Category - Part 16
Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Comment
Respiratory acidosis alone, even without clinical signs of respiratory muscle fatigue, was enough to return to the previous step. With PSV, the average weaning time showed a tendency to be shorter, but the difference between the two groups did not reach the significance level, which is not surprising given the small number of patients studied. A few prospective studies have assessed the potential benefits of PSV in weaning patients from MV but none were performed exclusively in patients with COPD. The preliminary results of the European multicenter trial have shown in difficult-to-wean patients that duration of successful weaning attempts was shorter with pressure support alone than with SIMV (PSV: 6±4 days in 36 patients vs SIMV; 10±7 days in 42 patients, p<0.05. With SIMV, the weaning duration appeared shorter in our study than in the European multicenter trial (5.3 ±1.0 days vs 10 ±7 days), and furthermore, our SIMV/PSV procedure seemed to provide shorter weaning periods than PSV alone (SIMV/PSV: 4.2±0.8 days vs 6±4 days with PSV for the European multicenter trial). It must be noticed that populations and procedures may be different, explaining perhaps these differences. Canadian health care mall in detail Nevertheless, SIMV provided satisfying weaning durations in our patients with COPD, with a little, but not significant, advantage arising for the SIMV/PSV modality. Our results on the success rate are in agreement with those of Chinski and coworkers who have compared IMV with and without PSV (10 cm H2O throughout the weaning process) in stable patients who fulfilled weaning criteria and have concluded that weaning success was not different between the two groups.
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Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Discussion
At the end of this study, all patients with COPD were extubated as they had undergone long periods of SB without clinical or/and blood gas value deterioration. The duration of the weaning period appeared lower in group 1 than in group 2: 4.2 ±0.8 days (SIMV/PSV) vs 5.3±1.0 days (SIMV), but the difference did not reach the significance level (p=0.0545) Link canadian neighbor pharmacy. Two patients of group 2 were reintubated less than 72 h after initial extubation, placed under SIMV mode for 2 more days, and thereafter extubated. In group 1, no patient needed reintubation. No significant difference was found in the need for reintubation between the two groups.
This study compares two modes of mechanical ventilation: SIMV/PSV vs SIMV for weaning 19 patients with COPD. Whereas our patients satisfied the widely accepted criteria for weaning success, they could not tolerate any reduction in SIMV rate without clinical and/or blood gas value deterioration. This is not surprising since it has been shown previously that conventional bedside weaning criteria have poor predictive capacity in patients requiring prolonged MV (>24 h). Multiple weaning criteria have been proposed and evaluated but no one has proved useful enough to obtain wide consensus.
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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).
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Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Measurements
At each step of SIMV rate (te, at each 2 cycles/min decrease), several measurements were performed when a ventilatory steady state was achieved on semirecumbent position: average systolic blood pressure (SBP) and heart rate (HR) from repeated measurements, spontaneous tidal volume (sVt), total and spontaneous minute ventilation (Ve and sVe). The steady state was arbitrarily defined as a stable level of Ve (±0.5 L/min). The ventilatory parameters were measured via the electronic spirometer of the respirator (Puritan Benett 7200) (accuracy ± 4.5 ml/ min, internal calibration performed twice a day). Thus, average values of Sf, sVt, Ve, and sVe were evaluated and arterial blood gases were sampled when the steady state was achieved for the step.
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Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Patients
This prospective study was designed for male COPD patients, intubated and mechanically ventilated because of an acute exacerbation of their disease. All patients exhibited clinically a chronic bronchitis defined as a productive cough with sputum production for 3 months per year for a 2-consecutive-year period (American Lung Association criteria and an irreversible chronic airflow limitation on spirometric data obtained from a previous clinically stable period: FEVi/VC ratio less than 60 percent of predicted, and a chronic hyperinflation with a RV/TLC ratio of more than 130 percent of predicted. Asthmatic patients were excluded. We also excluded COPD patients with confounding medical or surgical problems (unstable cardiovascular disease, liver disease, diabetes, malignant disease, or recent surgery).
Patients with COPD in ARF were intubated (orotracheally or nasotracheally) with a tube with an internal diameter of more than 8 mm and started on MV in the control mode for at least 48 h (tidal volume of 10 ml/kg and a respirator rate that did not result in respiratory alkalosis). Then patients were placed under SIMV mode until the following criteria were satisfied: (1) cause of the exacerbation controlled; (2) SIMV rate <12 cycles/min; (3) spontaneous tidal volume (sVt) >5 ml/kg of body weight; (4) arterial oxygen saturation above 90 percent with FI02 <0.40; (5) pH >7.38; (6) maximal inspiratory force (MIF) < —20 cm H2O; and (7) airway occlusion pressure (P0.1) less than 5 cm H20.
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Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation
The most critical time for patients with chronic obstructive pulmonary disease (COPD) mechanically ventilated for acute respiratory failure (ARF) is the weaning period. Asthma inhalers online Link Patients with hyperinflation and/or bad nutritional status2 are obviously exposed to difficulties in recovering sustained spontaneous breathing. Indeed, patients with COPD often do not tolerate discontinuation of mechanical ventilation (MV) due to the combination of a number of factors. During ARF, the increase in both inspiratory and expiratory flow resistances results in an increased mechanical load for the respiratory muscles, and leads to intrinsic positive end-expiratory pressure (PEEP) which acts as an inspiratory threshold load. Concurrently, the hyperinflation induces a flattening of the diaphragm which then operates on a less efficient portion of its force-length curve. So, COPD patients in ARF have to cope with an increased work of breathing that has to be overcome by respiratory muscles which are in a disadvantageous position. Furthermore, MV itself may aggravate intrinsic PEEP, may increase the mechanical load by the resistances of endotracheal tube and respirator cricuitry, and can be so considered as an additional burden for the respiratory muscles.
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Comparison of Four Methods for Calculating Diffusing Capacity by the Single Breath Method: Conclusion
Our results with the 3PIT method can be only loosely compared with results of Graham et al who documented the differences in Deo using Og, JM, ESP, and three-equation methods in patients with emphysema, asthma, and cystic fibrosis. For both Og and JM methods, Graham et al allowed a 1-L dead space washout volume and collected a 1-L gas sample, whereas we used either a 750-ml (VC > 2.0 L) or 500-ml (VC < 2.0 L) dead space washout volume and a 500-ml gas sample. In the three-equation method, Graham et al used the entire expired volume in the computation whereas we were limited to the 500-ml gas sample that was collected by the automated equipment. They found that the ESP method gave the largest calculated Deo compared with Og, JM, and three-equation Deo in patients with emphysema or cystic fibrosis, and 4 percent larger than three-equation Deo in patients with asthma. The pulmonary function abnormalities in our 46 patients with Og > 3PIT included restriction, obstruction, isolated low Deo and reduced FVC and FEVr Graham et al did not state the severity of obstruction in their patient groups, nor did they document differences in Deo by the various methods in patients with pulmonary function abnormalities other than airflow limitation.
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