Nowadays, VC mode is mostly used for ventilation in surgical operation. However, in the case of single-lung ventilation in VATS pulmonary segmentectomy, some patients may suffer from excessive airway pressure due to poor lung compliance and high airway resistance on the ventilated side. Therefore, protective pulmonary ventilation strategy should be adopted, that is, neap volume (4–6 mL/kg) combined with low level PEEP (usually 5 cm H2O) [2, 3]. This strategy avoids excessive airway pressure to a certain extent, but there are still a few patients suffered high airway pressure under the condition of good position of double-lumen tubes༻7༽. High airway pressure could lead to increased alveolar pressure, which can reduce the amount of blood returned to the heart and then cause a drop in blood pressure [4, 7]. Meanwhile, it can also induce airway injury, leading to acute lung injury and postoperative pulmonary complications.
In the traditional VC mode, the ventilator relies on preset tidal volume, inspiratory time and breathing frequency to ensure the patient's ventilation volume, and the size of the airway pressure is mainly affected by the patient's airway resistance and lung compliance [8]. In order to achieve the preset tidal volume, the alveolar ventilation of lung tissues with different compliance is uneven, which is likely to cause structural damage of lung parenchyma and pulmonary mesenchyme, leading to airway injury [9]. According to the lung protective ventilation strategy, the goal of ventilation management is to minimize ventilator-associated lung injury, and PRVC mode is well consistent with this strategy [10, 11]. On the basis of ensure the preset tidal volume and respiratory function of automatic continuous monitoring lung compliance and volume/pressure relationship, PRVC ventilation mode reduce airway pressure as much as possible, so as to reduce the pressure of the positive pressure ventilation [12]. PRVC ventilation for the first time for experimental ventilation, inspiratory pressure is low (5 cm H2O). The lung compliance and inspiratory pressure to reach the preset tidal volume was calculated by the microcomputer measure. The actual inspiration pressure of the next ventilation is 75% of the above calculated value. After several ventilation, the actual tidal volume can be consistent with the preset tidal volume [13, 14]. Since the waveform of inspiratory velocity is a deceleration wave, the vortex of gas can be reduced when the patient's airway resistance is large, so the pressure consumption and peak inspiratory pressure can be reduced while the preset tidal volume is ensured [15]. It has been reported that PRVC mode can better meet the requirement of tidal volume during mechanical ventilation and reduce the airway pressure as well as lung complications༻16༽.
In this study, the changes of respiratory mechanics, oxygenation index and respiratory mechanics under different ventilation modes in one-lung-ventilation were compared by using cross design method. The results indicated that, when using PRVC mode for ventilation, not only the airway pressure level was significantly lower than that of VC mode, but also the pulmonary static compliance was significantly higher than that of VC mode. In addition, the detection of inflammatory indicators in the lung showed that the levels of TNF-, IL-6, IL-8 and IL-10 from BALF in the PRVC group were significantly lower than those in the VC group, suggesting that excessive airway pressure may lead to the structural destruction of lung tissue with poor compliance, thus causing airway injury. This result is consistent with the results of related literatures [17–20] .
There was no significant difference in heart rate, blood pressure, oxygenation index and incidence of postoperative pulmonary complications between the two groups (P > 0.05) (Table 3). Further analysis shows, 9 cases of postoperative non-infectious acute lung injury (both in VC-group) with intraoperative airway pressure for a long time was up to 30 cm H2O, which may be important reasons of these patients appear postoperative respiratory dysfunction. Therefore, the use of intraoperative protective ventilation strategy to reduce the airway pressure is of great significance.
Table 3
pulmonary complications and length of hospital stay between groups
Variable | Group -VC | Group -PRVC | P value |
Respiratory dysfunction | 2 | 1 | > 0.05 |
pulmonary infection | 3 | 2 | > 0.05 |
Pulmonary atelectasis | 4 | 2 | > 0.05 |
Acute lung injury | 6 | 2 | > 0.05 |
Re-intubation | 1 | 0 | > 0.05 |
ICU stay t/d (x ± s) | 1.9 ± 0.7 | 1.3 ± 0.5 | 0.045 |
Hospital stay t/d (x ± s) | 7.6 ± 1.5 | 5.4 ± 1.2 | 0.03 |
In a conclusion, PRVC model has the advantages of lowering airway pressure and improving lung compliance, which could reduce the single lung ventilation during acute lung injury caused by high pressure. Therefore, PRVC mode is a good choice for patients with poor pulmonary ventilation function in VATS pulmonary segmentectomy (such as chronic bronchitis, COPD, etc.) during the operation, especially for single-lung ventilation.