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Eur J Cardiothorac Surg 2007;32:488-492. doi:10.1016/j.ejcts.2007.05.025
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved

Predictors of prolonged mechanical ventilation following aorta no-touch off-pump coronary artery bypass surgery

Sotirios N. Prapasa, Ioannis A. Panagiotopoulosa, Ashraf Hamed Abdelsalama,*, Vasilios N. Kotsisa, Dimitrios A. Protogerosa, Ioannis N. Linardakisa, Fotini N. Danoub

a Department of Cardiac Surgery, Henry Dunant Hospital, Athens, Greece
b Department of Anesthesia, Henry Dunant Hospital, Athens, Greece

Received 3 March 2007; received in revised form 22 May 2007; accepted 24 May 2007.

* Corresponding author. Current address: Department of Cardiothoracic Surgery, Faculty of Medicine, Zagazig University, Zagazig, Egypt. Tel.: +20105197377. (Email: ashrafhamid73{at}yahoo.com).


   Abstract
Top
 Abstract
1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 References
 
Objective: To identify parameters associated with prolonged mechanical ventilation (PMV) (>48 h) after off-pump coronary artery bypass (OPCAB) in our patient population. Materials and methods: From February 2001 to November 2005, we operated on 1359 patients for isolated coronary revascularization with the {pi}-circuit technique, consisting of: (1) beating heart, (2) OPCAB, (3) aorta no-touch, (4) use of composite grafts, and (5) arterial revascularization. Results: From the total number of our patients, 1320 patients had been extubated within 48 h postoperatively (Group A) and 39 patients needed PMV (Group B). In our study we have found that PMV were associated with advanced age (64.74 ± 9.85 Group A vs 68.43 ± 10.03 Group B, p < 0.02) as well as higher incidence with octogenarians (4.4% Group A vs 10.2% Group B, p = 0.09). Patients with preoperative history of transient ischemic attacks (TIAs) or stroke were more likely to belong to Group B (1.5% Group A vs 7.7% Group B, p < 0.02; 2.8% Group A vs 10.3% Group B, p < 0.02, respectively). Preoperative intra-aortic balloon pump (IABP) insertion was associated with PMV (1.6% Group A vs 15.4% Group B, p < 0.0005). Unexpectedly, neither COPD nor obesity was associated with PMV (4.9% Group A vs 7.7% Group B, p = NS, 21.7% Group A vs 23.1% Group B, p = NS, respectively). Conclusion: In this study, PMV following aorta no-touch OPCAB was related to preoperative variables: age, octogenarians, preoperative IABP, TIA, and stroke. There was no relation between PMV and any of the operative data.

Key Words: OPCAB • Aorta no-touch • Mechanical ventilation


   1. Introduction
Top
 Abstract
 1. Introduction
2. Materials and methods
 3. Results
 4. Discussion
 References
 
Previous studies [1,2] have shown that prolonged mechanical ventilation (PMV) after coronary bypass surgery is associated with increased mortality, development of multiorgan failure, and sepsis. Patients with these events had longer intensive care unit (ICU) and hospital stays as well as increased resource utilization.

A number of studies have examined the risk factors for PMV after coronary artery bypass grafting (CABG) [2–4]; these include age, smoking, left ventricular dysfunction, congestive heart failure, renal failure, and angina.

Another study [5] concluded that the causes of PMV are heterogeneous, vary with time, and have a varying impact on the duration of mechanical ventilation required after the patient undergoes CABG surgery.

We aim in this study to identify the preoperative and operative parameters that are associated with postoperative prolonged (>48 h) mechanical ventilation after off-pump coronary artery bypass (OPCAB) using the {pi}-circuit technique in our patient population.


   2. Materials and methods
Top
 Abstract
 1. Introduction
 2. Materials and methods
3. Results
 4. Discussion
 References
 
Our study is a prospective observational study in the Department of Cardiac Surgery, Henri Dunant Hospital, Athens, Greece. In the period from February 2001 to November 2005, 1359 patients with coronary artery disease necessitating coronary artery bypass surgery were operated on for coronary revascularization with the {pi}-circuit technique, consisting of (1) beating heart, (2) OPCAB, (3) aorta no-touch, (4) use of composite grafts, and (5) arterial revascularization.

2.1 Surgical technique
The standard approach was median sternotomy. Skeletonized internal mammary arteries and radial artery islet (from the non-dominant arm) were then harvested. We were planning to use one or both internal thoracic arteries, with or without the radial artery, designing composite arterial grafts (T-graft, Y-graft, extensions, {pi}-graft, sequential use) (Fig. 1 ).


Figure 1
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  		Fig. 1. The formation of the ({pi}) graft by the left and right internal mammary arteries.

 
We aimed to achieve complete arterial myocardial revascularization depending upon the native origin of the internal thoracic arteries with complete avoidance of any aortic manipulations. Thus, we decrease the risk of both aortic manipulations, circumvent the cardiopulmonary bypass, and thus avoid their known adverse effects.

The exposure of the left anterior descending (LAD) artery and the midportion of the right coronary artery (RCA) is simple as these arteries lie on the anterior surface of the heart. To improve the exposure and minimize the heart displacement, for the lateral and inferior vessels, the patient was kept in Trendelenburg's position with the bed rotated toward the surgeon. Deep pericardial traction sutures were used to manipulate the heart and expose the coronary arteries. Deep pericardial traction sutures were used to elevate and rotate the heart by placing tension on the pericardial wall and by distorting it.

The stabilization of the anastomotic site was achieved with the aid of octopus tissue stabilizer (Octopus II Medtronic's innovative contribution to minimally invasive instrumentation).

2.2 Definitions of variables
Diabetes is defined as fasting plasma glucose equal to or more than 126 mg/dl. Obesity is defined as body mass index greater than 30. Stroke is defined as a cerebrovascular accident, which leaves the patient with brain damage confirmed with computerized tomography (CT) or magnetic resonance imaging (MRI). Peripheral vascular disease refers to diseases of blood vessels outside the heart and the brain as diagnosed by X-ray angiography, Doppler study, or magnetic resonance angiography. Chronic obstructive pulmonary disease (COPD) occurs in patients with long-term bronchodilators or receiving steroids for lung disease. Renal failure is defined as an increase of the creatinine level more than 200 µmol/l on admission or history of renal transplant or dialysis. Emergency surgery is defined as the necessity to take the patient to the operating theatre on referral before the beginning of the next morning's operation schedule. Thirty-day death is defined as death within the first postoperative month, while 5-day death is within the first 5 days postoperatively. Psychological changes are defined as the changes in the mental condition as proved by the comparison of the mental component summary scale of short-form health survey (SF-36) preoperatively and 2 weeks postoperatively.

2.3 Anesthesia technique
Anesthesia was managed according to a standard protocol. All patients had one central venous catheter and a Swan-Ganz catheter was also used. Diazepam was administered as a pre-anesthetic agent. Then a combined dose of opioid/volatile agents: fentanyl (30 µg kg–1), etomidate (0.2 mg kg–1), and sevoflurane, associated with cis-atracurium as a neuromuscular blocker agent. Heparin was administered, at a dose of 100 IU/kg, before the start of the first anastomosis to achieve an activated clotting time (ACT) of 250–350 s. On completion of all anastomoses, protamine was given to reverse the effects of heparin and return the ACT to near the preoperative levels. Monitoring consisted of radial artery, central venous, and pulmonary arterial pressures in all patients.

2.4 Weaning protocol
Patients were extubated as soon as they fulfilled all the following extubation criteria: (1) patient alert, awake and hemodynamically stable, (2) temperature >36.5 °C, (3) bleeding <100 ml h–1 for >2 h, (4) tidal volume >8 ml kg–1, respiratory rate greater than 10 and less than 25 breaths min–1 with a pressure support ventilation of 5 cm H2O, and (5) PaO2 > 80 mmHg with FiO2 ≤ 0.5, pH > 7.35 and PaCO2 less than 45 mmHg for at least 1 h in the pressure support mode.

Patients with prolonged mechanical ventilation were defined as those requiring ventilatory support for more than 48 h postoperatively. Patients with mechanical ventilation for less than 48 h, died before 48 h, or need reintubation after early extubation, were not included in this definition.

2.5 Data collection and analysis
The preoperative baseline characteristics of the patients, operative data, and overall postoperative events were recorded. The data of patients needing mechanical ventilation for more than 48 h were recorded and correlation between them and the other patients was made as regard the preoperative risk factors and the operative data. All statistical tests were performed as two-tailed tests. Fisher's exact test and {chi} 2-test were used for the data analysis. A p-value <0.05 was considered to be statistically significant. Statistical analysis was performed using commercially available statistical software package (SPSS for windows ver. 13).


   3. Results
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
4. Discussion
 References
 
A total number of 1359 patients who underwent isolated off-pump CABG were studied. There were 1159 male patients and 200 female patients with a mean ± SD age of 64.85 ± 9.87 years. Other patients’ baseline characteristics are summarized in Table 1 .


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  		Table 1 Baseline characteristics of the patients
 
All the patients were operated on with the {pi}-circuit technique; beating heart off-pump CABG, aorta no-touch and use of composite grafts with exclusively arterial revascularization. The overall operative data of the patients are summarized in Table 2 .


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  		Table 2 Operative data of the study population
 
There were three ICU deaths in the first 5 days after surgery. Thirty-day mortality was 1.5% (21 patients). The patients had multiple postoperative complications as shown in Table 3 .


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  		Table 3 Postoperative events of the study population
 
Thirty-nine patients had mechanical ventilation for more than 48 h (2.9%); all other patients were extubated at varying periods before 48 h had elapsed. The study population was then divided into two groups: Group (A), patients with mechanical ventilation ≤48 h and Group (B), patients with prolonged mechanical ventilation >48 h.

The two study groups were compared regarding the preoperative and operative data to clarify factors that were significantly related to prolonged mechanical ventilation.

The preoperative variables are compared in Table 1. The mean age of patients with prolonged mechanical ventilation was significantly higher (68.4 ± 10 years in Group B vs 64.7 ± 9.8 years in Group A, p = 0.021), with an increase in the number of octogenarians among them, but without statistical significance (4.4% vs 10.2%, p = 0.098).

Comparison of the presence of obesity, diabetes mellitus, high serum cholesterol, and hypertension in patients in the two groups revealed no significant difference between Group A and Group B (21.7% vs 23.1%, p = 0.844; 32.3% vs 25.6%, p = 0.487; 37.9% vs 25.6%, p = 0.133; 43.1% vs 38.5%, p = 0.625, respectively).

We could also see that renal failure (7.8% vs 15.4%, p = 0.122) and even renal dialysis in the patients preoperatively (1.4% vs 2.5, p = 0.427) appeared to have no relation to the incidence of postoperative mechanical ventilation.

Despite the fact that the presence of peripheral vascular diseases showed no relation to the need for prolonged mechanical ventilation (6.2% in Group A vs 7.7% in Group B, p = 0.731), the latter was significantly related to the history of preoperative TIA (1.5% in Group A vs 7.7% in Group B, p = 0.026) or previous stroke (2.8% in Group A vs 10.3% in Group B, p = 0.027).

Comparison of the mean EuroScore in the two groups, in spite of being higher in Group B, showed no statistical significance of this increase (3.02 ± 0.73 in Group A vs 3.24 ± 0.81 in Group B, p = 0.359).

Interestingly, patients with chronic obstructive pulmonary diseases showed no tendency to require prolonged mechanical ventilation after surgery (4.9% in Group A vs 7.7% in Group B, p = 0.441). We had found in the same way that GIT problems, poor left ventricular function, emergency surgery, and even redo surgery had no significant influence on the incidence of prolonged mechanical ventilation. On the contrary, preoperative IABP entailed a highly significant increase among patients in Group B in comparison with patients in Group A (15.4% vs 1.6%, p = 0.0005).

As shown in Table 2, none of the operative data regarding the type of conduits, number or type of anastomoses, or site of revascularization were related to the incidence of prolonged mechanical ventilation.


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
References
 
The main objective of our study was to determine the preoperative and operative factors that could be associated with prolonged mechanical ventilation, after a special OPCAB technique (the {pi}-circuit technique).

In our study we have found that there are some preoperative factors that may be claimed to lead to an increased incidence of prolonged mechanical ventilation (>48 h). The main finding of this study is that patients with factors associated with delayed recovery of the central nervous system from anesthesia (old age, preoperative TIA, preoperative stroke) are more likely to require prolonged mechanical ventilation after off-pump CABG. We have also found that patients in need of preoperative IABP have a higher incidence of prolonged mechanical ventilation.

Branca et al. [6], in Saint Thomas Hospital (USA), had performed a large retrospective study on 4863 patients having undergone CABG to identify risk factors for prolonged postoperative ventilation. They had found that the patients who had required mechanical ventilation beyond 3 days, especially those who had received ventilation for more than 2 weeks, were most strongly characterized by preoperative medical instability and chronic medical problems. The most important independent predictors for prolonged mechanical ventilation in their study included mitral valve disease, advanced age, the use of preoperative vasopressors and/or inotropes, renal failure, urgent or emergent operation, concomitant valve surgery, preoperative mechanical ventilation, previous CABG surgery, female gender, preoperative acute MI, and history of stroke.

Wigfield et al [7] have studied patients to investigate whether obesity is a risk factor after cardiac surgery and found that obesity is associated with an increased rate of prolonged mechanical ventilation. Likewise, Jin et al. [8] have stated that prolonged mechanical ventilation increased significantly with the increase in the body mass index (BMI). On the other hand, Dunning et al. [9] had found that the mean BMI is not a risk for prolonged mechanical ventilation after cardiac surgery.

In our study, unpredictably we have found that obesity is not associated with prolonged mechanical ventilation among our study population.

Aging is one of the most important preoperative risk factors before coronary artery surgery. It is usually associated with a high incidence of morbidity, as well as increased mortality. As shown in our study, the incidence of prolonged mechanical ventilation is significantly higher in old age, with a less significant increase among octogenarians. So, age appears to be strongly related to the incidence of prolonged mechanical ventilation. Most of the published material agrees with this point, in studies of either OPCB or CABG [10,11].

Athanasiou et al. [12] have found that female gender is not related to the time of postoperative mechanical ventilation, and the incidence of major adverse outcome (they considered PMV as one of them) seems to be statistically comparable in the male and female genders.

But in our study we did not find that female gender is associated with this complication.

This may be also supported by the findings of Mack et al. [13], who have detected a decrease in respiratory complications in females with OPCAB.

The elective use of preoperative intra-aortic balloon counterpulsation appears to be beneficial. Among several studies in the literature, it was found that this is important and decreases the postoperative morbidity, including the incidence of prolonged mechanical ventilation and ICU stay [8,14–17].

In contrast, the preoperative use of the intra-aortic balloon in our study is strongly associated with a higher incidence of prolonged mechanical ventilation. Suzuki et al. [18], studying off-pump patients, have found that preoperative intra-aortic balloon pump in high-risk patients, despite its beneficial effect, is associated with a higher incidence of prolonged mechanical ventilation.

On the other hand, through another study comparing the elective use of IABP preoperatively with OPCAB, Vohra and Dimitri [19] have stated that the use of a preoperative intra-aortic balloon pump in OPCAB patients did not only increase the duration of mechanical ventilation but also have advantages on the postoperative outcome.

In our series of patients, we have detected that a history of COPD is not associated with an increased risk of prolonged mechanical ventilation. It could be considered as one of the important findings in our study. This factor was suggested to be one of the strong predictors of prolonged mechanical ventilation after CABG. It has been suggested that OPCAB when compared with conventional CABG is more beneficial for patients with COPD, but to be not related to prolonged ventilation is the interesting finding.

Thus, we can conclude that prolonged mechanical ventilation following OPCAB with aorta no-touch does not have operative predictors. We have found that the predictors of prolonged mechanical ventilation after this surgical strategy are preoperative statements: age, TIA, stroke, and, strangely, preoperative need for IABP. Unexpectedly, COPD patients did not show a tendency to have prolonged mechanical ventilation after surgery.


   Acknowledgments
 
The authors thank the ICU staff in Henry Dunant Hospital for their assistance, and would like to thank the biomedical statistician Dr A. Galanos.


   References
Top
 Abstract
 1. Introduction
 2. Materials and methods
 3. Results
 4. Discussion
 References
 

  1. Cohen AJ, Katz MG, Frenkel G, Medalion B, Geva D, Schachner A. Morbid results of prolonged intubation after coronary artery bypass surgery. Chest 2000;118:1724-1731.[CrossRef][Medline]
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  8. Jin R, Grunkemeier GL, Furnary AP, Handy Jr. JR. Is obesity a risk factor for mortality in coronary artery bypass surgery?. Circulation 2005;111:3359-3365.[Abstract/Free Full Text]
  9. Dunning J, Au J, Kalkat M, Levine A. A validated rule for predicting patients who require prolonged mechanical ventilation post cardiac surgery. Eur J Cardiothorac Surg 2003;24:270-276.[Abstract/Free Full Text]
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  11. Eagle KA, Guyton RA, Davidoff R, Edwards FH, Ewy GA, Gardner TJ, Hart JC, Herrmann HC, Hillis LD, Hutter Jr. AM, Lytle BW, Marlow RA, Nugent WC, Orszulak TA, American College of Cardiology, American Heart Association ACC/AHA 2004 guideline update for coronary artery bypass graft surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1999 Guidelines for Coronary Artery Bypass Graft Surgery). Circulation 2004;110:340-437.
  12. Athanasiou R, Al-Ruzzeh S, Stanbridge RD, Casula RP, Glenville BE, Amrani M. Is the female gender an independent predictor of adverse outcome after off-pump coronary artery bypass grafting? Ann Thorac Surg 75, 1153–1160.
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