Simultaneous Measurement of Multiple Parameters of a Subwavelength Structure Based on the Weak Value Formalism.

A mathematical extension of the weak value formalism to the simultaneous measurement of multiple parameters is presented in the context of an optical focused vector beam scatterometry experiment. In this example, preselection and postselection are achieved via spatially varying polarization control, which can be tailored to optimize the sensitivity to parameter variations. Initial experiments for the two-parameter case demonstrate that this method can be used to measure physical parameters with resolutions at least 1000 times smaller than the wavelength of illumination.

Effect of Nerve Stimulation Use on the Success Rate of Ultrasound-Guided Subsartorial Saphenous Nerve Block: A Randomized Controlled Trial.

BACKGROUND AND OBJECTIVES: Ultrasound-guided subsartorial saphenous nerve block is commonly used to provide complete surgical anesthesia of the foot and ankle in combination with a popliteal sciatic nerve block. However, in part owing to its small caliber and absence of a prominent vascular landmark in the subsartorial plane distal to the adductor canal, the saphenous nerve is more difficult to reliably block than the sciatic nerve in the popliteal fossa. Although the saphenous nerve is a sensory nerve only, neurostimulation can be used to elicit a "tapping" sensation on the anteromedial aspect of the lower leg extending toward the medial malleolus. Our objective was to test the hypothesis that the addition of nerve stimulation use to an ultrasound (US)-guided technique will increase the success rate of subsartorial saphenous nerve block. METHODS: With institutional human ethics board approval and participants' written informed consent, we enrolled 80 patients undergoing foot and ankle surgery in a randomized, single-blinded, parallel-group clinical trial. Patients were randomly assigned to receive US-guided subsartorial saphenous nerve block either alone (US group) or with the use of additional nerve stimulation (NS group; time limit, 5 minutes). For saphenous nerve blockade, all patients received 10 mL of 0.5% ropivacaine. The primary end point was complete absence of sensation to pinprick at 30 minutes at two different anatomic areas in the distribution of the saphenous nerve (2 cm proximal to the medial malleolus and 10 cm distal to the medial tibial condyle). Secondary end points included decreased sensation at 30 minutes and block failure (normal sensation) at 30 minutes. This trial was registered at ClinicalTrials.gov: NCT02382744. RESULTS: All 80 patients completed the trial (40 patients in each group). Twenty-two patients (55%) in the NS group versus 18 (45%) in the US group had complete absence of sensation to pinprick at 30 minutes at both anatomic areas of assessment (Fisher exact test, P = 0.25 [one sided]; 95% confidence interval of difference in proportions, -11.9% to 31.9%). The percentages of patients with any evidence of block (decreased or complete absence of sensation) at both areas at 30 minutes were 92.5% (NS) and 97.5% (US), respectively (P = 0.62 [two sided]); corresponding failure rates (normal sensation) were 7.5% (NS) and 2.5% (US). In the NS group, no response in the saphenous nerve distribution was elicited within 5 minutes of stimulation time limit in 20% of patients (n = 8). All of the patients in the NS group with normal sensation at 30 minutes (n = 3) were among this subcohort. CONCLUSIONS: The addition of the use of nerve stimulation did not improve the success rate of US-guided subsartorial saphenous nerve block. However, in the NS group, an inability to elicit a "tapping" sensation in the saphenous nerve distribution was associated with block failure.

Regional Versus General Anesthesia and the Incidence of Unplanned Health Care Resource Utilization for Postoperative Pain After Wrist Fracture Surgery: Results From a Retrospective Quality Improvement Project.

BACKGROUND AND OBJECTIVES: The establishment at our center of a dedicated regional anesthesia service in 2008-2009 has resulted in a marked increase in single-shot brachial plexus blocks (sBPBs) for ambulatory wrist fracture surgery. Despite the documented benefits of regional over general anesthesia (GA), there has been a perceived increase among sBPB patients in postoperative return rates for pain at our institution. We conducted a retrospective quality improvement project to examine this. METHODS: After exemption from human ethics board review, we sought to identify and contact all wrist fracture surgery patients treated at our center between 2003 and 2012. Our primary outcome was the incidence of unplanned physician visits (office/clinic or emergency department) for pain in the first 48 hours after surgery. Other main outcomes included the incidence of seeking any form of medical attention for pain and self-reporting of severe pain in the first 48 hours. RESULTS: Of 1008 identified patients, 419 could be contacted; 195 qualified for analysis. The incidence of unplanned physician visits in the first 48 hours was 12% (13 of 118) among sBPB patients versus 4% (3 of 77) in GA patients (odds ratio [OR], 3.1; 95% confidence interval [95% CI], 0.8-11.1; P = 0.11). More sBPB versus GA patients sought any form of medical attention for pain (20% vs 5%; OR, 4.7; 95% CI, 1.4-10.9; P = 0.003). Similarly, more sBPB patients reported severe postoperative pain (41% vs 10%; OR, 5.9; 95% CI, 2.6-13.4; P < 0.0001). CONCLUSIONS: Patients who received sBPBs for ambulatory wrist fracture surgery had a higher rate of unplanned health care resource utilization caused by pain after hospital discharge than those undergoing GA. These findings warrant confirmation in a prospective trial and emphasize the need for a defined postdischarge analgesic pathway as well as the potential merits of perineural home catheters.

Ultrasound guidance versus direct palpation for radial artery catheterization by expert operators: a randomized trial among Canadian cardiac anesthesiologists.

PURPOSE: The use of ultrasound (US) for radial arterial catheterization has been reported to result in faster insertion times with fewer complications when compared with traditional direct palpation (DP). We sought to determine if this applies to expert operators and tested the hypothesis that, among cardiac anesthesiologists, US-guided insertion similarly results in faster insertion times as well as fewer re-directs, attempts, and complications. METHODS: Following Research Ethics Board Approval, we conducted a randomized clinical trial in 125 patients scheduled for cardiac surgery at a single tertiary/quaternary care centre. Patients were randomized to either US- or DP-guided radial artery catheterization by attending cardiac anesthesiologists. The primary endpoint was time to catheter placement. Secondary endpoints included the number of attempts and re-directs as well as the failure rate. RESULTS: There were no differences between the DP- (n = 62) vs US-guided (n = 63) groups in median [interquartile range] time to placement (104 [76-212] sec vs 104 [68-270] sec, respectively; P = 0.66), number of re-directs (2 [0-6] vs 3 [1-5], respectively; P = 0.82), or number of attempts (1 [1-2] vs 1 [1-2], respectively; P = 0.08). The first-attempt success rate was 56.4% in the DP group and 71.4 % in the US group (P = 0.10). Failure rate and hematoma rate in the DP group were 21.0% and 22.6%, respectively, compared with 12.7% and 11.1% in the US group (P = 0.24 and 0.10, respectively). CONCLUSIONS: Among experienced cardiac anesthesiologists, the use of US to facilitate radial arterial catheterization did not affect insertion times, the number of re-directs, or the number of attempts when compared with DP. Ultrasound use had no significant effects on the rates of success on first attempt, failure, or hematoma formation. This trial was registered at www.clinicaltrials.gov : NCT02118441.

Hemidiaphragmatic paralysis following ultrasound-guided supraclavicular versus infraclavicular brachial plexus blockade: a randomized clinical trial.

BACKGROUND AND OBJECTIVES: The comparative incidences of hemidiaphragmatic paralysis associated with contemporary ultrasound-guided supraclavicular versus infraclavicular blockade have not received extensive study. We tested the hypothesis that the infraclavicular approach results in a lower incidence of hemidiaphragmatic paralysis compared with supraclavicular blockade when a standard local anesthetic volume and concentration are used. METHODS: With institutional human ethics board approval, we enrolled 64 patients undergoing right-sided upper extremity surgery in a randomized, blinded, parallel-group trial. Patients were assigned to ultrasound-guided supraclavicular or infraclavicular blockade with 30 mL of 0.5% ropivacaine. The primary end point was complete hemidiaphragmatic paralysis at 30 minutes, defined as a greater than 75% reduction in diaphragmatic excursion measured with the voluntary sniff test using M-mode ultrasonography. Partial paralysis was defined as a 25% to 75% reduction. RESULTS: Eleven (34%) of 32 patients in the supraclavicular group versus 1 (3%) of 32 in the infraclavicular group had complete hemidiaphragmatic paralysis (P = 0.001 [1-tailed]; relative risk, 11.0 [95% confidence interval, 1.5-80.3]); 44% versus 13% had any (complete or partial) paralysis (P = 0.006; relative risk, 3.5 [95% confidence interval, 1.3-9.5]). Eight (25%) of 32 patients in the supraclavicular group versus 5 (16%) of 32 in the infraclavicular group reported dyspnea (P = 0.54). CONCLUSIONS: Ultrasound-guided supraclavicular blockade with 30 mL of 0.5% ropivacaine produced complete hemidiaphragmatic paralysis in approximately one-third of patients. The infraclavicular approach greatly reduced this risk but did not eliminate it. These data may aid in the selection of the approach to brachial plexus blockade, particularly in ambulatory patients and/or those with respiratory comorbidities.

Ultrasound-guided saphenous nerve block--within versus distal to the adductor canal: a proof-of-principle randomized trial.

PURPOSE: Reliable saphenous nerve blockade is a desirable complement to popliteal sciatic nerve blockade for foot and ankle surgery. We compared two promising ultrasound-guided techniques, the supine adductor canal (AC) technique and the prone peri-saphenous branch of the descending genicular artery (Peri-SBDGA) technique, using 8 mL of 2% lidocaine with epinephrine 1:400,000. METHODS: Following Research Ethics Board approval, we conducted a randomized single-blinded parallel-group trial in 102 patients undergoing foot and ankle surgery at a single centre. The primary endpoint was saphenous nerve ease of visualization (0 = not visible; 1 = visible with difficulty; and 2 = easily visible). Other endpoints included vascular landmark visualization (0 = not visible; 1= visible with colour flow Doppler; 2 = visible without colour flow Doppler), block success, onset, and complications. RESULTS: Ninety-one patients were eligible for analysis. Saphenous nerve visibility was not different between the groups (visibility score = 2: AC group, n = 24/49 [49%] vs Peri-SBDGA group, 20/42 [48%]; P = 1.00). Vascular landmark visibility was better in the AC group than in the Peri-SBDGA group (visibility score = 2: 41/49 [84%] vs 25/42 [60%], respectively; P = 0.018). Block success rates were similar (AC group, 41/49 [84%] vs Peri-SBDGA group, 34/42 [81%]; P = 0.79), as were median [interquartile range] onset times (AC group, 5 [5-10] min vs Peri-SBDGA group, 8 [5-11] min; P = 0.38). CONCLUSION: In this randomized trial, we found no differences in nerve visibility, block success rate, or onset between the AC and Peri-SBDGA techniques of ultrasound-guided saphenous nerve blockade, although the former technique provided superior vascular landmark visibility. Neither technique produced a sufficiently high success rate to provide reliable surgical anesthesia per se.

A regional anesthesia-based "swing" operating room model reduces non-operative time in a mixed orthopedic inpatient/outpatient population.

PURPOSE: We recently reported on the efficacy of a new "swing" room model involving two alternating ORs and regional anesthesia in increasing operating room (OR) throughput in a dedicated ambulatory orthopedic surgery facility. The purpose of this study was to evaluate this model in a main OR suite setting with typical mixed inpatient/outpatient cases. METHODS: We conducted a retrospective matched-pair cohort study of 133 upper extremity surgery patients treated in the swing room model under ultrasound-guided brachial plexus blockade. We compared this cohort with case-matched historical controls treated in the traditional single OR model under general anesthesia. The primary endpoint was non-operative time, defined as the interval between skin closure and incision in the following case. Secondary endpoints included throughput estimated as the median number of cases per eight-hour day, postanesthesia care unit (PACU) bypass rates, and postoperative pain/nausea and vomiting (PONV) intervention rates. RESULTS: Compared with the control group, non-operative times in the swing room group were faster (swing: median 19 min; interquartile range [IQR 8-31] vs control: median 57 min; IQR [49-65]; P < 0.0001). In the swing room model, the estimated daily throughput was 33% greater (swing: median 5.6 cases; IQR [5.0-6.2] vs control: median 4.2 cases; IQR [4.0-4.4]; P < 0.0001), and the PACU bypass rate was higher (swing: 60% vs control: 0%; P < 0.0001). Fewer patients received postoperative opioids (swing: 20% vs control: 82%; P < 0.0001) and treatment for PONV (swing: 2% vs control: 20%; P < 0.0001) in the swing room model. CONCLUSION: The implementation of a "swing" room care model based on ultrasound-guided regional anesthesia in a typical mixed inpatient/outpatient population decreased non-operative times, increased throughput, and improved recovery profiles compared with case-matched historical controls in the traditional model under general anesthesia.

A "swing room" model based on regional anesthesia reduces turnover time and increases case throughput.

PURPOSE: Our centre recently implemented a new ambulatory care model featuring two alternate regional anesthesia "swing" operating rooms (RA-SRs) managed by a single anesthesiologist. We hypothesized that this model would be associated with decreased turnover times and improved recovery profiles when compared with a traditional model with a single operating room using general anesthesia. METHODS: We conducted a retrospective cohort study of 164 patients scheduled for hand and wrist surgery who were treated in the RA-SRs under brachial plexus blockade, and we compared the findings with a matched historical control group of patients who underwent general anesthesia in a single operating room (GA-OR). The primary endpoint was room turnover time. Secondary endpoints included home discharge time, postoperative interventions for nausea and pain, and number of cases possible per eight-hour day. RESULTS: Patients in the RA-SR group had faster turnover times than patients in the GA-OR group (median [interquartile range]: 15 min [8-22] vs 54 min [49-61], respectively) as well as faster home discharge times (28 min [20-46] vs 156 min [118-215], respectively) (P < 0.0001). In the RA-SR group, postoperative antiemetics were used in 3/164 patients (2%) vs 28/164 (17%) in the GA-OR group (P < 0.0001), and opioids were used in 1/164 (0.6%) vs 132/164 (80%), respectively (P < 0.0001). The median number of daily cases possible in the RA-SR group was 56% greater than in the GA-OR group (8.4 [7.5-9.4] vs 5.4 [5.1-5.8], respectively; P < 0.0001). CONCLUSION: Compared with a traditional model using general anesthesia in a single operating room, the implementation of a model using regional anesthesia with two swing operating rooms was associated with reduced room turnover times, improved recovery profiles, and a higher case throughput.

Infusate contamination in regional anesthesia: what every anesthesiologist should know.

Infection can be a devastating complication of regional anesthesia. Contaminated infusate as a cause of infection in neuraxial anesthesia or peripheral nerve blockade has rarely been reported in the literature. However, it may be an important source of morbidity, especially as increasing numbers of patients are being discharged with perineural catheters and portable pumps of local anesthetic, which may infuse for several days at home. Two important issues related to infusate contamination in regional anesthesia are that of "hang-time" and sterile compounding practices. Hang-time can be defined as the maximum length of time during which an admixture preparation (infusate) can be safely administered without risk of microbiological or chemical instability. In the United States, there are currently no national guidelines on the hang-times of regional anesthesia infusates. On the other hand, guidelines for the sterile compounding of infusions used in regional anesthesia are now established by United States Pharmacopeia and The National Formulary Chapter 797, entitled "Pharmaceutical Compounding, Sterile Preparations." These guidelines have significant implications for the anesthesiologist. In this review, we examined the available literature regarding contaminated infusate as a cause of infection in regional anesthesia, to discuss strategies for the prevention of such contamination including the appropriate hang-time for infusates, and to discuss the implications of United States Pharmacopeia and The National Formulary Chapter 797 for anesthesiologists.