Surfactants and cloud droplet activation: A systematic extension of Köhler theory based on analysis of droplet stability.

The activation of aerosol particles to form cloud droplets, a necessary first step in cloud formation, controls much of the impact that aerosols have on clouds and climate. Recently, there has been a surge of interest in extending the Köhler theory of cloud droplet activation to include surface active (typically organic) as well as water-soluble (typically inorganic) aerosol components, but a systematic framework for doing this has yet to be developed. Here, we apply a droplet stability analysis to this end. Ideal and Szyszkowski-Langmuir surfactant models are analyzed to demonstrate the new approach, but the underlying theoretical framework is fundamental and model free. A key finding is that superficial densities at the cloud activation threshold (Köhler maximum) are significantly sub-monolayer, with fractional coverage ranging from 69% to 85% for the organic compounds and mixtures studied. The result, significant for model inventories of cloud condensation nuclei, is a weakening of the surfactant effect relative to expectations based on bulk sample measurements. Analytical results are obtained for the loci of Köhler maxima and applied to aerosol mixtures containing an arbitrary number of water-soluble and surfactant components.

A unifying identity for the work of cluster formation in heterogeneous and homogeneous nucleation theory.

A unifying identity is derived relating the reversible work of cluster formation (W) and its molecular number content (n) and surface work (Φ) components, each ratioed to the corresponding values for a spherical capillary drop of critical size in classical nucleation theory. The result is a relationship that connects these ratios: fW = -2fN + 3fS, where fW = W/W*CNT, fN = n/n*CNT, and fS = Φ/Φ*CNT. Shown to generalize two early thermodynamic relationships of Gibbs, the new result is demonstrated here for Fletcher's model of heterogeneous nucleation, resulting in a unified treatment of condensation on flat and curved substrates and smooth passage to the homogeneous limit. Additional applications are made to clusters of non-critical as well as critical size and to a molecular-based extension of classical nucleation theory based on the Kelvin relation. The new identity serves as a consistency check on complicated theoretical expressions and numerical calculations and can be used to guide the construction of theory and interpretation of measurements.

How we developed a comprehensive resuscitation-based simulation curriculum in emergency medicine.

Over the past decade, simulation-based education has emerged as a new and exciting adjunct to traditional bedside teaching and learning. Simulation-based education seems particularly relevant to emergency medicine training where residents have to master a very broad skill set, and may not have sufficient real clinical opportunities to achieve competence in each and every skill. In 2006, the Emergency Medicine program at Queen's University set out to enhance our core curriculum by developing and implementing a series of simulation-based teaching sessions with a focus on resuscitative care. The sessions were developed in such as way as to satisfy the four conditions associated with optimum learning and improvement of performance; appropriate difficulty of skill, repetitive practice, motivation, and immediate feedback. The content of the sessions was determined with consideration of the national training requirements set out by the Royal College of Physicians & Surgeons of Canada. Sessions were introduced in a stepwise fashion, starting with a cardiac resuscitation series based on the AHA ACLS guidelines, and leading up to a more advanced resuscitation series as staff became more adept at teaching with simulation, and as residents became more comfortable with this style of learning. The result is a longitudinal resuscitation curriculum that begins with fundamental skills of resuscitation and crisis resource management (CRM) in the first 2 years of residency and progresses through increasingly complex resuscitation cases where senior residents are expected to play a leadership role. This paper documents how we developed, implemented, and evaluated this resuscitation-based simulation curriculum for Emergency Medicine postgraduate trainees, with discussion of some of the challenges encountered.

Communication: kinetics of scavenging of small, nucleating clusters: first nucleation theorem and sum rules.

Despite recent advances in monitoring nucleation from a vapor at close-to-molecular resolution, the identity of the critical cluster, forming the bottleneck for the nucleation process, remains elusive. During past twenty years, the first nucleation theorem has been often used to extract the size of the critical cluster from nucleation rate measurements. However, derivations of the first nucleation theorem invoke certain questionable assumptions that may fail, e.g., in the case of atmospheric new particle formation, including absence of sub-critical cluster losses and heterogeneous nucleation on pre-existing nanoparticles. Here, we extend the kinetic derivation of the first nucleation theorem to give a general framework to include such processes, yielding sum rules connecting the size dependent particle formation and loss rates to the corresponding loss-free nucleation rate and the apparent critical size from a naïve application of the first nucleation theorem that neglects them.

Computerized training system for ultrasound-guided lumbar puncture on abnormal spine models: a randomized controlled trial.

PURPOSE: A randomized controlled trial was carried out to determine whether Perk Tutor, a computerized training platform that displays an ultrasound image and real-time needle position in a three-dimensional (3D) anatomical model, would benefit residents learning ultrasound-guided lumbar puncture (LP) in simulation phantoms with abnormal spinal anatomy. METHODS: Twenty-four residents were randomly assigned to either the Perk Tutor (P) or the Control (C) group and asked to perform an LP with ultrasound guidance on part-task trainers with spinal pathology. Group P was trained with the 3D display along with conventional ultrasound imaging, while Group C used conventional ultrasound only. Both groups were then tested solely with conventional ultrasound guidance on an abnormal spinal model not previously seen. We measured potential tissue damage, needle path in tissue, total procedure time, and needle insertion time. Procedural success rate was a secondary outcome. RESULTS: The needle tracking measurements (expressed as median [interquartile range; IQR]) in Group P vs Group C revealed less potential tissue damage (39.7 [21.3-42.7] cm(2) vs 128.3 [50.3-208.2] cm(2), respectively; difference 88.6; 95% confidence intervals [CI] 24.8 to 193.5; P = 0.01), a shorter needle path inside the tissue (426.0 [164.9-571.6] mm vs 629.7 [306.4-2,879.1] mm, respectively; difference 223.7; 95% CI 76.3 to 1,859.9; P = 0.02), and lower needle insertion time (30.3 [14.0-51.0] sec vs 59.1 [26.0-136.2] sec, respectively; difference 28.8; 95% CI 2.2 to 134.0; P = 0.05). Total procedure time and overall success rates between groups did not differ. CONCLUSION: Residents trained with augmented reality 3D visualization had better performance metrics on ultrasound-guided LP in pathological spine models.

Assessment of lumbar puncture skill in experts and nonexperts using checklists and quantitative tracking of needle trajectories: implications for competency-based medical education.

UNLABELLED: CONSTRUCT: With the current shift toward competency-based education, rigorous assessment tools are needed for procedurally based tasks. BACKGROUND: Multiple tools exist to evaluate procedural skills, each with specific weaknesses. APPROACH: We sought to determine if quantitative needle tracking could be used as a measure of lumbar puncture (LP) performance and added discriminatory value to a dichotomous checklist. Thirty-two medical students were divided into 2 groups. One group was asked to practice an LP once (single practice [SP]) and the other 5 times (multiple practice [MP]). Experts (attending ER physicians, senior ER residents, and a junior anesthesia resident) were used as comparators. Medical students were assessed again at 1 month to assess skill retention. Groups were assessed performing an LP with an electromagnetic tracking device that allows the needle's 3-dimensional movements to be captured and analyzed, and a dichotomous checklist. RESULTS: Quantitative needle metrics as assessed by electromagnetic tracking showed a decreasing trend in needle movement distance with practice and with experience. The SP group made significantly more checklist mistakes initially as compared to the MP group (1.2 vs. 0.3, p <.05). At 1 month, there was a significant increase in both groups' mistakes (SP 3.4 vs. MP 1.3, p =.01). No correlation existed between individuals' needle motion and checklist mistakes. CONCLUSIONS: These findings suggest that quantitative needle tracking identifies students who struggle with needle insertion but are successful at completing the dichotomous checklist.

Using cognitive load theory to develop an emergency airway management curriculum: the Queen's University Mastery Airway Course (QUMAC).

Emergency airway management requires the simultaneous coordination of clinical reasoning and therapeutic interventions in the complex and time-sensitive setting of emergency resuscitation. The cognitive demand associated with these situations is invariably high and must be taken into consideration when designing training programs for this core professional competency. The four-component instructional design model (4C/ID), based on cognitive load theory, was used to develop a 1-year longitudinal airway management curriculum for Emergency Medicine residents. The simulation-based curriculum was designed with the goal of facilitating the construction and automation of schemas by individual residents in preparation for the high cognitive demand associated with emergency airway management in the clinical environment.

RéSUMé: La gestion des voies aériennes en urgence nécessite la coordination simultanée du raisonnement clinique et des interventions thérapeutiques dans le cadre complexe et sensible au temps de la réanimation d'urgence. La demande cognitive associée à ces situations est invariablement élevée et doit être prise en considération lors de la conception des programmes de formation pour cette compétence professionnelle essentielle. Le modèle de conception pédagogique à quatre composantes (4C/ID), fondé sur la théorie de la charge cognitive, a été utilisé pour élaborer un programme longitudinal de gestion des voies aériennes d'un an à l'intention des résidents en médecine d'urgence.

Formation of nanoparticles of blue haze enhanced by anthropogenic pollution.

The molecular processes leading to formation of nanoparticles of blue haze over forested areas are highly complex and not fully understood. We show that the interaction between biogenic organic acids and sulfuric acid enhances nucleation and initial growth of those nanoparticles. With one cis-pinonic acid and three to five sulfuric acid molecules in the critical nucleus, the hydrophobic organic acid part enhances the stability and growth on the hydrophilic sulfuric acid counterpart. Dimers or heterodimers of biogenic organic acids alone are unfavorable for new particle formation and growth because of their hydrophobicity. Condensation of low-volatility organic acids is hindered on nano-sized particles, whereas ammonia contributes negligibly to particle growth in the size range of 3-30 nm. The results suggest that initial growth from the critical nucleus to the detectable size of 2-3 nm most likely occurs by condensation of sulfuric acid and water, implying that anthropogenic sulfur emissions (mainly from power plants) strongly influence formation of terrestrial biogenic particles and exert larger direct and indirect climate forcing than previously recognized.

Reversible uptake of water on NaCl nanoparticles at relative humidity below deliquescence point observed by noncontact environmental atomic force microscopy.

The behavior of NaCl nanoparticles as a function of relative humidity (RH) has been characterized using non-contact environmental atomic force microscopy (e-AFM) to measure the heights of particles deposited on a prepared hydrophobic surface. Cubic NaCl nanoparticles with sides of 35 and 80 nm were found to take up water reversibly with increasing RH well below the bulk deliquescence relative humidity (DRH) of 75% at 23(∘)C, and to form a liquid-like surface layer of thickness 2 to 5 nm, with measurable uptake (>2 nm increase in particle height) beginning at 70% RH. The maximum thickness of the layer increased with increasing RH and increasing particle size over the range studied. The liquid-like behavior of the layer was indicated by a reversible rounding at the upper surface of the particles, fit to a parabolic cross-section, where the ratio of particle height to maximum radius of curvature increases from zero (flat top) at 68% RH to 0.7 ± 0.3 at 74% RH. These observations, which are consistent with a reorganization of mass on the solid NaCl nanocrystal at RH below the DRH, suggest that the deliquescence of NaCl nanoparticles is more complex than an abrupt first-order phase transition. The height measurements are consistent with a phenomenological model that assumes favorable contributions to the free energy of formation of a liquid layer on solid NaCl due both to van der Waals interactions, which depend partly upon the Hamaker constant, A(film), of the interaction between the thin liquid film and the solid NaCl, and to a longer-range electrostatic interaction over a characteristic length of persistence, ξ; the best fit to the data corresponded to A(film)= 1 kT and ξ = 2.33 nm.

Hydrogen-bonding interaction in molecular complexes and clusters of aerosol nucleation precursors.

Complexes and clusters bridge the gap between molecular and macroscopic levels by linking individual gaseous molecules to newly formed nanoparticles but the driving forces and mechanism for the formation of complexes and clusters in the atmosphere are not well understood. We have performed ab initio and density functional quantum chemical calculations to elucidate the role of organic acids in the formation of complexes with common atmospheric nucleating precursors such as sulfuric acid, water, and ammonia. A central feature of the complexes is the presence of two hydrogen bonds. Organic acid-sulfuric acid complexes show one strong and one medium-strength hydrogen bond whereas the corresponding hydrogen bonds in organic acid-ammonia complexes are characterized as medium-strength and weak. The formation of strong hydrogen bonds in organic acid-sulfuric acid complexes is explained by the well-established resonance-assisted hydrogen bonding theory. Organic acid-sulfuric acid and organic acid-organic acid complexes possess the largest binding energies among the homomolecular and heteromolecular dimers, about 18 kcal mol(-1) from the composite theoretical methods. Topological analysis employing quantum theory of atoms in molecules (QTAIM) shows that the charge density and the Laplacian at bond critical points (BCPs) of the hydrogen bonds of the organic acid-sulfuric acid complex (e.g., benzoic acid-sulfuric acid and cis-pinonic acid-sulfuric acid) are 0.07 and 0.16 au, respectively, which falls in or exceeds the range of one strong and one medium-strength hydrogen bonding criteria.

Deliquescence and efflorescence of small particles.

We examine size-dependent deliquescence/efflorescence phase transformation for particles down to several nanometers in size. Thermodynamic properties of inorganic salt particles, coated with aqueous solution layers of varying thickness and surrounded by vapor, are analyzed. A thin layer criterion (TLC) is introduced to define a limiting deliquescence relative humidity (RH(D)) for small particles. This requires: (1) equality of chemical potentials between salt in an undissolved core, and thin adsorbed solution layer, and (2) equality of chemical potentials between water in the thin layer and vapor phase. The usual bulk deliquescence conditions are recovered in the limit of large dry particle size. Nanosize particles are found to deliquesce at relative humidity just below the RH(D) on crossing a nucleation barrier, located at a critical solution layer thickness. This barrier vanishes precisely at the RH(D) defined by the TLC. Concepts and methods from nucleation theory including the kinetic potential, self-consistent nucleation theory, nucleation theorems, and the Gibbs dividing surface provide theoretical foundation and point to unifying features of small particle deliquescence/efflorescence processes. These include common thermodynamic area constructions, useful for interpretation of small particle water uptake measurements, and a common free-energy surface, with constant RH cross sections describing deliquescence and efflorescence related through the nucleation theorem.

Cognitive load theory as a framework for simulation-based, ultrasound-guided internal jugular catheterization training: Once is not enough.

OBJECTIVE: The main objective of this study was to use the principles of cognitive load theory to design a curriculum that incorporates a progressive part practice approach to teaching ultrasound-guided (USG) internal jugular catheterization (IJC) to novices. A secondary objective was to compare the technical proficiency of residents trained using this curriculum with the technical proficiency of residents trained with the current local standard of a single simulation session. METHODS: The experimental group included 16 residents who attended three 2-hour sessions of progressive part practice in a simulation lab. The control group included 46 residents who attended the current local standard of a single 2-hour simulation session just prior to their intensive care unit rotation. Technical proficiency was assessed using hand motion analysis and time to procedure completion. RESULTS: After three sessions, median scores for right hand motion (RHM) (34.5; [27.0-49.0]), left hand motion (LHM) (35.5; [20.0-45.0]), and total time (TT) (117.0 s; [82.7-140.0]) in the experimental group were significantly better than the control group (p<0.001). Results for eight experimental group residents who were assessed for retention at a later date revealed median scores for RHM (45.0; [32.0-58.0]), LHM (33.5; [20.0-63.0]), and TT (150.0 s; [103.0-399.6]), which were significantly better than those of the control group (p=0.01, p<0.01, and p=0.02, respectively). CONCLUSION: These results support multiple sessions of progressive part practice in a simulation lab as an effective competency-based approach to teaching USG IJC in preparation for the clinical setting.

Interprofessional resuscitation rounds: a teamwork approach to ACLS education.

PURPOSE: We developed and implemented a series of interprofessional resuscitation rounds targeting fourth year nursing and medical students, and junior residents from a variety of specialty programs. METHODS: Each two hour session was conducted in our patient simulation lab, and was held weekly during the academic year. Students were given specific instruction on the roles and responsibilities of resuscitation team members, and then teams of five worked through pre-defined Advanced Cardiac Life Support (ACLS) scenarios on a high fidelity patient simulator. At the end of each session students completed an anonymous evaluation of the program via a standardized questionnaire using Likert rating scales. RESULTS: A total of 222 evaluations (101 nursing students, 42 medical students, and 79 junior residents) were submitted from October 2005 to April 2006. Mean scores reflected a strong consensus that these rounds were valuable for their training, provided a vehicle for understanding team roles in resuscitation, and that these rounds should be mandatory for all medical and nursing trainees. Participants also expressed a desire for additional interprofessional training. CONCLUSION: Despite challenges inherent in teaching a diverse group of learners, these interprofessional resuscitation rounds were rated highly by nursing and medical trainees as valuable learning experiences.

Simulation in interprofessional education for patient-centred collaborative care.

AIM: This paper is a report of preliminary evaluations of an interprofessional education through simulation project by focusing on learner and teacher reactions to the pilot modules. BACKGROUND: Approaches to interprofessional education vary widely. Studies indicate, however, that active, experiential learning facilitate it. Patient simulators require learners to incorporate knowing, being and doing in action. A theoretically based competency framework was developed to guide interprofessional education using simulation. The framework includes a typology of shared, complementary and profession-specific competencies. Each competency type is associated with an intraprofessional, multiprofessional, or interprofessional teaching modality and with the professional composition of learner groups. METHOD: The project is guided by an action research approach in which ongoing evaluation generates knowledge to modify and further develop it. Preliminary evaluations of the first pilot module, cardiac resuscitation rounds, among 101 nursing students, 42 medical students and 70 junior medical residents were conducted in 2005-2007 using a questionnaire with rating scales and open-ended questions. Another 20 medical students, 7 junior residents and 45 nursing students completed a questionnaire based on the Interdisciplinary Education Perception scale. FINDINGS: Simulation-based learning provided students with interprofessional activities they saw as relevant for their future as practitioners. They embraced both the interprofessional and simulation components enthusiastically. Attitudinal scores and responses were consistently positive among both medical and nursing students. CONCLUSION: Interprofessional education through simulation offers a promising approach to preparing future healthcare professionals for the collaborative models of healthcare delivery being developed internationally.

Temperature Dependence in Heterogeneous Nucleation with Application to the Direct Determination of Cluster Energy on Nearly Molecular Scale.

A re-examination of measurements of heterogeneous nucleation of water vapor on silver nanoparticles is presented here using a model-free framework that derives the energy of critical cluster formation directly from measurements of nucleation probability. Temperature dependence is correlated with cluster stabilization by the nanoparticle seed and previously found cases of unusual increasing nucleation onset saturation ratio with increasing temperature are explained. A necessary condition for the unusual positive temperature dependence is identified, namely that the critical cluster be more stable, on a per molecule basis, than the bulk liquid to exhibit the effect. Temperature dependence is next examined in the classical Fletcher model, modified here to make the energy of cluster formation explicit in the model.  The contact angle used in the Fletcher model is identified as the microscopic contact angle, which can be directly obtained from heterogeneous nucleation experimental data by a recently developed analysis method. Here an equivalent condition, increasing contact angle with temperature, is found necessary for occurrence of unusual temperature dependence. Our findings have immediate applications to atmospheric particle formation and nanoparticle detection in condensation particle counters (CPCs).

Performance of emergency medicine residents on a novel practice examination using visual stimuli.

OBJECTIVES: In 2004, the format of the Royal College of Physicians and Surgeons of Canada certification exam in Emergency Medicine was modified to include an audiovisual session. Residents' performance on such stimuli is unknown. This study aims to determine the performance of Emergency Medicine postgraduate year 5 (PGY-5) on a novel practice examination using visual stimuli, in an effort to guide residents' preparatory study, and to help educators focus the teaching related to visual stimuli. METHODS: In this prospective observational study, 30 PGY-5 residents from 12 Emergency Medicine programs across Canada participated in a practice examination in which they had to answer 133 questions related to 80 visual stimuli. The stimuli included electrocardiograms, medical imaging and clinical photographs. Three experienced faculty provided "reference standard" answers for the visual stimuli. For analysis purpose, stimuli were classified into 9 clinical domains, outlined in The Model of the Clinical Practice of Emergency Medicine. RESULTS: Insufficient question numbers in 3 domains prevented reliable inferences. Correct answers were given for 65% of remaining questions, with the following domain distribution: 69% respiratory, 64% trauma, 73% cardiovascular, 62% head-eyes-ears-nose-throat (HEENT), 63% musculoskeletal and 69% cutaneous. Seventy-four percent of ECGs, 64% of imaging, and 62% of photograph-related questions were answered correctly. Incorrect answers were related to a lack of knowledge as well as imprecise or incomplete responses. CONCLUSIONS: PGY-5 subjects scored lowest in the HEENT and musculoskeletal domains. Medical educators should emphasize these domains in their teaching, and insist on precision and completeness of answers.

Accuracy of instructor assessment of chest compression quality during simulated resuscitation.

OBJECTIVES: The 2010 American Heart Association Guidelines stress the importance of high quality cardiopulmonary resuscitation (CPR) as a predictor of survival from cardiac arrest. However, resuscitation training is often facilitated and evaluated by instructors without access to objective measures of CPR quality. This study aims to determine whether instructors experienced in the area of adult resuscitation (emergency department staff and senior residents) can accurately assess the quality of chest compressions as a component of their global assessment of a simulated resuscitation scenario. METHODS: This is a prospective observational study in which objective chest compression quality data (rate, depth, and fraction) were collected from the simulation manikin and compared to subjective instructor assessment. Data were collected during weekly simulation training sessions for residents, medical students, and nursing students. RESULTS: We included data from 24 simulated resuscitation scenarios assessed by 1 of 15 instructors. Subjective assessment of chest compression quality identified an adequate compression rate (100-120 compressions per minute) with a sensitivity of 0.17 (confidence interval [CI] 0.02-0.32) and specificity of 0.06 (CI -0.04-0.15), adequate depth (>50 mm) with a sensitivity of 0 and specificity of 0.38 (CI 0.18-0.57), and adequate fraction (>80%) with a sensitivity of 1 and a specificity of 0.25 (CI 0.08-0.42). CONCLUSION: Instructor assessment of chest compression rate, depth, and fraction demonstrates poor sensitivity and specificity when compared to the data from the simulation manikin. These results support the use of objective and technologically supported measures of chest compression quality for feedback during resuscitation education using simulators.

Development and Evaluation of a Simulation-based Curriculum for Ultrasound-guided Central Venous Catheterization.

OBJECTIVE: To develop a simulation-based curriculum for residents to learn ultrasound-guided (USG) central venous catheter (CVC) insertion, and to study the volume and type of practice that leads to technical proficiency. METHODS: Ten post-graduate year two residents from the Departments of Emergency Medicine and Anesthesiology completed four training sessions of two hours each, at two week intervals, where they engaged in a structured program of deliberate practice of the fundamental skills of USG CVC insertion on a simulator. Progress during training was monitored using regular hand motion analysis (HMA) and performance benchmarks were determined by HMA of local experts. Blinded assessment of video recordings was done at the end of training to assess technical competence using a global rating scale. RESULTS: None of the residents met any of the expert benchmarks at baseline. Over the course of training, the HMA metrics of the residents revealed steady and significant improvement in technical proficiency. By the end of the fourth session six of 10 residents had faster procedure times than the mean expert benchmark, and nine of 10 residents had more efficient left and right hand motions than the mean expert benchmarks. Nine residents achieved mean GRS scores rating them competent to perform independently. CONCLUSION: We successfully developed a simulation-based curriculum for residents learning the skills of USG CVC insertion. Our results suggest that engaging residents in three to four distributed sessions of deliberate practice of the fundamental skills of USG CVC insertion leads to steady and marked improvement in technical proficiency with individuals approaching or exceeding expert level benchmarks.

Examination of Learning Trajectories for Simulated Lumbar Puncture Training Using Hand Motion Analysis.

OBJECTIVES: A prospective cohort study was conducted using hand motion analysis (HMA) to assess the acquisition and retention of technical proficiency among first-year medical students learning the lumbar puncture (LP) skill in a simulated setting. METHODS: Twenty-five subjects attended three or four simulation sessions at 6-week intervals. The initial session consisted of an introduction to the procedure and a baseline HMA assessment. This was followed by a session involving deliberate practice and evaluation using HMA. Subject HMA metrics were followed over time and compared to performance benchmarks to determine the volume of practice required to achieve and maintain technical proficiency in the simulated setting. Performance benchmarks were derived from the assessment of experts using HMA. RESULTS: Subject baseline metrics were significantly different from expert (p < 0.01). At the outset of session 2, none of the subjects achieved the performance benchmarks. At the outset of sessions 3 and 4, 40 and 60% of subjects, respectively, demonstrated retention of technical proficiency. However, there was evidence of significant skill erosion between sessions (p < 0.01). The mean number of practice attempts required to achieve technical proficiency declined between sessions. Regression analysis indicated that there was a significant training effect for all students (overall negative slopes) over time. When examining the group as a whole, the speed at which students reached the expert benchmark was not significantly associated with number of practices in the first three sessions, although for some individuals these factors did appear associated. A total of 76% of subjects retained technical proficiency by session 4 and required a mean of 14 practices (range = 5 to 19). CONCLUSIONS: These results show that the majority of students require three to four sessions of deliberate practice to achieve a sustainable level of proficiency in the LP procedure. There is considerable variation in learning progression and retention of technical proficiency. These results have important implications for the design and resource requirements of a competency-based medical education program targeting LP training.