Gas chromatograph calibration of gas mixtures using a versatile precision volumetric apparatus.

A compact, volumetric apparatus was developed for accurate automated preparation of standard gas and gas-liquid mixtures for gas chromatograph detector calibration, with accuracies comparable to those from gravimetric or Coriolis flow methods. The method developed by the principal author is not an adaptation or extension of any other apparatus or technology, and measurements involve only stepper motor steps, temperature, and pressure ratios. Mixture preparation is accomplished via the displacement of gas between chambers in a highly uniform cylinder, separated by a movable piston. Piston movement, with piston end rods of exactly equal diameter, ensures that there is no change in interior volume, and the volume of gas displaced from the bottom into the top compartment is exactly proportional to the piston travel measured to within 10 µm. The apparatus, operation, and previously unpublished measurements on common refinery gas mixtures over large concentration ranges are described in detail. These confirmed the accuracy and versatility of the apparatus and also the principle of no pressure change during mixture preparation, from sensitive pressure measurements. Conservative expanded uncertainties in prepared mixture mole fraction ranged from 0.001 to 0.002 over extended composition ranges. Absolute average deviations for the detector response factor for the mixtures ranged from 0.001 to 0.002. An exact new mathematical solution procedure permits the use of impure "pure" gases without loss of accuracy and can be applied to other procedures for standard gas mixture preparation. An exact expression is listed for determining "pure" gas purity.

Evaluating the optimal training paradigm for transcarotid artery revascularization based on worldwide experience.

BACKGROUND: Transcarotid artery revascularization (TCAR) is a new hybrid approach to carotid artery revascularization. Proctored training on live cases is an effort-, time-, and resource-intensive approach to learning new procedures. We analyzed the worldwide experience with TCAR to develop objective performance metrics for the procedure and compared the effectiveness of training physicians using cadavers or synthetic models to that of traditional in-person training on live cases. METHODS: Physicians underwent one of three mandatory training programs: (1) in-person proctoring on live TCAR procedures, (2) supervised training on human cadavers, and (3) supervised training on synthetic models. The training details and information from all subsequent independently performed TCAR procedures were recorded. The composite clinical adverse events (ie, transient ischemic attack, stroke, myocardial infarction, death) and composite technical adverse events (ie, aborted procedure, conversion to surgery, bleeding, dissection, cranial nerve injury, or device failure, occurring within 24 hours were recorded). Four procedural proficiency measures were recorded: procedure time, flow-reversal time, fluoroscopy time, and contrast volume. We compared the adverse event rates between the procedures performed by physicians after undergoing the three training modes and tested whether the proficiency measures achieved during TCAR after training on cadavers and synthetic models were noninferior to proctored training. RESULTS: From March 3, 2009 to May 7, 2020, 1160 physicians had undergone proctored (19.1%), cadaver-based (27.4%), and synthetic model-based (53.5%) TCAR training and had subsequently performed 17,283 TCAR procedures. The proctored physicians had treated younger patients and more patients with asymptomatic carotid stenosis and had had more prior experience with transfemoral carotid stenting. The overall 24-hour composite clinical and technical adverse event rates, adjusted for age, sex, and symptomatic status, were 1.0% (95% confidence interval, 0.8%-1.3%) and 6.0% (95% confidence interval, 5.4%-6.6%), respectively, and did not differ significantly by training mode. The proficiency measures of cadaver-trained and synthetic model-trained physicians were not inferior to those for the proctored physicians. CONCLUSIONS: We have presented key objective proficiency metrics for performing TCAR and an analytic framework to assess adequate training for the procedure. Training on cadavers or synthetic models achieved clinical outcomes, technical outcomes, and proficiency measures for subsequently performed TCAR procedures similar to those achieved with training using traditional proctoring on live cases.

Comparison of perioperative costs with fast-track vs standard endovascular aneurysm repair.

BACKGROUND: Perioperative health care utilization and costs in patients undergoing elective fast-track vs standard endovascular aneurysm repair (EVAR) remain unclear. METHODS: The fast-track EVAR group included patients treated with a 14 Fr stent graft, bilateral percutaneous access, no general anesthesia or intensive care monitoring, and next-day hospital discharge. The standard EVAR group was identified from Medicare administrative claims using a matching algorithm to adjust for imbalances in patient characteristics. Hospital outcomes included operating room time, intensive care monitoring, hospital stay, secondary interventions, and major adverse events (MAEs). Perioperative outcomes occurring from hospital discharge to 30 days postdischarge included MAE, secondary interventions, and unrelated readmissions. RESULTS: Among 1000 matched patients (250 fast-track; 750 standard), hospital outcomes favored the fast-track EVAR group, including shorter operating room time (2.30 vs 2.83 hrs, P<0.001), shorter hospital stay (1.16 vs 1.69 d, P<0.001), less need for intensive care monitoring (4.4% vs 48.0%, P<0.001), and lower secondary intervention rate (0% vs 2.4%, P=0.01). Postdischarge outcomes also favored fast-track EVAR with a lower rate of MAE (0% vs 7.2%, P<0.001) and all-cause readmission (1.6% vs 6.8%, P=0.001). The total cost to the health care system during the perioperative period was $26,730 with fast-track EVAR vs $30,730 with standard EVAR. Total perioperative health care costs were $4000 (95% CI: $3130-$4830) lower with fast-track EVAR vs standard EVAR, with $2980 in savings to hospitals and $1030 savings to health care payers. CONCLUSION: A fast-track EVAR protocol using a 14 Fr stent graft resulted in shorter procedure time, lower intensive care utilization, faster discharge, lower incidence of MAE, lower readmission rates, and lower perioperative costs compared to standard EVAR.

Perioperative Outcomes From the Prospective Multicenter Least Invasive Fast-Track EVAR (LIFE) Registry.

PURPOSE: To determine the feasibility, perioperative resource utilization, and safety of a fast-track endovascular aneurysm repair (EVAR) protocol in well-selected patients. METHODS: Between October 2014 and May 2016, the LIFE (Least Invasive Fast-track EVAR) registry ( ClinicalTrials.gov identifier NCT02224794) enrolled 250 patients (mean age 73±8 years; 208 men) in a fast-track EVAR protocol comprised of bilateral percutaneous access using the 14-F Ovation stent-graft, no general anesthesia, no intensive care unit (ICU) admission, and next-day discharge. The primary endpoint was major adverse events (MAE) through 30 days. The target performance goal for the MAE endpoint was 10.4%. RESULTS: Vascular access, stent-graft delivery, and stent-graft deployment success were 100%. A total of 216 (86%) patients completed all elements of the fast-track EVAR protocol. Completion of individual elements was 98% for general anesthesia avoidance, 97% for bilateral percutaneous access, 96% for ICU avoidance, and 92% for next-day discharge. Perioperative outcomes included mean procedure time of 88 minutes, median blood loss of 50 mL, early oral nutrition (median 6 hours), early mobilization (median 8 hours), and short hospitalization (median 26 hours). Fast-track EVAR completers had shorter procedure time (p<0.001), less blood loss (p=0.04), faster return to oral nutrition (p<0.001) and ambulation (p<0.01), and shorter hospital stay (p<0.001). With 241 (96%) of the 250 patients returning for the 30-day follow-up, the MAE incidence was 0.4% (90% CI 0.1% to 1.8%), significantly less than the 10.4% performance goal (p<0.001). No aneurysm rupture, conversion to surgery, or aneurysm-related secondary procedure was reported. There were no type III endoleaks and 1 (0.4%) type I endoleak. Iliac limb occlusion was identified in 2 (0.8%) patients. The 30-day hospital readmission rate was 1.6% overall. CONCLUSION: A fast-track EVAR protocol was feasible in well-selected patients and resulted in efficient perioperative resource utilization with excellent safety and effectiveness.

The malabsorptive very, very long limb Roux-en-Y gastric bypass for super obesity: results in 257 patients.

BACKGROUND: For the past 11 years, we have used a malabsorptive form of Roux-en-Y gastric bypass (RYGB), the "very, very long limb" RYGB, for selected patients with BMIs >50 kg/m(2) and in highly selected patients with BMI <50 kg/m(2). This modified distal gastric bypass establishes a 100-cm common channel (for digestion and absorption) and a "very, very" long Roux limb of 400 to 500 cm. METHODS: To determine long-term efficacy and complications, we followed prospectively 257 consecutive patients; 188 (73%) participated in a postoperative survey. RESULTS: Of the patients, 60% were female; overall age (x +/- SD) was 45 +/- 11 years, and BMI was 61 +/- 11 kg/m(2). Operative mortality was 1% with substantive postoperative morbidity occurring in 13%. Eighty-two percent of patients returning the survey an average of 48 months postoperatively (range, 12 to 148 months) lost >50% of excess body weight; BMI at follow-up was 37 +/- 9 kg/m(2). Resolution of comorbidities included diabetes mellitus (94%), hypertension (65%), sleep apnea (48%), and asthma (30%). Side effects included mild food intolerance (82%), occasional loose or watery stools (71%), nephrolithiasis (16%), and symptomatic steatorrhea (5%). Nine patients (4%) who developed or were developing impending protein/calorie malnutrition required proximal relocation of the enteroenterostomy with symptom resolution. CONCLUSIONS: Overall, 90% were satisfied with the operation, and 93% would recommend it to a friend. The very, very long limb RYGB is relatively safe and effective and has acceptable side effects in the treatment of selected patients with super obesity (BMI >50). Because of the possibility of malabsorptive sequelae, patients should be selected based on degree of medical sophistication, insight, and compliance.

Enteric hyperoxaluria, nephrolithiasis, and oxalate nephropathy: potentially serious and unappreciated complications of Roux-en-Y gastric bypass.

BACKGROUND: Neither the presence nor prevalence of enteric hyperoxaluria has been recognized after Roux-en-Y gastric bypass (RYGBP). We have noted a high rate of oxalate nephrolithiasis and even 2 patients with oxalate nephropathy in this patient population postoperatively. Our aim was to determine the frequency of the occurrence and effects of enteric hyperoxaluria after RYGBP. METHODS: Retrospective review of all patients at our institution diagnosed with calcium oxalate nephrolithiasis or oxalate nephropathy after standard (n = 14) or distal (n = 9) RYGBP. The mean postoperative follow-up was 55 months. RESULTS: A total of 23 patients (14 men and 9 women; mean age 45 years; mean preoperative body mass index 55 kg/m(2)) developed enteric hyperoxaluria after RYGBP, defined by the presence of oxalate nephropathy (n = 2) or calcium oxalate nephrolithiasis (n = 21) and increased 24-hour excretion of urinary oxalate and/or calcium oxalate supersaturation. Enteric hyperoxaluria was recognized after a mean weight loss of 46 kg at 29 months (range 2-85) after RYGBP. Two patients developed renal failure and required chronic hemodialysis. Of the 21 patients with nephrolithiasis, 14 had no history of nephrolithiasis preoperatively, and 19 of 21 required lithotripsy or other intervention. Of the 23 patients, 20 tested had increased oxalate excretion, and 14 of 15 tested had high urine calcium oxalate supersaturation. CONCLUSION: Enteric hyperoxaluria, nephrolithiasis, and oxalate nephropathy must be considered with the other risks of RYGBP. Efforts should be made to identify factors that predispose patients to developing hyperoxaluria.