Another important finding was that arterial pH consistently and significantly differed between survivors and non-survivors, as described elsewhere [40, 41] . During the first 72 hours acidosis had a major metabolic component, likely as a sign of hemodynamic impairment. After the first week, respiratory acidosis ensued, indicating either the effects of protective ventilation, or merely deterioration due to progressive shunt, profound ventilation/perfusion mismatch and increased deadspace.