Cycled light in the intensive care unit for preterm and low birth weight infants

Preterm and low birth weight infants are at an early stage of development, and do not receive adequate maternal circadian signals. They are often cared for over prolonged periods of hospitalisation in neonatal intensive care units (NICU), where environmental circadian stimuli are lacking. Exposure to artificial light-dark cycles may stimulate the development of the circadian system and improve clinical outcomes. However, it remains uncertain whether cycled light (CL) is preferable to near darkness (ND) or continuous bright light (CBL) in fostering development and maturation, and reducing adverse neonatal health outcomes. This is an update of an earlier Cochrane review, last published in 2016.

To evaluate the benefits and harms of CL in preterm and low birth weight infants compared to ND or CBL.

We searched CENTRAL, PubMed, Embase, and two trial registries to September 2023. We also checked reference lists, and searched for retractions of included studies.

We included randomised controlled trials (RCTs) or quasi-RCTs in preterm infants (< 37 weeks' postmenstrual age (PMA)), or those with a low birth weight (< 2500 g), admitted and cared for in an NICU or a step-down unit, comparing CL with ND or CBL.

We used the standard review methods of the Cochrane Neonatal Review Group to assess the methodological quality of studies. We used the fixed-effect model with risk ratio (RR) and mean difference (MD), with their 95% confidence intervals (CIs) for dichotomous data. Our primary outcomes were (1) growth at three and six months' corrected age, (2) major neurodevelopmental disability, and (3) adverse effects. Our secondary outcomes were (4) retinopathy of prematurity, (5) duration of initial hospitalisation, (6) duration of oxygen treatment, and (7) parent satisfaction. We used GRADE to assess the certainty of evidence for each outcome.

We included 20 studies with 1633 infants. Data for meta-analysis were available for 11 studies (1126 infants). One study with multiple arms was included in both comparisons. We rated the overall risk of bias at the study level as high or unclear for all 20 studies that had one or several unclear or high risk of bias judgements across the domains. Cycled light versus dimmed light or near darkness (10 studies) The evidence is very uncertain about the effect of cycled light compared to dimmed light (reduction of illumination levels) or near darkness on weight at three months (MD 24.79, 95% CI -262.33 to 311.91; 2 studies, 187 infants; very low-certainty evidence), and weight at six months (MD 202, 95% CI -109.68 to 513.68; 1 study, 147 infants; very low-certainty evidence). The studies did not report any data for major neurodevelopmental disability. No data are available for adverse effects; it is uncertain if the absence of adverse effects is because none occurred, or because they were not identified and recorded. The evidence is very uncertain about the effect of cycled light compared to dimmed light or near darkness on the likelihood of developing retinopathy of prematurity of any stage (RR 0.89, 95% CI 0.76 to 1.03; 3 studies, 307 infants; very low-certainty evidence), and severe retinopathy of prematurity of stage 3 or higher (RR 0.98, 95% CI 0.59 to 1.61; 4 studies, 454 infants; very low-certainty evidence). Cycled light compared to dimmed light or near darkness may have little to no effect on the duration of initial hospitalisation (MD -3.04, 95% CI -7.86 to 1.78; 5 studies, 550 infants; very low-certainty evidence), but the evidence is very uncertain. Cycled light versus continuous bright light (11 studies) No data are available on the following primary outcomes, as no studies reported them: growth at three and six months' corrected age, major neurodevelopmental disability, and adverse effects. It is uncertain if the absence of adverse effects is because none occurred or because they were not identified and recorded. No data are available on retinopathy of prematurity, as no studies reported it. Cycled light compared to continuous bright light may reduce the duration of initial hospitalisation, but the evidence is very uncertain (MD -9.86, 95% CI -10.09 to -9.63; 5 studies, 499 infants; very low-certainty evidence).

Despite identifying 20 studies, we remain uncertain about the effect of CL compared to ND or CBL on all outcomes of interest in this review. In addition, a few critical outcomes were not reported by any of the included studies. The evidence remains uncertain about whether CL is the right choice in the NICU. The physician should always weigh the benefits and risks, based on the effects of the different options in the specific setting.