Differential Ventilation and Selective PEEP During Anaesthesia in the Lateral Decubitus Posture

Abstract

The potential of differential ventilation (DV) with selective positive end-expiratory pressure (PEEP) has been tested versus conventional ventilation with and without general PEEP. Gas exchange and central haemodynamics were studied in 15 subjects with no clinical or radiological signs of pulmonary disease. The rationale of the method was to ensure ventilation of the well-perfused dependent lung and to counteract airway closure within that lung. The subjects were intubated with a double-lumen catheter prior to scheduled abdominal surgery. During general anaesthesia in the lateral posture, they were given DV. The mean inspired oxygen fraction was 0.32. Fifty per cent ("even" tidal volume (VT) distribution) or 70% ("inverted" VT distribution) of the inspired volume was administered to the dependent lung. Two synchronized ventilators were used. In eight subjects DV was also combined with PEEP applied solely to the dependent lung (selective PEEP). The major findings were that DV with even VT distribution reduced venous admixture by 26% (P less than 0.05) and the alveolo-arterial oxygen tension gradient (P(A-a)o2) by 30% (P less than 0.05) in comparison with conventional ventilation in the lateral position. The addition of selective PEEP further reduced the P(A-a)o2 by 13%. P(A-a)o2 was consequently 43% lower than during conventional ventilation without PEEP in the lateral posture (P less than 0.01). Selective PEEP also had less impact on cardiac output than general PEEP (P less than 0.05). It is concluded that DV with even distribution of VT and selective PEEP can reduce the P(A-a)o2 in anaesthetized lung-healthy subjects in the lateral position.

The influence of body position and differential ventilation on lung dimensions and atelectasis formation in anaesthetized man

“…The calculated lung volume changes caused by these dimensional changes are in accordance with earlier findings (9) showing an increased FRC in the dependent lung and an unchanged or slightly decreased FRC in the non-dependent lung during ventilation with selective PEEP. This suggests an interaction between the two hemithoraces, but the mechanisms remain to be clarified.…”

“…8,9). During differential ventilation, the ventilators were electronically synchronized, thereby keeping the respiratory frequency equal and the start of inspiration simultaneous for both lungs.…”

“…Differential ventilation with selective PEEP is a new ventilatory concept which has been used both during intensive care (8, 15) and during routine anaesthesia in the lateral position (9). It is based on: 1) positioning of the patient in the lateral posture; 2) even distribution of ventilation between the two lungs; and 3) application of PEEP solely to the dependent lung.…”

“…Although the detailed effects of differential ventilation with selective PEEP on ventilation/ perfusion matching remain hypothetical at present, the net effect in terms of reduced venous admixture and improved arterial oxygenation has in fact been demonstrated in patients with acute respiratory failure (8) and in clinically lung healthy patients during anaesthesia (9). Although the detailed effects of differential ventilation with selective PEEP on ventilation/ perfusion matching remain hypothetical at present, the net effect in terms of reduced venous admixture and improved arterial oxygenation has in fact been demonstrated in patients with acute respiratory failure (8) and in clinically lung healthy patients during anaesthesia (9).…”

“…They are, however, of particular interest when it comes to analysing the effects on gas exchange found during differential ventilation with PEEP selectively applied to the dependent lung, since this ventilation technique may improve arterial oxygenation both in patients with acute respiratory failure (8) and during routine anaesthesia (9). The lateral position alters lung geometry as the antero-posterior (sagittal) diameter of each lung is greater than its medio-lateral (transverse) diameter.…”