Hemodynamic response to changes in ventilatory patterns in patients with normal and poor left ventricular reserve

Area of Science:

• Cardiology
• Critical Care Medicine
• Respiratory Therapy

Background:

• Post-aortocoronary bypass surgery patients often require mechanical ventilation.
• Different modes of mechanical ventilation, including controlled mechanical ventilation (CMV) and intermittent mandatory ventilation (IMV), can impact hemodynamic stability.
• Positive end-expiratory pressure (PEEP) is a common adjunct in mechanical ventilation.

Purpose of the Study:

• To investigate the hemodynamic effects of CMV, IMV, and IMV with 5 cm H2O PEEP (IMV 5 PEEP) in patients following aortocoronary bypass surgery.
• To compare the impact of these ventilation modes on cardiac index (CI), stroke volume index (SI), and other hemodynamic variables in patients with varying degrees of left ventricular function.

Main Methods:

• Hemodynamic parameters were assessed in 20 post-aortocoronary bypass surgery patients.
• Patients were transitioned between CMV, IMV, and IMV 5 PEEP.
• Measurements included cardiac index (CI), stroke volume index (SI), left ventricular end-diastolic pressure (LVEDP), ejection fraction (EF), right atrial pressure (RAP), pulmonary artery occlusion pressure (PAOP), and mean arterial pressure (MAP).

Main Results:

• In patients with normal left ventricular function (normal LVEDP and EF), transitioning from CMV to IMV significantly increased CI and SI (p < 0.01).
• In patients with impaired left ventricular function (increased LVEDP, EF < 0.6), transitioning from CMV to IMV led to significant increases in RAP and PAOP, and decreases in MAP, CI, and SI (p < 0.01).
• Applying IMV 5 PEEP in patients with impaired left ventricular function returned hemodynamic variables to CMV levels, mitigating the adverse effects of IMV alone.

Conclusions:

• Changing from CMV to IMV has beneficial hemodynamic effects in patients with normal left ventricular function.
• In patients with a failing left ventricle, spontaneous respiration during IMV can cause right ventricular volume overload, leading to detrimental hemodynamic effects.
• IMV with 5 cm H2O PEEP effectively counteracts these adverse hemodynamic effects in patients with compromised left ventricular function.