Ultrasound-guided transversus abdominis plane block: A technically easier analgesic option in obese compared to epidural

Abstract

Ultrasound-guided transversus abdominis plane (TAP) block is an extremely attractive alternative to the technically difficult epidural in obese patients. It provides adequate perioperative analgesia and reduces the opioid requirement. The use of ultrasound has enhanced the accuracy of local anaesthetic deposition in the plane between internal oblique and transversus abdominis, thereby blocking the spinal nerves more effectively and hence enhancing the efficacy of analgesia. We present a case of 65-year-old male patient weighing 96 kg who underwent umbilical hernia repair and had adequate perioperative pain relief after the ultrasound-guided TAP block. Epidural analgesia planned for him was abandoned after we faced technical difficulty in securing the epidural, but the TAP block administered under ultrasound guidance ensured adequate pain relief perioperatively.

INTRODUCTION

The aim of transversus abdominis plane block (TAP) block is to deposit local anaesthetic in the plane between internal oblique and transversus abdominis, thereby blocking the spinal nerves. The use of ultrasound has enhanced the accuracy of local anaesthetic deposition and hence the efficacy of analgesia.[1]

TAP block provides adequate perioperative analgesia and reduces the opioid requirement, which can be detrimental to the respiratory function.[2,3]

This case report emphasises the importance of the TAP block to provide perioperative analgesia in obese patients in whom epidural (especially thoracic) may be technically difficult.

CASE REPORT

A 65-year-old male patient, known hypertensive on regular medication, weighing 96 kg, height 167 cm, body mass index (BMI) 34.5 kg/m², with no other known comorbidities was admitted with complaints of swelling, approximately 10 × 8 cm size over the lower abdomen, which was diagnosed as umbilical hernia. The patient was posted for umbilical hernia repair. The patient was evaluated the day prior to surgery and written and informed consent for anaesthesia was taken after explaining the various anaesthetic options and their perioperative implications. Preanaesthetic evaluation revealed his vitals: The heart rate of 90/min and blood pressure in the left arm supine position was 160/94 mmHg. The patient was a known hypertensive for 10 years on regular medication with a calcium channel blocker. Airway examination revealed modified mallampati class of four. Thoracic and lumbar intervertebral spaces were not felt due to subcutaneous fat. Preoperatively, complete blood picture, coagulation profile, serum electrolytes, and renal parameters were within normal limits. Electrocardiogram (ECG) showed left ventricular hypertrophy, but echocardiography was normal other than the same finding.

The patient was asked to continue his antihypertensive medication with tablet amlodipine 10 mg as scheduled. Antiaspiration prophylaxis was achieved with tablet ranitidine 150 mg and tablet metoclopramide 10 mg the night and 3 h prior to surgery. After assuring adequate nil per oral, the patient was shifted to the operation theatre. We had planned for epidural analgesia with general anaesthesia. Our preinduction monitors included five electrode ECG, noninvasive blood pressure, pulse oximetry, and capnography. Baseline vitals were recorded, heart rate of 90/min, blood pressure of 154/88 mmHg in the left arm supine position, and room air saturation was 98%. Using aseptic precautions, intravenous cannulation was done in the nondominant hand with 18 gauge cannula. An attempt was made to position the patient for epidural both in lateral decubitus and later in the sitting position, but could not be optimally attained due to his truncal obesity. Moreover, we could not appreciate the intervertebral spaces and spinous processes in either thoracic or lumbar region, so epidural plan was unsuccessful. The patient was explained about this eventuality. We planned for ultrasound-guided TAP block postinduction, for which written consent was taken. Since we expected this to be a difficult airway and the procedure was expected to last about 30-40 min as discussed with surgeons, we planned for general anaesthesia with ProSeal laryngeal mask airway (PLMA) on spontaneous/assisted ventilation without paralysis and USG-guided TAP block. The difficult airway cart was checked and kept ready in the operating room. After 5 min of preoxygenation in propped up position, anaesthesia was induced with 100 μg fentanyl and titrated dose of 250 mg propofol iv, till loss of verbal response. The anaesthetic plane was deepened with 2% isoflurane in 100% oxygen, size five ProSeal laryngeal mask airway was inserted, and position was confirmed after getting a capnograph trace and equal chest expansion bilaterally. Ryles tube was inserted and stomach was deflated. As patient was having inadequate spontaneous tidal volumes (200-300 mL), was put on synchronised Intermittent mandatory ventilation (SIMV) with mandatory rate of 12 breaths/min, tidal volume 600 mL, and a positive end expiratory pressure of 5 cm H₂O using the DatexOhmedaAespire machine. Anaesthesia was maintained on oxygen and nitous oxide (O₂: N₂O; 50:50) and 1.5% isoflurane. The TAP block was given bilaterally under ultrasound guidance, 15 mL of 0.5% bupivacaine was diluted with 15 mL normal saline (total volume 30 mL) was injected on each side, after placing the ultrasound probe transversely between the costal margin and iliac crest on the lateral abdominal wall, with the needle tip between the internal oblique and transversus abdominis. The pain relief was adequate as evidenced by the absence of tachycardia with skin incision and no supplemention was required with opioids or an anaesthetic throughout the procedure. The surgery was uneventful. Stomach was deflated again and antiemetic was given. PLMA was removed after patient was fully awake and breathing adequately. Intraoperatively, patient's hemodynamics were stable. Postoperatively, we monitored the pain scores using visual analogue scale (VAS) for next 24 every hour we monitored the VAS score and patient's comfort was ensured. During the first 14 h postoperatively, VAS was 1-2 and patient was not supplemented with any other analgesic. During the next 10 h, the effects of TAP block gradually weaned off and in the 15^th hour postoperatively, when the VAS was 4-5, the patient required additional analgesia in the form of 1 g (100 mL) of paracetamol intravenously over 15 min. At the end of 24 h postoperatively, the VAS was 4 and additional dose of paracetamol 1 g intravenously was given and shifted to ward. Thus, the requirement of opoids analgesics postoperatively.

Thus, the requirement of opoids analgesics reduced postoperatively by using the TAP block.

DISCUSSION

The TAP block given under ultrasound guidance is often the easier alternative to epidural for ensuring adequate analgesia in obese. Adequate pain relief after abdominal surgery is important as pain leads to many systemic adverse effects due to the stress response.[3] The overdose of opioids is associated with respiratory complications, and obese are more prone for it. Obesity is associated with a multiple systemic complications especially pulmonary abnormalities including decreased vital capacity, inspiratory capacity, expiratory reserve volume, and functional residual capacity (FRC).[4,5] Closing capacity in obese individuals is close to tidal volume specially in supine position leading to postoperative basal lung atelectasis. There is 50% reduction in FRC after general anaesthesia compared to 20% in non obese.[1] Postoperative splinting of diaphragm and reduction in lung compliance is more common in obese. The overdose of opioids postoperatively after a general anaesthetic can further aggravate these unwanted effects.

So, regional anaesthesia and analgesia is an alternative to avoid the adverse effects of general anaesthesia wherever possible. But it has its own technical limitations due to difficulty in identification of bony landmarks in obese patients. Also, there is a chance of exaggerated or unpredictable cephalad spread of local anaesthetics in epidural space in obese individuals.[4,6] Compared to regional analgesia, the advantages of the TAP block are absence of sympathetic and motor block and avoidance of possibility of damage to spinal cord structures.

The transversus abdominis plane is the fascial plane between the internal oblique and the transversus abdominis muscles. The deposition of local anaesthetic in this plane has shown to reliably produce block that extends from T 10 dermatome to L 1 dermatome and therefore is suitable for lower abdominal surgery. When we directly visualise all anatomical structures, the needle, and the spread of local anaesthetic by ultrasound guidance, it may be associated with an increased margin of safety and optimal block qualities. Also, obese patients, post lower abdominal surgeries are often put on deep vein thrombosis (DVT) prophylaxis, and epidural catheter if present, needs removal after timing with the DVT dose. The TAP block avoids all these problems and also leads to improved patient comfort. Adequate pain relief after abdominal surgery encourages the patient to have optimum respiratory function (by doing manoeuvres like incentive spirometry), avoiding complications like basal lung atelectasis. If the pain relief is attempted only with opioid use intravenously in obese where epidural catheter cannot be secured, there are chances of respiratory complications due to inadequate analgesia or opioid overdose. We feel that the TAP block under ultrasound guidance in obese patients will avoid the technical difficulties in securing epidural, yet provide excellent analgesia in lower abdominal surgeries.

Study on the TAP block done by Niraj et al. concluded that subcostal TAP catheter boluses may be an effective alternative to epidural infusion for providing postoperative analgesia after upper abdominal surgery.[7] TAP catheter infusions can prolong the pain relief postoperatively and will avoid interference with deep vein thrombosis (DVT) prophylaxis if given. We could have either inserted a TAP catheter to increase the duration of postoperative analgesia, in fact this could be done in future cases.

It has also been found that the analgesic effect of TAP block persists for atleast 24 h postoperatively and the block could be considered an integral part of multimodal analgesic strategy to control residual pain.[8]

The TAP block will also reduce the use of morphine and its complications like nausea, vomiting, sedation, and especially respiratory depression, in obese. Hence, it also ensures that the patient can be shifted to the ward from the postoperative intensive care unit much earlier in the absence of all these complications due to opioid use.

The disadvantage of the TAP block usage while ensuring adequate analgesia, is the requirement of the anaesthesiologist with expertise in ultrasound scanning, as it is essential to visualise the structures at all times to ensure the deposition of local anaesthetic in the correct plane. The other disadvantage being the inability to block visceral pain,[9] which can cause major discomfort, even though the main component of pain arising after abdominal surgery is from anterior abdominal wall itself.

Kadam et al. in their study described the ultrasound-guided continuous TAP block as a promising technique for postoperative analgesia even in major abdominal surgeries and demonstrated lower pain scores and reduced fentanyl requirement after the TAP block.[10] We feel the TAP block is an extremely attractive option for patients undergoing abdominal surgeries, especially in obese, on account of its relative simplicity, efficacy and safety.

CONCLUSION

Ultrasound-guided transversus abdominis plane block in obese patients scheduled for lower abdominal surgery can provide adequate perioperative analgesia and significantly reduces the systemic opioid requirement compared to standard general anaesthesia and avoids the difficulties and complications associated with epidural placement in obese.