Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Results
Ten patients were randomized to receive SIMV/ PSV (group 1) and nine were randomized to receive SIMV alone (group 2). The clinical and physical characteristics of the 19 studied patients are given in Table 1. Group 1 and group 2 patients were all cigarette smokers with obstructive lung disease documented by their pulmonary function test data and bood gas analysis (hypoxemia and hypercapnia) performed in steady state and at rest (Table 1). During the ARF, both hypercapnia and hypoxemia were worsened with respiratory acidosis (Table 2), and right heart catheterization data obtained during the weaning period showed precapillary pulmonary hypertension (Table 2).
The time of MV preceding the beginning of the weaning procedure was similar for the two groups: 3.2 ±1.1 days in group 1 vs 5.7 ±3.5 days in group 2. For all steps, patients with COPD under SIMV/ PSV mode had significantly higher sVt and significantly lower Sf than did group 2 patients (Fig 1 and Spontaneous total minute ventilation appeared significantly lower in group 1 than in group 2 for PSV >12 cm H2O (F.10 step: 5.8 ±0.8 L/min vs 7.4±1.6 L/min, p<0.03; F.8 step: 6.7±0.9 L/min vs 8.1 ± 1.4 L/min, p<0.05) without any difference in blood gases, but was similar to group 2 for PSV <9 cm H2O (F.6 step, SBT and SB periods). Canadian family pharmacy Link For any of the steps, there was no difference between both groups in HR, SBP, P.01, MIF, РаОг, РаСОг, and pH. Of course, from the beginning (F.10 step) to the end of the weaning period (SB period), Sf and sVe significantly increased in both groups concurrently to the recovery in respiratory autonomy (Fig 2). In the SIMV/PSV group, sVt remained constant throughout the study despite decreasing levels of PSV (Fig 1) and no correlation was found between the PSV levels and sVt. In group 2 patients, sVt did not change throughout the weaning period (Fig 1).
The Vo2tot did not change during weaning in either group. At any step of SIMV, no significant difference was observed between SIMV/PSV and SIMV groups in the OCB (Vo2resp and Vc^resp percent, Fig 3). Of course, the OCB significandy increased in both groups from F.10 step to SB step concurrently to the increase of the spontaneous ventilation (Fig 3). When the V02 is expressed per liter of ventilation, it significantly increased from F.10 step to SB step in patients without PSV, whereas it decreased in patients with PSV (Table 3 and Fig 4).
Table 1—Characteristics of the 19 COPD Patients
Croup 1 SIMV/PSV n=10 | Croup 2 SIMV n=9 | P | |
Age, yr | 67.1 ±8.3 (50-78) | 67.2 ±8.4 (51-79) | NS |
Weight, %pred | 82.1 ±9.4 (65-91) | 82.1 ±9.7 (65-92) | NS |
Smoking, pack-years | 38.6 ±12.8 (16-60) | 43.0 ±13.8 (9-55) | NS |
FEVi, ml | 846 ±300 (529-1,500) | 873 ±278 (640-1,500) | NS |
FEVi, %pred | 32.2 ±9.7 (23-50) | 33.8 ±9.9 (24-50) | NS |
FEVi/VC, %pred | 53.6 ±10.0 (31-65) | 49.9 ±11.7 (36-68) | NS |
TLC, %pred | 96.8 ±26.2 (62-140) | 94.3 ±14.6 (68-114) | NS |
RV/TLC, %pred | 162.7 ±29.5 (135-216) | 154.8 ±21.5 (131-200) | NS |
Baseline РаОг, mm Hg | 54.4 ±10.0 (41-67) | 58.0 ±10.1 (49-75) | NS |
Baseline РаСОг, mm Hg | 49.1 ±14.0 (43-75) | 49.0 ±7.5 (40-60) | NS |
Baseline pH | 7.42 ±0.04 (7.37-7.50) | 7.43 ±0.03 (7.40-7.48) | NS |
Table 2—Blood Gas Values
Group 1 SIMV/PSV n=10 | Group 2 SIMV n=9 | P | |
РаОг, mm Hg (acute episode) | 49.1 ±14.0 (34-70) | 48.6 ±9.7 (35-60) | NS |
РаСОг, mm Hg (acute episode) | 90.8 ±24.7 (62-130) | 90.1 ±27.2 (71-148) | NS |
pH (acute episode) | 7.21 ±0.07 (7.10-7.31) | 7.20 ±0.01 (7.03-7.31) | NS |
Mean PAP, mm Hg | 28.5 ±11.7 (18-39) | 27.0 ±4.4 (22-34) | NS |
PCWP, mm Hg | 9.3 ±4.2 (4-15) | 10.0 ±2.6 (7-15) | NS |
Table 3—Comparisons in Oxygen Cost of Breathing Between F.10 Step and Spontaneous Breathing
F.10 Step | SB Step | P | |
Group 1 (SIMV/PSV) | |||
Vo2tot, ml/min | 262 ±39 (188-284) | 294 ±47 (208-376) | NS |
Vc^resp, ml/min | 38.4 ±12.4 (17-62) | 63.4 ±16.4 (37-88) | <0.01 |
Vo2resp%, % Vogtot | 14.4 ±3.2 (7.3-17.8) | 21.6 ±4.9 (13.0-30.9) | <0.01 |
Vo2resp/sVE, ml/L | 6.78 ±2.5 (2.70-11.03) | 6.38 ±1.47 (3.90-8.39) | <0.01 |
Group 2 (SIMV) | |||
Vo2tot, ml/min | 264 ±53 (182-328) | 265 ±54 (196-336) | NS |
Vo2resp, ml/min | 37.1 ±14.1 (19-64) | 72.1 ±16.5 (50-108) | <0.01 |
Vo2resp%, % Vo2tot | 14.4 ±5.3 (6.7-21.3) | 28.1 ±7.9 (17.2-40.0) | <0.01 |
Vc>2resp/sVE, ml/L | 5.16 ±2.16 (1.62-5.40) | 6.99 ±1.70 (5.50-10.31) | <0.01 |
Figure 1. Comparison of the spontaneous tidal volume (sVt) during the weaning in SIMV mode with and without PSV. Data are expressed as mean (bars) + SD. There was a significant difference between the two groups at each step of SIMV rate, throughout the weaning period. Open diamonds=p<0.01, SIMV/PSV vs SIMV, at each step of SIMV rate.
Figure 2. Comparison of spontaneous breathing frequency (Sf) during the weaning in SIMV mode with and without PSV. Data are expressed as mean (bars) + SD. There was a significant difference between the two groups at each step of SIMV rate, throughout the weaning period. Open diamonds=p<0.01, SIMV/PSV vs SIMV, at each step of SIMV rate.
Figure 3. Comparison of the oxygen cost of breathing (expressed in percentage of the Vc^tot: Vc^resp (percent) during the weaning in SIMV mode with and without PSV. Data are expressed as mean (bars) + SD. There was no significant difference between the two groups at each step of SIMV rate. In each group, there was a significant increase in Vc^resp percent between F.10 and SB steps. Closed star=p<0.01, Vc^resp percent at F.10 vs Vogresp percent during SB—SIMV/PSV group. Open star=p<0.01, Vo^esp percent at F.10 vs Vo2resp percent during SB—SIMV/PSV group.
Figure 4. Comparison of the oxygen cost of breathing per liter of ventilation during the weaning in SIMV mode with and without PSV. Data are expressed as mean + SD. There was no significant difference between the two groups at each step of SIMV rate. In each group, there was a significant variation in Vo2resp/sVE between F.10 and SB steps. Closed star=p<0.01, Vojjresp/sVE at F.10 vs Vo^esp/sVE during SB—SIMV/PSV group. Open star =p <0.01, Vc>2resp/sVE at F.10 vs Vc^resp/sVE during SB—SIMV group.