|LETTER TO THE EDITOR
|Year : 2011 | Volume
| Issue : 2 | Page : 98-100
Sukhyanti Kerai, Kirti N Saxena
Maulana Azad Medical College and Associated Hospitals, New Delhi, India
|Date of Web Publication||17-Mar-2012|
D-65, MMTC Colony, Mehrauli Road, New Delhi 110017
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kerai S, Saxena KN. Author's reply. J Obstet Anaesth Crit Care 2011;1:98-100
I would like to thank Dr Athma Prasanna for reading our study with interest and commenting upon the same. I would like to clarify certain issues raised by him as follows:
- Both transversus abdominis analgesia plane block (TAP) and ilioinguinal/iliohypogastric nerve blocks are used to provide anesthesia for procedures involving lower abdominal wall. In TAP block, local anesthetics are injected into transversus abdominis plane, which is an anatomic space between internal oblique and transversus abdominis muscle and span the abdomen till these two muscles exit. The cadaveric studies , have shown that posterior TAP block is likely to involve T 10 -L 1 roots while the sub costal TAP block will involveT 9 ,T 10 and T 11 . The nerve endings anesthetized by blind landmark technique of TAP block, if given in correct plane, will include ilioinguinal/iliohypogastric nerves. These nerves, after emerging from first lumbar spinal root, superomedial to anterior superior iliac spine, pierce the transversus abdominis muscle to lie between it and the internal oblique. After traveling a short distance inferomedially, their ventral rami pierce the internal oblique to lie between the internal and external oblique muscles before giving off branches, which pierce the external oblique to provide cutaneous sensation.  The TAP block and the ilioinguinal/iliohypogastric nerve block both aim to block the same nerves supplying anterolateral abdominal wall. Therefore, the possibility of bilateral ilioinguinal/iliohypogastric nerve block by blind technique of TAP block cannot be ruled out. The analgesic efficacies of blind TAP block and ilioinguinal/iliohypogastric nerve block have not been compared. Recently Aveline et al, have compared ultrasound-guided TAP block and conventional ilioinguinal/iliohypogastric nerve block in day care open hernia repair in 273 patients. They found that patients who received TAP block expressed significantly less pain at rest on VAS score at 4, 12 and 24 h. The postoperative morphine requirement in first 24 h was also less in TAP group.
- Injection diclofenac 1 mg/kg was given by intramuscular route. The diclofenac preparation used in our study was available in a 3 ml vial containing 25 mg/ml. The drug for use was carefully calculated using an insulin syringe. For example, a 42 kg patient needed 42 mg of diclofenac, this 42 mg can be taken out by taking 1 ml (25mg) of drug in a 2 ml syringe and rest by adding 7 marks( 7 × 2.5=17.5mg) of insulin syringe.
- The patients were allowed to ambulate after subarachnoid block as soon as possible. The VAS score on movement after 30 min and onward were recorded by asking patient to cough, turn sideways, on walking, whichever was possible depending on the effect of residual SAB.
- The analgesic efficacy of landmark-based TAP block has been found to be last effective for 24-48 h on studies done by McDonnell et al,, [Table 1].
Use of landmark TAP block has been efficacious in pediatric population also. The 48-h mean morphine requirement (10.3 - 12.7 vs 22.3 -14.7 mg; P < 0.01) was reduced by TAP block in children after appendectomy compared to placebo block. 
In our study, the assessment was done till 24 h postoperatively and till that period the VAS score was less than 3 in TAP block group.
- Though the TAP is relatively avascular, Kato et al suggested that local anesthetic absorption after TAP block may in part result in leakage of injectate from TAP out into surrounding abdominal muscles, thereby leading to slow uptake.
- The drug used for TAP block in our study was 30 ml of 0.25% bupivacaine, which is 75 mg of bupivacaine. The weight in both the groups ranged from 42 to 65 kg; therefore, the dose of bupivacaine used was well within 2 mg/kg. We did not notice any clinical signs and symptoms that suggest the toxicity with bupivacaine; however, the serum concentration of bupivacaine was not measured in our study. The serum concentration of drugs with 40 ml of 1% lignocaine and 3mg/kg of ropivacaine diluted up to 40 ml in TAP block have been studied. , No study has been done yet with bupivacaine for TAP block. The high volume of local anesthetics used for TAP block has the potential to cause toxicity. Griffith et al, found that when 3 mg/kg of ropivacaine diluted up to 40 ml was used for bilateral ultrasound-guided TAP block, the mean peak total venous ropivacaine concentration exceed potential neurotoxic value (2.2 mcg/ml) at 15,30,60 and 90 min. Similarly Kato et al, found that use of 40 ml of 1% lignocaine resulted in peak mean serum concentration of lidocaine occurred 30 min after block (3.6±0.7 mcg/ml). The highest concentration of lidocaine (5.5mcg/ml) was reported after 15 min. The absence of adverse clinical signs and symptoms does not necessarily mean that drug has not crossed the blood toxic levels. The drug dose and volume, therefore, needs to be reduced and carefully selected. Apart from the absolute plasma level, the rate of increase in plasma local anaesthetic drug is also implicated in causing toxicity. The peak concentration of ropivacaine occurred 30 min post-injection in the study by Griffith et al, while the peak concentration of lignocaine was seen after 15min by Kato et al.  Therefore, the possibility of bupivacaine crossing the toxic serum concentration in our study, in absence of clinical effects, cannot be ruled out. However, the total dose of bupivacaine was less than 2 mg/kg and the total volume was 30 ml, in contrast to 40 ml as used in the above two studies.
| References|| |
|1.||Tran TM, Ivanusic JJ, Hebbard P, Barrington MJ. Determinants of spread of injectate after ultrasound -guided transversus abdominis plane block: A cadaveric study. Br J Anaesth 2009;102:123-7. |
|2.||Barrington MJ, Ivanusic JJ, Rozen WM, Hebbard P. Spread of injectate after ultrasound-guided subcostal subcostal transversus abdominis plane block: A cadaveric study. Anaesthesia 2009;64:745-50. |
|3.||Gray H. Anatomy of human the body. 12th ed. New York: Bartleby.com; 2000. p. 211-2. |
|4.||Aveline C, Le Hetet H, Le Roux A, Vautier P, Cognet F, Vinet E, et al. Comparison between ultrasound-guided transversus abdominis plane and conventional ilioinguinal/iliohypogastric nerve blocks for day-case open inguinal hernia repair. Br J Anaesth 2011;106:380-6. |
|5.||O'Donnell BD, McDonnell JG, McShane AJ. The transversus abdominis plane block (TAP) in open retropubic prostatectomy. Reg Anesth Pain Med 2006;31:91. |
|6.||McDonnell JG, O'Donnell B, Curley G, Hefferman A, Power C, Laffey JG. The analgesic efficacy of transversus abdominis plane block after abdominal surgery: A prospective randomized controlled trial. Anesth Analg 2007;104:193-7. |
|7.||McDonnell JG, Curley G, Carney J, et al. The analgesic efficacy of transversus abdominis plane block after caesarean delivery: A randomized controlled trial. Anesth Analg 2008;106:186-91. |
|8.||Carney J, Finnerty O, Rauf J, Curley J, McDonell JG, Laffey JG. Ipsilateral transversus abdominis plane block provides effective analgesia after appendecetomy in children: A randomized controlled trial. Anesth Analg 2010;111:998-1003. |
|9.||Kato N, Fujiwara Y, Harato M, Kurokawa S, Shibata Y, Harada J, et al. Serum concentration of lidocaine after transversus abdominis plane block. J Anesth 2009;23:298-300. |
|10.||Griffiths JD, Barron FA, Grant S, Bjorksten AR, Hebbard P, Royse CF. Plasma ropivacaine concentration after ultrasound guided transversus abdominis plane block. Br J Anaesth 2010;105:853- 6. |