Neuropediatrics 2006; 210 - V56
DOI: 10.1055/s-2006-946338

Buffering Acidosis during Permissive Hypercapnia to Restore Physiologic PH May Increase the Degree of Lung Injury in Surfactant Deficient Rabbits

HD Hummler 1, A Engelmann 1, A Merinsky 1, S Häring 1, AR Franz 2, M Ebsen 3, MR Wolfson 4, F Pohlandt 1
  • 1Universitätsklinikum Ulm, Ulm, D
  • 2Universitätsklinikum Bonn, Bonn, D
  • 3Abt. Pathologie, Universität Bochum, Bochum, D
  • 4Dept. of Physiology and Pediatrics Philadelphia, Philadelphia, USA

Background: Buffering hypercapnic acidosis is commonly performed in the ICU when patients with respiratory failure are exposed to permissive hypercapnia.

Objective: To study the hypothesis that buffering hypercapnic acidosis worsens the degree of lung injury in an animal model of surfactant deficiency.

Methods: 28 anesthetized, surfactant-depleted rabbits were mechanically ventilated with an FiO2=1.0, Vt=4.5ml/kg, PEEP=6cmH2O with the rate adjusted to obtain a target PaCO2=75–85mmHg, and were randomized into a buffer group (receiving NaHCO3 infusions to restore pH >7.25) and a control group. Surviving animals were sacrificed after 6h. Primary outcome measure was lung wet/dry weight ratio, secondary outcome measures were blood gases, BAL-Protein, Plasma and lung tissue IL-8, macroscopic and histologic evaluation of the lungs (both blinded), cardiac output (by thermodilution) and plasma lactate. All data presented refer to mean±SD or median (25.-75. Perc.).

Results: 3 vs. 0 animals (buffer vs. control) died before the end of study time. Wet/dry weight ratio [11.9 (8.5–12.8) vs. 7.7 (6.4–9.6); p<0.05] and BAL-Protein [907 (510–1328) vs. 434 (189–775)mg/l; p<0.05] were higher in buffered animals. Furthermore we observed trends towards lung tissue IL-8 values in buffered animals. Macroscopic evaluation revealed higher injury scores for the buffered group [3 (0–5) vs. 0.5 (0–3.5), p<0.01], histology revealed a trend towards higher injury scores in buffered animals [6.9 (3.0–12.5) vs. 4.8 (3.0–14.3), p=0.19). Although there was no difference in cardiac output between groups, oxygen delivery was higher and plasma lactate was lower in control animals. There was no significant difference in plasma IL-8.

Conclusion: We conclude that restoring physiologic pH during permissive hypercapnia may increase the degree of lung injury and plasma lactate, and impair oxygen delivery in this animal model of surfactant deficient rabbits.