Assessment of radiant temperature in a closed incubator.

In closed incubators, radiative heat loss (R) which is assessed from the mean radiant temperature (Tr) accounts for 40-60% of the neonate's total heat loss. In the absence of a benchmark method to calculate Tr--often considered to be the same as the air incubator temperature-errors could have a considerable impact on the thermal management of neonates. We compared Tr using two conventional methods (measurement with a black-globe thermometer and a radiative "view factor" approach) and two methods based on nude thermal manikins (a simple, schematic design from Wheldon and a multisegment, anthropometric device developed in our laboratory). By taking the Tr estimations for each method, we calculated metabolic heat production values by partitional calorimetry and then compared them with the values calculated from V(O2) and V(CO2) measured in 13 preterm neonates. Comparisons between the calculated and measured metabolic heat production values showed that the two conventional methods and Wheldon's manikin underestimated R, whereas when using the anthropomorphic thermal manikin, the simulated versus clinical difference was not statistically significant. In conclusion, there is a need for a safety standard for measuring TR in a closed incubator. This standard should also make available estimating equations for all avenues of the neonate's heat exchange considering the metabolic heat production and the modifying influence of the thermal insulation provided by the diaper and by the mattress. Although thermal manikins appear to be particularly appropriate for measuring Tr, the current lack of standardized procedures limits their widespread use.

Warming the premature infant in the delivery room: Quantification of the risk of hyperthermia.

AIM: The efficacy and safety of three polyethylene bags commonly used to prevent hypothermia in premature infants was assessed. METHODS: To simulate transfer from the delivery room to a secondary care unit, a thermally stable, bonneted mannequin (skin temperature: 34.4 °C) was placed in a climate chamber under different conditions: with a radiant warmer, with various polyethylene bags (open on one side, closed by a draw-string at the neck, or a "life support pouch" with several access points) or without a bag. RESULTS: With the radiant warmer turned on, the mean reduction in heat loss from the nude mannequin was 50.8 ±â€¯1.7% (p < 0.0001, vs. warmer off). The mean reduction in heat loss (vs. no bag) was 55.0 ±â€¯0.9% for the drawstring bag, 49.0 ±â€¯2.2% for the standard bag (p = 0.0001), and 48.1 ±â€¯0.7% for the life support pouch (p = 0.006). When a radiant warmer + polyethylene bag were used, heat stress (body temperature: 38 °C) and severe hyperthermia (40 °C) occurred after 11 and 34 min, respectively. CONCLUSION: Caution must be taken when using a radiant warmer and polyethylene bag with a premature infant. Heat stress can occur in only 11 min. Continuous body temperature monitoring is therefore required.

Use of a Polyethylene Bag to Reduce Perioperative Regional and Whole-Body Heat Losses in Low-Birth-Weight Neonates.

In the delivery room, wrapping a low-birth-weight neonate (defined as ≤2.499 g) in a polyethylene bag reduces the risk of hypothermia. However, extended use of the bag (e.g., during neonatal surgery) might conceivably increase the risk of thermal stress and thus body overheating. Here, we assessed the efficacy of a polyethylene bag in infants assigned to wrap (W) or nonwrap (NW, control) groups during placement of a percutaneous vena cava catheter by applying a new mathematical model that calculates heat exchanges for covered and uncovered body segments. At the end of the placement procedure, the W and NW groups did not differ significantly in terms of whole-body heat loss (15.80 versus 14.97 kJ·h-1·kg-1, resp.), whereas the abdominal skin temperature was slightly but significantly higher (by 0.32°C) in the W group. Greater evaporation in the W group (2.49 kJ·h-1·kg-1) was primarily balanced by greater whole-body radiant heat loss (3.44 kJ·h-1·kg-1). Wrapping the neonate in a polyethylene bag provides a small thermal benefit when catheter placement takes a long time. Given that polyethylene is transparent to radiant energy, it might be of value to incorporate polymers that are less transparent at infrared wavelengths.

Effect of posture on the thermal efficiency of a plastic bag wrapping in neonate: assessment using a thermal "sweating" mannequin.

To assess the various heat exchanges with the environment a multisegment, anthropometric, thermal mannequin representing a neonate with a birth weight of 900 g has been designed. The mannequin simulates not only dry heat loss (radiative+conductive+convective body heat exchanges) but also the evaporative skin water loss which can be encountered in low-birth-weight neonates. The model was placed in the supine or prone position in a closed incubator (air temperature, 33 C; relative air humidity, 50%; air velocity below 0.1 m s(-1)). Experiments were performed with the mannequin either naked or wrapped in a flexible, plastic bag (with the head exposed) used to prevent excessive body water loss at delivery and during the following hours About 30% of the model's total surface was wetted with water. Our results demonstrated that body position does not modify dry and evaporative heat losses, whatever the experimental conditions. The plastic bag acts rapidly and reduces total heat loss by 30% to 34%, primarily through a reduction in evaporative water loss (between 5.4 and 6.7 g kg(-1) h(-1)). When the bag is present, the uncovered surface of the head accounts for about 50% of the total heat loss. This simple and inexpensive solution can be used to prevent thermal stress and dehydration in very small premature neonates.

Polyethylene bag wrapping to prevent hypothermia during percutaneous central venous catheter insertion in the preterm newborn under 32 weeks of gestation.

AIM: In preterm neonates, during nursing procedures, body temperature decreases. This study evaluates the interest of polyethylene bag wrapping to prevent this decrease during percutaneous central venous catheter (PCVC) insertion procedure, in preterm neonates under 32 weeks of gestation nursed in closed incubators. METHODS: This prospective observational study compared two periods: [May 2009-September 2009]: "without polyethylene bag wrapping" and [October 2009-March 2010]: "with polyethylene bag wrapping". The main criterion was newborn skin temperature at the end of the procedure. RESULTS: There was no difference between the two groups for skin temperature before the procedure (36.9 ± 0.3 °C versus 36.9 ± 0.3 °C; p = NS). The skin temperature at the end of the procedure was lower in the "without bag wrapping" group (36.0 ± 0.5 °C) compared to the "bag wrapping" group (36.4 C ± 0.5 °C; p = 0.01). Furthermore, no skin temperature at the end was higher than 37.4 °C in the bag wrapping group. CONCLUSION: The use of a polyethylene bag was effective in decreasing skin temperature fall during a PCVC insertion procedure in our population. No side effects were observed. The benefit of prolonged wrapping or for shorter procedure should be evaluated.