Endoscopic vein harvest (EVH) for coronary artery bypass grafting surgery has many advantages compared with the traditional open-vein harvest technique. It decreases wound-related complications and postoperative pain. It does not prolong the operating time significantly or compromise vein quality [1–3]. EVH of the saphenous vein is performed with carbon dioxide (CO2) insufflation for visualization and dissection. The insufflated CO2 is rapidly absorbed into the body and may influence the haemodynamics, which could cause serious problems for a patient undergoing coronary artery bypass grafting surgery. However, the haemodynamic changes during EVH have not been clearly defined, even though EVH is commonly performed for coronary artery bypass grafting surgery [4–7].
The study evaluated the haemodynamic effects during EVH of the saphenous vein for off-pump coronary artery bypass grafting surgery (OPCAB).
Study population and protocol
After obtaining Institutional Review Board approval and informed consent from the patients, they were prospectively studied from among patients undergoing OPCAB using EVH of the saphenous vein. Patients were excluded if any of the following criteria were present: urgent or emergent case, re-do case, reduced left and right ventricular function (ejection fraction <40%), preoperative dysrhythmia, valvular heart disease, intracardiac shunt, pulmonary artery hypertension, severe peripheral vascular obstructive diseases, previous infrainguinal vascular surgery, varicose veins, a history of deep vein thrombosis in the legs, and previous insult with neurologic sequelae in the legs. One hundred study patients were enrolled.
After establishing routine invasive (invasive arterial blood pressure) and noninvasive patient monitoring [electrocardiography, pulse oximetry, bispectral index, and cerebral oximetry (INVOS Cerebral/Somatic Oximeter, Somanetics, Troy, USA)], anaesthesia was induced and maintained using target-controlled infusion (Orchestra Base Primea, Fresenius Vial, Brezins, France) of propofol (target concentration 1.2–1.3 μg ml−1) and remifentanil (target concentration 10–20 ng ml−1). Muscle relaxation was obtained with the administration of a bolus of rocuronium under the guidance of peripheral monitoring of neuromuscular transmission. A pulmonary artery catheter (Swan-Ganz CCOmbo CCO/SvO2, Edwards Lifesciences, Irvine, USA) was inserted after anaesthesia induction.
After anaesthesia induction, the following ventilator settings were used: total fresh gas flow of 2 l min−1, consisting of air (1.5 l min−1) and O2 (0.5 l min−1), tidal volume = ideal body weight (calculated by obsolete formulas) × 8 ml, respiratory rate controlled using the end-tidal CO2 pressure (PETCO2), which ranged from 35 to 40 mmHg through capnography (S/5 Compact Anesthesia Monitor, Datex-Ohmeda, Finland), no positive end expiratory pressure, and inspiratory/expiratory ratio = 1: 2. Cases in which the respiratory rate was changed concomitantly to improve the operating field after fixing the position for harvesting of the left internal mammary artery were not included in the analysis. The ventilator settings were not changed throughout the study period.
At 5 min after fixing the position for harvesting of the left internal mammary artery, EVH of the saphenous vein was started. EVH was performed using the following technique. A 2-cm transverse linear incision was made medially above the knee. The saphenous vein was identified and elevated with a vessel loop or silk tie. A Guidant VasoView endoscopic harvesting system (Guidant Corporation, Santa Clara, USA) was used. A disposable conical tip was attached to a 7-mm extended-length endoscope, and the endoscope was inserted into the incision. Blunt dissection of the surrounding tissue from the saphenous vein was done toward the groin, whereas CO2 was insufflated into the sealed-off subcutaneous tunnel at a maximum CO2 pressure of 12 mmHg and a flow of 3 l min−1 (Stryker 40L Core Insufflator, Stryker Endoscopy, San Jose, USA). Side branches of the saphenous vein were divided using integrated bipolar electrocautery. After division, a vein cradle was run along the length of the saphenous vein to ensure that it was free from tissue and branches. The saphenous vein was then removed.
Haemodynamic parameters before CO2 insufflation were measured at 5 min after fixing the position for harvesting of the left internal mammary artery. Then, CO2 was insufflated and EVH was performed. Haemodynamic parameters after CO2 insufflation were measured just after the end of EVH. For cases in which the PETCO2 reached 60 mmHg before the end of EVH, the study was ended and the case was not included in the analysis. Temperature was maintained between 36 and 37°C.
The haemodynamic parameters included the mean systemic blood pressure, mean pulmonary artery blood pressure, central venous pressure, heart rate, mixed venous oxygen saturation (SvO2), cardiac index, PETCO2, partial pressure of arterial CO2 (PaCO2), partial pressure of arterial oxygen (PaO2), cerebral oxygen saturation (ScO2), and peak inspiratory pressure (PIP). Blood samples were analysed using with analyzer (Stat Profile Critical Care Xpress Analyzer, Nova Biomedical Corporation, Waltham, USA).
One hundred patients were studied. Statistics were analysed using the program SPSS ver. 11.0 (SPSS, Chicago, IL, USA). The changes in the haemodynamic parameters between before and after CO2 insufflation were compared using the paired t-test. All data were expressed as numbers of patients or the mean ± standard deviation. A value of P < 0.05 was considered statistically significant.
EVH of the saphenous vein was performed in 100 patients (Table 1), and all patients tolerated the procedure well. Mean duration of CO2 insufflation was 29.1 ± 3.5 min. There were no perioperative complications with CO2 insufflation and no cases with PETCO2 exceeding 60 mmHg during CO2 insufflation.
The PETCO2, PaCO2, SvO2, cardiac index, and ScO2 differed significantly between before and after CO2 insufflation (Table 2). By contrast, the mean systemic blood pressure, mean pulmonary artery blood pressure, central venous pressure, heart rate, PaO2, and PIP did not differ significantly between before and after CO2 insufflation.
Our results showed that the PETCO2 and PaCO2 were significantly higher after CO2 insufflation. Subcutaneously insufflated CO2 is absorbed systemically, resulting in hypercarbia . Absorption occurs due to the high solubility of CO2 and its partial pressure gradient between the subcutaneous space and blood . Vitali et al. reported that CO2 insufflation during EVH, at a maximum CO2 pressure of 12 mmHg and a flow of 4 l min−1, did not cause appreciable changes in PETCO2, systemic CO2 absorption, or haemodynamics. Unlike in our study, their method of instrumentation was changed intermittently, which caused the collapse of the cavity, thereby removing CO2 from the subcutaneous space. This probably tended to minimize the effects. Maslow et al. reported that EVH, at a maximum CO2 pressure of 14 to 15 mmHg and a flow of 4 l min−1, caused significant systemic absorption of CO2, as reflected by increases in PETCO2 and PaCO2. They found haemodynamic differences between EVH and open-vein harvesting. However, they also reported that the mean systemic blood pressure, mean pulmonary blood pressure, central venous pressure, and heart rate did not change significantly with CO2 insufflation in EVH, as seen in our study.
Cerebral oximetry monitors continuously regional cerebral perfusion, similar to pulse oximetry [9,10]. It is based on the absorption of infrared light by biological tissues. It employs two wavelengths (730 and 810 nm) to measure changes in the oxygenation of haemoglobin and contains one transmitter and two detectors. It uses mathematical algorithms based on the modified Beer-Lambert law, subtracting the superficial signal from the total signal to give only the value of the deep signal. Consequently, the final ScO2 value will result in a balance between oxygen supply and consumption. Awake preoperative ScO2, in 250 coronary artery bypass grafting surgery patients, ranged from 47 to 83% . Although cerebral oximeter has several limitations of representing regional condition, compared with jugular venous saturation, and technological limitations, it is useful noninvasive monitoring to help identify vulnerable periods during coronary artery bypass grafting surgery, which may require immediate interventions to avoid adverse events.
There is a clear correlation between the extent of coronary artery disease and the incidence of vascular disease . Cerebrovascular accident (CVA) remains one of the most serious complications of coronary artery bypass grafting surgery. The incidence of CVA in coronary artery bypass grafting surgery is 1.6–5.2% . Although OPCAB is supported as a technique for reducing CVA, especially in high-risk patients , cerebral blood flow (CBF) should be maintained to help prevent the occurrence of CVA. The correlation between PaCO2 and CBF is well established [15,16]. Cerebral perfusion increases with the PaCO2. Our results showed significantly increased ScO2 after CO2 insufflation. The SvO2 and the cardiac index also increased after CO2 insufflation in our study, which would be important in increasing ScO2. An increase in PaCO2 may improve the neurological outcome during OPCAB.
There are several studies on severe hypercarbia during EVH [5,17]. Severe hypercarbia is a potential complication during laparoscopic surgery. It is more likely to occur in extraperitoneal surgery than in intraperitoneal surgery because insufflated CO2 gas can easily diffuse into the surrounding tissues . If the internal mammary artery is harvested simultaneously, the decreased minute ventilation used to improve the operating field will aggravate the hypercarbia. This results in a greater degree of acidosis, because physiological buffering systems are unable to cope. The studies on severe hypercarbia during EVH showed PaCO2 above 60 mmHg and pH below 7.20 [5,7,17]. Therefore, we intended to end the study and change the ventilator settings for patient's safety when the PETCO2 reached 60 mmHg after CO2 insufflation. There were no cases with PETCO2 exceeding 60 mmHg after CO2 insufflation in this study.
The mean maximum PaCO2 is 67 mmHg in permissive hypercarbia for protective lung ventilation strategies . Although permissive hypercarbia is intended to avoid the deleterious effects of high lung stretch , it can be applied in EVH of the saphenous vein for OPCAB. In an animal study, assessed by rabbit ear chamber (REC) methods, permissive hypercarbia (PaCO2, around 60 mmHg) increased the arteriolar diameter (121.6 ± 7.1%) and blood flow velocity (134.5 ± 11.3%) compared with normocarbia (PaCO2, 40 mmHg) as a control (100%) . Hypercarbia also increased the oxygen-carrying capacity of blood in an animal study . These results support the postulate that hypercarbia after CO2 insufflation in EVH for OPCAB increases cerebral oxygenation.
Hypercarbia is associated with increased catecholamines and increased systolic blood pressure, pulmonary artery pressure, heart rate, and cardiac output [23–26]. Nevertheless, in an animal study, the systemic blood pressure and cardiac output remained unchanged, whereas the heart rate increased and stroke volume decreased . Our results showed that the SvO2 and cardiac index were significantly higher after CO2 insufflation, without increasing the blood pressure or heart rate. For the induction and maintenance of anaesthesia, high-dose remifentanil was used. This might have been associated with a decrease in blood pressure and heart rate. In addition, the demographic data showed that our patients had taken beta blockers (50%), calcium channel blockers (43%), and nitroglycerin (40%). The administration of these medications might have attenuated the increase in blood pressure and heart rate, although this needs more investigation.
Our study had two considerations. First, additional measurements, when PETCO2 or PaCO2 returned to baseline values (before EVH of the saphenous vein), would make constant results. We had essentially intended this but faced several limitations. Just after EVH of the saphenous vein, harvesting of the left internal mammary artery was simultaneously ended and revascularization was performed using stabilizer. In animal study, time from peak PaCO2 after CO2 insufflation to baseline PaCO2 (from 68.3 to 41.8 mmHg) was about 120 min . Namely, we did not have enough time. If we evaluated haemodynamics during revascularization using stabilizer, the haemodynamics could be influenced by many biases. Second, could tolerable range of hypercarbia increase intracerebral pressure (ICP)? Hypercarbia increases CBF and ICP. Increased ICP can influence the neuropsychological outcomes during coronary artery bypass grafting surgery. Hino et al. reported that permissive hypercapnia increased CBF but was neurologically unaffected. Cardenas et al. reported that acute hypercapnia, induced within 1 h, was associated with significant increases in cardiac output, organ blood flow and ICP, and these changes could be significantly attenuated by correction of blood pH without adverse effects on haemodynamics. Mean PaCO2 after CO2 insufflation was 52.5 mmHg and pH was not below 7.2 in our study. Therefore, we could assume that increase of ICP was minimal or ignorable after CO2 insufflation, and could not influence the adverse effects of neuropsychological aspects. However, cerebral perfusion pressure is that ICP is subtracted from mean systemic blood pressure. Our study showed steady mean systemic blood pressure. Theses results need more investigations.
In conclusion, EVH, at a maximum CO2 pressure of 12 mmHg and a flow of 3 l min−1, of the saphenous vein for OPCAB was associated with hypercarbia and a tolerable range of hypercarbia (PaCO2 < 60 mmHg) increased the cardiac index and ScO2 without any complications.
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