This randomized, double-blind study demonstrated DSPB, SSPB or PVB combined with PCIA reduced the postoperative pain and showed similar satisfaction with analgesia in patients undergoing VATS. Intraoperative opioid consumption remained significantly lower in PVB. SSPB showed less PCIA pressed times and PCIA dosage than PVB. Furthermore, DSPB and SSPB were easy for anesthetist to operate, with significantly lower operating duration than PVB. PVB was associated with maintaining hemodynamic stability. However, PVB consumed more atropine intraoperatively.
There were different opinions about the postoperative analgesic effect of DSPB, SSPB and PVB. PVB has long been referred as the best possible choice for postoperative analgesia of VATS(18). In recent studies, SSPB proponents have described successful analgesia without the potentially hazardous need for advancing the needle deeper toward the pleura(15, 17). However, anatomy arguably favored DSPB as injection in the fascial plane below the serratus muscle which blockade of the lateral cutaneous branches of the intercostal nerves, might show better analgesic effect(19). In our study, DSPB, SSPB and PVB showed similar postoperative analgesic effect, and most patients were satisfied with the analgesic effect. All three can be used for postoperative analgesia of VATS. However, in the early postoperative period (12hrs), SSPB group provided a superior pain relief with significantly lower effective PCIA pressed times and dosage compared to PVB group. Some studies showed that the duration of the sensory blockade produced by SSPB and DSPB was 730–780 min and 380–400 min respectively(20–22). The effective time of PVB persisted for 48hrs postoperatively(23). In our study, the duration of postoperative analgesia for PVB was shorter, probably due to the pharmacological properties of ropivacaine.
During operation, compared with DSPB and SSPB, PVB showed superior analgesic effect. PVB significantly decreased intraoperative consumption of opioids comparing to DSPB and SSPB, which indicated the short-term analgesic effect of PVB was better than that of DSPB and SSPB. These findings support observations from previous reports that showed the effectiveness of PVB(24).
The ideal analgesic techniques should not only have perfect analgesia effect, but also have the advantages of simple operation, accurate control, high success rate and few complications. The puncture duration of PVB was significantly longer than that of DSPB and SSPB in our study. It might be related to the difference of anatomical position. The serratus anterior muscle was superficial which could be scanned by high-frequency linear array ultrasound probe to easily obtain clear images of the serratus anterior muscle and its neighbors. During the puncture, the angle between the needle and skin was small that the puncture needle could be imaged clearly(25). J Richardson et al also found that the deep fascia of the serratus anterior muscle had poor adhesion to the intercostal external muscles and was easier to separate than the superficial plane of the serratus anterior muscle, which was also showed in our study(26). The location of thoracic paravertebral nerve was deeper and should be scanned low-frequency convex array probe or high-frequency linear array probe. The puncture needle was difficult to image due to the large angle.
A few studies have described analgesia effect of SSPB was similar to an epidural but perhaps with less hemodynamic instability(17). In our study, both DSPB and SSPB, as well as PVB could maintain hemodynamic stability. However, PVB consumed more atropine intraoperatively. Previous studies also have shown that PVB can cause the incidence of bradycardia and hypotension with rate of 0.47% ~ 2.2%, which might be related to sympathetic block(27).
In addition, the incidence of side effects did not show significant differences in three groups. There were 6 patients who had motion sickness reported severe nausea and vomiting. After stopping PCIA, the side effects were disappeared, which indicated that might be associated with the opioid. They withdrew from our study on the basis of exclusion criteria. We did not report any complication associated with nerve block, but pneumothorax was potential. The deep surface of the paravertebral area was the pleura, and there was a risk of puncture of the pleura, pneumothorax and other complications. Naja et al performed PVB in 662 patients, and the probability of developing pneumothorax was about 0.5%(28). J Richardson’s study showed that PVB punctures occasionally entered the epidural or puncture the pleura, and had a transient occurrence of Horner syndrome(26). This could explain why many clinicians are reluctant to operate PVB in daily work. Accordingly, patients with narrow intercostal space, obesity, poor coagulation function should use DSPB or SSPB.
Nonetheless, the present study had several limitations. First, as an observational study, our conclusions might have been limited by inadequate data collection, the pain of nerve block procedure was not recorded. Meanwhile, due to the time limitation of preoperative preparation, we could only confirm the diffusion of local anesthetics by ultrasound, but did not collect the data of spread level of analgesia. Second, the research subjects recruited in this study were not performed by the same surgeon, and there were uncontrollable differences. Third, it should be noted that during operation, when surgeons cut open the skin and subcutaneous tissue of patients who received DSPB or SSPB, it showed a slight edema of subcutaneous tissue, which indicated the possible loss of local anesthetics. Finally, this study did not explore the appropriate local anesthetic dose for nerve block, which will be described in further research.