A multicentre study on admission hypothermia in very low-birth weight preterm infants in China: distribution, causes and risk factors

Background Neonatal hypothermia, defined as a temperature < 36.5°C, is a major contributor to neonatal mortality and morbidity. Hypothermia in preterm infants remains a challenge in the neonatal intensive care unit (NICU) for many reasons. Objective To investigate the incidence of admission hypothermia (AH) in very low-birth weight (VLBW) infants in multiple NICUs in Shandong Province, China, and to provide clinical evidence for the implementation of quality improvement practices to reduce the incidence of AH in NICU. Methods This retrospective, observational study was carried out over a period of 12 months, from January 1, 2018 to December 31, 2018. The correlations between hypothermia preventive measures and the incidence of AH were analysed by descriptive statistical methods and a Spearman analysis. The associations between AH and maternal and neonatal variables were tested with bivariate analyses, followed by stepwise logistic regression. P <0.05 was considered statistically significant. Results A total of 1639 in-born infants who were born at a weight less than 1500 g were enrolled in the study on their day of birth. Among them, 1295 VLBW infants fulfilled the inclusion criteria. The incidence of AH was 87.9% in VLBW infants among the 28 NICUs. We investigated whether team training and education, such as monthly chart reporting on hypothermia in preterm infants on admission to the NICU, which was associated with 10.7% of all the cases, could decrease the rate of AH. Indeed, transport with a heated transport incubator was associated with 9.3% of the cases. here was a negative correlation between the incidence of AH and the number of quality improvement measures implemented to prevent hypothermia (r= -0.242, p <0.05). A low birth weight, intubation in the delivery room , and a low 5-min Apgar score were significantly associated with AH. Conclusion: The incidence of AH was high. There was a negative correlation between the membranes.

Ri-ming Zhao ju country people's hospital incidence of AH and the number of quality improvement measures implemented to prevent hypothermia. It is important to monitor for AH in newborns who have a low birth weight, who have a low Apgar score at 5 min and who require intubation in the delivery room.

Background
Because of the immature physiological development of preterm infants, they are susceptible to heat loss, potentially leading to hypothermia, especially very low-birth weight (VLBW) infants and extremely low-birth weight (ELBW) infants [1]. The incidence of hypothermia on admission to the neonatal intensive care unit (NICU) in VLBW preterm infants is 31%-78% [2,3]. Admission hypothermia (AH) is a vital risk factor for neonatal mortality and morbidity inpreterm infants [4,5].
Maintaining normothermia in infants has been shown to improve survival and outcomes [6,7]. In a multicentre study, Caldas et al. [8] reported that AH was significantly associated with early neonatal death regardless of hospital performance. In Korea, Lee et al. [9] reported that 74.1% of 5860 VLBW preterm infants (< 33 weeks of gestational age) with AH were admitted to neonatal units, and AH was associated with high mortality and several notable morbidities. Wilson et al. [10] reported that hypothermia occurred in 53.4% of 5697 infants born at <32 weeks of gestational age in a population-based study with samples from 11 European countries, and AH after very preterm birth was a significant factor associated with an increased risk of early and late neonatal mortality.
Lyu et al. [11] showed that the rates of the composite outcome, severe neurological injury, severe retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC), bronchopulmonary dysplasia (BPD), and nosocomial infection had U-shaped relationships with admission temperature, and the lowest rates of adverse outcomes were associated with admission temperatures between 36.5°C and 37.2°C.
To reduce the rates of these complications, many clinical studies have suggested various measures to prevent hypothermia, including plastic wrapping without drying [12,13,14], the use of incubators [15], and the use of chemical mattresses [16]. Despite the knowledge and development of new approaches to better maintain infant body temperatures, recent studies have noted that a significant proportion of VLBW infants in undeveloped countries are not kept sufficiently warm immediately after birth [10,17].
The aim of this study was to investigate the distribution, causes and risk factors of AH in VLBW infants in multiple NICUs in China. Data measurement, data collection and data quality control procedures

Study design and time period
The admission temperature was defined as the infant's axillary or rectal temperature measured on admission to the NICU within one hour after birth, in accordance with local routines. Since January 1, 2018, homogeneous neonatal cooperative research platforms have been established. The admission temperatures, mortality incidence and morbidity data of VLBW infants born in 28 level-III NICUs in Shandong Province were collected prospectively. The database provided maternal, delivery, and neonatal data until the first NICU discharge, and the data were collected by trained staff using a standardized operating procedure [18]. The entered data were analysed for statistical adjustment of possible confounders with a multivariate analysis.

Study population
The study population included all VLBW infants who were admitted to the NICUs of 24 level-III hospitals in Shandong Province, China, from January 1, 2018, to December 31, 2018, and their mothers.
Exclusion criteria VLBW infants who were out-born, families who rejected treatment, and infants with missing temperature data were excluded.

Dependent variable
The dependent variable was AH. Independent variables 9 The following obstetric and neonatal variables were considered independent variables: diabetes, maternal hypertension, premature rupture of the membranes (PROM) (>24 hours), and caesarean section. The following neonatal variables were considered independent variables: multiple birth (twins or more), sex, gestational age (GA), birth weight (BW), small for gestational age (SGA) (defined as growth below the 10th percentile), Apgar scores at 1 min and 5 min, and intubation in the delivery room. Data on the implementation of measures to prevent hypothermia were collected using a retrospective questionnaire. The measures to prevent hypothermia were based on a review of the medical literature [19], best practice recommendations from the California Perinatal Quality Care Collaborative (CPQCC) [20], evidence-based principles from the Neonatal Resuscitation Program [21,22], and recommendations by the World Health Organization (WHO) on ambient air temperatures in the delivery room [23]. The implementation of the measures to prevent hypothermia are described in Table 1

Statistical analysis
Demographic data are expressed as means (± standard deviations (SDs)) or percentages.
The correlation between the hypothermia preventive measures and the incidence of AH was analysed by descriptive statistical methods and Spearman analysis. Associations between perinatal variables and hypothermia were tested with a bivariate analysis, followed by stepwise logistic regression. Separate models were constructed for combined moderate/severe and mild hypothermia. We also studied the potential contribution of hypothermia to the risk factors. Separate models were constructed for risk factors in which severe/moderate or mild hypothermia was the independent variable. P <0.05 was considered statistically significant. The statistical analyses were conducted using SPSS v. 25.0 (SPSS Inc., Chicago, Illinois).

Results
The 28 recruited hospitals included 20 general hospitals and 8 maternal and child health care hospitals, with an average of 59 and 40 beds in the neonatology departments and NICUs, respectively. A total of 1639 in-born infants born at a weight less than 1500 g were enrolled in the study on their day of birth; 97 infants were excluded because they were out-born. Additionally, 135 infants with families who ceased treatment and 94 infants who had missing temperature data were excluded. The remaining 1295 infants were included in this analysis (Fig. 1). The final cohort had a mean (±SD) BW and GA of 1225 ± 205 g and 29.7 ± 2.1 weeks, respectively.

Hypothermia
The mean (SD) admission temperature was 35.8°C (0.6°C), with a range of 32°C to 37.5°C.
Only 12% of the study population had an admission temperature in the WHO

Cause of hypothermia
Quality improvement methodologies such as Pareto charts were used to identify and prioritize the contributing reasons for AH (Fig. 3). We investigated whether team training and education could decrease the rate of AH, including monthly chart reporting on hypothermia in preterm infants on admission to the NICU, which was associated with 10.7% of all the cases. Indeed, transport with a heated transport incubator was associated with 9.3% of the cases. In addition, 8.8% of the cases of hypothermia were associated with no measured and recorded body temperature 10 min after birth. There was a negative correlation between the incidence of AH and the number of quality improvement measures implemented to prevent hypothermia (r = -0.227, p<0.05). (Fig. 4).

Risk factors for hypothermia
The univariate analysis of the risk factors of severe/moderate hypothermia indicated that BW, caesarean section, low 5-min Apgar scores, intubation in the delivery room, maternal hypertension, and SGA were associated with AH (

Discussion
This is the first large national cohort study to investigate the incidence of AH and its association with in-hospital mortality and morbidity in the eastern region of China.
Neonates regulate their body temperature much less efficiently than adults, and both hypothermia and hyperthermia can easily occur. Despite measures that were established in 2010 according to the recommendations of the Neonatal Resuscitation Program guidelines [21] to maintain normothermia in the delivery room, the incidence of AH is still high in China, occurring in 87.9% of VLBW infants. Mank et al. [24] reported that in 93% of infants, hypothermia occurred within the first three hours after admission. The proportion of infants with normal temperature ranges on NICU admission (12.0%) is much lower in China than in other developed countries, such as US infants less than 29 weeks (52.9%) [25], Canadian infants less than 33 weeks (57.2%) [11] and European infants less than 32 weeks (42.2%) [10].
The most notable infant characteristics that were associated with hypothermia were a low BW, intubation in the delivery room and a low Apgar score at 5 min. A low BW is associated with a large surface area-to-body mass ratio, a low amount of subcutaneous fat, an increased body water content, immature skin leading to increased evaporative water and heat losses, a poorly developed metabolic mechanism for responding to thermal stress and the delayed development of skin blood-flow control, reducing the ability to maintain heat by vasoconstriction [3,4,5], all of which may lead to hypothermia. Similar to our study, Laptook et al. [26] reported associations between BW and intubation in the delivery room and hypothermia. In addition, Lee et al. [9] reported that a low Apgar score at 5 min was a risk factor for hypothermia at admission. This may be related to the inadequate implementation of thermal protection measures during resuscitation.
The results of the correlation analysis indicated that the incidence of AH was effectively reduced with an increased number of hypothermia prevention measures, as there was a negative correlation between the incidence of AH and the number of implemented intervention measures. A retrospective study from the Vermont Oxford Network's (VON) VLBW database showed that the use of chemical warming packs in addition to routine care may be a useful intervention in achieving normothermia during the transition from delivery to admission to the NICU [27]. Recent studies reported that the use of plastic wrapping without drying reduced the rate of AH [12,13,14]. Wilson et al. [28] investigated the different strategies used in 11 European countries to prevent hypothermia. The results of the study showed that very preterm infants had a reduced risk of hypothermia at NICU admission if the unit used systematic prevention strategies and that all the strategies had similar effects, possibly due to implementation rather than a strategy's specific efficacy.
In addition, a retrospective analysis of the practices to prevent hypothermia revealed that team training and education, including monthly chart reporting on hypothermia in preterm infants on admission to the NICU and transportation with a heated transport incubator, were key drivers of change. Although special space for the implementation of these interventions is not required, the reluctance to implement such measures may be associated with poor awareness by medical staff, a lack of infrastructure or funding, and so on. Based on these findings, implementing interventions to prevent hypothermia and enhancing team building were identified as key drivers of change. Based on recent studies in developed countries, after initiating quality improvement projects [29,30,31,32], the incidence of AH dramatically declined. Thus, we need to implement evidence-based practices for improving quality (EPIQ) to reduce the incidence of AH in VLBW infants.
Our study had several limitations. We investigated only the incidence of AH and studied the association between AH and risk factors; we could not conduct a quality improvement project considering VLBW infants. Based on the results of this study, our next research project will be to carry out a multicentre quality improvement project to reduce the incidence of AH according to international EPIQ.

Conclusions
The incidence of AH was high. There was a negative correlation between the incidence of AH and the number of quality improvement measures implemented to prevent hypothermia. It is important to monitor for AH in newborns who have a low BW, who have a low Apgar score at 5 min and who require intubation in the delivery room.
Abbreviations VLBW, very low-birth weight; NICU, neonatal intensive care unit; AH, admission hypothermia; OR, odds ratio; CI, confidence interval; SGA, small for gestational age; PROM, premature rupture of the membranes.
Declarations because this study was retrospective and observational study.  Ambient temperature at 25°C and the resuscitation bed on manual control with maximum heat output 02 Pre-warmed hat and blanket prepared 03 Polyethylene wrap prepared Birth 04 Infant immediately wrapped with a polyethylene wrap without drying 05 Infant wrapped in a pre-warmed blanket wrap after the umbilical cord is cut 06 Infant quickly weighed after being placed in a pre-warmed blanket 07 A pre-warmed hat is placed on the head 08 Body temperature measurement and recording 10 min after birth Before and at NICU admission 09 Infant transported with a heated transport incubator 10 All surfaces that the infant will contact are pre-warmed 11 Infant is immediately placed in the admission bed (e.g. Giraffe OmniBed) 12 Infant's body temperature is measured within 1 hour after birth 13 Infant receives hypothermic rewarming 14 The time of admission temperature ≥ 36.5°C is recorded Team training and education 15 Both nursing and medical operations implemented 16 Monthly chart reporting on hypothermia in preterm infants on admission to the NICU 17 Temperature measurement standardized 18 Training and assessments on temperature measurement for nurses 19 Implementing quality improvement projects to reduce hypothermia in preterm infants on admission to the NICU  Abbreviations: OR, odds ratio; CI, confidence interval; SGA, small for gestational age; PROM, premature rupture of the membranes *Adjusted for caesarean section, BW, SGA, Apgar score <7 at 5 min, and intubation in the delivery room.
a odds ratios with p <0.05 Figure 1 Flow diagram of the study population.

Figure 2
Temperature distribution according to birth weight.  The correlation between the number of measures implemented and the incidence of AH.