Biomedical subjects
Publications and source records attributed to S Baumgart.
In this article, the authors introduce the concept of a transitional physiology which governs fluid and electrolyte balance in the immediate postnatal period. The important impact of the extrauterine environment on fluid balance is also discussed. Finally, the pathophysiology of diuresis in RDS, and fluid shifts in the VLBW infant with therapeutic recommendations are presented.
Inductive plethysmography is a noninvasive method of measuring lung volumes in infants. This technique, however, has had very limited use in premature newborns because of the difficulty of calibrating the device with regard to the small tidal volumes (VT) in such infants. The present study describes a facilitated calibration of the inductive plethysmograph in low birth weight infants. The technique depends on generating significantly different compartmentalization of VT into rib cage and abdominal components by changing the infant's position from supine to upright. Linear regression analyses were performed to compare VT measurements made in 9 premature infants with the inductive plethysmograph and the pneumotachygraph; an overall Z-transformed correlation of 501 breath-to-breath comparisons yielded an r value of 0.80; the mean VT (pneumotachygraph) was 13.9 +/- 4.7 ml SD; the mean VT (inductive plethysmograph) was 14.3 +/- 5.1 ml SD. It is concluded that inductive plethysmography is an accurate method to measure VT in small premature infants. Moreover, the ease of the two-position technique for calibration of the device gives the inductive plethysmograph greater utility as a clinical and research tool for measuring lung volumes in premature infants.
We describe the clinical syndrome, medical management, etiology, and neurologic outcome of stroke diagnosed by computed tomographic scan in 11 full-term neonates encountered during a two-year period. Neonatal stroke is relatively common and may appear in the setting of diverse cerebrovascular disorders such as hypoxic-ischemic encephalopathy, polycythemia, acute severe hypertension, and embolization. Repetitive, persistently unifocal motor seizures heralded localized cerebral injuries in eight infants. The majority of patients did not display any other lateralized clinical neurologic signs. An electroencephalogram revealed a focal or lateralized functional central nervous system abnormality in ten cases. All of the initial computed tomographic scans were focally abnormal. However, cranial ultrasound examinations were insensitive to stroke in nine patients. Medical management included careful cardiorespiratory support, correction of coexisting metabolic or system abnormalities, and aggressive administration of anticonvulsants to promptly eliminate seizures. Limited follow-up suggests that many affected infants may enjoy favorable outcomes.
A spontaneous diuresis that precedes the improvement of pulmonary function has been described in patients with respiratory distress syndrome (RDS). The developmental changes in renal physiology responsible for this spontaneous diuresis are not completely understood. To describe the mechanisms responsible for the spontaneous diuresis, serial renal function studies were performed during the first five days of life in nine premature neonates with RDS. Diuresis was defined as a urine output that was at least 80% of fluid intake; prediuretic, diuretic, and postdiuretic periods were observed in all study infants. Oxygenation did not improve until the postdiuretic period. Renal function studies disclosed a significant increase in free water clearance during the diuresis with the production of dilute urine and a reciprocal rise in serum sodium concentration and plasma osmolality. The glomerular filtration rate increased at the onset of diuresis and remained elevated after the diuresis ended; however, the proportion of filtrate excreted was significantly elevated during the diuresis compared with prediuretic and postdiuretic values. These data suggest that the diuresis in patients with RDS is a water diuresis secondary to an endogenous water load.
The use of umbilical artery catheters has become commonplace in the intensive care nursery and has facilitated management in the very ill newborn infant. Thrombotic complications associated with the use of such catheters may be as high as 30%. The successful, nonsurgical management of either complete or partial aortic thrombosis, associated with renovascular hypertension, is reported in three infants. Aggressive supportive medical management resulted in a satisfactory outcome in all three infants.
The purpose of our study was to compare the effects of narrow-spectrum blue light and broad-spectrum white light on the production of bilirubin photo-isomers in human infants with jaundice. Twelve preterm infants were studied under both white and blue light. Irradiance at 450 nm was controlled at 12 microW/cm2/nm for both light sources. Each light condition (white or blue) was administered for 12 hours. Bilirubin isomers (4Z,15E-bilirubin and lumirubin) were measured before therapy and after 12 hours of each sequential light condition. The percentage of 4Z,15E-bilirubin was greater under blue light than under white light (P less than 0.01) phototherapy. There was no significant difference in percentage lumirubin under white or blue light therapy. Our data indicate that blue light is more effective than white light in producing 4Z,15E-bilirubin in vivo. Our study demonstrates that when irradiance in the bilirubin absorbance spectrum is constant, the color of light (spectral distribution) will determine the relative concentrations of photo-isomers produced.
Despite the frequency with which theophylline is administered to premature infants, there are few reported cases of neurotoxicity. We describe a theophylline-treated premature infant with chronic bronchopulmonary dysplasia and hepatitis who displayed a focal seizure and irritability followed by other systemic signs of theophylline intoxication, at a postnatal age of 5 months. An unrecognized accidental drug overdose combined with a prolonged elimination half-life were responsible for clinical intoxication. The potential mechanisms of theophylline's neurotoxicity are discussed briefly.
The partition of heat loss into convective and evaporative components, and heat gain into metabolic rate of production and radiant heat needed to maintain thermal equilibrium was determined in ten premature neonates (weight 1.39 +/- .08 [SEM] kg, gestation 31 +/- 1 weeks) who were nursed naked and supine on open radiant warmer beds. Warmer beds were servocontrolled to maintain each infant's abdominal skin temperature at three different levels: 35.5, 36.5, and 37.5 degrees C. The quantity of radiant heat delivered by the warmer in vivo was measured directly and compared with the heat need calculated from the partition. Convective heat loss comprised the major component of net heat loss and increased significantly with servocontrol temperature from 2.86 +/- .24 to 3.27 +/- .23 kcal/kg/h (P less than .01), and to 3.72 +/- .26 kcal/kg/h (P less than .001). Evaporative heat loss increased with servocontrol temperature from .96 +/- .13 to 1.41 +/- .33 kcal/kg/h, and to 1.35 +/- .32 kcal/kg/h, but this increase was not significant. Metabolic rate decreased from 2.08 +/- .17 to 1.90 +/- .14 kcal/kg/h, and to 1.78 +/- .16 kcal/kg/h with increased servocontrol temperature, but this decrease was not significant. Radiant heat needed to maintain infants at higher temperatures increased from 1.73 to 2.80 kcal/kg/h, and to 3.32 kcal/kg/h. The radiant heat delivered by the warmer to infants was directly proportional to the heat need calculated from the partition (r = .68, P less than .001).
Photoisomerization of native bilirubin to more polar configurational isomers (Z,E-bilirubin) and structural isomers (lumirubin) was studied in 20 premature infants with physiologic jaundice to determine the effect of low-dose (6 microW/cm2/nm) v high-dose (12 microW/cm2/nm) phototherapy. Patients were assigned prospectively to receive either low- or high-dose treatment. Study groups were comparable with regard to birth weight, gestational age, and total bilirubin prior to the initiation of phototherapy. Treatment was administered with white light produced by a commercially available halogen-tungsten lamp. Dose was measured periodically during the study to ensure a uniform distribution of irradiance and constant exposure. Sera for photoisomers were obtained before initiation of treatment and at two, four, and eight hours. Photoisomers expressed as a percent of total bilirubin were determined using high-pressure liquid chromatography. Serum proportion of both configurational and structural isomers increased with the duration of phototherapy in both treatment groups. There was no significant difference between the percent of configurational isomers in low- and high-dose phototherapy groups. However, high-dose treatment produced a significantly higher proportion of the structural isomer lumirubin after four hours (0.7% low dose v 1.3% high dose, P less than .05). These data confirm that phototherapy results in both configurational and structural isomerization of bilirubin in vivo. Furthermore, the previously described "dose" effect of phototherapy may be attributed to the production of the structural isomer, lumirubin.
Eight very low-birth-weight premature infants (mean birth weight 1.11 +/- 0.05 [SEM]kg, mean gestation 30 +/- 1 weeks, and mean age 9 +/- 2 days) were studied under servocontrolled radiant warmers with and without a loosely fitted, transparent, and flexible Saran plastic blanket. Metabolic rate was significantly less in all infants when covered by the blanket (oxygen consumption was 7.99 +/- 1.13 mL/kg/min v 9.00 +/- 1.10 mL/kg/min uncovered, P less than .001). There were also significant reductions in insensible water loss (1.86 +/- 0.18 v 1.25 +/- 0.20 mL/kg/h, P less than .01) and in heat demand from the radiant warmer (14.3 +/- 1.3 v 9.9 +/- 1.4 mW/cm2, P less than .001) when infants were nursed under the blanket compared with the control condition, respectively. Covering the critically ill, very low-birth-weight infant nursed under a radiant heater with a thin, transparent layer of Saran is beneficial in reducing oxygen consumption, insensible water loss, and the need for exposure to high levels of radiant heat. Further investigation to confirm the benefits and possible complications of plastic blankets should be conducted before routine use can be recommended.
Coagulase-negative staphylococci are infrequently recognized as pathogens responsible for life-threatening nosocomial infections in high-risk neonates. To determine the incidence, appearance, and antibiotic sensitivity of infections with these organisms, 416 infants were surveyed. Fifty infants (12%) had blood cultures positive for coagulase-negative Staphylococcus. Fourteen cultures (13 infants; mean birth weight +/- SD, 1.91 +/- 1.13 kg; gestational age +/- SD, 34 +/- 6 weeks) were identified as representing true bacteremia (pure growth of the organism in both bottles of one or more blood cultures exhibiting identical antibiotic sensitivities). Twelve cultures exhibited clinical signs of sepsis, and WBC counts were suggestive of sepsis in seven cases. Thirteen organisms were penicillin resistant, eight were oxacillin resistant, and all were sensitive to vancomycin. Coagulase-negative staphylococci are currently the most common nosocomial pathogens at our hospital. Therapy for suspected coagulase-negative staphylococcal sepsis should include vancomycin hydrochloride.
Thirteen premature infants receiving mechanical ventilation for respiratory distress syndrome developed pneumopericardium. All had high peak inflation pressures (mean, 42 mm Hg; range, 26 to 60 mm Hg), and all were on positive end-expiratory pressure (PEEP) ventilation (mean, 3.1 mm Hg; range, 2.1 to 5.7 mm Hg) at the time that pneumopericardium occurred. Arterial blood gases, indices of respiratory support, and hemodynamic data were reviewed before and after the onset of pneumopericardium in all patients. There was a statistically significant increase in peak inflation pressure (PIP) over the 16 hours prior to onset of pneumopericardium (p less than 0.05). There was, however, no significant relationship between onset of pneumopericardium and other respiratory variables, including PEEP. In the majority of patients, pneumopericardium was associated with cardiac air tamponade. Various forms of treatment for pneumopericardium were attempted, including observation, needle aspiration, and insertion of pericardial tubes. Review of the therapy indicates that insertion of a pericardial tube under direct vision is the safest and most effective means of treating pneumopericardium in infants. These data also suggest that PIP is more important than PEEP in predisposing neonates with respiratory distress syndrome to pneumopericardium.
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To study the effects of two different heat shields commonly used under radiant warmers (thin plastic blanket vs a plastic body hood) on premature newborn infants, eight neonates were studied to measure insensible water loss and radiant power density at the skin under control and two shielded conditions. The body hood was found to diminish transmission of radiant heat to the infant's skin by 80%, absorbing heat and becoming warm (P less than 0.001). The plastic blanket absorbed only 15% of radiant warmer heat output (P less than 0.01). Insensible water loss was significantly less under the plastic blanket (1.88 +/- 0.4) ml/kg/hour) than under control (2.70 +/- 0.50 ml/kg/hour, P less than 0.01) and hood (2.86 +/- 0.32 ml/kg/hour, P less than 0.05) conditions. There was no decrease in insensible water loss under the hood compared to controls. This study demonstrates that a thin plastic blanket is the more effective shield against insensible water loss under a radiant warmer. Caution should be exercised with any shielding device to prevent interference with radiant heat delivery.
To correlate radiant warmer bed power output with state of hydration in the critically ill infant, warmer power input was measured by a wattmeter and recorded by an on-line computer every 5 sec for 2 periods of 8-24 h each in 11 newborns with respiratory distress syndrome (mean birth weight 1.42 kg, mean gestational age 31.4 weeks). The 2 periods were compared to define a high and a low radiant power period. Fluid intake and urine output, urine and serum osmolalities, serum electrolytes, and free water clearance during each study period (high vs low radiant power) were also compared. Mean radiant power density received during periods of high radiant power output (8.93 mw/cm2) was significantly greater than during periods of low radiant power output (7.85 mw/cm2, p less than 0.001). Mean urine osmolality and fluid intake to output ratio were also significantly increased during periods of high radiant power density. There was a trend toward increased serum osmolality and decreased free water clearance during periods of high radiant power; however, these differences were not significant. This study suggests that prospective measurement of radiant power density delivered to critically ill newborns may be clinically significant in predicting an infant's state of hydration.
The low birth weight premature newborn, less than 1000 gm, represents a difficult problem in the management of parenteral fluid, electrolyte, and glucose maintenance. To assess this problem, six infants (mean weight 720 gm, range 575-835 gm; mean gestation 26.5 +/- 0.4 SEM wk) nursed under radiant warmers were evaluated during the first three days of life to determine volume of fluid intake, sodium and dextrose intakes, and urine output. Insensible water loss (IWL) was measured on a metabolic scale. In accordance with current recommendations, infant received fluid volumes of 111 +/- 10, 152 +/- 16, and 191 +/- 27 ml/kg/day on days 1, 2, and 3, respectively. Sodium intake (usually as 0.2% saline) ranges 0-8.5 mEq/kg/day. Dextrose infusions (as 10% solution) ran from 3.3 to 13.7 mg/kg/min. Insensible water loss measured 159 +/- 15 ml/kg/day. Despite increasing fluid intake, serum sodium concentration increased from 141 +/- 3 mEq/l on day 1 to 155 +/- 7 mEq/l on day 3 (p less than 0.05). None of the infants became oliguric and only two urine specimens had specific gravity greater than 1.015. These data demonstrate a larger insensible water loss than reported previously in small infants, but increasing the administration of standard 10% dextrose and 0.2% saline solution to balance insensible losses may result in sodium and glucose overload. Recommendations are made for adjusting parenteral fluid therapy for birth weight groups 600-800, 801-1000, 1001-1500, and 1501-2000 grams and for environmental conditions or radiant warmer or incubator, with or without plastic shielding or phototherapy.
Radiant warmers are a powerful and efficient source of heat serving to warm the cold-stressed infant acutely and to provide uninterrupted maintenance of body temperature despite a multiplicity of nursing, medical, and surgical procedures required to care for the critically ill premature newborn in today's intensive care nursery. A recognized side-effect of radiant warmer beds is the now well-documented increase in insensible water loss through evaporation from an infant's skin. Particularly the very-low-birth-weight, severely premature, and critically ill neonate is subject to this increase in evaporative water loss. The clinician caring for the infant is faced with the difficult problem of fluid and electrolyte balance, which requires vigilant monitoring of all parameters of fluid homeostasis. Compounding these difficulties, other portions of the electromagnetic spectrum (for example, phototherapy) may affect an infant's fluid metabolism by mechanisms that are not well understood. The role of plastic heat shielding in reducing large insensible losses in infants nursed on radiant warmer beds is currently under intense investigation. Apparently, convective air currents and not radiant heat energy may be the cause of the observed increase in insensible water loss in the intensive care nursery. A thin plastic blanket may be effective in reducing evaporative water loss by diminishing an infant's exposure to convective air currents while being nursed on an open radiant warmer bed. A rigid plastic body hood, although effective as a radiant heat shield, is not as effective in preventing exposure to convection in the intensive care nursery and, therefore, is not as effective as the thin plastic blanket in reducing insensible water loss. Care should be exercised in determining the effect of heat shielding on all parameters of heat exchange (convection, evaporation, and radiation) before application is made to the critically ill premature infant nursed on an open radiant warmer bed.