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Ann Thorac Surg 1999;68:29-32
© 1999 The Society of Thoracic Surgeons

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Original Articles

Hemodynamic effects of carbon dioxide insufflation under single-lung ventilation during thoracoscopy

^a Department of Cardiothoracic Surgery, University of Tokyo, Tokyo, Japan

Address reprint requests to Dr Ohtsuka, Department of Cardiothoracic Surgery, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655 Japan
e-mail: ohtsuka-tho{at}h.u-tokyo.ac.jp

	Abstract

Top Abstract Introduction Material and methods Results Comment References

 
Background. The hemodynamic effects of carbon dioxide insufflation under single-lung ventilation were studied in 22 consecutive thoracoscopic harvests of the left internal mammary artery, which was used for minimally invasive coronary artery bypass grafting.

Methods. An electrocardiograph, arterial catheter, Swan-Ganz catheter, and transesophageal echocardiograph were used to monitor seven hemodynamic variables. Baseline data were obtained during ventilation of both lungs and the measurements were repeated after the left lung was collapsed and at 5 and 30 minutes after hemithorax insufflation with low-flow (2 to 3 L/minute) carbon dioxide gas was begun. The intrapleural pressure was maintained at 8 to 10 mm Hg.

Results. Thoracoscopic harvest of the internal mammary artery was completed in all cases with a mean insufflation time of 44 ± 12 minutes. There were no significant changes in the mean arterial pressure, heart rate, cardiac index, and left ventricular ejection fraction throughout the procedure, whereas the central venous pressure, mean pulmonary arterial pressure, and pulmonary capillary wedge pressure (p < 0.05 for each variable) during insufflation.

Conclusions. Low-flow carbon dioxide insufflation into the left hemithorax with an intrapleural pressure of 8 to 10 mm Hg under selective right-lung ventilation does not compromise the human heart with normal to moderately depressed function and can be an efficacious adjunct in specific thoracoscopic procedures.

	Introduction

Top Abstract Introduction Material and methods Results Comment References

 
Carbon dioxide insufflation was developed for laparoscopy and has proved to be a safe, efficacious technique that allows the creation of an intraabdominal space for operative procedures [1, 2]. Insufflation rarely has been used for thoracoscopy with selective single-lung ventilation, which involves the complete collapse of one lung [3, 4]. There are few reports of the hemodynamic impact of intrapleural insufflation in the clinical setting [5].

We used insufflation to facilitate the thoracoscopic harvest of the internal mammary artery (IMA) with single-lung ventilation in patients who had minimally invasive coronary artery bypass grafting. We studied the effects of insufflation on human hemodynamics during thoracoscopic IMA harvest.

	Material and methods

Top Abstract Introduction Material and methods Results Comment References

 
Since August 1997, thoracoscopic harvest of the left IMA was performed for 22 consecutive patients who had minimally invasive coronary artery bypass grafting to the left anterior descending artery, which was a single or culprit vessel causing angina pectoris. Eighteen (81.8%) of the patients were men. The mean age was 71.5 ± 6.5 years. In most of the patients, left ventricular function had been mildly to moderately impaired because of occlusive coronary artery disease. Preoperative pulmonary function was within normal limits in all but 1 patient with previous segmentectomy of the right lung, in whom forced expiratory volume in 1 second (2.0 L, 60% of predicted) was mildly impaired. All protocols were reviewed and approved by the internal review board for human studies.

All patients were intubated with a double-lumen endotracheal tube (Broncho-Cath, Mallinckrodt Medical, Athlone, Ireland) for selective right-lung ventilation. The patients were placed in the 30-degree right lateral decubitus position, and their left upper arm was abducted for extensive exposure along the left axilla to the lateral chest wall. General anesthesia was induced with propofol (1 to 2 mg/kg), fentanyl (20 to 40 µg/kg), and vecuronium, and was maintained using fentanyl (20 to 40 µg/kg) and inhalation of isoflurane (1% to 2%) in oxygen, together with infusion of propofol (1 to 2 mg/kg per hour) in some cases. In each case, nitroglycerin (0.5 to 1.0 µg/kg per hour) was infused continuously throughout the procedure. No ß-blocking agents were used during thoracoscopic IMA harvest. Selective mechanical ventilation was done for the right lung, maintaining a tidal volume from 6 to 8 mL/kg and a positive end-expiratory pressure from 3 to 5 cm H₂O.

The electrocardiograph leads were placed in the usual fashion. The intraarterial pressure was measured continuously via a right radial artery catheter. A Swan-Ganz pulmonary catheter was introduced into the right jugular vein and was advanced into the pulmonary artery until the pulmonary capillary wedge pressure was obtained. A transesophageal echocardiograph probe was introduced orally, and was advanced until the left ventricle could be viewed distinctly. The mean arterial pressure, heart rate, central venous pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, cardiac index, and left ventricular ejection fraction were obtained. The cardiac index was determined by the thermodilution technique using three values within 10% of each other. No more than five values were obtained at each measurement. The left ventricular ejection fraction was assessed in the cross-sectional long-axis view obtained by transesophageal echocardiography. The left ventricular volumes in the end-systolic and end-diastolic phases were calculated using the area-length method by measuring the traced areas of the left ventricle and the distances from the posterior aortic root to the apex. Baseline data of the seven variables were recorded just after positioning of the patients while both lungs were ventilated, and then selective right-lung ventilation was started. After preparing the patient and positioning the drapes, a 10-mm port was positioned at the forth or fifth intercostal space on the anterior axillary line, and the left hemithorax was investigated thoracoscopically using a rigid 30-degree endoscope (A5282A, Olympus, Tokyo, Japan). The hemodynamic variables were recorded again when it was confirmed thoracoscopically that the left lung had been collapsed satisfactorily, and then insufflation with carbon dioxide was started. A low flow of gas, of 2 or 3 L/minute, was delivered into the left pleural space through the side orifice of a port or an access needle. The insufflator (UHI; Olympus, Tokyo, Japan) was capable of regulating the gas flow and maintaining a constant positive pressure in the closed space. Two 5-mm ports, for the working instruments, were positioned in the third and fourth intercostal spaces on the posterior axillary line (Fig 1). Each port had a valve or diaphragm so that sufficient pressure could be maintained in the cavity during insufflation. A pedicle of the left IMA was harvested thoracoscopically, while the left lung remained collapsed and with a pleural pressure of 8 to 10 mm Hg. A thoracoscopic technique of the IMA harvest has been described elsewhere [6]. In the present series, this procedure was performed by the first author (T. O.). Values of the seven hemodynamic variables were recorded 5 and 30 minutes after insufflation was started.

View larger version (136K): [in this window] [in a new window]   Fig 1. Photograph showing instruments and port placements for thoracoscopic harvest of the left internal mammary artery. A 30-degree rigid scope (left) in fifth intercostal space on the anterior axillary line, endoscopic dissector (middle), and ultrasonic coagulator (right) in the fourth and third spaces on posterior catheter were used, and carbon dioxide was delivered through tube (arrowhead) connected to the side orifice of the port.

	Results

Top Abstract Introduction Material and methods Results Comment References

 
Thoracoscopic left IMA harvest was completed in all patients by using continuous carbon dioxide insufflation under selective single-lung ventilation. The mean insufflation time was 44 ± 12 minutes. No specific attempt was made in each patient to prevent hemodynamic changes due to insufflation; volume expanders and inotropic agents were not administered.

The electrocardiograph data showed that no arrhythmias or ischemic changes were induced in any patients while the hemithorax was insufflated. The hemodynamic changes detected during thoracoscopic IMA harvest are shown in Table 1. In comparison with the baseline data, central venous pressure, mean pulmonary arterial pressure, and pulmonary capillary wedge pressure increased significantly during insufflation (p < 0.05 for each variable). Compared with the increase in central venous pressure, the increase in pulmonary capillary wedge pressure was mild. Conversely, the values of mean arterial pressure, heart rate, cardiac index, and left ventricular ejection fraction showed no significant changes throughout the procedure. The short-axis cardiac views obtained by transesophageal echocardiography showed that the left ventricle was shifted backward and slightly compressed during insufflation.

	Comment

Top Abstract Introduction Material and methods Results Comment References

 
Currently, insufflation is seldom required for thoracoscopy unless selective single-lung ventilation is impractical or imperfect. Some surgeons might use insufflation for thoracoscopy as an adjunct to promote deflation of the emphysematous pulmonary tissue trapping much air. In our experience, insufflation is rarely used in thoracoscopic surgery except during specific procedures.

In minimally invasive coronary artery bypass grafting, compared with the direct procedure via a small anterior thoracotomy, thoracoscopy allows higher dissection of the left IMA, and the harvest procedure is facilitated by insufflation of the hemithorax [6, 7]. The IMA lies longitudinally along the sternum at the medial margin of the pleural cavity and access to it is obtained by the thoracoscopic approach through a limited space between the anterior chest wall and the mediastinum. This marginal pleural space is narrow, particularly in patients with cardiomegaly and in patients who had previous sternotomies. Insufflation allows enlargement of this space by pushing the mediastinum backward along the aortic arch to the heart, as well as pushing the mediastinal septum contralaterally. Insufflation also improves visualization of the IMA through the pleura by expanding the whole pleural cavity; the IMA itself or its pulsation can be perceived directly through the stretched parietal pleura overlying the IMA. In the present series, a positive insufflation pressure of 8 to 10 mm Hg enabled us to have an excellent view and sufficient room for the thoracoscopic IMA harvest. We used an ultrasonic coagulator to dissect the IMA. This device generates minimal smoke during coagulation so smoke evacuation was unnecessary throughout the procedure [6, 8].

To reduce gas leakage around the port, we recommend using screw-in type ports, which can be placed tightly in the intercostal spaces. Moreover, positioning of ports at the best places and in the correct direction is important to minimize the leakage. Instrument movement is minimized through appropriately placed ports, and the ports can stay stably in the intercostal spaces. In our clinical experience, although gas flow was slightly increased temporarily in some patients to compensate for minor leakage, a constant positive intrapleural pressure of 8 to 10 mm Hg was maintained in all the patients during 40 minutes of the IMA harvest procedure.

It has been reported previously that insufflation with single-lung ventilation increases central venous pressure, while mean arterial pressure and heart rate remain stable [5]. Those findings agree with our data collected during a specific procedure that was performed consistently by a single surgeon and with the patients in the same position. The present data also demonstrate stable cardiac function throughout the procedure. The observed increases in the values of central venous pressure, mean pulmonary artery pressure and pulmonary capillary wedge pressure were most likely caused by the artificial positive intrapleural pressure, as well as by hypoxic vasoconstriction in the collapsed pulmonary parenchyma.

Hill and colleagues [9] reported adverse effects of hemithorax insufflation with one-lung ventilation in pigs and suggested that thoracotomy was preferable to a thoracoscopic approach in cases requiring insufflation. Their experimental study was done in the right hemithorax in a porcine model, whereas the left hemithorax was insufflated in our clinical study. In comparison with the left side of the heart, the right side has lower pressures and might be more susceptible to the positive insufflation pressure; direct compression by gas against the venae cava and the right atrium and ventricle could cause significant reduction of venous return and greater hemodynamic damage. Anatomic differences between humans and pigs might be another reason why the effects of insufflation on hemodynamics were different. Compared with human mediastinal anatomy, the heart and other components in the porcine mediastinum hang down in the thoracic cavity and the connective tissues are thinner. Therefore, the hemodynamics of the porcine heart can be affected seriously by the positive insufflation pressure, whereas in humans the effects on cardiac function are less marked.

In our clinical experience with insufflation during thoracoscopy, rapid delivery of carbon dioxide into the chest cavity was dangerous and caused significant reduction of heart rate and arterial pressure. Hemodynamic effects of prolonged insufflation or intrapleural pressure greater than 10 mm Hg are unknown in humans. Further investigation and clinical studies should be done to determine safe and efficacious ranges of duration, flow velocity, and pressure setting of insufflation into the hemithorax.

In conclusion, the human heart with normal to moderately depressed left-ventricular function can tolerate about 40 minutes of low-flow (2 to 3 L/minute) carbon dioxide insufflation into the left hemithorax with an intrapleural pressure of 8 to 10 mm Hg with selective right-lung ventilation. Most thoracoscopic procedures, however, can be accomplished without insufflation under satisfactory single-lung ventilation. Insufflation-related complications during endoscopy, which were serious and even fatal, have been reported [10–12]. Nevertheless, insufflation can be a vital, efficacious adjunct for thoracoscopy in specific procedures or circumstances. In such cases, insufflation should be performed meticulously with sufficient hemodynamic monitoring.

	Acknowledgments

 
We are grateful to many anesthesiologists from the University of Tokyo Hospital, the Toranomon General Hospital, the Asahi General Hospital, and the Kyorin University Hospital, Tokyo and Asahi Japan, for their collaboration in collecting the clinical data.

	References

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Toshiya Ohtsuka Tadasu Kohno Jun Nakajima Yutaka Kotsuka Shinichi Takamoto Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ohtsuka, T. Articles by Takamoto, S. Search for Related Content PubMed PubMed Citation Articles by Ohtsuka, T. Articles by Takamoto, S. Related Collections Related Article