Pediatrics Vomiting (Step 1 question) - met alk or met acid?

[quepatho]

In class they taught us that when babies vomit they do lose HCl so you would think they would go into metabolic alkalosis, but apparently the stress of vomiting is so hard on a baby it induces metabolic acidosis (but I can't remember why now, was it lactic acidosis or something?)

One of my review sources just said babies vomit, they lose HCl, so they develop metabolic alkalosis period, end of story.

Does anyone know what *actually* happens?

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[ArcGurren]

I... kinda doubt they'll go into that much depth to be honest, that seems more like something you'd learn during your pediatrics rotation. I think for the purpose of the Step 1, vomiting = metabolic alkalosis due to HCl loss.

 

[ScubaStarved]

I... kinda doubt they'll go into that much depth to be honest, that seems more like something you'd learn during your pediatrics rotation. I think for the purpose of the Step 1, vomiting = metabolic alkalosis due to HCl loss.

Plus contraction alkalosis from increased RAAS.

 

[WellWornLad]

Does anyone know what *actually* happens?

They're both true (welcome to medicine). Just because a patient is alkalemic is no reason to think they can't have another acid-base disorder superimposed. No one can tell you what *actually* happens because patients are not carbon copies. In class they're just trying to explain the concepts to you, not give you a blueprint for what happens every time a baby vomits. Metabolic stress can cause acidosis, vomiting can cause alkalosis, and the two together will cause acidemia or alkalemia (or neither) depending on which is dominant. The pH will tell you which is dominant, and the deviation from expected respiratory compensation will tell you that there's more than one acid-base disorder present. If you're presented with a baby who has been vomiting for days and is on O2 and is pH neutral with an anion gap and increased bicarb, well, you know why now - but you just as easily could be presented with an acidemia with the same underlying mechanisms. Or just a simple metabolic alkalosis without significant lactic acidosis.

* Also, make sure you read up on paradoxical aciduria, it's germaine to this topic and will easily screw you up if you see it on an exam and don't recognize it.

 

[quepatho]

They're both true (welcome to medicine). Just because a patient is alkalemic is no reason to think they can't have another acid-base disorder superimposed. No one can tell you what *actually* happens because patients are not carbon copies. In class they're just trying to explain the concepts to you, not give you a blueprint for what happens every time a baby vomits. Metabolic stress can cause acidosis, vomiting can cause alkalosis, and the two together will cause acidemia or alkalemia (or neither) depending on which is dominant. The pH will tell you which is dominant, and the deviation from expected respiratory compensation will tell you that there's more than one acid-base disorder present. If you're presented with a baby who has been vomiting for days and is on O2 and is pH neutral with an anion gap and increased bicarb, well, you know why now - but you just as easily could be presented with an acidemia with the same underlying mechanisms. Or just a simple metabolic alkalosis without significant lactic acidosis.

* Also, make sure you read up on paradoxical aciduria, it's germaine to this topic and will easily screw you up if you see it on an exam and don't recognize it.

Thank you!