Abstract
In cardiac surgery, patients are at risk of phrenic nerve injury, which leads to diaphragm dysfunction and acute respiratory failure. Diaphragm dysfunction (DD) is relatively frequent in cardiac surgery and particularly affects patients after coronary artery bypass graft. The onset of DD affects patients’ prognosis in term of weaning from mechanical ventilation and hospital length of stay. The authors present a narrative review about diaphragm physiology, techniques used to assess diaphragm function, and the clinical application of diaphragm ultrasound in patients undergoing cardiac surgery.
Highlights
Introduction published maps and institutional affilDiaphragm is the most important inspiratory muscle and is innerved by the phrenic nerve
This review aims to report the physiological aspects of diaphragm muscle and phrenic nerve, the radiological and non-radiological techniques used to assess diaphragm function, and the clinical applications of diaphragm ultrasound in cardiac surgery
Diaphragm dysfunction is common in Intensive Care Unit (ICU) and affects prognosis, respiratory outcomes, length of hospital stay, and weaning process [4]
Summary
The diaphragm is the main inspiratory muscle, contributing to 60–70% of the total ventilation at rest. The diaphragm shortens and moves caudally in a piston-like manner, with an increase of the abdominal pressure and a decrease of the pleural pressure, leading to a decrease of the alveolar pressure, below atmospheric pressure. This generates airflow into the lungs against a resistance, following the principles stated by Ohm’s Law [12]. The left phrenic nerve, after crossing the scalenus muscle, runs along the left subclavian artery and behind the thoracic duct, before crossing the left IMA and descending in the thorax, closer to the pericardium, adjacent to the left ventricle, and reaches the diaphragm. Since the phrenic nerves are closer to the IMA in the apical region of the chest, they are vulnerable during the harvesting phase [8]
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