought to develop a simplified method for determination of this value. STUDY DESIGN: Ten healthy nonpregnant women between the ages of 18 and 40 years were studied over 2 days. All patients were hospitalized, and morning euhydration was ensured by oral water hydration (5-10 mL/kg) the evening before the study. On the first study day, patients were fed a standard no-salt-added diet; plasma osmolality and sodium values were checked just before and 1 and 2 hours after meals. On the second study day, after fasting blood samples were obtained, patients received an intravenous infusion (0.06 mL. kg(-1). min(-1) for 120 minutes) of hypertonic (5%) saline to gradually increase the plasma sodium level. Blood samples were obtained every 15 minutes for measurement of plasma electrolytes and arginine vasopressin. Plasma arginine vasopressin concentrations were regressed against plasma osmolality and sodium concentration to calculate the osmotic threshold for arginine vasopressin secretion. RESULTS: Hypertonic saline injection significantly increased plasma sodium (from 139 +/- 1 to 149 +/- 1 mEq/L) and osmolality (from 284 +/- 2 to 304 +/- 2 mOsm/kg H(2)O). Plasma arginine vasopressin significantly increased (from 5 +/- 1 to 30 +/- 10 pg/mL). The mean sodium and osmolality thresholds for arginine vasopressin secretion were calculated as 137 +/- 2 mEq/L and 285 +/- 15 mOsm/kg H(2)O. The mean morning fasting sodium level was nearly identical to the calculated sodium threshold, whereas the morning fasting osmolality value was significantly different. CONCLUSIONS: The morning fasting, euhydrated sodium level can be used as a simplified index for the plasma osmotic threshold for arginine vasopressin secretion. This index may provide a useful predictive measure for pregnant women in whom the plasma volume does not expand.

Impact of FDA advisory on reported vacuum-assisted delivery and morbidity.

OBJECTIVE: In May 1998 the US Food and Drug Administration (FDA) issued a health advisory reporting neonatal injuries/deaths following vacuum delivery and encouraged voluntary reports of future adverse events. We compared FDA reports of vacuum delivery adverse events prior to and following the advisory. METHODS: The FDA database (MAUDE) was searched for vacuum deliveries using brand name, manufacturer name, and procedure "string searches." Cases were sorted by report date, source, and manufacturer. Neonatal morbidity was quantified as deaths and life-threatening or nonlife-threatening events. RESULTS: A total of 80 reported adverse cases were identified after duplicate cases were consolidated. Twenty-five were reported to the FDA prior to the 1998 advisory and 55 in the immediate 6-month period following the advisory. There was a 22-fold increase in reported events from five events/year prior to the advisory to an estimated 110 events/year following the advisory. The distribution of reporting sources changed significantly following the advisory with increased "manufacturer" (8-43%) and decreased "voluntary" reports (56-20%). All major brand names were represented. During the 6 months following the FDA advisory there were 10 neonatal deaths, 30 life-threatening events, 12 nonlife-threatening events, and three equipment-related reports. Infant deaths were due to intracranial or subgaleal hematomas. Injuries included skull fracture, scalp abrasions, and cephalohematomas. CONCLUSIONS: The FDA advisory was associated with a 22-fold increase in the rate of reported adverse events. This increase in reporting likely represents both enhanced awareness of complications as well as an increase in vacuum-related adverse neonatal sequelae. As vacuum delivery is associated with greater neonatal morbidity/ mortality than was previously recognized, the adage that the vacuum is "designed to come off before infant damage occurs" appears unsubstantiated. It is recommended that manufacturers quantify the suction and traction capabilities of present and new proposed vacuum cup designs.

Prognostic significance of antenatally detected fetal pyelectasis.

In order to evaluate the prognostic significance of ultrasonographically detected fetal pyelectasis, a retrospective review was performed of patients evaluated for fetal pyelectasis over a 24-month period. From 84 patients a total of 98 fetal kidneys with pyelectasis were identified. Fetal pyelectasis was more common in the left kidney and in males. Postpartum evaluation revealed 48 (57.1%) neonates with hydronephrosis. Among these, mean (SD; range) values of antenatal fetal pyelectasis were 17.0 mm (8.4; 5-26) before 33 weeks and 16.9 mm (8.5; 5-34) after 33 weeks in the left kidney and 15.4 mm (3.3; 10-24) and 17.1 mm (5.1; 5-36), respectively, in the right kidney. Thirteen infants (15.4%) with hydronephrosis required surgical pyeloplasties (mean age 6 months; range 3-18 months). It was found, from a receiver-operating characteristic curve, that fetal pyelectasis of 8 mm was 91% sensitive and 72% specific in predicting subsequent hydronephrosis. Use of a threshold of 5 mm yielded a sensitivity of 100% and a specificity of 24%. On the basis of these findings, we recommend that women with ultrasonographically detected antenatal fetal pyelectasis of > or = 5 mm at any gestational age have follow-up ultrasound examinations and detailed postnatal evaluation.