This prospective, observational study was approved by the Ethics Committee of Shanghai Sixth People's Hospital(2019-53) and was registered at www.chictr.org.cn(ChiCTR1900023763). From June to August 2019, 20 patients scheduled for surgical reduction and fixation of unilateral isolated rib fractures in our hospital, were enrolled in this study. Informed consent was obtained from all patients. The inclusion criteria were American Society of Anesthesiologists physical status I and II, age 18–70 years, body mass index (BMI)<30, preoperative PaO2> 60mmHg, and preoperative PaCO2< 50mmHg. The exclusion criteria were difficult airway, esophageal reflux, myasthenia gravis, abnormal coagulation system, gastric ulcer or hemorrhage, allergy to anesthesia-related drugs, asthma or chronic obstructive emphysema, major thoracic vascular injuries, and pregnant women.
All patients fasted for at least 8 h. BP, SpO2, and electrocardiography were performed when the patients were admitted into the operating room.
Ultrasound-guided TPB was performed using the S-Nerve™ Ultrasound System (Fujifilm SonoSite Inc. Bothell, WA, USA). The patient was placed in the lateral decubitus position. The transversal Inferior Articular Process (IAP) in-plane approach was applied. A convex array probe (5-2 MHz; C60x; Fujifilm SonoSite Inc. Bothell, WA, USA) was used to visualize the vertebral lamina, internal intercostal membrane and parietal pleura (Figure 1A). A 22gauge, 8cm puncture needle (KDL medical apparatus and instruments Co. Wenzhou, China) was inserted into the thoracic paravertebral space (TPVS) from the lateral side. Ropivacaine 0.375% (20-30ml) was injected with no air or blood aspiration.
The injection points of TPVS were selected according to the fractured rib segments requiring surgery (hereinafter referred to as "surgical segments"). If the surgical segments did not have more than 4 sequential ribs, 20ml of ropivacaine was injected into the TPVS of the second fractured rib, referred to as a single-level block. If the surgical segments had more than 4 sequential ribs, 15 ml of ropivacaine was injected into the TPVS of the second and fifth fractured ribs, referred to as a double-level block. We adopted a two-person mode in TPB: one physician operated the ultrasound probe and needle while the other performed the injection and aspiration. Color Doppler ultrasound was initially used to ensure that there were no vessels in the pathway of the needle insertion while approaching the TPVS.
In the case of posterior rib fractures, ESPB was performed to enhance the regional effect of the patient’s back and to supply more effective analgesia of posterior rib fractures as well. Ropivacaine 0.375% (20ml) was injected between the fifth thoracic vertebral transverse process and erector spinae muscle (ESM) on the operative side using the transversal in-plane approach under ultrasound guidance (Figure 1B).
The effect of the regional block was evaluated 15 min after nerve blockade, and the dermatomes of sensory loss were measured by acupuncture and rubbing with alcohol gauze. If the patient felt no pain while deep-breathing and vigorous coughing, and the range of reduction area of cold or pinprick sensation covered the incision, we considered the regional effect to be satisfactory. The patient was then given LMA anesthesia and was included in this study. Otherwise, the patient was administered ETI anesthesia and excluded from the observational analysis.
Anesthesia was induced with 0.1µg/kg sufentanil, 3mg/kg propofol and 0.3mg/kg rocuronium successively. We inserted an LMA SupremeTM(Teleflex Medical Co. Westmeath, Ireland) and ensured the LMA was correctly positioned. Mechanical ventilation commenced with a pressure control ventilation-volume guaranteed mode, at 6 ml/kg and respiratory rate(RR) of 12 breaths/min. The inspiratory to expiratory ratio was 1:2. A 14# gastric tube was placed for drainage of the fluid and/or gas that might escape into the stomach during positive pressure ventilation.
Anesthesia was maintained with sevoflurane at 0.7-1.2 age-adjusted minimum alveolar concentration (MAC) in 50% oxygen in air mixture depending on the hemodynamic responses to surgical intervention. Spontaneous breathing was maintained after recovery. A supplementary dose of 0.03 µg/kg sufentanil was allowed if the HR was 20% faster than the basic value, or RR was more than 20 breaths/min for surgical stimulation. Phenylephrine and atropine were injected if necessary. Sevoflurane inhalation was withdrawn and 50mg flurbiprofen was infused intravenously at 15 min before the end of the surgery. The muscle relaxant antagonist and neuromuscular blockade monitoring were not used in this study and all patients were allowed to recover on their own.
The patient was converted to ETI anesthesia as one of the following occurred: 1. The surgical field was difficult to expose because of muscular tension 2. The LMA could not be placed in the correct position after three attempts 3. Hemodynamic instability occurred 4. The SpO2 was less than 90% or the concentration of EtCO2 was more than 70mmHg.
PCA (infusion rate 2ml/h, total volume 100ml) containing 500mg tramadol and 16mg lornoxicam was routinely administered to all patients. The 50mg flurbiprofen was infused intravenously twice a day. If the patient’s NRS was >4, an analgesia rescue of 50mg pethidine was administered intramuscularly.
Vital signs during the anesthesia, tidal volume (Vt), RR, and EtCO2during spontaneous breathing were recorded. The time to removal of LMA and the events of agitation or hoarseness in the Post-Anesthesia Care Unit (PACU) were also recorded. Preoperative and postoperative arterial blood gas analysis and chest X-ray were routinely obtained.
Postoperative nausea and vomiting (PONV) within 48 h after surgery and NRS pain score were assessed at 6(T1), 12(T2), and 24(T3) hours after surgery. We also recorded dosages of sufentanil and vasoactive drugs administered and the cases that were converted to ETI during the operation. The perioperative complications such as regurgitation, aspiration, and injuries relating to nerve block were recorded as well.
SPSS19.0 software was used for statistical analysis. The sample size was calculated based on the change of PaO2. Seventeen patients were required to detect a mean difference of 10 mmHg and standard deviation of 10 mmHg, power of 0.8, and α-value of 0.05. We factored in a 15% dropout rate and enrolled 20 patients. Quantitative variables were expressed as mean±SD. Categorical variables were expressed as quantitative values or in percentage. The results of arterial blood gas analysis that were measured pre- and post-operatively, were compared using the Student's t-test. p < 0.05 was considered statistically significant.