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I have run my own PFT lab for the past 1+ year now and I have not yet run into the need to get an outpatient ABG. However given the absence of options for getting an ABG outpatient, I have opted to get an iSTAT machine from Abbott. I figure I sometimes need to get a stat K and pH on an advanced CKD patient who might be about ready to start HD or might be presenting with an acute decompensation.
As far as I am can tell, these are some useful (but limited) reasons for outpatient ABG from a pulmonary and renal perspective.
1) Trying to get the diagnosis of OHS with chronic respiratory acidosis paCo2 > 45 and rule out other etiologies to get a patient BiPAP therapy as an outpatient
2) A patient who has a serum bicarbonate over 32 and has hypertension and obesity. If a secondary hypertension workup were underway, then identifying a primary metabolic alkalosis would prove somewhat useful in helping narrow the differential diagnosis and help suggest if primary hyperaldo, Liddle's syndrome, etc... were present versus this being primary chronic respiratory acidosis from OHS or something.
3) Obtaining the proper PaO2 values for ordering supplemental oxygen in the rare event that SpO2 just cannot be measured
4) Spo2 is 85% (by the book) and the patient just crawled out of a sewer or got some methylene blue at a surgery recently. gotta get that Met-Hb or SulfHb value.
5) Doing ABGs during a CPET if I want to calculate Vd/Vt the proper way. This might be useful in a patient in whom has PH or ILD and I really want to prove the point that the ILD is causing most of the dyspnea (and not their COPD and CHF)... though its probably not that clinically useful to jump through these hoops. I do noninvasive CPETS in my office. I cannot imaging having to try to draw an ABG in someone who is cycling and panting and getting it in one shot without the patient going vasovagal... probably not a good idea outside of an academic centers CPET lab where an A Line and Swan catheter are placed by the cath lab first.
6) If one wants to do a HAST for air flight testing oxygen assessment. Usually if their 6MWT is concerning, I just tell the patient they must have a portable o2 concentrator for the flight. though one could be academic about things.
These are not really useful reasons to get outpatient ABG
1) Calculating formal acid base equation. First, one would need to get a simultaneous serum BMP from the same blood draw. Given some delays in outpatient labs resulting, this is not as useful as one might think compared to doing it in the hospital. Even if you had the true acid base status, you probably won't get any new information about chronic processes. If a patient has acute processes, that patient would likely be very symptomatic and one would probably be sending the patient to the hospital
2) using respiratory alkalosis as a justification for having PE. There are clinical prediction tools for PE. Moreover just get a D-dimer (I ask lab for stat and it comes out the next morning) or use the in office point of care U/S for a quick focused echo or LE DVT.
3) routine use in advanced CKD patients. no matter how low the serum bicarbonate looks, many of these patients will be compensated from the respiratory standpoint. Someone who is decompensated and needs urgent HD will be very tachypneic and will already be sent to the ED.
just some thoughts that popped into my mind.
As far as I am can tell, these are some useful (but limited) reasons for outpatient ABG from a pulmonary and renal perspective.
1) Trying to get the diagnosis of OHS with chronic respiratory acidosis paCo2 > 45 and rule out other etiologies to get a patient BiPAP therapy as an outpatient
2) A patient who has a serum bicarbonate over 32 and has hypertension and obesity. If a secondary hypertension workup were underway, then identifying a primary metabolic alkalosis would prove somewhat useful in helping narrow the differential diagnosis and help suggest if primary hyperaldo, Liddle's syndrome, etc... were present versus this being primary chronic respiratory acidosis from OHS or something.
3) Obtaining the proper PaO2 values for ordering supplemental oxygen in the rare event that SpO2 just cannot be measured
4) Spo2 is 85% (by the book) and the patient just crawled out of a sewer or got some methylene blue at a surgery recently. gotta get that Met-Hb or SulfHb value.
5) Doing ABGs during a CPET if I want to calculate Vd/Vt the proper way. This might be useful in a patient in whom has PH or ILD and I really want to prove the point that the ILD is causing most of the dyspnea (and not their COPD and CHF)... though its probably not that clinically useful to jump through these hoops. I do noninvasive CPETS in my office. I cannot imaging having to try to draw an ABG in someone who is cycling and panting and getting it in one shot without the patient going vasovagal... probably not a good idea outside of an academic centers CPET lab where an A Line and Swan catheter are placed by the cath lab first.
6) If one wants to do a HAST for air flight testing oxygen assessment. Usually if their 6MWT is concerning, I just tell the patient they must have a portable o2 concentrator for the flight. though one could be academic about things.
These are not really useful reasons to get outpatient ABG
1) Calculating formal acid base equation. First, one would need to get a simultaneous serum BMP from the same blood draw. Given some delays in outpatient labs resulting, this is not as useful as one might think compared to doing it in the hospital. Even if you had the true acid base status, you probably won't get any new information about chronic processes. If a patient has acute processes, that patient would likely be very symptomatic and one would probably be sending the patient to the hospital
2) using respiratory alkalosis as a justification for having PE. There are clinical prediction tools for PE. Moreover just get a D-dimer (I ask lab for stat and it comes out the next morning) or use the in office point of care U/S for a quick focused echo or LE DVT.
3) routine use in advanced CKD patients. no matter how low the serum bicarbonate looks, many of these patients will be compensated from the respiratory standpoint. Someone who is decompensated and needs urgent HD will be very tachypneic and will already be sent to the ED.
just some thoughts that popped into my mind.
