The Effect of External PEEP on Work of Breathing in Patients with Auto-PEEP / 결핵

BACKGROUND: Auto-PEEP which develops when expiratory lung emptying is not finished until the beginning of next inspiration is frequently found in patients on mechanical ventilation. Its presence imposes increased risk of barotrauma and hypotension, as well as increased work of breathing (WOB) by adding inspiratory threshold load and/or adversely affecting to inspiratory trigger sensitivity. The aim of this study is to evaluate the relationship of auto-PEEP with WOB and to evaluate the effect of PEEP applied by ventilator (external PEEP) on WOB in patients with auto-PEEP. METHOD: 15 patients, who required mechanical ventilation for management of acute respiratory failure, were studied. First, the differences in WOB and other indices of respiratory mechanics were examined between 7 patients with auto-PEEP and 8 patients without auto-PEEP. Then, we applied the 3 cm H2O of external PEEP to patients with auto-PEEP and evaluated its effects on lung mechanics as well as WOB. Indices of respiratory mechanics including tidal volume (V(T)), repiratory rate, minute ventilation (V(E)), peak inspiratory flow rate (PIFR), peak expiratory flow rate (PEFR), peak inspiratory pressure (PIP), T(I)/T(TOT), auto-PEEP, dynamic compliance of lung (Cdyn), expiratory airway resistance (RAWe), mean airway resistance (RAWm), P(0.1), work of breathing performed by patient (WOB), and pressure-time product (PTP) were obtained by CP-100 Pulmonary Monitor (Bicore,USA). The values were expressed as meanSEM (standard error of mean). RESULTS: 1) Comparison of WOB and other indices of respiratory mechanics in patients with and without auto-PEEP: There was significant increase in WOB (1.71 +/-0.24 vs 0.500.19 J/L, p=0.007), PTP (317+/-70 vs 98+/-36 cm H2O * sec/min, p=0.023), RAWe (35.6+/-5.7 vs 18.2+/-2.3 cm H20/L/sec, p=0.023), RAWm (28.8+/-2.5 vs 11.9+/-2.0 cm H2O/L/sec, p=0.001) and P0.1 (6.21.0 vs 2.9+0.6 cm H2O, p=0.021) in patients with auto-PEEP compared to patients without auto-PEEP. The differences of other indices including V(T), PEFR, V(E) and T(I)/T(TOT) showed no significance. 2) Effect of 3 cm H2O external PEEP on respiratory mechanics in patients with auto-PEEP: When 3 cm H2O of external PEEP was applied, there were significant decrease in WOB (1.71+/-0.24 vs 1.20+/-0.21 J/L, p=0.021) and PTP (317+/-70 vs 231+/-55 cm H2O * sec/min, p=0.038). RAWm showed a tendency to decrease (28.8+/-2.5 vs 23.9+/-2.1 cm H2O, p=0.051). But PIP was increased with application of 3 cm H2O of external PEEP (16+/-2 vs 22+/-3 cm H2O, p=0.008). V(T), V(E), PEFR, T(I)/T(TOT) and Cdyn did not change significantly. CONCLUSION: The presence of auto-PEEP in mechanically ventilated patients was accompanied with increased WOB performed by patient, and this WOB was decreased by 3 cm H2O of externally applied PEEP. But, with 3 cm H2O of external PEEP, increased PIP was noted, implying the importance of close monitoring of the airway pressure during application of external PEEP.

The Effect of Pressure Support on Respiratory Mechanics in CPAP and SIMV / 결핵

BACKGROUND: Pressure support(PS) is becomimg a widely accepted method of mechanical ventilation either for total unloading or for partial unloading of respiratory muscle. The aim of the study was to find out if PS exert different effects on respiratory mechanics in synchronized intermittent mandatory ventilation(SIMV) and continuous positive airway pressure (CPAP) modes. METHODS: 5, 10 and 15 cm H2O of PS were sequentially applied in 14 patients(69+/-12 yrs, M:F=9:5) and respiratory rate (RR), tidal volume(VT), work of breathing(WOB), pressure time product(PTP), P(0.1), and T(1)/T(TOT) were measured using the CP-100 pulmonary monitor(Bicore, USA) in SIMV and CPAP modes respectively. RESULTS: 1) Common effects of PS on respiratory mechanics in both CPAP and SIMV modes As the level of PS was increased(0, 5, 10, 15 cm H2O), VT was increased in CPAP mode(0.28+/-0.09, 0.29+/-0.09, 0.31+/-0.11, 0.34+/-0.12 L, respectively, p=0.001), and also in SIMV mode(0.31+/-0.15, 0.32+/-0.09, 0.34+/-0.16, 0.36+/-0.15 L, respectively, p=0.0215). WOB was decreased in CPAP mode(1.40+/-1.02, 1.01+/-0.80, 0.80+/-0.85, 0.68+/-0.76 joule/L, respectively, p=0.0001), and in SIMV mode(0.97+/-0.77, 0.76+/-0.64, 0.57+/-0.55, 0.49+/-0.49 joule/L, respectively, p=0.0001). PTP was also decreased in CPAP mode(300+/-216, 217+/-165, 179+/-187, 122+/-114cm H2O * sec/min, respectively, p=0.0001), and in SIMV mode(218+/-181, 178+/-157, 130+/-147, 108+/-129cm H2O.sec/min, respectively, p=0.0017). 2) Different effects of PS on respiratory mechanics in CPAP and SIMV modes By application of PS (0, 5, 10, 15 cm H2O), RR was not changed in CPAP mode(27.9+/-6.7, 30.0+/-6.6, 26.1+/-9.1, 27.5+/-5.7/min, respectively, p=0.505), but it was decreased in SIMV mode (27.4+/-5.1, 27.8+/-6.5, 27.6+/-6.2, 25.1+/-5.4/min, respectively, p=0.0001). P(0.1) was reduced in CPAP mode(6.2+/-3.5, 4.8+/-2.8, 4.8+/-3.8, 3.9+/-2.5 cm H2O, respectively, p=0.0061), but not in SIMV mode(4.3+/-2.1, 4.0+/-1.8, 3.5+/-1.6, 3.5+/-1.9 cm H2O, respectively, p=0.054). T(1)/T(TOT) was decreased in CPAP mode(0.40+/-0.05, 0.39+/-0.04, 0.37+/-0.04, 0.35+/-0.04, respectively, p=0.0004), but not in SIMV mode(0.40+/-0.08, 0.35+/-0.07, 0.38+/-0.10, 0.37+/-0.10, respectively, p=0.287). 3) Comparison of respiratory mechanics between CPAP+PS and SIMV alone at same tidal volume. The tidal volume in CPAP+PS 10 cm H2O was comparable to that of SIMV alone. Under this condition, the RR(26.1+/-9.1, 27.4+/-5.1/min, respectively, p=0.516), WOB(0.80+/-0.85, 0.97+0.77 joule/L, respectively, p=0.485), P0.1(3.9+/-2.5, 4.3+/-2.1 cm H2O, respectively, p=0.481) were not different between the two methods, but PTP(179+/-187, 218+/-181 cmH2O.sec/min, respectively, p=0.042) and T(1)/T(TOT)(0.37+/-0.04, 0.40+/-0.08, respectively, p=0.026) were significantly lower in CPAP+PS than in SIMV alone. CONCLUSION: PS up to 15 cm H2O increased tidal volume, decreased work of breathing and pressure time product in both SIMV and CPAP modes. PS decreased respiration rate in SIMV mode but not in CPAP mode, while it reduced central respiratory drive(P(0.1)) and shortened duty cycle (T(1)/T(TOT)) in CPAP mode but not in SIMV mode. By 10 cm H2O of PS in CPAP mode, same tidal volume was obtained as in SIMV mode, and both methods were comparable in respect to RR, WOB, P(0.1), but CPAP+PS was superior in respect to the efficiency of the respiratory muscle work (PTP) and duty cycle(T(1)/T(TOT)).