Neil K. Edwards

Apnea in premature infants and incubator-air-temperature changes.

Abstract The thermal events associated with apneic spells-were recorded during the monitoring of selected premature infants housed in incubators controlled by servo mechanism to maintain skin temperature between 35.8 and 36.6°C. The temperature changes that occurred during the 120 seconds before the onset of apnea were compared to the changes measured exactly 15 minutes before each episode. Of the 126 apneic spells 70 occurred during a rise, 44 during a fall, and 12 during a plateau (no change) in air temperature. During the nonapneic control periods, there were 41 rises, 64 falls and 21 plateaus in temperature. The onsets of apnea, therefore, were preceded by rising air temperatures more commonly (p less than 0.001) than matched moments without apnea. This correlation, supported by dramatic examples of apnea with sudden increases in air temperature, adds to the evidence that present incubator thermal control may help trigger apnea.

The transparent baby bag. A shield against heat loss.

Abstract Swaddling of newborn infants in double-layered, clear-plastic bags with a head shield allowed less heat loss than a radiant heater alone. Protection against heat loss is increased if the plastic bag is combined with a radiant heater. This protection is accomplished without severe compromise of either visualization or handling of the infant.

Neonatal hypocalcemia in infants with birth asphyxia

Summary Forty-two infants with birth asphyxia (1 minute Apgar Score of 6 or less) and 42 control infants matched for gestational age and sex were studied serially from birth to 72 hours of age. In infants with birth asphyxia, serum Ca at 12 and 24 hours was lower than that of control infants and serum Mg was lower from 12 to 48 hours. No differences were detected in urinary Ca and Mg excretion. A calcemic response to parathyroid extract was elicited. Lower serum Ca values were found in asphyxiated infants who received sodium bicarbonate therapy, even when gestational age was considered. Serum P was higher in infants with birth asphyxia, whereas urinary P excretion was not different from infants without asphyxia. It is speculated that bicarbonate therapy, increased phosphate loads, and functional hypoparathyroidism may play contributory roles in the pathogenesis of the hypocalcemia of birth asphyxia.

Artifacts in the measurement of skin temperature under infant radiant warmers

All skin temperature probes measure, to some extent, operative temperature as well as skin temperature, and thus artifactually measure a temperature different from true skin temperature. To assess the magnitude and direction of these artifacts in the measurement of surface temperature in radiant warmers designed for human infants, the artifactual deviation of measured surface temperatures from mean surface temperature was determined under a short-wavelength warmer and a long-wavelength radiant warmer, using a copper ball as an experimental model. The measuremends were made using both a disk-shaped thermistor and a tubular thermistor. All measurements were made near the top of the hemisphere of the ball facing the heating element of the warmer. In all cases, the average artifact was negative. That is, even on the surface of the ball near the radiant heat source, the surface temperature probes recorded an artifactually low temperature. In the analogous clinical setting, a some-what larger negative artifact would be expected.

A computer-generated blood gas display in a newborn intensive care unit.

A computer was programmed to collect, store, analyze, and display blood gas data in a newborn intensive care unit. Data were displayed if they were (1) markedly abnormal or (2) represented a worsening trend. A controlled study demonstrated that, with the display, the markedly abnormal blood gas values were followed by normal values in a shorter period, and fewer worsening trends progressed. However, with the computer-generated display, there were more overcorrections of both the markedly abnormal blood gas values and the detected worsening trends. The occurrence of pneumothoraces was associated with these overcorrected blood gas values. There were no significant differences in duration of supplemental oxygen administration, duration of tracheal intubation, or mortality between the infants cared for during the time of the computer-generated display and those cared for during the control period. This study demonstrates both benefits and risks of computer-generated displays and emphasizes the need for thorough evaluations of such systems.

Thermal Patterns on the Backs of Cold Stressed Babies

A Barnes M-101 Infrared Radiometer was used to map the skin temperature changes occurring on the backs of nine selected unswaddled newborn babies in a room air conditioned at 26.3°C (range 24.4–28.1°C). Polaroid photographs of the serial thermal variations observed during cooling were analysed with a densitometer to provide quantitative support for grossly evident difference in rates of cooling over the surfaces examined. In particular, not only the interscapular but also the posterior flank skin regions cooled significantly less (p < 0.05) than skin over the coccyx, deltoid, midback, and lateral flank regions. Brown fat collections have been identified in the interscapular fat pads of newborns, and thermography may prove a valuable aid in monitoring the activity of this tissue. On tghe other hand only small amounts of multilocular fat have been identified in subcutaneous flank tissue. Since in this ealy experience with thermography the flank tissue has been found to mirror the interscapular tendency to cool relatively little in cold stressed babies, continued caution must be exercized in interpreting the significance of the ‘warm nape of the newborn’ as it relates to brown fat activity. Further experience with radiometry may prove useful in clarifying this and other enigmatic problems relating to the complex flux of hear in newborn babies.

1322 INCUBATOR HUMIDITY WITH DIFFERENT HUMIDITY RESERVOIR BAFFLE SYSTEMS

Although important in reducing heat and water losses from newborns, incubator humidities are difficult to predict and control. A removable metal baffle for use in an incubator humidity reservoir has been recently modified by one manufacturer and contributes to this unpredictability. Using an electric hydrometer, the relative humidities (R.H.) of 7 Air-Shields incubators were measured 1) with no baffle in the humidity reservoir, 2) with the manufacturers older and larger iron baffle and 3) with a recently introduced smaller steel “W” shaped baffle. Incubator temps. were servo controlled to 34°C, and full humidity reservoirs were opened to maximum settings.Both baffles increase incubator humidity, but the variability was greater with the smaller steel baffles, and the 3.7% increase with this steel baffle is significantly less (p<0.01) than the 14.1% increase with the larger iron baffle. Since this observation, excess heat and water losses from newborns have been corrected by replacing the newer and smaller baffles with the larger iron baffles. This experience reinforces the opinion that incubators must not only be designed and modified carefully, but also used knowledgeably.

1011 Computer-Assisted Newborn Care

Of 173 infants between 500-2400 grams with RDS and born in the same hospital, 33 were provided care in computer-monitored & controlled enclosed incubators. Only the availability of an unocupied computerized incubator at the time of each of their admissions determined their selection. For purposes of analysis each of the 33 infants in the computer-assisted care study group was matched with the one infant in the remaining group of 140 routinely cared for infants that best matched the study infant for birth weight, sex, color, gestation, Apgar scores, maternal age, gravidity, parity, birth date, economic status, and major admission diagnoses. The matching of infants was confirmed statistically and was done by a neonatologist uninvolved with the study and having no foreknowledge of any infants survival outcome. Four (12%) of the 33 study infants and 14 (42%) of the control infants died within the first 7 days of life. This difference was significant at p<.01. Although there was no significant difference in the number of infants in the two groups requiring mechanical respiratory support, the mortality rates of 17 study infants who received respirator care was significantly lower (11.8%) than the rate tabulated for 17 matched respirator-cared-for control infants (65%), (p<.005). Computer-assisted care, therefore, enhances infant survival by some mechanism that alters the outcome but not the need to support some infants with a respirator.