Postoperative myocardial injury phenotypes and self-reported disability in patients undergoing noncardiac surgery: a multicentre observational study

Background: Postoperative myocardial injury (PMI) comprises a spectrum of mechanisms resulting in troponin release. The impact of different PMI phenotypes on postoperative disability remains unknown. Methods: This was a multicentre prospective cohort study including patients aged ≥50 yr undergoing elective major noncardiac surgery. Patients were stratified in five groups based on the occurrence of PMI and clinical information on postoperative adverse events: PMI classified as myocardial infarction (MI; according to fourth definition), PMI plus adverse event other than MI, clinically silent PMI (PMI without adverse events), adverse events without PMI, and neither PMI nor an adverse event (reference). The primary endpoint was 6-month self-reported disability (assessed by WHO Disability Assessment Schedule 2.0 [WHODAS]). Disability-free survival was defined as WHODAS ≤16%. Results: We included 888 patients of mean age 69 (range 53–91) yr, of which 356 (40%) were women; 151 (17%) patients experienced PMI, and 625 (71%) experienced 6-month disability-free survival. Patients with PMI, regardless of its phenotype, had higher preoperative disability scores than patients without PMI (difference in WHODAS; β: 3.3, 95% confidence interval [CI]: 0.5–6.2), but scores remained stable after surgery (β: 1.2, 95% CI: –3.2–5.6). Before surgery, patients with MI (n=36, 4%) were more disabled compared with patients without PMI and no adverse events (β: 5.5, 95% CI: 0.3–10.8). At 6 months, patients with MI and patients without PMI but with adverse events worsened in disability score (β: 11.2, 95% CI: 2.3–20.2; β: 8.1, 95% CI: 3.0–13.2, respectively). Patients with clinically silent PMI did not change in disability score at 6 months (β: 1.39, 95% CI: –4.50–7.29, P=0.642). Conclusions: Although patients with postoperative myocardial injury had higher preoperative self-reported disability, disability scores did not change at 6 months after surgery. However, patients experiencing myocardial infarction worsened in disability score after surgery

The Effects of Continuous Positive Airway Pressure on the Work of Breathing at Rest and during Exercise

Ventilation may limit exercise. Wearing a gas mask may further compromise ventilation. Continuous positive airway pressure (CPAP) improves ventilation by reducing airway resistance and thus the work of breathing. We investigated the effects of wearing a gas mask with and without CPAP on the work of breathing (WOB) during resting and exercise conditions to determine (a) whether wearing a gas mask increases the WOB and (b) whether the application of CPAP to a gas mask will mitigate (reduce) said increase to the WOB. Ten healthy males completed two test protocols with three stages each, and in three mask conditions. Physiological and dyspnea parameters were measured. Wearing a gas mask increased the metabolic cost and work of breathing. When the portable CPAP device was applied, there was no change in the calculated work of breathing, but metabolic cost of breathing was significantly reduced. CPAP also significantly reduced the sensation of dyspnea.MAS

End-inspiratory rebreathing reduces the end-tidal to arterial PCO2 gradient in mechanically ventilated pigs

Noninvasive monitoring of the arterial partial pressures of CO2 (PaCO2) of critically ill patients by measuring their end-tidal partial pressures of CO2 (PetCO(2)) would be of great clinical value. However, the gradient between PetCO(2) and PaCO2 (Pet-aCO(2)) in such patients typically varies over a wide range. A reduction of the Pet-aCO(2) gradient can be achieved in spontaneously breathing healthy humans using an end-inspiratory rebreathing technique. We investigated whether this method would be effective in reducing the Pet-aCO(2) gradient in a ventilated animal model. Six anesthetized pigs were ventilated mechanically. End-tidal gases were systematically adjusted over a wide range of PetCO(2) (30-55 mmHg) and PetO(2) (35-500 mmHg) while employing the end-inspiratory rebreathing technique and measuring the Pet-aCO(2) gradient. Duplicate arterial blood samples were taken for blood gas analysis at each set of gas tensions. PetCO(2) and PaCO2 remained equal within the error of measurement at all gas tension combinations. The mean +/- A SD Pet-aCO(2) gradient (0.13 +/- A 0.12 mmHg, 95% CI -0.36, 0.10) was the same (p = 0.66) as that between duplicate PaCO2 measurements at all PetCO(2) and PetO(2) combinations (0.19 +/- A 0.06, 95% CI -0.32, -0.06). The end-inspiratory rebreathing technique is capable of reducing the Pet-aCO(2) gradient sufficiently to make the noninvasive measurement of PetCO(2) a useful clinical surrogate for PaCO2 over a wide range of PetCO(2) and PetO(2) combinations in mechanically ventilated pigs. Further studies in the presence of severe ventilation-perfusion (V/Q) mismatching will be required to identify the limitations of the method

Postoperative myocardial injury phenotypes and self-reported disability in patients undergoing noncardiac surgery:a multicentre observational study

Background: Postoperative myocardial injury (PMI) comprises a spectrum of mechanisms resulting in troponin release. The impact of different PMI phenotypes on postoperative disability remains unknown. Methods: This was a multicentre prospective cohort study including patients aged ≥50 yr undergoing elective major noncardiac surgery. Patients were stratified in five groups based on the occurrence of PMI and clinical information on postoperative adverse events: PMI classified as myocardial infarction (MI; according to fourth definition), PMI plus adverse event other than MI, clinically silent PMI (PMI without adverse events), adverse events without PMI, and neither PMI nor an adverse event (reference). The primary endpoint was 6-month self-reported disability (assessed by WHO Disability Assessment Schedule 2.0 [WHODAS]). Disability-free survival was defined as WHODAS ≤16%. Results: We included 888 patients of mean age 69 (range 53–91) yr, of which 356 (40%) were women; 151 (17%) patients experienced PMI, and 625 (71%) experienced 6-month disability-free survival. Patients with PMI, regardless of its phenotype, had higher preoperative disability scores than patients without PMI (difference in WHODAS; β: 3.3, 95% confidence interval [CI]: 0.5–6.2), but scores remained stable after surgery (β: 1.2, 95% CI: –3.2–5.6). Before surgery, patients with MI (n=36, 4%) were more disabled compared with patients without PMI and no adverse events (β: 5.5, 95% CI: 0.3–10.8). At 6 months, patients with MI and patients without PMI but with adverse events worsened in disability score (β: 11.2, 95% CI: 2.3–20.2; β: 8.1, 95% CI: 3.0–13.2, respectively). Patients with clinically silent PMI did not change in disability score at 6 months (β: 1.39, 95% CI: –4.50–7.29, P=0.642).Conclusions: Although patients with postoperative myocardial injury had higher preoperative self-reported disability, disability scores did not change at 6 months after surgery. However, patients experiencing myocardial infarction worsened in disability score after surgery.</p

RISK AVERSION AND EXPECTED-UTILITY THEORY: A Calibration Theorem

Within the expected-utility framework, the only explanation for risk aversion is that the utility function for wealth is concave: A person has lower marginal utility for additional wealth when she is wealthy than when she is poor. This paper provides a theorem showing that expected-utility theory is an utterly implausible explanation for appreciable risk aversion over modest stakes: Within expected-utility theory, for any concave utility function, even very little risk aversion over modest stakes implies an absurd degree of risk aversion over large stakes. Illustrative calibrations are provided

Non-invasive accurate measurement of arterial PCO2 in a pediatric animal model

<p>The PCO2 in arterial blood (PaCO2) is a good parameter for monitoring ventilation and acid-base changes in ventilated patients, but its measurement is invasive and difficult to obtain in small children. Attempts have been made to use the partial pressure of CO2 in end-tidal gas (PetCO(2)), as a noninvasive surrogate for PaCO2. Studies have revealed that, unfortunately, the differences between PetCO(2) and PaCO2 are too variable to be clinically useful. We hypothesized that end-inspiratory rebreathing, previously shown to equalize PetCO(2) and PaCO2 in spontaneously breathing humans, would also be effective with positive pressure ventilation. Eight newborn Yorkshire pigs were mechanically ventilated via a partial rebreathing circuit to implement end-inspiratory rebreathing. Arterial blood was sampled and tested for PaCO2. A variety of alveolar ventilations resulting in different combinations of end-tidal PCO2 (30-50 mmHg) and PO2 (35-500 mmHg) were tested for differences between PetCO(2) and PaCO2 (Pet-aCO(2)). The Pet-aCO(2) of all samples was (mean +/- 1.96 SD) 0.4 +/- 2.7 mmHg. Our study demonstrates that, in ventilated juvenile animals, end-inspiratory rebreathing maintains Pet-aCO(2) to what would be a clinically useful range. If verified clinically, this approach could open the way for non-invasive monitoring of arterial PCO2 in critically ill patients.</p>