Impact of One-Lung Ventilation on Oxygenation and Ventilation Time in Thoracoscopic Heart Surgery: A Comparative Analysis with Median Thoracotomy

Introduction

In the 1990s, Chitwood et al completed the world’s first thoracoscopic heart valve replacement operation, initiating the application of thoracoscopic technology in heart surgery [1]. Many heart operations, including valve replacement and valvuloplasty, require very precise operation [2]. Thoracoscopy can not only provide a stable and reliable light source, but can also help the surgeon accurately identify and separate various micro-tissues [3]. All of these advantages make the thoracoscopic treatment of valvular heart disease gradually accepted and recognized by an increasing number of people.

Minimally invasive thoracoscopic cardiac surgery has the advantages of a small incision, preservation of the integrity of the thorax, reduced postoperative pain, and rapid recovery [4]. Presently, many large and medium heart centers in China have conducted thoracoscopic cardiac surgery. According to preliminary statistics in 2016, there were more than 10 000 cases of thoracoscopic cardiac surgery in China [5]. A typical thoracoscopic cardiac surgery requires double lumen endotracheal intubation and one-lung ventilation outside of cardiopulmonary bypass, to ensure a good surgical field on the right side. One-lung ventilation has been shown to have a certain effect on lung function [6].

One-lung ventilation is the separation of the lungs by mechanical methods to allow ventilation of only one lung, particularly when pathology, such as malignancy, involves a single lung. One-lung ventilation has been proven to have a certain impact on lung function. Piccioni et al [7] reported that one-lung ventilation could result in a low incidence of acute respiratory distress syndrome and comparable postoperative complications in adult patients undergoing elective lung resection. The most common postoperative complications after cardiopulmonary bypass are pulmonary dysfunction and diseases of the respiratory system [8–10]. Questions remain, however, including whether one-lung ventilation and thoracoscopic cardiac surgery have a greater impact on lung function, and whether its associated postoperative pulmonary complications are more severe. Therefore, this retrospective study of a single center aimed to compare 49 patients undergoing thoracoscopic cardiac surgery using one-lung ventilation with 48 patients undergoing thoracoscopic cardiac surgery with median thoracotomy.

Material and Methods

ETHICS COMMITTEE APPROVAL:

This study was approved by the Ethics Committee of Chongqing General Hospital (approval No. S2019-033-01). All patients provided their written informed consent to participate in this study.

PATIENTS:

A total of 49 patients undergoing adult heart surgery with one-lung ventilation thoracoscopy in our hospital from January 5, 2018, to March 1, 2019, were selected as the experimental group (n=49). In addition, 48 patients undergoing adult heart operation with median thoracotomy in the same period were selected as the comparison group (n=48; Table 1). The one-lung ventilation thoracoscopic cardiac surgery and positive end-expiratory pressure were performed according to a previous study [11].

The inclusion criteria were as follows: (1) patients undergoing heart surgery (one-lung ventilation thoracoscopic cardiac surgery or median thoracotomy heart operation), and (2) patients with complete preoperative and postoperative data.

The exclusion criteria were as follows: (1) preoperative chronic obstructive pulmonary disease, preoperative arterial blood gas PO₂ <60 mmHg; (2) grade IV preoperative cardiac function, left ventricular ejection fraction <35%; (3) difficulty in operation or cardiopulmonary bypass time >360 min; (4) reopening and hemostasis due to bleeding after the operation; (5) difficulty in postoperative rebound, low cardiac output syndrome, or use of auxiliary devices; and (6) conversion from thoracoscopic operation to median thoracotomy.

ANESTHESIA METHODS:

Anesthesia was induced by administering midazolam 1 to 2 mg, etomidate 0.3 mg/kg, atracurium cis-benzenesulfonate 0.15 mg/kg, and sufentanil 0.8 to 1.2 UG/kg. After induction, patients in the comparison group were placed on a single lumen trachea catheter, while the patients in the experimental group were placed on a double lumen trachea catheter (left branch), and depth was adjusted with a fiberbronchoscope. The right internal jugular vein was placed into a superior lumen drainage tube.

Anesthetization was performed by continually injecting 1% propofol at a dose of 2 mg/kg/h, and intermittently administering sufentanil, atracurium cis-benzenesulfonate, and inhaled sevoflurane to maintain the appropriate depth of anesthesia. After tracheal intubation, patients in both groups underwent intermittent positive pressure ventilation, with a tidal volume of 6 to 8 mL/kg, frequency of 10 to 12 times/min, inhaled oxygen concentration of 60%, and end-expiratory carbon dioxide partial pressure of 35 to 45 mmHg.

CARDIOPULMONARY BYPASS:

In the experimental group, the catheterization of the right jugular vein and catheterization of the femoral vein were used to drain the vena cava, and the catheterization of the femoral artery was used as an artery pump tube to block the superior and inferior vena cava in the pericardium. The comparison group was intubated by the superior and inferior vena cava and the ascending aorta in the pericardium to establish cardiopulmonary bypass, using a heart-lung machine system (LivaNova Deutschland GmbH, Germany) and membrane oxygenator (Medtronic, Inc, USA). In the experimental group, cardiopulmonary bypass was started before the incision of the open heart bag and stopped after the incision of the heart and chest wall completely stopped bleeding. In the comparison group, cardiopulmonary bypass was started and stopped. In both groups, 20 mg of dexamethasone was added before cardiopulmonary bypass, but no ulinastatin was used. The rapid BLS blood filter was used after shutdown.

Furthermore, during cardiopulmonary bypass, continuous positive airway pressure (5–10 cmH2O), or low tidal volume (3–5 mL/kg) plus low positive end-expiratory pressure (5 cmH2O) were applied to reduce the inflammatory response of the extracorporeal circulation and protect postoperative pulmonary function [12].

OPERATIVE METHODS:

In the experimental group, the right side was raised 15° to 20° in the supine position, and the endoscopic hole was located at the sixth intercostal space between the axillary front line. The main operation hole was located at the fourth intercostal space between the right clavicular midline and the axillary front line. The auxiliary operation hole was located at the fourth intercostal space between the axillary front line. For the comparison group, the sternum was split, and the pericardium was suspended to complete the operation.

OBSERVATION INDEX:

After the operation, the patients were transferred to the Intensive Care Unit (ICU), and the blood gas analysis data were recorded immediately and at 4 h, 8 h, 12 h, and 16 h after the operation. Then, the tracheal intubation was pulled out, and the use time of the ventilator was recorded. The ventilator was operated in the patients according to the weaning systems as the instrument instructions.

STATISTICAL ANALYSIS:

In this study, SPSS 21.0 software was used for analysis, and multivariate analysis of variance (ANOVA) was used to analyze the data. The biases and confounding factors were excluded with the logistic regression modeling method. A P value less than 0.05 was considered statistically significant.

Results

NO DIFFERENCES IN OXYGENATION INDEX WERE DISCOVERED BETWEEN THE EXPERIMENTAL AND COMPARISON GROUPS:

The results of the blood gas analysis showed that there was no significant difference in the immediate oxygenation index between the experimental group and the comparison group (Table 1, P>0.05). Meanwhile, in both the experimental group and comparison group, there were no significant differences in the immediate oxygenation index between men and women (Table 1, P>0.05).

CARDIOPULMONARY BYPASS TIME AFFECTED THE OXYGENATION INDEX:

The findings of the multivariate ANOVA indicated that the cardiopulmonary bypass time significantly affected the immediate oxygenation index after the operation (Table 2, F=7.200, P=0.009).

TREND OF FITTING CURVE OF POSTOPERATIVE OXYGENATION INDEX:

The fitting curve of the oxygenation index of the experimental group (Figure 1A) and the comparison group (Figure 1B) was drawn immediately, and at 4 h, 8 h, 12 h, and 16 h after surgery. According to the findings of the blood gas analysis, the curve indicated that the oxygenation index of the comparison group decreased at 8 h after the operation, while that of the experimental group increased slightly at 8 h after the operation; however, there were no statistically significant differences between the 2 groups (Figure 1, P>0.05).

INFLUENCE FACTORS FOR POSTOPERATIVE VENTILATOR USE TIME:

The results of ANOVA of postoperative ventilator use time showed that operation mode (experimental group and comparison group) significantly affected the postoperative ventilator use time (Table 3, F=8.337, P=0.005). The findings of ANOVA also showed that cardiopulmonary bypass time (Table 3, F=16.002, P=0.000) and age (Table 3, F=4.384, P=0.039) significantly affected the use of ventilator time after the operation. However, sex (Table 3, F=0.75, P=0.389) had no significant effect on ventilator use time.

Discussion

The present findings showed that there was no significant difference in the immediate oxygenation index between the experimental group and the comparison group and between men and women in both groups. Cardiopulmonary bypass time affected the oxygenation index. Operation methods (one-lung ventilation or median thoracotomy) affected postoperative ventilator use time. Cardiopulmonary bypass time and age significantly affected ventilator use time. However, there was no significant effect of sex on ventilator use time. The one-lung ventilation thoracoscopic cardiac surgery demonstrated better clinical outcomes than did traditional median thoracotomy cardiac surgery.

With the development of minimally invasive thoracoscopic surgery, thoracoscopic technology has been widely used in lobectomy, esophageal surgery, mediastinal surgery, and heart surgery [13]. One-lung ventilation is usually needed in thoracoscopic surgery, providing a good operating field and operating space, especially for heart surgery. When thoracoscopic single-lung ventilation is used to cut open the heart bag, the right lung collapses as well, which can avoid damaging the lung tissue. After cardiopulmonary bypass, complete hemostasis is the key to the operation of the whole heart. Good right lung collapse can help doctors thoroughly check and stop bleeding. One-lung ventilation is the exposure to thoracic surgery through double lumen endotracheal intubation or a bronchial blocker. During one-lung ventilation, the collapsed side of the lung will lack oxygen due to the lack of ventilation and oxygen exchange. However, hypoxia will lead to pulmonary vasoconstriction and the flow from the collapsed side will flow to the ventilating side. The results showed that the pulmonary blood flow on the operative side represented 40% of the total pulmonary blood flow and the pulmonary blood flow on the ventilating side represent 60% [14]. As a result of hypoxia and a series of inflammatory interstitial reactions, the flow of the collapsed side of the lung is diverted by at least 40% to 50% to the pulmonary vessels on the ventilating side to correct the state of hypoxia [15]. The mechanism of one-lung ventilation on lung injury is complex and multifactor [9]. The question of how to reduce lung injury caused by one-lung ventilation has always been the focus of research on one-lung ventilation [16]. The lung protection method of one-lung ventilation is still improving. Some researchers have proposed that the pressure control ventilation mode is better than the volume control mode when one-lung ventilation is used [17]. Some researchers also suggested that when one-lung ventilation is used, the oxygen catheter is put into the collapsed side of the lung, and the oxygen input lasts for 3 L/min, which will obviously improve the hypoxic attack during the operation and reduce postoperative lung complications [12].

Although cardiopulmonary bypass materials continue to improve, acute lung injury after cardiopulmonary bypass is still the most common complication [18]. The clinical manifestations of postoperative pulmonary dysfunction are atelectasis, pleural effusion, lower respiratory tract infection, symptomatic or asymptomatic hypoxemia, and adult respiratory distress syndrome. According to some reports, the rate of pulmonary complications after cardiopulmonary bypass ranges from 10% to 25% [19,20]. One study [21] showed that even in cardiopulmonary bypass without severe cardiac dysfunction, postoperative pulmonary function will continue to be affected for weeks or longer. The incidence of adult respiratory distress syndrome after cardiopulmonary bypass is as high as 0.6% to 20%. Once adult respiratory distress syndrome occurs, the mortality rate is as high as 80% [22]. Similarly, 43% of patients who returned to the ICU after cardiopulmonary bypass return due to postoperative respiratory dysfunction [23]. The causes of lung injury in cardiopulmonary bypass include the following: lung injury caused by cardiopulmonary bypass, lung injury caused by blood transfusion, lung injury caused by mechanical ventilation, and lung injury caused by cardiac insufficiency. During cardiopulmonary bypass, a series of factors, such as hemodilution, excessive volume load, hypoxia, systemic heparinization, continuous non-pulsating blood flow, and blood contact with the surface of the external pipeline, will activate the cascade of human inflammatory media, produce a large number of inflammatory media, and affect postoperative pulmonary function [24,25]. Less postoperative volume load is helpful for the recovery of lung function [26]. During cardiopulmonary bypass, the complete disconnection of mechanical ventilation can well expose the field of cardiac surgery. However, during cardiopulmonary bypass, 5 to 10 cmH2O of continuous positive airway pressure or low tidal volume of 3 to 5 mL/kg plus low positive end-expiratory pressure of 5 cmH2O can reduce the inflammatory response of extracorporeal circulation and protect postoperative lung function [12]. Mechanical ventilation before and after cardiopulmonary bypass can also significantly affect pulmonary function after cardiac surgery. A previous study [27] showed that protective mechanical ventilation strategies with low intraoperative volume of 6 to 8 mL/kg, positive end-expiratory pressure, lung recruitment technique, and an air oxygen ratio (FiO2) less than 80% can significantly reduce surgery mortality, incidence of postoperative pulmonary complications, and postoperative hospital stay.

In the present study, the factors influencing lung function after minimally invasive heart surgery with one-lung ventilation and cardiopulmonary bypass were observed. The results showed that cardiopulmonary bypass time had a significant effect on the oxygenation index of blood gas (F=7.200, P=0.009). However, one-lung ventilation did not have a significant effect on the blood gas oxygenation index (F=0.234, P=0.630). In contrast, minimally invasive surgery with one-lung ventilation significantly reduced postoperative mechanical ventilation use time (F=8.337, P=0.005), which can be related to the pain relief after minimally invasive surgery. However, traditional open heart surgery, due to the pain that limits patient early activity, deep breathing, and coughing, will increase the incidence of postoperative pulmonary complications [28]. Our results showed that minimally invasive one-lung ventilation thoracoscopy did not increase the incidence of postoperative pulmonary complications and did not prolong the postoperative mechanical ventilation time, which is consistent with the report of Piccioni et al [7]. However, Piccioni et al found that only lung ventilation resulted in a significantly lower incidence of complications; however, the present study showed no increase in complications. Marongiu et al [29] found that the pathophysiological changes in cardiac and respiratory functions caused by one-lung ventilation are difficult to predict and have suggested making a personalized mechanical ventilation and prompting the use of advanced monitoring methods. However, the present study did not make attempts to monitor pathophysiological changes. Furthermore, our findings showed that one-lung ventilation had a shorter surgery time, while Piccioni et al [7] showed a shorter hospital length of stay and lower mortality. Therefore, the present study has made up for the shortcomings of the previous literature in certain aspects. Furthermore, sex did not affect the postoperative oxygenation index and postoperative mechanical ventilation use time. Age did not have an effect on the postoperative oxygenation index, but affected postoperative mechanical ventilation use time. There results suggest that age might be an influencing factor for mechanical ventilation use time.

This study had some limitations. First, the diffusing capacity of the lung for carbon monoxide was not performed before and after surgery in the lung examination laboratory to obtain full assessment of the gas exchange. Second, one-lung ventilation thoracoscopic cardiac surgery, although it does not change oxygen parameters, may cause changes in lung tissue, which is observed in postoperative imaging and results from the surgical technique, manipulation, and compression of the lung tissue causing local perfusion problems. However, this study did not determine lung injury, such as with postoperative lung X-ray examination. Third, there are no data on surgical treatment and postoperative complications. Fourth, we attempted to reduce the biases and confounding factors with the logistic regression modeling method. However, we involved only a few potential exposure factors when modeling, which may have affected the reduction of biases and confounding factors. Fifth, in this study, it is hard to determine if just a median thoracotomy causes enough damage to cause the above results rather than just single lung ventilation being as adequate. In future investigations, we will conduct an investigation to clarify the effects of median thoracotomy and one-lung ventilation on lung functions.

Conclusions

This study showed that one-lung ventilation thoracoscopic cardiac surgery did not affect the immediate postoperative oxygenation index; however, cardiopulmonary bypass time did significantly affect the immediate postoperative oxygenation index. At the same time, one-lung ventilation thoracoscopic cardiac surgery demonstrated a shorter postoperative mechanical ventilation time than did traditional median thoracotomy cardiac operation. Therefore, one-lung ventilation thoracoscopic cardiac surgery could improve lung function after the operation. We will endeavor to improve the operative process of one-lung ventilation thoracoscopic cardiac surgery and increase its clinical application.