A pilot evaluation of respiratory mechanics during prehospital manual ventilation.

INTRODUCTION: Respiratory mechanics, such as tidal volume (VT) and inspiratory pressures, may affect outcome in hospitalized patients with respiratory failure. Little is known about respiratory mechanics in the prehospital setting. METHODS: In this prospective, pilot investigation of patients receiving prehospital advanced airway placement, paramedics applied a device to measure respiratory mechanics. We evaluated tidal volume (VT) per predicted body weight (VTPBW) to determine the proportion of breaths within the lung-protective range of 4-10 mL/kg per PBW overall, according to ventilation bag volume (large versus small) and cardiac arrest status (active CPR, post-ROSC, non-arrest). RESULTS: Over 16-months, 7371 post-intubation breaths were measured in 54 patients, 32 patients with cardiac arrest and 22 with other conditions. Paramedics ventilated 19 patients with a small bag and 35 patients with a large bag. Overall, mean VT was 435 mL (95% CI 403, 467); VTPBW was 7.0 mL/kg (95% CI 6.4, 7.6) with 75% within the lung-protective range. Mean VTPBW and peak pressure differed according to arrest status (absolute difference -0.36 mL/kg and 32 cmH2O for active CPR compared to post-ROSC), though not according to bag size. CONCLUSIONS: We observed that measuring respiratory mechanics in the prehospital setting was feasible. Tidal volumes were generally delivered within a safe range. Respiratory mechanics varied most significantly with active CPR with lower VTPBW and higher peak pressures, though did not seem to be affected by bag size. Future work might examine the relationship between respiratory mechanics and outcomes, which may identify opportunities to improve clinical outcomes.

Selenide Targets to Reperfusing Tissue and Protects It From Injury.

OBJECTIVES: Since blood selenium levels decrease after ischemia and reperfusion injury, and low blood selenium correlates with negative outcome, we designed and performed experiments to determine how selenium distribution is affected by ischemia reperfusion injury. Furthermore, we tested whether different chemical forms of selenium would affect outcome after ischemia and reperfusion injury. We also examined the metabolic effects of selenide administration. DESIGN: Laboratory investigation. SETTING: Animal research laboratory. SUBJECTS: Adult male C57BL/6 mice. INTERVENTIONS: To determine selenium localization, we administered tracer doses of radioactive selenium 75 in the form of selenite or selenide and measured blood and tissue selenium levels after ischemia and reperfusion injury. Anesthetized mice were subjected to myocardial ischemia reperfusion injury (coronary artery occlusion for 60 min followed by 5 min of reperfusion after occlusion was removed) or hindlimb ischemia reperfusion injury (left leg tourniquet for 90 min followed by 5 min reperfusion after tourniquet removal). To determine whether exogenous selenium administration could reduce ischemia reperfusion injury, we synthesized and administered sodium hydroselenide and sodium selenite solutions (0.05-2.4 mg/kg). Solutions were administered at the end of coronary artery occlusion but before reperfusion. In order to determine the metabolic effects of selenide administration, we exposed mice to hydrogen selenide gas (0-5 ppm) mixed into air (20.95% oxygen) for up to 3 hours. MEASUREMENTS AND MAIN RESULTS: In targeting assays, we measured blood and tissue selenium levels. We observed that blood selenium decreases after myocardial ischemia reperfusion and displays an inverse correlation with injury severity; selenium accumulation in heart correlates directly with injury severity. We also measured whether oxidized selenium, selenite, and reduced selenium, selenide, would target to injured heart tissue in myocardial ischemia reperfusion and injured leg muscle in a hindlimb model of ischemia reperfusion. Only selenide targets to injured tissue. We also measured damage after myocardial ischemia reperfusion injury using morphometry, neutrophil accumulation, blood cardiac troponin levels, and echocardiography and observed in all assays that selenide reduced damage to the heart; selenite was not effective. And finally, to assay metabolism, we measured oxygen consumption, carbon dioxide production, and body core temperature before, during, and after hydrogen selenide administration. All measurements indicate that selenide decreases metabolism. CONCLUSIONS: Selenide targets to reperfusing tissue and reduces reperfusion injury perhaps by affecting oxygen metabolism.

Surviving blood loss using hydrogen sulfide.

BACKGROUND: Reduced metabolic activity improves outcome in many clinical and experimental models of injury and diseases that result in insufficient blood supply. Recently, we demonstrated that inhaled hydrogen sulfide gas can be used to reversibly reduce metabolic activity in mice. We hypothesize that hydrogen sulfide will confer benefit in injuries and diseases related to insufficient blood supply. METHODS: Sprague-Dawley rats were subjected to controlled hemorrhage to remove 60% of total blood. Hydrogen sulfide was administered to rats either via airway as gas, or intravenous infusion as liquid. Outcome was assayed by survival. RESULTS: Using inhaled hydrogen sulfide gas, 75% of treated and 23% of untreated rats survived longer than 24 hours. Using intravenous administered sulfide, 67% of treated and 14% of untreated rats survived longer than 24 hours. Using log-rank analysis, p < 0.001. Surviving rats showed no functional or behavioral abnormalities. Blood chemistry analysis at the end of hemorrhage showed minor but significant differences between treated and control animals. Respirometry results show that hydrogen sulfide stabilized metabolic output during and after hemorrhage. CONCLUSION: These data indicate that sulfide can protect rats from lethal hemorrhage. Future studies are needed to analyze the mechanism of benefit as well as whether sulfide is beneficial in other models of human injury and disease.