William F. Urmey

One hundred percent incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus anesthesia as diagnosed by ultrasonography

Interscalene brachial plexus anesthesia for shoulder surgery routinely includes sensory anesthesia of the fourth and fifth cervical nerves. The authors reasoned that some degree of diaphragm paralysis should result from interscalene blocks that produce surgical C3-C5 sensory anesthesia. In this investigation, ultrasonography was used to study the incidence of ipsilateral hemidiaphragmatic paresis during, routine interscalene block, as it is a practical, sensitive, and low‐risk method for diagnosing hemidiaphragmatic function without radiation exposure. Thirteen healthy patients received interscalene blocks using a paresthesia technique with 34–52 mL 1.5% mepivacaine with added epinephrine and bicarbonate. All developed cervical sensory anesthesia. Data were collected before and 2, 5, and 10 min after injection, and, when possible (11 of 13 patients), at hourly intervals after surgery. Changes from normal to paradoxical motion of the ipsilateral hemidiaphragm were seen in all 13 patients during sniff and Mueller maneuvers within 5 min (in 11 of 13 patients at 2 mid. Diaphragmatic motion returned to normal in 10 of11 patients between 3 and 4 h after injection and in the remaining patient by the fifth hour after injection. Diaphragmatic paresis appears to be an inevitable consequence of interscalene brachial plexus block when providing anesthesia sufficient for shoulder surgery.

Hemidiaphragmatic paresis during interscalene brachial plexus block: effects on pulmonary function and chest wall mechanics.

We studied the effects of unilateral hemidiaphragmatic paresis caused by interscalene brachial plexus block on routine pulmonary function in eight patients. In an additional four patients, we studied changes in chest wall motion during interscalene block anesthesia by chest wall magnetometry. Ipsilateral hemidiaphragmatic paresis, as diagnosed by ultrasonography, developed in all patients within 5 min of interscalene injection of 45 mL of 1.5% mepivacaine with added epinephrine and bicarbonate. Large decreases in all pulmonary function variables were measured in every patient. Forced vital capacity and forced expiratory volume at 1 s decreased 27% +/- 4.3% and 26.4% +/- 6.8%, respectively (P = 0.0001). Peak expiratory and maximum midexpiratory flow rates were also significantly reduced. Interscalene block caused changes in pulmonary function and chest wall mechanical motion that were similar to those published in previous studies on patients with hemidiaphragmatic paresis of pathological or surgical etiology. Interscalene block probably should not be performed in patients who are dependent on intact diaphragmatic function and in those patients unable to tolerate a 25% reduction in pulmonary function.

Inability to Consistently Elicit a Motor Response following Sensory Paresthesia during Interscalene Block Administration

BackgroundTwo methods of nerve block based on eliciting neural feedback with the block needle currently exist. The paresthesia technique uses sensory feedback to ascertain that the needle tip is close to the nerve. By contrast, a peripheral nerve stimulator makes use of motor responses to electrical

Combined spinal-epidural anesthesia for outpatient surgery. Dose-response characteristics of intrathecal isobaric lidocaine using a 27-gauge Whitacre spinal needle.

Background : Combined spinal-epidural anesthesia (CSE) may offer theoretic advantages for outpatient surgery, because it produces the rapid onset of spinal anesthesia, with the option to extend the blockade with an epidural catheter. In this study, the authors attempted to determine an appropriate initial dose of a short-acting local anesthetic, 2% lidocaine, to administer for outpatient knee arthroscopy using CSE. Methods : Data were collected from 90 patients undergoing outpatient knee arthroscopy. Using a double-blinded, prospective study design, patients were randomly assigned to receive CSE with an initial dose of intrathecal 2% lidocaine of 40, 60, or 80 mg. A 27-G 4 11/16-inch Whitacre needle was placed through a 17-G Weiss needle. Onset and regression of sensory anesthesia and motor blockade were measured by a blinded observer at frequent intervals. Results : All 90 patients had adequate anesthesia. Durations of thoracic and lumbar sensory and lower limb motor blockade were significantly shorter in the 40-mg group compared with the 60- or 80-mg groups (P < 0.0002 Mantel-Cox, Survivorship Analysis). Indices of neural blockade resolved 30-40 min more rapidly in the 40-mg group than in either the 60- or 80-mg group. Times to urinate, sit upright in a chair, take oral fluids, and be discharged were all significantly shorter (between 30 and 60 min) in the 40-mg group compared with the 60- and 80-mg groups (P < 0.01). Seven patients required intraoperative epidural supplementation : three in the 40-mg group, three in the 60-mg group, and one in the 80-mg group. Conclusions : Combined spinal-epidural anesthesia with a 40-mg initial intrathecal dose of lidocaine provided reliable anesthesia for knee arthroscopy. Duration of spinal anesthesia with lidocaine was dose related.

Percutaneous electrode guidance: a noninvasive technique for prelocation of peripheral nerves to facilitate peripheral plexus or nerve block.

Background and Objectives Typically, peripheral nerve block is done by approximating nerve location, usually by use of anatomical landmarks. Precise nerve location has been done by needle exploration. A new method, percutaneous electrode guidance (PEG) of the block needle, was performed. A transcutaneous stimulating cylindrical electrode was used to indent the skin, locate the underlying nerve, and guide a block needle near it. Methods PEG was used to prelocate the desired nerve or neural plexus by use of a shielded cylindrical electrode with a 1-mm-diameter conductive area of skin contact at the distal end, the center of which contained a 22-gauge (1/2 mm) hole, which precisely matched a shielded conventional block needle. Transcutaneous stimulation began at less than 10 mA and was decreased to minimal amperage that elicited the desired motor response. Electrode position was fixed, and electrode current was discontinued. A shielded 22-gauge block needle was advanced through the electrode guide to near the underlying nerve. Initial needle current was only 0.5 mA. Local anesthetic was injected to block the targeted nerve or nerves. Standard sensory/motor testing was performed at 20 minutes. Results Nine upper or lower extremity blocks were performed on 7 patients. All were successful. Minimal stimulating currents were 1.3 to 8.2 mA for transcutaneous electrode stimulation and 0.20 to 0.70 for needle stimulation. Needle depth was 0.4 to 1.1 cm beyond the electrode tip and correlated with minimal electrode stimulating current. Conclusions A smooth, metal-tipped electrically shielded skin electrode probe can be used to comfortably and accurately indent the skin over a desired nerve or plexus, define its anatomical course, and subsequently guide a block needle near it.

Relationship between evoked motor response and sensory paresthesia in interscalene brachial plexus block

Background and Objectives: This study sought to define the relationship between a paresthesia and a motor response (MR) to electrical nerve stimulation using a peripheral nerve stimulator (PNS) during interscalene block. We sought to determine if at a low amperage (≤1.0 mA) a MR would precede a paresthesia. Methods: Twenty-two interscalene blocks were performed using insulated needles and a PNS. A MR was obtained at 0.5 mA and then the PNS was turned off. The needle was further advanced until a paresthesia was elicited. The PNS was again turned on, the needle held immobile, and the amperage increased in 0.1 mA increments up to 0.5 mA, or an MR obtained, whichever occurred first. If no MR was obtained, the needle was withdrawn at 0.5 mA in the same direction as it entered until MR was again observed. Results: A MR was obtained at 0.5 mA in all the patients. After the PNS was turned off and the needle further advanced, a paresthesia was elicited in 21 patients. When the PNS was turned on again, a MR was produced at 0 to 0.5 mA in 13 patients. In a subset of 8 patients without a second MR to stimulation up to 0.5 mA, the needle was withdrawn at that amperage. A MR was subsequently obtained during withdrawal in each patient in this subset. Conclusions: MR preceded paresthesia in every patient. The most likely explanation for this observation is that MR can be achieved at a small distance from the nerve, whereas elicitation of mechanical paresthesia requires either nerve contact or more intimate location of the needles tip relative to the nerve. Another possible explanation is that motor fibers are located in a more superficial position and are therefore encountered first. Motor and sensory responses are separate and discrete phenomena.

The direction of the Whitacre needle aperture affects the extent and duration of isobaric spinal anesthesia.

The use of Whitacre spinal needles results in directional flow out of the needle aperture, diverting local anesthetic from the longitudinal axis of the needle.Thus, a change in orientation of the needle aperture would be expected to result in a different local anesthetic distribution in the subarachnoid space. We studied 40 outpatients undergoing elective knee arthroscopy under spinal anesthesia with 60 mg plain lidocaine 2% in a prospective, double-blinded manner. Patients were randomly assigned to either Group I (needle aperture oriented in a cephalad direction throughout intrathecal injection) or Group II (aperture directed caudally). Onset and offset of sensory and motor block were analyzed at frequent intervals. Times to completion of ambulatory milestones, including discharge, were recorded. Group I was characterized by a higher sensory level (T 3.4 +/- 1.3 vs T 6.6 +/- 2.8, P < 0.001). Group I had significantly shorter duration of lumbar sensory anesthesia (149.2 +/- 30.6 min vs 177.8 +/- 23.5 min, P < 0.01) and motor blockade (117.6 +/- 26.1 min vs 150.0 +/- 22.8 min, P < 0.001). Mean time to outpatient discharge was approximately 32 min shorter in Group I. The orientation of the Whitacre needle aperture exerts a major influence on sensory level, as well as the duration of isobaric lidocaine spinal anesthesia. (Anesth Analg 1997;84:337-41)

Interscalene block: The truth about twitches

Anethesia of the brachial plexus was first accomplished more than one century ago when surgeons (the first ‘‘regional anesthetists’’) dissected, then directly and separately injected the roots of the brachial plexus in the neck. Subsequently, percutaneous techniques for brachial plexus block that involved multiple separate injections of local anesthetic were described and practiced. Perhaps the most significant conceptual advance in brachial plexus anesthesia, both in terms of our scientific understanding as well as practical clinical application, can be attributed to Alon Winnie. Winnie promoted the concept of the brachial plexus as being enveloped by a fascial sheath. This conceptual sheath serves to isolate the plexus in a functional anatomical compartment. Based on this concept, he proposed that a single injection of local anesthetic anywhere along the tubular plexus sheath would result in successful brachial plexus anesthesia. The sheath concept paved the way for Winnie’s original description of the interscalene technique of brachial plexus block in 1970.1 Brachial plexus block thus became analogous to epidural anesthesia; i.e., once the compartment is entered, a single injection of an adequate volume of local anesthetic results in successful anesthesia in the vast majority of cases. The consistent objective for the anesthetist performing the block reduced simply to reliably ascertaining that the needle tip is within the confines of the brachial plexus sheath. Whereas this problem appears to be straightforward, traditional teaching has included misconceptions and myths with regard to which paresthesias or twitches are acceptable when performing interscalene blocks. Only recently have some misconceptions been disproved by careful clinical research. Although often misreferenced to include the use of a nerve stimulator, Winnie’s original technique of interscalene block was in fact a single paresthesia technique. In his writings, Winnie emphasized that ‘‘only a paresthesia below the level of the shoulder is acceptable, since a paresthesia to the shoulder could result from stimulation of the suprascapular nerve inside or outside the sheath.’’2 Regional anesthesia textbooks also recommended that shoulder paresthesias be ‘‘discarded’’ and that more distal paresthesias be sought.2-5 Winnie’s technique has since been modified following the advent of the use of a peripheral nerve stimulator to incorporate this useful aid. Nigel Sharrock first promoted the acceptance of a shoulder paresthesia in clinical practice when performing interscalene block. He emphasized that nerve roots supplying sensory innervation to the shoulder were more superficial and, upon advancing the needle, were therefore more characteristically encountered earlier than were more distal paresthesias. Indeed, work in his department by Roch et al.6 in 1992 reinforced his clinical experience; a shoulder paresthesia was the first paresthesia encountered in 45% of patients in this study of 45 patients who underwent interscalene block. These results indicated that a shoulder paresthesia was as effective as a more distal paresthesia. The investigators discussed that further needle probing in search of a distal paresthesia may increase patient discomfort and theoretically increase block-related neuropraxia.

Spinal anaesthesia for outpatient surgery.

Spinal anaesthesia in the outpatient is characterized by rapid onset and offset, easy administration, minimal expense, and minimal side effects or complications. Spinal anaesthesia offers advantages for outpatient lower extremity, perineal, and many abdominal and gynaecological procedures. Development of small-gauge, pencil-point needles are responsible for the success of outpatient spinal anaesthesia with acceptable rates (0-2%) of postdural puncture headache (PDPH). Compared with peripheral nerve blocks, spinal anaesthesia has a more predictable offset. There are many possible choices of local anaesthetics for outpatient spinal anaesthesia. These include lidocaine, prilocaine, mepivacaine and small doses of bupivacaine. Meperidine has local anaesthetic properties in addition to its opiate properties. It has been used as the sole intrathecal agent for spinal anaesthesia but has no real advantages over lidocaine. Mepivacaine and lidocaine have each been associated with transient neurological symptoms (TNS) following intrathecal administration. This has stimulated development of alternative agents, including combinations of local anaesthetics and opioids. Lidocaine remains the most useful agent for outpatient spinal anaesthesia. For longer procedures, mepivacaine is an excellent spinal anaesthetic agent. Attention to technique, reduction of dose and addition of fentanyl to lidocaine result in effective spinal anaesthesia with rapid recovery and a low incidence of significant side effects or complications.

Use of Sequential Electrical Nerve Stimuli (sens) for Location of the Sciatic Nerve and Lumbar Plexus

Background and Objectives: Conventional electrical stimulation has been done by continuous adjustment of current amplitude at a single, set pulse duration (conventionally, 0.1 ms). This study evaluated a novel technique for nerve location by utilization of a peripheral-nerve stimulator (PNS) programmed to deliver sequential electrical nerve stimuli (SENS). A repeating series of alternating sequential pulses of 0.1, 0.3, and 1.0 ms at 1/3-second period intervals between pulses were generated so that at a greater distance from the nerve, only higher-duration pulses would stimulate the targeted nerve and result in 1 or 2 motor responses (MR) per second. Three MR per second at 0.5 mA or less signified the conventional endpoint for nerve location (≤0.5 mA, 0.1 ms) because that value indicated that the 0.1-ms pulse was effective. The conventional 0.1-ms pulse served as a built-in control to which the SENS was compared. Methods: Sixteen sciatic/psoas blocks were performed on 8 patients. Nerve location was by SENS, with an 80-mm block needle. Needle advance began at 1.0 mA until MR. If 1 or 2 MR/s occurred, the needle was advanced until 3 MR/s were obtained. When 3 MR/s occurred at 0.5 mA or less, needle position was fixed (final position), and mA further decreased until MR disappeared. Two digital video cameras separately recorded needle depth and MR for analysis. Final needle position was designated as zero, and distance was calculated relative to it. Results: In 12 of 16 of the performed blocks, SENS resulted in advanced notification (1 or 2 MR/s), which yielded additional visual feedback compared with control before final nerve location and, thus, increased range. In 15 of 16 blocks, MR did not disappear, once elicited, through final needle location. Conclusions: SENS resulted in increased sensitivity without compromising specificity of nerve location.