Gastric Intramucosal pH is Stable During Titration of Positive End-Expiratory Pressure to Improve Oxygenation In Acute Respiratory Distress Syndrome

Ibrahim Ozkan Akinci, Nahit Çakar, Gökhan Mehmet Mutlu, Simru Tugrul, Perihan Ergin Ozcan, Musa Gitmez, Figen Esen Lutfi Telci


Crit Care. 2003;7(3) 

In This Article

Abstract and Introduction

Background: Optimal positive end-expiratory pressure (PEEP) is an important component of adequate mechanical ventilation in acute lung injury and acute respiratory distress syndrome (ARDS). In the present study we tested the effect on gastric intramucosal pH of incremental increases in PEEP level (i.e. PEEP titration) to improve oxygenation in ARDS. Seventeen consecutive patients with ARDS, as defined by consensus criteria, were included in this clinical, prospective study. All patients were haemodynamically stable, and were not receiving vasopressors. From an initial level of 5 cmH2O, PEEP was titrated at 2 cmH2O increments until the partial arterial oxygen tension was 300 mmHg or greater, peak airway pressure was 45 cmH2O or greater, or mean arterial blood pressure decreased by 20% or more of the baseline value. Optimal PEEP was defined as the level of PEEP that achieved the best oxygenation. The maximum PEEP was the highest PEEP level reached during titration in each patient.
Results: Gastric mucosal pH was measured using gastric tonometry at all levels of PEEP. The thermodilution technique was used for measurement of cardiac index. Gastric mucosal pH was similar at baseline and at optimal PEEP levels, but it was slightly reduced at maximum PEEP. Cardiac index and oxygen delivery remained stable at all PEEP levels.
Conclusion: Incremental titration of PEEP based on improvement in oxygenation does not decrease gastric intramucosal perfusion when cardiac output is preserved in patients with ARDS.

Positive end-expiratory pressure (PEEP) is an important component of the ventilatory management of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). PEEP improves oxygenation by redistributing the alveolar fluid and restores functional residual capacity by keeping the alveoli open. However, PEEP can be detrimental because it may, particularly at high levels, decrease cardiac output by decreasing the venous return as a result of diminished pressure gradient between the systemic veins and right atrium,[1] and consequently it may lead to hypoperfusion of vital organs. Ultimately, despite improving arterial oxygen content, PEEP may decrease oxygen delivery to various organs, among which the splanchnic vascular bed appears to be particularly at risk because of its predisposing features and the influence of PEEP on regional blood flow distribution.

Maintenance of splanchnic blood flow is important because splanchnic hypoperfusion may play a critical role in the pathogenesis of multiorgan dysfunction syndrome.[2,3] Mechanical ventilation has been suggested to potentiate the adverse effects of underlying critical illness on splanchnic vasculature and contribute to the development of multiorgan dysfunction syndrome, particularly when 'injurious' ventilatory strategies that produce high end-inspiratory lung volumes are employed.[3] Experimental studies suggested that mechanical ventilation with considerably high levels of PEEP can lead to splanchnic hypoperfusion and marked reduction in hepatic blood flow.[4,5,6] Furthermore, PEEP may decrease splanchnic blood flow in patients with no underlying lung disease.[7,8] Most available evidence regarding the effects of PEEP from animal studies has been extrapolated to humans based on the assumption that the effects of mechanical ventilation on humans and animals are similar. However, a recent study conducted in humans explored the effect of PEEP in patients with ALI[9] and did not find a consistent effect on splanchnic blood flow.

Because of the difficulties associated with measurement of pressure-volume curves, incremental titration of PEEP in an attempt to find the 'best' PEEP, based on improvement in oxygenation, is common practice in the management of hypoxaemic respiratory failure. However, it is unknown whether this strategy has an adverse effect on splanchnic perfusion. The aim of the present study was to investigate the impact of PEEP titration (based on improvement in oxygenation) on gastric mucosal perfusion in patients with ARDS, as assessed by measurement of gastric mucosal pH (pHi).


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