Utah's Salt Lake Research Articles

Gender Representation in Speakers at ASA: It's Not a Patience, Part-Time, or Pipeline Issue.

To the Editor In Speaker Gender Representation at the American Society of Anesthesiology Annual Meeting: 2011–2016, Moeschler et al1 highlight the significant underrepresentation of women as speakers at the American Society of Anesthesiologists (ASA) annual meeting compared to the percentage of female ASA members. Specifically, all-male panels are more common, and women are underrepresented as single speakers (168 out of 831, or 20.2%), particularly in the narrower category of plenary speaker (3 out of 41, or 7.3%). In response, Guzman-Reyes and Pivalizza2 propose 3 possible explanations for these findings, and encourage women to be more proactive in submitting proposals and “urge patience” in waiting for women to gain “experience commensurate with speaking engagements at national meetings.” While we agree there has been progress in the representation of women at ASA meetings, we strongly disagree with explanations by Guzman-Reyes and Pivalizza2 of the notable disparities, as well as their recommendation of “patience.” Guzman-Reyes and Pivalizza2 suggest that the current percentage of women entering anesthesiology is too recent for enough women to have the relevant experience. In 2007, approximately 26% of practicing anesthesiologists ranging from 36 to 45 years of age were women.3 Thus, the “pipeline” of women should have been sufficient by the 2010s. A better explanation for the comparative lack of female single, and especially plenary, speakers is that individual hard work and merit, while required, do not reliably overcome the well-documented negative impact of gender bias on opportunity. Guzman-Reyes and Pivalizza2 note that most panel presentations at the ASA meeting result from “voluntary submissions with a limited acceptance rate.” We agree that information on acceptance rates by gender would be valuable, but we strongly disagree that the discussion of the possible influence of a “friendship bonus” “diminishes the voluntary effort and commitment of ASA colleagues in the peer review process.” There is extensive evidence of gender bias in reviews of journal articles and grant proposals, so a differential acceptance rate is possible.4 Even if the difference is explained by fewer women submitting panel proposals, the preponderance of all-male panels suggests a tendency for all-male panels to be disproportionately formed and/or accepted. Such a concentration of all-male panels might indeed result from a “friendship bonus.” The phrase “friendship bonus” does not imply intentionality; rather, men are a “known quantity,” and are therefore more likely to be selected. ASA plenary speakers are chosen by a committee. Lack of an open nomination process amplifies existing gender bias and facilitates the friendship bonus. Selection committees with <35% women are less likely to select a woman. Thus, increasing the representation of women on selection committees and implementing a wider nomination process is more likely to result in increased representation of women as plenary speakers than “a call to action to academic women faculty to increase panel submissions.”5 Guzman-Reyes and Pivalizza2 suggest that the disparity may be due to the “personal choice” of part-time work. According to a 2015 Rand Corporation survey commissioned by ASA, only 15% of all female anesthesiologists work part time. Even in studies comparing only men and women who work full time, men have more rapid professional advancement than women.6 Many women with part-time academic appointments present on panels at ASA (personal experience), suggesting that it does not preclude successful contributions to advancing the specialty. We agree with Moeschler et al1 that their data “illuminate an opportunity to improve gender representation and enrich professional networks at the ASA Annual Meeting.” We look forward to the day when women are fairly and equitably represented in the speaker rosters of ASA and other medical societies. Rekha K. Chandrabose, MDDepartment of AnesthesiologyUniversity of California San DiegoSan Diego, California[email protected]Harriet W. Hopf, MDDepartment of AnesthesiologyUniversity of UtahSalt Lake City, Utah

The Wintertime Covariation of CO2 and Criteria Pollutants in an Urban Valley of the Western United States

AbstractNumerous mountain valleys experience wintertime particulate pollution events, when persistent cold air pools (PCAPs) develop and inhibit atmospheric mixing, leading to the accumulation of pollutants. Here we examine the relationships between trace gases and criteria pollutants during winter in Utah's Salt Lake Valley, in an effort to better understand the roles of transport versus chemical processes during differing meteorological conditions as well as insights into how targeted reductions in greenhouse gases will impact local air quality in varying meteorological conditions. CO2 is a chemically inert gas that is coemitted during fossil fuel combustion with pollutants. Many of these coemitted pollutants are precursors that react chemically to form secondary particulate matter. Thus, CO2 can serve as a stable tracer and potentially help distinguish transport versus chemical influences on pollutants. During the winter of 2015–2016, we isolated enhancements in CO2 over baseline levels due to urban emissions (“CO2ex”). CO2ex was paired with similar excesses in other pollutant concentrations. These relationships were examined during different wintertime conditions and stages of pollution episodes: (a) Non‐PCAP, (b) beginning, and (c) latter stages of an episode. We found that CO2ex is a good indicator of the presence of gaseous criteria pollutants and a reasonable indicator of PM2.5. Additionally, the relationships between CO2ex and criteria pollutants differ during different phases of PCAP events which provide insight into meteorological and transport processes. Lastly, we found a slight overestimation of CO:CO2 emission ratios and a considerable overestimation of NOx:CO2 by existing inventories for the Salt Lake Valley.

Coupling between Chemical and Meteorological Processes under Persistent Cold-Air Pool Conditions: Evolution of Wintertime PM2.5 Pollution Events and N2O5 Observations in Utah's Salt Lake Valley.

The Salt Lake Valley experiences severe fine particulate matter pollution episodes in winter during persistent cold-air pools (PCAPs). We employ measurements throughout an entire winter from different elevations to examine the chemical and dynamical processes driving these episodes. Whereas primary pollutants such as NOx and CO were enhanced twofold during PCAPs, O3 concentrations were approximately threefold lower. Atmospheric composition varies strongly with altitude within a PCAP at night with lower NOx and higher oxidants (O3) and oxidized reactive nitrogen (N2O5) aloft. We present observations of N2O5 during PCAPs that provide evidence for its role in cold-pool nitrate formation. Our observations suggest that nighttime and early morning chemistry in the upper levels of a PCAP plays an important role in aerosol nitrate formation. Subsequent daytime mixing enhances surface PM2.5 by dispersing the aerosol throughout the PCAP. As pollutants accumulate and deplete oxidants, nitrate chemistry becomes less active during the later stages of the pollution episodes. This leads to distinct stages of PM2.5 pollution episodes, starting with a period of PM2.5 buildup and followed by a period with plateauing concentrations. We discuss the implications of these findings for mitigation strategies.

Turbulent Fluxes and Pollutant Mixing during Wintertime Air Pollution Episodes in Complex Terrain

Cold air pools (CAPs) are stagnant stable air masses that form in valleys and basins in the winter. Low wintertime insolation limits convective mixing, such that pollutant concentrations can build up within the CAP when pollutant sources are present. In the western United States, wintertime CAPs often persist for days or weeks. Atmospheric models do not adequately capture the strength and evolution of CAPs. This is in part due to the limited availability of data quantifying the local turbulence during the formation, maintenance, and destruction of persistent CAPs. This paper presents observational data to quantify the turbulent mixing during two CAP episodes in Utah's Salt Lake Valley during February of 2004. Particulate matter (PM) concentration data and turbulence measurements for CAP and non-CAP time periods indicate that two distinct types of mixing scenarios occur depending on whether the CAP is dry or cloudy. Where cloudy, CAPs have enhanced vertical mixing due to top-down convection from the cloud layer. A comparison between the heat and momentum fluxes during 5 days of a dry CAP episode in February to those of an equivalent 5 day time period in March with no CAP indicates that the average turbulent kinetic energy during the CAP was suppressed by approximately 80%.

Relationship between particulate air pollution and meteorological variables in Utah's Salt Lake Valley

Critical meteorological factors affecting daily particulate concentrations during winter for Utah's urbanized Salt Lake Valley are examined on the basis of forty years of data. In a typical winter, the National Ambient Air Quality Standard for particulate matter with aerodynamic diameter less than 2.5 microns (PM2.5) is exceeded during 6 multi-day events comprising 18 winter days. Multi-day episodes of high stability produce these events, as synoptic-scale high-pressure ridges transit across Utah. The valley heat deficit, a bulk measure of atmospheric stability, exhibits large winter-to-winter variations that are highly related to similar variations in PM2.5. While control strategies have led to downward trends in concentrations for some primary pollutants, no long-term trends in valley heat deficit are evident over the 40 years. PM2.5 concentrations rise gradually over a period of days after a heat deficit threshold is exceeded as the air within the valley becomes decoupled from generally stronger winds aloft. Concentrations climb at a typical rate of about 10 μg m−3 d−1 over a four-day period to about 60 μg m−3 during these episodes. During episodes when PM2.5 concentrations exceed 35 μg m−3, the atmospheric column in the valley is characterized by: temperature below 0 °C; relative humidity in excess of 50%; and light wind speeds. PM2.5 concentrations in excess of 35 μg m−3 are four times more likely when the valley is snow covered than when it is not. A stepwise multiple linear regression based upon selected meteorological variables is used to estimate daily values of PM2.5 during two independent winters. The correlation between observed and estimated PM2.5 for these winters reaches 0.81.

Reply

We appreciate the comments of Hahn and Vinks and their active interest in the optimization of vancomycin dosing practices in children. The authors share results from a recent investigation into the complex relationship between pediatric vancomycin dosing, trough attainment and AUC, which we commend. We agree that the target vancomycin trough for an individual child that predicts AUC > 400 will vary based on age, size, maturation, kidney function, dosing interval, etc. More personalized approaches to vancomycin dosing including the use of individual Bayesian estimates of vancomycin clearance to predict AUC would be helpful to optimize target exposures in children. Unfortunately, this approach to predict AUC is not always available to providers, and the trough instead is used to guide dosing. Hahn and Vinks report that among 6 patients with trough concentrations in the 8–10 mcg/mL range, only 67% achieved the desired AUC >400, whereas our model and simulation analysis predicted that over 90% of children with troughs in this range would achieve the desired AUC. Although our study was only a simulation study, we urge the use of caution in drawing conclusions based on such a small sample of 6 subjects, especially given the wide range of age (1–17 years) and dose (45–102 mg/kg/day) used. Clearly, larger sample sizes are needed. We wish to reiterate, however, that the main conclusion to be derived both from our study and the work of Hahn and Vinks is that trough goals in the range of 15–20 mcg/mL are unnecessary for most children. Adam Frymoyer, MD Department of Pediatrics Stanford University Standford, CA Adam L. Hersh, MD, PhD Department of Pediatrics University of Utah Salt Lake City, UT

Improving Medical Student Understanding of the Scope of Plastic Surgery

Division of Plastic and Reconstructive Surgery Department of Surgery, University of Utah Salt Lake City, UT

Acceptance of Circulatory Determination of Death and Donation

Department of PediatricsSchool of MedicineUniversity of UtahSalt Lake City, Utah * See also p. 897. The authors have not disclosed any potential conflicts of interest.

Receptor model source attributions for Utah's Salt Lake City airshed and the impacts of wintertime secondary ammonium nitrate and ammonium chloride aerosol

Communities along Utah's Wasatch Front are currently developing strategies to reduce daily average PM2.5 levels to below National Ambient Air Quality Standards during wintertime persistent stable atmospheric conditions, or cold-air pools. Speciated PM2.5 data from the Wasatch Front airshed indicate that wintertime exceedances of the PM2.5 standard are mainly driven by high levels of ammonium nitrate. Stable wintertime conditions foster the formation of ammonium nitrate aerosol when sufficient sources of NOx, ammonia, and oxidative capacity exist. However, this work demonstrates that secondary ammonium chloride aerosol can also be a significant source of secondary wintertime PM2.5 if sufficient sources of atmospheric chlorine exist. Two factor analysis techniques, positive matrix factorization (PMF) and Unmix, were used to identify contributors to PM2.5 at three monitoring stations along Utah's Wasatch Front: Bountiful, Lindon, and Salt Lake City. The monitoring data included chemically speciated PM2.5 data for 227, 227, and 429 days at each location, respectively, during the period from May 2007 through May 2011. PMF identified 10–12 factors and Unmix identified 4–5 factors for each of the locations. The wintertime PMF and Unmix results showed large contributions from secondary PM2.5 when PM2.5 concentrations exceeded 20 μg/m3. PMF identified both ammonium nitrate and ammonium chloride aerosol as significant secondary contributors to PM2.5 (10–15% of total PM2.5 from ammonium chloride) during wintertime pollution episodes. Subsequent ion balance analysis of the monitoring data confirmed the presence of significant ammonium chloride aerosol on these highly polluted days at all three monitoring sites. The directly emitted primary PM2.5 portions of the source attribution results were further compared to county-level emissions inventories and showed generally good agreement for Salt Lake City and Lindon during wintertime except for wood smoke and fugitive dust, which have higher contributions in the receptor modeling results than in the emissions inventories. Implications: The study suggests that secondary ammonium chloride aerosol can be a significant source of wintertime PM2.5 in an ammonia-rich environment, like the Wasatch Front airshed, if sufficient sources of atmospheric chlorine exist. During wintertime, cold-air-pool events, the source attribution results generally agree with the county emission inventories with the exception of wood smoke and cooking sources. At the Salt Lake City monitoring station, the estimated contributions from wood smoke and cooking are nearly double those of the corresponding inventory, suggesting that they are nearly as important as gasoline emissions.

The Persistent Cold-Air Pool Study

The Persistent Cold-Air Pool Study (PCAPS) was conducted in Utah's Salt Lake valley from 1 December 2010 to 7 February 2011. The field campaign's primary goal was to improve understanding of the physical processes governing the evolution of multiday cold-air pools (CAPs) that are common in mountain basins during the winter. Meteorological instrumentation deployed throughout the Salt Lake valley provided observations of the processes contributing to the formation, maintenance, and destruction of 10 persistent CAP episodes. The close proximity of PCAPS field sites to residences and the University of Utah campus allowed many undergraduate and graduate students to participate in the study. Ongoing research, supported by the National Science Foundation, is using the PCAPS dataset to examine CAP evolution. Preliminary analyses reveal that variations in CAP thermodynamic structure are attributable to a multitude of physical processes affecting local static stability: for example, synoptic-scale processes impact changes in temperatures and cloudiness aloft while variations in boundary layer forcing modulate the lower levels of CAPs. During episodes of strong winds, complex interactions between the synoptic and mesoscale f lows, local thermodynamic structure, and terrain lead to both partial and complete removal of CAPs. In addition, the strength and duration of CAP events affect the local concentrations of pollutants such as PM2.5.

Liver transplantation in septuagenarians receiving model for end-stage liver disease exception points for hepatocellular carcinoma: The national experience

We thank Dr. Perkins1 for lending his perspective on the complicated issue of performing transplantation for elderly patients with hepatocellular carcinoma, and we submit that the frequency with which transplant selection committees face this issue is greater than what most readers appreciate. Because the publicly available Scientific Registry of Transplant Recipients database does not further stratify patients older than 65 years, we have returned to the Standard Transplant Analysis and Research files2 and have determined that the actual percentage of septuagenarians undergoing liver transplantation with respect to the entire liver transplant database is 1.52% (ie, 1602 of 105,405 patients). With the rough figure of 1.5%, septuagenarians account for approximately 90 transplants per year (if we assume that roughly 6000 transplants are performed annually). In fact, in the most recent year for which data are available, 143 septuagenarians underwent transplantation. This is double the figure quoted for the increase in liver transplants to be expected from proposed changes in organ allocation policy. For example, liver simulated allocation modeling predicts 77 fewer deaths per year across all regions if a wholesale regional distribution policy is enacted.3 With the controversy surrounding recent changes in organ allocation as a backdrop, certainly the fate of 90 to 140 transplants per year is worth discussing. Often, as Perkins points out,1 the decision to approve an elderly patient for liver transplantation is framed in terms of the justice-versus-utility equation. In these cases, we agree with Perkins that the availability of other treatment options and a particular recipient's expected survival (both with and without liver transplantation) must be taken into consideration. In our study,4 we revealed that on the national stage, elderly liver transplant recipients (≥70 years) have a 5-year survival rate of only 55.2%. However, in contrast to younger cohorts, a diagnosis of hepatocellular carcinoma in this age group does not appear to influence survival (the rates are equally poor). Because survival is no different for elderly cohorts with and without hepatocellular carcinoma, on the basis of current United Network for Organ Sharing policy (which does not limit transplantation at the extremes of age), we have concluded that as long as chronological age does not eliminate an individual's transplant candidacy, a tumor diagnosis should not prejudice the granting of Model for End-Stage Liver Disease exception points for elderly recipients otherwise falling within accepted criteria for transplantation. However, we believe that Perkins1 may have misinterpreted our intentions. Basing our conclusions on current policy does not in any way speak to the policy's wisdom or signal support for the aggressive pursuit of liver transplantation in patients at advanced age. In fact, we are in agreement with Perkins that if patients in the same elderly subgroup were to undergo radiofrequency ablation, there would be lower cost expenditures, less morbidity, and similar, or perhaps even greater survival. In our article,4 we were merely attempting to frame the issue in the context of the national data and as a logical extension of allocation policy as it is currently written. In doing so, we hope that the availability of these data will be of use to members of transplant selection committees, policy makers, and others tasked with determining the eligibility of transplant recipients. Jason Schwartz M.D.*, Heather Thiesset M.P.H. , Terry Box M.D. , William Hutson M.D.§, John Sorensen, M.D. , * Division of Surgical Transplantation Department of Surgery, University of Texas Southwestern Medical Center, Dallas, TX, Departments of General Surgery (Section of Transplantation), Medicine, University of Utah Salt Lake City, UT, § Division of Gastroenterology and Hepatology University of Maryland School of Medicine College Park, MD.

Filling the Blank Element of Pain

Pain Research and Management Center Department of Anesthesiology University of Utah Salt Lake City, UT

End-tidal alveolar dead space ratio

Division of Critical Care Department of Pediatrics University of Utah Salt Lake City, Utah * See also p. e18. The authors have not disclosed any potential conflicts of interest.

Dynasthetics Disclosure

To the Editor A recent article about activated charcoal1 omitted the disclosure that we are cofounders of Dynasthetics LLC, the device manufacturer. We regret the omission. Dwayne Westenskow, PhD Joseph Orr, PhD Department of Anesthesiology University of Utah Salt Lake City, UT [email protected]

Climatology of persistent deep stable layers in Utah's Salt Lake Valley, USA

Abstract. The characteristics of winter season persistent deep stable layers (PDSLs) over Utah's Salt Lake Valley are examined using 30-year twice daily rawinsonde soundings. The results highlight the basic climatological characteristics of the PDSLs, including the strengths of the inversion, the frequency of the occurrence, and the duration of the events. The data analyses also reveal linear trend, interannual variability, as well as the relationship between the interannual variability of PDSLs and the variability of large-scale circulations. Finally, the study investigates the large-scale atmosphere conditions accompanying the formation and destruction of the PDSL episodes.

Vascular Neurology: Questions and Answers

Nancy Futrell, MD and Dara G. Jamieson MD. Demos Medical Publishing LLC, New York, NY, 2008. ISBN 978-1-933864-24-2, $75.00. Scope: This is a study guide presented in question-and-answer format for physicians preparing for board certification by the American Board of Psychiatry and Neurology (APBN) in vascular neurology. It contains more than 500 questions and is divided into nine sections, covering basic sciences and clinical topics. One third of the book is devoted to clinical stroke, but the authors also cover basic science, cardiology, hematology, pediatric stroke, pathology, imaging, pharmacology, and rehabilitation. Strengths: This study guide is comprehensive, well-written, and easy to read. Most sections reference pertinent and appropriate literature in the field. Questions and answers provide a good review of the basic science, epidemiology, pathophysiology, evaluation, treatments, and outcomes. Questions are quite representative of those found on the APBN board. Particularly strong sections are those on clinical stroke, pharmacology, rehabilitation, and pathology. Weaknesses: Although the text deals mostly in well-accepted and scientifically based evidence, the authors occasionally present personal cases and anecdotes as definitive practice. The basic science section has very little anatomy and not enough illustrations. Many of the black and white images are of poor quality. The cardiology and hematology sections rely heavily on single texts for references. Recommended Audience: This book successfully targets its intended audience of those preparing for the vascular neurology board examination, but residents preparing for the general neurology APBN board examination will probably find this book useful as well. Critical Appraisal: This book fills a much-needed niche. It is thorough, relevant, accessible, and worth reading. However, its value is slightly diminished by the low quantity and uneven quality of photos as well as the authors’ occasional use of personal anecdotes. Michael J. Wilder, MD Jennifer Juhl Majersik, MD, MS Department of Neurology University of Utah Salt Lake City, Utah

Stepwise Logistic Regression

In Response: We thank Dr. Arunajadai for his comments about the statistical simulations in our editorial (text NLP, algorithm WMB) demonstrating the perils of stepwise logistic regression.1 This allows us to clarify an ambiguity in the nomenclature of the stepwise automatic variable selection algorithm. Correctly specified, the algorithm should be described as either stepwise forward selection, stepwise backward elimination, or stepwise with forward selection and/or backward elimination; however, the word stepwise itself is also commonly used to refer to any of the three variants or to just the third variant. Arunajadai2 has correctly stated that our particular simulations used the stepwise backward elimination variant. Our simulations used randomly created covariates to demonstrate how commonly there was the creation of spurious associations by stepwise modeling (backward elimination variant). Dr. Arunajadai has also provided R software code to perform the other two variants; he reports that there were no spurious associations with no covariate significant at P < 0.05 using either the forward selection or the forward selection/ backward elimination variants. In his code, Arunajadai estimates a mean intercept model object, i.e., “fit <- glm(y ∼ 1, data = w, family = binomial),” for submission to the stepwise function. The submission of a mean intercept model to the stepwise process cannot identify any association, true or spurious. When a full (all covariates) model, i.e., “fit <- glm(y ∼., data = w, family = binomial)” is used, all three variants have qualitatively the same results of numerous spurious associations (appendix available at www.anesthesia-analgesia.org). The inclusion of noise variables during stepwise modeling regardless of the variant has been demonstrated elsewhere.3–5 Dr. Arunajadai also raised the very interesting question of which information criterion should be used at each step for adding or removing a covariate; he advocates the Bayesian Information Criterion (BIC) in contrast to the Akaike Information Criterion (AIC) used in our simulation. Both the AIC and the BIC are indexes in which twice the negative maximized log likelihood of the model fit is penalized by subtracting either twice the number of model parameters (AIC) or the number of model parameters multiplied by the log of the sample size (BIC). Of the candidate models possible, the model with the higher AIC or higher BIC is favored. As Arunajadai noted, the BIC is more heavily penalized and will produce more parsimonious models (fewer significant covariates). However, there is a competition in choosing between AIC and BIC; the AIC will yield optimal regression estimation while the BIC represents consistent model identification rules. It is not possible to create models with the properties favored by both the AIC and the BIC.6 Using the BIC index in our simulation still produces spurious associations. Automatic variable selection via a stepwise process is a hazardous undertaking. As J. B. Copas3 humorously noted, “If you torture the data for long enough, in the end they will confess …. What more brutal torture can there be than subset selection? The data will always confess, and the confession will usually be wrong.” Nathan L. Pace, MD, MStat Department of Anesthesiology University of Utah Salt Lake City, Utah William M. Briggs, PhD Department of Emergency Medicine New York Methodist Hospital Brooklyn, New York [email protected]

Reply

Sir: We appreciate Dr. Freshwater’s comments. Thumb replantation is a technically difficult procedure. Comments and discussion about this procedure should benefit us all. The intent of the article was to present a different technique for revascularization of an amputated thumb. The technique combines a vein transposition from the dorsum of the index metacarpal to the thumb, providing venous outflow with one anastomosis. An arterial conduit, rather than a venous conduit, is used to re-establish arterial inflow. As cited, others have described these techniques for different circumstances. We combined these techniques to provide blood supply to the replanted thumb. Our data do not allow us to claim that this technique is better than another. Rather, it is a suitable alternative. Arterial grafts have advantages and disadvantages over vein grafts. The article discusses these elements. Having used both arterial and venous grafts, we prefer arterial grafts, but we cannot prove that they are better. To our knowledge, to date, the use of an arterial graft has not impaired subsequent medical care to a patient. Our patients have had no local vascular issues following arterial graft harvest. Our cardiac surgeons do use radial artery for coronary bypass but have not progressed to using the deep inferior epigastric artery. In that regard, our patients have been fortunate. Are arterial grafts more than is needed? We cannot say. Have we used a free flap for reconstruction when a less invasive technique would have allowed healing of a wound? Yes. But in the end, the sum total of the advantages and disadvantages of the free flap outweighed that of the less involved alternatives. We believe the same is true of arterial grafts in this instance. We appreciate the reviewer’s insightful comments on our article and will incorporate them into future medical decisions. W. Bradford Rockwell, M.D. Jaime Haidenberg, M.D. K. Bo Foreman, Ph.D. Plastic Surgery University of Utah Salt Lake City, Utah

Service-Learning From Passion to Objectivity: International and Cross-Disciplinary Perspectives on Service-Learning Research.

Director of Clinical Education and Associate Professor (Clinical) Department of Physical Therapy College of Health Professions The University of Utah Salt Lake City, UT

Outpatient Continuous Peripheral Nerve Catheters

In Response: We appreciate the comments of Drs. Chidiac and Perov (1) regarding our series of outpatients with continuous peripheral nerve blocks (CPNB). It is reassuring to learn that other programs have produced results similar to our own with respect to outpatient CPNB management. As more institutions adopt these protocols, patient care will be improved and the need for in-hospital pain control will be reduced. We agree that the use of lower anesthetic concentrations during catheter infusion is beneficial. In fact, after sending more than 1,000 patients home with CPNB, we also have transitioned to the use of 0.125% bupivicaine for all outpatient catheters. This change was due in large part to reports by patients of being “too numb.” We have observed that 0.125% bupivicaine provides adequate analgesia while sparing motor function in most cases. With respect to nerve stimulation, we could not disagree more strongly with Chidiac and Perov. For many years, nerve stimulation has been the “de facto” gold standard for peripheral nerve blocks because it was the only alternative to paresthesia techniques. This is despite evidence that nerve stimulators vary greatly in their accuracy of current output (2). Much worse, motor response (even at currents of 1 mA) is not a reliable indicator of direct needle contact with the nerve (3). As for the “further refinement” of stimulating catheters mentioned by Chidiac and Perov, we would direct the readers to recent publications comparing nerve stimulating versus nonstimulating catheters (4,5). These studies do not show any benefit of stimulating over nonstimulating catheters. The largest of these studies (419 patients), concluded, “a convincing argument has yet to be made for the routine use of the stimulating catheter …” (6). Ultrasound has been a welcome relief for those of us who are seeking a better alternative to NS techniques. In 2005, Marhofer reported more than 4000 blocks performed using only ultrasound guidance with success rates approaching 100% (7). Since that time, his numbers have almost certainly increased. Regarding ultrasound techniques, Marhofer accurately states, “Nerves are not blocked by the needle but by the local anesthetic.” Likewise, at the University of Utah, we stopped using the nerve stimulator over 2 years ago. We too, have performed over 3500 blocks (2000 catheters) using only ultrasound guidance. It should be no surprise that a technique successful for single injections would also work for catheter placement. The result has been a generation of residents from our program who have learned to “stay away from the nerve with the needle but reach the nerve with local anesthetic.” A prospective study at our institution shows a success rate of 97% for single blocks and catheters placed using only ultrasound guidance (8). This same study shows the cost savings (by eliminating the cost of stimulating needles) to be more than $16,000/yr when performing more than five nerve blocks per day. Ultrasound is ideal for catheter placement as a “stand alone” technique. We believe the nerve stimulation will soon take its place beside the copper kettle as a technique of only historical interest. In other words, yesterday’s “gold standard” has become today’s “old standard.” Jeffrey D. Swenson, MD Byron Bankhead, MD Department of Anesthesiology University of Utah Orthopaedic Center University of Utah Salt Lake City, Utah [email protected]