Background Hypocarbia, defined as a PaCO₂<4.7 kPa, is a risk factor for chronic lung disease, severe intraventricular haemorrhage, periventricular leucomalacia and cerebral palsy.

Aims To quantify ELBW exposure to hypocarbia during mechanical ventilation and to document the cranial ultrasound findings in exposed infants.

Methods Retrospective chart review of ventilated preterm infants <1.5 kg and gestational age <32 weeks. All documented blood gases taken while on mechanical ventilation were reviewed and the degree and duration of hypocarbia noted. Cranial ultrasound and MRI findings of IVH, severe IVH and PVL were noted. This study was performed as an audit of current unit practice. All results are expressed as median (range).

Results ELBW infants admitted to the NICU between January and December 2006 were identified. Notes were obtained on 50 infants, of whom 26 experienced a PCO₂ <4.7 kPa (52%). The median lowest PaCO₂ reading was 3.65 (2.0–4.65) kPa. The median time between identification of hypocarbia and achieving a normal CO₂ was 9.58 hours. 15.4% of infants who experienced a CO₂<4.7 kPa had PVL and/or a severe IVH.

Conclusion ELBW infants are frequently exposed to severe and prolonged hypocarbia during mechanical ventilation. While both IVH and PVL are multifactorial, 15.4% of infants exposed to hypocarbia had either severe IVH or PVL on scan.