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Simple Rules for the Interpretation of Arterial Blood Gases. Nicholas Sadovnikoff, MD, FCCM Assistant Professor, Harvard Medical School Co-Director, Surgical Intensive Care Units Brigham and Women’s Hospital Boston, MA Kuwait City, Kuwait November 24, 2011. “Mantra”. 1 for 1 10 for 7 1

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Simple rules for the interpretation of arterial blood gases l.jpg
Simple Rules for the Interpretation of Arterial Blood Gases

Nicholas Sadovnikoff, MD, FCCM

Assistant Professor, Harvard Medical School

Co-Director, Surgical Intensive Care Units

Brigham and Women’s Hospital

Boston, MA

Kuwait City, Kuwait

November 24, 2011


Mantra l.jpg
“Mantra”

1 for 1

10 for 7

1

4

2

5


Mantra3 l.jpg
Mantra

Metabolic Acidosis: 1HCO3 => 1PCO2

Metabolic Alkalosis: 10  HCO3 => 7 PCO2

Acute Resp Acid: 10  PCO2 = 1  HCO3

Chronic Resp Acid: 10  PCO2 = 4  HCO3

Acute Resp Alk: 10  PCO2 => 2  HCO3

Chronic Resp Alk: 10  PCO2 => 5  HCO3


Examples l.jpg
Examples

pH = 7.33, PCO2=30, HCO3=15

diagnosis


Examples5 l.jpg
Examples

pH = 7.33, PCO2=30, HCO3=15

Diagnosis:

metabolic acidosis or

Metabolic acidosis with respiratory compensation

or

metabolic acidosis with compensatory respiratory alkalosis


Suggestion l.jpg
Suggestion:

Delete the word compensation from your acid base vocabulary.


Mantra7 l.jpg
Mantra

Metabolic Acidosis: 1HCO3 => 1PCO2

Metabolic Alkalosis: 10  HCO3 => 7 PCO2

Acute Resp Acid: 10  PCO2 = 1  HCO3

Chronic Resp Acid: 10  PCO2 = 4  HCO3

Acute Resp Alk: 10  PCO2 => 2  HCO3

Chronic Resp Alk: 10  PCO2 => 5  HCO3


Definition l.jpg
Definition

Acidemia

Acidosis


Definition9 l.jpg
Definition

Acidemia – an abnormally low pH (high proton concentration)


Definition10 l.jpg
Definition

Acidemia – an abnormally low pH (high proton concentration)

Acidosis – a process which produces an excess of protons


Example l.jpg
Example

  • pH=7.22, PCO2=38, HCO3=15

  • diagnosis


Example12 l.jpg
Example

  • pH=7.22, PCO2=38, HCO3=15

  • diagnosis:

    Met and Resp acidosis

    or

    Undercompensated Met Acidosis


Example13 l.jpg
Example

  • pH=7.38, PCO2=28, HCO3=16

  • diagnosis


Example14 l.jpg
Example

  • pH=7.38, PCO2=28, HCO3=16

  • diagnosis: Met Acid with Resp Alk or Overcompensated Met Acid


Example15 l.jpg
Example

  • pH=7.47, PCO2=47, HCO3=34

  • diagnosis


Example16 l.jpg
Example

  • pH=7.47, PCO2=47, HCO3=34

  • diagnosis metabolic alkalosis


Mantra17 l.jpg
Mantra

Metabolic Acidosis: 1HCO3 => 1PCO2

Metabolic Alkalosis: 10  HCO3 => 7 PCO2

Acute Resp Acid: 10  PCO2 = 1  HCO3

Chronic Resp Acid: 10  PCO2 = 4  HCO3

Acute Resp Alk: 10  PCO2 => 2  HCO3

Chronic Resp Alk: 10  PCO2 => 5  HCO3


Example18 l.jpg
Example

  • pH=7.51, PCO2=42, HCO3=34

  • diagnosis


Example19 l.jpg
Example

  • pH=7.51, PCO2=42, HCO3=34

  • diagnosis Met and Resp alkalosis


Example20 l.jpg
Example

  • pH=7.42, PCO2=52, HCO3=34

  • diagnosis


Example21 l.jpg
Example

  • pH=7.42, PCO2=52, HCO3=34

  • diagnosis metabolic alkalosis and respiratory acidosis


Example22 l.jpg
Example

pH=7.35, PCO2=60, HCO3=32

diagnosis


Example23 l.jpg
Example

pH=7.35, PCO2=60, HCO3=32

diagnosis chronic respiratory acidosis


Example24 l.jpg
Example

pH=7.25, PCO2=60, HCO3=26

diagnosis


Example25 l.jpg
Example

pH=7.25, PCO2=60, HCO3=26

diagnosis acute respiratory acidosis


Example26 l.jpg
Example

pH=7.30, PCO2=60, HCO3=29

diagnosis


Example27 l.jpg
Example

pH=7.30, PCO2=60, HCO3=29

diagnosis acute on chronic resp acid


Example28 l.jpg
Example

pH=7.45, PCO2=25, HCO3=17

diagnosis


Example29 l.jpg
Example

pH=7.45, PCO2=25, HCO3=17

diagnosis chronic respiratory alkalosis


Mantra30 l.jpg
Mantra

Metabolic Acidosis: 1HCO3 => 1PCO2

Metabolic Alkalosis: 10  HCO3 => 7 PCO2

Acute Resp Acid: 10  PCO2 = 1  HCO3

Chronic Resp Acid: 10  PCO2 = 4  HCO3

Acute Resp Alk: 10  PCO2 => 2  HCO3

Chronic Resp Alk: 10  PCO2 => 5  HCO3


Example31 l.jpg
Example

pH=7.33, PCO2=30, HCO3=15

Na= 147, Cl=110

diagnosis


What is an anion gap l.jpg
What is an Anion Gap?

  • Qualitative

  • Quantitative

  • Why not include H+ ? K+ ?


What is an anion gap33 l.jpg
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 l.jpg
DDx of AG Met Acid

  • Ketones

  • Uremia

  • Salicylates

  • Methanol

  • Alcohols

  • Lactate

  • Ethylene Glycol

  • What are the unmeasured anions?


Additional rule l.jpg
Additional Rule

The HCO3 normally falls 1 for every 1 increase in anion gap, with the exception of sepsis.


The anions of sepsis l.jpg
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 l.jpg
What Lowers Anion Gap?

  • Hypoalbuminemia

  • Lithium

  • Myeloma


Example38 l.jpg
Example

  • pH = 7.20, HCO3=10, PCO2=25

  • Na=140, Cl=110

  • diagnosis


Example39 l.jpg
Example

  • pH = 7.20, HCO3=10, PCO2=25

  • Na=140, Cl=110

  • diagnosis AG Met acid and Non-AG met acid


Ddx of nonag met acid used cars l.jpg
DDx of NonAG Met AcidUSED CARS

  • Ureterosigmoidostomy / Fistulae

  • Saline

  • Early Renal Failure

  • Diarrhea

  • CAI

  • AAs

  • RTA

  • Supplements


Urine anion gap l.jpg
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.


Example42 l.jpg
Example

  • pH = 7.35, HCO3=19, PCO2=35

  • Na=140, Cl=100


Example43 l.jpg
Example

  • pH = 7.35, HCO3=19, PCO2=35

  • Na=140, Cl=100

  • diagnosis AG metabolic acidosis and metabolic alkalosis


Example44 l.jpg
Example

  • pH = 7.31, HCO3=15, PCO2=30

  • Na=138, Cl=112

  • diagnosis


Example45 l.jpg
Example

  • pH = 7.31, HCO3=15, PCO2=30

  • Na=138, Cl=112

  • diagnosis non AG metabolic acidosis


Example46 l.jpg
Example

  • pH = 7.12, HCO3=10, PCO2=33

  • Na=138, Cl=95

  • diagnosis


Example47 l.jpg
Example

  • pH = 7.12, HCO3=10, PCO2=33

  • Na=138, Cl=95

  • diagnosis AG metabolic acidosis and metabolic alkalosis and respiratory acidosis


Example48 l.jpg
Example

  • pH = 7.38, HCO3=14, PCO2=23

  • Na=138, Cl=95


Example49 l.jpg
Example

  • pH = 7.38, HCO3=14, PCO2=23

  • Na=138, Cl=95

  • diagnosis AG metabolic acidosis and metabolic alkalosis and respiratory alkalosis


Example50 l.jpg
Example

  • pH = 7.40, HCO3=24, PCO2=40

  • Na=140, Cl=96

  • diagnosis


Example51 l.jpg
Example

  • pH = 7.40, HCO3=24, PCO2=40

  • Na=140, Cl=96

  • diagnosis AG metabolic acidosis and Metabolic alkalosis


Example52 l.jpg
Example

  • pH = 7.40, HCO3=24, PCO2=40

  • Na=140, Cl=104


Example53 l.jpg
Example

  • pH = 7.40, HCO3=24, PCO2=40

  • Na=140, Cl=104, albumin=1.1


Last rule l.jpg
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


Example55 l.jpg
Example

  • pH = 7.40, HCO3=24, PCO2=40

  • Na=140, Cl=104, albumin=1.1


Example56 l.jpg
Example

  • pH = 7.40, HCO3=24, PCO2=40

  • Na=140, Cl=104, albumin=1.1

  • Diagnosis: Anion Gap Metabolic Acidosis Metabolic Alkalosis


Dogmatic statement l.jpg
Dogmatic Statement

  • You cannot interpret arterial blood gases without looking at the electrolytes.


Dogmatic statement58 l.jpg
Dogmatic Statement

  • You cannot interpret arterial blood gases without looking at the electrolytes.

  • Be sure to check the albumin as well.


Summary l.jpg
Summary

Metabolic Acidosis: 1HCO3 => 1PCO2

Metabolic Alkalosis: 10  HCO3 => 7 PCO2

Acute Resp Acid: 10  PCO2 = 1  HCO3

Chronic Resp Acid: 10  PCO2 = 4  HCO3

Acute Resp Alk: 10  PCO2 => 2  HCO3

Chronic Resp Alk: 10  PCO2 => 5  HCO3


Summary60 l.jpg
Summary

Metabolic Acidosis: 1HCO3 => 1PCO2

Metabolic Alkalosis: 10  HCO3 => 7 PCO2

Acute Resp Acid: 10  PCO2 = 1  HCO3

Chronic Resp Acid: 10  PCO2 = 4  HCO3

Acute 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 l.jpg
Thank you for your attention

Metabolic Acidosis: 1HCO3 => 1PCO2

Metaboli Alkalosis: 10  HCO3 => 7 PCO2

Acute Resp Acid: 10  PCO2 = 1  HCO3

Chronic Resp Acid: 10  PCO2 = 4  HCO3

Acute 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!



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