Respiratory acidosis in adolescents with anorexia nervosa hospitalized for medical stabilization: A retrospective study

Objective: To examine the effect of malnutrition due to anorexia nervosa (AN) on venous blood gases of adolescents with AN hospitalized for medical stabilization. Method: This retrospective study included 45 adolescents with recent onset (<1 year) AN diagnosed by DSM-IV criteria and excluded subjects with a history of lung disease. Results: Mean (±SD) age at hospitalization was 15.0 ± 2.0 years; time from onset of symptoms was 6.8 ± 3.0 months; body mass index (BMI) was 15.2 ± 1.5 kg/m ²; and minimal nocturnal heart rate (MNHR) was 39.8 ± 7.2 beats/min. On admission, pH was 7.32 ± 0.02, pCO ₂ was 53.8 ± 4.6 mm Hg, and HCO ₃ was 28.1 ± 2.1 mEq/l. Significant changes (p <.001) occurred during the relatively short hospitalization (9.7 ± 5.1days): venous pH increased, pCO ₂ decreased, HCO ₃ decreased, MNHR increased, and heart rate orthostasis decreased. Mild respiratory acidosis (pH < 7.35 and pCO ₂ > 45 mm Hg) was observed in 78% of the patients on admission and only in 35% at discharge (p =.0003). Positive correlations were found between % of weight loss and pCO ₂ on admission and between BMI on admission and the delta pCO ₂ during hospitalization. Discussion: Mild respiratory acidosis is common in adolescents with recently diagnosed AN, hospitalized for medical stabilization. Respiratory acidosis improves with bed rest and refeeding. The clinical significance of these findings should be further evaluated.