Respiratory alkalosis can cause metabolic acidosis?

[devildoc2]

OK so I have an asthma patient, who is breathing rapidly. I dont have an ABG, but his anion gap is 21 and his HCO3 is 18. I dont know what his PCO2 is.

He doesnt have any reason to have a metabolic acidosis, and his rapid breathing makes me think that he has a respiratory alkalosis that is in turn causing a metabolic acidosis in response.

Does this seem reasonable? I know tehre is incomplete data and you need an ABG to know for sure, but is this thinking logical or am I missing something?

I went thru the SLUMPED and MUDPILES etiology for metabolic acidosis and this kid doesnt seem to have anything that would cause him a primary metabolic acidosis.

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[SexPanther]

OK so I have an asthma patient, who is breathing rapidly. I dont have an ABG, but his anion gap is 21 and his HCO3 is 18. I dont know what his PCO2 is.

He doesnt have any reason to have a metabolic acidosis, and his rapid breathing makes me think that he has a respiratory alkalosis that is in turn causing a metabolic acidosis in response.

Does this seem reasonable? I know tehre is incomplete data and you need an ABG to know for sure, but is this thinking logical or am I missing something?

I went thru the SLUMPED and MUDPILES etiology for metabolic acidosis and this kid doesnt seem to have anything that would cause him a primary metabolic acidosis.

Just from what you are giving we know he has a AG metabolic acidosis as well as a possible(??) metabolic alkalosis (delta AG = 9, delta HCO3 = 6, assuming 12 & 24 as normal respectively; delta/delta = 9/6 which may be close enough to call, really here nor there).

Plug in Winter's formula (1.5[HCO3] + 8 +-2) which will tell you what the PCO2should be and compare with the ABG, that will tell you if a respiratory process is also present.

The big worry to me is the AG met. acidosis, this was continually pounded into me by a nephrology attending. We were always taught to look at the AG 1st and foremost. It doesn't matter if this kid's pH is 7.4, he still has that going on. Does he have an osmolal gap?

If we eliminate the AG stuff, the compensation for an acute & chronic resp. alkalosis is a decrease in the HCO3 by 2 & 5 respectively for every decrease of the PCO2 by 10. Once again, if we didn't know about the AG, it is possible that the HCO3 is decreased as compensation for a primary resp. process, but we need the ABG to know for sure.

But he has an AG metabolic acidosis!!

 

[EtOHWithdrawal]

He likely has a mixed picture...respiratory alkalosis with a metabolic acidosis. However you need an ABG to know for sure, and base your judgement on expected compensation.

In a pure disorder the expected PCO2 will equal the actual PCO2, whereas in a mixed disorder the calculated or expected PCO2 will not equal the actual PCO2.

Then if you really want to screw your head on you can calculate delta anion gap and delta HCO3 and the comparison of the two will yield what type of disorder you have.

Oops, beaten to the punch...

 

[USAF MD '05]

Could be a respiratory acidosis. In asthma, often the exhalation is the problem. If you are unable to fully exhale, you breath stack and your PC02 goes up. Asthma peeps often have a high PC02. That's how we know they are failing even when the wheezes stop (quiet chest). As for any metabolic component, may have a bump in lactate just from poor perfusion/oxygenation. Again, I would not expect alkalosis here. In hyperventilation, yes. Not in an asthmatic. Check out the flattened diaphragms on the CXR. Hyper-expanded, just like A COPDer's As for the above posters, they are absolutely right. I however have forgotten what the hell a delta gap is! Steve

 

[Apollyon]

Asthma peeps often have a high PC02.

I would usually NEVER argue jargon, but, right here, saying "peeps" instead of "people" or "patients" could be VERY confusing to someone learning about asthma, respiration, and vents, where PEEP is used (for those not understanding, PEEP is "Peak End-Expiratory Pressure" - which is a level that can be dialed in on a ventilator, and it is like a puff at the end, supposedly to keep alveoli open).

 

[DropkickMurphy]

I would usually NEVER argue jargon, but, right here, saying "peeps" instead of "people" or "patients" could be VERY confusing to someone learning about asthma, respiration, and vents, where PEEP is used (for those not understanding, PEEP is "Peak End-Expiratory Pressure" - which is a level that can be dialed in on a ventilator, and it is like a puff at the end, supposedly to keep alveoli open).

Actually it's not a puff at the end....it's just an level below which the pressure is not allowed to fall (that is, the pressure in the airways in a patient with a PEEP setting of anything other than zero will never drop to ambient atmospheric pressures).

The best way to look at it is to remember that it's basically CPAP- continuous positive airway pressure, which physiologically the same thing. The term PEEP (positive end expiratory pressure) is used in mechanical ventilation when there are mechanical breaths being delivered by the ventilator.

OK so I have an asthma patient, who is breathing rapidly.

Just because he's breathing rapidly, doesn't imply he's hyperventilating he's going to be alkalotic (or have a low PaCO2). If he is not moving much, if any, air- as USAF MD pointed out, they tend to "breath stack"- he can be breathing 50 times a minute and still have a PaCO2 of >70mmHg. Don't confuse the presence of tachypnea (rapid breathing) with the hyperventilation (a supranormal minute ventilation). You can be tachypneic and not be hyperventilating.

If anyone has any further vent, ABG or pulmonary questions, feel free to PM me.

 

[Apollyon]

Actually it's not a puff at the end....it's just an level below which the pressure is not allowed to fall (that is, the pressure in the airways in a patient with a PEEP setting of anything other than zero will never drop to ambient atmospheric pressures).

Above is what happens when one posts when one should be sleeping. I even know that the first "P" is "positive"...

Thanks for clearing up my screw up!

 

[USAF MD '05]

You peeps need to keep your PEEP straight, yo. Or these peeps trying to learn about auto-PEEP and vent PEEP are gonna get real peep-ed off! That's just one peeps opinion on PEEP. Steve