Are Pulse Oximeters Useful for Diagnosing High Altitude Pulmonary Edema (HAPE)?

Pulse oximeters are useful for measuring oxygen saturation in the blood.  They have no capability to measure pH or carbon dioxide.  In fact, that is a potential problem with them.  People can have fairly normal oxygen saturations because of compensatory hyperventilation.  So what looks good could in fact can be bad e.g., oxygen saturation is maintained near-normal at the expensive of hard respiratory work cause by an underlying pulmonary problem.  You would know this by measuring the respiratory rate or, if you could, by measuring pH and/or carbon dioxide levels.  There are other caveats as well e.g.; the interference caused by carbon monoxide.

Assuming that the person has good skin perfusion, a pulse oximeter works the same at altitude as it does at sea level.  As ambient atmospheric pressure decreases, the amount of oxygen in air decreases correspondingly.  Respirations increase to help compensate for this.  In general, however, resting saturations will continue to decrease as one ascents to a higher altitude.

The device itself is not a good tool for diagnosing HAPE/high altitude pulmonary edema.  It could give you the impression that things are better than they really are because of what I mentioned above.  A history of a person’s activity level (decrease in exercise tolerance), vital sign assessment including mental state and lung exam with a stethoscope are in the end cheaper and more accurate.



One Response to “Are Pulse Oximeters Useful for Diagnosing High Altitude Pulmonary Edema (HAPE)?”

  1. Robert Comey

    Three years later, we have pulse oximeters that give “fairly accurate” results and can be had for under twenty dollars. They weigh less then a cell phone. These characteristics would seem to make them an obvious item for inclusion in a wilderness first aid kit. I say “fairly accurate” because there are limitations here in getting a good reading with a hypothermic cold and wet person.
    The post here was specific regarding the benefits of a pulseox in diagnosing HAPE. I follow the logic, but I suggest that this device can give still useful information to the caregiver. More specifically, one can follow trends in a patient’s condition, and perhaps intervene before they become a patient.
    Case in point, a 13 y.o. student on a class ski/snowshoe trip to a backcountry hut located at 12,000 ft. +/- 3 miles from a trail head presents as lethargic and complains of fatigue upon reaching the hut, an effort requiring about two hours of moderate activity in temperatures in the the mid twenties (F). The individual lives at 6,200 ft. and had recently (about a week) recovered (sic) from an unspecified respiratory illness. The Pt’s pulse and respiration rates were somewhat elevated but this did not raise concern as everyone’s pulse and RR were somewhat elevated on account of the elevation gain and mild dehydration that is pretty normal for active teens in the Rockies. The patient socialized with his peers, ate and drank normally, and slept well with occasional dry cough over the course of the evening.
    The next day, after breakfast, the student asked if he could remain at the hut and forgo the day’s outdoor activities as he felt really tired. This was permitted and the Pt was monitored at several points over the course of the day. He remained lethargic and fatigued with a slightly elevated RR and HR, slightly pale, and periodic dry cough. At this point, it was believed that he had relapsed to his respiratory condition, i.e. his “recovery” the week prior had been overstated and his condition had deteriorated when stressed by the gain in altitude and activity of the class trip. The plan was made to re-assess late in the afternoon and determine if an evac was necessary.
    Late in the afternoon, his signs appeared improved, he was more active, less pale, but still with an elevated HR and RR, and still exhibiting a cough.
    The three leaders discussed his condition and agreed that since there was no apparent deterioration in the student’s condition – in fact, he seemed to be improving slightly – that he would continue to be monitored, and would remain with the trip until its conclusion the next day. He remained unchanged into the evening.
    During the night after bedtime, his cough became nearly continuous. At 2 a.m., he took a hot shower to get some moist air which provided only short term relief from his coughing, allowing him to get an hour sleep. At 3:30 a.m., his cough had become wet which, upon exam by stethoscope, proved to be wet and slightly crackly. HR was more elevated, and he had become pale This Pt was exhibiting respiratory distress, having to take long, slow, deep breathes to avoid coughing.
    The decision was made to evacuate the Pt to definitive care given his rapid deterioration and condition. This was complicated by the fact that it was snowing and dark, and that ambulating the Pt would likely worsen his condition. We opted to call SAR to facilitate the evac (we had spotty cell service), were given an ETA of 2 hours, and continued to monitor the Pt’s condition. The “cavalry” arrived around 6 a.m. bringing, amongst other things, the “tank of love”, i.e. O2. The lead EMT checked level of Oxygenation and did a visible double take when he got a reading of 56. Yeah, yikes. They had a Gamow bag but opted not to use at it presented difficulty in transport on the snowmo trailer. High-flow supplemental O2 provide immediate and visible relief to the Pt.
    End of story, Pt is evac’d to a medical center where he spends two days recovering. HAPE was a factor combined with rapid onset of pneumonia. Turns out, the Pt had had pneumonia eight years earlier under similar circumstances of altitude exposure following respiratory illness. The things we don’t find out from med forms…
    While there are many things to be learned here – not least of which is that just because early teens eat like an adult and look like an adult they can often still compensate like a child, when we discussed the level of blood O2 with the attending MD after the fact, she indicated that had we been able to track perfusion trend over the course of the day prior, we could have made the call to evac sooner, and possibly ambulated the Pt out safely.
    So, the premise here is that a pulseOx gives another piece of information that a caregiver can use in making a call. Agreed, that heuristically speaking, one would not want to use this as the sole go/no-go determinator, still the point is to offer better care to a person in distress in a wilderness setting. For under 30 bucks, it sure seems that this device could be a game changer. I can’t help but think that we would have made a different plan had we had this information. By the time the lung sounds are wet and the lips are blue, a Pt is dealing with a critical life threat. Wouldn’t a pulse oximeter in this situation have given us a better “glimpse behind the curtain”?

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