The other night we had a 16 year old girl come in for shortness of breath and anxiety. She had just had a typical fight with another girl over a boy. Of course I imagine there was quite a lot of drama as there tends to be with nearly any argument between teenagers. However, in this case I was pretty impressed. Not with the details of the argument but with the numbers she was able to achieve (as we will see below). She came in breathing at about 50 times a minute! Her oxygenation was normal and her heart rate was slightly tachycardic. However, we decided to get some labs and do a CXR on her just to be safe (also I think to appease the parents a little). Her HCO3- (bicarb level) was pretty low (16) so we thought of acidosis. However, why would she be acidotic? Made no sense. So, we got an arterial blood gas. Would you believe her Ph was 7.71!!!!! (normal is 7.42) I have never seen such an alkalotic patient. Her bicarb repeated was 11 and her PCO2 was 14! She was hyperventilating so much that her body began to dump bicarbonate to try to bring the Ph back down! I can’t believe she did not pass out. We gave her 2 doses of ativan and told her to breath into a bag. When my shift was over, I signed her out still breathing about 30 into the bag! She needed more ativan I think!
With those numbers I’m hoping you ruled out salicylate toxicity. Probably not with a pH that high, but it is hard to acutely dump bicarb that fast.
Her tox screen including salicylates and tylenol was negative. However, if you have ASA poisoning, you would be acidotic not alkylotic.
Bram, the bicarb dumping is to compensate for the respiratory alkalosis, the primary acid-base disturbance here. In salicylate poisoning, the initial insult is a metabolic acidosis, and we blow off CO2 to compensate.
Hmm, nevermind, salicylates cause a mixed disorder, initially a respiratory alkalosis and then a metabolic acidosis (according to Merck Manual)…guess I have some more studying to do for Step 1
I’m not quite sure this can be dismissed as hyperventilation:
1. As mentioned above regulating the st-HCO3 to a level of 11 is something that takes hours to days
2. Why is the patients respiratory work suddently greatly insufficient, as the PC02 of 14 indicates? She should be compensating for her (secondary) metabolic alkalosis. Could this be explained as a effect of the sedation?
/Anders, MD
Small Correction, the PCo2 was 11 and the bicarb 14 not the other way around. I followed up on this case and in fact the acid base disturbance resolved the following day once she started breathing at a normal rate. Otherwise, completely negative tox screen. I am still shocked that someone could hyperventilate this much and not pass out. I have never seen a Ph above 7.7 either!
ASA toxicity can present with any pH. They get a mixed disorder due to salicylate’s direct stimulation of the respiratory center. The classic initial presentation is a mixed respiratory alkalosis with a metabolic acidosis, presenting with an alkalotic or normal pH. When they present acidotic, they are extremely sick and compensatory mechanisms have failed. The stages of ASA toxicity are usually defined by the presenting pH (although serum K is also involved).
Glad to hear that ASA was considered and ruled out as that could have been a disaster if she was given lorazepam.
Hmmmm – I know about the mixed acid base picture that can be seen in ASA poisoning – but I have never seen anyone alkalotic with it. I have seen some people partially compensated with a slightly low or almost normal Ph but never over 7.4. And some of these were acute poisoning and some were chronic poisoning. Anyway, no one I have spoken to about it had heard of a Ph so high and not ultimately found to be really sick.
I’ve seen a few that were alkalotic. Usually it is early on in the course. I do have to agree that a pH of 7.7 is very high and requires almost a profound respiratory or mixed respiratory/metabolic alkalosis. It would be hard to maintain that pH with any metabolic acidosis. Somehow the serum bicarb just doesn’t fit (unless she took something unmeasured and basic…)
Regardless of all the finite details and shit, it’s still fucking cool.