Abgs Made Easy

Arterial Blood Gases Made Easy

Purpose of ABG * Assess degree to which lungs are able to provide adequate oxygen & remove CO2 & degree to which the kidneys are able to reabsorb or excrete HCO3

YOU MUST KNOW WHAT IS NORMAL TO BE ABLE TO KNOW WHAT IS ABNORMAL * pH = 7.35 to 7.45 * PaCO2 = 35 to 45 mm Hg * PaO2 = 80 to 100 mm Hg * HCO3 = 22 – 26 mEq/l

What you MUST LOOK AT TO INTERPRET ABGS

LOOK AT YOUR pH
*Is it normal?
* is it high?
*is it low?

EXAMPLES
*pH = 7.36 *pH = 7.23 * pH = 7.47
*a high pH indicates alkalosis
*a low pH indicates acidosis

LOOK AT YOUR PaCO2
*is it normal?
*Is it high?
*is it low?
*This is the respiratory component
*An abnormality in the PaCO2 will indicate a respiratory problem 1

EXAMPLES
*PaCO2 = 40 mm Hg *pAco2 = 23 mm Hg
*a high PaCO2 indicates acidity
*a low PaCO2 indicates alkalosis

PaCO2
*Lungs will increase or decrease ventilation to remove the appropriate amount of CO2
*Lung compensation begins quickly

NOW LOOK AT YOUR HCO3
*is it normal?
* is it high?
*is it low?
*This is the metabolic component
*an abnormality in the HCO3 indicates a metabolic problem

EXAMPLES
*HCO3 = 25 mEq/l *HCO3 = 19 mEq/l
*a low HCO3 indicates acidity
*a high HCO3 indicates alkalosis

HCO3
*the kidneys excrete Hydrogen (acid) & retain bicarbonate (base) to help maintain pH
*Renal compensation is slow

2
LET’S LOOK AT THE 4 SITUATIONS THAT CAN OCCUR

ACIDOSIS
*develops when:
*excess accumulation of acid
*decreased amount of alkali
*can be respiratory or metabolic

METABOLIC ACIDOSIS
ABG:
Low pH (below 7.35)
Decreased HCO3 (below 22)
PaCO2 will be normal
Remember both the pH & HCO3 will be low

METABOLIC ACIDOSIS
*caused by too much acid in the body or loss of bicarbonate
*diarrhea (loss of HCO3)
Diabetic ketoacidosis
Renal failure

RESPIRATORY ACIDOSIS
*ABG
*Low pH (below 7.35)
*increased PaCO2 (above 45)
*HCO3 will be normal
*remember the pH will be low & PaCO2 will be elevated (opposite) 3

RESPIRATORY ACIDOSIS
*caused by acid buildup due to lungs not eliminating CO2
*anything that decreased respirations can cause respiratory acidosis
*chronic respiratory disease
*CNS depression

ALKALOSIS
*develops when:
*Excess accumulation of bicarbonate
*loss of acid

METABOLIC ALKALOSIS
*ABG
*increase in pH (greater than 7.45)
*Increased HCO3 (greater than 26)
*PaCO2 will be normal
*remember both the pH & the HCO3 will be elevated

METABOLIC ALKALOSIS
*loss of acid or increase in HCO3
*vomiting or NG drainage (loss of hydrogen)
*excessive use of antacids

4
RESPIRATORY ALKALOSIS
*ABG
*increase in pH (greater than 7.45)
*decrease in PaCO2 (less than 35)
*HCO3 will be normal
*remember the pH will be high & PaCO2 will be low (opposite)

RESPIRATORY ALKALOSIS
*caused by too much CO2 being excreted by the lungs
Hyperventilation

INTERPRETATING ABGS

1ST STEP LOOK AT pH
*is it normal (7.35 to 7.45)
*does it reflect acidosis (less than 7.35)
*does it reflect alkalosis (greater than 7.45)
*label accordingly

NEXT LOOK AT PaCO2
*this is the respiratory component
*is it normal
*does it reflect alkalosis (less than 35)
*does it reflect acidosis (greater than 45)
*label accordingly

5
NEXT LOOK AT THE HCO3
*this is the metabolic component
*is it normal
*does it reflect acidosis (less than 22)
*does it reflect alkalosis (greater than 26
*label accordingly

LET’S PUT IT ALL TOGETHER

PROBLEMS
*pH of 7.33
*PaCO2 of 40 mm Hg
*HCO3 of 20 mEq/L
*what does this indicate
*break it down

pH = acidosis
PaCO2 = normal
HCO3 = acidosis
An abnormal HCO3 indicates a metabolic problem

METABOLIC ACIDOSIS
PROBLEM
*pH of 7.59
*PaCO2 of 29 mm Hg
*HCO3 of 24mEq/L
*What does this indicate 6
*Break it down

pH=alkalosis
PaCO2 = alkalosis
HCO3 = normal
An abnormal PaCO2 indicates a respiratory problem

RESPIRATORY ALKALOSIS

PROBLEM
*pH of 7.25
*PaCO2 of 61 mmHg
*HCO3 of 26 mEq/L
*What does this indicate
*Break it down

*pH = acidosis
*PaCO2 = acidosis
*HCO3 = normal
*an abnormal PaCO2 indicates a respiratory problem

RESPIRATORY ACIDOSIS

PROBLEM
*pH of 7.51
*PaCO2 of 44 mmHg
*HCO3 of 56
*What does this indicate 7
*Break it down

*pH = alkalosis
*PaCO2 = normal
*HCO3 = alkalosis
*an abnormal HCO3 indicates a metabolic problem

METABOLIC ALKALOSIS

YOU ARE DOING GREAT

COMPENSATION
*occurs as the body begins to correct the acid base imbalance
*pH will be normal or near normal if total compensation
*pH will be abnormal if partial compensation

COMPENSATION
*both the PaCO2 & HCO3 will be abnormal
*respiratory imbalances are compensated for by the renal system
*metabolic imbalances are compensated for by the respiratory system

EXAMPLE
*pH of 7.27
*PaCO2 of 27 mm Hg
*HCO3 of 10 mEq/l
*note that both the PaCO2 & the HCO# are low 8
LET’S BREAK IT DOWN
*low pH = acidosis
*low PaCO2 = alkalosis
*low HCO3 = acidosis
*HCO3 corresponds with the pH
*this is a metabolic problem
*metabolic acidosis with partial compensation

PROBLEMS
*pH of 7.52
*PaCO2 of 47 mmHg
*HCO3 of 36 mEq/L
*What does this indicate
*Break it down

*pH = alkalosis
*PaCO2 = acidosis
*HCO3 = alkalosis
*which 2 go together

METABOLIC ALKALOSIS WITH PARTYIAL COMPENSATION

PROBLEMS
*pH of 7.45
*PaCO2 of 50 mmHg
*HCO3 of 33 mEq/L
*what does this indicate 9
*break it down

*pH = normal
*PaCO2 = acidosis
*HCO3 = alkalosis
*your pH leans toward the alkalosis side
FULLY COMPENSATED METABOLIC ALKALOSIS

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