Permissive hypercapnia and gas exchange in lungs with high Qs/Qt: a mathematical model

Abstract

Low volume ventilation with permissive hypercapnia is becoming widely used in the treatment of acute respiratory distress syndrome. A mathematical model was developed to examine the effects of hypoventilation on pulmonary gas exchange in lungs with a range of shunt fractions. Hypoventilation did not worsen gas exchange, provided the inspired oxygen concentration was high enough to maintain PAO2 at an adequate level. In lungs with a high shunt fraction, some improvement in gas exchange may result, but these effects are small. A rightwards shift of the oxygen-haemoglobin dissociation curve induced by hypercapnia, is likely to be beneficial rather than detrimental in patients with acute respiratory distress syndrome. This analysis was limited to the direct effects of hypoventilation in lungs with constant shunt fractions, and did not encompass a number of possible secondary effects such as changes in cardiac output with PaCO2, changes in shunt fraction associated with a reduction in mean airway pressure and possible direct effects of hypercapnia on the pulmonary vasculature or airways.

Clinical Results of Extracorporeal Membrane Oxygenation (ECMO) Support for Acute Respiratory Failure: A Comparison of a Centrifugal Pump ECMO with a Roller Pump ECMO

“…According to these criteria, the PaO 2 levels (PF ratio: 60) were almost the same as the previous criteria (SaO 2 95% at an FIO 2 1.0); however, PaCO 2 levels were elevated due to the ventilation with "permissive hypercapnia." Low volume ventilation, known as permissive hypercapnia or controlled hypoventilation, which maintains adequate pulmonary gas exchange, [3][4][5] limits lung distension, and minimizes the risk of volutrauma, 6,7 thus resulting in a decreased mortality and improvement in the clinical outcomes in patients with ARF. 7 Compared with the induction criteria published in other references, our criteria may still be restrictive.…”

Modelling: a core technique in anaesthesia and critical care research

“…As papers published in this 1 and previous editions of the journal [2][3][4][5] illustrate, modelling is assuming a more prominent role in mainstream anaesthesia and critical care research, becoming an accepted methodology and an ever-more useful part of the research process. This editorial explores the phenomenon of modelling and its uses and limitations.…”