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ObjectivesWith large numbers of COVID-19 patients requiring mechanical ventilation and ventilators possibly being in short supply, in extremis two patients may have to share one ventilator. Careful matching of patient ventilation requirements is necessary. However, good matching is difficult to achieve as lung characteristics can have a wide range and may vary over time. Adding flow restriction to the flow path between ventilator and patient gives the opportunity to control the airway pressure and hence flow and volume individually for each patient. This study aimed to create and validate a simple model for calculating required flow restriction.Design/SettingExperimental/Secondary CareMethodsWe created a simple linear resistance-compliance model, termed the BathRC model, of the ventilator tubing system and lung allowing direct calculation of the relationships between pressures, volumes, and required flow restriction. Experimental measurements were made for parameter determination and validation using a clinical ventilator connected to two test lungs. For validation, differing amounts of restriction were introduced into the ventilator circuit.ResultsThe BathRC model was able to predict tidal lung volumes with a mean error of 4% (min:1.2%, max:9.3%).ConclusionWe present a simple model validated model that can be used to estimate required flow restriction for dual patient ventilation. The BathRC model is freely available; this tool is provided to demonstrate that flow restriction can be readily estimated.ARTICLE SUMMARYStrengths and limitations of this studyData collected on a clinical systemSimple model, easy to implementValidation performedLimited to 2 types of restrictors testedData from only one ventilator type

Objective The Cardiothoracic Surgical Trials Network reported that left ventricular reverse remodeling at 2 years did not differ between patients with moderate ischemic mitral regurgitation randomized to coronary artery bypass grafting plus mitral valve repair (n = 150) or coronary artery bypass grafting alone (n = 151). To address health resource use implications, we compared costs and quality-adjusted survival. Methods We used individual patient data from the Cardiothoracic Surgical Trials Network trial on survival, hospitalizations, quality of life, and US hospitalization costs to estimate cumulative costs and quality-adjusted life years. A microsimulation model was developed to extrapolate to 10 years. Bootstrap and deterministic sensitivity analyses were performed to address uncertainty. Results In-hospital costs were $59,745 for coronary artery bypass grafting plus mitral valve repair versus $51,326 for coronary artery bypass grafting alone (difference $8419; 95% uncertainty interval, 2259-18,757). Two-year costs were $81,263 versus $67,341 (difference 13,922 [2370 to 28,888]), and quality-adjusted life years were 1.35 versus 1.30 (difference 0.05; −0.04 to 0.14), resulting in an incremental cost-effectiveness ratio of $308,343/quality-adjusted life year for coronary artery bypass grafting plus mitral valve repair. At 10 years, its costs remained higher ($107,733 vs $88,583, difference 19,150 [−3866 to 56,826]) and quality-adjusted life years showed no difference (−0.92 to 0.87), with 5.08 versus 5.08. The likelihood that coronary artery bypass grafting plus mitral valve repair would be considered cost-effective at 10 years based on a cost-effectiveness threshold of $100K/quality-adjusted life year did not exceed 37%. Only when this procedure reduces the death rate by a relative 5% will the incremental cost-effectiveness ratio fall below $100K/quality-adjusted life year. Conclusions: The addition of mitral valve repair to coronary artery bypass grafting for patients with moderate ischemic mitral regurgitation is unlikely to be cost-effective. Only if late mortality benefits can be demonstrated will it meet commonly used cost-effectiveness criteria.

Measurement of outcomes from medical or surgical interventions is part of good practice, but publication of individual doctors' results remains controversial. The authors discuss this issue in the context of cardiothoracic surgery

Objectives: To compare rates of revascularisation in south Asian and white patients undergoing coronary angiography in relation to the appropriateness of revascularisation and clinical outcome. Design: Prospective cohort study of patients with two and a half years9 follow up; appropriateness of revascularisation rated by nine experts with no knowledge of ethnicity of patient. Setting: Tertiary cardiac centre in London with referral from five contiguous health authorities. Participants: Consecutive patients (502 south Asian, 2974 white) undergoing coronary angiography in the appropriateness of coronary revascularisation study (ACRE). Main outcome measures: Coronary revascularisation, non-fatal myocardial infarction, mortality. Results: There was no difference between south Asian and white patients in the proportions deemed appropriate for revascularisation (72% (361) v 68% (2022)) or in the proportions for whom the physician9s intended management was revascularisation (39% (196) v 41% (1218)). Among patients appropriate for revascularisation, age adjusted rates of coronary angioplasty (hazard ratio 0.69, 95% confidence interval 0.47 to 1.00, P=0.058) and coronary artery bypass grafting (0.74, 0.58 to 0.91, P=0.007) were lower in south Asian than in white patients. These differences were smaller but still present after adjustment for socioeconomic status and after restriction of analysis to those patients for whom the intended management was revascularisation. There were no differences in mortality and non-fatal myocardial infarction between south Asian and white patients (1.07, 0.78 to 1.47). Conclusion: Among patients deemed appropriate for coronary artery bypass grafting, south Asian patients are less likely than white patients to receive it. This difference is not explained by physician bias.

Treatment with the combination of aspirin and dipyridamole is believed to reduce the incidence of coronary vein graft occlusion. A double blind randomised controlled trial was carried out in which aspirin 990 mg and dipyridamole 225 mg daily or placebo were added to the routine postoperative management (warfarin for three months) of 320 patients undergoing coronary bypass grafting. The trial treatment was given for 12 months, after which the results were assessed by coronary and graft angiography. The two randomised groups, each of 160 patients, were comparable in age, sex, symptomatic state, angiographic findings, and operative procedure. Repeat coronary arteriography was carried out on 266 patients, 133 in each group. All grafts and distal anastomoses were patent in 68% (91/133) of the placebo patients and in 75% (100/133) of those receiving active treatment. Overall graft patency was 87% (306/352) and 89% (342/385) respectively. Retrospective subgroup analysis showed patency rates of 72% (26/36) and 78% (39/50) of grafts to vessels requiring preliminary endarterectomy, and 80% (36/45) and 91% (40/44) of distal anastomoses to vessels measured at operation to have a diameter of less than or equal to 1 mm. None of these differences was significant at the 5% level. Thus in this group of patients with high graft patency rates, treatment with aspirin and dipyridamole conferred no appreciable advantage.