(1183) Is Spontaneous Breathing in Intubated Patients a Stress Test for the Myocardium?

Introduction: Transitioning from volume assist control (VC-AC) to spontaneous breathing (Pressure Support
Ventilation; PSV) allows for assessment for ventilation weaning, but such a transition may increase
the workload on the myocardium and make it prone to ischemic injury. We tested the hypothesis
that spontaneous breathing trial alters the relationship between the key determinant of oxygen
delivery (cardiac output) and surrogates myocardial oxygen demand (heart rate, left ventricular
filling pressure, and mean arterial pressure).

Methods: The study involved patients (n=18) who were on mechanical ventilation for at least 24 hours. Serial measurements of stroke volume (SV), heart rate (HR), the ratio between early mitral inflow velocity and mitral annular early diastolic velocity (E/e'), the maximum velocity of tricuspid regurgitation (TRmax ), mean arterial pressure (MAP) was measured before and 10 minutes after transitioning from VC-AC to PSV. Paired student t-test used for calculating difference among variables. Mean airway pressure (MAwP) was adjusted to meet the patient’s ventilatory requirements during PSV. This study was approved by the Institutional Review Board (IRB) at the Albert Einstein College of Medicine (IRB # 2023-15068).

Results: Statistically significant (p < 0.05) increase in CO of 619 ml/min (95% CI: 205-1033) , HR by 7 bpm (95% CI: 1.54-12.67), MAP increased by 6.83 mmHg (95% CI 1.07-12.6) with significant decrease in MAwP by 2.72 mmH20 (95% CI: -3.75 to -1.68) while no significant change was observed in SV, E/e’, TRmax, Tidal Volumes and Minute Ventilation (MV). The use of sedative and vasopressor medications was unchanged between the groups.

Conclusions: There was a statistically significant increase in CO, with a concurrent increase in HR, and no difference in other surrogate markers of myocardial oxygen demand (LV filling pressure assessed by E/e’) during spontaneous breathing trial. While increasing HR increases myocardial oxygen demand the matched increase in oxygen delivery by a similar magnitude by increase in CO, suggest that the relationship between myocardial oxygen demand and delivery is preserved during PSV, and such transition may not pose a risk of myocardial ischemia.