Disposable low-cost cardboard incubator for thermoregulation of stable preterm infant – a randomized controlled non-inferiority trial

Abstract

Background Incubators and radiant warmers are essential equipment in neonatal care, but the typical 1,500 to 35,000 USD cost per device makes it unaffordable for many units in low and middle-income countries. We aimed to determine whether stable preterm infants could maintain thermoregulation for 48 h in a low-cost incubator (LCI).

Methods The LCI was constructed using a servo-heater costing 200 USD and cardboard infant-chamber. We conducted this open-labeled non-inferiority randomized controlled trial in a tertiary level teaching hospital in India from May 2017 to March 2018. Preterm infants on full feeds and receiving incubator or radiant warmer care were enrolled at 32 to 36 weeks post-menstrual age. We enrolled 96 infants in two strata (Strata-1< 33 weeks, Strata-2 ≥ 33 weeks at birth). Infants were randomized to LCI or standard single-wall incubator (SSI) after negative incubator cultures and monitored for 48 h in air-mode along with kangaroo mother care. The incubator temperature was adjusted manually to maintain skin and axillary temperatures between 36.5 °C and 37.5 °C. During post-infant period after 48 h, SSI and LCI worked for 5 days and incubator temperatures were measured. The primary outcome was maintenance of skin and axillary temperatures with a non-inferiority margin of 0.2 °C. Failed thermoregulation was defined as abnormal axillary temperature (< 36.5 °C or >37.5 °C) for > 30 continuous-minutes. Secondary outcomes were incidence of hypothermia and required incubator temperature. Trial registration details: Clinical Trial Registry - India (CTRI/2015/10/006316).

Findings Prior to enrollment 79(82%) infants were in radiant warmer and 17(18%) infants were in incubator care. Median weight at enrollment in Strata-1 and Strata-2 for SSI vs. LCI was 1355(IQR 1250–1468) vs. 1415(IQR 1280–1582) and 1993(IQR 1595–2160) vs. 1995(IQR 1632–2237) grams. Mean skin temperature in Strata-1 and Strata-2 for SSI vs. LCI was 36.8 °C ± 0.2 vs. 36.7 °C ± 0.18 and 36.8 °C ± 0.22 vs. 36.7 °C ± 0.19. Mean axillary temperature in Strata-1 and Strata-2 for SSI vs. LCI was 36.9 °C ± 0.19 vs. 36.8 °C ± 0.16 and 36.8 °C ± 0.2 vs. 36.8 °C ± 0.19. Mixed-effect model done for repeated measures of skin and axillary temperatures showed the estimates were within the non-inferiority limit; -0.07 °C (95% CI -0.11 to -0.04) and -0.06 °C (95% CI -0.095 to -0.02), respectively. Failed thermoregulation did not occur in any infants. Mild hypothermia occurred in 11 of 48(23%) of SSI and 16 of 48(33%) of LCI, OR 1.28 (95%CI 0.85 to 1.91). Incubator temperature in LCI was higher by 0.7 °C (95%CI 0.52 to 0.91). In the post-infant period SSI and LCI had excellent reliability to maintain set-temperature with intra-class correlation coefficient of 0.93 (95%CI 0.92 to 0.94) and 0.96 (95%CI 0.96 to 0.97), respectively.

Interpretation Maintenance of skin and axillary temperature of stable preterm infants in LCI along with kangaroo mother care was non-inferior to SSI, but at a higher incubator temperature by 0.7 °C. No adverse events occurred and LCI had excellent reliability to maintained set-temperature.