Intraosseous Pressure Monitoring in Healthy Volunteers.

STUDY OBJECTIVE: Invasively monitoring blood pressure through the IO device has not been thoroughly demonstrated. This study attempted to establish baseline values of IO pressure in a healthy human population. METHODS: This was a prospective, healthy volunteer, observational study. Participants had two IO devices placed (humerus and tibia), and participant IO pressures, vital signs, and pain scores were monitored for up to 60 minutes. Participants were contacted at 24-hours and 7 days post-testing to assess for adverse events. Summary statistics were calculated for systolic, diastolic, and mean humeral and tibial IO pressure. The ratio of IO to non-invasive blood pressure was calculated, and Bland Altman plots were created. The slope (linear) of the mean humeral and the tibial IO pressures were also calculated. RESULTS: Fifteen subjects were enrolled between April and July 2015. Fourteen of 15 humeral IOs were placed successfully (93.3%) and all 15 of the tibial IOs were placed successfully. Mean tibial systolic, diastolic, and mean IO pressure were 55.8 ± 27.9, 49.3 ± 27.1, and 48.4 ± 29.4 mm Hg, respectively. Humeral systolic, diastolic, and mean IO pressure were 32.9 ± 16.0, 27.4 ± 15.2, and 24.5 ± 14.3 mm Hg. The mean tibial IO pressure was 52.5% ± 32.0% of external cuff pressure ratio. The mean humeral IO pressure was 26.5% ± 15.2% of the external mean blood pressure. The Bland Altman plots showed an inconsistent relationship between the systolic and diastolic cuff pressure and the IO pressures. We observed a 1% per minute decrease in IO pressure from the initial placement until the final reading. CONCLUSIONS: Intraosseous pressure readings can be obtained in healthy human volunteers. However, absolute IOP values were not consistent between subjects. Future research may determine how IO pressure can be used to guide therapy in ill and injured patients.

Characteristics of demand oxygen delivery systems: maximum output and setting recommendations.

BACKGROUND: Demand oxygen delivery systems (DODS) allot oxygen by interrupting the oxygen flow during exhalation, when it would mostly be wasted. Because DODS conserve oxygen by various methods, there are important performance differences between DODS. We studied certain performance factors that have not previously been carefully examined. METHODS: A bench model was constructed to simulate a nose, airway, and alveolar chamber. A breathing simulator generated 4 respiratory patterns, at frequencies of 15, 20, 25, and 30 breaths/min. Eighteen models of DODS were tested at 4 settings, each up to the maximum output, and compared to continuous-flow oxygen. The variable of interest was the fraction of inspired oxygen (F(I)O(2)) in the alveolar chamber, which was measured for each condition. RESULTS: The DODS differed from continuous-flow oxygen, delivering 0.5-2.1 times (mean = 1.13 times) the F(I)O(2) increase at similar settings. During maximum output the DODS showed a wide range of F(I)O(2), from 0.27 to 0.46. There was a direct relationship between volume output per pulse in the first 0.6 s of inhalation and the delivered F(I)O(2). CONCLUSIONS: DODS settings were not equivalent to continuous-flow oxygen in a bench model assessment; with equivalent settings the DODS tended to deliver greater F(I)O(2) than did continuous-flow oxygen. The maximum output capacity differed markedly among the DODS, and the user should know the device's capacity. A volume-referenced setting system for DODS should be adopted that would allow more predictable oxygen prescription and delivery via DODS.