|Year : 2013 | Volume
| Issue : 1 | Page : 27-31
A comparative study between positive end expiratory pressure and high peak inspiratory pressure as a lung recruitment strategy during off-pump coronary artery bypass grafting
Mohamed A. Khalil1, Hassan M. Al-Sisi2, Amr S. Omar3
1 Department of Anesthesia, Faculty of Medicine, Cairo University, Giza, Egypt
2 Department of Cardiothoracic Surgery, Faculty of Medicine, Cairo University, Giza, Egypt
3 Department of Critical Care, Faculty of Medicine, Cairo University, Giza, Egypt
|Date of Submission||01-Sep-2012|
|Date of Acceptance||01-Oct-2012|
|Date of Web Publication||26-Jun-2014|
Source of Support: None, Conflict of Interest: None
The respiratory function is impaired in off-pump coronary artery bypass (OPCAB). This study was carried out to detect whether a positive end expiratory pressure (PEEP) is essential to improve lung compliance and arterial pressure of oxygen (PaO2) in patients undergoing OPCAB.
Patients and methods
Sixty patients scheduled for undergoing OPCAB were randomized to receive either peak inspiratory pressure (PIP) at 30 cm H2O with PEEP at 10 cm H2O for 1 min, after which PIP was raised to 40 cm H2O together with PEEP at 15 cm H2O for another minute (group P) or PIP at 30 cm H2O for 1 min, followed by PIP at 40 cm H2O for another minute without any PEEP (group NP). Both lung compliance and PaO2 were measured at four time points: T1, after induction of general anesthesia; T2, before raising the PIP and PEEP; T3, 30 min after raising the PIP and PEEP; and T4, at the end of surgery. In the ICU, PaO2 was measured 30 min after admission to ICU (T5), 1 h after raising the PIP to 30 cm H2O (T6), and 4 h later (T7).
As regards pulmonary compliance and intraoperative and postoperative PaO2, there was no statistically significant difference between the two groups. However, the mean arterial pressure after applying PEEP was significantly lower in group P than in group NP, both during surgery and in the ICU (P<0.05).
Both recruitment strategies, PEEP and high PIP, are protective and tolerable in patients undergoing OPCAB.
Keywords: lung recruitment, off-pump coronary artery bypass, positive end expiratory pressure
|How to cite this article:|
Khalil MA, Al-Sisi HM, Omar AS. A comparative study between positive end expiratory pressure and high peak inspiratory pressure as a lung recruitment strategy during off-pump coronary artery bypass grafting. Egypt J Cardiothorac Anesth 2013;7:27-31
|How to cite this URL:|
Khalil MA, Al-Sisi HM, Omar AS. A comparative study between positive end expiratory pressure and high peak inspiratory pressure as a lung recruitment strategy during off-pump coronary artery bypass grafting. Egypt J Cardiothorac Anesth [serial online] 2013 [cited 2020 Feb 26];7:27-31. Available from: http://www.ejca.eg.net/text.asp?2013/7/1/27/135459
| Introduction|| |
Off-pump coronary artery bypass (OPCAB) has replaced to a great extent conventional coronary artery bypass graft surgery (CABG) using the heart–lung machine 1,2. Some studies showed that OPCAB is associated with minimal intraoperative and postoperative pulmonary complications, in comparison with standard CABG surgery 3. However, other studies 4,5 concluded that lung compliance might be affected markedly during OPCAB. Two factors were implicated in this deterioration. The first one is the trial to minimize left ventricular outflow tract obstruction during heart manipulation, which was prevented by the trial to raise the intravascular volume through increasing intravenous fluid administration. The second factor is surgically related, in which the surgeon compresses the heart in the right chest, together with compressing the left lung using an abdominal pad, usually in a trial to make more space in order to easily revascularize the posterolateral vessels 4. Owing to the fact that general anesthesia is associated with a high incidence for postoperative lung collapse 6–8, many trials were carried out to find means to minimize lung atelectasis, which might be associated with a raised intrapulmonary shunt with consequent postoperative hypoxemia 9–12. As regards OPCAB, a trial was carried out to determine the effect of including a recruitment strategy with positive end expiratory pressure (PEEP) in order to reduce intraoperative and postoperative pulmonary atelectasis 13. The aim of the present study was to assess the effectiveness of PEEP in reducing intraoperative and postoperative hypoxemia during OPCAB.
| Materials and methods|| |
This prospective randomized clinical study took place at Cairo University Hospitals between January and October 2008. After approval of the local ethical research committee and obtaining written informed consent, 60 adult patients with coronary artery disease scheduled for OPCAB were enrolled into the study. Patients with severe impairment of left ventricular function (ejection fraction<40%), chronic obstructive pulmonary disease, redo patients, and those with coexisting aortic or mitral valve disease requiring surgical intervention were excluded from the study. Any patient who developed any hemodynamic instability (mean arterial pressure<60 mmHg) during the surgical procedure or during institution of the recruitment strategy was excluded from the study. In addition, any patient who developed any postoperative hemodynamic alteration or bleeding necessitating surgical exploration was also excluded.
All patients were anesthetized according to a standard protocol. Preoperatively, an 18 or 16 G peripheral venous cannula was inserted under local anesthesia together with 0.05 mg/kg midazolam intravenously. In the OR, a 20 G left radial arterial catheter was inserted under local anesthesia. Before induction of anesthesia, standard monitors were applied including, a two-channel five-lead ECG with ST-segment analysis, pulse oximetry, and continuous arterial blood pressure monitoring along with a blood gas sample to obtain a baseline for oxygenation, ventilation, acid–base status, and electrolytes. Induction was performed using thiopental at 3 mg/kg, fentanyl at 3–5 μg/kg, and cisatracurium at 0.2 mg/kg. After induction of anesthesia, a triple lumen internal jugular venous catheter was inserted together with a nasopharyngeal temperature probe; end-tidal CO2, urine output, and activated clotting time analyses (celite-activated clotting time) were carried out. Anesthesia was maintained with sevoflurane (1–2% in oxygen/air mixture 50%). Analgesia was achieved by continuous infusion of fentanyl at a rate of 1–2 μg/kg/h. Muscle relaxation was achieved by continuous infusion of cisatracurium at a rate of 2–3 μg/kg/min. The goal of intraoperative fluid management was to achieve a central venous pressure of 10–15 cm H2O; this was started from induction of anesthesia until the end of revascularization to reduce the hemodynamic alterations that might result from cardiac manipulation.
The Dräger anesthesia machine (Zeus Turbovent; Dräger and Siemens Company, Lubeck, Germany) was used in this study. It has the capability to give both volume and pressure modes of ventilation in addition to measuring lung compliance. The pressure control mode was used in ventilating all patients with a peak inspiratory pressure (PIP) of 20–25 cm H2O, together with a frequency of 10–15 breaths/min, usually aiming to reach an exhaled tidal volume ranging between 6 and 8 ml/kg. These parameters were set to reach an end-tidal CO2 tension ranging between 35 and 40 mmHg. At the end of the proximal anastomoses, the patients were randomly assigned to two groups: group P and group NP. Group P included 30 patients who received a PIP of 30 cm H2O with PEEP at 10 cm H2O for 1 min. The PIP was then raised to 40 cm H2O with PEEP at 15 cm H2O for another minute 13,14. Group NP included 30 patients who received the same recruitment regimen as group P, in the form of raising the PIP, but without any PEEP. During surgery, both lung compliance and arterial oxygen tension (PaO2) were measured at four time points: T1, after induction of general anesthesia; T2, before raising the PIP and PEEP; T3, 30 min after raising the PIP and PEEP; and T4, at the end of surgery. After finishing the recruitment process, the ventilation was set again to the prerecruitment values. Any patient who developed any hemodynamic instability with a mean arterial blood pressure less than 60 mmHg during the recruitment process was excluded from the study. It is also noteworthy that all patients were transferred to the ICU with a portable ventilator, setting the tidal volume at 6–8 ml/kg together with a respiratory rate of 10 breaths/min. In the case of a reduction in systolic blood pressure by more than 20% from baseline, hypotension was treated by phenylephrine boluses.
All operations were performed by the same cardiac surgeon. A conventional median sternotomy was performed and the pedicled internal mammary artery technique was adopted. Pericardial traction sutures were used for ease of visibility and access, and elevating gauze pads were used to rotate the heart, if necessary, to obtain an unobstructed view of the target coronary arteries. In addition, an abdominal pad was used to compress the left lung in order to provide more space during revascularization of the posterolateral vessels. Stabilization of the target arteries was accomplished using an Octopus II stabilizer (Wast End Ave, Nashville), USA. Tourniquet-mounted two-pledge 4-0 Prolene sutures were used to occlude temporarily the proximal vessel during anastomotic time. Visualization of the anastomotic site was enhanced using a surgical blower–humidifier. Proximal anastomoses of vein grafts were carried out with the aid of a partially occluding aortic side clamp.
Intensive care unit management
In the ICU, hemodynamic monitoring along with full ventilatory support was continued. Hemodynamic monitoring included a continuous ECG, invasive arterial blood pressure monitoring, oxygen saturation monitoring, and central venous pressure monitoring. In addition, shortly after admission and stabilization of the hemodynamic condition, ventilation was set at a pressure mode of 20–25 cm H2O, respiratory rate of 10–15 breaths/min, and FiO2 of 50%. Thereafter, full laboratory tests, blood gas analysis to check for adequate oxygenation, ventilation, and electrolyte and acid–base status, and chest radiography were performed. Morphine infusion was used at a rate of 1–2 mg/h to control postoperative pain. The patients were assigned again into two groups according to their recruitment parameters: group P and group NP. In group P, the PIP was raised to 30 cm H2O with PEEP at 10 cm H2O for 1 min; the PIP was then raised again to 40 cm H2O with PEEP at 15 cm H2O for another minute. In group NP, the patients received the same recruitment regimen as group P but without PEEP. With the onset of recovery, the weaning process was commenced using simultaneous intermittent mandatory ventilation and pressure support instead of the pressure control mode. In the ICU, PaO2 was measured 30 min after admission to the ICU, (T5) 1 h after raising the PIP to 30 cm H2O (T6), and 4 h later (T7). It is also noteworthy that serial blood gas analyses and chest radiography were performed routinely daily and when indicated.
Sample size calculation
The sample size was calculated on the basis of intraoperative lung compliance, PaO2 at the end of surgery, and postoperative PaO2 in the ICU. However, the calculation was based mainly on lung compliance as a primary outcome because it yielded more number of patients in comparison with PaO2. Previous literature reported that the mean±SD of lung compliance in the group that received high PIP and PEEP was 50.8±6.9 ml/mbar, whereas that for the PEEP only group was 45.7±6.8 ml/mbar. Using the t-test for comparison and setting the α value to 0.05, we calculated a minimum of 30 patients in each group to detect a similar difference with 80% power. Calculations were done using PS Power and Sample Size Calculations Software version 2.1.30 for MS Windows (William D. Dupont and Walton D. Vanderbilt, USA).
Data were statistically described in terms of mean±SD or frequencies (number of cases) and percentages, when appropriate. The numerical variables between the study groups were compared using the Student t-test for independent samples. For comparing categorical data, the &khgr;2-test was performed. The exact test was used instead when the expected frequency was less than 5. P values less than 0.05 were considered statistically significant. All statistical calculations were performed using the statistical package for the social science (SPSS Inc., Chicago, Illinois, USA) version 15 for Microsoft Windows.
| Results|| |
As regards the preoperative and demographic data, there was no significant difference between the two groups [Table 1].
As for the intraoperative and postoperative PaO2, there was no significant difference between both groups after induction and just before raising the PIP. Moreover, there was no significant difference between the two groups 30 min after raising the PIP, at the end of surgery, 30 and 60 min after ICU admission, and 4 h later. However, the PaO2 was slightly higher in group P than in group NP, usually without any significant difference [Table 2].
As regards the intraoperative compliance, it was higher in group P than in group NP but without any significant difference [Table 3].
As regards the postoperative pulmonary complications, there was no significant difference between the two groups, but the incidence was slightly higher in group NP than in group P [Table 4].
The mean arterial pressure was significantly lower in group P than in group NP after raising the PIP, at the end of surgery, and after raising the PIP in the ICU (67.32±4.98, 65.14±3.94, and 66.14±5.25 mmHg, respectively, in group P in comparison with 70.96±7.05, 68.94±8.47, and 70.20±7.86 mmHg, respectively, in group NP) (P<0.05) [Table 5].
As for the heart rate and central venous pressure, there was no significant difference between the two groups. No barotrauma or mortality was recorded during the course of the study.
| Discussion|| |
The present study showed that there was no statistically significant difference between patients who received high PIP with PEEP and those who received high PIP only without any PEEP, as regards lung compliance and PaO2, both during surgery and during ICU stay. However, there was a statistically significant difference between the two groups as regards the mean arterial pressure.
Changes in respiratory mechanics with consequent perioperative atelectasis were found to affect about 90% of surgical patients 15. Three main factors were found to be implicated in the high incidence of pulmonary atelectasis, namely, compression, lack of surfactant, and gas absorption. In addition, some types of surgical procedures were found to carry a high risk for postoperative lung collapse, such as upper abdominal, laparoscopic, and thoracic surgeries 16. Some studies showed that cardiac surgery with a heart–lung machine is associated with postoperative pulmonary hypoxemia due to intrapulmonary shunting 17,18. Despite the fact that OPCAB was thought to be associated with a good gas exchange and less duration of intubation and ventilation when compared with conventional CABG 4, Babik et al. 5 reported that OPCAB might be associated with a reduction in lung tissue function. This deterioration in lung mechanics was attributed to two main reasons. The first one is the raised intravascular volume, which is usually planned to reach during OPCAB in order to reduce the incidence of left ventricular outflow tract obstruction during heart manipulation. The second reason is a surgical factor wherein the surgeon is usually trying to build more surgical space during revascularization of the posterolateral vessels; this is usually achieved by compressing the heart in the right chest in addition to compressing the left lung using an abdominal pad 4.
Many studies were carried out to ascertain means to reduce the incidence of lung collapse with the consequence of postoperative hypoxemia. Tusman and Böhm 19 reported that patients undergoing any type of surgery may benefit from the institution of lung recruitment maneuvers. In addition, Abdel-Hamid et al. 13 reported that an alveolar recruitment strategy with PEEP was effective in reducing postoperative collapse and hypoxemia. In this study, raising the PIP from 30 to 40 cm H2O together with raising the PEEP from 10 to 15 cm H2O was found to improve oxygenation markedly in patients undergoing OPCAB, in comparison with those who received PEEP only. However, in our study, there was no significant difference between the patients who received high PIP with PEEP and those who received high PIP only. In addition, Lumb et al. 20 reported that lung recruitment and positive airway pressure do not improve postoperative oxygenation in the postanesthesia care unit.
In contrast, the study by Reinius et al. 9 to investigate the effect of recruitment followed by PEEP in morbidly obese patients using computed tomography reported that there was a reduction in postoperative atelectasis, together with an improvement in arterial oxygenation. Moreover, Talab et al. 10 reported that intraoperative recruitment followed by PEEP at 10 cm H2O was effective in reducing lung atelectasis and improving oxygenation, together with short a recovery stay and reduction in postoperative pulmonary complications in morbidly obese patients undergoing bariatric surgery. To detect the value of alveolar recruitment and PEEP in pediatric cardiac patients undergoing cardiac surgery, Scohy et al. 11 in their study, reported that these maneuvers were effective in improving arterial oxygenation. All these studies showed that PEEP was important in improving lung compliance and PaO2, which is in contrast to our study in which we did not detect any significant difference between patients who received high PIP with PEEP and those who received high PIP only. The study by Almarakbi et al. 12 which compared four recruitment strategies to improve lung compliance and PaO2 during laparoscopic gastric banding, showed that the group that received repeated inspiratory maneuvers with PEEP had the best PaO2 in comparison with the group that received high PEEP only. This study agrees with our results that the most important factor in improving lung compliance and consequently PaO2 is raising the PIP and repeating the recruitment maneuver in contrast to using PEEP.
Suborov et al. 21 carried out a study to investigate the effect of an alveolar recruitment strategy in the ICU after OPCAB and reported that this maneuver helped in correlating microstream capnography with PaCO2 and myocardial contractility. In our study, although there was a statistically significant difference between the two groups as regards the mean arterial pressure, reduction of mean arterial pressure responded to patient positioning, intravenous fluid administration, or intravenous vasopressors. Our results are in agreement with those of Jauncey-Cooke et al. 22 who concluded that a recruitment maneuver was associated with harmful hemodynamic sequelae.
This study had certain limitations. It included a limited number of patients. Although a sample size was calculated, a larger sample of patients needs to be investigated. In addition, the group of patients who might benefit more from this recruitment strategy, namely, those with chronic obstructive pulmonary disease, was not investigated. Therefore, we recommend that in the future this recruitment strategy be tried in patients who might benefit more compared with those with normal preoperative pulmonary functions. As there was no statistically significant difference between the two groups, we recommend that PEEP be usually reserved for patients with poor preoperative pulmonary functions. In addition, a recruitment maneuver in the form of raising the PIP only should be used in patients with normal preoperative pulmonary functions, in those with hemodynamic instability, and in those who cannot withstand the possible harmful hemodynamic effects of PEEP.
| Conclusion|| |
This study showed that in patients with normal respiratory function and preserved myocardial contractility, both recruitment strategies, namely, PEEP and high PIP, are protective and tolerable in patients undergoing OPCAB.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]