Daily comparison of respiratory functions between on-pump and off-pump patients undergoing CABG

[김기환/강원대]

Daily comparison of respiratory functions between on-pump and off-pump patients undergoing CABG

Serdar Çimen^a, Vedat Özkul^b, Bülent Ketenci^a, Nurgül Yurtseven^b, Rafet Günay^{, , a}, Banu Ketenci^c, Hakan Gerçeko lu^a and Murat Demirta ^a

^a Thoracic and Cardiovascular Surgery Department, Dr Siyami Ersek Thoracic and Cardiovascular Surgery Center, Istanbul, Turkey

^b Anesthesiology Department, Dr Siyami Ersek Thoracic and Cardiovascular Surgery Center, Istanbul, Turkey

^c Heybeliada Thoracic Disease Center, Istanbul, Turkey

Received 26 August 2002; 

revised 3 December 2002; 

accepted 23 December 2002. ;

Available online 10 March 2003.

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Abstract

Objective: Widespread application of on-pump revascularization procedures is increasing due to the thought of elimination of untoward effects of cardiopulmonary circuit. Thus, whether off-pump coronary artery surgery eliminates side effects especially related to respiratory functions is still controversial. Although many previous studies have eval‎uated these respiratory functions, daily comparison of 12 parameters was not included in any of the studies. The aim of our prospective study was to ascertain whether off-pump coronary operation improves pulmonary functions and postoperative recovery period when compared with on-pump technique and whether early discharge of patients with off-pump surgery is the result of respiratory improvement. Methods: Eighteen patients in each group were included: on-pump group underwent coronary revascularization with cardiopulmonary bypass and off-pump with stabilization. Respiratory function tests and arterial blood gas analyses were performed preoperatively and daily after operation function tests included forced expiratory volume (FEV) in 1 s, forced vital capacity (FVC), expiratory reserve volume, vital capacity, quotient of FEV in 1 s to FVC, maximal voluntary ventilation (MVV), tidal volume, and forced midexpiratory flow. Blood gas analyses included partial arterial oxygen and carbon dioxide pressure, arterial pH and hematocrit (Hct). Results: Preoperative pulmonary functions and arterial blood gases were not statistically significant between groups except MVV and partial arterial oxygen pressure. MVV was slightly higher in on-pump group and partial arterial oxygen pressure was slightly lower in on-pump group. During postoperative first day Hct (P=0.004) and FEV in 1 s (P=0.049) values and third day partial arterial oxygen pressure (P=0.011) and Hct (P=0.011) values were lower in on-pump group. Mean extubation, duration in postoperative suit and hospital discharge times, mean blood loss were not statistically significant between groups postoperatively. Conclusion: Pulmonary functions and arterial blood gases were not improved in off-pump patients when compared with on-pump patients. Patients going to be surgically revascularized should not be altered to off-pump surgery merely with the hope of improving respiratory functions with off-pump technique. As the postoperative stay times at surgical theatre and hospital is not different and the extubation times were similar, early discharge of patients with off-pump surgery cannot be related merely to better preservation of respiratory functions.

Author Keywords: Respiratory functions; Coronary revascularization; Off-pump; On-pump

Article Outline

1. Introduction

2. Patients and methods

2.1. Anesthesiologic management

2.2. Operative procedure

2.3. Pulmonary function tests and blood gas analyses

2.4. Statistical analysis

3. Results

4. Discussion

References

1. Introduction

Respiratory deterioration following myocardial revascularization using cardiopulmonary bypass (CPB) is a well-established clinical entity [1 and 2]. Besides the effects of sternotomy [3] and harvesting of internal mammary artery [4], CPB [5] has been the most offended factor of respiratory dysfunction. Many publications claim that improvement in patients with off-pump technique is due to the avoidance of CPB [6]. As a result, naturally, this thought also reminds that postoperative pulmonary functions in off-pump patients should be better than patients operated with on-pump technique.

Our main purpose in this study was to compare and investigate how pulmonary function tests and arterial blood gases were affected postoperatively between on-pump and off-pump patients and also whether early discharge is in part a consequence of improved respiratory functions in off-pump group almost universally emphasized in literature.

2. Patients and methods

From October 2002 through March 2002, 36 consecutive patients undergoing coronary revascularization operation was included in this trial. The preoperative exclusion criteria for participation in the study were patients with severely restricted or obstructed pulmonary diseases, hemodynamically unstable patients either before or after revascularization in whom respiratory function tests could not be applied and patients could not be discharged from intensive care unit for whatever is the cause on the first postoperative day (POD). Patients were divided into two groups and the trial kept on until 18 patients in each group included. On-pump group (Group A) included 18 patients and off-pump group included 18 patients (Group B).

The patient characteristics, preoperative respiratory functions and blood gases are shown in Table 1. The two groups did not differ significantly with respect to age, gender, preoperative risk factors and ejection fraction (EF). Preoperative blood gas analyses were similar except PaO₂ value which was higher in off-pump group and statistically significant (P=0.04). Preoperative pulmonary functions of two groups were comparable. The only difference was in MVV which was quiet high in on-pump group (0.04).

Table 1. Patient demographics and preoperative respiratory functions and blood gas analysis of patientsa

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2.1. Anesthesiologic management

Cardiac medication consisting of beta-adrenergic receptor antagonists, nitrates and calcium channel entry blockers continued until the morning of surgery. The anesthesia protocol for both groups was the same. Premedication was performed with administration of 5 mg of dormicum intramuscularly 1 h before operation. Anesthesia was induced with 2.5 mg of fentanyl and 2 mg kg⁻¹ of propofol. Before intubation 0.1 mg kg⁻¹ of pancuroniumwas administered intravenously. Maintenance of anesthesia included infusion of 100 mg h⁻¹ of propofol. After transfer to the intensive care unit, all patients received positive pressure ventilation of the lungs with an FIO₂ of one which was gradually diminished up to 0.4 before extubation. Novalgine or fentanyl (only in surgical intensive unit) was administered intravenously for postoperative analgesia, when required. Patients were considered ready for extubation if they were normothermic, awake, hemodynamically stable with no or minimal inotropic support and had good gas exchange.

2.2. Operative procedure

For Group A, coronary bypass grafting was carried out through median sternotomy using standard CPB with single venous right atrial and ascending aortic cannulation. Moderate systemic hypothermia (28°C) was applied and CBP was carried out with disposable membrane oxygenator (Sorin-Biomedica, Dideco, d 708 simplex III, Mirandola (MO), Italy) and centrifugal pump (Bio-Pump BPX-80, Medtronic, Medtronic. Inc., Minneapolis, MN, USA). Myocardial preservation was achieved with aortic root infusion of mild blood cardioplegia, repeated every 20 min both from the aortic root and saphenous veins during the cross-clamp period. The distal anastomosis was performed by using two polypropylene (Ethicon, Johnson–Johnson Brussels, Belgium) sutures. Epicardial temporary pacing wires were not inserted routinely. The chest was closed using six to eight steel wires after inserting two chest drains subxiphoidally. If pleural has been opened one of the drains was inserted subxiphoidally and placed transmediastinally to the thorax.

For Group B, coronary bypass operation was carried out by using stabilizer Octobus III (Medtronic 28 400, Tissue stabilizer, Medtronic Inc., 710 Minneapolis, MN, USA). Two polypropylene (Ethicon, Johnson–Johnson Brussels, Belgium) sutures were used for each distal anastomosis. Following distal anastomosis, proximal anastomosis was done using partial side clamp. A vessel shunt was not used and epicardial temporary pacing wires were not inserted unless needed. At the termination of procedure, protamine was not given to reverse heparin. As in on-pump surgery two chest drains were inserted subxiphoidally and when needed one is placed to pleural space transmediastinally. Again, sternal closure was achieved by using six to eight sternal wires.

The surgical intensivists achieved postoperative care of patients as usual. On POD 1, chest drains were removed in both groups and patients were discharged from postoperative suit. Criteria for hospital discharge of patients included functional capacity sufficient to accommodate daily facilities at home, no dyspnea present at least for the last 2 consecutive days, hematocrit (Hct) values greater than 25, biochemical values less or equal to preoperative levels.

2.3. Pulmonary function tests and blood gas analyses

Pulmonary function tests including forced expiratory volume (FEV) in 1 s (FEV₁), forced vital capacity (FVC), expiratory reserve volume (ERV), vital capacity (VC), quotient of FEV in 1 s to FVC (FEV₁/FVC), maximal voluntary ventilation (MVV), tidal volume (TV), and forced midexpiratory flow (FEF 25/75) were performed at preoperative first day and every day following the operation until hospital discharge using portable spirometer (Spirolab MIR, Medical International Research, Rome, Italy). Each test was performed three times and the best results were selected for analysis.

Arterial blood gases on room air were analyzed preoperatively before anesthesia and everyday following operation until hospital discharge by femoral artery puncture. Blood gas analyses included partial arterial oxygen pressure (PaO₂), partial arterial carbon dioxide pressure (PaCO₂), arterial pH and Hct.

2.4. Statistical analysis

Data were analyzed with Mann–Whitney's U test and Fisher exact text for continuous and qualitative variable type, respectively. Repeated measures analysis of variance (ANOVA) was used for between groups and Student–Newman–Keuls test for post hoc multiple comparisons. All values are expressed as mean±SD. P values less than 0.05 were considered to be statistically significant.

3. Results

In perioperative variables (Table 2) the only significant difference was the number of bypass grafts. Mean number of bypass grafts was 2.61±0.78 in on-pump group and 1.53±0.92 in off-pump group (P=0.0009). In all patients ITA were used and no perioperative myocardial infarction was detected clinically in both groups. Mean extubation times of on-pump and off-pump patients were 7.69±047 and 7.13±2 h, respectively (P=0.47); mean duration in postoperative suit was 1.06±0.24 and 1.15±0.55 days, respectively (P=0.53); and mean hospital discharge times were 5.16±1.35 and 4.9±1.38 days, respectively (P=0.53). Mean blood loss in on-pump and off-pump patients were 896±227 and 797±239 ml, respectively (P=0.35); and mean transfused blood or blood products were 3.2±1.3 and 2.92±1.62 units (P=0.62), respectively.

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Table 2. Perioperative variables of patientsa

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Postoperative first day values of on pump and off-pump groups in FEV₁ (Fig. 1) were 0.69±0.27 and 0.90±0.25 l, respectively, and in both groups some increase occurred and on the fifth POD reached 1.42±0.59 and 1.56±0.48 l, respectively, which were comparable in both groups.

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Fig. 1. Values of predicted, preoperative and daily measurements of FEV in 1 s (FEV₁) and FVC in on-pump and off-pump groups. Data are shown as the mean±SD (preop, preoperative; POD, postoperative day; *P<0.05.)

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Preoperative FVC (Fig. 1) values were 3.01±0.73 and 2.68±0.71 l in on pump and off-pump groups, respectively, and dropped to 0.79±0.31 and 1.03±0.33 l on the first POD. A steady increase occurred and on the fifth POD increased to 1.56±0.61 and 1.7±0.46 l in on-pump and off-pump groups, respectively.

ERV (Fig. 2) values were comparable both before and after operation in both groups. Preoperative values of ERV were 0.55±0.33 and 0.46±0.30 l in on-pump and off-pump groups, respectively, and on the first POD ERV values dropped about 83 and 65% of the preoperative values, but no statistically significant difference was present between groups.

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Fig. 2. Values of predicted, preoperative and daily measurements of ERV and VC in on-pump and off-pump groups. Data are shown as the mean±SD (preop, preoperative; POD, postoperative day).

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VC (Fig. 2) dropped from 3.25±0.78 to 1.01±0.45 l (31% of preoperative value) in on-pump group and dropped from 2.8±0.77 to 1.11±0.23 l (39% of preoperative value) in off-pump group on the first POD. Thereafter, although the values of VC improved in both groups until the day of discharge they did not differ from each other significantly and no significant increase occurred during discharge.

The value of FEV₁/FVC (Fig. 3) did not change within groups and between groups preoperatively and postoperatively. Preoperative and postoperative first day values of on-pump were 87.84 and 86.35%, respectively, and of off-pump group were 85.87 and 88.65%, respectively.

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Fig. 3. Values of predicted, preoperative and daily measurements of quotient of FEV in 1 s to FVC (FEV₁/FVC) and MVV in on-pump and off-pump groups. Data are shown as the mean±SD (preop, preoperative; POD, postoperative day; *P<0.05).

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MVV (Fig. 3) values were different preoperatively between groups (P=0.043), but in the postoperative period in both groups no statistically significant difference was present between groups. Preoperative values of on-pump and off-pump groups were 91.56±33.5 and 70.97±20.4 l/min, respectively, and dropped 28.96±8.26 and 34.39±6.47 l/min on the first POD. On the fifth POD mean values of each group were approximately the same.

TV (Fig. 4) of on-pump group decreased to 0.58±0.26 l on the first POD and on the fifth POD, TV was 0.72±0.25 l. Values of off-pump group were 0.65±0.27 l on the first POD and 0.74±0.07 l on the fifth POD. No statistical significance was present on the fifth POD (P=0.21).

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Fig. 4. Values of predicted, preoperative and daily measurements of TV and FEF 25/75 in on-pump and off-pump groups. Data are shown as the mean±SD (preop, preoperative; POD, postoperative day).

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FEF 25/75 (Fig. 4) dropped from 3.26±1.43 to 1.24±0.33 l/s in on-pump group and dropped from 2.50±0.85 to 1.38±0.39 l/s in off-pump group on the first POD and increased thereafter steadily but no significant difference occurred between two groups.

Preoperative PaO₂ (Fig. 5) levels were 80.92±10.13 mmHg in on-pump group and 89.44±6.24 mmHg in off-pump group (P=0.036). On the first POD, levels of PaO₂ were 72.8±11.3 and 77.1±10.6 mmHg in on-pump and off-pump groups, respectively. Maximal drop was on the second POD in both groups that were 17% less than preoperative value.

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Fig. 5. Values of predicted, preoperative and daily measurements of PaO₂ and PaCO₂ in on-pump and off-pump groups. Data are shown as the mean±SD (preop, preoperative; POD, postoperative day; *P<0.05).

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Preoperative PaCO₂ (Fig. 5) levels of on-pump and off-pump groups were 38.1±4.5 and 39.17±3.1 mmHg, respectively. On the first POD, PaCO₂ levels were 35.4±3.7and 37.7±6.6 mmHg in the two groups, respectively. No disparity occurred during postoperative course in both groups.

pH (Table 3) values were 7.42±0.05 and 7.43±0.01 preoperatively in on-pump and off-pump groups and on the third POD, value of on-pump group was 7.52±0.05 whereas off-pump group was 7.47±0.02 which was significant (P=0.006). On the other days no differences were present between groups.

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Table 3. Values of predicted, preoperative and daily measurements of Hct and arterial pH in on-pump and off-pump groupsa

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Hct (Table 3) values were 41±5.36 and 40±2.75% preoperatively in on-pump and off-pump groups, respectively. On the first POD Hct dropped to 28.94±3.86% in on-pump group and 33.29±3.65% in off-pump group statistically significant between groups (P=0.004).

4. Discussion

Our results clearly disclosed that in both groups all respiratory function tests and arterial blood gases dropped comparably. The greatest drop was on the first POD in all parameters as expected. Thereafter, all parameters improved gradually but never reached preoperative values during hospital stay.

On the first POD only the Hct levels differed between groups. Since untoward effect of CPB on blood elements is a well-established entity, difference in Hct values was not a surprise.

Despite the serious drops in respiratory lung functions, neither the PaO₂ levels, nor the PaCO₂ levels decreased significantly to intervene during hospital stay in both groups. In a recent study comparing early pulmonary functions after coronary bypass operations in on-pump and off-pump groups, it is mentioned that there was no statistical difference in gas exchange between groups [7]. It was also stated in the same report that although postoperatively the mean static and dynamic lung compliances were by some means lower in off-pump group, it was not statistically significant. In this study pulmonary dysfunction in off-pump group was attributed to pulmonary congestion resulting from cardiac manipulation, cardiac immobilization, coronary vessel occlusion, drugs used during operation and trendelenberg position consistent also in our trial.

In our series the mean extubation times and the respiratory functions and blood gas analyses did not differ significantly between groups during the early postoperative period. In some reports it is claimed that early extubation is the consequence of better preservation of respiratory functions [6 and 8]. As our results are not consistent with the literature, some other factors should be present if discrepancies persist between extubation times. Mean postoperative stay times and mean duration of hospital discharge of on-pump and off-pump groups were comparable. Therefore, improved respiratory functions cannot be taken as the main decisive feature of early hospital discharge in off-pump patients if being discharged earlier.

Respiratory compensation may be conspicuously limited in the postoperative heart patients due to diverse reasons. Median sternotomy [3] and harvesting of internal mammary artery [4] are two major surgical factors associated with the cardiac operations. Altered surfactant function due to residual effects of anesthesia [9] and reduced chest wall compliance and atelectasis [10] are contended as the anesthetic factors of postoperative pulmonary deterioration which are consistent for all major surgical procedures. Postoperative pain, retained secretions and especially, infections such as pneumonia do also have profound impact on pulmonary system. The incidence of pneumonia after coronary artery bypass surgery is being reported 3–16% [11]. Atelectasis, being implicated as the most important and frequent problem after thoracic surgery, occurs in 73% of patients after internal mammary artery grafting [12] that reduces lung compliance and functional residual capacity.

Pneumonia and remarkable atelectasis did not occur in our group and minor atelectasis was not taken into consideration. The development of interstitial edema contributes significantly to the mechanical and gas exchange abnormalities. CBP has been implicated as the major source of alterations in human alveoli structure [5]. In this study, Ratliff and colleagues reported that cell swellings, interstitial edema and hemorrhage, and miliary atelectasis occurred in postcardiopulmonary period, but these changes were not exclusive to patients undergoing CPB. For instance, in major vascular procedures aortic cross clamping is being implicated as a factor of extravascular lung water accumulation [13].

Thus, it should not be regarded as CPB does not have any influence on postoperative respiratory functions because as mentioned in literature postoperative deterioration of lung function is significantly more profound after cardiac operations than after lung resection procedures performed through the same surgical approach due to negative effects of CPB [14], but our study gave the idea that factors other than CPB should have more significant power.

The limitation of our trial is that our cohort of patients was small and patients with significantly impaired pulmonary function were not present. Although we accomplished a prospective study, no randomization was performed. Also, pleural effusions and atelectasis that occurred in postoperative period were not taken into consideration though no patient needed toracentesis. How these factors would influence postoperative outcome with regard to pulmonary functions and blood gases is controversial.

The aim of cardiovascular surgical operations is to improve cardiac functions while creating minimal damage to other systems. Cardiac surgical operations have long been performed by using CPB and CPB has long been implicated as the main source of postoperative pulmonary dysfunction. Many innovative techniques have been designed to reduce postoperative and hospital stay and perioperative complications. Our study clearly shows that elective off-pump surgery has no great deal of beneficial effects over on-pump surgery with respect to postoperative pulmonary function tests and blood gases in patients with mild to moderate chronic obstructive pulmonary disease. Regardless of the avoidance of CPB off-pump coronary surgery had comparable deterioration of pulmonary functions and blood gases with on-pump coronary surgery. Patients going to be surgically revascularized should not be altered to off-pump surgery merely with the hope of improving respiratory functions with off-pump technique.

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