P. Hebbard

Determination of spread of injectate after ultrasound-guided transversus abdominis plane block: a cadaveric study

BACKGROUND The transversus abdominis plane (TAP) block is a new regional anaesthesia technique that provides analgesia after abdominal surgery. It involves injection of local anaesthetic into the plane between the transversus abdominis and the internal oblique muscles. The TAP block can be performed using a landmark technique through the lumbar triangle or with ultrasound guidance. The goal of this anatomical study with dye injection into the TAP and subsequent cadaver dissections was to establish the likely spread of local anaesthesia in vivo and the segmental nerve involvement resulting from ultrasound-guided TAP block. METHODS An ultrasound-guided injection of aniline dye into the TAP was performed for each hemi-abdominal wall of 10 unembalmed human cadavers and this was followed by dissection to determine the extent of dye spread and nerve involvement in the dye injection. RESULTS After excluding one pilot specimen and one with advanced tissue decomposition, 16 hemi-abdominal walls were successfully injected and dissected. The lower thoracic nerves (T10-T12) and first lumbar nerve (L1) were found emerging from posterior to anterior between the costal margin and the iliac crest. Segmental nerves T10, T11, T12, and L1 were involved in the dye in 50%, 100%, 100%, and 93% of cases, respectively. CONCLUSIONS This anatomical study shows that an ultrasound-guided TAP injection cephalad to the iliac crest is likely to involve the T10-L1 nerve roots, and implies that the technique may be limited to use in lower abdominal surgery.

Plasma ropivacaine concentrations after ultrasound-guided transversus abdominis plane block

BACKGROUND The transversus abdominis plane block is a novel technique involving injection of local anaesthetic between the internal oblique and the transversus abdominis muscles of the abdominal wall. It is possible that injection of a large dose of local anaesthetic into a relatively vascular plane may result in toxic concentrations. One previously published study examined plasma lidocaine concentrations after transversus abdominus plane block and showed potentially toxic plasma concentrations. Although ropivacaine is most commonly used for this technique, plasma concentrations of ropivacaine after this block have not been reported previously. METHODS Adult female patients undergoing elective open gynaecological surgery received bilateral ultrasound-guided transverse abdominal plane blocks before surgical incision (3 mg kg(-1) of ropivacaine diluted to 40 ml). Venous blood was collected each 15 min for the first hour, each 30 min for the second hour, and then at 3, 4, 12, and 24 h post-block. RESULTS Twenty-eight patients were recruited. The mean (sd) peak total ropivacaine concentration occurred 30 min post-injection and was 2.54 (sd 0.75) µg ml(-1). The highest measured concentration was 4.00 µg ml(-1), also 30 min post-injection. Mean total concentrations remained above 2.20 µg ml(-1) for up to 90 min post-injection. The mean unbound peak venous concentration was 0.14 (0.05) µg ml(-1), and the peak was 0.25 µg ml(-1). CONCLUSIONS Transversus abdominus plane block using 3 mg kg(-1) of ropivacaine produces venous plasma concentrations that are potentially neurotoxic, although broadly consistent with plasma levels found after injection at other comparable sites.

Ultrasound-Guided Continuous Oblique Subcostal Transversus Abdominis Plane Blockade Description of Anatomy and Clinical Technique

Background: Recently, ultrasound-guided transversus abdominis plane blockade for abdominal wall analgesia has been described, and it involves injection of local anesthetic into the transversus abdominis plane. The posterior approach involves injection of local anesthetic in the lateral abdominal wall between the costal margin and the iliac crest and is suitable for postoperative analgesia after surgery below the umbilicus. The subcostal approach is suitable after abdominal surgery in the periumbilical region. The subcostal block can be modified, and the needle can be introduced along the oblique subcostal line from the xyphoid process toward the anterior part of the iliac crest. Objective: The purpose of this brief technical report was to describe in detail the anatomy and the technique of continuous oblique subcostal blockade. The goal of this approach was to produce a wider sensory blockade suitable for analgesia after surgery both superior and inferior to the umbilicus. Conclusions: A catheter can be placed along the oblique subcostal line in the transversus abdominis plane for continuous infusion of local anesthetic. Multimodal analgesia and intravenous opioid are used in addition because visceral pain is not blocked. Continuous oblique subcostal transversus abdominis plane block is a new technique and requires both a detailed knowledge of sonographic anatomy and technical skill for it to be successful.

Spread of injectate after ultrasound-guided subcostal transversus abdominis plane block: a cadaveric study

Ultrasound‐guided transversus abdominis plane (TAP) block can be performed using a subcostal technique. This technique was simulated using dye injection in cadavers in order to determine segmental nerve involvement and spread of injectate using either single or multiple‐injection techniques. Dye most commonly spread to affect T9 and T10 nerves with the single injection technique and T9, T10 and T11 with multiple injections. The median (IQR [range]) spread of dye was 60 (36–63 [32–78]) cm2 using the single‐injection technique and 90 (85–96 [72–136]) cm2, in the multiple‐injection technique, and this difference was statistically significant (p = 0.003). These results indicate that ultrasound‐guided subcostal TAP block will involve nerve roots T9, T10 and T11 and that a multiple‐injection technique may block more segmental nerves and increase spread of injectate.

Symptomatic local anaesthetic toxicity and plasma ropivacaine concentrations after transversus abdominis plane block for Caesarean section

BACKGROUND The transversus abdominis plane (TAP) block involves injecting a large volume of local anaesthetic between the muscles of the abdominal wall. Plasma concentrations of ropivacaine after gynaecological laparotomy are potentially high enough to result in systemic toxicity, and there are pharmacokinetic reasons why pregnancy may increase susceptibility to local anaesthetic toxicity. METHODS Adult female patients (n=30) undergoing elective Caesarean section under spinal anaesthesia received bilateral ultrasound-guided TAP blocks after wound closure (2.5 mg kg(-1) of ropivacaine diluted to 40 ml). Venous blood samples were collected at 10, 20, 30, 45, 60, 90, 120, 180 and 240 min following the block. Blood samples were assayed for total and free ropivacaine concentrations. Patients were assessed for symptoms of local anaesthetic toxicity. RESULTS The mean [standard deviation (SD)] peak total concentration of ropivacaine occurred at 30 min post-injection and was 1.82 (0.69) μg ml(-1). The maximum detected concentration in any patient was 3.76 μg ml(-1) (at 10 min post-injection). Three patients reported symptoms of mild neurotoxicity, and the mean (SD) peak levels were elevated in these patients, 2.70 (0.46) µg ml(-1). CONCLUSIONS TAP blocks can result in elevated plasma ropivacaine concentrations in patients undergoing Caesarean section, which may be associated with neurotoxicity.

Transversalis fascia plane block, a novel ultrasound-guided abdominal wall nerve block

To the Editor, The lateral cutaneous branches (LCB) of the thoracoabdominal nerves (T6 to L1) arise proximal to the angle of the rib, run a short distance with the main nerve, and emerge obliquely through the overlying muscles in the midaxillary line. They pass superficially to supply the skin of the lateral thorax, the abdomen, the iliac crest, and the upper thigh as far as the greater trochanter of the femur. As previously described, it is rare to produce block of the LCB of the subcostal (T12) and iliohypogastric (L1) nerves when performing ultrasound-guided posterior transversus abdominis plane (TAP) block. The subcostal and iliohypogastric nerves normally send out their LCB preceding entry or very proximal in the TAP. The LCB leave the TAP in a more posterior position than the local anesthetic of the ultrasound-guided posterior TAP block, which appears on imaging as being restricted from spreading posterior to the extent of the muscle belly. The subcostal and iliohypogastric nerves pass deep over the anterior surface of the quadratus lumborum muscle, which extends from the 12th rib to the iliac crest. The subcostal nerve then continues a short distance deep to the aponeurotic posterior extension of the transversus abdominis muscle before passing through the aponeurosis into the TAP. The iliohypogastric nerve continues deep to the transversus muscle aponeurosis and belly to penetrate the transversus in a more anterior and highly variable position. Local anesthetic injected between the transversus abdominis muscle and its deep investing transversalis fascia will spread over the inner surface of the quadratus lumborum muscle and block the proximal portions of the T12 and L1 nerves. This will produce block of both the anterior and the lateral branches of these nerves. This transversalis fascia block (TFP) targets these nerves anatomically between the lumbar plexus block and the TAP block. With the patient in a supine position, the needle is advanced from the anterior using an in-plane technique. A linear or curvilinear ultrasound probe is orientated transversely over the lateral abdomen between the iliac crest and the costal margin. The external oblique, internal oblique, and transversus abdominis muscles are imaged, and the more posterior transversus aponeurosis is distinguished. The reflection of the peritoneum curving away from the muscles from anterior to posterior is identified, and the perinephric fat, which lies behind the peritoneum and deep to the transversalis fascia, identified. The perinephric fat is generally more prominent closer to the iliac crest. The quadratus lumborum is identified medial to the aponeurosis of the transversus abdominis. It may be confused with the partly overlying erector spinae muscle, which is more superficial and often more prominent on ultrasound (Fig. 1). To minimize the risk of peritoneal penetration or liver trauma, the block area should be sufficiently posterior so that the perinephric fat, rather than the peritoneum and liver, underlies the transversalis fascia. To enhance needle visibility, the needle insertion point is selected such that a 100–150 mm needle is introduced relatively perpendicular to the ultrasound beam, and the probe is slid anteriorly to image the needle throughout its course. The end point is more visible if the needle is passed through the posterior ‘‘tail’’ of the transversus muscle, as the transversus aponeurosis is thinner and less distinct as a separate layer. P. D. Hebbard, FANZCA (&) Anaesthesia and Pain Management Unit, University of Melbourne, Melbourne, VIC, Australia e-mail: p.hebbard@bigpond.com

TAP block nomenclature

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Ultrasound guided posterior approach to the infraclavicular brachial plexus.

Technique The ultrasound probe is placed on the anterior shoulder inferior to the clavicle and medial to the coracoid process (Fig. 1). The axillary vessels are identified in cross-section in the parasagittal plane. The ultrasound probe may be scanned medially at this point to confirm adequate separation from the pleural cavity and ribs. The needle insertion point is over the trapezius muscle sufficiently posterior to allow the needle to pass between the clavicle and the scapula in the direction of the axillary artery (Fig. 2). The insertion point is strictly aligned with the long axis of the ultrasound beam. The approximate insertion length to pass into the ultrasound beam is noted, about 30–40 mm. With the probe in one hand and needle in the other, a 100-mm needle is inserted in the inferior direction to the predetermined depth for initial visualisation and the probe alignment is manipulated until the needle is seen prominently in long axis in the ultrasound image. The needle is then manipulated to approach the brachial plexus (Fig. 3). If the scapula obstructs the needle, a sandbag placed to elevate the shoulder increases the gap between the scapula and clavicle, or a more medial approach may be used. The block is completed using visual perineural targeting of the nerve cords, a nerve stimulator or by perivascular infiltration. The local anaesthetic solution is seen as a black space surrounding the nerves (Fig. 4). Although the block needle passes through a longer course to reach the target, the superior visualisation of the entire tip section of the needle allows more confident alignment relative to neurovascular structures. The block needle is also more easily directed posterior to the artery than when using the conventional approach. Further information on this and other new ultrasound guided approaches may be found at www.heartweb.com.au

Ultrasound-guided supra-inguinal fascia iliaca block: a cadaveric evaluation of a novel approach

Existing descriptions of ultrasound‐guided fascia iliaca block focus on injection of local anaesthetic inferior to the inguinal ligament, relying on supra‐inguinal spread to block the lateral femoral cutaneous nerve in the iliac fossa. In this study, we explored injectate spread and nerve involvement in a cadaveric dye‐injection model, using a supra‐inguinal ultrasound‐guided technique that places local anaesthetic directly into the iliac fossa. Bilateral injections of 20 ml 0.25% aniline blue dye were made in six unembalmed cadavers. The femoral nerve was stained by the dye in all twelve injections. The lateral femoral cutaneous nerve was stained bilaterally in five cadavers, but the nerve was absent on both sides in the sixth cadaver. The ilio‐inguinal nerve passed into the iliac fossa over the iliacus muscle in eight of the hemi‐pelvi and was stained in seven of these occasions. We have performed more than 150 blocks in patients using this approach without complications. Injection using this technique in cadavers leads to extensive fluid spread throughout the iliac fossa. In patients this approach may allow a lower volume block of the femoral nerve and lateral femoral cutaneous nerve while still injecting at a distance from the femoral nerve.

Ultrasound-guided transversalis fascia plane block provides analgesia for anterior iliac crest bone graft harvesting

To the Editor, The iliac crest is primarily innervated by the L1 nerve root via the iliohypogastric and ilioinguinal nerves. We describe our preliminary experience with a transversalis fascia plane (TFP) block, which targets these nerves in the plane between the transversus abdominis (TA) aponeurosis or muscle and the deeper transversalis fascia. It can thus provide effective analgesia for anterior iliac crest bone graft (ICBG) harvesting. This technique is distinct from the transversus abdominis plane block, which does not reliably block the L1 dermatome, although its use has been described in ICBG harvesting. Following Ethics Board approval, we reviewed the records of 27 adult patients who underwent harvesting of an anterior ICBG as part of surgery on the distal forearm and wrist between November 1, 2009 and February 28, 2011 at the Toronto Western Hospital. All patients underwent general anesthesia preceded by a single-shot brachial plexus block with 30–40 mL of local anesthetic (1:1 mixture of 2% lidocaine and 0.5% bupivacaine, with epinephrine 2.5 lg mL). Twelve (44%) patients also underwent an ultrasound-guided TFP block. The ultrasound probe was placed in a transverse orientation above the iliac crest; and the external oblique, internal oblique (IO), and TA muscles were identified and traced posteriorly until first the TA muscle and then the IO muscle tapered into their common aponeurosis, adjacent to the quadratus lumborum muscle (Figure, A). The tip of a 22-gauge 80-mm block needle was positioned just deep to the TA muscle and its aponeurosis at the point where the TA tapered off. Ropivacaine 0.5% (20 mL) with epinephrine 5 lg mL was injected into the plane between the TA and underlying transversalis fascia (Figure, B). Intraoperative and postoperative analgesia of the ICBG harvest site was provided by systemic opioids at the discretion of the operating theatre and postanesthesia care unit (PACU) staff. We extracted data on opioid consumption and pain scores during the immediate perioperative period, defined as the time at which the patient entered the operating room to the time the patient left the PACU. We converted all opioid doses into intravenous morphine equivalents and divided patients into two groups for comparison based on whether they had undergone a TFP block. The mean (standard deviation) perioperative opioid dose was substantially lower in the patients who underwent a TFP block [18.5 (9.6) mg of intravenous morphine equivalent] than in those who did not [32.6 (12.4) mg] (P = 0.006). These patients received less intravenous morphine during both the intraoperative period [10.2 (5.6) mg vs 17.4 (6.6) mg; P = 0.009] and the PACU period [8.3 (9.6) mg vs 15.1 (11.2) mg; P = 0.114]. It is of note that only one (8%) patient received intravenous ketorolac 30 mg in the TFP group compared with five (33%) patients in the other group. Patients who underwent a TFP block also had lower resting pain scores in the PACU. Pain scores (median [range]) were lower in the TFP group both at admission to the PACU (2 [0–6] vs 6 [5–7]; P = 0.015) as K. J. Chin, MBBS (&) V. Chan, MD M. Harris, MB BChir Toronto Western Hospital, University of Toronto, Toronto, ON, Canada