Thermal management for premature births

Maintaining normothermia immediately after birth in preterm infants <34 weeks' gestation: A systematic review and meta-analysis

AIM

To evaluate delivery room (DR) interventions to prevent hypothermia and improve outcomes in preterm newborn infants <34 weeks' gestation.

METHODS

Medline, Embase, CINAHL and CENTRAL were searched till 22nd July 2022. Randomized controlled trials (RCTs), non-RCTs and quality improvement studies were considered. A random effects meta-analysis was performed, and the certainty of evidence was evaluated using GRADE guidelines.

RESULTS

DR temperature of ≥23 °C compared to standard care improved temperature outcomes without an increased risk of hyperthermia (low certainty), whereas radiant warmer in servo mode compared to manual mode decreased mean body temperature (MBT) (moderate certainty). Use of a plastic bag or wrap (PBW) improved normothermia (low certainty), but with an increased risk of hyperthermia (moderate certainty). Plastic cap improved normothermia (moderate certainty) and when combined with PBW improved MBT (low certainty). Use of a cloth cap decreased moderate hypothermia (low certainty). Though thermal mattress (TM) improved MBT, it increased risk of hyperthermia (low certainty). Heated-humidified gases (HHG) for resuscitation decreased the risk of moderate hypothermia and severe intraventricular hemorrhage (very low to low certainty). None of the interventions was shown to improve survival, but sample sizes were insufficient.

CONCLUSIONS

DR temperature of ≥23 °C, radiant warmer in manual mode, use of a PBW and a head covering is suggested for preterm newborn infants <34 weeks' gestation. HHG and TM could be considered in addition to PBW provided resources allow, in settings where hypothermia incidence is high. Careful monitoring to avoid hyperthermia is needed.

Can Mathematical Models of Body Heat Exchanges Accurately Predict Thermal Stress in Premature Neonates?

Mathematical models of body heat exchanges can be used to define the thermal limits needed to protect premature neonates nursed in incubators against thermal stress–stress that can have potentially devastating impairments on neurological development and body growth. Predictive models can help caregivers to keep a neonate’s body temperature within the normal range and to solve problems that arise during intensive care, such as the risk of hyperthermia during phototherapy, the risk of hypothermia during transport from one clinical centre to another, and the use of a plastic bag to reduce skin water loss and body dehydration. Here, we review the strengths and limitations of models used to predict the risk of thermal stress, with a focus on uncertainties in the algorithms governing heat transfers between the neonate’s skin and the complicated thermal environment encountered in incubators. We describe attempts to reduce the large number of empirical assumptions and uncertainties in this field, and suggest ways of more accurately modelling optimal thermal conditions for neonates nursed in closed incubators.

Interventions to prevent hypothermia at birth in preterm and/or low birth weight infants

BACKGROUND

Newborn admission temperature is a strong predictor of outcomes across all gestations. Hypothermia immediately after birth remains a worldwide issue and, if prolonged, is associated with harm. Keeping preterm infants warm is difficult even when recommended routine thermal care guidelines are followed in the delivery room.

OBJECTIVES

To assess the efficacy and safety of interventions designed for prevention of hypothermia in preterm and/or low birth weight infants applied within 10 minutes after birth in the delivery room, compared with routine thermal care or any other single/combination of intervention(s) also designed for prevention of hypothermia in preterm and/or low birth weight infants applied within 10 minutes after birth in the delivery room.

SEARCH METHODS

We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 5), MEDLINE via PubMed (1966 to 30 June 2016), Embase (1980 to 30 June 2016), and CINAHL (1982 to 30 June 2016). We also searched clinical trials databases, conference proceedings, and reference lists of retrieved articles for randomised controlled trials and quasi-randomised trials.

SELECTION CRITERIA

Trials using randomised or quasi-randomised allocations to test interventions designed to prevent hypothermia (apart from 'routine' thermal care) applied within 10 minutes after birth in the delivery room for infants at < 37 weeks' gestation and/or birth weight ≤ 2500 grams.

DATA COLLECTION AND ANALYSIS

We used Cochrane Neonatal methods when performing data collection and analysis.

MAIN RESULTS

Twenty-five studies across 15 comparison groups met the inclusion criteria, categorised as: barriers to heat loss (18 studies); external heat sources (three studies); and combinations of interventions (four studies).Barriers to heat loss Plastic wrap or bag versus routine carePlastic wraps improved core body temperature on admission to the neonatal intensive care unit (NICU) or up to two hours after birth (mean difference (MD) 0.58°C, 95% confidence interval (CI) 0.50 to 0.66; 13 studies; 1633 infants), and fewer infants had hypothermia on admission to the NICU or up to two hours after birth (typical risk ratio (RR) 0.67, 95% CI 0.62 to 0.72; typical risk reduction (RD) -0.25, 95% CI -0.29 to -0.20; number needed to treat for an additional beneficial outcome (NNTB) 4, 95% CI 4 to 5; 10 studies; 1417 infants). Risk of hyperthermia on admission to the NICU or up to two hours after birth was increased in infants in the wrapped group (typical RR 3.91, 95% CI 2.05 to 7.44; typical RD 0.04, 95% CI 0.02 to 0.06; number needed to treat for an additional harmful outcome (NNTH) 25, 95% CI 17 to 50; 12 studies; 1523 infants), but overall, fewer infants receiving plastic wrap were outside the normothermic range (typical RR 0.75, 95% CI 0.69 to 0.81; typical RD -0.20, 95% CI -0.26 to -0.15; NNTH 5, 95% CI 4 to 7; five studies; 1048 infants).Evidence was insufficient to suggest that plastic wraps or bags significantly reduce risk of death during hospital stay or other major morbidities, with the exception of reducing risk of pulmonary haemorrhage.Evidence of practices regarding permutations on this general approach is still emerging and has been based on the findings of only one or two small studies.External heat sourcesEvidence is emerging on the efficacy of external heat sources, including skin-to-skin care (SSC) versus routine care (one study; 31 infants) and thermal mattress versus routine care (two studies; 126 infants).SSC was shown to be effective in reducing risk of hypothermia when compared with conventional incubator care for infants with birth weight ≥ 1200 and ≤ 2199 grams (RR 0.09, 95% CI 0.01 to 0.64; RD -0.56, 95% CI -0.84 to -0.27; NNTB 2, 95% CI 1 to 4). Thermal (transwarmer) mattress significantly kept infants ≤ 1500 grams warmer (MD 0.65°C, 95% CI 0.36 to 0.94) and reduced the incidence of hypothermia on admission to the NICU, with no significant difference in hyperthermia risk.Combinations of interventionsTwo studies (77 infants) compared thermal mattresses versus plastic wraps or bags for infants at ≤ 28 weeks' gestation. Investigators reported no significant differences in core body temperature nor in the incidence of hypothermia, hyperthermia, or core body temperature outside the normothermic range on admission to the NICU.Two additional studies (119 infants) compared plastic bags and thermal mattresses versus plastic bags alone for infants at < 31 weeks' gestation. Meta-analysis of these two studies showed improvement in core body temperature on admission to the NICU or up to two hours after birth, but an increase in hyperthermia. Data show no significant difference in the risk of having a core body temperature outside the normothermic range on admission to the NICU nor in the risk of other reported morbidities.

AUTHORS' CONCLUSIONS

Evidence of moderate quality shows that use of plastic wraps or bags compared with routine care led to higher temperatures on admission to NICUs with less hypothermia, particularly for extremely preterm infants. Thermal mattresses and SSC also reduced hypothermia risk when compared with routine care, but findings are based on two or fewer small studies. Caution must be taken to avoid iatrogenic hyperthermia, particularly when multiple interventions are used simultaneously. Limited evidence suggests benefit and no evidence of harm for most short-term morbidity outcomes known to be associated with hypothermia, including major brain injury, bronchopulmonary dysplasia, retinopathy of prematurity, necrotising enterocolitis, and nosocomial infection. Many observational studies have shown increased mortality among preterm hypothermic infants compared with those who maintain normothermia, yet evidence is insufficient to suggest that these interventions reduce risk of in-hospital mortality across all comparison groups. Hypothermia may be a marker for illness and poorer outcomes by association rather than by causality. Limitations of this review include small numbers of identified studies; small sample sizes; and variations in methods and definitions used for hypothermia, hyperthermia, normothermia, routine care, and morbidity, along with lack of power to detect effects on morbidity and mortality across most comparison groups. Future studies should: be adequately powered to detect rarer outcomes; apply standardised morbidity definitions; focus on longer-term outcomes, particularly neurodevelopmental outcomes.

Is unplanned out-of-hospital birth managed by paramedics 'infrequent', 'normal' and 'uncomplicated'?

Background

Unplanned out-of-hospital birth is often perceived as precipitate in nature, ‘infrequent’, ‘normal’ and ‘uncomplicated’. However, international studies report unplanned out-of-hospital birth is associated with increased rates of maternal and neonatal morbidity and mortality. This research describes intrapartum, immediate postpartum and neonatal care provided by paramedics in Queensland, Australia. The objectives were to (1) determine the number of cases where the paramedic documented birth or imminent birth during the study period (2) to describe the incidence of births prior to or during paramedic care (3) to detail any risk factors and/or complications recorded by paramedics during these cases, (4) identify paramedic pain management practices for intrapartum care, and (5) to examine the maternal and neonatal outcomes as documented by paramedics.

Method

A retrospective analysis of Queensland Ambulance Service (QAS) de-identified patient care records, generated from clinical case data between the 1st of Jan 2010 and 31st of Dec 2011, was undertaken. Descriptive analysis and x² tests were used to test associations between categorical variables, and the Wilcoxon rank-sum for associates between continuous variables which were not normally distributed. Content analysis was utilised to code free text fields.

Results

Six thousand one hundred thirty-five records were identified as intrapartum cases. This represented approximately 0.5% of the annual QAS caseload; 5722 were classified as maternal records and 413 were neonatal records. Paramedics recorded antenatal and/or intrapartum complications in 27.3% (n = 1563) of cases. Abnormal maternal vital signs were recorded in 30.1% (n = 1725) of cases. Of the 5722 women attended by paramedics during their labour, a birth occured in 10.8% (n = 618) of cases. Parity was documented in 41.4% (n = 256) of mothers who birthed. Neonatal records were available for 66.8% (n = 413) of actual births, 60.0% (n = 248) recorded a full set of neonatal vital signs and an Apgar score. When an Apgar score was recorded, 21.8% (n = 91) scored ≤7 out of 10.

Conclusions

The research described intrapartum, immediate postpartum and neonatal care provided by paramedics and identified factors that may complicate paramedic clinical management of labouring and birthing women. Further research is required to determine if there are opportunities to improve the paramedic management of such cases.

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.

The effect of coverings, including plastic bags and wraps, on mortality and morbidity in preterm and full-term neonates

Neonatal hypothermia is an important risk factor for mortality and morbidity, and is common even in temperate climates. We conducted a systematic review to determine whether plastic coverings, used immediately following delivery, were effective in reducing the incidence of mortality, hypothermia and morbidity. A total of 26 studies (2271 preterm and 1003 term neonates) were included. Meta-analyses were conducted as appropriate. Plastic wraps were associated with a reduction in hypothermia in preterm (⩽29 weeks; risk ratio (RR)=0.57; 95% confidence interval (CI) 0.46 to 0.71) and term neonates (RR=0.76; 95% CI 0.60 to 0.96). No significant reduction in neonatal mortality or morbidity was found; however, the studies were underpowered for these outcomes. For neonates, especially preterm, plastic wraps combined with other environmental heat sources are effective in reducing hypothermia during stabilization and transfer within hospital. Further research is needed to quantify the effects on mortality or morbidity, and investigate the use of plastic coverings outside hospital settings or without additional heat sources.

Short- and Long-Term Outcomes in Very Low Birth Weight Infants with Admission Hypothermia

BACKGROUND

Neonatal hypothermia remains a common problem and is related to elevated morbidities and mortality. However, the long-term neurodevelopmental effects of admission hypothermia are still unknown. This study attempted to determine the short-term and long-term consequences of admission hypothermia in VLBW preterm infants.

STUDY DESIGN

This retrospective study measured the incidence and compared the outcomes of admission hypothermia in very low birth weight (VLBW) preterm infants in a tertiary-level neonatal intensive care unit. Infants were divided into the following groups: normothermia (36.5-37.5°C), mild hypothermia (36.0-36.4°C), moderate hypothermia (32.0-35.9°C), and severe hypothermia (< 32°C). We compared the distribution, demographic variables, short-term outcomes, and neurodevelopmental outcomes at 24 months of corrected age among groups.

RESULTS

We studied 341 infants: 79 with normothermia, 100 with mild hypothermia, 162 with moderate hypothermia, and 0 with severe hypothermia. Patients in the moderate hypothermia group had significantly lower gestational ages (28.1 wk vs. 29.7 wk, P < .02) and smaller birth weight (1004 g vs. 1187 g, P < .001) compared to patients in the normothermia group. Compared to normothermic infants, moderately hypothermic infants had significantly higher incidences of 1-min Apgar score < 7 (63.6% vs. 31.6%, P < .001), respiratory distress syndrome (RDS) (58.0% vs. 39.2%, P = .006), and mortality (18.5% vs. 5.1%, P = .005). Moderate hypothermia did not affect neurodevelopmental outcomes at 2 years' corrected age. Mild hypothermia had no effect on short-term or long-term outcomes.

CONCLUSIONS

Admission hypothermia was common in VLBW infants and correlated inversely with birth weight and gestational age. Although moderate hypothermia was associated with higher RDS and mortality rates, it may play a limited role among multifactorial causes of neurodevelopmental impairment.

Occlusive bags to prevent hypothermia in premature infants: a quality improvement initiative

The aim of this quality improvement initiative was to improve the neonatal intensive care unit (NICU) admission rectal temperatures of premature infants less than 28 weeks' gestation by placing them in an occlusive bag from the neck down immediately after birth. The historical control group consisted of a convenience sample of 46 very low-birth-weight infants from March 1, 2010, to August 31, 2010. A convenience sample of 35 very low-birth-weight infants from October 1, 2010, to April 30, 2011, was recruited during the prospective phase. A quasi-experimental design was used. A retrospective medical record review was performed to collect data on NICU admission rectal temperatures for the historical control group. During the prospective phase, infants were placed in a bag from the neck down immediately after birth and NICU admission rectal temperatures were recorded. In both groups, NICU rectal temperatures were measured immediately upon admission. Application of the bag resulted in a higher mean NICU admission rectal temperature in the intervention group compared with the historical control group. Occlusive bags applied at delivery decreased heat loss in premature infants. The results support previous findings and resulted in a change in clinical practice.

Application of plastic wrap to improve temperatures in infants born less than 30 weeks gestation: a randomized controlled trial

PURPOSE

The primary aim of the study was to evaluate whether the application of a plastic wrap immediately after birth is more effective than the standard care of temperature management for improving admission temperatures to the neonatal intensive care unit (NICU) in infants <30 weeks gestation.

DESIGN

A randomized controlled trial was conducted. Infants in the intervention group were transferred to a prewarmed radiant heater immediately after birth and encased in NeoWrap from the neck down without being dried. The infant's head was dried with a prewarmed towel and a hat added. The control group received usual care for the unit; the infant was transferred to the prewarmed radiant warmer and dried, and warm towels and a hat are then applied.

SAMPLE

A total of 92 infants were analyzed: 49 in the control group and 43 in the intervention group; 48 (52.2 percent) were <27 weeks gestation, and 44 (47.8 percent) were <30 weeks gestation. The infants' temperatures were assessed for two hours following admission.

The effect of three nursing interventions on thermoregulation in low birth weight infants

PURPOSE

The primary aim of this study was to evaluate the use of three nursing interventions--occlusive wrap, chemical mattress, and regulation of delivery room temperature--singly and in combination in consecutive years on thermoregulation in six groups of low birth weight infants.

DESIGN

A quasi-experimental design was used. Prospective data were collected on 133 infants weighing <1,500 g. Interventions were tested on different groups of infants in each of three years. The control group comprised 295 infants on which retrospective chart data were available over an earlier three-year period.

SAMPLE

Infants weighing <1,500 g participated in the study.

MAIN OUTCOME VARIABLE

The main outcome variable was NI CU admission temperatures of infants weighing <1,500 g. For data analysis, infants were divided into two groups: those weighing <1,000 g and those weighing between 1,000 and 1,500 g.

RESULTS

For each of the three interventions, the percentage having a normal NICU admission temperature in each intervention group exceeded the control group percentage, but the increase was not significant. Use of each intervention--occlusive wrap alone, occlusive wrap in addition to chemical mattress, and occlusive wrap in addition to chemical mattress and increased delivery room temperature--appeared to influence thermoregulation positively.

Reducing hypothermia in preterm infants with polyethylene wrap

BACKGROUND

Occlusive plastic applied immediately after birth to reduce evaporative heat loss has been proven effective in preterm infants <28 weeks' gestation. However its effectiveness on preterm infants >28 weeks' gestation has not been shown. This study aimed to determine the effect of occlusive wrap at birth on the temperature at neonatal intensive care unit (NICU) admission among infants of greater than or equal to 24 weeks' and less than 34 weeks' gestation.

METHODS

Study infants were randomly assigned to "wrap" or "control" groups. Newborns in the wrap group were wrapped with polyethylene plastic sheets within the first min after birth. Infants randomized to the control group were dried immediately after birth with warmed towels under a warmer, according to the guidelines of Neonatal Resuscitation. Infants' axillary temperatures were measured on admission to the NICU, and after having been stabilized in incubators in the NICU.

RESULTS

A total of 110 infants were recruited into the study. The mean admission temperature was significantly higher in the wrap group (35.8 vs 34.8°C, P < 0.01). Admission hypothermia (axillary temperature <36.5°C) was present in 38 (78%) and 58 (98%) infants in the wrap and control groups, respectively. Among infants of <28 weeks' gestation, the post-stabilization temperature was significantly higher in the wrap group.

CONCLUSIONS

Wrapping premature infants with gestational age <34 weeks in polyethylene plastics immediately after birth is associated with lower incidence of hypothermia.

Optimal body temperature in transitional extremely low birth weight infants using heart rate and temperature as indicators

OBJECTIVE

To explore body temperature in relationship to heart rate in extremely low birth weight (ELBW) infants during their first 12 hours to help identify the ideal set point for incubator control of body temperature.

DESIGN

Within subject, multiple-case design.

SETTING

A tertiary neonatal intensive care unit (NICU) in North Carolina.

PARTICIPANTS

Ten infants born at fewer than 29 weeks gestation and weighing 400 to 1,000 g.

METHODS

Heart rate and abdominal body temperature were measured at 1-minute intervals for 12 hours. Heart rates were considered normal if they were between the 25th and 75th percentile for each infant.

RESULTS

Abdominal temperatures were low throughout the 12-hour study period (mean 35.17-36.68 degrees C). Seven of 10 infants had significant correlations between abdominal temperature and heart rate. Heart rates above the 75th percentile were associated with low and high abdominal temperatures; heart rates less than the 25th percentile were associated with very low abdominal temperatures. The extent to which abdominal temperature was abnormally low was related to the extent to which the heart rate trended away from normal in 6 of the 10 infants. Optimal temperature control point that maximized normal heart rate observations for each infant was between 36.8 degrees C and 37 degrees C.

CONCLUSIONS

Hypothermia was associated with abnormal heart rates in transitional ELBW infants. We suggest nurses set incubator servo between 36.8 degrees C and 36.9 degrees C to optimally control body temperature for ELBW infants.

Point-of-admission hypothermia among high-risk Nigerian newborns

Background

Facilities which manage high-risk babies should frequently assess the burden of hypothermia and strive to reduce the incidence.

Objective

To determine the incidence and outcome of point-of-admission hypothermia among hospitalized babies.

Methods

The axillary temperatures of consecutive admissions into a Nigerian Newborn Unit were recorded. Temperature <36.5°C defined hypothermia. The biodata and outcome of these babies were studied.

Results

Of 150 babies aged 0 to 648 hours, 93 had hypothermia with an incidence of 62%. Mild and moderate hypothermia accounted for 47.3% and 52.7% respectively. The incidence of hypothermia was highest (72.4%) among babies aged less than 24 hours. It was also higher among out-born babies compared to in-born babies (64.4% vs 58.3%). Preterm babies had significantly higher incidence of hypothermia (82.5%) compared with 54.5% of term babies (RR = 1.51; CI = 1.21 – 1.89). The incidence of hypothermia was also highest (93.3%) among very-low-birth-weight babies.

The Case-Fatality-Rate was significantly higher among hypothermic babies (37.6% vs 16.7%; RR = 2.26, CI = 1.14 – 4.48) and among out-born hypothermic babies (50% vs 17.1%; RR = 0.34, CI = 0.16 – 0.74). CFR was highest among hypothermic babies with severe respiratory distress, sepsis, preterm birth and asphyxia.

Conclusion

The high incidence and poor outcome of hypothermia among high-risk babies is important. The use of the 'warm chain' and skin-to-skin contact between mother and her infant into routine delivery services in health facilities and at home may be useful.

Keeping infants warm: challenges of hypothermia

Hypothermia is a major cause of morbidity and mortality in infants; therefore, maintaining normal body temperatures in the delivery room is crucial. An understanding of how infants produce heat and what can be done to maintain normal body temperatures in full-term and preterm infants is essential for the preservation of thermal stability in this population. This article reviews the consequences of hypothermia, mechanisms of heat exchange and heat production in full-term and low birth-weight infants, and discusses interventions in the delivery room to alleviate hypothermia.