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Introduction
In patients with acute lung injury (ALI), the prone position is a well-established method to improve gas exchange by reopening atelectasis and secret drainage. This approach might lead, however, to increased intra-abdominal pressure and thereby impaired gastric mucosal perfusion. Therefore, we studied the effect of the prone position on both intragastric pressure and gastric mucosal-arterial PCO2 gradients in patients with ALI.
Patients/methods
So far, 10 patients with ALI (PaO2/FiO2 <250 mmHg) and clinical indication for mechanical ventilation in the prone position were studied. In addition to ventilator settings, systemic hemodynamics and gas exchange, we semi-continuously measured the gastric mucosal PCO2 (PCO2 gm) (Tonocap) via a nasogastric tube as well as the intragastric pressure continuously via one lumen of the nasogastric tube using a common pressure transducer. After 60 min of stable conditions baseline measurements were made. Then the patient was turned to prone position and further measurements were obtained 60 and 120 min later.
Results/statistics
See Table. Friedmann test/Student-Newman-Keuls: #P<0.05 vs baseline.
Conclusion
Despite major individual variability, we could not find a significant overall change in gastric mucosal-arterial PCO2 gradient after turning to prone position. Increased intragastric pressure (>5 mmHg), however, was associated with an increased gastric mucosal-arterial PCO2 gradient despite stable systemic hemodynamics. Positioning induced variations of intra-abdominal pressure, hence, may impair gastric mucosal energy balance possibly due to compromised regional blood flow.
Table.
| (median/percentile) | Baseline | 60 min | 120 min |
|---|---|---|---|
| Ci l/min/m2 | 3.8/4.7-3 | 3.8/4.1-3.3 | 3.9/4.6-3.4 |
| MAP mmHg | 85/93-77 | 81/88-66 | 78/88-70 |
| CVP mmHg | 14/15-12 | 14/15-8 | 13/16-10 |
| PCO2gm mmHg | 53/57-49 | 57/63-55 | 58/71-51 |
| PCO2art mmHg | 47/50-42 | 48/52-44 | 44/48-43 |
| Gastric pressure mmHg | 12/14-6 | 12/16-9 | 10/13-7 |
| PCO2gm-PCO2art mmHg | 6/11-3 | 8/17-6 | 10/18-3 |