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Biomedical subjects

W W Fox

Publications and source records attributed to W W Fox.

At least 55 records · Page 3Linked to original sources
PubMed1982

Physiologic implications of two different heat shields for infants under radiant warmers.

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.

Hot Temperature↗
PubMed1982

Effect of increased radiant warmer power output on state of hydration in the critically ill neonate.

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.

Critical Care↗
PubMed1982

Fluid, electrolyte, and glucose maintenance in the very low birth weight infant.

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.

Fluid Therapy↗
PubMed1982

Improvement in lung mechanics as a function of age in the infant with severe bronchopulmonary dysplasia.

Pulmonary function tests were performed in two groups of infants with bronchopulmonary dysplasia; a group less than 7 months of age with severe ventilator-dependent respiratory failure (Group A), and a group 7-22 months of age during resolution of their disease (Group B). Group A patients had significantly elevated minute volume, low specific compliance, elevated inspiratory and expiratory pulmonary resistance, and low functional residual capacity. Group B patients also demonstrated elevated minute volume, whereas specific compliance, inspiratory pulmonary resistance and functional residual capacity were within normal limits, and expiratory pulmonary resistance was only slightly above normal. With the exception of minute volume, the differences between the groups were significant (P less than 0.05). Sequential studies of resistance and compliance over 4-5 months in two patients in the younger group demonstrated values that approached or achieved normal range. It is concluded that pulmonary mechanics improve with age in the infant with severe bronchopulmonary dysplasia.

Aging↗
PubMed1981

Insensible water loss in the critically III neonate. Combined effect of radiant-warmer power and phototherapy.

To quantitate radiant power and insensible water loss under phototherapy, 12 neonates were studied under radiant warmers for one hour each with and without phototherapy. Warmer power was measured by wattmeter and thermopile. Power density received from phototherapy was 4.4 mW/sq cm. Addition of phototherapy to the servocontrolled warmer caused a disease in power density received from the warmer (17.1 to 12.9 mW/sq cm). However, the total radiant-power density received with phototherapy and the warmer combined (17.3 mW/sg cm) did not differ from net power density received without phototherapy (17.1 mW/sq cm). Insensible water loss, measured with a metabolic balance, increased from 2.54 to 3.73 mL/kg/hr, with addition of phototherapy. Since the total radiant-power density did not change, mechanisms other than increased radiant-power delivery must exist to explain the increased insensible water loss observed with phototherapy.

Female↗
PubMed1981

Effect of heat shielding on convective and evaporative heat losses and on radiant heat transfer in the premature infant.

Ten premature infants nursed on servocontrolled radiant warmer beds were studied in three environments designed to alter one or more factors affecting heat transfer (convection, evaporation, and radiation). In the control environment, infants were nursed supine on an open warmer bed. The second environment (walled chamber) was designed to reduce convection and evaporation by placing plastic walls circumferentially around the bed. In the third environment convection and evaporation were minimized by covering infants with a plastic blanket. Air turbulence, insensible water loss, and radiant warmer power were measured in each environment. There was a significant reduction in mean air velocity in the walled chamber and under the plastic blanket when compared to the control environment. A parallel decrease in insensible water loss occurred. In contrast, radiant power demand was the same for control and walled environments, but decreased significantly when infants were covered by the plastic blanket. This study suggests that convection is an important factor influencing evaporation in neonates nursed under radiant warmers. The thin plastic blanket was the most effective shield, significantly reducing radiant power demand.

Bedding and Linens↗
PubMed1981

The diuretic phase of respiratory distress syndrome and its relationship to oxygenation.

To determine the relationship between improvement in pulmonary function and diuresis in respiratory distress syndrome, ten consecutive premature infants requiring mechanical ventilation for severe RDS were studied. Every infant had a diuresis (output/intake greater than 80%), which began at 26 to 34 hours of life and which lasted for an additional 64-72 hours. The diuresis preceded significant improvement in AaDo2 and ventilator settings (IMV, PIP, PEEP) by 52 hours. There was a significant decrease in body weight among all study infants during the first four days of life despite an increase in fluid intake. This study suggests a relationship in RDS between improvement in oxygenation and removal of interstitial lung edema.

Body Weight↗
PubMed1981

Clinical correlates of successful weaning from mechanical ventilation in severe bronchopulmonary dysplasia.

The hospital records of 7 patients with severe bronchopulmonary dysplasia (BPD) were reviewed. All patients were ventilator dependent for prolonged periods (mean duration intermittent mandatory ventilation (IMV) 14.3 +/- 3.5 months) but eventually were successfully weaned from mechanical ventilation and sent home. The early phase of the disease was characterized by excessive CO2 retention, tachypnea, and inability to tolerate reductions in IMV. A turning point was reached halfway through the course of mechanical ventilation (7.3 +/- 1.4 months) which was identified by a persistent and significant reduction in PaCO2 and spontaneous respiratory rate. Thereafter, gradual reductions in IMV were generally well tolerated. Average monthly weight gain was less prior to the turning point it was subsequently.

Bronchopulmonary Dysplasia↗
PubMed1981

Successful extubation of neonates: clinical and physiological factors.

Arterial blood gases, pulmonary mechanics, lung volume measurements and clinical profiles were determined pre and postextubation in 19 infants recovering from respiratory disease. This study evaluated clinical and physiological factors which may be valuable in predicting successful extubation in neonates. Of the 19 patients, 4 required reintubation within 72 h. In this group of patients, the combined profile of low birth weight (1050 g), low gestational age (31 weeks), and high pulmonary resistance (inspiratory 278 cm H2O/L X sec, expiratory 309 cm H2O/L X sec) was significantly different from the 15 patients who were successfully extubated. In addition, lower pHa after extubation was also characteristic of those infants requiring reintubation.

Airway Resistance↗
PubMed1981

Use of external expiratory resistance in intubated neonates to increase lung volume.

Ten intubated neonates (weights 0.90 to 2.58 kg) recovering from respiratory disease had lung mechanics, respiratory patterns, and functional residual capacity measured at 0 cmH2O continuous positive airways pressure and then after application of serially increasing levels of external expiratory resistance. At an external expiratory resistance greater than 40 cmH2O/1 per second, there was a significant increase in mean functional residual capacity compared with control levels. Immediately after the application of external expiratory resistance, there was a significant decrease in flow which returned to control values after a few breaths. Tidal volume and respiratory rate decreased for a few breaths after the application of the external expiratory resistance, but returned to control values after several seconds. Study age, gestational age, or study weight had no appreciable effect on the relationship between functional residual capacity and external expiratory resistance. Application of external expiratory resistance may be useful for stabilising lung volume in neonates recovering from respiratory disease.

Humans↗
PubMed1981

Radiant warmer power and body size as determinants of insensible water loss in the critically ill neonate.

Twelve critically ill neonates mechanically ventilated for respiratory failure (mean weight 1.33 kg, mean gestation 31 wk) were studied to quantitate the effects of radiant power from a radiant warming device, body weight, and body surface area on insensible water loss. Radiant power density (Mw/cm2) was measured using a wattmeter and thermopile transducer. Insensible water loss was measured using a Potter Baby Scale. Weight correlated inversely with insensible water loss, (r = -0.86, P less than 0.001). Radiant power density correlated inversely to weight, (r = -0.71, P less than 0.001). There was a significant increase in insensible water loss as radiant power density increased, (r = 0.54, P less than 0.05). Net radiant power received (W/kg) by infants over their exposed surface area, correlated directly to insensible water loss, (r = 0.67, P less than 0.01) irrespective of body weight. Critically ill neonates ventilated for respiratory failure and nursed under radiant warmers incurred greater insensible water losses than previously reported for well infants. The magnitude of this increased insensible water loss is inversely related to body size and is determined directly by the radiant power density required to maintain body temperature.

Apnea↗
PubMed1980

The effect of external expiratory resistance on lung volume and pulmonary function in the neonate.

To investigate the acute physiologic effects of external expiratory resistance on lung function in extubated neonates recovering from respiratory disease, lung mechanics, respiratory patterns, and functional residual capacity were measured in ten neonates dueing a control period and immediately after application of an external expiratory resistance of 30 cm H2O/l/second via a face mask. Following application of EER, mean FRC increased by 40.8% (P less than 0.05). The work of breathing was significantly increased after the EER was applied; there was also a significant increase in measured expiratory resistance and a decrease in inspiratory-expiratory time ratio. The change in lung volume was rapid, requiring less than five seconds for the new end-expiratory level to be reached. Dynamic lung compliance, inspiratory resistance, and respiratory rate did not change during any phase of the study. The application of external expiratory resistance may have potential therapeutic value by increasing lung volume in infants recovering from respiratory disease.

Airway Resistance↗
PubMed1980

A noninvasive method for recording central and obstructive apnea with bradycardia in infants.

A noninvasive method for recording central and obstructive apnea with bradycardia is described. A polygraphy was used to record impedance pneumography, heart rate, and air flow with a nasally positioned thermistor. Episodes of apnea both central and obstructive were measured. In addition, episodes of bradycardia were recorded and the relationship to respiratory events documented. The application of the method to 12 patients with 13 clinical diagnosis for observed episodes demonstrated that the clinical diagnoses were inaccurate in 10 of 13. The method improved diagnoses by detecting apnea, both central and obstructive, not detected by the use of routine monitoring.

Apnea↗
PubMed1980

Monitoring radiant power in the critically ill newborn under a radiant warmer.

To evaluate radiant power received by infants under radiant warmers, 11 neonates (mean gestational age 32.2 weeks, mean weight 1.50 kg) were monitored. A wattmeter was used to evaluate warmer power (watts), and a thermopile placed at bed level was used to correlate warmer power to radiant power density received (mw/cm2). Warmer power ranged from 133-301 watts. A linear relationship existed between warmer power and radiant power density received (r = 0.97, p < 0.001). After establishing that radiant power delivery could be monitored with a wattmeter, this technique was used to quantitate radiant power in a small series of infants with and without a plastic shield. Radiant power density received decreased in all infants when shielded (mean 14.6-11.2 mw/cm2, p < 0.01). This study demonstrates: (1) radiant warmer power can be monitored with a wattmeter; (2) warmer power correlates to radiant power density received; and (3) radiant power monitoring can be used to evaluate radiant power demands in specific clinical situations.

Apnea↗