Femoral Arterial Doppler Use During Active Cardiopulmonary Resuscitation.

STUDY OBJECTIVE: This study explored femoral arterial Doppler during active cardiopulmonary resuscitation (CPR) to identify and characterize the resumptions of cardiac activity without stopping CPR. METHODS: This was a proof-of-concept study exploring arterial Doppler during cardiac arrest. Patients in cardiac arrest undergoing active CPR were prospectively enrolled. Arterial Doppler of the common femoral artery was recorded during CPR and during pauses in CPR. CPR-induced arterial tracings and native cardiac-induced tracings were analyzed for rate and peak systolic velocity. Cardiac activity on echocardiogram during pause in CPR was classified as "absent," "disorganized," or "organized." Descriptive data and survival are presented as mean and 95% confidence intervals (CI), as well as sensitivity and specificity of Doppler during active CPR in detecting native cardiac pulsations. RESULTS: Sixteen patients with 48 paired Doppler recordings during active CPR, pause in CPR, and associated echocardiogram were enrolled. Native cardiac-induced tracings were visible during 39.6% of pauses in CPR (19 of 48) and during 18.8% of the periods of active CPR (9 of 48). Arterial pulsations were more frequently visualized with organized contractions by echocardiogram (10 of 14, 71%) than disorganized contractions (9 of 22, 41%). Arterial Doppler was 100% specific and 50% sensitive in detecting organized cardiac activity during active CPR. Patients with visible native cardiac pulsations during active CPR demonstrated 0% mortality compared with 67% mortality without visible arterial pulsations. CONCLUSION: Arterial Doppler tracings may identify the resumption of native cardiac activity during active CPR; however, more research is needed.

A Multicenter, Prospective Study Comparing Subxiphoid and Parasternal Views During Brief Echocardiography: Effect on Image Quality, Acquisition Time, and Visualized Anatomy.

BACKGROUND: Recent literature has suggested echocardiography (echo) may prolong pauses in chest compressions during cardiac arrest. OBJECTVES: We sought to determine the impact of the sonographic approach (subxiphoid [SX] vs. parasternal long [PSL]) on time to image completion, image quality, and visualization of cardiac anatomy during echo, as performed during Advanced Cardiac Life Support. METHODS: This was a multicenter, randomized controlled trial conducted at 29 emergency departments (EDs) assessing the time to image acquisition and image quality between SX and PSL views for echo. Patients were enrolled in the ED and imaged in a simulated cardiac arrest scenario. Clinicians experienced in echo performed both SX and PSL views, first view in random order. Image quality and time to image acquisition were recorded. Echos were evaluated for identification of cardiac landmarks. Data are presented as percentages or medians with interquartile ranges (IQRs). RESULTS: We obtained 6247 echo images, comprising 3124 SX views and 3123 PSL. Overall time to image acquisition was 9.0 s (IQR 6.7-14.1 s). Image acquisition was shorter using PSL (8.8 s, IQR 6.5-13.5 s) compared with SX (9.3 s, IQR 6.7-15.0 s). The image quality was better with the PSL view (3.86 vs. 3.54; p < 0.0001), twice as many SX images scoring in the worst quality category compared with PSL (8.6% vs. 3.7%). Imaging of the pericardium, cardiac chambers, and other anatomic landmarks was superior with PSL imaging. CONCLUSIONS: Echo was performed in < 10 s in > 50% of patients using either imaging technique. Imaging using PSL demonstrated improved image quality and improved identification of cardiac landmarks.

Abscess Incision and Drainage With or Without Ultrasonography: A Randomized Controlled Trial.

STUDY OBJECTIVE: We hypothesize that clinical failure rates will be lower in patients treated with point-of-care ultrasonography and incision and drainage compared with those who undergo incision and drainage after physical examination alone. METHODS: We performed a prospective randomized clinical trial of patients presenting with a soft tissue abscess at a large, academic emergency department. Patients presenting with an uncomplicated soft tissue abscess requiring incision and drainage were eligible for enrollment and randomized to treatment with or without point-of-care ultrasonography. The diagnosis of an abscess was by physical examination, bedside ultrasonography, or both. Patients randomized to the point-of-care ultrasonography group had an incision and drainage performed with bedside ultrasonographic imaging of the abscess. Patients randomized to the non-point-of-care ultrasonography group had an incision and drainage performed with physical examination alone. Comparison between groups was by comparing means with 95% confidence intervals. The primary outcome was failure of therapy at 10 days, defined as a repeated incision and drainage, following a per-protocol analysis. Multivariate analysis was performed to control for study variables. Our study was designed to detect a clinically important difference between groups, which we defined as a 13% difference. RESULTS: A total of 125 patients were enrolled, 63 randomized to the point-of-care ultrasonography group and 62 to physical examination alone. After loss to follow-up and misallocation, 54 patients in the ultrasonography group and 53 in the physical examination alone group were analyzed. The overall failure rate for all patients enrolled in the study was 10.3%. Patients who were evaluated with ultrasonography were less likely to fail therapy and have repeated incision and drainage, with a difference between groups of 13.3% (95% confidence interval 0.0% to 19.4%). Abscess locations were predominantly torso (21%), buttocks (21%), lower extremity (18%), and axilla or groin (16%). There was no difference in baseline characteristics between groups relative to abscess size, duration of symptoms before presentation, percentage with cellulitis, and treatment with antibiotics. CONCLUSION: Patients with soft tissue abscesses who were undergoing incision and drainage with point-of-care ultrasonography demonstrated less clinical failure compared with those treated without point-of-care ultrasonography.

Pulmonary effects of intravenous atropine induce ventilation perfusion mismatch.

Atropine is used for a number of medical conditions, predominantly for its cardiovascular effects. Cholinergic nerves that innervate pulmonary smooth muscle, glands, and vasculature may be affected by anticholinergic medications. We hypothesized that atropine causes alterations in pulmonary gas exchange. We conducted a prospective interventional study with detailed physiologic recordings in anesthetized, spontaneously breathing rats (n = 8). Animals breathing a normoxic gas mixture titrated to a partial arterial pressure of oxygen of 110-120 were exposed to an escalating dose of intravenous atropine (0.001, 0.01, 0.1, 5.0, and 20.0 mg/kg body mass). Arterial blood gas measurements were recorded every 2 min (×5) at baseline, and following each of the 5 doses of atropine. In addition, the animals regional pulmonary blood flow was measured using neutron-activated microspheres. Oxygenation decreased immediately following intravenous administration of atropine, despite a small increase in the volume of inspired air with no change in respiratory rate. Arterial blood gas analysis showed an increase in pulmonary dysfunction, characterized by a widening of the alveolar-arteriole gradient (p < 0.003 all groups except for the lowest dose of atropine). The microsphere data demonstrates an abrupt and marked heterogeneity of pulmonary blood flow following atropine treatment. In conclusion, atropine was found to decrease pulmonary gas exchange in a dose-dependent fashion in this rat model.

A randomized controlled trial of incision and drainage versus ultrasonographically guided needle aspiration for skin abscesses and the effect of methicillin-resistant Staphylococcus aureus.

STUDY OBJECTIVE: The incidence of skin and soft tissue infections has increased dramatically during the last decade, in part because of increased prevalence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Incision and drainage is considered the primary intervention; however, some clinicians prefer ultrasonographically guided needle aspiration because it represents a less invasive alternative. Our hypothesis is that ultrasonographically guided needle aspiration is equivalent to incision and drainage in treating simple skin and soft tissue abscesses. METHODS: This study was a nonblinded randomized controlled trial. Patients with uncomplicated superficial abscesses were randomized to incision and drainage with packing or ultrasonographically guided needle aspiration. Purulence obtained from the abscess was cultured to identify the causative organism. Bedside ultrasonography was performed pre- and postintervention to confirm the presence or absence of an abscess cavity. Patients were followed up at 48 hours (in person by a clinician) and on day 7 (telephone follow-up by research staff). The primary outcome was a combination of sonographic resolution and clinical resolution of the signs and symptoms of ongoing infection at day 7. The signs and symptoms of ongoing infection include increasing pain, erythema, and the presence of pus. Resolution was assessed with both sonographic resolution (day 0 and day 2) and improvement of clinical symptoms (day 2) and resolution of clinical symptoms (day 7) without further intervention. RESULTS: A total of 101 patients were enrolled, 54 incision and drainage and 47 ultrasonographically guided needle aspiration patients. At initial presentation, 60% (95% confidence interval [CI] 45% to 70%) of needle aspirations yielded little or no purulence, despite sonographic visualization of an abscess cavity and sonographic guidance during the procedure. The overall success of ultrasonographically guided needle aspiration was 26% (95% CI 18% to 44%) compared with 80% (95% CI 66% to 89%) success in patients randomized to incision and drainage. The difference between groups was 54% (95% CI 35% to 69%). Overall success of both incision and drainage and ultrasonographically guided needle aspiration was lower in patients with CA-MRSA. Patients with CA-MRSA (n=33) were less likely to receive successful drainage with needle aspiration (8% versus 55%) or incision and drainage (61% versus 89%). The difference for needle aspiration and incision and drainage was 47% (95% CI 15% to 57%) and 28% (95% CI 4% to 45%), respectively. CONCLUSION: Ultrasonographically guided needle aspiration is insufficient therapy for skin abscesses. The presence of CA-MRSA decreases the success of both incision and drainage and ultrasonographically guided needle aspiration.

Tools for Measuring Clinical Ultrasound Competency: Recommendations From the Ultrasound Competency Work Group.

Competency in clinical ultrasound is essential to ensuring safe patient care. Competency in clinical ultrasound includes identifying when to perform a clinical ultrasound, performing the technical skills required for ultrasound image acquisition, accurately interpreting ultrasound images, and incorporating sonographic findings into clinical practice. In this concept paper, we discuss the advantages and limitations of existing tools to measure ultrasound competency. We propose strategies and future directions for assessing competency in clinical ultrasound.

Learning curve of bedside ultrasound of the gallbladder.

Existing guidelines for the number of ultrasounds required before clinical competency are based not on scientific study but on consensus opinion. The objective of this study was to describe the learning curve of limited right upper quadrant ultrasound. This was a prospective descriptive study. Ultrasounds collected over 1 year were reviewed for interpretive and technical errors. Possible errors during bedside ultrasound of the gallbladder include incorrect interpretation, incomplete image acquisition, and improper or poor imaging techniques resulting in poor image quality. The ultrasound image quality was rated on a 4-point scale, with 1 = barely interpretable and 4 = excellent image quality. Required images were rated on an additional 4-point scale, with 4 = all required images were included and 1 = minimal images were recorded. There were 352 patients enrolled by 42 emergency physicians (35 residents and 7 attendings). Gallstones were identified in 13.9% of the patients, and 4.3% of the ultrasounds were indeterminate. Interpretive and technical error rates decreased as the clinician gained experience. The number of poor quality ultrasounds decreased after an average of seven ultrasounds. Inclusion of all required images increased after 25 ultrasounds. Sonographers who had performed over 25 ultrasounds showed excellent agreement with the expert over-read, with only two disagreements, both from a single individual. It was concluded that clinicians are clinically competent after performing 25 ultrasounds of the gallbladder.

Pathophysiology of respiratory failure following acute dichlorvos poisoning in a rodent model.

Organophosphate (OP) poisoning causes a cholinergic crisis with a wide range of clinical effects including central apnea, pulmonary bronchoconstriction and secretions, seizures, and muscle weakness. The morbidity and mortality from acute OP poisoning is attributed to respiratory failure but the relative contributions of the central and peripheral effects in producing collapse of the respiratory system are unclear. In this study we used a novel adult rat model of acute OP poisoning to analyze the pathophysiology of acute OP poisoning. We found that poisoning caused rapidly lethal central apnea. In animals sustained with mechanical ventilation, we found that following central apnea there ensued progressive pulmonary insufficiency that was variable in timing and severity. Our findings support the hypothesis that OP poisoning in this animal model causes a sequential "two hit" insult, with rapid central apnea followed by delayed impairment of pulmonary gas exchange with prominent airway secretions.

Multidrug resistance in pediatric urinary tract infections.

Urinary tract infections (UTIs) represent a common infection in the pediatric population. Escherichia coli is the most common uropathogen in children, and antimicrobial resistance in this species complicates the treatment of pediatric UTIs. Despite the impact of resistance on empiric antibiotic choice, there is little data on multidrug resistance in pediatric patients. In this paper, we describe characteristics of multidrug-resistant E. coli in pediatric patients using a large national database of uropathogens antimicrobial sensitivities. Antimicrobial susceptibility patterns to commonly prescribed antibiotics were performed on uropathogens isolated from children presenting to participating hospitals between 1999 and 2001. Data were analyzed separately for four pediatric age groups. Single and multidrug resistance to ampicillin, amoxicillin-clavulanate, cefazolin, ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole (TMP-SMX) were performed on all specimens. There were a total of 11,341 E. coli urine cultures from 343 infants (0-4 weeks), 1,801 toddlers (5 weeks-24 months), 6,742 preteens (2-12 years), and 2,455 teens (13-17 years). E. coli resistance to ampicillin peaked in toddlers (52.8%) but was high in preteens (52.1%), infants (50.4%), and teens (40.6%). Resistance to two or more antibiotics varied across age groups, with toddlers (27%) leading preteens (23.1%), infants (21%), and teens (15.9%). Resistance to three or more antibiotics was low in all age groups (range 3.1-5.2%). The most common co-resistance in all age groups was ampicillin/TMP-SMZ. In conclusion, less than half of all pediatric UTIs are susceptible to all commonly used antibiotics. In some age groups, there is a significant percentage of co-resistance between the two most commonly used antibiotics (ampicillin and TMP-SMZ).

Bedside ultrasound of the soft tissue of the face: a case of early Ludwig's angina.

A case is reported of a 38-year-old man presenting with early Ludwig's angina. It is difficult to differentiate superficial from deep infections of the face and neck by physical examination alone. The diagnosis of this condition with bedside soft tissue ultrasound of the face is described. Ludwig's angina is an uncommon infection of the deep tissues of the face and neck that usually evolves from more superficial infections such as dental abscesses.

Antibiotic resistance trends in paediatric uropathogens.

The antimicrobial susceptibility patterns of paediatric uropathogens to six of the most common antibiotics in use for urinary tract infections were determined. The bacterial isolates came from the urine of children presenting as outpatients to participating US hospitals between April 2002 and May 2004. Strains of the six most common uropathogens were included in the analysis. Results were stratified by paediatric age group. In total, 11174 female and 1557 male positive cultures were analysed. The overall resistance rates for females and males, respectively, were as follows: ampicillin 44.3% and 44.6%; sulphamethoxazole/trimethoprim 24.5% and 36.7%; amoxicillin/clavulanic acid 12.4% and 27.5%; cefazolin 10.9% and 27.1%; ciprofloxacin 0.9% and 2.4%; and nitrofurantoin 4.4% and 11.0%. Uropathogen resistance to commonly used antibiotics in the paediatric population was high.

Learning curves in emergency ultrasound education.

OBJECTIVES: Proficiency in the use of bedside ultrasound (US) has become standard in emergency medicine residency training. While milestones have been established for this training, supporting data for minimum standard experience are lacking. The objective of this study was to characterize US learning curves to identify performance plateaus for both image acquisition and interpretation, as well as compare performance characteristics of learners to those of expert sonographers. METHODS: A retrospective review of an US database was conducted at a single academic institution. Each examination was scored for agreement between the learner and expert reviewer interpretation and given a score for image quality. A locally weighted scatterplot smoothing method was used to generate a model of predicted performance for each individual examination type. Performance characteristics for expert sonographers at the site were also tracked and used in addition to performance plateaus as benchmarks for learning curve analysis. RESULTS: There were 52,408 US examinations performed between May 2007 and January 2013 and included for analysis. Performance plateaus occurred at different points for different US protocols, from 18 examinations for soft tissue image quality to 90 examinations for right upper quadrant image interpretation. For the majority of examination types, a range of 50 to 75 examinations resulted in both excellent interpretation (sensitivity > 84% and specificity > 90%) and good image quality (90% the image quality benchmark of expert sonographers). CONCLUSIONS: Educational performance benchmarks occur at variable points for image interpretation and image quality for different examination types. These data should be considered when developing training standards for US education as well as experience requirements for US credentialing.

Early death due to severe organophosphate poisoning is a centrally mediated process.

OBJECTIVE: To distinguish whether early death from severe organophosphate (OP) poisoning with dichlorvos is mediated through peripheral or central nervous system (CNS) actions. METHODS: Wistar rats (n = 72) were randomized to pretreatment with either: normal saline (controls), peripheral anticholinergics (glycopyrrolate [low, medium, or high dose] or nebulized ipratropium bromide), or CNS + peripherally acting anticholinergics (diphenhydramine, nebulized atropine, or injected atropine). All treatments were given prior to a subcutaneous injection of 25 mg/kg dichlorvos (n = 8 per group). Survival was assessed at 10 minutes (early death) and 24 hours (delayed death). Kaplan-Meier (95% confidence intervals [95% CIs]) and chi-squared analysis was then performed to determine differences between treatments. RESULTS: Regardless of treatment, all animals exhibited profound nicotinic effects (fasciculations) without obvious seizures within 2 minutes of poisoning. In rats pretreated with peripherally acting agents, the fasciculations were rapidly followed by reduced motor activity, sedation, and death. Mortality at 10 minutes for saline controls, glycopyrrolate, and ipratropium was 88%, 96%, and 100%, respectively. The single control animal surviving beyond 10 minutes went on to develop peripheral cholinergic manifestations, including hypersalivation, urination, and defecation. Only one of 24 animals treated with injected atropine, nebulized atropine, or diphenhydramine died during the early phase of poisoning; all others survived to 24 hours (p < 0.01). CONCLUSIONS: Death in acute, severe OP poisoning is prevented by pretreatment with anticholinergic agents that cross the blood-brain barrier, but not by agents with only peripheral actions. Early death due to OP poisoning appears to be a centrally mediated process.

Diphenhydramine as a protective agent in a rat model of acute, lethal organophosphate poisoning.

OBJECTIVE: To evaluate the effects of diphenhydramine chloride (DPH) on mortality in a rat model of acute, severe organophosphate poisoning (OP). METHODS: Wistar rats (n = 40) were randomized to pretreatment with either normal saline (controls), 5 mg/kg atropine, 3 mg/kg DPH, 15 mg/kg DPH, or 30 mg/kg DPH given as a single intramuscular injection 5 minutes prior to a subcutaneous injection of 25 mg/kg dichlorvos (n = 8 per group). The primary endpoint was 10-minute survival. Survival at 24 hours was a secondary endpoint. Comparison of survival rates between groups was carried out by ANOVA and the Student-Newman-Keuls test. RESULTS: Dichlorvos exposure resulted in profound fasciculations within 2 minutes of injection in all cohorts. In controls, fasciculations were followed by respiratory arrest within 10 minutes (0% survival). The rats receiving atropine pre-treatment exhibited similar fasciculations (nicotinic effects) without subsequent respiratory arrest, resulting in a significant improvement in survival (88%, p < 0.001). The DPH-treated rats exhibited a significant dose-dependent reduction in mortality, with the 3 mg/kg, 15 mg/kg, and 30 mg/kg groups demonstrating 0%, 25%, and 100% survival, respectively. There was no additional mortality between 10 minutes and 24 hours in any group. There was no significant difference in survival between the high-dose DPH and the atropine groups. CONCLUSIONS: Diphenhydramine chloride significantly reduced mortality in rats with acute, severe dichlorvos exposure.

Diazepam inhibits organophosphate-induced central respiratory depression.

OBJECTIVES: Current evidence suggests that mortality from acute organophosphate (OP) poisoning is partially mediated through central nervous system (CNS) respiratory center depression (CRD). However, the exact mechanism of OP-induced CRD is unknown. In these studies, the authors investigated the hypothesis that OP-induced CRD is the result of overstimulation of CNS respiratory centers. METHODS: Wistar rats received prophylaxis with either normal saline (controls), atropine, the peripherally acting anticholinergics glycopyrrolate (GLYC), ipratropium bromide (IB), or the CNS respiratory center attenuator diazepam. To determine if a dual CNS/peripheral cholinergic mechanism is responsible for animal death, two additional groups received combination treatment with diazepam plus either IB or GLYC. All treatments were completed 5 minutes before OP with subcutaneous dichlorvos. Differences in 10-minute and 24-hour mortality were assessed by the Fisher exact test. RESULTS: Dichlorvos poisoning resulted in profound fasciculations without obvious seizure in all cohorts. In controls and animals treated with peripherally acting anticholinergics, fasciculations were followed by sedation and respiratory arrest (0% 10-minute survival in all cohorts). In contrast, pretreatment with either atropine or diazepam significantly improved 10-minute survival (100% and 44%, respectively). Although GLYC or IB afforded no protection when given alone, when delivered in conjunction with diazepam, the combination significantly improved survival (both groups 88% at 24 hours), suggesting a dual CNS/pulmonary muscarinic mechanism of lethality. CONCLUSIONS: The central respiratory depressant diazepam paradoxically attenuates organophosphate-induced respiratory depression, and when combined with peripherally acting anticholinergic agents, reduces mortality in a rat model of severe acute OP poisoning.

Correlation of corrected flow time in the carotid artery with changes in intravascular volume status.

PURPOSE: Assessment of volume status remains a challenge in critical care. Our purpose was to determine if Doppler waveform analysis of carotid artery blood flow correlates with changes in volume status. MATERIALS AND METHODS: Dehydrated patients receiving an intravenous fluid bolus were enrolled with exclusions including age less than 18 years, pregnancy, vasopressor administration, or atrial fibrillation. Ultrasound examination with Doppler analysis of the carotid artery was performed with measurements taken to calculate corrected flow time (FTc). Corrected flow time, mean arterial pressure, and pulse rate before and after fluid administration were compared using Wilcoxon matched-pairs signed rank test. RESULTS: Fifty-six patients were enrolled with mean fluid administration of 1110 mL. Corrected flow time increased with fluid resuscitation from prefluid mean of 299 milliseconds (95% confidence interval [CI], 282-317 milliseconds) to a postfluid mean of 340 milliseconds (95% CI, 323-358 milliseconds) (P<.0001). Mean percentage change in FTc was 14.9% (95% CI, 8.4-21.3). There were no significant changes in mean arterial pressure or heart rate from pre- to post-fluid administration. CONCLUSION: Intravenous fluid administration in dehydrated patients resulted in significant changes in FTc in the carotid artery despite no change in vital signs. Corrected flow time measured from carotid arterial blood flow may be a useful means of assessing volume status in volume-depleted patients.

The Massachusetts abscess rule: a clinical decision rule using ultrasound to identify methicillin-resistant Staphylococcus aureus in skin abscesses.

OBJECTIVES: Treatment failure rates for incision and drainage (I&D) of skin abscesses have increased in recent years and may be attributable to an increased prevalence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). Previous authors have described sonographic features of abscesses, such as the presence of interstitial fluid, characteristics of abscess debris, and depth of abscess cavity. It is possible that the sonographic features are associated with MRSA and can be used to predict the presence of MRSA. The authors describe a potential clinical decision rule (CDR) using sonographic images to predict the presence of CA-MRSA. METHODS: This was a pilot CDR derivation study using databases from two emergency departments (EDs) of patients presenting to the ED with uncomplicated skin abscesses who underwent I&D and culture of the abscess contents. Patients underwent ultrasound (US) imaging of the abscesses prior to I&D. Abscess contents were sent for culture and sensitivity. Two independent physicians experienced in soft tissue US blinded to the culture results and clinical data reviewed the images in a standardized fashion for the presence or absence of the predetermined image characteristics. In the instance of a disagreement between the initial two investigators, a third reviewer adjudicated the findings prior to analysis. The association between the primary outcome (presence of MRSA) and each sonographic feature was assessed using univariate and multivariate analysis. The reliability of each sonographic feature was measured by calculating the kappa (κ) coefficient of interobserver agreement. The decision tree model for the CDR was created with recursive partitioning using variables that were both reliable and strongly associated with MRSA. RESULTS: Of the total of 2,167 patients who presented with skin and soft tissue infections during the study period, 605 patients met inclusion criteria with US imaging and culture and sensitivity of purulence. Among the pathogenic organisms, MRSA was the most frequently isolated, representing 50.1% of all patients. Six of the sonographic features were associated with the presence of MRSA, but only four of these features were reliable using the kappa analysis. Recursive partitioning identified three independent variables that were both associated with MRSA and reliable: 1) the lack of a well-defined edge, 2) small volume, and 3) irregular or indistinct shape. This decision rule demonstrates a sensitivity of 89.2% (95% confidence interval [CI] = 84.7% to 92.7%), a specificity of 44.7% (95% CI = 40.9% to 47.8%), a positive predictive value of 57.9 (95% CI = 55.0 to 60.2), a negative predictive value of 82.9 (95% CI = 75.9 to 88.5), and an odds ratio (OR) of 7.0 (95% CI = 4.0 to 12.2). CONCLUSIONS: According to our putative CDR, patients with skin abscesses that are small, irregularly shaped, or indistinct, with ill-defined edges, are seven times more likely to demonstrate MRSA on culture.