|Year : 2018 | Volume
| Issue : 3 | Page : 147-153
Weaning of chronic obstructive pulmonary disease patients after coronary artery bypass graft surgery
Heba M Fathi1, Dina M Osman2
1 Department of Anesthesia and Surgical Intensive Care, Faculty of Medicine, Zagazig University, Zagazig, Egypt
2 Department of Cardiothoracic, Faculty of Medicine, Zagazig University, Zagazig, Egypt
|Date of Submission||30-May-2017|
|Date of Acceptance||10-Sep-2017|
|Date of Web Publication||31-Aug-2018|
Heba M Fathi
Department of Anesthesia and Surgical Intensive Care, Zagazig University Hospitals, Zagazig, 44519
Source of Support: None, Conflict of Interest: None
Background Cardiac surgery has become more common in chronic obstructive pulmonary disease (COPD) patients, but this category is still at a high risk of postoperative prolonged ventilation. Finding of the appropriate mode for faster weaning is important to improve a patient’s outcome.
Objective This study aimed to evaluate the effect of adaptive support ventilation (ASV) as a weaning mode in comparison with the pressure support mode in COPD patients in the postoperative period after a coronary artery bypass grafting (CABG) surgery.
Patients and methods A randomized-controlled trial was conducted on 90 COPD (stage I and II) patients between 40 and 65 years old in the postoperative cardiothoracic ICU after CABG surgeries. Patients were initially ventilated with synchronized intermittent mandatory ventilation and were then allocated randomly to two equal groups to wean either by ASV group or pressure support ventilation group. The primary outcome was the number of patients weaned successfully from the first trial. The secondary outcomes were duration of mechanical ventilation, duration of weaning, number of arterial blood gas samples before extubation, length of ICU stay, cardiac and respiratory parameters at extubation, and mortality.
Result In the ASV group, significantly higher numbers of patients were weaned from first trial, there was a shorter duration of weaning and mechanical ventilation and ICU stay, with fewer times of manual ventilator adjustments and arterial blood gas samples drawing during weaning. At extubation, this group showed a significantly lower respiratory rate, higher tidal volume, and lower peak airway pressure, with less tachycardia and lower systolic blood pressure compared with the pressure support ventilation group.
Conclusion The ASV mode improves the quality of weaning and shortens ICU stay in COPD patients after CABG surgery.
Keywords: adaptive support ventilation pressure support ventilation, chronic obstructive pulmonary disease, coronary artery bypass, weaning
|How to cite this article:|
Fathi HM, Osman DM. Weaning of chronic obstructive pulmonary disease patients after coronary artery bypass graft surgery. Res Opin Anesth Intensive Care 2018;5:147-53
|How to cite this URL:|
Fathi HM, Osman DM. Weaning of chronic obstructive pulmonary disease patients after coronary artery bypass graft surgery. Res Opin Anesth Intensive Care [serial online] 2018 [cited 2018 Nov 12];5:147-53. Available from: http://www.roaic.eg.net/text.asp?2018/5/3/147/240270
| Introduction|| |
The prevalence of coronary artery disease was shown to be high in patients with chronic obstructive pulmonary disease (COPD) ,,. The two diseases shared a common risk factors such as smoking, older age, and a sedentary lifestyle . In addition, the epidemiologic evidence indicated the role of systemic inflammatory disease, which was prominent in patients with COPD in the pathogenesis of atheroma formation and ischemic heart disease ,,,,. C-reactive protein, a marker of systemic inflammation, has been proven to be elevated in COPD during under stable and exacerbation conditions ,, and also in coronary artery disease patients . Some studies reported that the use of corticosteroids and bronchodilator drugs by COPD patients may increase the risk of development of myocardial infarction .
In the past, significant pulmonary disease was considered a contraindication to open heart surgery . As a result of improvements in cardiac anesthesia, techniques of cardiopulmonary bypass, and progress in critical care management, cardiac surgeries have become acceptable and more common in patients with COPD. As a consequence of prolonged life expectancy and increasing prevalence of COPD, surgeons and anesthesiologists are coping nowadays with large numbers of high-risk respiratory patients . Although advancements in surgical and anesthesia techniques have reduced postoperative complications in this patient category , COPD patients still have a risk for postoperative prolonged mechanical ventilation . Adaptive support ventilation (ASV), which is an improved closed-loop ventilation mode, provides both pressure-controlled ventilation and pressure support ventilation (PSV) according to the needs of the patient. It adjusts tidal volume (TV) and respiratory rate on a breath-by-breath basis to achieve preset minute ventilation according to the equation of Otis et al. , which determines a respiratory rate that achieves minimal work of inspiration on the basis of the time constant of the respiratory system ,. The benefit of using ASV in weaning after cardiac surgery has been proved ,.
Although the use of ASV in patients with COPD has been described before ,, no available data in the literature have reported evaluation of this mode in weaning COPD patients after coronary artery bypass grafting (CABG) surgery. The aim of this study was to evaluate the effect of the ASV mode on weaning of such patients after CABG surgery by comparing it with the conventional pressure support mode in the postoperative cardiothoracic ICU.
| Patients and methods|| |
This study was carried out in the Zagazig Postoperative Cardiothoracic ICU from March 2014 till March 2016 after the approval of the local ethical committee and preoperative patients’ informed consent were obtained. The inclusion criteria were adult patients scheduled for elective CABG with from COPD stages I and II identified by the Global Initiative for Obstructive Lung Disease classification of disease severity [stage I (mild): forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) <70% and FEV1 ≥80% predicted with or without chronic symptoms (cough, sputum production) and stage II (moderate): FEV1/FVC <70% and FEV1 <80% predicted and ≥50% predicted with or without chronic symptoms (cough, sputum production)]. Their ages ranged between 40 and 65 years. Preoperative exclusion criteria were stages III and IV COPD according to the Global Initiative for Obstructive Lung Disease classification [stage III (severe): FEV1/FVC <70% and FEV1 <50% and ≥30% predicted with or without chronic symptoms (cough, sputum production) and stage IV (very severe): FEV1/FVC <70% and FEV1 <30% predicted or FEV1 <50% predicted plus chronic respiratory failure (PaO2<8.0 kPa with or without PaCO2>6.7 kPa while breathing air at sea level], age older than 65 years, left ventricular ejection fraction less than 50%, significant hepatic or renal disease, and a history of seizure or stroke. Postenrollment exclusion criteria were postoperative myocardial ischemia (ST-segment depression) lasting more than 30 min, postoperative cardiac failure that required high-dose inotropes or an intra-aortic balloon pump, severe early postoperative hemorrhage (chest tube drainage >500 ml/h), or surgical complications requiring reoperation, or occurrence of neurologic deficits.
All the patients in the study were anesthetized using a standard approach: premedication with 2 mg lorazepam the night before surgery, induction with 5–10 μg/kg fentanyl, 3–5 mg midazolam, 2 mg/kg propofol titrated to effect, and muscle relaxation with 0.6–1.2 mg/kg rocuronium. Anesthesia was maintained by a continuous intravenous infusion of 1 μg/kg/h fentanyl, 1 mg/kg/h propofol, repeated doses of 0.1–0.2 mg/kg rocuronium, and supplementation by sevoflurane as required.
CABG was performed using the on-pump technique using a membrane oxygenator and a nonpulsatile pump with ACT more than 400 s using heparin 3–5 mg/kg, a perfusion pressure of 60–80 mmHg, α-stat management of pH, mild hypothermia (33–34°C by a nasopharyngeal temperature probe), and hematocrit more than 20%.
During transfer to the ICU, all patients were sedated with a propofol infusion of 1–2 mg/kg/h.
In the ICU, patients were monitored for arterial blood pressure, central venous pressure, ECG, and pulse oximetry. Routine investigations were performed and abnormal values were corrected. Normal saline and gelatin-based colloid solutions were used for fluid resuscitation. Hemoglobin concentrations were maintained at 10 g/dl or higher by blood transfusion. Dopamine or epinephrine was used to maintain the mean arterial pressure at 60 mmHg or greater, and sodium nitroprusside were used to treat hypertension (mean arterial pressure >100 mmHg). The bedside nurses assessed analgesic requirements and administered boluses of 1–2 mg morphine to a total of 10 mg/6 h on patient request if the patient was fully awake or when hypertensive and restless if the patient was still sedated.
Initially, all patients were ventilated with the synchronized intermittent mandatory ventilation (SIMV) mode using a microprocessor-controlled mechanical ventilator (Galileo GOLD; Hamilton Medical AG, Bonaduz, Switzerland) and were receiving standard medical therapy with nebulized bronchodilators, corticosteroids, and antibiotics.
The initial ventilation settings were as follows: respiratory rate of 12/min, TV 8–10 ml/kg, decelerated flow wave form, FiO2 titrated to obtain a saturation of 90% with a positive end expiratory pressure (PEEP) of 5 cm H2O, I : E ratio (ratio of the duration of inspiration to the duration of expiration) of 1 : 3, and inspiratory trigger sensitivity set at −1 cm H2O. Settings of the ventilator and each modification were checked arterial blood gas (ABG) analysis after 10 min.
Weaning trials were initiated with the recovery of sustained spontaneous 6 breaths/min or more for 20 min with an acceptable ABG analysis (pH>7.35 and SaO2 of 88% or more and PaO2/FIO2>150 for FiO2 of 40% or less).
Patients were randomized equally to two groups using a computer-generated number sequence for weaning using either ASV group or PSV group.
Adaptive support ventilation group
We determined the patients’ height and sex. The ventilator then calculated the ideal body weight. We started with 100% target minute ventilation, FiO2 40%, high-pressure alarm limit at 30 cm H2O, inspiratory trigger sensitivity at 2 l/min, and expiratory trigger sensitivity at 40%. Minute ventilation was then decreased by 50% after 30 min and another assessment of the patients was performed. If the assessment was satisfactory, the minute ventilation was decreased to 30%, which is equivalent to pressure support 7 cm H2O after 30 min. A spontaneous breathing trial was performed at this level for 2 h and if it succeeded at this level (rapid shallow breathing index: respiratory rate/TV ≤105, PaO2/FiO2 >200 with FiO2 ≤40%, hemodynamic and neurological stability), extubation was performed after pulmonary physiotherapy. If the patients showed signs of poor tolerance at any time (respiratory rate ≥35 beats/min, arterial oxygen saturation <88% with FiO2 ≤40%, pH<7.25, change of heart rate or blood pressure more than 20% of the basal, disturbed conscious level, signs of anxiety, somnolence or dyspnea, use of accessory respiratory muscle, and rapid shallow breathing index >105), the weaning trial was stopped and full support ventilation was provided with a preweaning ventilator setting.
Pressure support ventilation group
The initial pressure support (above PEEP) was set at 15 cm H2O and was then decreased gradually by 2 cm H2O/30 min according to patients’ tolerance to 7 cm H2O and a 2 h trial of spontaneous breathing with this pressure support level was performed before extubation. As in the ASV group, if signs of poor tolerance appeared, the trial was stopped and the ventilator was returned to the preweaning setting.
In case of a failed trial, the cause of failure was identified and corrected if possible and SBT was repeated every 24 h ([Figure 1]).
The primary outcome was the number of patients weaned successfully from the first trial. The secondary outcomes were patients’ outcomes (duration of mechanical ventilation, duration of weaning, number of ABG samples before extubation, length of ICU stay, and mortality), hemodynamic parameters (heart rate, blood pressure, and central venous pressure), respiratory parameters (TV, respiratory rate, minute ventilation, peak inspiratory pressure, occlusion pressure), and ABG variables (pH, PaO2, PaCO2, O2 saturation, and HCO3) at extubation.
Sample size was calculated to be 45 patients in each group using Open Epi version 3 (Open Source Epidemiologic Statistics for Public Health, Version 3.01, available at www.OpenEpi.com), depending on a 6 h reduction in the mean weaning time, with a SD of 10 h  to achieve 80% power and a 95% confidence interval, permitting a type-1 error rate of 0.05.
Data were tabulated and analyzed using the statistical package for the social sciences version 18.0 (SPSS Inc., Chicago, Illinois, USA). We expressed continuous data as mean±SD, whereas categorical data were expressed as frequency and percentage. Student’s t-test was used to compare the mean of continuous data. Categorical data were compared using the χ2-test. P value that was less than 0.05 was considered statistically significant.
| Result|| |
Out of 203 patients examined for eligibility, 90 patients fulfilled the inclusion criteria. All of these patients completed the study.
As shown in [Table 1], the preoperative criteria were comparable in both groups.
[Table 2] shows patients’ outcome in the ICU. The duration of mechanical ventilation, weaning, and ICU stay were significantly shorter in the ASV group compared with the PSV group. Totally, 26 patients in the ASV group were extubated from the first trial in the ASV group, which was significantly higher compared with the PSV group, in which only 15 patients were extubated from the first trial; this was accompanied by significantly lower numbers of ventilator adjustment and ABG samples drawing during the weaning period in the ASV group. A total of three patients died while in the ICU; one patient died in the ASV group because of severe pneumonia and two patients (one in each group) died because of cardiac complications after surgery. No adverse events related to both modes of ventilation were observed.
At extubation, the respiratory rate and peak inspiratory pressure were significantly lower in ASV with higher TV in the same group compared with the PSV group. Other respiratory parameters showed nonsignificant differences ([Table 3]).
In terms of the circulatory parameters, the heart rate and systolic blood pressure showed significantly lower values in patients weaned by the ASV mode compared with patients weaned by the PSV mode; however, there were no significant differences between the two groups in the other circulatory parameters ([Table 4]).
| Discussion|| |
In the current study, ASV in COPD patients improved ventilator outcomes after the CABG operation. Compared with PSV, ASV decreased the weaning time and the ventilator time postoperatively.
Cassina et al.  used ASV for weaning of 155 cardiac surgery patients and found that it was safe, easy to use, and allowed 86% of patients to be extubated within 6 h, with a mean extubation time of 3.6 h.
Another randomized-controlled trial conducted by Petter et al.  compared ASV with SIMV+PSV during weaning of 45 cardiac surgery patients and reported a significantly lower duration of mechanical ventilation and need to change the ventilator settings with ASV. Sulzer et al.  also compared ASV and SIMV with pressure support in a randomized-controlled study. They concluded that a respiratory weaning protocol of ASV is more practical. It accelerated tracheal extubation and simplified ventilatory management in fast track patients after cardiac surgery.
Although these findings suggest that ASV can be used for fast and early extubation in postcardiac surgeries, none of the previously mentioned studies included COPD patients.
Kirakli et al. , in their study on COPD patients, found that the ASV mode significantly decreased the duration of weaning, where the median weaning duration in ASV was 24 h and that in PSV was 72 h.
Evaluation of ASV as a weaning mode in COPD undergoing cardiac surgery has not been discussed in the literature and, to our knowledge, this is the first randomized-controlled trial to focus on this mode in this population.
ASV maintains spontaneous activity of the diaphragm that protects against ventilator-induced diaphragmatic dysfunction , which prevents ventilator dependence and provides faster weaning; in addition, the automation of inspiratory pressure levels and reduced manipulation and time spent for adjusting the ventilator in the ASV mode  may also explain the shorter weaning time in the ASV group.
The automation of inspiratory pressure with a computer-driven system is more comfortable to the patient ; this was clear in our study from the significantly lower heart rate and blood pressure in patients weaned by ASV compared with those weaned by PSV, although other postsurgery cardiac parameters showed no significant differences.
Tassaux et al.  compared ASV and SIMV+PSV and concluded that ASV provided less muscle load and patient–ventilator dyssynchrony, which increased patients’ comfort with the ASV mode, and this supports our finding.
In agreement with our result, Han et al.  compared ASV with SIMV in COPD patients with respiratory failure and found a significant decrease in the heart rate, systolic and diastolic blood pressure, and central venous pressure in the ASV mode.
Data showed that the ASV mode maintains normal ventilation and promotes the best energetic. Taking into account spontaneous breathing, it is useful to prevent tachypnea as well as the development of auto-PEEP and excessive dead space ventilation .
In the current study, patients were weaned at a pressure support of 7 mmHg in the PSV group and at 30% of the calculated minute ventilation in the ASV group, which is associated with an inspiratory pressure level less than 10 cm H2O . Levels of pressure support between 5 and 10 cm H2O were suggested to be effective in overcoming the resistance and workload of endotracheal tube and respiratory circuits .
The VT in this study at extubation were 450±40 and 393±38 in the ASV and the PSV groups, respectively. Alvisi et al.  reported that the threshold values for minute volume, VT, and VT (ml)/patients (kg) ratio for weaning success in COPD patients were 8.6 l/min, 340 ml, and 5.0 ml/kg, respectively.
We found a significant decrease in peak airway pressure and respiratory rate, with a significantly higher TV in the ASV group compared with the PSV group. In agreement with our finding, Gruber et al.  compared the ASV mode with the pressure-regulated volume controlled mode and recorded lower peak airway pressure with the ASV mode.
Also, Belliato et al.  studied ASV in different clinical conditions; eight of the patients had acute exacerbation of COPD, and recorded high expiratory time, with very low respiratory rates, up to 6–8 beats/min during ASV. They observed that these patients had almost clinically negligibly low values of auto-PEEP. Arnal et al. , in their study, concluded that the ability of ASV to adjust the TV–respiratory rate combination depended on respiratory mechanics, detection of spontaneous breathing, and adjustment of the ventilator support according to limited intrinsic PEEP and reducing weaning time.
In our study, ASV could reduce the length of ICU stay, number of manual ventilator adjustments and number of ABG samples, with increased numbers of patients weaned successfully from first trial. In a previous study comparing ASV and pressure assist/control ventilation in medical patients in the ICU, patients in the ASV group required fewer total numbers of manual settings on the ventilator to reach the desired pH and PaCO2 levels and in agreement with our study, the number of patients extubated successfully on the first attempt was significantly higher in the ASV group .
Weaning with ASV shows promising results in COPD patients ; it decreases the time of ICU stay, and the need for continuous attendance by intensivists and respiratory therapist .
| Conclusion|| |
The ASV mode significantly improves weaning in patients with COPD and reduces the length of ICU stay by reducing the peak inspiratory pressure, shortening the time of weaning, and stabilizing hemodynamics in comparison with the PSV mode after CABG surgeries.
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Conflicts of interest
There are no conflicts interest.
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[Table 1], [Table 2], [Table 3], [Table 4]