Dynamics of spontaneous breathing during patient-triggered partial liquid ventilation

This study evaluates different ventilator strategies during gas (GV) and pa rtial liquid ventilation (PLV) in spontaneously breathing animals. We hypot hesized that during PLV, spontaneously breathing animals would self-regulat e respiratory parameters by increasing respiratory rate (RR) and minute ven tilation (V'(E)) when compared to animals mechanically ventilated with gas, and further that full synchronization of each animal's effort to the venti lator cycle would decrease RR at stable tidal volumes (V-T). We studied 12 newborn piglets (1.54 +/- 0.24 kg) undergoing GV and PLV in 3 different mod es: intermittent mandatory ventilation (IMV), synchronized IMV (SIMV), and assist control ventilation (AC). Modes occurred sequentially in random orde r during GV first, with the same order then repeated during PLV. Animals in itially received continuous positive airway pressure (CPAP) and returned to CPAP during PLV at the end of the experiment. Pressure-limited, volume-tar geted ventilation was used with a tidal volume goal of 13 cc/kg. Rate was s et at 10/min during IMV and SIMV, with a back-up rate of 10/min during AC. RR, V'(E), mechanical (V-T) and spontaneous tidal volumes (sV(T)) were meas ured breath-to-breath using a computer-assisted lung mechanics analyzer; me an values were determined over 30-min periods. Data analysis used paired t- tests with Bonferroni correction as needed (P < 0.05). Blood gases were stable in all modes during GV and PLV. RR (min(-1)) and V' (E) (L.min(-1)/kg) increased in all modes from GV to PLV (RR: CPAP 71 vs. 1 28; IMV 69 vs. 112, SIMV 65 vs. 107, AC 33 vs. 47. V'(E): CPAP 0.47 vs. 0.7 2; IMV 0.46 vs. 0.61; SIMV 0.45 vs. 0.61; AC 0.38 vs. 0.53; P < 0.05). Inte rmode comparisons during PLV showed a tower RR with AC (P < 0.02), and a hi gher V'(E) with CPAP (P < 0.05). V-T and dynamic respiratory system complia nce decreased from GV to PLV (V-T P < 0.05; C-rs,C-dyn P < 0.01); sV(T) rem ained unchanged. V-T and sV(T) did not differ in intermede comparisons. We conclude that during PLV, spontaneously breathing piglets with normal lungs maintain physiologic blood gases by increasing V'(E) through increased RR. AC produced the most efficient respiratory pattern during PLV, with increa sed V'(E) achieved by a modest increase in RR. Pediatr Pulmonol. 1998; 26:3 19-325. (C) 1998 Wiley-Liss, Inc.