ABSTRACT
Background:
Fast-tracking plays a significant role in reducing perioperative morbidity and postoperative hospital stay by facilitating early extubation and optimal pain control. Attenuating the stress response to surgery also has a crucial function in enhancing recovery. Serratus anterior plane block (SAPB) is a recently described technique for chest wall analgesia. More data is required to find out the effectiveness of analgesia by SAPB for minimally invasive cardiac surgery (MICS).
Aim:
The study aimed to assess the efficacy and safety of ultrasound-guided SAPB compared to fentanyl for controlling post-thoracotomy pain and stress response in patients undergoing MICS.
Setting and Design:
Time framed comparative, prospective, and observational study.
Materials and Methods:
Patients undergoing MICS for coronary artery bypass grafting under general anesthesia were randomly assigned into two groups. SAPB group (Group A) patients were given 0.2% of 20 ml ropivacaine followed by catheter insertion for continuous infiltration at the end of the procedure. Fentanyl group (Group B) patients were given fentanyl infusion for postoperative analgesia. The primary outcome measured changes in visual analog scale (VAS) score (pain) and cortisol levels (for stress response) in both groups.
Results:
VAS score was significantly low in Group A when compared to Group B (P < 0.0001). Cortisol levels were also lower in the SAPB group. Hemodynamic parameters (systolic blood pressure, diastolic blood pressure, pulse rate, and oxygen saturation) were more stable in Group A with a lesser requirement of top-up analgesics.
Conclusion:
SAPB was more effective than fentanyl in managing post-thoracotomy pain after MICS. Cortisol level was lower in the group that received SAPB.
Keywords: Cortisol level, minimally invasive cardiac surgery, serratus anterior plane block, stress response
INTRODUCTION
Minimally invasive cardiac surgery (MICS) aims for reduced hospital stay and optimal postoperative analgesia to enable early ambulation and recovery.[1] Attenuating the stress response to surgery is an important element in enhancing recovery. Enhanced recovery after surgery (ERAS) approaches to opioid-sparing analgesia, which is increasingly standardized, evidence-based, and patient-centric.[1,2] This aims to ensure the best postoperative analgesics to guarantee the best recovery profile.[3] Serratus anterior plane block (SAPB) is a recently described technique for analgesia of the chest wall, providing anesthesia of dermatomes T2 to T9 targeting the plane above or below the serratus anterior muscle in the mid-axillary line.[4] The procedure consists of the administration of local anesthetics between the muscle planes of the chest wall targeting the lateral cutaneous branches of the intercostal nerves.[4,5] SAPB has already shown its efficacy in the management of postoperative pain following breast surgery, thoracoscopy, thoracotomy, and multiple rib fractures.[4,6,7] The effectiveness of analgesia by SAPB for MICS has not been well documented.
Our study demonstrated the effects of the SAPB for postoperative analgesia in MICS.
This study aims to compare the efficacy and safety of ultrasound-guided SAPB compared to fentanyl for controlling thoracotomy pain and stress response in a patient undergoing MICS. We also looked for any complications like hemodynamic instability, respiratory depression, and severity of pain.
MATERIALS AND METHODS
Patients undergoing elective MICS were included
Patients with opioid dependence and difficulty in communication were excluded from our study.
The sample size was 80.
Berthoud et al.[8] conducted their study and 46 patients were allocated. The proportion of the patients in this study was 46%. So for this study P = 0.46.
Thus the number of patients required for this study was 80 with a power of 87%. Around 80 patients were taken and divided into two groups.
The formula used for calculation of sample size is
n = 4pq/(L2),
where
n = required sample size,
p = 0.46 (as per the study by Berthoud et al.),[8]
q = 1 − p,
L = Loss % (Loss of information).
Calculation:
Here P = 0.46,
q = 1 − P = 1 − 0.46 = 0.54,
4pq = 4 × 0.46 × 0.54 = 0.9936,
L2 = 0.0124,
n = 4pq/(L2) = 0.9936/0.0124 = 80.13 = 80.
This time framed comparative observational study was done after obtaining clearance from the ethical committee. The patients were randomly assigned to Group A and Group B containing 40 patients each.
In Group A (SAPB group), SAPB was given with a bolus dose of 0.2% of 20 ml ropivacaine, and the catheter was inserted for continuous infusion of ropivacaine at the end of the surgery in the theater. With the patient in a supine position and a lateral tilt, the fifth rib was detected in the mid-axillary line. Serratus anterior, latissimus dorsi, and the intercostal muscles were identified in the fourth and fifth intercostal space with a linear probe (10–12 Hz). A 20G 10 cm needle was directed under serratus anterior and intercostal muscles, and the correct plane was identified by appreciating the spread of normal saline through the plane. An initial bolus dose of 0.2% ropivacaine was given and subsequently a catheter was placed for continuous infusion of 0.2% ropivacaine at the rate of 15–20 mg/h by an infusion pump in the postoperative period.
In Group B (fentanyl group), intravenous (IV) fentanyl infusion was given at the rate of 10–30 mcg/h by a continuous infusion pump.
Both groups were monitored postextubation for 48 h at intervals of 15 min, 30 min, 1, 2, 4, 6, 12, 24, 36, and 48 h, respectively. IV paracetamol was given to all patients at the interval of 6 h. The pain was assessed using the VAS score, and patients were monitored for 48 h postoperatively for hemodynamic changes. VAS score is a unidimensional measure of pain intensity, where patient rates their pain on a simple scale marked from 0 to 10, where 0 is no pain and 10 is the worst pain.
Serum cortisol (S. cortisol) levels were measured preoperatively on the first and second postoperative days.
Incentive spirometry volumes were recorded, chest X-ray improvement was noted, and the requirement for additional analgesia was documented.
For statistical analysis, data was entered into a Microsoft Excel spreadsheet and analyzed by Statistical Package for Social Sciences (version 25.0; SPSS Inc., Chicago, IL, USA) and GraphPad Prism version 5. Data has been outlined as mean and standard deviation (SD) for numerical variables and count and percentages for categorical variables.
P-value ≤0.05 was considered statistically significant.
RESULTS
The data from 80 patients were analyzed in our study. The main indication of surgery included triple vessel coronary artery disease and double vessel coronary artery disease. Demographic data was comparable in both groups as demonstrated in Table 1.
Table 1.
Demographic profile and preoperative values of the patients
| Parameter | SAPB group | Fentanyl group | P |
|---|---|---|---|
| Age (yrs) | 63.27±9.27 | 60.27±10.88 | 0.1876 |
| BMI (Kg/m2) | 24.11±1.83 | 24.84±2.07 | 0.0973 |
| Preop pO2 (mmHg) | 85.57±9.4 | 88.44±19.24 | 0.4002 |
| Surgery duration (h) | 3.68±0.66 | 3.44±0.87 | 0.1721 |
Data in the table are represented as mean±SD
In the fentanyl group, the mean value of S. cortisol on postoperative day 1 (POD1) was higher than the SAPB group as discussed in Table 2. However, the difference was not statistically significant (P = 0.3036).
Table 2.
Comparison of S. cortisol (mcg/dl) in both groups preoperatively and postoperatively
| Parameter | SAPB group | Fentanyl group | P |
|---|---|---|---|
| S.cortisol (preoperative) | 14.53±5.6 | 12.30±6.21 | 0.0988 |
| S.cortisol (POD1) | 24.87±12.03 | 28.70±20.07 | 0.3036 |
| S.cortisol (POD2) | 21.85±8.5 | 21.33±7.71 | 0.7771 |
Data in the table are represented as mean±SD
Comparison of pain scores, spirometry values, and intensive care unit (ICU) stay between two groups were discussed in Table 3. VAS scores were significantly higher in the fentanyl group than in the SAPB group and the difference in mean VAS at 15 min, 1, 2, 4, 6, 10, 24, and 48 h postoperative were statistically significant (P < 0.0001).
Table 3.
Comparison of pain scores, spirometry values, and ICU stay between two groups
| Parameter | SAPB group | Fentanyl group | P |
|---|---|---|---|
| VAS score | 1.55±1.15 | 3.42±1.19 | <0.0001 |
| Spirometry in ml at 48 h | 603.75±172.6 | 598.71±255.07 | 0.9183 |
| ICU stay (days) | 3.77±1.02 | 5.05±0.90 | <0.0001 |
Mean values of spirometry were higher in the SAPB group at 2, 6, 10, 12, and 48 h postoperatively, but the difference of mean was not statistically significant.
Duration of ICU stay was significantly less in the SAPB group (P < 0.0001)
No patient in the SAPB group required reintubation. On the contrary, two patients in the fentanyl group required bilevel positive airway pressure because of hypoxemia.
Comparison of hemodynamic parameters between the two groups did not show any significant difference in mean heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) at various time intervals postoperatively as depicted in Figure 1.
Figure 1.
Comparison of hemodynamic parameters between two groups. *HR in beats per minute ⍏SBP, DBP in mmHg
Peripheral capillary oxygen saturation (SpO2) was measured postoperatively at 15 min, 30 min, 1, 2, 6, 10, 12, 24, and 48 h. The mean SpO2 was higher for the SAPB group, but the difference of mean was not statistically significant [Figure 2].
Figure 2.
Distribution of mean SpO2 at different time intervals in two groups
There was no statistically remarkable difference between the mean partial pressure of oxygen (pO2) values of both groups at various time intervals. The partial pressure of carbon dioxide (pCO2) values at 2, 18, and 26 h postoperatively were higher in the fentanyl group. The difference in mean was statistically appreciable at 2 h (P = 0.0233) and 26 h (P = 0.0025) in both groups [Figure 3].
Figure 3.
Comparison of postoperative pO2 and pCO2 between two groups (Mean-mmHg)
Comparison of chest X-ray between two groups on POD1 and POD2 was illustrated in Figure 4. Postoperatively, there was less incidence of basal atelectasis in Group A as compared to Group B on POD1 and POD2. On POD1, 75% patients of SAPB group had mild basal atelectasis, other 25% of patients had no basal atelectasis, while 35% patients of fentanyl group had moderate and 65% of patients had mild basal atelectasis. P value was <0.001 which was statistically significant.
Figure 4.
Comparison of chest X-ray on POD1 and POD2 in two groups
On POD2, only 17.5% of patients in the SAPB group were left with mild basal atelectasis as compared to 62.5% patients of fentanyl group.
DISCUSSION
In our study, we have compared SAPB to fentanyl infusion in patients undergoing MICS. In a study conducted by Berthoud et al.[8] wherein 20 patients undergoing MICS received SAPB and 26 received continuous wound infiltration. VAS scores were recorded for 48 h, which demonstrated that patients receiving SAPB had significantly lower consumption of morphine during the first 48 h following MICS and a lower numerical rating scale (NRS) (P < 0.01).
Studies conducted by Okmen et al.[6] and Park et al.[9] concluded that VAS scores were significantly lower in the SAPB group. In our study, we found that mean value of VAS score at 15 min, 1, 2, 4, 6, 12, 24, 36, and 48 h were 2.52, 2.55, 2.45, 2.25, 2.20, 2.02, 1.80, 1.55, 1.12, 0.85 in Group A (SAPB group), whereas in Group B (fentanyl group), it was 4.07, 4.07, 4.02, 3.95, 3.85, 3.80, 3.575, 3.42, 3.02, 2.20, and median values were 3.00, 3.00, 2.00, 2.00, 2.00, 2.00, 2.00, 1.0, 1.0, 1.0 in Group A and 4.00, 4.00, 4.00, 4.00, 4.00, 4.00, 3.0, 3.0, 3.0, 2.0 in Group B. VAS score was significantly lower in Group A with P < 0.0001. Therefore, the requirement for top-up analgesia in the form of tramadol was significantly less in Group A as compared to Group B.
In the study conducted by Grossi et al.[10] in comparison of postoperative pain, stress response, and quality of life in minimally invasive versus standard sternotomy coronary bypass patients, they measured stress-related metabolites in each group which was significantly lower in the minimally invasive group (P = 0.005). In our study, we measured S. cortisol levels in both groups, the S. cortisol level was found to be higher in the fentanyl group on the POD1. However, the difference of mean in the two groups was not statistically significant.
A study by Khalil et al.[11] concluded that there was no remarkable change in mean arterial pressure in the SAPB group. In our study, we found that the mean value of pulse rate (PR) in Group A was significantly lower than Group B after 10 h postoperatively. Mean values of SBP and DBP were significantly higher in the fentanyl group.
The study conducted by Bainbridge et al.[12] showed that all patients after thoracotomy exhibited a fall in pO2, characterized by the greatest reduction in pO2 on the first two postoperative days, followed by a gradual return toward preoperative values. In our study, there was a significant fall in pO2 in the fentanyl group after 10 h and carbon dioxide (CO2) retention starting from the second hour postoperatively compared to the SAPB group.
Richardson et al.[13] concluded that thoracotomy potentially produces a marked reduction in postoperative pulmonary function and the choice of pain management has major implications. Spirometry monitoring should be standard in all thoracic units and is essential for objective comparison of the efficacy of different methods of pain management. In our study, there was no statistically major difference in spirometry performed by the two groups, but patients in the SAPB group were able to perform spirometry with higher volume from the first hour onward and fentanyl group from the fourth hour onward.
A study by Moghadam and Mohammadipoor[14] demonstrated that based on chest X-ray results, 47.5% of patients had developed atelectasis after thoracotomy. We found that basal atelectasis developed commonly after surgery. In our study on POD0, while 95% of patients in the fentanyl group developed moderate basal atelectasis, no patients in the SAPB group had moderate basal atelectasis (P < 0.001). On POD1, moderate basal atelectasis persisted in 35% of the patients and 65% had mild atelectasis in the fentanyl group. However on POD1, in the SAPB group no patients had moderate atelectasis and only 75% had mild atelectasis. On POD2, only 17.5% of patients in the SAPB group had mild atelectasis but the corresponding number in the fentanyl group was 62.5% (P < 0.001).
Opioid-sparing anesthesia techniques aid in achieving the goal of ERAS guidelines which includes early recovery and shorter hospital stay. In our study, the mean ICU stay was 3.7 days in the SAPB group and 5.0 days in the fentanyl group which was statistically significant (P < 0.0001).
There are various limitations to our study. The sample size was limited to a modest 80 patients because of both time and logistical constraints. A similar study with a larger sample size might have addressed the issue in a more credible and practically validated manner. A similar study conducted over a comparatively longer duration is desirable. The study design is an observational one, and randomized trials are necessary for better extrapolation and validation.
CONCLUSION
In our study, we found that the VAS score was significantly lower in the SAPB group than in the fentanyl group. Hemodynamic parameters (SBP, DBP, PR, and SpO2) were stable in the SAPB group. Stress response in the form of S. cortisol level was lower on the POD1 in the SAPB group. The requirement for top-up analgesic was notably less in Group A as compared to Group B. Patients in the SAPB group had lower incidence of CO2 retention. It was significantly higher in the fentanyl group as compared to the SAPB group in the immediate postoperative period and even after 24 h. The incidence of hypoxemia was not statistically significant in both groups, but after 24 h the pO2 levels were comparatively higher in the SAPB group than in the fentanyl group. Patients in the SAPB group were able to perform spirometry better than the fentanyl group till 12 h postoperatively after which there was no statistically significant difference between the spirometry performed by the two groups. The chest X-ray showed significant improvement postoperatively in the SAPB group compared to the fentanyl group. The duration of ICU stay was significantly lower in the SAPB group as compared to the fentanyl group, which aids in the early mobilization of the patient and early discharge. Therefore, SAPB in MICS patients is superior to fentanyl for control of postoperative pain. In addition, it also reduces stress response to a certain extent and helps patients to perform chest physiotherapy, thus improving the overall chest compliance, helping early ambulation, thereby reducing the ICU stay and early discharge. It is also easy to perform, less time consuming, and safe with fewer hemodynamic complications.
To conclude, we found that pain scores were significantly lower in Group A as compared to Group B. Although S. cortisol level was lower on POD1 in Group A, there was no statistically significant difference in both groups.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Author contributions
All five authors were associated with the conception and design of the study, acquisition of data, and its analysis and interpretation of data. They have all been responsible for drafting the article and revising it critically for important intellectual content. Final approval of the version to be published has been ratified by all five authors.
Acknowledgments
The authors would like to thank Dr. Enam Murshed Khan, Director of Lab Services, Apollo Multispeciality Hospital, Kolkata for the help in estimation of the S. cortisol values.
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