Successful weaning from mechanical ventilation after Serratus Anterior Plane block in a chest trauma patient

Case report

A 54 year old male patient was admitted to hospital for blunt chest trauma (fall from height). A CT scan showed bilateral pneumothorax, multiple rib fractures (I to X) on the right side with flail chest (II to IV), rib fractures on the left side (IV to VIII), a left diaphragmatic breach (8 cm) and herniation of the omentum into mediastinum associated to a peripheral lesion of the left lower lobe of the lung. After performing a bilateral pleural drainage, the patient underwent urgent thoracotomy with rib fracture stabilization, left lower pulmonary wedge resection, and left diaphragmatic plastic. Following surgery, the patient was admitted to ICU and protective mechanical ventilation was provided with continuous infusion of neuromuscular blockade alongside with sedation and analgesia using propofol and remifentanil. One day after surgery, a repeated CT scan showed thoracic cage stabilization, with no more lesions of the mediastinum, and a weaning from mechanical ventilation was started. A multi-modal protocol of analgesia was initiated, with morphine IV continuous infusion (30 mg/24 h) and paracetamol 1 gr tid IV. At the suspension of sedation, the patient appeared agitated, tachypnoeic, unable to achieve an adequate tidal volume, and there was asynchrony with the mechanical ventilator. We postulated that pain, secondary to rib fractures and to the surgical trauma, could produce inadequate ventilation due to the reduced thoracic expansion and to patient-ventilator asynchrony. Sedation was resumed, and transdermal fentanyl (25 mcg/h) was added to morphine and paracetamol. The following day a further trial of weaning from mechanical ventilator was again unsuccessful. Before proceeding to a tracheostomy, which was planned in order to facilitate the weaning process, we decided to perform an ultrasound-guided continuous Serratus Anterior Plane block (SAPB) for pain relief. This is a new ultrasound-guided fascial plane block initially described by Blanco et al. [1], which provides effective analgesia for the chest wall, blocking the lateral branches of the intercostal nerves from T2 to T12 [2]. SAPB has been found to be very effective for controlling rib fracture pain [3] and improving spirometry volumes [4], while producing a continuous analgesia with catheter insertion. The SAPB with catheter placement can be accomplished in the patient in the supine position.

Under ultrasound-guidance, a continuous SAPB was performed using a 20G catheter-over-needle (Silverstim, Vygon) technique, in the space between the VII-VIII rib on the left and the IV-V rib on the right. A high frequency linear probe (12.5 MHz) was positioned at the level of the eighth rib on the left along the midaxillary line, and on the fifth rib along the midaxillary line on the right. Before introducing the catheter, on the top of the rib underneath the Serratus Anterior muscle, with an in-plane technique and a cranial-to caudal direction, a total of 20 mL of 0.375% ropivacaine was injected into this space bilaterally. Continuous infusion of ropivacaine 0.2% at 6 mL/h in both catheters was started and the intravenous multimodal analgesia was suspended. The patient was extubated 1 day after the block, but needed non-invasive ventilation (NIV) with facemask. Pulmonary function ameliorated, as demonstrated also by a chest X-ray (Figure 1 chest X-ray one day after the SAPB; Figure 2 chest X-ray four days after the SAPB). Respiratory mechanics also improved and the patient could start respiratory physiotherapy. Two days after the block, his blood gas analysis had a remarkable improvement in oxygenation (in NIV, the PaO2-FiO2 ratio passed from 192 mmHg [25.6 kPa] to 287 mmHg [38.3 kPa]), and he was switched to standard oxygen therapy. The catheters were removed bilaterally after 5 days from positioning, before transferring him to the ward. His pain abated, and he did not request any pain relief during ward stay. The patient was discharged home after 18 days from the accident. This case demonstrates the complexity of pain management in thoracic trauma with associated rib fractures. Pain control, often underestimated, greatly affects mortality and morbidity in patients with chest trauma [5]. Pain leads to lung atelectasis and increase the risk of postoperative pulmonary complications [5]. Early analgesia should be considered for pain relief in complex chest trauma. SAPB has fewer risk than neuraxial blockade, it is easier to perform under ultrasound guidance and provides adequate analgesia [3, 4]. When there are contraindications (e.g. anticoagulants use) to deep blocks (epidural, paravertebral block), or there is risk of hypotension, or the patient should maintain the supine position, the SAPB is the first choice for pain control in rib fractures [6]. This superficial block is mostly employed for providing analgesia after breast and thoracic surgery [7]. Ropivacaine, bupivaicane and levobupivacaine are the most used local anesthetics for bolus and continuous infusion in SAPB [8]. Rare complications are represented by nausea and vomiting, respiratory complications, hypotension, and dizziness [9]. The guidelines on pain management for blunt thoracic trauma from the Eastern Association for the Surgery of Trauma and Trauma Anesthesiology Society [5] conditionally recommend epidural analgesia over non-regional modalities of pain control (i.e., intravenous or analgesics such as opioids), without making any recommendation on the SAPB. The latter has demonstrated to be safer and equally effective in pain control compared to epidural analgesia in patients with chest trauma [10, 11]. Moreover, thoracic epidural analgesia has some drawbacks, such as inadvertent high block, local anesthetic toxicity, total spinal anesthesia, hypotension, and vomiting. Trauma patients have frequently contraindications to neuraxial anesthesia, such as reduced mobility, altered cognition, anticoagulants use or coagulopathy. SAPB does not produce sympathetic block, providing excellent analgesia without hemodynamic instability [12, 13]. Apart from epidural analgesia and the SAPB, different types of regional anesthesia can be employed for pain management in thoracic trauma patients, such as the Erector Spinae plane (ESP) block, the intercostal block (ICB), the paravertebral block (PVB), and the rhomboid intercostal block (RIB). The PVB is performed in the patient in the prone or lateral position. PVB is a unilateral technique, which does not produce complete sympathetic blockade and may be associated to a low risk of hypotension and urinary retention. Even if rare, severe complications can manifest after PVB, such as pneumothorax, vascular puncture, total spinal anesthesia and nerve injury [14]. ICB provides a satisfactory analgesic effect for ribs fracture. However, this block requires multiple injections due to the limited cranial-caudal spread of the local anesthetic to the adjacent intercostal spaces after a single injection. Moreover, pneumothorax is not uncommon after the ICB [15]. ESP block is associated with improved inspiratory capacity and provide excellent analgesia for rib fractures. The ESP block is less difficult to perform than epidural analgesia or PVB, and use of anticoagulants or antiplatelet drugs are not absolute contraindications for ESP block. However the patient should be placed in either a seated or lateral position [16]. Complications of the ESP block include vascular puncture, pneumothorax and local anesthetic systemic toxicity. Contrary to the SAPB, ESP block, PVB and epidural analgesia all require patient cooperation [13]. RISS (Rhomboid Intercostal and Sub-Serratus) block is a novel two-injection block of both the rhomboid intercostal and sub-serratus space recently described by Elsharkawy et al. [17], for rib fractures pain. The RISS block is performed in the prone or lateral position, it is easier to perform compared to PVB and provide excellent analgesia. Pneumothorax and local anesthetic systemic toxicity are possible rare complications of the RISS block. Moreover, this technique requires an adequate training before performing it properly, mostly for the correct identification of the sono-anatomical structures [18].

Figure 1:

Chest X-ray one day after the Serratus Anterior Plane block showing reduced lung transparency in the middle and lower pulmonary right lobe.

Figure 2:

Chest X-ray 4 days after the Serratus Anterior Plane block showing an improvement in lung transparency in the middle and lower pulmonary right lobe.

In our case, the patient, after the SAPB, had a reduction in pain intensity and an improvement in both respiratory mechanics and blood gas analysis allowing a weaning from mechanical ventilator. If the patient had failed another weaning trial, we would have performed tracheostomy, prolonging the mechanical ventilation, the ICU and hospital length of stay and increasing the risk of infections.