Performance and reliability of two frequently used point-of-care blood gas analyzers at 423 and 4,559 m.

BACKGROUND AND OBJECTIVES: Blood gas analyzers (BGA) aid medical decision-making. Their specified performance criteria are based on sea level conditions. However, millions of people are living at high altitude (HA) where the performance of BGAs is poorly characterized. We investigated the effect of exposure to 4,559 m on the reliability and robustness of two BGAs widely used at HA. METHODS: In this prospective study arterial blood samples from 13 volunteers (2 female) with susceptibility to the development of high-altitude pulmonary edema were collected once near sea level at 423 m (nSL423) and three times at high altitude (HA4,559). Samples were measured in triplicate with the cartridge BGAs Rapidpoint 500 (SIE; Siemens Healthcare) and the ABL90 (RAD; Radiometer) to calculate coefficients of variation (CV) and intraclass correlation coefficients (ICC) within a mixed model. RESULTS: At nSL423 and HA4,559, 3% and 17% of all data were not reported with SIE, mainly due to clotting of the sample caused by delays because of the frequent automated calibration routines. No data were missing with RAD. ICCs were not significantly lower (mean (min-max) 0.87 (0.68-0.98) vs. 0.94 (0.84-1.00); p = 0.217) with SIE at nSL423, but significantly lower at HA4,559 (0.87 (0.49-1.00) vs. 0.99 (0.96-1.00); p = 0.025). All CVs, except that for arterial oxygen saturation at HA4,559,were higher with SIE . CONCLUSION: In this study, the reliability of RAD was superior to SIE at nSL423 and HA4,559. In contrast to RAD, the performance of SIE declined at HA4,559. SIE was more prone to not reporting all variables, especially at HA4559.

Effects of acetazolamide on pulmonary artery pressure and prevention of high-altitude pulmonary edema after rapid active ascent to 4,559 m.

Acetazolamide prevents acute mountain sickness (AMS) by inhibition of carbonic anhydrase. Since it also reduces acute hypoxic pulmonary vasoconstriction (HPV), it may also prevent high-altitude pulmonary edema (HAPE) by lowering pulmonary artery pressure. We tested this hypothesis in a randomized, placebo-controlled, double-blind study. Thirteen healthy, nonacclimatized lowlanders with a history of HAPE ascended (<22 h) from 1,130 to 4,559 m with one overnight stay at 3,611 m. Medications were started 48 h before ascent (acetazolamide: n = 7, 250 mg 3 times/day; placebo: n = 6, 3 times/day). HAPE was diagnosed by chest radiography and pulmonary artery pressure by measurement of right ventricular to atrial pressure gradient (RVPG) by transthoracic echocardiography. AMS was evaluated with the Lake Louise Score (LLS) and AMS-C score. The incidence of HAPE was 43% versus 67% (acetazolamide vs. placebo, P = 0.39). Ascent to altitude increased RVPG from 20 ± 5 to 43 ± 10 mmHg (P < 0.001) without a group difference (P = 0.68). Arterial Po2 fell to 36 ± 9 mmHg (P < 0.001) and was 8.5 mmHg higher with acetazolamide at high altitude (P = 0.025). At high altitude, the LLS and AMS-C score remained lower in those taking acetazolamide (both P < 0.05). Although acetazolamide reduced HAPE incidence by 35%, this effect was not statistically significant, and was considerably less than reductions of about 70%-100% with prophylactic dexamethasone, tadalafil, and nifedipine performed with the same ascent profile at the same location. We could not demonstrate a reduction in RVPG compared with placebo treatment despite reductions in AMS severity and better arterial oxygenation. Limited by small sample size, our data do not support recommending acetazolamide for the prevention of HAPE in mountaineers ascending rapidly to over 4,500 m.NEW & NOTEWORTHY This randomized, placebo-controlled, double-blind study is the first to investigate whether acetazolamide, which reduces acute mountain sickness (AMS), inhibits short-term hypoxic pulmonary vasoconstriction, and also prevents high-altitude pulmonary edema (HAPE) in a fast-climbing ascent to 4,559 m. We found no statistically significant reduction in HAPE incidence or differences in hypoxic pulmonary artery pressures compared with placebo despite reductions in AMS and greater ventilation-induced arterial oxygenation. Our data do not support recommending acetazolamide for HAPE prevention.

Validity of Peripheral Oxygen Saturation Measurements with the Garmin Fenix® 5X Plus Wearable Device at 4559 m.

Decreased oxygen saturation (SO2) at high altitude is associated with potentially life-threatening diseases, e.g., high-altitude pulmonary edema. Wearable devices that allow continuous monitoring of peripheral oxygen saturation (SpO2), such as the Garmin Fenix® 5X Plus (GAR), might provide early detection to prevent hypoxia-induced diseases. We therefore aimed to validate GAR-derived SpO2 readings at 4559 m. SpO2 was measured with GAR and the medically certified Covidien Nellcor SpO2 monitor (COV) at six time points in 13 healthy lowlanders after a rapid ascent from 1130 m to 4559 m. Arterial blood gas (ABG) analysis served as the criterion measure and was conducted at four of the six time points with the Radiometer ABL 90 Flex. Validity was assessed by intraclass correlation coefficients (ICCs), mean absolute percentage error (MAPE), and Bland-Altman plots. Mean (±SD) SO2, including all time points at 4559 m, was 85.2 ± 6.2% with GAR, 81.0 ± 9.4% with COV, and 75.0 ± 9.5% with ABG. Validity of GAR was low, as indicated by the ICC (0.549), the MAPE (9.77%), the mean SO2 difference (7.0%), and the wide limits of agreement (-6.5; 20.5%) vs. ABG. Validity of COV was good, as indicated by the ICC (0.883), the MAPE (6.15%), and the mean SO2 difference (0.1%) vs. ABG. The GAR device demonstrated poor validity and cannot be recommended for monitoring SpO2 at high altitude.