The correct measurement of oxygen saturation at high altitude

The Use of Pulse Oximetry in the Assessment of Acclimatization to High Altitude

“…Hb exists in two forms: (1) the deoxyhemoglobin (HHb) without attached O2 and (2) the oxyhemoglobin (O2Hb) with bound O2 molecules. O2 molecules change the light absorption of Hb at specific wave lengths [6,13].…”

“…However, certain parameters may require increased attention when the decision for a specific pulse oximeter has to be made: (1) accuracy, precision, and bias of the device [12]; (2) environmental conditions such as maximum operating altitude respectively minimum air pressure or the minimum operating temperature; (3) the availability of advanced algorithms to reduce motion artifacts or the detection of low perfusion; (4) the selection of the sensor location, typically using the finger [12,15,27,28]-however, other common positions such as the forehead may be considered, in particular if the measurement is conducted during motion [28][29][30]; (5) if required: the opportunity to sense carboxyhemoglobin and methemoglobin. In addition to the technical aspects, however, the measurement process itself becomes more error-prone with increasing altitude [6,12]. Table 1 summarizes the most significant pitfalls that may lead to inaccurate SpO2 readings and possible countermeasures particularly for healthy people visiting high altitudes.…”

“…The application of standardized procedure by trained users can prevent incorrect measurements and data interpretation [6,12]. Unfortunately, there exists no uniform standard for measuring protocols at high altitudes but there are some specific recommendations available to minimize measurement uncertainties which largely coincides with the countermeasures listed in Table 1: (1) The test person should remain in a sitting position for about 5 min, (2) the measuring site (normally the finger) should be kept as warm as possible, e.g., by wearing gloves, (3) motions of the sensor should be prevented, (4) the sensor should be shielded from ambient light, (5) a trained and experienced examiner should perform the measurements, and (6) SpO2 values should be monitored and averaged over a period of 2-3 min [6,12,31]. Additionally, if the device offers the ability to display the pulse wave graphically, it should be ensured that it remains as stable as possible [31].…”

“…Although the usefulness of pulse oximetry for the prediction and diagnosis of AMS is still debated [103][104][105], there is increasing evidence confirming that subjects developing AMS are more hypoxic (lower SpO2 values) than those who stay free from AMS, provided conditions (e.g., level of pre-acclimatization, health status, etc.) are comparable and measurement methods are appropriate [6,8,12,106,107]. Various studies reported certain SpO2 cut-off values differentiating between AMS+ and AMS-at a certain level of altitude.…”

“…Such information may be gathered by continuous or spot measurements depending on specific objectives. For example, the monitoring of bio-vital markers like heart rate and peripheral oxygen saturation has become a standard of patient care [4] but is also frequently applied by people visiting high altitudes for sight-seeing, trekking, skiing or climbing [5,6]. Simple and inexpensive devices, finger pulse oximeters, are widely used to monitor physiological responses to high-altitude exposure, the progress of acclimatization, and/or the potential development of high-altitude related diseases [7][8][9].…”