Preetham J. Suresh

Continuous Femoral Nerve Blocks: Varying Local Anesthetic Delivery Method (Bolus versus Basal) to Minimize Quadriceps Motor Block while Maintaining Sensory Block

Background: Whether the method of local anesthetic administration for continuous femoral nerve blocks—basal infusion versus repeated hourly bolus doses—influences block effects remains unknown. Methods: Bilateral femoral perineural catheters were inserted in volunteers (n = 11). Ropivacaine 0.1% was concurrently administered through both catheters: a 6-h continuous 5 ml/h basal infusion on one side and 6 hourly bolus doses on the contralateral side. The primary endpoint was the maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle at hour 6. Secondary endpoints included quadriceps MVIC at other time points, hip adductor MVIC, and cutaneous sensation 2 cm medial to the distal quadriceps tendon in the 22 h after initiation of local anesthetic administration. Results: Quadriceps MVIC for limbs receiving 0.1% ropivacaine as a basal infusion declined by a mean (SD) of 84% (19) compared with 83% (24) for those receiving 0.1% ropivacaine as repeated bolus doses between baseline and hour 6 (paired t test P = 0.91). Intrasubject comparisons (left vs. right) also reflected a lack of difference: the mean basal-bolus difference in quadriceps MVIC at hour 6 was −1.1% (95% CI −22.0–19.8%). The similarity did not reach the a priori threshold for concluding equivalence, which was the 95% CI decreasing within ± 20%. There were similar minimal differences in the secondary endpoints during local anesthetic administration. Conclusions: This study did not find evidence to support the hypothesis that varying the method of local anesthetic administration—basal infusion versus repeated bolus doses—influences continuous femoral nerve block effects to a clinically significant degree.

Continuous femoral versus posterior lumbar plexus nerve blocks for analgesia after hip arthroplasty: a randomized, controlled study.

BACKGROUND:Hip arthroplasty frequently requires potent postoperative analgesia, often provided with an epidural or posterior lumbar plexus local anesthetic infusion. However, American Society of Regional Anesthesia guidelines now recommend against epidural and continuous posterior lumbar plexus blocks during administration of various perioperative anticoagulants often administered after hip arthroplasty. A continuous femoral nerve block is a possible analgesic alternative, but whether it provides comparable analgesia to a continuous posterior lumbar plexus block after hip arthroplasty remains unclear. We therefore tested the hypothesis that differing the catheter insertion site (femoral versus posterior lumbar plexus) after hip arthroplasty has no impact on postoperative analgesia. METHODS:Preoperatively, subjects undergoing hip arthroplasty were randomly assigned to receive either a femoral or a posterior lumbar plexus stimulating catheter inserted 5 to 15 cm or 0 to 1 cm past the needle tip, respectively. Postoperatively, patients received perineural ropivacaine, 0.2% (basal 6 mL/hr, bolus 4 mL, 30-minute lockout) for at least 2 days. The primary end point was the average daily pain scores as measured with a numeric rating scale (0–10) recorded in the 24-hour period beginning at 07:30 the morning after surgery, excluding twice-daily physical therapy sessions. Secondary end points included pain during physical therapy, ambulatory distance, and supplemental analgesic requirements during the same 24-hour period, as well as satisfaction with analgesia during hospitalization. RESULTS:The mean (SD) pain scores for subjects receiving a femoral infusion (n = 25) were 3.6 (1.8) versus 3.5 (1.8) for patients receiving a posterior lumbar plexus infusion (n = 22), resulting in a group difference of 0.1 (95% confidence interval −0.9 to 1.2; P = 0.78). Because the confidence interval was within a prespecified −1.6 to 1.6 range, we conclude that the effect of the 2 analgesic techniques on postoperative pain was equivalent. Similarly, we detected no differences between the 2 treatments with respect to the secondary end points, with one exception: subjects with a femoral catheter ambulated a median (10th–90th percentiles) 2 (0–17) m the morning after surgery, in comparison with 11 (0–31) m for subjects with a posterior lumbar plexus catheter (data nonparametric; P = 0.02). CONCLUSIONS:After hip arthroplasty, a continuous femoral nerve block is an acceptable analgesic alternative to a continuous posterior lumbar plexus block when using a stimulating perineural catheter. However, early ambulatory ability suffers with a femoral infusion.

Treatment of postmastectomy pain with ambulatory continuous paravertebral nerve blocks: a randomized, triple-masked, placebo-controlled study.

Background We aimed to determine with this randomized, triple-masked, placebo-controlled study if benefits are afforded by adding a multiple-day, ambulatory, continuous ropivacaine paravertebral nerve block to a single-injection ropivacaine paravertebral block after mastectomy. Methods Preoperatively, 60 subjects undergoing unilateral (n = 24) or bilateral (n = 36) mastectomy received either unilateral or bilateral paravertebral perineural catheter(s), respectively, inserted between the third and fourth thoracic transverse process(es). All subjects received an initial bolus of ropivacaine 0.5% (15 mL) via the catheter(s). Subjects were randomized to receive either perineural ropivacaine 0.4% or normal saline using portable infusion pump(s) [5 mL/h basal; 300 mL reservoir(s)]. Subjects remained hospitalized for at least 1 night and were subsequently discharged home where the catheter(s) were removed on postoperative day (POD) 3. Subjects were contacted by telephone on PODs 1, 4, 8, and 28. The primary end point was average pain (scale, 0–10) queried on POD 1. Results Average pain queried on POD 1 for subjects receiving perineural ropivacaine (n = 30) was a median (interquartile) of 2 (0–3), compared with 4 (1–5) for subjects receiving saline (n = 30; 95% confidence interval difference in medians, −4.0 to −0.3; P = 0.021]. During this same period, subjects receiving ropivacaine experienced a lower severity of breakthrough pain (5 [3–6] vs 7 [5–8]; P = 0.046) as well. As a result, subjects receiving perineural ropivacaine experienced less pain-induced physical and emotional dysfunction, as measured with the Brief Pain Inventory (lower score = less dysfunction): 14 (4–37) versus 57 (8–67) for subjects receiving perineural saline (P = 0.012). For the subscale that measures the degree of interference of pain on 7 domains, such as general activity and relationships, subjects receiving perineural saline reported a median score 10 times higher (more dysfunction) than those receiving ropivacaine (3 [0–24] vs 33 [0–44]; P = 0.035). In contrast, after infusion discontinuation, there were no statistically significant differences detected between treatment groups. Conclusions After mastectomy, adding a multiple-day, ambulatory, continuous ropivacaine infusion to a single-injection ropivacaine paravertebral nerve block results in improved analgesia and less functional deficit during the infusion. However, no benefits were identified after infusion discontinuation.

Ultrasound-guided root/trunk (interscalene) block for hand and forearm anesthesia.

Background Historically, the anterolateral interscalene block—deposition of local anesthetic adjacent to the brachial plexus roots/trunks—has been used for surgical procedures involving the shoulder. The resulting block frequently failed to provide surgical anesthesia of the hand and forearm, even though the brachial plexus at this level included all of the axons of the upper-extremity terminal nerves. However, it remains unknown whether deposition of local anesthetic adjacent to the seventh cervical root or inferior trunk results in anesthesia of the hand and forearm. Methods Using ultrasound guidance and a needle-in-plane posterior approach, a Tuohy needle was positioned with the tip located between the deepest and next-deepest visualized brachial plexus root/trunk, followed by injection of mepivacaine (1.5%). Grip strength and the tolerance to cutaneous electrical current in 5 terminal nerve distributions were measured at baseline and then every 5 minutes following injection for a total of 30 minutes. The primary end point was the proportion of cases in which the interscalene nerve block resulted in a decrease in grip strength of at least 90% and hand and forearm anesthesia (tolerance to >50 mA of current in all 5 terminal nerve distributions) within 30 minutes. The primary hypothesis was that a single-injection interscalene brachial plexus block produces a similar rate of anesthesia of the hand and forearm to the published success rate of 95% for other brachial plexus block approaches. Results Of 55 subjects with blocks placed per protocol, all had a successful block of the shoulder as defined by inability to abduct at the shoulder joint. Thirty-three subjects had measurements at 30 minutes following local anesthetic deposition, and only 5 (15%) of these subjects had a surgical block of the hand and forearm (P < 0.0001; 95% confidence interval, 6%–33%). We therefore reject the hypothesis that the interscalene block as performed in this study provides equivalent anesthesia to the hand and forearm compared with other brachial plexus block techniques. Block failures of the hand and forearm were due to inadequate cutaneous anesthesia of the ulnar (n = 27; 82%), median (n = 26; 78%), or radial (n = 22; 67%) distributions; the medial forearm (n = 25; 76%); and/or the lateral forearm (n = 14; 42%). Failure to achieve at least a 90% reduction in grip strength occurred in 16 subjects (48%). Conclusions This study did not find evidence to support the hypothesis that local anesthetic injected adjacent to the deepest brachial plexus roots/trunks reliably results in surgical anesthesia of the hand and forearm.

Electrical velocimetry demonstrates the increase in cardiac output and decrease in systemic vascular resistance accompanying cesarean delivery and oxytocin administration

pain returned again in a few hours to NRS 5 to 6, and it took approximately 5 hours before the pain level was back to NRS 2 to 3. She used this combination for three months with persistent pain reduction. This treatment regimen reduced the pain more than 50% from baseline. Side effects such as a sensation of slight derealization due to the psychotropic effects of both drugs, were mild. Blood pressure was not affected. Furthermore, careful titration of ketamine cream volume and the cannabis cookies is possible so as to achieve an optimal balance between efficacy and psychotropic side effects. Cannabis is available in the Netherlands as a prescription drug. One of the main indications for its use is neuropathic pain [5], for which cannabis is generally seen as acceptable third-line treatment [4]. Cannabinoids are agonists for the central and peripheral cannabinoid receptors, CB1 and CB2, both playing an important role in pain modulation [6,7]. Ketamine acts on the N-Methyl-D-aspartate (NMDA) receptors, which, as with the cannabinoid receptors, are located centrally and peripherally [8]. Besides the NMDA receptors, ketamine acts also on many others, such as opioid, monoaminergic, and muscarinic receptors [9]. Ketamine and cannabis may act synergistically because cross-talk exists and the cannabinoid and the opioid receptor systems also have synergistic interactions [10,11].

Exploring Mixed Reality in Specialized Surgical Environments

Recent technology advances in both Virtual Reality and Augmented Reality are creating an opportunity for a paradigm shift in the design of human-computer interaction systems. Delving into the Reality-Virtuality Continuum, we find Mixed Reality - systems designed to augment the physical world with virtual entities that embody characteristics of real world objects. In the medical field, Mixed Reality systems can overlay real-time and spatially accurate results onto a patients body without the need for external screens. The complexity of these systems previously required specialized prototypes, but newly available commercial products like the Microsoft HoloLens make the technology more available. Through a combination of literature review, expert analysis, and prototyping we explore the use of Mixed Reality in healthcare. From the experience of prototyping Patiently and HoloSim, two applications for augmenting medical training, we outline considerations for the future design and development of virtual interfaces grounded in reality.

Ultrasound-guided infraclavicular block

To the Editor Although we applaud the continued investigation by Fredrickson et al. of a single infraclavicular injection in comparison with the triple-injection technique, we question the validity of their conclusion that both groups have the same success rate when both the tripleinjection success rate of 55% and the single-injection rate of 49% are much less than the published results of others (70%–100%), when a successful block is defined as the surgical anesthesia without either complete sensory blockade or the need for supplementation. We suggest that the low success rates may be the result of inadequate visualization combined with the absence of a true single injection. Fredrickson et al. visualized 3 cords in 12% (6 of 49) of the patients, 2 cords in 65% (32 of 49) of patients, and 1 or no cord in 22% (11 of 49) of patients. In the majority (88%) of their patients, local anesthetic was injected at 1 or more arbitrary points. For the single-injection group, Fredrickson et al. did not attempt visualization of the cords. Instead, they relied on the best image of the second part of the axillary artery and injected posterior to it by moving the needletip in a cephalad–caudad direction. Thus, their “single” injection was manipulated to involve up to 50% circumference of the artery. However, a periarterial injection technique is a significant limitation because there is variability in the arrangement of the cords and septa can influence the spread of local anesthetic. In our experience, all 3 cords are visualized in greater than 99% of infraclavicular blocks. Thus the finding that single-injection technique was not significantly inferior to the triple-injection technique reflects that both groups had unacceptably low success rates secondary to inadequate visualization of the cords and lack of a true single injection. In conclusion, although we believe that the multipleinjection technique is preferable, the question of whether a single-injection technique guided by ultrasound after locating the cords can achieve comparable efficacy and efficiency to a multiple-injection technique remains open.

Ultrasound-guided infraclavicular block: to target the axillary artery or the cords?

To the Editor Although we applaud the continued investigation by Fredrickson et al. of a single infraclavicular injection in comparison with the triple-injection technique, we question the validity of their conclusion that both groups have the same success rate when both the tripleinjection success rate of 55% and the single-injection rate of 49% are much less than the published results of others (70%–100%), when a successful block is defined as the surgical anesthesia without either complete sensory blockade or the need for supplementation. We suggest that the low success rates may be the result of inadequate visualization combined with the absence of a true single injection. Fredrickson et al. visualized 3 cords in 12% (6 of 49) of the patients, 2 cords in 65% (32 of 49) of patients, and 1 or no cord in 22% (11 of 49) of patients. In the majority (88%) of their patients, local anesthetic was injected at 1 or more arbitrary points. For the single-injection group, Fredrickson et al. did not attempt visualization of the cords. Instead, they relied on the best image of the second part of the axillary artery and injected posterior to it by moving the needletip in a cephalad–caudad direction. Thus, their “single” injection was manipulated to involve up to 50% circumference of the artery. However, a periarterial injection technique is a significant limitation because there is variability in the arrangement of the cords and septa can influence the spread of local anesthetic. In our experience, all 3 cords are visualized in greater than 99% of infraclavicular blocks. Thus the finding that single-injection technique was not significantly inferior to the triple-injection technique reflects that both groups had unacceptably low success rates secondary to inadequate visualization of the cords and lack of a true single injection. In conclusion, although we believe that the multipleinjection technique is preferable, the question of whether a single-injection technique guided by ultrasound after locating the cords can achieve comparable efficacy and efficiency to a multiple-injection technique remains open.

Hemodynamic Collapse Following a Mainstem Intubation

This case examines an unrecognized mainstem intubation resulting in tension pneumothorax physiology in a healthy young patient. We also cover tracheal anatomy, proper use and understanding of the laryngeal mask airway, the differential for the “inability to ventilate” scenario, correct airway mask technique, ideal positioning of the endotracheal tube, and the pharmacology of succinylcholine.

Vascular Absorption of Local Anesthetic Producing Systemic Toxicity

Local anesthetic toxicity is an infrequent but potentially life-threatening complication of a medication we use commonly in day-to-day practice. There is a wide array of presenting signs of toxicity that we should recognize when using high volumes of local anesthetics. There are many contributors to the eventual plasma concentration of local anesthetics including but not limited to dose, concentration, and block site. In addition to identifying the presence of local anesthetic toxicity, we should be able to quickly treat the symptoms to prevent escalation of events that may lead to more devastating consequences.