Cardiovascular surgical procedures confer significant morbidity and mortality risks [1,2]. Acute poststernotomy pain reported by some patients is severe, and there is an estimated incidence of poststernotomy persistent pain at 1 year of 24% [3,4]. Severe acute poststernotomy pain is associated with chronic pain at 1 year in 35% of patients . If this prevalence is representative of the broader population exposed to cardiac surgery, then chronic poststernotomy pain represents a public health issue.
The increased awareness of opioid dependence, community overuse and misuse, opioid-related tolerance and hyperalgesia has opened up a dialog regarding methods to minimize perioperative opioid use [6,7▪]. Multimodal and regional analgesia are recommended opioid-sparing techniques. Enhanced recovery after surgery (ERAS) protocols and opioid-sparing techniques reduce length of stay, decrease complications and improve efficiency of healthcare resources [8,9▪,10,11]. When employed, regional anesthesia blocks should be considered as one component of a clinical pathway aiming to optimizing perioperative care within a multidisciplinary cardiac ERAS program.
Recently developed ultrasound-guided interfascial plane blocks have likely been fuelled by increasing expertise in ultrasound-guided techniques, their exposure in social media and the opioid crisis evident in multiple geographic regions [7▪]. However, these novel ultrasound-guided blocks: erector spinae, serratus anterior, pectoral, transversus thoracic muscle and pecto-intercostal fascial plane blocks have become popularized in advance of randomized clinical trials evaluating their efficacy. To help guide clinical decision-making and future research this review evaluates the contemporary body of evidence regarding the benefits of novel and traditional regional anesthesia techniques for cardiovascular surgery. Table 1 summarizes the original research articles included in this review. This review is intended to complement recent comprehensive reviews [12,13].
THORACIC EPIDURAL ANALGESIA
Epidural analgesia for cardiac surgery has a risk of epidural hematoma. This risk is perceived as being increased because of the associated systemic anticoagulation required for cardiopulmonary bypass. A 2015 meta-analysis estimated the risk of epidural hematoma in this cohort at one in 3500 . While the risk of epidural hematoma secondary to thoracic epidural analgesia (TEA) in cardiac surgery may be rare, its effects can be devastating.
High TEA induces bilateral cardiac sympathetic blockade improving myocardial oxygen delivery and therefore may reduce cardiac morbidity . A 2010 meta-analysis did not detect a mortality benefit . However, in 2015, a meta-analysis including both randomized clinical trials and case-matched studies concluded that high TEA for cardiac surgery reduced mortality [risk ratio 0.65, 95% confidence interval (CI) 0.48–0.86] . However, a more recent review suggests that there may be no mortality benefit with use of TEA for cardiac surgery [16▪].
Moderate quality evidence from 14 randomized clinical trials and 698 study participants indicate that paravertebral block and TEA have comparable postoperative analgesic profiles following thoracotomy . Both paravertebral blockade and epidural analgesia are techniques recommended for thoracotomy by the Procedure-Specific Postoperative Pain Management working group . Because TEA induces bilateral sympathetic block, the incidence and magnitude of postoperative hypotension is increased compared with paravertebral blockade . Compared with TEA, paravertebral block has a more favorable minor complication profile following thoracotomy (eight randomized clinical trials and 445 participants) including a reduced risk of hypotension (risk ratio 0.16, 95% CI 0.07–0.38, P value <0.0001), nausea and vomiting, pruritis and urinary retention . Similarly, a meta-analysis of 23 randomized clinical trials (1120 participants) determined that TEA and continuous paravertebral blockade had similar analgesic outcomes, however the latter technique had reduced incidence of nausea, vomiting (five trials), hypotension (eight trials) and urinary retention (five trials) . Of 18 trials comparing TEA and continuous paravertebral blockade only two had a cardiac surgical cohort (remainder thoracotomy and rib fracture).
The overall adverse event rate of ultrasound-guided paravertebral blockade has been reported as 0.35% (99.2% CI 0.00–2.66%) in patients receiving unilateral blockade and 0.88% (99.2% CI 0.18–2.51%) in patients receiving bilateral paravertebral blockade . Reported complications include pleural puncture and pneumothorax (0%; 99.2% CI 0.00–0.35%), hypotension and bradycardia (0.47%; 99.2% CI 0.07–1.50%), and suspected local anesthetic systemic toxicity (0.23%; 99.2% CI 0.01–1.11%). Low-quality evidence showed no significant difference in mortality and major complications when paravertebral was compared with epidural blockade .
Paravertebral block is typically implemented for unilateral major surgery, providing ipsilateral somatic and sympathetic block. Midline sternotomy cardiac surgery requires bilateral blockade, and theoretically, bilateral sympathetic blockade may improve myocardial oxygen balance. In contrast, despite paravertebral blockade being a nonneuraxial technique, issues regarding anticoagulation required for cardiopulmonary bypass and the risk of hematoma are still relevant. The paravertebral space is deep, bleeding may occur undetected and external compression is not possible. The incidence of hematoma associated with paravertebral block and systemic anticoagulation required for cardiopulmonary bypass is unknown. A double-blinded randomized controlled trial has compared continuous bilateral thoracic paravertebral blockade with subcutaneous lidocaine infusions in patients undergoing coronary artery bypass surgery [22▪▪]. Catheters were inserted either into the paravertebral space or the subcutaneous tissue at the T3–T4 level and 20–30 ml 0.5% lidocaine injected bilaterally followed by an infusion of 1 mg/kg/h (mean 1.4 mg/min) for 48 h. The primary outcome was postoperative morphine consumption at 48 h. There was no significant difference in morphine consumption between patients randomly assigned to the study groups. Potential reasons for failure to demonstrate a difference between groups include the statistical power (Type II error), mode of initial injection, choice of lidocaine as infusate and intrinsic therapeutic benefits of systemic lidocaine. Furthermore, the methods do not explicitly describe if the initial lidocaine bolus was through the catheter or through the needle. This is relevant as catheter tip misplacement during insertion is a recognized risk of continuous paravertebral blockade. Appropriately, the author's highlight the risk of local anesthetic systemic toxicity with continuous bilateral paravertebral blockade in patients with ischemic heart disease and extensive medical comorbidities. Potentially, this risk would be increased further if a potent longer acting amide local anesthetic and adjuncts such as epinephrine (risk of arrythmia) were used. The risk of local anesthetic systemic toxicity is highlighted in a pilot study of patients (n = 8) having coronary artery bypass surgery with continuous bilateral thoracic paravertebral block, where plasma ropivacaine concentrations consistent with toxicity occurred with dosages in the range recommended by manufacturers . In summary, because of lack of demonstrated efficacy and safety concerns, the routine use of continuous bilateral paravertebral blockade for adult patients undergoing cardiac surgery is not recommended.
PARAVERTEBRAL BLOCK VARIANTS: ERECTOR SPINAE PLANE BLOCK
The erector spinae plane block is an ultrasound-guided regional analgesia technique described in 2016 for treatment of thoracic neuropathic pain, which has subsequently been used for treatment of postoperative pain . The plane of injection is between a vertebral transverse process (usually mid thoracic) and the erector spinae muscle group. This plane of injection is distinctly different to paravertebral block where the local anesthetic is injected anterior to both the transverse process and the costotransverse ligament so as to access the thoracic spinal nerves. Whether erector spinae blockade results in ventral and dorsal rami blockade is controversial, and the exact mechanism of erector spinae block and its injectate spread remains unclear [25,26]. One positive attribute of erector spinae plane block compared with paravertebral blockade is relative ease of insertion using ultrasound guidance and likely this has contributed to its popularity. Erector spinae plane blocks have been increasingly utilized for truncal surgical procedures, and in 2019, a review from 85 publications yielded 242 case reports [27▪].
To date, there are few controlled clinical trials. Bilateral continuous erector spinae plane block has been compared with TEA in a relatively young adult cardiac surgical cohort (age: 45–50 years) having median sternotomy [28▪]. In this pilot randomized clinical trial (n = 50), with absence of group allocation and observer masking, the author's report statistically significant improved pain scores between 24 and 48 h in patients receiving erector spinae block. Interpreting these results is challenging because of trial methodology. A randomized clinical trial has compared bilateral single-shot erector spinae plane block (3 mg/kg of ropivacaine 0.375%) with conventional treatment (paracetamol/tramadol) in 106 cardiac surgical patients (with normal left ventricular function for whom early extubation was planned) [29▪▪]. Patients were excluded if the blocks were unsuccessful or re-exploration was required for postoperative bleeding (n = 4, two from each group). Defining features include the young surgical cohort (age: 49–50 years) and the short aortic cross clamp time (24–27 min). In this trial, pain (primary endpoint) was assessed until 12 h post operatively by investigators blinded to group assignment, and the author's report improved duration and quality of analgesia in patients receiving erector spinae block. The author's report secondary outcome improvements in patients receiving erector spinae block: reduced intraoperative opioid requirements, reduced time to extubation, earlier ambulation, reduced duration of intensive care admission and reduced time until rescue opioid was required. The efficacy of continuous erector spinae blocks in a cardiac ERAS program was evaluated using a consecutive, patient-matched, historical controlled before-and-after study [30▪]. The author's report reduced morphine consumption, shorter time to chest tube removal, earlier mobilization, and improved analgesia in the erector spinae plane block group. Case studies generate the hypothesis further that bilateral erector spinae plane blocks provide effective analgesia and decreased postoperative opioid consumption following cardiovascular surgery [31–33]. The rate of adverse events following erector spinae plane block is unknown and it is important to note that trials with small cohorts are not powered to reliably detect adverse events. In the abovementioned review, a pneumothorax following erector spinae plane block was reported [27▪] Although the improved outcomes to date are encouraging, these results need to be replicated in randomized clinical trials with minimal risk of bias before we can recommend that continuous erector spinae plane blockade be routinely implemented in adult cardiac surgery. The mechanism, safety profile and efficacy of continuous erector spinae plane blocks require further investigation. The erector spinae plane block represents a promising potential option for perioperative analgesia following cardiovascular surgery.
STERNAL BED, PECTO-INTERCOSTAL FASCIAL AND TRANSVERSUS THORACIC MUSCLE PLANE BLOCKS
The pecto-intercostal fascial block, described for analgesia following breast surgery involves ultrasound-guided local anesthetic injection between the pectoralis major and external intercostal muscles to block the anterior cutaneous intercostal branches . Pecto-intercostal fascial block for cardiovascular surgery has been described in a case report wherein the block was utilized effectively for rescue analgesia postoperatively . Patients who received surgeon administered sternal bed blocks combined with systemic analgesia (compared with systemic analgesia alone as the standard of care) reported clinically significant reduced pain scores for 24 h following coronary artery bypass graft surgery . This study included a 6-month follow-up, where there was no difference in the incidence of chronic pain.
The transversus thoracic muscle plane block involves ultrasound-guided injection of local anesthetic between the transversus thoracic muscle and internal intercostal muscle lateral to the sternum aiming to block multiple anterior intercostal branches in the neurovascular plane, and it has been successfully combined with pectoral nerves II blocks for breast surgery [37,38]. Case reports by Ueshima et al.[39–42] describe the effective use of transversus thoracic muscle plane blocks for pericardiocentesis, midline sternotomy and for apical transcatheter aortic valve implantation. Sternal bed blocks represent a potentially effective method for post operative or rescue analgesia for patients undergoing sternotomy.
PECTORAL NERVES AND SERRATUS ANTERIOR BLOCKS
Pectoral nerves block and the serratus anterior plane block were described as simpler ultrasound-guided alternatives to paravertebral block [43–45]. The serratus anterior plane block involves placement of local anesthetic into the fascial plane between the serratus anterior and latissimus dorsi muscles, thus targeting the lateral cutaneous branches of the intercostal nerves . The targets of the pectoral nerves I block are the pectoral nerves located between pectoralis major and minor muscles . The pectoral nerves II block is the pectoral nerves I block combined with targeting the lateral cutaneous intercostal branches (T2–T6) between the pectoralis minor and serratus anterior muscles .
Kumar et al.[46▪▪] conducted a randomized clinical trial comparing postoperative insertion of combined bilateral pectoral nerves II blocks and drain site infiltration (35 ml bupivacaine 0.25%) with no block (all participants received paracetamol/tramadol) in patients undergoing cardiac surgery via median sternotomy. The author's reported that patients who received postoperative pectoral blocks/drain infiltration required reduced intensive care resources and had lower pain scores. Similarly, Kaushal et al.[47▪▪], in a randomized clinical study compared serratus anterior plane, pectoral II and intercostal nerve blocks for the management of pain after pediatric cardiac surgery (ligation of patent ductus arteriosus, coarctation of aorta repair and Blalock Taussig shunt) performed via thoracotomy. The author's report statistically significant (however clinically modest) improvements in pain scores in patients randomized to receive either serratus anterior or pectoral II blocks compared with the intercostal nerve blockade. Utilizing study measurements beyond 12 h and employing strategies to achieve blinding of both research and clinical personnel as well as patients and their families from group allocation would have improved the validity of the trial findings. Case reports in adult patients, describe the use of serratus anterior plane blocks and pectoral nerves blocks for transcatheter and transapical aortic valve replacement [40,48].
No single block will dramatically improve patient outcomes, because the clinical pathway and bundle of care that comprises the ERAS program is the key instrument in delivering care. Therefore, we propose a more nuanced question: what ultrasound-guided blocks for cardiovascular ERAS programs?
Trials evaluating ultrasound-guided interfascial plane blocks frequently employ short-term primary study outcomes (e.g. pain scores and opioid consumption within 24-h). Employing a broader perspective on the potential benefits of regional anesthesia interventions include the use of outcomes that capture recovery from the patients’ perspective and demonstrate benefits beyond the early postoperative period such as a reduced incidence of chronic pain . Randomized clinical trials should include as comparators, interventions that are considered standard of care and/or can be implemented with relative ease, for example local anesthetic interventions implemented by the surgeon such as parasternal blocks [36,50]. Trial methods and protocols investigating ultrasound-guided interfascial plane blocks should be embedded into bundles of care such as ERAS, and should be mindful of the complex multidisciplinary care that cardiac patients typically receive. Comprehensive data collection and feedback can occur in other formats including quality-improvement programs.
Furthermore, the meta-analysis as a tool of evidence-based medicine has limitations. In addition to issues of heterogeneity of comparator groups and outcome measures, often a meta-analysis of regional anesthesia randomized clinical trials includes a modest number of trials with results that are not replicated in a subsequent large randomized clinical trials using the same intervention and comparators . Regardless of the meta-analysis quality, implementing randomized clinical trials in the perioperative environment is demanding and acquiring the evidence takes years. Alternatively trials with design flexibility and efficiencies in patient recruitment can be utilized so that new knowledge can be acquired in a timely manner .
Ultrasound-guided fascial plane blocks potentially will reduce postoperative opioid requirements and facilitate cardiovascular ERAS programs. Further information on the safety (bleeding, local anesthetic systemic toxicity) of bilateral continuous blockade for cardiac surgery is required. Therefore, bilateral continuous paravertebral blockade is not recommended in routine adult cardiac anesthetic practice. Novel ultrasound-guided fascial plane blocks require further investigation with randomized controlled trials with minimal risk of bias. Trial protocols should be embedded into ERAS programs. Patient-reported and long-term outcomes such as chronic pain are recommended study measurements.
Financial support and sponsorship
The work was supported by the Department of Anaesthesia and Acute Pain Medicine, St Vincent's Hospital, Melbourne, Australia.
Conflicts of interest
There are no conflicts of interest.
REFERENCES AND RECOMMENDED READING
Papers of particular interest, published within the annual period of review, have been highlighted as:
- ▪ of special interest
- ▪▪ of outstanding interest
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