The Time When the Metabolic Compensation for Hypercapnia Begin to Occur in Very Low Birth Weight Infants

ABSTRACT

PURPOSE: Lung injury from mechanical ventilation is one of the major pathogenetic factors of bronchopulmonary dysplasia. Permissive hypercapnia (PH) is one of the strategies for reducing lung injury. However, PH is frequently infeasible in very low birth weight infants (VLBWI) due to their immature renal compensation for respiratory acidosis. The purpose of this study was to identify time when metabolic compensation for hypercapnia begin to occur in VLBWIs. METHODS: Data were retrospectively collected from 82 VLBWI who were admitted to Seoul National University Bundang Hospital from January 2011 to December 2012. The postnatal day when the difference between actual bicarbonate and expected bicarbonate levels became less than 2.0 mmol/L consistently for the first time under hypercapnea (>40 mmHg) was defined as the time when metabolic compensation for hypercapnea occurred. RESULTS: Metabolic compensation for hypercapnea occurred on 9.1+/-3.9 postnatal day. The younger the gestational age (GA) was and the smaller the birth weight was, the later metabolic compensation for hypercapnea occurred. Late metabolic compensators (> or =9 days) were significantly younger in GA (P=0.001), lighter at birth (P=0.041), intubated longer (P=0.002), and less frequently afflicted with respiratory distress syndrome (P=0.036) compared to early metabolic compensators (<9 days). However, logistic regression analysis revealed only young GA was associated with late metabolic compensation with marginal significance (P=0.068). CONCLUSION: Metabolic compensation for hypercapnea occurred 9 days after birth on average. PH strategy for reducing lung injury should be considered after renal metabolic compensation for hypercapnea occurs in VLBWI.