Aneasthesia Pearls July 2013

ANAESTHESIA PEARLS

Transversus abdominis plane blocks

Transversus abdominis plane blocks
The landmark-based transversus abdominis plane (TAP) block involves the injection of local anaesthetic into the TAP plane via the triangle of Petit using a loss of resistance technique.
This approach is widely used in clinical practice as part of a multimodal analgesic regimen after major abdominal and gynaecological surgery involving both upper and lower abdominal incisions.
A number of distinct ultrasound-guided approaches have been described. Specifically, an anterior oblique-subcostal approach, a mid-axillary and a more lateral approach are in widespread clinical use.
TAP anatomy
There is a fascial sheath between the internal oblique and transverses abdominis muscles. The nerves lie deep to this fascia.
Nerves of T6-T9 enter the TAP medial to the anterior axillary line. T6 enters the TAP just lateral to the linea alba, and T7-T9 at progressively increasing distances from the linea alba. Nerves T9-L1 lies lateral to the anterior axillary line.
There is extensive branching and communication of the segmental nerves in the TAP. In particular the T9-L1 branches form a so-called “TAP plexus” that runs with the deep circumflex iliac artery. This may partly account for the ability of a single injection to cover several segmental levels.
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Plane of injection of local anesthetic:
TAP plane, between the transversus abdominis muscle and the fascial layer deep to the internal oblique muscle.
Dose: A total of 20-30 mL of local anesthetic (e.g., ropivacaine 0.5 to 0.75%) is injected into this plane on each side. The maximum recommended dose of local anesthetic (3 mg/kg of ropivacaine) should not be exceeded.
Approach:
Subcostal and sub-costal oblique TAP block
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The transversus plane may also be used for analgesia superior to the umbilicus and as far superiorly as the xyphoid process by deposition of the local anaesthetic into the transversus plane along the costal margin.
This subcostal TAP block is performed by identifying the rectus abdominis near the costal margin and imaging the underlying transversus abdominis muscle. The transversus can usually be followed right along from near the xyphoid to the iliac crest in one line, this is called the sub-costal oblique line.(fig)
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copy righr @ 2011 The Authors, Anaesthesia _ 2011 The Association of Anaesthetists of Great Britain and Ireland
At the level of the 8th or 9th costal cartilage there is often an aponeurotic area between the lateral edge of rectus abdominus and the medial edge of internal oblique. In this area transversus is the only muscle between skin and peritoneum.
For subcostal TAP block the needle is introduced several cm from the probe to come into view in plane and near perpendicular to the probe. With a 20cm needle the block may be continued right along the costal margin to provide the most extensive blockade of the anterior abdominal wall. When blocking near the xyphoid care needs to be taken to avoid the superior epigastric arteries.
(For further details watch the video)
Mid-axillary approach
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Copy right@ 2011 The Authors, Anaesthesia _ 2011 The Association of Anaesthetists of Great Britain and Ireland
In the supine position and the ultrasound probe was placed between the iliac crest and the costal margin and the TAP identified. The needle entry point on the skin was chosen based on adequate identification of the muscle layers. The needle was seen using an in-plane technique (For optimal imaging of the needle it should be held parallel to the long axis of the ultrasound probe), and gradually advanced in an antero posterior direction so that the injectate was at the posterior part of the TAP at approximately the mid-axillary line.
Posterior approach
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Copy right @ 2011 The Authors, Anaesthesia _ 2011 The Association of Anaesthetists of Great Britain and Ireland
The ultrasound probe was placed obliquely over the postero-lateral abdominal wall, posterior to the mid-axillary line between the costal margin and iliac crest. The needle was inserted and advanced using an in-plane technique passing from anterior to posterior until the needle tip was positioned at the intersection of the quadratus lumborum and the lateral abdominal muscles, superficial to the transversalis fascia. The injectate was directed in a superomedial manner towards the thoracic region.
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Traditional (Blind) Approach
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In this approach, the lumbar triangle of Petit is identified. The triangle of Petit is formed by the iliac crest as the base, the external oblique muscle as the anterior border, and the latissimus dorsi muscle as the posterior border. The floor of the triangle is made up of the fascia from both the external and internal oblique muscles. A needle is inserted perpendicular to the skin just cephalad to the iliac crest near the midaxillary line. The TAP is identified using a 2-pop sensation (loss of resistance). The first pop indicates penetration of the fascia of the external oblique muscle, and the second indicates penetration of the fascia of the internal oblique muscle. Local anesthetic is then injected with multiple aspirations.
VIDEOS
Ref:
1.US-Guided Thoracolumbar Nerve (TAP and Rectus Sheath) Blocks.Peter Hebbard ASRA Spring meeting 2012
2.Studies on the spread of local anaesthetic solution in transversus abdominis plane blocks Anaesthesia, 2011, 66, pages 1023–1030
3.Update in Anaesthesia: The Transversus Abdominis Plane (TAP) block: Abdominal plane regional anaesthesia
4.Ultrasound-guided Subcostal Transversus Abdominis Plane Block.Ultrasound-guided Subcostal Transversus Abdominis Plane Block International Journal of Ultrasound and Applied Technologies in Perioperative Care, January-April 2010;1(1):9-12
Downloads:
TRANSVERSUS ABDOMINIS PLANE (TAP) BLOCK – NYSORA
Ultrasound-guided RA & PM education:Ultrasound-guided transversus abdominis plane (TAP) block by Dr. Salinas

Post-operative residual curarization (PORC)

Post-operative residual curarization (PORC) – A Big Issue for Patients’ Safety
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Definition
PORC is an abbreviation for postoperative residual curarization, identified by instrumental signs (TOF Ratio <0.9 -1.0) and clinical signs such as:
Evident muscle fatigue or ‘fade’
Attenuation of the hypoxic reflex
Pharyngolaryngeal dysfunction with loss of airway patency and the risk of “aspiration”
Reduction of the cough reflex
Incidence
Study Pancuronium Atracurium Vecuronium Rocuronium
Bevan et al 36% 4% 9%
Hayes et al 52% 64% 39%
Baillard et al 42%
Kim et al 25% 15%
Murphy et al 40% 5.9%
Adverse effects of residual neuromuscular block
Volunteer studies
Impaired pharyngeal function
Increased risk of aspiration
Upper airway obstruction
Impaired hypoxic ventilatory drive
Profound symptoms of muscle weakness
Clinical studies in surgical patients
Delays in meeting PACU discharge criteria and achieving actual discharge
Symptoms and signs of profound muscle weakness
Increased risk of postoperative hypoxemia
Prolonged postoperative intubation times (cardiac surgical patients)
Increased risk of postoperative respiratory complications
Assessment of residual neuromuscular block
Visual and tactile evaluation (for surface muscles): Subjective method and therefore dependent on the individual assessment.
Among the various clinical criteria, there are some proved unreliable (tongue protrusion, eye opening, normal or near normal vital capacity, inspiratory pressure < -25 cm H2O, arm raised toward the opposite shoulder), others not very reliable (head lift test, holding hand for 5 seconds, lifting leg for 5 seconds, maximum inspiratory pressure > – 50 cmH2O), and finally the only one that seems pretty reliable, the tongue depressor test, which seems to correspond to a value of TOF> 0.8 -0.9.
Clinical tests used to assess adequacy of reversal for neuromuscolar blockade:
Induction of muscle relaxation
Reduction or disappearance of the respiratory movements
Fasciculations (succinylcholine)<
Easy extension of the head
Easy positive pressure mask ventilation
mouth opening
Easy tracheal intubation
Absence of cough during intubation
Maintenance of muscle relaxation
Relaxation of the abdominal muscles
If partial paralysis: maladaptation to mechanical ventilation, diaphragmatic movements, increased peripheral muscle tone, contraction of frontal muscles, eyelid reflex
Recovery of muscle relaxation: Testing of awakening
Ability to lift the eyelids
Ability to protrude the tongue
Ability to cough
Ability to shake hands
Ability to keep an arm raised
Ability to lift head
Vital capacity greater than 15 ml / kg
Inspiratory force of at least -25 cmH20
Tongue-depressor test: ability to squeeze an object between the teeth, resisting the removal
Standard peripheral nerve stimulator
The ulnar nerve at the wrist is the most popular site for neurostimulation, and the response at the adductor pollicis is observed. The facial nerve is also frequently used as a monitoring/stimulation site, and contraction of the muscles around the eye evaluated.
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Single twitch: In the single-twitch mode of stimulation, single supramaximal electrical stimuli are applied to a peripheral motor nerve at frequencies ranging from 1.0 Hz (once every second) to 0.1Hz (once every 10 seconds) Twitch height will begin to decrease when 75% of nicotinic acetylcholine receptors are blocked and will disappear when 90-95% of the receptors are occupied.
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TOF: TOF stimulation is the most frequently used pattern of neurostimulation in the perioperative setting. In TOF nerve stimulation, introduced by Ali and associates during the early 1970s, four supramaximal stimuli are given every 0.5 seconds (2 Hz) The TOF count is simple to perform and does not require a control twitch height. When 70-75% of the nicotinic acetylcholine receptors are blocked, the forth response (T4) is decreased. The T3, T2, And T1 responses are abolished when 85%, 85-90%, and 90-98% of the nicotinic acetylcholine receptors are occupied, respectively.
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Tetanic stimulation and post-tetanic count: stimulation of motor nerves at frequencies >30 Hz results in fusion of twitch responses and a sustained muscle contraction. Fade (decrease in muscle response to rapid stimulation) is observed during tetanic stimulation when more than 70-75% of the nicotinic acetylcholine receptors are blocked. The degree of fade can be used to estimate the intensity of neuromuscular blockade. When a single twitch stimulus is applied within 2 min of a tetanic stimulus, an enhanced response occurs as a result of posttetanic potentiation. A post-tetanic count is performed by applying supramaximal stimuli once every second following a 5-s 50 Hz tetanic stimulus. The post-tetanic count can be used to assess deep neuromuscular blockade and to estimate time to recover twitches when no response to TOF stimulation is present.
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Double-burst stimulation (DBS): DBS involves the application of 2 short bursts of tetanic stimuli (50 Hz) separated by a 750 ms interval. Each burst consist of a series of 3 and 2 impulses (DBS3,2) or 3 and 3 impulses (DBS3,3). DBS was developed to allow clinicians to more accurately assess small degrees of residual paresis using visual or tactile observations. Pattern of electrical stimulation and evoked muscle responses to TOF nerve stimulation and double-burst nerve stimulation:
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Clinical uses of stimulation
Nerve stimulation in clinical anesthesia is usually synonymous with TOF nerve stimulation. Therefore, the recorded response to this form of stimulation is used to explain how to evaluate the degree of neuromuscular blockade during clinical anesthesia.
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Which modes of nerve stimulation can be used at various periperative times
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Quantitative neuromuscular monitoring
Quantitative neuromuscular monitoring was developed in order to allow clinicians to accurately measure single twitch height and TOF ratio values. Three methods of recording evoked responses are available:
Mechanomyography: mechanomyography measures the mechanical force of a muscle contraction. Isometric contraction of the adductor pollicis is quantified following ulnar nerve stimulation.
However, since the equipment is bulky and difficult to set up and use, mechanomyography is rarely used in clinical practice.
Electromyography (EMG): EMG measures the electrical activity (compound muscle action potentials) of the stimulated muscle. Typically, EMG responses are measured with electrodes at the thenar eminence, the hypothenar eminence, or the first dorsal interosseous muscles of the hand.
EMG is rarely used in the operating room setting.
Acceleromyography: mechanomyography and electromyography are utilized primarily as research tools. Acceleromyography technology was developed for routine clinical use in the operating room, PACU, and ICU.
Acceleromyography is based on Newton’s second law which states that force = mass x acceleration. If mass is constant, force can be calculated by measuring acceleration. Acceleration of the stimulated muscle is quantified using a small piezoelectric crystal embedded in a transducer. A small electrical signal is generated in the transducer during movement of a muscle, which is amplified and displayed on the device. Since no preload is required on the stimulated muscle, additional monitoring sites can be used (muscles surrounding the eyes).
Algorithm illustrating the logic for the use of a PNS during the course of Anaesthesia
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Methods to reduce the risks of residual neuromuscular blockade
Avoidance of long-acting NMBAs
Use of routine neuromuscular monitoring in the operating room
Acceleromyography monitoring during the surgical procedure and prior to tracheal extubation may have a beneficial impact on the incidence of residual paresis.
Avoidance of total twitch suppression(Reversal of neuromuscular blockade should not be attempted until spontaneous recovery of neuromuscular function has occurred (at least 1 response to TOF stimulation). The risk of intense neuromuscular block at the conclusion of the surgical procedure is increased if a TOF count of 0 is maintained intraoperatively. Fortunately, profound muscle relaxation is rarely required in the operating room. A TOF count of 0 should be maintained during a surgical procedure only if patient movement or coughing could result in serious injury (i.e., during ophthalmic surgery on an open globe or during procedures on patients with critically elevated intracranial pressure). Adequate surgical relaxation (abdominal surgery) is usually present at a TOF count of 1-2.)
Routine reversal of NMBAs’
Reversal of neuromuscular blockade at a TOF count of 2-3
Early antagonism of neuromuscular blockade (Since full reversal of more intense levels of neuromuscular block may require up to 20-30 min, anticholinesterases should be used at least 15-30 before the anticipated time of tracheal extubation. Antagonism of NMBAs should be initiated when muscle relaxation is no longer needed instead of at the conclusion of skin closure)
Note
It is difficult, and often impossible, by clinical evaluation of recovery of neuromuscular function, to exclude with certainty clinically significant residual curarization.
Absence of tactile fade in the response to TOF stimulation, tetanic stimulation and DBS does not exclude significant residual block
Ref:
1. Post-Operative Residual Curarization (PORC): A Big Issue for Patients’ Safety A. Castagnoli, M. Adversi, G. Innocenti, G.F. Di Nino and R.M. Melotti Anesthesiology and Intensive Care, S. Orsola-Malpighi Hospital, University of Bologna,Italy.
2. Residual neuromuscular blockade: incidence, assessment, and relevance in the postoperative period. G. S. MURPHY, MINERVA ANESTESIOL 2006;72:97-109
3. Neuromuscular Monitoring – Jørgen Viby-Mogensen
4. Neuromuscular monitoring and postoperative residual curarization: a meta-analysis British Journal of Anaesthesia 98 (3): 302–16 (2007)
5. Postoperative Residual Curarization: Clinical Observation in the Post-anesthesia Care Unit. Chang Gung Med J Vol. 31 No. 4 July-August 2008
6. Postoperative residual curarization from intermediate-acting neuromuscular blocking agents delays recovery room discharge. Br. J. Anaesth. (2010) 105 (3): 304-309.
7. Bevan DR, Smith CE, Donati F. Postoperative neuromuscular blockade: a comparison between atracurium, vecuronium, and pancuronium. Anesthesiology 1988;69:272-6.
8. Hayes AH, Mirakhur RK, Breslin DS, Reid JE, McCourt KC. Postoperative residual block after intermediateacting neuromuscular blocking drugs. Anaesthesia 2001;56:312-8.
9. Baillard C, Gehan G, Reboul-Marty J, Larmignat P, Samama CM, Cupa M. Residual curarization in the recovery room after vecuronium. Br J Anaesth 2000;84:394-5.
10. Debaene B, Plaud B, Dilly MP, Donati F. Residual paralysis in the PACU after a single intubating dose of nondepolarizing muscle relaxant with an intermediate duration of action. Anesthesiology 2003;98:1042-8.
11. Kim KS, Lew SH, Cho HY, Cheong MA. Residual paralysis induced by either vecuronium or rocuronium after reversal with pyridostigmine. Anesth Analg 2002;95:1656-60.
12. Murphy GS, Szokol JW, Franklin M, Marymont JH, Avram MJ, Vender JS. Postanesthesia care unit recovery times and neuromuscular blocking drugs: a prospective study of orthopedic surgical patients randomized to receive pancuronium or rocuronium. Anesth Analg 2004;98:193-200.
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