European Journal of Cardiovascular Medicine

In cardiac surgery sternotomy pain is most severe on first day after surgery , and later decrease but may persist upto one week.¹  Post-sternotomy pain further leads to decreased patient satisfaction, delirium, cardiovascular complications (hypertension, tachycardia, arrhythmias), hyperglycemia and respiratory complications (like bronchial secretion stasis, atelectasis and pneumonia). Now a days in cardiac surgery regional anesthesia can be used for post sternotomy pain and it can be a part of multimodal analgesia technique. ²

Opioids such as fentanyl are used mainly for the management of pain after cardiac surgery. However, perioperative opioids are known to be associated with dose-dependent side effects such as nausea and vomiting, pruritus and respiratory depression. Median sternotomy for cardiac surgery, patients can experience significant pain and standard treatment with oral and intravenous analgesics is not always adequate. ^3-4

Nowadays, fast track anesthesia has become popular, opoid use and its associated side effect can be reduced with other modality like non-opoids analgesic and regional anesthesia . Use of regional anesthesia have effective role in aiding early extubation as well as ambulation and also decrease ICU stay for patient undergoing cardiac surgery. ⁵

Even multimodal approach such as the use of NSAIDs may not be optimal after cardiac surgery due to the risk of bleeding and renal failure. Regional analgesia has opioid-sparing effect and can be a good choice for perioperative analgesia.

A recent meta-analysis found that regional anesthesia can reduce the risk of chronic postoperative pain in patients underwent thoracotomy, but there are few specific data on cardiac surgery^.6 The risk factors for acute severe pain after cardiac surgery include age (<60 years), longer duration of surgery, and surgery extent.7 Studies have confirmed that after sternotomy, 30% to 50% of patients have chronic pain, and 5% to 10% of patients have severe pain (visual analogue scale [VAS]>5).^6-8

Transversus thoracic muscle plane (TTP) block, first reported as a peripheral nerve block in 2015, supports pain relief along with pectoralis nerve (PECS) II block.  ^9,10

Transversus thoracic muscle plane (TTP) block covers the anterior branches of intercostal nerves T2 to T6. It has been described in cardiac surgical patients that provides analgesia for sternotomy. TTP block is a superficial block and therefore is relatively safe when compared with thoracic epidural and paravertebral nerve block during heparinization.

Now, the goal of enhanced recovery after surgery is to reduce the patient surgical stress response, optimize their physiologic function, and facilitate recovery. Some studies have indicated that replacing opioids with other analgesics can reduce postoperative complications and shorten the recovery time. 11,12 Due to less pain patient involved in early mobilization and spirometry which keeps the respiratory rate lower side and good PO2 level and SO2 level.

This study was approved by ethic committee of UNMICRC (approval no. UNMICRC/C.Anes/2023/13) done on date 23/03/2023. Risk and benefits of procedure in this study was explained to participant and their relatives, written and informed consent was taken before enrollment. This was a single center prospective study in adult patient undergoing for cardiac surgery   via median sternotomy.

Randomization

All patients were randomized by biostatistician into two groups by computer generated random number table (Microsoft Office 365 Excel, Microsoft, Redmond, WA) and information kept in sealed envelopes.  ICU technique opened envelop only technician is knowing whether injected liquid was local saline before case study. After shifting case from OT., Intensivist do USG guided TTP block. The prior who taken data had no knowledge of patient’s treatment the intensivist, patient, nurse and surgeon were blinded throughout the study.

Inclusion and Exclusion Criteria

Adult patient with valve surgery was included. We exclude emergency surgeries, coronary artery bypass surgery, person allergic to local anesthetic, congestive heart failure patient, , patient with hepatic or renal failure, history of thoracotomy or redo surgery, history of chronic pain or psychiatric illness, refuse for consent.

Intraoperative anaesthesia and surgery

Patient was pre-medicated with midazolam 0.1 mg/kg. Anesthetic induction done as per institutional protocol etomidate 0.3mg/kg, fentanyl 5 mcg/kg and vecuronium 0.1 mg/kg for tracheal intubation. Tube is confirmed with etco2 and bilateral auscultation. The maintenance of anesthesia was achieved with fentanyl, propofol and vecuronium according to the clinical needs following induction in both groups. Postoperatively acetaminophen 15mg/kg and tramadol 2 mg/kg was given to both patient and on increasing NRS scale (> 4) additional fentanyl dose was given.

USG Guided TTP Block

The TTP block was performed in a supine position using high-frequency linear ultrasound (US) probe immediate after shifting in post-operative ICU. block was given by trained anesthetist who is not involved in study. US guidance increases the safety profile of TTP Block by real-time visualization of needle tip, evaluation of adjacent vital structure and distribution of local. The probe was placed at 2 cm lateral from sternum and parallel to the sternum in 4th intercostal space, then we could find the pectoralis major muscle, the external intercostal muscle, internal intercostal muscle innermost internal intercostal muscle, transverse thoracic muscle, the costal cartilage, the pleura and the lungs from top to bottom sequence.

Transverse thoracic plane was located between the internal intercostal muscle and transverse thoracic muscle. After ensuring that the internal thoracic artery (ITA) and the vein were not in the area, with color-flow Doppler. A 20-gage, 90 mm touhy needle was placed under the internal intercostal muscle and transverse thoracic muscle without - plane approach and confirming the needle location by hydro-dissection (giving test bolus of 2 ml saline), to determine that the tip has been placed in the correct fascial layers. Finally, 20 ml of 0.25% bupivacaine was injected to this plane at 4th intercostal space after negative aspiration, monitoring of local anesthetic spread and depression of pleura that confirm the accurate site of injection. Drain site local infiltration was done in both group. The same method on the other side was repeated.

Local anesthetic systemic toxicity (LAST), pneumothorax, hematoma and local site infection will be monitored after the intervention. Physical examination, Ultrasound, and/or X-ray will be used to assess the adverse events. The LAST will be prevented by using US-guided technique, aspiration before local anesthetics injection, and incremental administration of local anesthetics. Pneumothorax and hematoma will be prevented by using US-guided technique. We will use aseptic technique practice when performing the procedure to prevent pathogens contamination.

OUTCOME

The primary outcome measure in our study were opioid consumption on day 1 and postoperative pain at 4 hr , 8 hr ,12hr, 24 hr after extubation as well as at rest and deep breathing or coughing. Postoperative pain was measured by numerical rating scale (NRS) score from 0 (no pain) to 10 (worst pain).  Secondary outcome included heart rate, respiratory rate, systolic blood pressure, po2 at same time interval, ventilation time.

Sample size calculation

Based on the pilot study published by Satoru Fujii et al. in 2019, with α error of 5%, confidence interval of 95% with power of interval being 90%, total sample size was calculated to be 50, with 25 in each group. In this study we have taken sample size of 80, with 40 patients in each group.

STATISTICAL ANALYSIS

Descriptive analysis was carried out by frequency and proportion for categorical variables. Continuous variables were presented as Mean ± SD for normally distributed random variable and median (IQR) for non-normal variable. The chi-square test was used to test the statistical significance of cross-tabulation between categorical variables. The Man Whitney U test was used to compare Median (IQR) non-normally distributed continuous variables. The independent t test was used to compare Mean ± SD for normally distributed random variable

Table 1: Demographic characteristics of the study population (N=80)

The mean age for both groups is provided, with case participants having an average age of 45.5 years (±13.5), and control participants having an average age of 44.3 years (±13.4). The comparison of ages between the two groups reveals a non-significant p-value of 0.69, indicating that there is no statistically significant difference in age distribution between cases and controls. Additionally, the sex distribution shows that 65.0% of the case group and 62.5% of the control group are male, while 35.0% of the case group and 37.5% of the control group are female, with a non-significant p-value of 1.00. Furthermore, the mean Body Mass Index (BMI) is reported for both groups, indicating an average BMI of 24.9 (±3.7) for cases and 25.6 (±3.4) for controls. The comparison of BMI between the two groups yields a non-significant p-value of 0.39, suggesting no significant difference in BMI between the case and control groups.

Table 2: Comparison of parameters across the different time points (N=80)

The parameters under consideration include heart rate at various stages post-opearative and after extubation. Notably, statistically significant differences are observed at each time point between the case and control groups. Post-operative heart rates after shifting and 30 minutes later, at the time of reversal and CPAP, and after extubation at 4, 8, 12, and 24 hours exhibit significant variations (p-values ranging from < 0.001 to 0.042). The findings suggest that the two groups experience distinct cardiac responses during these critical periods. For instance, the case group consistently demonstrates lower heart rates compared to the control group, indicating potential differences in the cardiovascular recovery trajectories. (Figure1 A)

Table 3: Comparison of parameters across the different time points (N=80)

The comparison of respiratory rate (RR) across different time points for the case (n=40) and control (n=40) groups. Noteworthy variations are evident at several time intervals. At the time of reversal and CPAP, as well as after extubation at 4 and 8 hours, the case group exhibits significantly lower respiratory rates compared to the control group, with significant p-values .These findings suggest that individuals in the case group experience a distinct respiratory response during these specific post-operative and extubation periods. However, at 12 and 24 hours after extubation, no statistically significant differences in respiratory rates are observed between the two groups, as indicated by p-values of 0.753 and 0.322, respectively. (Figure 1B)

The comparison of Fentanyl requirements at different time points between two groups. At the time of Reversal and CPAP, none of the individuals in the study's Case group required Fentanyl, while 27.5% of the Control group did, and this difference was statistically significant (P = 0.001). Similarly, after extubation, no individuals in the Case group required Fentanyl, in contrast to 35.0% of the Control group, with a highly significant P-value (<0.001). Fentanyl requirements at 4 and 8 hours after extubation also exhibited statistically significant differences between the groups (P = 0.001 and P = 0.002, respectively). At 12 hours after extubation, 5.0% of the Case group required Fentanyl compared to 20.0% of the Control group (P = 0.091). However, 24 hours after extubation, the difference in Fentanyl requirements became no significant (P = 0.735), with 10.0% of the Case group and 15.0% of the Control group needing Fentanyl.(Figure 2)

Table 4: Comparison of parameters across the different time points (N=80)

In Table 4, the comparison of total ventilation time between the Case group (n=40) and the Control group (n=40) reveals statistically significant differences (P < 0.001). The median total ventilation time for the Case group is reported as 5 hours (interquartile range, IQR: 4.5 to 6.0 hours), while the Control group exhibits a higher median total ventilation time of 7 hours (IQR: 6.4 to 8.0 hours).(Figure3)

This observational study, showed that TTP block in post-operative cardiac recovery ICU decrease NRS pain score and keep patient more hemodynamic stable compare to “no block” at time of awakening and reversal as well as extubation . Furthermore, it also helps in early involvement, chest physiotherapy, respiratory exercise and mobilization which later decrease length of ICU stay and cost of treatment.

The parasternal area is innervated by the anterior branch of the T2 to T6th intercostal nerves which run between Transverse thoracic muscle (TTM) (deeper) and IIM (superficial). Injecting local anesthetic drugs bilaterally between the TTM and IIM in the 3rd to 4th intercostal can block the 2nd to 6th anterior branch of intercostal nerves.

The TTM locates behind the sternum body and costal cartilage, which is on the pleura. The extremely thin structure of TTM makes it difficult to be distinguished by ultrasound. Therefore, IMA and internal mammary vein, which run along the surface of TTM, would be important positioning marks. 

During cardiac surgery, the painful stimulation of sternum sawing often causes dangerous hemodynamic fluctuations. Due to the large wound of the sternum, 36% of patients have sternal pain after surgery. ¹³ Ueshima and Kitamura 9 and Ueshima and Otake 10 reported that combination of general anesthesia and TTP block presented better perioperative analgesic effect and hemodynamic stability response to surgical stress. 

Absence of adequate analgesia may expose the patients to development of chronic pain such as poststernotomy pain syndrome. ^14,15 In this study, one single-shot TTP block bilaterally is effective for sternotomy pain in cardiac surgery.

Deng, Qiweixi MM et al. done a study in 104 cases and divided cases into G group (without TTP block) and TTP group (with TTP) and found that the postoperative visual analogue scale pain scores and the compression times of patient-controlled intravenous analgesia in the TTP group were significantly decreased compared with G group (P < .01). The postoperative duration of invasive ventilation of patients with normal and mildly impaired pulmonary function was significantly correlated to the use of sufentanil (P = .027, .009).¹⁶

In our study the post-operative NRS pain score at time of extubation and up to 12 hr during rest and exercise is statistically significant (p<0.005) in cases group than control group. Due to less pain score, patient was early involved in post-operative respiratory exercise which further leads improvement in respiratory parameter and early mobilization.(Figure 4A and B) 

Most cardiac surgery patients are mechanically ventilated under sedation during the postoperative period. ¹⁷ Prolonged mechanical ventilation is associated with postoperative respiratory complications. ¹⁸ Effective pain management may be a good method to decrease the duration of sedation for mechanically ventilation. ¹⁹ The finding of Reddi et al. ²⁰ suggests that deranged pulmonary function test parameters are associated with a prolonged postoperative ventilation and the duration of ICU length of stay in cardiac surgery.  TTP block, which has a definite regional analgesic effect, would have some benefits for early expectoration and early activities postoperatively.

In our study at the time of reversal and CPAP, as well as after extubation at 4 and 8 hours, the case group exhibits significantly lower respiratory rates, with significant p-values. This can be explained as deep breath taken by cases group due to less pain than control group. However, at 12 and 24 hours after extubation, no statistically significant differences in respiratory rates are observed between the two groups, as indicated by p-values of 0.753 and 0.322, respectively. This may be due to wearing off analgesic effect of TTP block. Same result also found with when patient doing intensive spirometry. 

Epidural analgesia and paravertebral nerve block are the other source of analgesia  postoperative pain management undergoing open cardiac surgery.¹⁷  However, these are not done routinely because of concerns about hemorrhage and hematoma after coagulopathy and heparinization.18 Continuous infusion of local anesthetics for postoperative analgesia in post op cardiac patients  is affected by the location of the catheter and drug concentration, that’s why these technique is not widely accepted.¹⁹ Therefore, the present study demonstrated that ultrasound-guided TTP block is a novel, effective, promising, and safe regional analgesic technique that can be used in post op cardiac patient and should be used widely.

Limitation

There are few limitations in this study first, Block area and duration of analgesic effect of TTP block is still uncertain which needs further research. Secondly, we use non opioids drugs in both group as analgesia. So, we don’t know about synergistic effect of both and duration of analgesia.

The analgesic effect of TTP block is irrefutable and it can reduce the postoperative use of opoids cardiac surgery as well as effectively enhance involvement of respiratory and ambulatory exercise. furthermore, it decreases ventilation time and also decrease cost of treatment. As it is very easy to perform TTP block without change in position, so can be a part of fast track strategy in cardiac surgery and also as multimodal analgesia.

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