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21-02-2019 | Ophthalmology | News | Article

Biphasic oxygen targets help prevent retinopathy of prematurity

medwireNews: Biphasic oxygen targets can decrease the incidence and severity of retinopathy of prematurity (ROP) without increasing the risk of death, cohort study findings suggest.

The results showed that the incidence of treatment-requiring ROP (type 1) among 562 infants born at a corrected gestational age (CGA) of 31 weeks or younger and weighing 1500 g or less was 4% lower with the use of biphasic protocol target saturations than with the introduction of static high oxygen targets, as recommended by SUPPORT (The Surfactant, Positive Pressure, and Pulse Oximetry Randomized Trial).

Static high oxygen saturation targets of 91% to 95% were recommended following SUPPORT on finding that lower static oxygen targets reduced ROP but also increased the risk of death.

However, this outcome could be avoided by using a biphasic approach, whereby a saturation target of 85% to 92% is maintained for infants born at a CGA of less than 34 weeks and increased to greater than 95% for infants with a CGA of 34 weeks or more, when at this later phase hyperoxia is needed to decrease neovascularisation and vasodilation, as shown in the STOP-ROP (Supplemental Therapeutic Oxygen for Prethreshold Retinopathy of Prematurity) study.

Indeed, the incidence of any type of ROP was 20% among 260 infants treated using a biphasic approach, versus 28% among 321 infants treated according to SUPPORT recommendations, giving a significant 1.6-fold increased risk of ROP with the static approach.

This increased risk with the static approach remained significant after adjusting for known risk factors such as GA, birthweight, sepsis and meningitis.

The corresponding rates of ROP type 1 were 2% and 6%, with a significant 2.7-fold increased risk using the static saturation target.

When outcomes were studied according to GA, the 131 infants aged 28 weeks and younger treated with biphasic oxygen targets had a significantly lower incidence of any ROP compared with 148 infants of the same GA treated with static targets (34 vs 49%, odds ratio=1.8), as well as a nonsignificant trend towards lower incidence of ROP type 1 (5 vs 12%). By comparison, there was no difference between interventions in infants older than 28 weeks.

In the younger GA group, a biphasic approach was also associated with a significantly shorter time to full vascularisation of the retina, at a median of 67 days versus 89 days. And the researchers note that infants younger than 28 weeks were less likely to be fully vascularised with the introduction of SUPPORT recommendations and the delay was associated with an increase in the number of retinal examinations. They estimate that infants of this GA are 40% more likely to have avascular retinas with a static approach than a biphasic one.

There was also no difference in mortality between the biphasic and static approaches in either GA group.

“These findings do not contradict the outcomes of SUPPORT nor do they contradict the outcomes of Supplemental Therapeutic Oxygen for Prethreshold Retinopathy of Prematurity (STOP-ROP)”, say Jonathan Sears (Cleveland Clinic, Ohio, USA) and co-researchers in JAMA Ophthalmology.

They continue: “The timing of the switch to higher oxygen settings follows the natural history of ROP: early, physiologic hypoxia (oxygen targets 85%-92% saturation) coincides with phase 1 but induces retinal growth to remove the substrate for disease, whereas late hyperoxia coincides with phase 2 to reduce abnormal neovascularization”.

Referring to the article in a related commentary, Lois Smith (Harvard Medical School, Boston, Massachusetts, USA) and colleagues say: “This study is an important first step in defining the use of oxygen while considering the timing of oxygen supplementation as well as the saturation targets.

“The use of lower [oxygen saturation] targets early and higher during a later period has the potential to become a preventive strategy for ROP.”

 By Lucy Piper

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