This is a case series without clinical intervention. This study was approved by the ethical committee of Akashi Medical Center on 17 October 2016 (approval number: 28-14). We collected demographic and clinical data of 87 adult patients who had undergone elective MICS with lateral thoracotomy between March 2009 and May 2016. All patients were well informed on the procedure, and consent for continuous paravertebral block (CPVB) was obtained prior to surgery. We retrospectively assessed CPVB-related complications, postextubation respiratory failure, duration of intubation after surgery, perioperative fentanyl consumption, and other analgesic use.
Anesthetic and analgesic protocol
In all patients, sedation was performed with midazolam (1 mg) and fentanyl citrate (100 μg) followed by induction with thiamylal sodium (3–4 mg/kg), esmolol hydrochloride (1 mg/kg), and vecuronium bromide (0.1 mg/kg) immediately after the radial artery was cannulated. Anesthesia was maintained with sevoflurane 1.5% and intermittent fentanyl and vecuronium injections at the discretion of anesthesiologist. After induction, intubation was performed with a single-lumen tube (Parker Flex-Tip™ PFHV, Japan Medicalnext, Osaka, Japan) and bronchial blocker tube (COOPDECH Endobronchial Blocker Tube, Daiken Medical, Osaka, Japan) or a double-lumen tube (Mallinckrodt™ Endobronchial Tube, Covidien Japan, Tokyo, Japan) for one-lung ventilation. A pulmonary artery catheter (Swan-Ganz CCOmbo V, Edwards Lifescience Japan, Tokyo, Japan) was inserted via the left internal jugular vein. An 18-gauge intravenous line was inserted via the right internal jugular vein in order to facilitate placement of the cannula to drain venous flow from the superior vena cava during cardiopulmonary bypass. For the initiation of cardiopulmonary bypass, 300 units/kg of unfractionated heparin was administered to achieve activated coagulation time of more than 400 s. Routine monitoring included continuous arterial, central venous, and pulmonary artery pressure, pulse oximetry, five-lead electrocardiogram, regional saturation of oxygen of brain (INVOS OXIMETER, Covidien Japan, Tokyo, Japan), bladder temperature, end-tidal carbon dioxide concentration, airway pressure, and transesophageal echocardiography (EPIQ 7, Philips Electronics Japan, Tokyo, Japan).
Ultrasound-guided CPVB was performed after induction of anesthesia in the lateral decubitus position. We confirmed that no antiplatelet or anticoagulant was administered preoperatively. An 18-gauge Tuohy’s needle was placed at T5/6 or T6/7 paravertebral spaces using an in-plane approach followed by a catheter (Perifix custom kit, B Braun Aesculap Japan, Tokyo, Japan). We performed bolus infusion of 40–60 mL ropivacaine 0.2% followed by continuous infusion of 4–6 mL/h of ropivacaine 0.2%. We confirmed by ultrasound that local anesthetic infused via the catheter spread in paravertebral space successfully in all patients (Fig. 1). Continuous infusion of ropivacaine and 3 mL bolus with a 60-min lockout interval was postoperatively maintained for 48–72 h under patient-controlled analgesia (PCA) (Coopdech balloonjecter 300, Daiken Medical, Osaka, Japan).
Postoperative assessment
We postoperatively assessed CPVB-related complications every 2 hours: nausea and vomiting, leakage of local analgesics, bleeding, neuropathy, and abscess. If required, we gave patients a postoperative analgesic regimen consisting of intravenous pentazocine hydrochloride (15 mg), intravenous buprenorphine hydrochloride (0.2 mg), and oral loxoprofen sodium hydrate (60 mg). Complication and analgesic use was recorded by nurses.
Outcomes
CPVB-related postoperative complications included leakage of local analgesic and bleeding from the puncture point, neuropathy, abscesses, nausea and vomiting.
Postextubation respiratory failure was defined as the presence and persistence of any of the following: postoperative pneumonia, respiratory acidosis (pH < 7.35 with PaCO2 > 45 mmHg), hypoxemia (SpO2 < 90% or PaO2 < 60 mmHg with FiO2 ≥ 0.5), tachypnea > 35 breaths/min, respiratory muscle fatigue, and/or low level of consciousness [6]. Postoperative pneumonia was defined as the presence and persistence of signs of respiratory infection, such as fever, purulent sputum, leukocytosis, increased level of blood C-reactive protein, and worsening oxygenation with a new radiographic infiltrate [6].
Statistical analysis
Continuous variables are presented as means and standard deviations. Chi-square test was used to estimate relevance of international normalized ratio of prothrombin time (PT-INR)- and CPVB-related bleeding. P value of < 0.05 was considered statistically significant.