Charles L Paxson

Collection and use of autologous fetal blood

A prospective study was completed to evaluate the feasibility of autologous fetal blood collection. Following puncture on the umbilical vein, fetal blood was drawn into sterile heparinized plastic syringes and aliquots were subjected to coagulation and culture studies. None of the blood samples exhibited significant growth of bacterial pathogens and all patients had normal coagulation studies at 24 hours of age. These data demonstrate that fetal blood can be safely collected and given to infants subjected to shock or iatrogenic blood loss.

BREAST MILK MACROPHAGES

Animal studies suggest that preterm infants gavage fed human breast milk receive pretection against enteric infection by the presence of macrophages (BMM), as well as immunoglobulins. We have been concerned about the effects of collection, storage, route of administration and other factors which may alter the survival of BMM.Samples of fresh human breast milk from healthy mothers 3 mo. postpartum were collected into plastic containers. BMM were separated by dilution 1:3 with phosphate buffered saline, centrifugation, and resuspension in saline or veronal HCL buffer. Cells were examined by microscopy, counted, and viability tested by phagocytosis of trypan blue dye. Aliquots of BMM were exposed to alterations in temperature to simulate storage procedures (-5 to 56°C), pH changes to simulate gastric vs duodenal feedings (2-8), alterations in osmolality to simulate mixing BMM with infant formulas (200-400 mOsm/kg water), and addition of albumin to simulate variations in formula protein content.Total BMM counts decreased with increasing postpartum age. Freezing markedly decreased survival, but heating to pasteurization did not. At pH above 7.2 survival and phagocytosis decreased, but the cells survived lowered pH ranges. Osmolality alterations produced no changes, but the addition of albumin diminished phagocytosis. We conclude that methods of procuring and feeding breast milk may markedly affect survival and phagocytic ability of BMM.

Evaluation and testing of in vitro labeled technetium Tc-99m red blood cells in two animal models for neonatal RBC volume determinations.

Summary: The present study was designed to evaluate the red blood cell (RBC) radiolabeling technique utilizing the short half-lived radio-nuclide technetium-99m and to compare the results with the well-recognized standard chromium-51 method. The procedure was evaluated in a canine and a newborn lamb model utilizing dual radionuclide labeling and counting techniques. With the express purpose of providing a significant radiation dose reduction, the procedure presented was adapted for utilization in a neonatal patient population. Statistical analysis of the data revealed that there was no significant difference in the radiolabeling efficiency for the two methods (Cr-51, 86.6%; Tc-99m, 92.4%). Assessment of the in vivo stability for technetium-99m RBCs showed that less than a 4% loss of radiolabel from the RBC was seen in a 4-hr time span in the canine model (15 min, 90.5%; 2 hr, 88.9%; 4 hr, 86.6%) when compared to the 15 min equilibrium sample.Evaluation of newborn lamb RBC volumes showed that the technetium-99m RBC volume did not significantly differ from the chromium-51 labeling technique (Cr-51, 24.0 ml/kg; Tc-99m, 23.2 ml/kg). Summarization of the whole-body radiation dose showed that greater than a 30-fold reduction in absorbed dose was achieved in the newborn (Cr-51,30.0 mrad; Tc-99m, 0.9 mrad). The modified procedure presented for the radiolabeling of the RBC with the short half-lived radionuclide technetium-99m provides a technique comparable to the utilized standard chromium-51 RBC method, yet with a large reduction in absorbed radiation dose. This procedure is presented as a superior technique for the determination of pediatric RBC volumes.Speculation: Demonstration of the efficacy of radionuclide dilution techniques in two species (animal models) predicates for the application of this procedure in neonates. The accurate assessment of circulating red blood cell volume affords the neonatologist a unique management tool while accruing significant radiation dose reduction using the short half-lived technetium-99m rather than the standard chromium-51 technique.

885 EFFECT OF PLACENTAL LACTOGEN AND INSULIN INFUSIONS ON UTERINE GLUCOSE METABOLISM

We have previously shown that placental lactogen induces an increase in uterine glucose uptake (Q). These studies were designed to determine the combined effects of insulin and placental lactogen (PL) on Q.Five pregnant near-term Western ewes were chronically prepared by placement of catheters and electromagnetic flow probes. Following baseline studies, all ewes received infusions of PL and insulin. Initial infusions of insulin were also followed by superimposed “pulses” of PL.Initial infusions of insulin and PL produced significant increases in Q, but no changes in maternal glucose or in uterine blood flow. The insulin increased Q, peaked at 1 hr of infusion and slowly decreased, although Q remained consistently above baseline values. The PL “pulse” infusions produced no further rise above the insulin elevated Q.We conclude that both insulin and PL regulate uterine metabolism in the near-term pregnant ewe. The failure of PL pulses to further augment the insulin induced Q peaks may indicate the presence of common PL-insulin receptors which become “saturated” by the initial infusions, or the ratio of insulin to PL may be an important determinant of uterine glucose uptake.

1005 NEONATAL HYPOTENSION: THERAPY WITH BLOOD VS. DOPAMINE

We have compared the efficacy of blood versus dopamine HC1 infusions for resuscitation of the hypotensive newborn. Polyvinyl catheters were placed in 10 newborn lambs (5.4 - 7.7 kg) and the animals were sujected to hypotension by withdrawal of 25% circulating red cell volume (RCV). Serial blood volume determinations were completed using a technique of 51 Cr and Tc-99m labeled red cells as blood pressure (BP) and vital signs were continuously monitored. The animals were then alternately resuscitated with heparinized blood and/or dopamine HC1 (1-50 ug/kg/min).All animals became hypotensive, tachycardic, tachypneic, and hypovolemic. The fall in BP was directly related to the reduction of circulating volume (BP = 1.6 RCV + 15).Resuscitation with blood resulted in a prompt predictable rise in BP. As BP rose, heart rate returned to normal. However, dopamine infusions produced unpredictable results: 3 animals exhibited fluctuations in BP between normal and hypotensive levels. Two animals had no rise in BP with dopamine; when blood was infused, they developed hypertension (180 mm Hg, n1 = 85 mm Hg), and died of cardiac arrest.We conclude that blood transfusions to hypotensive, hypovolemic newborn lambs produces a predictable rise in BP. We are concerned about the clinical use of IV dopamine HC1 in small preterm babies until further studies in animals have demonstrated its safety.

144 HYPOVOLEMIA AND PERSISTENT FETAL CIRCULATION

Animal studies have demonstrated that acute blood loss may produce an increase in pulmonary vascular resistance. We postulate that hypovolemia may be one factor in the etiology of persistent fetal circulation (PFC). Circulating red cell volume (using 51 Cr labeling techniques) was measured in 5 neonates who presented with clinical findings of PFC (tachypnea, extra-pulmonary right-to-left shunting and normal cardiovascular anatomy at catheterization and/or autopsy).Birth weights of the 5 infants ranged from 2420-4140 (mean 3772) grams; gestational ages were 35-41 (mean 39) weeks, and all infants had normal 5-minute Apgar scores. Blood loss was not suspected in any of the 5 infants, nor were any transfused prior to their red cell volume studies. The initial hematocrits, glucose concentrations and calcium values were ≥ 55%, ≥ 95mg/dl, and ≥ 7.8mg/dl respectively. Four of the 5 infants expired despite vigorous resuscitative efforts, including transfusion.Red cell volume in all infants was deficient (30-42%, mean 36%). These data suggest that diminished circulating red cell volume may be involved in the etiology of persistent fetal circulation.

RESUSCITATION OF PRETERM INFANTS WITH EARLY POSTNATAL CARDIOVASCULAR SHOCK

This study was designed to evaluate the vascular compartment of infants born in the presence of maternal vaginal bleeding, and to describe one regimen for fluid and pharmacologic resuscitation. Eleven infants born to mothers with abruptio placentae exhibiting tachycardia (HR>150) and hypotension at 1 hr. age received empiric infusions of 20 ml/kg lactated Ringers solution (LR) and 20 ml/kg fresh blood. Blood volume (BV) determinations using the 51Cr RBC dilution technique were completed and BV deficits were then corrected by rapid transfusions of fresh blood. BV determinations were repeated and infants were given 1 μg/kg per min. continuous infusion of Dopamine if BV was normal and hypotension persisted.Eleven infants were studied and BV were markedly deficient as reflected in the mean red cell volume of 35 ml/kg (nl = 64), and mean total BV of 67 ml/kg (nl = 108). Two infants were infected (Group B strep, E. coli), and 2 infants remained hypotensive following BV restoration with a second transfusion. The infant with Strep infection and 1 infant given Dopamine expired.We conclude that preterm infants with hypotension resulting from abruptio placentae are markedly volume deficient and that proper management of these babies required BV determinations. Although early resuscitation with LR is efficacious (survival = 82%), treatment with Dopamine requires further evaluation.

Narcotic depression, feeding techniques, and lower esophageal sphincter (LES) pressures in newborn infants

Previous reports suggest that neonates subjected to maternal narcotic depression (MND) and/or fed by conventional orogastric feeding techniques are at high risk for aspiration pneumonia. We have evaluated this risk by determining LES pressure in 16 neonates of 30-42 weeks gestational age (GA). Neonates were fed 20 cal/oz. commercial similac in consecutive 24 hour time periods by intermittent gastric Ravage, continuous drip gastric gavage, and by continuous drip duodenal gavage. Before termination of each feeding period, LES pressures were determined using a single lumen side opening perfused catheter system currently being investigated at our institution.Narcotic depression was mimicked with 50 mg/kg body weight chloral hydrate given orally and LES pressure measurements were repeated in 90 min. After completion of LES studies at termination of the continuous drip duodenal period, the duodenal side opening feeding catheter was perfused with water at a rate of 1.3 ml/min. and pyloric sphincter (PS) pressures were recorded.The results obtained revealed that LES pressures are not affected by GA, mimicked MND, or the type of feeding technique utilized. Although we have demonstrated a functionally competent PS in the preterm infant as immature as 30 weeks GA, all preterm infants studied exhibited a competent LES and no advantages of nasoduodenal drip feedings are apparent.

DEMONSTRATION OF All ADEQUATE BARRIER TO GASTROESOPHAGEAL REFLUX IN THE NEWBORN AND PRETERM INFANT

Previous investigators have stated that newborn and preterm infants have an incompetent lower esophageal sphincter (LES) and are therefore susceptible to gastroesophageal reflux (GER) and aspiration pneumonia. We tested this hypothesis by comparing 5 “healthy” preterm and 10 fullterm infants to 10 infants under 1 yr. age with GER. GER was defined by free reflux of barium on barium swallow roentgcnograms, or the persistence of acidic fluid (pH 4) in the lower esophagus following gastric infusion on 0.1N HCL in a dose of 173 cc/m2 body surface area. LES pressure gradients were measured by withdrawing a single lumen side opening catheter perfused with H2O at 1.3 cc/min. from the stomach into the esophagus. Pressure gradients across the LES were as follows:All normal preterm and fullterm neonates exhibited LES pressure gradients strikingly higher than infants with GER (p<0.001).Our data suggest that infants with LES pressure gradients of less than 25 mmHg may be at risk for GER, and that healthy preterm and fullterm neonates have a competent lower esophageal sphincter.

SINGLE LUMEN PERFUSED CATHETER MANOMETRICS: A SENSITIVE NEW TECHNIQUE FOR MEASUREMENT OF LOWER ESOPHAGEAL SPHINCTER PRESSURES IN YOUNG INFANTS

Lower esophageal sphincter pressures (LESP) are generally measured during esophageal motility studies using multilumen water perfused catheters. Because of the large size of this assembly, gagging occurs, sedation is required and acceptable tracings may not be obtained. We have compared a large catheter assembly (three 1.2 mm single lumen catheters bound together with a 4.0 mm total diameter) with a 1.2 mm single lumen catheter with 1.0 mm side orifice. Triplicate studies were obtained by perfusing the catheters with water at 1.3 cc/min and slowly withdrawing from the stomach to LES. LESP were obtained in 10 fullterm newborns 3 hours after feeding; infants were then sedated and 90 min. later triplicate studies repeated. LESP were as follows:In two patients, gagging prevented the recording of adequate tracings from triple lumen catheters. Our data indicates that LESP can be successfully measured in the unsedated infant using a small single lumen catheter, and that higher pressures are obtained with the single lumen assembly.