Changes in respiratory mechanics during cardiac surgery

Area of Science:

• Anesthesiology
• Cardiovascular Surgery
• Respiratory Physiology

Background:

• Cardiac surgery often involves cardiopulmonary bypass (CPB), which may impact lung function.
• Understanding the effects of CPB on respiratory mechanics is crucial for patient outcomes.
• Off-pump coronary artery bypass (OPCAB) serves as a comparison for CPB effects.

Purpose of the Study:

• To investigate the role of cardiopulmonary bypass (CPB) in compromising lung function during cardiac surgery.
• To compare respiratory impedance (Zrs) changes in patients with and without CPB.
• To assess the effect of dopamine (DA) on lung function during CPB.

Main Methods:

• Low-frequency respiratory impedance (Zrs) was measured in three groups: CPB (n=30), OPCAB (n=29), and CPB with dopamine (CPB-DA) (n=12).
• Measurements were taken before skin incision and after chest closure.
• Airway resistance, inertance, tissue damping, and elastance were derived from Zrs data; extravascular lung water was measured in a subset of CPB patients.

Main Results:

• Airway resistance significantly increased in the CPB group but remained unchanged in the OPCAB group.
• Dopamine administration in the CPB-DA group led to a significant decrease in airway resistance.
• Tissue damping increased in both CPB and OPCAB groups, while elastance increased in all groups; extravascular lung water did not change significantly.

Conclusions:

• Cardiopulmonary bypass deteriorates lung function by inducing heterogeneous airway constriction.
• This negative effect on lung function was not observed in patients undergoing cardiac surgery without bypass (OPCAB).
• Dopamine administration effectively counteracted the airway narrowing induced by CPB.