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Advances in neonatal intensive care, such as ventilation support, have dramatically reduced neonatal deaths. However, they have not substantially reduced the risk of cerebral palsy and other neurodevelopmental disorders among low birthweight (LBW) infants.
Mechanical ventilation of newborns can result in hypocapnia (low levels of carbon dioxide in the blood) and hyperoxia (high levels of oxygen in the blood), both of which can result in reduced cerebral blood flow. Ventilated newborns with hypocapnia, hyperoxia, or unusually prolonged duration of ventilation support have a two- to three-fold increased risk of being diagnosed with disabling cerebral palsy (DCP) by age 2, according to a study supported by the Agency for Healthcare Research and Quality (HS08385).
The researchers examined a population-based cohort of 1,105 infants with birthweights of 500-2000 grams (roughly 1-4 pounds), substantially the largest such cohort study examining ventilatory practices as risks for cerebral palsy. The investigators constructed an index of exposure to hypocapnia based on both the degree and duration of low levels of arterial carbon dioxide concentrations.
Among 902 survivors to age 2 years, 657 had both neurodevelopmental assessments at age 2 and records of blood gas measurements in the first week of life. DCP was subsequently diagnosed in 2.3 percent of the 257 unventilated newborns, 9.4 percent of the 320 ventilated newborns without exposure to unusual levels of hypocapnia, and 27.5 percent of the 80 ventilated infants with exposure to significant hypocapnia. The strong associations with ventilation and with hypocapnia persisted after adjustment for gestational age and other possible correlates of risk for cerebral palsy.
Prolonged duration of ventilation and hyperoxia also were risk factors for DCP among ventilated infants, with all three factors independently contributing a two- to three-fold increased risk of DCP. When any two of these risk factors were present, the risk of DCP was increased about eight-fold. The increase was 20-fold when all three risk factors were present, when compared with ventilated infants without any of the risk factors.
Although duration of mechanical ventilation in LBW newborns probably reflects severity of illness, both hypocapnia and hyperoxia can be largely controlled by ventilatory practice. The researchers recommend that neonatologists avoid arterial PCO2 levels less than 35 mm Hg and arterial PO2 levels greater than 60 mm Hg whenever possible in ventilated LBW infants.
See "Hypocapnia and other ventilation-related risk factors for cerebral palsy in low birth weight infants," by Michael P. Collins, M.D., John M. Lorenz, M.D., James R. Jetton, B.A., and Nigel Paneth, M.D., in Pediatric Research 50(6), pp. 712-719, 2001.
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