Abstract
Prolonged mechanical ventilation (MV) places patients at an increased risk for ventilator-induced diaphragm dysfunction (VIDD), which can delay weaning from MV. We previously reported that intraoperative phrenic stimulation may preserve diaphragm fiber contractile function in those undergoing cardiac surgeries, but benefits are unclear in those with significant pulmonary disease who require extracorporeal membrane oxygenation (ECMO) support.
A 55-year-old male with end-stage pulmonary fibrosis underwent bilateral lung transplantation (LTX) after a two-week pre-operative hospitalization that included ECMO support. Phrenic stimulation commenced upon initial surgical exposure of the diaphragm, and supramaximal twitch stimulations were administered every 30 minutes to one hemidiaphragm over 136 minutes. The contralateral side served as an inactive control. Diaphragm biopsies of the LTX patient were acquired after 5 stimulations. Maximal single-fiber diaphragm twitch force was then compared to nine male participants (56 (12) years) admitted for cardiac bypass or valvuloplasty surgery, who underwent 6 (1) bouts of unilateral intraoperative stimulation followed by diaphragm biopsy. In each subject, we tested maximal single-fiber force on an average of 22 (4) slow- and 22 (3) fast-twitch fibers. Compared to cardiac surgical patients, the LTX subject had increased slow fiber cross-sectional area (CSA) (Control side, cardiac: slow 5166 (1645) mm
; fast 6792 (732) mm
; LTX: slow 6827 (1504) mm
; fast 6159 (1173) mm
). Diaphragm fiber CSA of the stimulated side trended higher in the LTX patient (slow: 8588 (1908) mm
, p=0.080 vs control side; fast: 7232 (1976) mm
, p=0.094 vs control). Specific force (absolute force normalized to fiber CSA) in LTX was reduced by ~32% in slow fibers and ~30% in fast fibers (Table), as compared to cardiac patients. Specific force of stimulated fibers trended higher for slow- but not fast-twitch fibers in LTX; response to stimulation resembled that of cardiac surgical patients. The patient was extubated 26 hours post-LTX, as compared to 12 (7) hours in the cardiac patients.
This novel model of functional electrical stimulation suggests that phrenic stimulation preserved fiber CSA in an ECMO-dependent adult with pulmonary fibrosis. Phrenic stimulation increased maximal specific force in slow-twitch fibers, but responding forces remained well below expected values. These findings suggest that critically ill adult recipients of LTX may require additional duration and volume of diaphragm training, whether through voluntary or evoked contractions, to recover functional inspiratory muscle strength post-operatively.