Factors that influence flow through intravascular catheters: the clinical relevance of Poiseuille's law.

BACKGROUND: The physics of ideal fluid flow is well characterized. However, the effect of catheter size, tubing types, injection port adjuncts, and viscosity on flow is not well described. We used a simulated environment to determine how various permutations of common elements affect fluid flow. STUDY DESIGN AND METHODS: We tested 16 peripheral and central venous catheters to assess flow through several standard infusion sets and a rapid infuser set; tested flow through standard and blood infusion sets with the addition of intravenous extension tubing, stopcocks, and a needleless connector; and compared the relative viscosity of commonly used blood products and colloids to that of normal saline. RESULTS: The maximal flow rate was 200 mL/min for the standard infusion set but 800 mL/min for the rapid infusion set. Choice of infusion tubing was the rate-limiting component for many larger catheters. A 14-gauge, single-lumen central venous catheter (CVC) and 18-gauge peripheral intravenous catheter (PIV) had equivalent flow rates with all infusion sets. A 16-gauge single-lumen CVC allowed a flow rate that was slower than that of a 20-gauge PIV, and faster than that of a 22-gauge PIV. The addition of adjuncts slowed flow rate. Needleless connectors had the greatest impact, reducing flow by 75% for the blood infusion set. Packed red blood cells had a viscosity 4.5 times that of normal saline and thereby reduced flow. CONCLUSION: Catheter and tubing choice, adjuncts, and fluid viscosity influence flow rates. Our results will help inform adequate vascular access planning in the perioperative environment.

Remote Obstetric Anesthesia: Leveraging Telemedicine to Improve Fetal and Maternal Outcomes.

In the United States, the prevalence of pregnancy-related deaths has risen significantly over the past 20 years. Pregnant women at high risk for peripartum complications should undergo anesthesia consultation before delivery so that a management plan can be created between the obstetrician, anesthesiologist, and patient to ensure optimal outcomes for both the mother and newborn. However, few hospitals outside of major, urban, academic medical centers have dedicated anesthesiologists specially trained in obstetric anesthesia and the resources available to expedite optimization of high-risk parturient comorbidities. Telemedicine is a valuable tool by which evaluation, triaging, and multidisciplinary coordination can be provided for high-risk obstetric patients living in remote or rural communities without access to specialized, maternal care medical facilities. This review examines the existing literature regarding telemedicine use in preoperative anesthesia and antenatal obstetrics and identifies areas for future research. Furthermore, the benefits and potential barriers of implementing a telemedicine program specifically dedicated to obstetric anesthesia are discussed.

Training novice anaesthesiology trainees to speak up for patient safety.

BACKGROUND: Effectively communicating patient safety concerns in the operating theatre is crucial, but novice trainees often struggle to develop effective speaking up behaviour. Our primary objective was to test whether repeated simulation-based practice helps trainees speak up about patient management concerns. We also tested the effect of an additional didactic intervention over standard simulation education. METHODS: This prospective observational study with a nested double-blind, randomised controlled component took place during a week-long simulation boot camp. Participants were randomised to receive simulation education (SE), or simulation education plus a didactic session on speaking up behaviour (SE+). Outcome measures were: changes in intrapersonal factors for speaking up (self-efficacy, social outcome expectations, and assertiveness), and speaking up performance during four simulated scenarios. Participants self-reported intrapersonal factors and blinded observers scored speaking up behaviour. Cognitive burden for each simulation was also measured using the National Aeronautics and Space Administration Task Load Index. Mixed-design analysis of variance was used to analyse scores. RESULTS: Twenty-two participants (11 per group) were included. There was no significant interaction between group and time for any outcome measure. There was a main effect for time for self-efficacy (P<0.001); for social outcome expectations (P<0.001); for assertive attitude (P=0.003); and for speaking up scores (P=0.001). The SE+ group's assertive attitude scores increased at follow-up whereas the SE group reverted to near baseline scores (P=0.025). CONCLUSIONS: In novice anaesthesia trainees, intrapersonal factors and communication performance benefit from repeated simulation training. Focused teaching may help trainees develop assertive behaviours.

Evaluation of 3 Cognitive Load Measures During Repeated Simulation Exercises for Novice Anesthesiology Residents.

INTRODUCTION: Maintaining an appropriate level of cognitive load during simulations is crucial to optimize learning. We evaluated 3 subjective measures of cognitive load in a simulated operating room (OR) context across multiple scenarios of varying complexity. METHODS: This observational study of 25 first-year anesthesiology residents took place during a 5-day simulation "Boot Camp." Each day, participants completed 2 different high-fidelity scenarios in a fully equipped simulated OR. After each simulation, participants completed 3 cognitive load measures: the Paas scale, NASA Task Load Index (TLX), and Cognitive Load Component (CLC) questionnaire. Two-way repeated-measures and mixed-design analyses of variance, with the cognitive load measures and scenarios as independent factors, were used to determine the effect of using different measures to report cognitive load. RESULTS: Cognitive load scores reported by all measures correlated significantly with one another (P < 0.01): TLX and Paas (r = 0.65); Paas and CLC (r = 0.63); and TLX and CLC (r = 0.61). The CLC subscale scores (intrinsic, extraneous, germane) also correlated significantly with composite TLX and Paas scores (P < 0.01). Scenarios and measures displayed significant interaction: F(10, 210) = 3.01, P = 0.001. Participants reported highest overall cognitive load using the Paas scale. CONCLUSIONS: All cognitive load measures were sensitive to scenario variability and showed similar fluctuation patterns across the 10 scenarios. The findings suggest that cognitive load measures can help create benchmarks based on learner perceptions of cognitive burden for different simulation scenarios.

Development of a scale to measure intrapersonal factors influencing speaking up in the operating room.

INTRODUCTION: This paper reports on the development of a scale to measure intrapersonal factors (IPF) that may influence speaking up behaviour in the operating room. METHODS: Participants were postgraduate year 2, 3, and 4 anaesthesiology residents and practising faculty anaesthesiologists at a large quaternary care academic hospital. Based on a literature review, the authors constructed the initial scale. Exploratory factor analysis was conducted to identify the underlying factor structure for the scale. A set of one-way ANOVAs and multiple ordinal regressions were carried out to provide additional validity evidence for the new scale. RESULTS: Exploratory factor analysis indicated a three-factor solution accounting for 73% of the variance. The self-efficacy subscale included four items (Cronbach's α = 0.86), and the social outcome expectations (Cronbach's α = 0.86) and assertive attitude (Cronbach's α = 0.67) subscales contained three items each. The effect of training level was significantly associated with self-efficacy (p < 0.001) and assertive attitude subscale scores (p < 0.001). Multiple ordinal regressions indicated that IPF predicted participants' likelihood of speaking up in various hypothetical scenarios. DISCUSSION: Our analyses provided initial evidence for the validity and reliability of a 10-item IPF scale. This instrument needs to be validated in other cohorts.

Can changes in vital signs be used to predict the response to lumbar facet blocks and radiofrequency denervation? A prospective, correlational study.

BACKGROUND: Facet joint radiofrequency (RF) ablation is characterized by a high failure rate, which is partly due to the fact that pain relief after diagnostic blocks is inherently subjective. An area that has yet to be explored is whether more objective measures, such as changes in vital signs after blocks, might be used to predict treatment outcomes. METHODS: A multicenter, prospective study was performed in 223 patients who underwent diagnostic lumbar medial branch blocks, of whom 87 proceeded to RF denervation. Blood pressure (BP), heart rate (HR), and pain scores were recorded preblock and 20 minutes postblock. A positive vital sign response was designated as a decrease of less than 7.5 units in BP or HR, and a positive facet block as pain relief of 50% or greater based on 6-hour pain diary scores. RESULTS: Overall, 125 subjects (56.1%; 95% confidence interval, 49.3%-62.6%) experienced a positive facet block, and 71 had 3-month follow-up information after denervation. Correlations between changes in NRS scores and HR (r = -0.01, P = 0.893), systolic BP (r = 0.05, P = 0.47), diastolic BP (DBP) (r = 0.08, P = 0.22), and mean arterial pressure (r = 0.08, P = 0.21) were weak and nonsignificant. No associations were found between facet block results and any vital sign. Six (85.7%) of 7 patients who experienced a decrease in DBP of greater than 7.5 mm Hg after facet block had a positive RF denervation outcome at 3 months, compared with 43.8% who did not (odds ratio, 7.52; 95% confidence interval, 0.84-363.8; P = 0.049). A classification tree based on significant decrease in DBP, pain duration, and baseline NRS pain score showed a 76.7% (range, 65.8%-86.3%) accuracy rate. CONCLUSIONS: Although a decrease in DBP of more than 7.5 mm Hg had 97.3% specificity and 85.7% positive predictive value for predicting positive RF ablation outcomes, the low negative predictive value (56.3%) precludes its use as a solitary screening tool. An algorithm based on age, baseline NRS pain score, and a significant decrease in DBP was able to predict 76.7% (range, 65.8%-86.3%) of RF denervation outcomes.