Different Indications for Inert Gas Rebreathing in the Management of LVAD Patients

Objectives: Understanding how cardiac output (CO) is regulated in LVAD patients is crucial. Right heart catheterization for CO determination is invasive, and not always practicable in the context of LVAD patients especially during exercise.

In the present study we have performed CO determination in LVAD patients using the non-invasive inert gas rebreathing method at rest and during exercise. Relevant parameters (CO, AVDO₂) were obtained regarding their exercise capacity after implantation, before and in the long-term follow-up after forced weaning from LVAD because of severe driveline infection.

Methods: On the basis of previous spiroergometry results stepwise protocol (3 steps/each 4 minutes) according to the peak work load was fixed for inert gas rebreathing. In 18 LVAD patients (12 male, mean age 52.7 years, HeartWare n = 8, HeartMate II n = 3, HeartMate III n = 1) CO was measured using inert gas rebreathing (Innocor) at rest and during exercise at the end of inpatient rehabilitation. In a further young patient (18-year-old), inert gas rebreathing was performed to monitor the long-term success after forced weaning in severe drive line infection. In a 56-year-old man, inert gas rebreathing was used as a decision-making aid in planned weaning.

Results: During spiroergometry mean peak VO₂ was 10.9 mL/kg/m² (±2.9 mL/kg/m²) at a maximal mean work load of 64.8 Watt (±13.4 Watt), mean VE/VCO₂ slope was 39.5 (±7.4). During inert gas rebreathing mean cardiac output at rest was 3.9 L. The three defined loads were 15.8, 31.6, and 47.5 Watts. Cardiac output during each load was 5.9, 6.4, and 7.1 L, respectively. The corresponding AVDO₂ was 59, 70, and 73.2%, respectively. CO determination in the weaned patient indicates a sufficient but lower than predicted increase of CO during exercise in the long-term follow-up of three years after weaning. In the case of planned weaning exercise testing revealed insufficient increase of CO during exercise.

Conclusion: The noninvasively measured cardiac output increased significantly during exercise in LVAD patients shortly after implantation. Nevertheless, the reached values were lower than the predicted values at every time and nearly all patients presented high-grade limitation of their exercise capacity. According to the determined AVDO₂ values patients may have a benefit from mild exercise training in the long-term follow-up. Inert gas rebreathing may be a helpful tool before and after weaning from LVAD.