This survey indicates that most centers in Taiwan employ DLT for separated lung ventilation. Arterial catheter and BIS are the commonly used perioperative monitoring systems, and 50% of these centers consider IVPCA for postoperative pain control. During OLV, most thoracic anesthesiologists recommended high oxygen fraction supplement (FiO2>80%) and ventilated the patients with a tidal volume of 6–8 ml/kg/PBW and a PEEP of 2–6 cmH2O using the dual-controlled mode. A PIP less than 30 cmH2O is considered the threshold to avoid barotrauma. Most thoracic anesthesiologists try to maintain relatively normal levels of CO2 and SpO2 during OLV. Manual hand squeezing method is more often used for lung recruitment at the end of operation. The Taiwanese thoracic anesthesiologists urge for an international practice guideline for protective lung ventilation during OLV.
One similar nationwide survey was reported by the Italian group in 2013. Consistent with our survey, 96% of the Italian centers used a DLT as the first choice for intraoperative lung separation . A total of 39% of the Italian centers recommended epidural analgesia for postoperative pain management. Similar to our analysis, very few centers conducted paravertebral or intercostal block for pain control. According to the American Pain Society clinical practice guidelines, thoracic epidural analgesia is the gold standard for management of surgical pain after thoracotomy . However, less invasive loco-regional techniques, such as paravertebral block, intercostal block and serratus anterior plane block are the more favorable approaches than epidural analgesia for the mini-invasive thoracoscopic surgery due to less side effects and improved safety profile . Since majority of the thoracic surgeries are underwent using video-assisted thoracoscopy in Taiwan , the fact that fewer centers listed epidural analgesia as the first-line analgesia method is therefore reasonable. Nevertheless, the applications of other loco-regional blocks for pain control after thoracic surgery should be encouraged.
The main objective of this survey was to determine the strategies of ventilatory support during and after OLV. Compared with the Italian study reported 6 years ago, more Taiwanese thoracic anesthesiologists ventilated the patients using the dual-controlled ventilatory modes (PRVC or PCV-VG mode) during OLV. These dual-controlled modes deliver the preset tidal volumes with lowest optimal airway pressure, which may theoretically reduce the risk of barotrauma . Although there were several clinical studies suggested that dual-controlled modes enhanced oxygenation parameters with improved respiratory mechanics during separated lung ventilation [13–15], large-scale clinical trials are needed to confirm the overall pulmonary protective outcomes of these modern ventilator modes in the dependent lung during thoracic surgery.
Low tidal volume (6–8 ml/kg PBW) is one of the hallmark parameters for IOLPV during non-thoracic surgery. However, the application of an “optimally low” tidal volume during OLV is not standardized. Our survey and other retrospective database analysis suggest that there are a considerably large proportion of patients continue to receive relatively high tidal volume (>7 ml/kg PBW) during OLV, which was associated with increased respiratory complications and major postoperative morbidity . On the other hand, the Italian and Japanese anesthesiologists tend to recommend a low tidal volume (4 to 6 ml/kg PBW) for OLV [1, 17]. Nevertheless, opinions from the expert anesthesiologists highlight that protective ventilation in thoracic anesthesia is not simply synonymous of a low tidal volume, but also involves the appropriate application of PEEP, alveolar recruitment and other ventilatory settings during OLV [18, 19]. Most recently, a double-blind, randomized controlled trial conducted at the Samsung Medical Center (Seoul, Korea) demonstrated that driving pressure-guided ventilation (median ∆P of 9 cmH2O) during OLV significantly reduced the incidence of postoperative pulmonary complications compared with the conventional protective ventilation (tidal volume 6 ml/kg PBW, PEEP 5 cmH2O and recruitment) in thoracic surgery . PEEP is another important element in practicing IOLPV. This survey found that most of the thoracic anesthesiologists in Taiwan apply a PEEP level of 4–6 cmH2O during OLV, which is comparable with mean levels (4.2±1.6 cmH2O) reported in a large retrospective analysis of the US database . The authors concluded that low tidal volume failed to reduce postoperative pulmonary complications without application of adequate PEEP . A previous study also indicated that individualized PEEP determined by a PEEP decrement trial significantly increased oxygenation and lung mechanics than the standardized PEEP (5 cmH2O) . However, the appropriate PEEP levels for OLV are yet to be determined by the ongoing clinical trials (Table 3).
Collapse of nondependent lung and atelectasis of dependent lung during OLV increases intrapulmonary shunt and leads to the development of intraoperative hypoxemia . Therefore, higher oxygen fractions are more commonly supplemented during lung isolation procedures than the non-thoracic surgeries [17, 23]. However, oxygen therapy in clinical anesthesia is considered as a two-edged sword and excessive oxygen supplement should be avoided to prevent the potential oxygen toxicity . An observational study found that higher FiO2 during OLV was associated with significantly higher incidence of postoperative pulmonary complications (OR 1.30; 95% CI 1.04–1.65) . High quality-controlled studies are thus essential to compare the clinical outcomes of low versus high fractions of oxygen used for OLV.
The most important message addressed by the Taiwanese thoracic anesthesiologists is the lack of consensus in the IOLPV during thoracic surgery, particularly at the OLV phase. This study found that the agreement in the ventilator-derived parameters (i.e. tidal volume, PIP, PEEP and ∆P) for the guidance of lung protection during OLV is very low among the thoracic anesthesiologists (degrees of agreement: Vt >PIP >PEEP >FiO2 >∆P >mode >recruitment; Fig. 1). In fact, a number of prospective randomized controlled trials are currently undertaking, including several international multicenter studies, to determine the strategy for lung protective ventilation during thoracic surgery (Table 3).