Acute renal response to changes in carbon dioxide in mechanically ventilated female pigs.

Kidney response to acute and mechanically induced variation in ventilation associated with different levels of PEEP has not been investigated. We aimed to quantify the effect of ventilatory settings on renal acid-base compensation. Forty-one pigs undergoing hypo- (<0.2 Lkg^-1 min^-1, PEEP 25 cmH₂O), intermediate (0.2-0.4 Lkg^-1 min^-1 with either PEEP 5 or 25 cmH₂O), or hyper-ventilation (>0.4 Lkg^-1 min^-1, PEEP 5 cmH₂O) for 48 h were retrospectively included. The decrease in pH paralleled the decrease in plasma strong ion difference (SID) in hyper- and intermediately ventilated groups with lower PEEP. In contrast, the plasma SID remained nearly constant in hypo- and intermediately ventilated groups with higher PEEP. Changes in plasma chloride concentration accounted for the changes in plasma SID (conditional R² = 0.86). The plasma SID changes were paralleled by mirror changes in urinary SID. Higher PEEP (25 cmH₂O), compared to lower PEEP (5 cmH₂O) dampened or abolished the renal compensation through its effect on hemodynamics (higher central venous and mean pulmonary pressures), irrespective of minute ventilation. During mechanical ventilation, the compensatory renal response to respiratory derangement is immediate and progressive but can be dampened by high PEEP levels.