Invasive ventilation at the boundary of viability: A respiratory pathophysiology study of infants born between 22 and 24 weeks of gestation

Abstract

Background

Invasive ventilation of infants born before 24 weeks of gestation is critical for survival and long-term respiratory outcomes, but currently there is a lack of evidence to guide respiratory management. We aimed to compare respiratory mechanics and gas exchange in ventilated extremely preterm infants born before and after 24 weeks of gestation.

Methods

Secondary analysis of two prospective observational cohort studies, comparing respiratory mechanics and indices of gas exchange in ventilated infants born at 22–24 weeks of gestation (N=14) compared to infants born at 25–27 weeks (N=37). The ventilation/perfusion ratio (V_A/Q), intrapulmonary shunt, alveolar dead space (V_Dalv) and adjusted alveolar surface area (S_A) were measured in infants born at the Neonatal Unit of King’s College Hospital NHS Foundation Trust, London, UK.

Results

Compared to infants of 25–27 weeks, infants of 22–24 weeks had higher median (IQR) intrapulmonary shunt [18 (4 - 29) % vs 8 (2 – 12) %, p=0.044] and higher V_Dalv [0.9 (0.6 – 1.4) vs 0.6 (0.5 – 0.7) ml/kg, p=0.036], but did not differ in V_A/Q. Compared to infants of 25–27 weeks, the infants of 22–24 weeks had a lower adjusted S_A [509 (322- 687) vs 706 (564 - 800) cm², p=0.044]. The infants in the two groups did not differ in any of the indices of respiratory mechanics.

Conclusion

Ventilated infants born before 24 completed weeks of gestation exhibit abnormal gas exchange, with higher alveolar dead space and intrapulmonary shunt and a decreased alveolar surface area compared to extreme preterms born after 24 weeks of gestation.