REVIEW OF BLOOD GASES(ABGS)

  (Practice Table for Interpreting Blood Gases--Click here! )

 To review specific acid-base disorders go to: Adult Health II, Topic 1

INTERPRETING BLOOD GASES: Example: ph= 7.41; pCO2= 40; HCO3= 26 (Answer: WNL=Normal)

ph= 7.35 to 7.45

pCO2= 35 to 45

HCO3= 22 to 26

 

A. FOUR STEPS* FOR INTERPRETING:

 *Reference: This method is taken from the Journal Article: "Interpreting ABGs in Four Easy Steps", by Susan Romanski, Nursing '86, 16 (9), pp. 58-64.

1. Check the ph to determine the cause of the imbalance--acidosis or alkalosis:

 

Ask yourself, does it indicate acidity or alkalinity?

Example: ph= 7.49; pCO2= 27; HCO3= 19

Answer: 7.49 is alkaline, so this indicates alkalinity

 

If the ph looks like it is WNL(7.35-7.45) then the "cutoff point" for acidity is 7.35-7.40 and for alkalinity is between 7.41-7.45. Of course, the other values of pCO2 and HCO3 have to be abnormal:

Example: ph= 7.35; pCO2= 55; HCO3= 33

Answer: 7.35 using above criteria is on the acid side, because pCO2 is acid, and HCO3 is rising(both abnormal)

 

 

2. Evaluate each of the other values separately(pCO2 & HCO3) and then match with ph:

ph--if the pCO2 matches, the problem is respiratory:

 

Example: ph= 7.50; pCO2= 28; HCO3= 20

Answer: pCO2 is toward alkaline side and this matches the ph of 7.50 which is also alkaline; HCO3 is acid--this is respiratory alkalosis

 

If the HCO3 matches the ph, the problem is metabolic:

Example: ph= 7.31; pCO2= 30; HCO3= 15

Answer: HCO3 is toward the acid side and this matches the ph of 7.31 which is also acid; the pCO2 is alkaline; this is metabolic acidosis

 

3. Name the Disorder: Either respiratory alkalosis or acidosis or metabolic alkalosis or acidosis

 

Examples:

ph= 7.29; pCO2= 25; HCO3= 14

Answer: HCO3(acid) matches the ph(acid); therefore, this is metabolic acidosis

 

ph= 7.43; pCO2= 48; HCO3= 32(remember to use cutoff value for ph-- 7.41-7.45)

Answer: HCO3 matches the ph(both alkaline); therefore, this is metabolic alkalosis

 

ph= 7.30; pCO2= 70; HCO3= 34

Answer: pCO2 matches the ph(both acid); therefore, this is respiratory acidosis

 

4. Determine the extent of Compensation:

 

LOOK AT THE VALUE THAT DOESN'T MATCH THE PH:

If this value is WNL, then there is NO compensation.

 

Example: ph= 7.25; pCO2= 55; HCO3= 25

This is _____________with NO compensation! (Answer: Respiratory Acidosis--HCO3 is WNL)

 

If this value is abnormal, but the ph is still abnormal, then there is partial compensation.

Example: ph= 7.25; pCO2= 55; HCO3= 31

This is_______________with PARTIAL compensation! (Answer: same as above--HCO3 is rising)

 

If the non-matching value is abnormal, and the ph is WNL, then we have complete or total or full compensation

Example: ph= 7.35; pCO2= 55; HCO3= 33

 

This is ________________with COMPLETE compensation! (Answer: same as above--ph is WNL)

 

What is this? ph= 7.26; pCO2= 65; HCO3= 10

 

Answer: both respiratory and metabolic acidosis--What could cause this?

 

B. PRACTICE WITH MORE LAB VALUES:

 

C. CONDITIONS CAUSING ACID-BASE IMBALANCES:

 

 Can you guess which imbalance goes with each condition?

(Metabolic Acidosis or Alkalosis; Respiratory Acidosic or Alkalosis?)

 

COPD

Shock

Cardiac arrest

Respiratory failure

Renal failure

Diabetic Ketoacidosis

Acute Anxiety

NG Suction or Vomiting

Sepsis

 

 Site for help with ABGs: http://www.mtsinai.org/pulmonary

 

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