Hypothermia is a major cause of morbidity and mortality particularly in very low birth weight (VLBW) infants 1. Preterm infants are particularly vulnerable because of increased heat loss, primarily through evaporation, and immature and/or absent thermoregulatory mechanisms 2. At birth, the infant is exposed to a colder temperature than it has experienced in utero. The fetus is surrounded by amniotic fluid at maternal body temperature. Following birth, there is a significant decrease (>10°C) in the surrounding temperature. Considerable amount of heat can be further lost through conduction (placed on a cold blanket), convection (cold air draft), radiation (to cold objects), and evaporation (through transcutaneous loss of water), which is the most important contributor in preterm infants 3.
Current resuscitation guidelines recommend placing the infant under a radiant warmer, drying the skin, removing wet linen, and placing the infant on a dry prewarmed blanket to reduce heat loss. Despite these measures, very preterm infants are at a high risk for cold stress 3.
However, irrespective of these attempts to reduce heat loss in the delivery room, the incidence of hypothermia among preterm neonates born at or below 1500 g still varies from 31 to 78% 1. Prevention and management of hypothermia is one of the key interventions for reducing neonatal mortality and morbidity. According to UNICEF, such interventions can help reduce neonatal mortality or morbidity by 18–42% 4. The introduction of different transparent membranes has made it possible to limit evaporative and convective heat loss and to permit heat gain through radiation 3.
Recently, in the year 2010, the American Academy of Pediatrics and American Heart Association's Neonatal Resuscitation Program guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care repeated the recommendation of covering the VLBW infant with plastic wrapping as an additional warming technique to decrease heat loss 5,6.
The aim of the present work was to evaluate the effectiveness, safety, and feasibility of polyethylene occlusive skin wrapping in preventing initial postnatal hypothermia in VLBW infants, and also to evaluate the thermal stability of the wrapped neonates over diurnal and seasonal variations and to correlate admission temperature of the studied neonates and the morbidity and mortality outcomes.
Participants and methods
The study was carried out on babies delivered at El-Shatby Alexandria University Maternity and Children’s Hospital and admitted to the newborn intensive care unit (NICU) between December 2008 and August 2009. The minimum required sample size was calculated to be 50 infants in each of a study and a control group 7.
The inclusion criterion for both groups was preterm infants of less than 1500 g birth weight who were potentially eligible if they were born in the study center.
Infants whose deliveries had not been attended by a neonatal team were excluded from the study. In addition, all full-term or late preterm large for gestational size, preterm infants with major congenital abdominal wall defects, or those with a congenital or a perinatal infection and maternal temperature more than 38°C during labor were excluded.
The study was carried out in the delivery room and followed up in the NICU at El-Shatby Alexandria University Maternity and Children’s Hospital. This quasi experimental nonrandomized study was carried out on 100 VLBW infants allocated to a wrap (group A, n=50) and a nonwrap (group B, n=50) group. The preterm infants of group A (not dried) were placed immediately after delivery in the prewarmed transparent plastic wraps, made of low-density polyethylene. Skin wrapping of the wet baby should be from the neck down to the feet (only the heads were dried). They were fixed with adhesive strips away from the skin. Because of ethical concerns, the control group (group B) was selected retrospectively from among 50 consecutive newborn infants with similar demographics and not wrapped. Initial evaluation and immediate resuscitation guidelines, according to the last Neonatal Resuscitation Program protocol, were carried out similarly for both groups.
Heart rate, respiratory effort, and color were assessed continuously until NICU admission. Temperatures were taken per axilla in the observational room, on NICU admission, and after 1 and 2 h of NICU stay. An appropriate-sized hole was cut through the covering to facilitate the introduction of a cannula or measurement of random blood sugar if required. Plastic wraps of the studied cases were removed after NICU admission by one hour (after achieving a normal temperature range, i.e. 36.5–37°C), except for one case, who was hyperthermic (38°C) on NICU admission, where the wrap was removed once admitted.
Group B preterms were placed immediately after delivery under the radiant warmer without being wrapped. They were dried in a prewarmed dry blanket. Resuscitation guidelines were followed in the observational room. Temperatures were recorded in the same pattern as group A. Both groups were transported to the NICU in portable incubators.
Both groups were evaluated for the following:
- The primary outcomes in the NICU including the axillary and incubator temperatures on admission, and axillary and incubator temperatures after 1 and 2 h of NICU admission.
- Secondary outcomes during stay (morbidities) including early hypoglycemia (detected by blood glucose level of approximately <40 mg/dl within 2 h of birth), severe metabolic acidosis (defined by pH<7.20 and/or base deficit >10 mmol/l) 8, respiratory distress syndrome, surfactant intake, oxygen therapy, duration of O2 therapy, necrotizing enterocolitis, renal impairment (defined by a serum creatinine level of >1 mg/dl, and oliguria: urine output <1 ml/kg/h 9), intraventricular hemorrhage (IVH) (diagnosed by clinical diagnosis and from cranial ultrasound) 10, and length of NICU stay.
- Secondary outcome during stay in terms of mortality.
- Group A was evaluated in terms of the occurrence of adverse outcomes associated with using the wrap and up to 2 h after admission including hyperthermia, skin laceration or abrasions, interference with resuscitation, and altered electrolyte balance±dehydration.
The data were analyzed using the Student t-test, analysis of variance test, the χ2-test, Monte Carlo and Fisher exact techniques, and two-way repeated-measures analysis of variance 11.
The study was ethically approved by the faculty ethical review committee, and NICU authority - taking permission to apply the intervention in the delivery room and follow up them in the unit. Informed consent of the parents was also obtained.
The baseline characteristics of both groups (A and B) showed no statistically significant differences in terms of sex, gestational age, birth weight, and apgar scores at 1 and 5 min (Table 1).
The initial temperatures were similar in both the study groups. However, the mean axillary temperatures of the wrap group on NICU admission and during their stay were significantly higher than those of the controls (Table 2). The table also shows that the mean incubator temperatures of group A in the NICU and up to 2 h of their stay were significantly lower than those of group B at all levels of measurements.
There was a significantly prolonged duration of oxygen therapy and increased requirement for assisted mechanical ventilation among the infants of group B (Table 3). In addition, the latter group had significantly higher incidences of early hypoglycemia and metabolic acidosis. Incidences of renal impairment and IVH were significantly higher among the infants of the nonwrap group. The neonates of group A were 77, 73, 45, and 12% less likely to develop IVH, acute renal impairment, severe metabolic acidosis, and hypoglycemia, respectively, in comparison with group B (RR were 0.23, 0.27, 0.55, and 0.88, respectively).
Finally, the number of neonatal mortalities in group B was higher than that of group A (Table 4). Also, neonates of group B had longer stays in the NICU compared with group A neonates. These results were statistically significant.
Thermal management of the preterms, especially VLBW infants, is one of the cornerstones of neonatology. The study of the outcome of the survival and rates of disability of extremely premature babies (EPICure study) showed that with decreasing gestational age, there was a very high incidence of cold stress 12. However, hypothermia is a potentially preventable event even for VLBW infants. At present, there is the standard care for reducing heat loss after birth described by the Neonatal Resuscitation Program 13.
As evaporative heat loss is the main cause of labor-room heat loss 14, the introduction of different transparent membranes had made it possible to limit such evaporative and convective heat losses and to allow heat gain through radiation 3. The main determinant of evaporative heat loss is the water vapor pressure in the layer of air immediately adjacent to the fetal skin. It seems probable that when a wet infant covered with amniotic fluid is placed in an occlusive wrap or a vinyl bag, the evaporative water loss from the skin surface that is not in contact with the bag membrane will contribute toward high humidity and vapor pressure in the air between the membrane and the skin and this will lead to a decrease in evaporative heat loss 15. All areas of the vinyl bag and the skin under this transparent bag that face the radiant warmer will be heated through radiation, resulting in heat gain for the infant. The area of the bag in direct contact with the skin may lead to conductive heat loss or gain depending on the temperature. The absence of drying also retains vernix caseosa (if any present in a premature infant). It is possible that retention of a highly hydrated biological material such as vernix would decrease evaporative heat loss 16.
In the present study, among the two groups studied, there was no significant difference in their first recorded mean axillary temperatures once received on the resuscitiare in the observational room, where both groups were hypothermic. The effect of protection of wrapping can be anticipated through the significant higher axillary temperatures of group A than group B on admission to the NICU and after one and 2 h of their stay. Also, the temperatures of the incubators of group A were significantly lower than those of group B on admission to the NICU and after one and 2 h thereafter (Table 2).
Similar to the present study, Vohra et al.17,18 and Knobel et al.19 had carried out randomized-controlled studies using polyethylene and polyurethane skin wrapping, respectively, in VLBW infants. They recommended their use as being a very inexpensive and effective mode of preventing hypothermia in extremely premature infants. However, Duman et al.2 found no significant difference between both wrapped and nonwrapped groups in the mean incubator temperature after the first hour, but the temperature was significantly higher in the nonwrap group after the second hour of NICU admission.
The ambient temperatures in our delivery and operating resuscitation rooms are lower than the WHO-recommended temperatures (21°C compared with 26.7°C, respectively), and this may also explain the high incidence of hypothermia in the control group and the lower than optimum temperature (but significantly better) in the plastic wrap group 3.
In the present study, there was significant prolonged duration of oxygen therapy and increased requirement for assisted mechanical ventilation among controls. This was in agreement with the results of Mathew et al.3 but in contrast to those of Wimmer et al.20, who reported no significant differences in the duration of oxygen therapy between both groups among infants of gestational age less than 29 completed weeks. Also, our group B had higher incidences of early hypoglycemia, metabolic acidosis, renal impairment, and IVH compared with group A. In contrast, Mathew et al.3 found no statistically significant difference in terms of the development of IVH in both groups. Furthermore, the latter study reported statistically significant worst pH and base deficit among the unwrapped group. Cold stress can lead to both metabolic acidosis and hypoglycemia 21,22. If cold stress continues, glomerular filtration decreases, and fluid balance is further complicated by poor gastrointestinal absorption and decreased peristalsis. This renal impairment may finally lead to renal failure 23.
In the present study, group B had a significantly longer stay in the NICU than group A, which is in contrast to Wimmer et al.’s 20 study, who did not find a significant difference in the duration of hospitalization between both groups. The longer hospitalization of group B can be explained by the greater morbidities they experienced during their NICU stay.
Moreover, our study reported significantly higher mortalities among group B than group A during their NICU stay. Scleroderma, persistent pulmonary hypertension, hypoglycemia, arrhythmia, thrombosis, and disseminated intravascular coagulopathy are other complications of prolonged hypothermia that are considered as signs of severe underlying morbidities, associated with the worst prognostic outcome, that may have contributed toward the high incidence of death in the unwrapped group. Vohra et al. 17,18 reported no mortalities among their gestational age group of 28–31 weeks during their hospital stay, whereas the mortalities of those with a gestational age less than 28 weeks were higher among the unwrapped group. Mathew et al. 3 also reported the same results, but with no statistical significance. Lesser number of infants in the control group received a complete course of antenatal steroids (also statistically insignificant) than the infants in the vinyl bag group, which may have contributed toward the higher incidence of death in this group. These results may be considered as evidence suggesting that plastic wrap reduces the risk of mortality within hospital stay.
Conclusion and recommendations
The inclusion of polyethylene wrapping to the routine care immediately after birth effectively prevents the initial postnatal hypothermia of VLBW infants, especially those of less than 30 weeks gestational age, and helps to achieve better admission temperatures without increasing the incidence of hyperthermia. It is an easy inexpensive, practical, and fast method, with no side effects, and can be adopted in delivery rooms of developing countries. It has been shown that it decreases the morbidities and mortalities of the preterms. Hence, it is recommended to include this safe intervention for preterms of VLBW and extremely low birth weight with further large-scale researches to ensure its effect.
Conflicts of interest
There are no conflicts of interest.
1. Bissinger RL, Annibale DJ. Thermoregulation in very low-birth-weight infants during the golden hour: results and implications. Adv Neonatal Care. 2010;10:230–238
2. Duman N, Utkutan S, Kumral A, Köroǧlu TF, Özkan H. Polyethylene skin wrapping accelerates recovery from hypothermia
in very low-birthweight infants. Pediatr Int. 2006;48:29–32
3. Mathew B, Lakshminrusimha S, Cominsky K, Schroder E, Carrion V. Vinyl bags prevent hypothermia
at birth in preterm
infants. Indian J Pediatr. 2007;74:249–253
4. Progress for children: a world fit for children statistical review. 2007 New York, NY United Nations Children’s Fund Quoted from: Wariki WMV, Mori R. Interventions to prevent hypothermia
at birth in preterm
and/or low-birth-weight infants: the WHO Reproductive Health Library commentary (last revised: 1 June 2010). The WHO Reproductive Health Library; Geneva: World Health Organization. Available at: http://apps.who.int/rhl/newborn/cd004210-warikiwmv-com/en/index.html
5. Kattwinkel J, Jeffery MP, Aziz K, Colby C, Fairchild K, Gallagher J, et al. Guidelines for cardiopulmonary resuscitation and emergency cardiovascular care. Pediatrics. 2010; 126:e1400–e1413
6. Bhatt DR, White R, Martin G, Van Marter LJ, Finer N, Goldsmith JP, et al. Transitional hypothermia
newborns. J Perinatol. 2007;27(Suppl 2):S45–S47
7. Daniel WW Biostatistics: a foundation for analysis in the health science. 19997th ed. New York John Wiley and Sons
8. McCall EM, Alderdice FA, Halliday HL, Jenkins JG, Vohra S. Interventions to prevent hypothermia
at birth in preterm
and/or low birth weight babies. Cochrane Database Syst Rev. 2005 Available at: http://www.thecochranelibrary.com
. [Accessed March 2010]
9. Stapleton FB, Jones DP, Green RS. Acute renal failure in neonates: incidence, etiology and outcome. Pediatr Nephrol. 1987;1:314–320
10. Papile LA, Burstein J, Burstein R, Koffler H. Incidence and evolution of subependymal and intraventricular hemorrhage: a study of infants with birth weights less than 1,500 gm. J Pediatr. 1978;92:529–534
11. Leslie E, Geoffrey J, James MRusling J. Statistical analysis. Interpretation and uses of medical statistics. 19914th ed. Oxford Blackwell Scientific Publications:411–416
12. Costeloe K, Hennessy E, Gibson AT, Marlow N, Wilkinson AR. The EPICure study: outcomes to discharge from hospital for infants born at the threshold of viability. Pediatrics. 2000;106(I):659–671
13. Kattwinkel J Textbook of neonatal resuscitation (Lesson 86). 20065th ed. Elk Grove, IL American Academy of Pediatrics
14. Hammarlund K, Nilsson GE, Oberg PA, Sedin G. Transepidermal water loss in newborn infants. V. Evaporation from the skin and heat exchange during the first hours of life. Acta Paediatr Scand. 1980;69:385–392
15. Sedin G. To avoid heat loss in very preterm
infants. J Pediatr. 2004;145:720–722
16. Visscher MO, Narendran V, Pickens WL, LaRuffa AA, Meinzen-Derr J, Allen K, Hoath SB. Vernix caseosa in neonatal adaptation. J Perinatol. 2005;25:440–446
17. Vohra S, Frent G, Campbell V, Abbott M, Whyte R. Effect of polyethylene occlusive skin wrapping on heat loss in very low birth weight infants at delivery: a randomized trial. J Pediatr. 1999;134:547–551
18. Vohra S, Roberts RS, Zhang B, Janes M, Schmidt B. Heat loss prevention (HeLP) in the delivery room: a randomized controlled trial of polyethylene occlusive skin wrapping in very preterm
infants. J Pediatr. 2004;145:750–753
19. Knobel RB, Wimmer JE Jr, Holbert D. Heat loss prevention for preterm
infants in the delivery room. J Perinatol. 2005;25:304–308
20. Wimmer J, Knobel R, Ahearn C, Morton M, Holbert D. Placing infants <29 weeks gestation in polyurethane bags after birth to reduce hypothermia
. J Perinatol. 2002;22:602–603
21. . Neonatal thermoregulation. University of Arkansas for Medical Sciences. 2005;778:1–12
23. Çinar ND, Filiz TM Neonatal thermoregulation. Journal of Neonatal Nursing 2006; 12:69–74