Dew-point hygrometry system for measurement of evaporative water loss in infants.

Evaporation of water from the skin is an important mechanism in thermal homeostasis. Resistance hygrometry, in which the water vapor pressure gradient above the skin surface is calculated, has been the measurement method of choice in the majority of pediatric investigations. However, resistance hygrometry is influenced by changes in ambient conditions such as relative humidity, surface temperature, and convection currents. We have developed a ventilated capsule method that minimized these potential sources of measurement error and that allowed second-by-second, long-term, continuous measurements of evaporative water loss in sleeping infants. Air with a controlled reference humidity (dew-point temperature = 0 degree C) is delivered to a small, lightweight skin capsule and mixed with the vapor on the surface of the skin. The dew point of the resulting mixture is measured by using a chilled mirror dew-point hygrometer. The system indicates leaks, is mobile, and is accurate within 2%, as determined by gravimetric calibration. Examples from a recording of a 13-wk-old full-term infant obtained by using the system give evaporative water loss rates of approximately 0.02 mgH2O.cm-2.min-1 for normothermic baseline conditions and values up to 0.4 mgH2O.cm-2. min-1 when the subject was being warmed. The system is effective for clinical investigations that require dynamic measurements of water loss.

Light variability in the modern neonatal nursery: chronobiologic issues.

The role that nursery light variability may play in modulating infant biological rhythms is being studied in Stanford Medical Center's Neonatal Intensive Care (NICU) and Intermediate Care (IN) Nurseries. In this investigation, spatial and temporal variability in illuminance was determined at 20 sites within each nursery over a 5-day period. The analysis of 240 measurements at 30 min intervals from each site revealed marked variability in illumination with respect to both time and position in the nursery. These aperiodic lighting patterns differed greatly from the published characterization of NICUs as having 'constant' illumination. Light pulses of variable frequency, intensity, and duration were common at each of the 40 bedsites studied. Given the powerful impact of light on circadian rhythmicity and sleep in adults, the results from this study suggest that modern NICU lighting, while implemented to facilitate intensive care, may have adverse effects on infant development. Future studies on the influence of light on biological rhythmicity and sleep are essential to provide a framework for clinical and environmental interventions, which may play a significant role in improving developmental outcome in hospitalized preterm or term infants.

Distribution of waste anesthetic gases in the operating room air.

Epidemiologic and animal studies identify a strong relationship between chronic exposure to anesthetic gases and health hazards. Efforts to reduce exposure of personnel require an understanding of the distribution of anesthetic waste gases in the operating room air. Concentrations of nitrous oxide and halothane were measured at numerous stations throughout an operating room and a delivery room in the absence of personnel. Air conditioning flow rates and flow patterns were varied, as was the height of the anesthetic gas source. Air flow patterns were found to dominate the anesthetic gas distribution, while buoyancy effects were negligible. Venting waste gases at the floor does not significantly reduce exposure of personnel. Areas of high concentration were observed; their occurrences and locations varied strongly with air flow patterns. The exhaust grille is the best location for a single measurement of the average room concentration. Recirculating air-conditioning systems reduce energy costs; however, only the non-recirculating portion of the air exchanges reduces waste gas concentrations.