Ventilation

Kirby, Robert R.

doi:10.1017/cbo9780511933837.003

Cited by 1 publication

(1 citation statement)

References 1,229 publications

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“…It is noteworthy that, remembering the physiological dead space equation, modelling studies have shown that (PaCO 2 -PETCO 2 )/PaCO 2 has a more linear correlation with alveolar dead space fraction than the simpler PaCO 2 -PETCO 2 [29,30]. Although dependent on, for example, age, the inhaled/ exhaled gas volume and mode of ventilation, a PaCO 2 -PETCO 2 ,5 mmHg (0.7 kPa) is considered normal [31,32] and is supported by PETCO 2 being close to 36 mmHg (4.8 kPa) in a small number of normal subjects [33]. PaCO 2 -PETCO 2 has been shown to correlate with alveolar dead space fraction and alveolar recruitment in animal models of ARDS [34].…”

Section: Wasted Ventilation (Physiological Dead Space)mentioning

confidence: 99%

Gas exchange and ventilation–perfusion relationships in the lung

2014

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This review provides an overview of the relationship between ventilation/perfusion ratios and gas exchange in the lung, emphasising basic concepts and relating them to clinical scenarios. For each gas exchanging unit, the alveolar and effluent blood partial pressures of oxygen and carbon dioxide (PO 2 and PCO 2 ) are determined by the ratio of alveolar ventilation to blood flow (V9A/Q9) for each unit. Shunt and low V9A/Q9 regions are two examples of V9A/Q9 mismatch and are the most frequent causes of hypoxaemia. Diffusion limitation, hypoventilation and low inspired PO 2 cause hypoxaemia, even in the absence of V9A/Q9 mismatch. In contrast to other causes, hypoxaemia due to shunt responds poorly to supplemental oxygen. Gas exchanging units with little or no blood flow (high V9A/Q9 regions) result in alveolar dead space and increased wasted ventilation, i.e. less efficient carbon dioxide removal. Because of the respiratory drive to maintain a normal arterial PCO 2 , the most frequent result of wasted ventilation is increased minute ventilation and work of breathing, not hypercapnia. Calculations of alveolar-arterial oxygen tension difference, venous admixture and wasted ventilation provide quantitative estimates of the effect of V9A/Q9 mismatch on gas exchange. The types of V9A/Q9 mismatch causing impaired gas exchange vary characteristically with different lung diseases. @ERSpublications A review of ventilation-perfusion relationships and gas exchange, basic concepts and their relation to clinical cases

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