CARDIOVASCULAR JOURNAL OF AFRICA • Volume 33, No 3, May/June 2022 106 AFRICA a transvers spinalis muscle group that lies deep to the spinalis and immediately adjacent to the bony vertebrae, and includes multifidus, rotators and intertransverse muscles. The rotators and intertransverse muscles, together with several ligamentous structures, such as the superior costotransverse ligament, span the gap between adjacent vertebral transverse processes. This ‘intertransverse tissue complex’ is a permeable posterior boundary of the paravertebral space (Fig. 7). The ESP block is performed under ultrasound guidance with the patient sitting, prone or in the lateral decubitus position. Using an aseptic technique, a high-frequency (12–15 MHz) linear-array transducer is placed in the parasagittal plane and moved from a lateral to medial direction until the ribs are no longer visualised and the transverse processes of T3 to T5 with overlying trapezius, rhomboid major and erector spine muscles are identified. The most caudal vertebral attachment of the rhomboid major muscle is the T5 spinous process, and tapering out of the rhomboid at this level may be useful confirmation of the desired probe position. An in-plane needle is inserted in the craniocaudal direction and advanced below the erector spine muscle, with the tip contacting the T5 transverse process. This block can be used with rib fractures, chest wall surgery and cardiac surgery (Fig. 8). Significant variations among cadaver studies have been found regarding injectate spread into the ventral rami after magnetic resonance imaging and dissection assessment, but all studies report significant distribution along the craniocaudal plane and the lateral cutaneous branches of the intercostal nerves. Schwarzmann et al.13 report radiological confirmation of notable craniocaudal spread with a single ESP injection. Athar et al.14 conducted a randomised, double-blind, controlled trial assessing the efficacy of an ESP block in cardiac surgery. Their study included 30 patients aged 18 to 60 years, body mass index ranging between 19 and 30 kg/m2, undergoing elective on-pump, single-vessel coronary artery bypass grafting or valve replacement under general anaesthesia. Patients were randomly categorised into two groups of 15 patients each receiving bilateral ESP blocks with 20 ml of 0.25% levobupivacaine per side, or placebo blocks with 20 ml of normal saline per side. Endpoints included total opioid dose in 24 hours, time-to-rescue analgesia, duration of mechanical ventilation, Ramsay sedation score (one of the most commonly used measures of sedation) six-hour post-extubation, postoperative nausea and vomiting, pruritus and the incidence of pneumothorax. According to their study, a single-shot ESP block provided superior analgesia compared with a placebo block. It decreased the first 24-hour postoperative analgesic consumption by 64.5% and risk of pain by five times in the authors’ population. It also reduced the duration of mechanical ventilation (88 vs 103 hours) in their postcardiac surgery patients.14 In this edition of the journal, Turkmen and Mutlu15 (page 153) compared the efficacy of ultrasound-guided PECS II block with a parasternal (PS) block in 100 patients undergoing open-heart surgery through midline sternotomy. This is the first study comparing two blocks between two groups after openheart surgery via sternotomy. For postoperative analgesia, 50 patients received a PECS II block and 50 a PS block at the end of surgery. They were then compared in terms of sedation scores, ventilation duration, and pain scores at rest after extubation as first endpoints. Block duration and cumulative morphine consumption were secondary endpoints, while complications such as postoperative nausea and vomiting were also compared. Interestingly in this study, the VAS scores at rest, a tool widely used to measure pain, were higher in the PECS II block group over the first six hours than in the PS group (p < 0.01). This was associated with a block duration that lasted longer in the PS block group. The cumulative morphine consumption (p < 0.01) and the Richmond agitation–sedation scale scores (RASS, a medical scale used to measure the agitation or sedation level of a person) (p < 0.01) were also higher in the PECS II block group than in the PS block group over the first four hours. There was no difference in the ventilation duration, block durations, pain and sedation scores over the first two hours. The final conclusion from the authors was that a PS block provides longer block duration with lower postoperative pain and sedation scores, as well as lower cumulative morphine consumption than a PECS II block for patients receiving a heart operation via median sternotomy. We must keep in mind that there is a strong trend towards performing cardiac surgery via a minimally invasive and minimal-access approach. This is usually performed through a mini-thoracotomy, which makes these procedures also amenable to other thoracic plane blocks. The discussion about analgesia for thoracotomy procedures is however not comprehensively covered in this editorial. Fig. 8. Erector spinae plane block anatomy. Fig. 7. Erector spinae plane block anatomy.
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