|Year : 2015 | Volume
| Issue : 4 | Page : 648-652
The analgesic efficacy of ultrasound-guided transversus abdominis plane block in comparison with subarachnoid morphine after cesarean section in morbidly obese parturients
Nasr A Hegazy MD , Khaled F Elmetwaly
Department of Anesthesia and Intensive Care, Faculty of Medicine, Ain Shams University, Cairo, Egypt
|Date of Submission||19-Jan-2015|
|Date of Acceptance||11-May-2015|
|Date of Web Publication||29-Dec-2015|
Nasr A Hegazy
119 Abd El-Aziz Fahmy St, Apt 5, Heliopolis, Cairo
Source of Support: None, Conflict of Interest: None
Cesarean section is one of the most commonly performed surgical procedures. Intrathecal morphine is a popular and effective option for pain management following cesarean section. It is associated with side effects such as nausea, vomiting, pruritus, urinary retention, reactivation of oral herpes, and, rare but life-threatening, respiratory depression. The interest in transversus abdominis plane (TAP) block as a post-cesarean-delivery analgesic modality has surged in the past few years, and many studies have evaluated and compared its efficacy with intrathecal morphine.
The aim of the study was to compare spinal morphine and bilateral TAP block in cesarean section in morbidly obese parturients with respect to their postoperative analgesic efficacy and narcotic consumption.
Settings and design
This was a prospective randomized, double-blinded study.
Materials and methods
Parturients, 20 years or older, with BMI greater than 35 kg/m 2 , who were scheduled to undergo elective cesarean section were recruited for the study. They were assigned to receive either intrathecal morphine (the ITM group) 0.1 mg or TAP block (the TAP group) using ropivacaine 0.5% 20 ml on each side. The primary outcome was pain on movement, from supine to sitting position. The secondary outcomes were the presence and severity of nausea and pruritus and the presence of respiratory depression.
We enrolled 60 patients, of whom 59 were analyzed. The numeric rating scale score for pain was less in the ITM group than in the TAP block group, and this difference was statistically significant. Both pruritus and nausea happened in more patients in the ITM group than in the TAP block group, and this difference was statistically significant in both the 8 and 16 h observations.
In morbidly obese parturients, intrathecal morphine has superior post-cesarean-delivery analgesic efficacy compared with the TAP block.
Keywords: intrathecal morphine, obese parturients, post-cesarean-delivery analgesia, transversus abdominis plane block
|How to cite this article:|
Hegazy NA, Elmetwaly KF. The analgesic efficacy of ultrasound-guided transversus abdominis plane block in comparison with subarachnoid morphine after cesarean section in morbidly obese parturients
. Ain-Shams J Anaesthesiol 2015;8:648-52
|How to cite this URL:|
Hegazy NA, Elmetwaly KF. The analgesic efficacy of ultrasound-guided transversus abdominis plane block in comparison with subarachnoid morphine after cesarean section in morbidly obese parturients
. Ain-Shams J Anaesthesiol [serial online] 2015 [cited 2021 Apr 12];8:648-52. Available from: http://www.asja.eg.net/text.asp?2015/8/4/648/172760
| Introduction|| |
Cesarean section is one of the most commonly performed surgical procedures. About 15% of births worldwide occur through cesarean section  . Neuroaxial anesthesia has become the anesthetic technique of choice in this surgery as it is safer than general anesthesia and has resulted in significant reduction in maternal mortality  . Effective postoperative analgesia is crucial to facilitate early ambulation, infant care, and prevention of postoperative morbidity such as thromboembolism , . Inappropriately managed postoperative pain after cesarean section may lead to the development of chronic pain syndrome (which was estimated to happen in up to 12% of women after this procedure)  , and a three-fold risk for postpartum depression  .
Post-cesarean-delivery pain management is challenging, as we need to provide safe and effective analgesia with minimal side effects for the mother and the newborn. The American College of Obstetricians and Gynecologists (ACOG) states that an important objective of postoperative pain management in obstetrics is minimization of the cumulative maternal opioid dosage to reduce maternal and neonatal side effects  . Intrathecal morphine is a popular and effective option for pain management following cesarean section and is often seen as the 'gold standard' strategy. Although it meets the criteria of easy administration, minimum to no effects on the newborn through breastfeeding, and effective analgesic effect  , it is associated with side effects such as nausea, vomiting, pruritus, urinary retention, reactivation of oral herpes, and, rare but life threatening, respiratory depression  . After intrathecal morphine, respiratory depression is a potential serious risk, which is delayed because of rostral spread in the cerebrospinal fluid and slow penetration into the brain stem  .
Post-cesarean-delivery pain consists of both somatic and visceral components. Visceral pain originates from uterine incision and contractions, whereas the somatic component arises from nociceptors within the surgical wound. Nerves supplying the anterior abdominal wall are derived from T6L1 and pass through the plane between the transversus abdominis and internal oblique muscles  . Using a localized abdominal wall nerve block after a cesarean section may be an alternative for the opioid use for postoperative analgesia. Transversus abdominis plane (TAP) block is a regional, simple, and safe analgesic technique that blocks T6L1 nerve branches and has been shown to decrease postoperative pain and analgesic requirements following lower abdominal surgeries , . The interest in TAP block as a post-cesarean-delivery analgesic modality has surged in the past few years and many studies have evaluated and compared its efficacy with intrathecal morphine ,,,, .
Although many studies have compared the TAP block with spinal morphine to control post-cesarean-section pain, to our knowledge no one has studied that in morbidly obese parturients.
The aim of this prospective study was to compare spinal morphine and bilateral TAP block in cesarean section in morbidly obese parturients with respect to their postoperative analgesic efficacy and narcotic consumption
| Materials and methods|| |
This randomized, double-blind study was approved by the institutional research ethics board of King Fahd Hospital, KSA. Parturients, aged 20 years or older, with BMI greater than 35 kg/m 2 who were scheduled to undergo elective cesarean section received written information about the study at their consultation at the obstetric outpatient clinic between November 2012 and May 2014. Patients were recruited after evaluation at the preoperative anesthesia clinic 1 week before the surgery, and those who accepted to participate in the study gave informed written consent. The patients who were enrolled in the study were educated regarding symptoms of local anesthetic toxicity and the numeric rating scale (NRS) for pain score assessment in addition to the routine anesthetic education and counselling. They were assigned to either the intrathecal morphine group (ITM group) or the TAP block group (TAP group) (1 : 1 allocation, parallel trial design), based on a computer-generated randomization list created by an independent researcher. Group assignment was concealed in opaque envelopes that were opened only after enrollment. Patients were excluded if there was multiple gestation, a relevant drug allergy, known history of chronic pain, tolerance to opiates, or contraindication to a neuroaxial block.
The obstetrical surgeons, the patients, and nursing staff involved in direct patient care were unaware of the study group allocations. For all study patients anesthesia was induced by two anesthetists who are experts in obstetric anesthesia as well as in TAP block and not involved in the data collection. The anesthesia technique was standardized. In the operating room, all parturients were monitored with an ECG, noninvasive arterial blood pressure monitor, and pulse oximeter. While in the sitting position, all women received spinal anesthesia at the L2-L3 or L3-L4 interspace with hyperbaric bupivacaine 0.75 mg (Lake Forest, Illinois, USA) 10-12 mg plus fentanyl 10 mg. Women in the ITM group received 100 mg of preservative-free morphine intrathecally mixed with hyperbaric bupivacaine 0.75 mg (Lake Forest, Illinois, USA) 10-12 mg and fentanyl 10 mg. We chose this dose of intrathecal morphine on the basis of the study conducted by Palmer et al.  , who suggested a ceiling analgesic effect of intrathecal morphine with doses above 75 mg and pruritus severity directly linked to intrathecal morphine dose. A pencil-point (whitacre) spinal needle G25 was used to perform the spinal anesthesia, and the study medications were prepared in the same volume by a pharmacist who was not involved in the study to ensure blindness of the investigators.
After the spinal anesthesia was administered and the target sensory level (T4T6) was confirmed, a drape was placed to prevent the woman from visualizing the performance of the TAP block (in the TAP group) or the sham TAP block procedure (in the ITM group). Under sterile conditions, the anesthesiologist identified the TAP using an ultrasound scanner (Sonosite, Bothell, Washington, USA) with a 6-13-MHz linear probe. Once the TAP was visualized, an 80-mm, 22-G, short beveled echogenic needle (SonoPlex Stim Cannula; Pajunk, USA) was introduced into the fascia between the internal oblique and transversus abdominis muscles. The patients in the TAP block group received ropivacaine 0.5% 20 ml on each side in 5 ml increments with negative aspiration in between. Satisfactory spread of the local anesthetic solution creates a hypoechoic lens-shaped area deep to the fascial layer between the two muscles. Patients were monitored for an increase in heart rate or symptoms and signs of local anesthetic toxicity, such as tinnitus, perioral numbness, and metallic taste in the mouth, slurred speech or change in mental status. Intravenous crystalloids and phenylephrine were administered as needed to treat the hypotension. Patients in the ITM group received a sham TAP block in which a capped needle was pushed against the skin to mimic the pressure sensation of the TAP block.
Each patient received rectal acetaminophen 975 mg and naproxen 500 mg at the end of the surgery. All patients were prescribed a standard postoperative analgesic regime of oral acetaminophen 1 g every 6 h and rectal naproxen every 12 h. Rescue analgesia for breakthrough pain was oral hydromorphone IR 1-2 mg administered every 2 h when required. Moderate and severe nausea or vomiting was treated with intravenous ondansetron 4 mg every 8 h when required. Also, diphenhydramine 25-50 mg was given intravenously every 4 h when required to treat moderate and severe pruritus. Respiratory depression, defined as respiratory rate less than 10 breaths/min, was treated with naloxone.
Patients were interviewed at regular intervals (8 h) for the first 24 h postoperatively by an investigator unaware of group allocation to determine pain scores on movement and the severity of opioid side effects. The time to first request for additional analgesia and the total consumption of opioids were recorded.
The primary outcome was pain on movement, from supine to sitting position. This was evaluated using a NRS pain score ranging from 0 to 10, where 0 = no pain and 10 = worst imaginable pain. The secondary outcomes were the presence and severity of nausea and pruritus and the presence of respiratory depression. Nausea and pruritus were evaluated using a four-point ordinal scale (0 = none, 1 = mild, 2 = moderate, and 3 = severe).
The sample size calculation was based on the previous study conducted by McDonnell et al.  . A calculation based on a = 0.05 and a power of 80% determined that 25 patients be included per group, using a two-tailed test. To compensate for dropouts, we planned to recruit 60 patients.
Descriptive statistics were evaluated using SPSS 16 (SPSS Inc., Chicago, Illinois, USA), and normality of data distribution was assessed with the KolmogorovSmirnov test. Continuous data were presented as mean and SD (mean ± SD) and were analyzed using Student's t-test (normal distributions) or the Wilcoxon rank-sum test (non-normal distributions). Categorical data were reported as numbers and percentages and were analyzed using the c2 -test or Fisher's exact test as appropriate. Nonparametric data were reported as median and range and analyzed using the MannWhitney U-test. All P values were two-sided, and a P value less than 0.05 was considered statistically significant.
| Results|| |
Eighty-four patients were initially screened for the inclusion criteria. Seventy-five patients met the inclusion criteria. Sixty patients were recruited and consented to participate in the study [Figure 1]. One patient from the TAP block group was excluded from the study as the anesthesiologist was not satisfied with the local anesthetic distribution for the TAP block. Data from 59 patients, 30 allocated to the ITM group and 29 to the TAP group, were analyzed. The sensory level of spinal anesthesia reached T4T6 dermatomal level in all parturients, allowing surgery without pain and without requirement for any additional analgesics not mentioned in the study protocol.
Both study groups were comparable in terms of age, BMI, gestational age, the number of previous cesarean deliveries, and the length of surgery [Table 1].
As shown in [Table 2], the NRS was less in the ITM group than in the TAP block group, and this difference was statistically significant during the whole study period. Opioid consumption was also shown in [Table 2]. Hydromorphone doses were not normally distributed and nonparametric tests were performed. The cumulative hydromorphone use at all time points on the first postoperative day was significantly less in the spinal morphine group than in the TAP block group. Also, the time to the first hydromorphone demand was statistically shorter in the ITM group than in the TAP block group.
[Table 3] shows that both pruritus and nausea occurred in more patients in the ITM group than in the TAP block group, and this difference was statistically significant in both the 8 and 16 h observation.
There were no complications in the TAP block group, and no one in the ITM group experienced respiratory depression.
| Discussion|| |
Maternal obesity has increased in concordance with increased prevalence of obesity in the general population. The prevalence of obesity among pregnant women ranges from 1.8 to 25.3%  . The obese parturient presents many challenges to the anesthesiologists. Many studies have documented an increased rate of adverse pregnancy outcomes in morbidly obese women, including significant prolongation of first stage of labor and a higher rate of cesarean section  .
As neuroaxial anesthesia has been established as the safest and best modality of anesthesia for cesarean section, spinal morphine has been an integral part of multimodal analgesic regimens  . Although a low dose of morphine given intrathecally is a very effective widely used post-cesarean-section analgesic technique, it has a few side effects, of which delayed respiratory depression is the most feared one  . In a study conducted by Abouleish et al.  , there were no cases of bradypnea (respiratory rate ≤10 breaths/min) in 856 women after 0.2 mg subarachnoid morphine for cesarean delivery but eight women exhibited episodes of oxygen desaturation (SpO 2 <85) during sleep; all of them were extremely obese.
It is well recognized that local anesthetic techniques can improve the quality of postoperative pain management. TAP block has been shown to decrease postoperative pain and analgesic requirements following open and laparoscopic abdominal surgeries  . Many studies demonstrated its analgesic efficacy for post-cesarean-delivery pain , . Our study looked at a group of parturients, morbidly obese, who are more liable for the delayed respiratory depression from intrathecal morphine  . Our study found that an ultrasound-guided TAP block did not provide analgesia as effective as ITM in the first 24 h after cesarean section in morbidly obese parturients. This is demonstrated by higher doses of postoperative opioid requirement as well as earlier request by the patient. Although the side effects, such as pruritus and nausea, were significantly higher in the intrathecal morphine group, none of the study patients experienced respiratory depression. The analgesic efficacy of TAP block in our study can be attributed to the following:
Anatomically guided TAP blocks performed in the triangle of Petit can produce prolonged analgesia compared with ultrasound-guided techniques and this can be attributed to paravertebral spread  .
- The dose of ropivacaine used in our study (ropivacaine 0.5% 20 ml on each side) was not calculated according to body weight, which may have decreased the analgesic efficacy and duration;
- We elected to use the ultrasound technique for the TAP block and not the landmark technique used in the study by McDonnell et al.  .
The findings of this study add to the evidence shown in other studies ,, , which concluded that subarachnoid morphine provides superior analgesia when compared with ultrasound-guided TAP block after cesarean section.
In our study, we performed sham block in the ITM group by imitating the pressure sensation of performing the block without breaking the skin, as we believed that, under spinal anesthesia, the woman already had altered sensation over the abdomen and pushing a capped needle against the skin was sufficient to provide the blinding.
| Conclusion|| |
In this study, ITM had a superior analgesic efficacy after cesarean section than TAP block in morbidly obese parturients, as indicated by our findings that women who received the ultrasound-guided TAP block had a higher analgesic consumption after cesarean delivery associated with higher early pain score compared with those who received 100 mg of intrathecal morphine. However, this was associated with a lower incidence of opioid-related side effects in the TAP block group.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]