INTRODUCTION

Postoperative pain management, in addition to relieving patient's suffering, is essential to reduce morbidity, length of stay and hospital costs. ¹ The perception depends on multiple factors such as the site, extension and severity of the surgical trauma, preoperative anxiety and analgesic techniques used. ² Furthermore, postoperative pain is associated with cardiovascular and pulmonary complications, poor response to surgical trauma, delirium, chronic pain and persistent use of opioids. ²

Regional analgesia is essential in perioperative pain management ³, and it is recommended by the ERAS (Enhanced Recovery After Surgery) program in heart surgery to reduce the use of opioids and decrease its side effects. ^1,4 Different regional anesthesia techniques have been studied, whether as single dose or via continued infusion catheters, for surgery with sternotomy; these include epidural analgesia ⁵, paravertebral ⁶ and interfascial plane blocks such as the Erector Spinae Plane Block (ESP) and parasternal blocks, inter alia. ^4,7,8 All of these techniques have shown analgesic benefits and limitations or relevant considerations. For instance, epidural analgesia is associated with hypotension, urinary retention, epidural hematoma, motor block, dura mater rupture, and may also be affected by anti-aggregation or anticoagulation. ^9,10 The paravertebral block is operator-dependent and variable with regards to the ultrasound visualization of the anatomic structures, with a high risk of developing pneumothorax and a lack of conclusive evidence about its safety in terms of intra and post-operative anticoagulation. ^4,10 Parasternal blocks - such as the pecto-intercostal block or the transversus thoracic plane block, facilitate pain control but do have limitations in terms of the duration of analgesia and of the limited sensitive block area. ^11-13 Consequently, regional analgesia with bilateral continuous erector spine plane block (BC-ESPB) represents an alternative because of its analgesic effect similar to paravertebral block ¹⁴, provides improved safety by limiting the invasion to the neuroaxis in patients that will be anticoagulated ¹⁵, is easy to perform under ultrasound guidance and allows for placement of catheters for continuous analgesia.

The BC-ESPB with catheter for continuous analgesia, although was initially described for thoracic surgery and breast surgery ^16,17 in sternotomy approaches, has shown adequate postoperative pain control, decreased opioid use, favors early mobilization and exhibits less adverse effects and complications as compared to the other techniques discussed. ^1,14,18-20 However, the information in the literature varies with regards to programming of continuous analgesia regimens with local anesthetic agents through catheters, describing the use of ropivacaine or bupivacaine in intermittent automatic boluses or as a continuous infusion during the first 48 hours. ^1,14,20 This study assessed postoperative pain control in patients undergoing cardiac surgery through sternotomy, who received a multimodal analgesia regimen including BC-ESPB at the level of T5, with catheter-based continuous infusion and rescue boluses of 0.125 % bupivacaine.

METHOD

RESULTS

Eleven patients aged between 65 and 89 years were included, of which 9 were males with a mean BMI of 24.9 kg/m2. All patients underwent cardiovascular surgery through sternotomy, 7 of them underwent myocardial revascularization, and 4 valve surgery. The most frequent pre-existing pathologies included hypertension 72.7 %, diabetes 18.1 % and chronic kidney disease 18.1 %.

During the intraoperative period, 9 of 11 patients required extracorporeal circulation and aortic cross-clamping, with an average time for extracorporeal circulation of 68 minutes and of 50 minutes for ischemia. In terms of PCA, an average of 6 boluses per day (3 on each side) of 0.125% bupivacaine were administered. The use of intraoperative fentanyl was in average 2.35 µg/kg, ranging from 0 to 4.35 µg/kg, in addition to an average of 111 minutes of postoperative mechanical ventilation, with subsequent successful extubation in all patients. The average ICU stay was 3 days, with a total hospital stay of 7 days in average. Table 1 summarizes the clinical and demographic characteristics of the study group, as well as the specifics of the surgical intervention and the postoperative period.

Only one patient experienced an episode of psychomotor agitation and delirium. The adverse symptoms included 4 patients with nausea, 2 of which led to emesis. With regards to block-associated complications, only one case of bilateral ecchymosis was identified on the catheter insertion sites, but this event was spontaneously resolved with no further complications. Moreover, a patient died on the fifth day after surgery due to a new acute myocardial infarction (Table 1).

With regards to postoperative pain, all patients reported controlled pain (NRS-P ≤ 3) at the time of extubation, both at rest as in motion, at 4 and 12 hours after extubation. After 24 hours, NRS pain was ≤ 3 in 100 % of the patients assessed at rest and in 63.6 % in motion; the remaining 36.4 % presented NRS pain of 4. At 48 hours, 81 % of the patients reported NRS pain ≤ 3 at rest and in motion. At 72 hours, 100 % of the patients reported NRS pain ≤ 3 at rest and 82 % in motion, the remaining 19 % reported NRS pain between 5 and 7. Table 2 depicts the postoperative pain assessment.

The use of hydromorphone rescue doses (Table 1) was recorded during the first 72 hours, with the following findings: in the first 12-24 hours, 9 of 11 patients required rescue doses with an average of 5.6 mg total dose. In the following 24 h, 7 of 11 patients required rescue doses with an average of 4.1 mg, and in the last 24 hours of follow-up, only 5 patients required rescue doses with an average of 3.3 mg.

DISCUSSION

The acute pain control of patients during the first 72 hours after surgery was satisfactory. Acute pain, both at rest as in motion of the upper limbs during the first 24, 48 and 72 hours was milder, usually NRS-P ≤ 3, which is similar to the reports in other studies ^1,14 and case series ²⁰ of patients receiving BC-ESPB, but administered as a local anesthetic infusion with no on demand boluses. Similarly, these results confirm the reports of comparative studies with groups of patients that did not receive regional anesthesia, evidencing that there is a significant postoperative pain improvement and a considerable reduction in opioid use when administering the ESP block, whether as a single dose ^18,21 or as a continuous infusion via catheters. ¹

This study showed a very low use of intraoperative fentanyl - average of 2.3 µg/kg-, which is consistent with the literature indicating that regional analgesia with BC-ESPB reduces the use of opioids during both the intraoperative and postoperative periods ^1,10,20; this favors the opioid-sparing strategy recommended by the ERAS guidelines in cardiac surgery. ^22,23

With regards to the postoperative use of opioids, the average consumption recorded was 5.6 mg of IV hydromorphone over the first 24 hours, which is equivalent to 284 µ|g of intravenous fentanyl; this data is comparable with the study by Athar et al., using in average 225 µg of fentanyl during the first 24 hours postoperatively. However, Macaire et al. ¹ and Muñoz-Leyva et al. ²⁰ reported zero use of opioids during the infusion of local anesthetic, which differs from the findings herein described.

Moreover, although Macaire et al. ¹ were unable to document a significant difference in the mobility of patients receiving BC-ESPB in contrast with patients receiving the traditional analgesia, this study shows that pain in motion of the upper extremities in patients with BC-ESPB is usually below 3 in the numerical rating pain scale, which may help in the rehabilitation process and early mobility of patients.

The current scientific literature in cardiac surgery is quite diverse in terms of the local anesthetic and its ESP block administration regimens: use of ropivacaine or bupivacaine, whether as a single intraoperative dose or via catheters for intra and post-operative continuous infusion administration, automatic or on demand boluses. Macaire et al. ¹⁾ described their technique using 0.5% ropivacaine, but this drug is not available in Colombia. Moreover, Nagaraja et al. ¹⁴ and Muñoz-Leyva et al. ²⁰ used 0.125% bupivacaine, which is the medication used in this study.

With regards to the administration regimens of the local anesthetic agent via catheters in cardiac surgery through sternotomy, Nagaraja et al. ¹⁴ implanted two bilateral catheters at the level of T6, administering an initial bolus of 15 mL of 0.5% bupivacaine on each side, and continued with 0.125% bupivacaine infusion at 0.1 mg/kg/h up to 48 hours post-extubation. Similarly, Munoz-Leyva et al. ²⁰ placed their catheters at the level of T4, administering initial boluses of 20 mL of 0.25% bupivacaine with epinephrine 2.5 µg/mL, and continued with 0.125% bupivacaine infusion at 8 mL/h per catheter. In the cases herein described, the catheters were placed at the level of T5-T6, and 0.375% levobupivacaine boluses of 40 mL were administered, 20 mL on each side; subsequently, PCA with 0.125% bupivacaine was initiated on each side with 8 mL/h infusion if the body weight was between 40 and 80 kg or 10 mL/h if the body weight was over 80 kg, with on demand boluses of 5 mL, with a minimum safety interval of 1 hour between boluses. This anesthesia regimen was selected by the anesthesiologists participating in the study, based on the fact that both the patient's body weight and the possibility of using regional anesthesia as rescue analgesia were considered; hence, not only is the infusion adapted to the patient's needs, but there is also a reduction in the use of rescue doses of opioids, preventing a potential catheter obstruction by maintaining patency.

The average duration of mechanical ventilation in these patients was 111 minutes; early extubation was probably facilitated by the opioid-sparing strategy and by an adequate pain control at awakening provided by the BC-ESPB which enabled ultra-fast-track or fast-track ²⁴ extubations in the 11 patients involved. These events made it possible to leverage the benefits of these types of early extubation protocols in cardiac surgery, in terms of reduced ICU stay ²⁵, reduced hospital length of stay ²⁶, lower cardiovascular morbidity ²⁷ and improved cost-effectiveness of care. ²⁸

With regards to complications, no major adverse events were recorded among the study patients, such as local anesthetic toxicity, spinal hematoma, pneumothorax, inter alia. There was only one case of bilateral ecchymosis at the catheter insertion site, with no impact on the patient's evolution; this is consistent with reports in the available literature, evidencing a very low incidence of BC-ESPB-associated complications. ^{1,14,18,20,21}

Finally, the limitations of this study include the limited number of patients, the absence of a control group, failure to assess chronic pain, failure to assess pain sensation related to dermatomes using a Pinprick test, and the variability in the types of catheters used for continuous regional analgesia; i.e., Pajunk's E-Cath® and Contiplex® S Ultra 360 B. Braun. On one hand, the E-Cath® catheter, classified as catheter over needle, in which the tip of the catheter is at the same site as the tip of the needle, limits the catheter insertion to a very small space inside the block plane and hence increases the likelihood of catheter migration and complications such as intramuscular administration of the local anesthetic agent or outside the block plane. In contrast, the Contiplex® S Ultra 360 catheter is classified as a catheter-through-needle system in which the tip of the catheter advances beyond the tip of the needle, placing the distal end of the catheter inside a pocket created by hydro-dissection, which reduced the potential of catheter migration and associated complications.

CONCLUSION

Intraoperative and postoperative analgesia in cardiac surgery through sternotomy, using a thoracic BC-ESPB with administration of 0.125% bupivacaine in PCA as continuous infusion and on demand boluses, facilitates acute pain control, reduces opioid use, facilitates extubation and early mobilization, with no significant adverse effects. Considering the significance of the benefits derived from this analgesic technique, it is possible that its implementation in patients undergoing cardiac surgery, particularly those programmed for accelerated recovery, may be extremely helpful and safe.

ETHICAL RESPONSIBILITIES

ACKNOWLEDGEMENTS