Effect of intra-abdominal pressure on respiratory mechanics

There has been an exponentially increasing interest in intra-abdominal hypertension (IAH). The intra-abdominal pressure (IAP) markedly affects the function of the respiratory system.

This review will focus on the available literature from the past few years. A Medline and Pubmed search was performed in order to find an answer to the question "What is the impact of increased IAP on respiratory function in the critically ill?".

In particular, increased IAP increases chest wall elastance (or decreases compliance) and promotes cranial shift of the diaphragm, with consequent reduction in lung volume and atelectasis formation. Compression of the lung parenchyma also triggers pulmonary infection. During general anaesthesia, in normal subjects, IAP does not affect the chest wall mechanics, but plays a relevant role in the caudal-cranial displacement of the abdominal content, the diaphragm and consequent changes in lung mechanics and function. In obese patients, the increased IAP is the major determinant of the reduction in lung volume, atelectasis formation and alterations in chest wall mechanics. In ARDS patients the measurement of IAP and chest wall mechanics is important for a better interpretation of respiratory mechanics, hemodynamics and appropriate setting of the ventilator. Furthermore, increased IAP promotes lung oedema, ventilator induced lung injury and reduced lymphatic flow in normal and diseased lungs.

Increased IAP markedly affects respiratory function in such a way that it has an impact on daily clinical practise.