Assessment of pulmonary function in resolving chronic lung disease of prematurity

Abstract

Aim: To investigate the longitudinal changes of interstitial and airways disease in resolving chronic lung disease of prematurity (CLD).

Methods: Thirty three infants were studied between 35 and 40 weeks of postconceptional age, and then at three monthly intervals throughout their first year. Measurements of mean arterial oxygen saturation (MSaO2) and its variability (delta MSaO2) were recorded. PaCO2 and PaO2 were determined while the infants breathed steady state 50% oxygen via a hood. From these, the alveolar arterial difference (A-a) DO2(50) was calculated. Airway disease was assessed by the measurement of partial forced expiratory flow volume curves (PEFC) to give Vmax Frc.

Results: The cohort mean +/- 95% confidence intervals measured between 35 and 40 weeks were for MSaO2 (89.25 +/- 1.87%, range 75-96.5%) and delta MSaO2 (4.79 +/- 0.8%, range 0.16-9.64%), PaCO2 (5.89 +/- 0.56 kpa, range 4.2-10.11 kpa), (A-a) DO2(50) (22.7 +/- 2.56 kpa, range 6.67-31.4 kpa) and VmaxFrc (41.5 +/- 8.65 mls/second, range 8.5-103.7 ml/second). The most significant improvement in all measurements occurred within the first three months (P = 0.05). An MSaO2 of less than 90% in room air at 1 year of age was predicted between 35 and 40 weeks postconceptional age by an (A-a) DO2(50) of greater than 29 kpa, with a sensitivity of 0.85 and a specificity of 0.88, and a PaCO2 greater than 7 kpa predicted a specificity of 0.78 and a sensitivity of 0.88. Predictions were strengthened by combining the above criteria and these then gave a sensitivity and specificity of 1.

Conclusion: Measurements of (A-a) DO2(50) and PaCO2 taken between 35 and 40 weeks can be used to assess the degree of pulmonary dysfunction at 1 year. Quantification of the severity of CLD could be used as a measurable end point for early neonatal intervention studies.

Figure 1

Longitudinal changes in (A-a) Do₂⁵⁰ and PaCO₂ (group means and confidence interval).

Figure 2

Longitudinal changes in V̇_maxFrc.

Figure 3

Longitudinal changes in MSaO₂ and δMSaO₂ (cohort means and 95% confidence intervals).