simple rules for the interpretation of arterial blood gases nicholas sadovnikoff, md, fccm assistant...
TRANSCRIPT
Simple Rules for the Interpretation of Arterial
Blood Gases
Nicholas Sadovnikoff, MD, FCCM
Assistant Professor, Harvard Medical SchoolCo-Director, Surgical Intensive Care Units
Brigham and Women’s HospitalBoston, MA
Kuwait City, KuwaitNovember 24, 2011
“Mantra”
1 for 110 for 7
1425
Mantra
Metabolic Acidosis: 1HCO3 => 1PCO2Metabolic Alkalosis: 10 HCO3 => 7 PCO2Acute Resp Acid: 10 PCO2 = 1 HCO3Chronic Resp Acid: 10 PCO2 = 4 HCO3Acute Resp Alk: 10 PCO2 => 2 HCO3 Chronic Resp Alk: 10 PCO2 => 5 HCO3
Examples
pH = 7.33, PCO2=30, HCO3=15
diagnosis
Examples
pH = 7.33, PCO2=30, HCO3=15
Diagnosis: metabolic acidosis orMetabolic acidosis with respiratory compensation ormetabolic acidosis with compensatory respiratory alkalosis
Suggestion:
Delete the word compensation from your acid base vocabulary.
Mantra
Metabolic Acidosis: 1HCO3 => 1PCO2Metabolic Alkalosis: 10 HCO3 => 7 PCO2Acute Resp Acid: 10 PCO2 = 1 HCO3Chronic Resp Acid: 10 PCO2 = 4 HCO3Acute Resp Alk: 10 PCO2 => 2 HCO3 Chronic Resp Alk: 10 PCO2 => 5 HCO3
Definition
Acidemia Acidosis
Definition
Acidemia – an abnormally low pH (high proton concentration)
Definition
Acidemia – an abnormally low pH (high proton concentration)
Acidosis – a process which produces an excess of protons
Example
• pH=7.22, PCO2=38, HCO3=15
• diagnosis
Example
• pH=7.22, PCO2=38, HCO3=15
• diagnosis:Met and Resp acidosisorUndercompensated Met Acidosis
Example
• pH=7.38, PCO2=28, HCO3=16
• diagnosis
Example
• pH=7.38, PCO2=28, HCO3=16
• diagnosis:Met Acid with Resp Alk
or
Overcompensated Met Acid
Example
• pH=7.47, PCO2=47, HCO3=34
• diagnosis
Example
• pH=7.47, PCO2=47, HCO3=34
• diagnosismetabolic alkalosis
Mantra
Metabolic Acidosis: 1HCO3 => 1PCO2Metabolic Alkalosis: 10 HCO3 => 7 PCO2Acute Resp Acid: 10 PCO2 = 1 HCO3Chronic Resp Acid: 10 PCO2 = 4 HCO3Acute Resp Alk: 10 PCO2 => 2 HCO3 Chronic Resp Alk: 10 PCO2 => 5 HCO3
Example
• pH=7.51, PCO2=42, HCO3=34
• diagnosis
Example
• pH=7.51, PCO2=42, HCO3=34
• diagnosisMet and Resp alkalosis
Example
• pH=7.42, PCO2=52, HCO3=34
• diagnosis
Example
• pH=7.42, PCO2=52, HCO3=34
• diagnosismetabolic alkalosis and
respiratory acidosis
Example
pH=7.35, PCO2=60, HCO3=32
diagnosis
Example
pH=7.35, PCO2=60, HCO3=32
diagnosischronic respiratory acidosis
Example
pH=7.25, PCO2=60, HCO3=26
diagnosis
Example
pH=7.25, PCO2=60, HCO3=26
diagnosisacute respiratory acidosis
Example
pH=7.30, PCO2=60, HCO3=29
diagnosis
Example
pH=7.30, PCO2=60, HCO3=29
diagnosisacute on chronic resp acid
Example
pH=7.45, PCO2=25, HCO3=17
diagnosis
Example
pH=7.45, PCO2=25, HCO3=17
diagnosischronic respiratory alkalosis
Mantra
Metabolic Acidosis: 1HCO3 => 1PCO2Metabolic Alkalosis: 10 HCO3 => 7 PCO2Acute Resp Acid: 10 PCO2 = 1 HCO3Chronic Resp Acid: 10 PCO2 = 4 HCO3Acute Resp Alk: 10 PCO2 => 2 HCO3 Chronic Resp Alk: 10 PCO2 => 5 HCO3
Example
pH=7.33, PCO2=30, HCO3=15
Na= 147, Cl=110
diagnosis
What is an Anion Gap?
• Qualitative
• Quantitative
• Why not include H+ ? K+ ?
What is an Anion Gap?
• Qualitative – unmeasured anions
• Quantitative - Na+ - Cl– - HCO3–
• Why not include H+ - too small K+ - always ~
4
DDx of AG Met Acid
• Ketones• Uremia• Salicylates• Methanol• Alcohols• Lactate• Ethylene Glycol• What are the unmeasured anions?
The HCO3 normally falls 1 for every 1 increase in anion gap, with the exception of sepsis.
Additional Rule
The Anions of Sepsis
• HPLC studies have failed to identify the anions responsible for the AG in sepsis.
• Lactate accounts for a portion.• H+ is likely from ATP hydrolysis
which drives the fall in bicarbonate and is not coupled to lactate production.
What Lowers Anion Gap?
• Hypoalbuminemia• Lithium• Myeloma
Example
• pH = 7.20, HCO3=10, PCO2=25
• Na=140, Cl=110
• diagnosis
Example
• pH = 7.20, HCO3=10, PCO2=25
• Na=140, Cl=110
• diagnosisAG Met acid andNon-AG met acid
DDx of NonAG Met AcidUSED CARS
• Ureterosigmoidostomy / Fistulae• Saline• Early Renal Failure• Diarrhea• CAI• AAs• RTA• Supplements
Urine Anion Gap• UAG = Na+ + K+ - Cl-
• largely reflects NH4+ and therefore is
usually negative due to renal ammoniagenesis
• In non-AG metabolic acidosis, a negative UAG implies extra-renal cause of the disorder.
• If positive, renal ammoniagenesis is likely impaired.
Example
• pH = 7.35, HCO3=19, PCO2=35
• Na=140, Cl=100
Example
• pH = 7.35, HCO3=19, PCO2=35
• Na=140, Cl=100
• diagnosisAG metabolic acidosis andmetabolic alkalosis
Example
• pH = 7.31, HCO3=15, PCO2=30
• Na=138, Cl=112
• diagnosis
Example
• pH = 7.31, HCO3=15, PCO2=30
• Na=138, Cl=112
• diagnosisnon AG metabolic acidosis
Example
• pH = 7.12, HCO3=10, PCO2=33
• Na=138, Cl=95
• diagnosis
Example
• pH = 7.12, HCO3=10, PCO2=33
• Na=138, Cl=95
• diagnosisAG metabolic acidosis andmetabolic alkalosis and
respiratory acidosis
Example
• pH = 7.38, HCO3=14, PCO2=23
• Na=138, Cl=95
Example
• pH = 7.38, HCO3=14, PCO2=23
• Na=138, Cl=95
• diagnosisAG metabolic acidosis andmetabolic alkalosis and
respiratory alkalosis
Example
• pH = 7.40, HCO3=24, PCO2=40
• Na=140, Cl=96
• diagnosis
Example
• pH = 7.40, HCO3=24, PCO2=40
• Na=140, Cl=96
• diagnosisAG metabolic acidosis and Metabolic alkalosis
Example
• pH = 7.40, HCO3=24, PCO2=40
• Na=140, Cl=104
Example
• pH = 7.40, HCO3=24, PCO2=40
• Na=140, Cl=104, albumin=1.1
Last rule!
• For every 1.0 g/dl that the serum albumin is below 4.0, the upper limit of the anion gap is decreased by 2.5
• Normal upper limit = 12• Alb 3.0 upper limit = 9.5• Alb 2.0 upper limit = 7.0• Alb 1.9 upper limit = 4.5
Example
• pH = 7.40, HCO3=24, PCO2=40
• Na=140, Cl=104, albumin=1.1
Example
• pH = 7.40, HCO3=24, PCO2=40
• Na=140, Cl=104, albumin=1.1
• Diagnosis:Anion Gap Metabolic
Acidosis Metabolic Alkalosis
Dogmatic Statement
•You cannot interpret arterial blood gases without looking at the electrolytes.
Dogmatic Statement
•You cannot interpret arterial blood gases without looking at the electrolytes.
•Be sure to check the albumin as well.
Summary
Metabolic Acidosis: 1HCO3 => 1PCO2Metabolic Alkalosis: 10 HCO3 => 7 PCO2Acute Resp Acid: 10 PCO2 = 1 HCO3Chronic Resp Acid: 10 PCO2 = 4 HCO3Acute Resp Alk: 10 PCO2 => 2 HCO3 Chronic Resp Alk: 10 PCO2 => 5 HCO3
Summary
Metabolic Acidosis: 1HCO3 => 1PCO2Metabolic Alkalosis: 10 HCO3 => 7 PCO2Acute Resp Acid: 10 PCO2 = 1 HCO3Chronic Resp Acid: 10 PCO2 = 4 HCO3Acute Resp Alk: 10 PCO2 => 2 HCO3 Chronic Resp Alk: 10 PCO2 => 5 HCO3
But don’t forget to check the anion gap and the serum albumin!
Thank you for your attention
Metabolic Acidosis: 1HCO3 => 1PCO2Metaboli Alkalosis: 10 HCO3 => 7 PCO2Acute Resp Acid: 10 PCO2 = 1 HCO3Chronic Resp Acid: 10 PCO2 = 4 HCO3Acute Resp Alk: 10 PCO2 => 2 HCO3 Chronic Resp Alk: 10 PCO2 => 5 HCO3
But don’t forget to check the anion gap and the serum albumin!
Thank you for your attention