resp practice problems acid-base imbalances interpretation of arterial blood gases (abg)
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RESPRESP
Practice Problems Acid-Base Imbalances
interpretation of Arterial Blood Gases (ABG)
Getting an arterial blood gas sample
Radial Artery
Ulnar Artery
Blood Gas Report
•Acid-Base Information• pH
• PCO2
• HCO3 [calculated vs measured]
•Oxygenation Information
• PO2 [oxygen tension]
• SO2 [oxygen saturation]
Acid-Base Disorder Primary Change Compensatory Change
Respiratory acidosis PCO2 up HCO3 upRespiratory alkalosis PCO2 down HCO3 downMetabolic acidosis HCO3 down PCO2 downMetabolic alkalosis HCO3 up PCO2 up
PRIMARY AND SECONDARY ACID-BASE DERANGEMENTS
[HCO[HCO33--] ]
pHpH = 6.1 + log --------------------------------- PCOPCO22 + 0.225
Steps for interpretation of ABG
1.Know normal values of pH, (PCO2), and (HCO3-).
2.Look at the patient's ABG's to determine what's abnormal high or low.
3.Correlate the abnormal values of PCO2 and HCO3- to the abnormality of pH.
4.Name the disorder, the cause, and the source of any compensation.
2- Evaluate the patient's ABG's: • is the pH normal? Is it too high or too low? Is it acidosis or
alkalosis?
• Is the HCO3- normal? Is it too high or too low? Will it cause
acidosis or alkalosis? Will it correct acidosis or alkalosis?
• Is the CO2 normal? Is it too high or too low? Will it cause acidosis or alkalosis? Will it correct acidosis or alkalosis?
1- Normal values for ABG's:
• If only one of the two parameters (CO2 or HCO3-) is abnormal,
then its value should be consistent with the pH (for example, if the CO2 is high, since that causes a drop in pH, the pH should be low).
• If both of the parameter are abnormal, then usually one is CAUSING the problem, and the other is trying to CORRECT (COMPENSATE FOR) the problem.
(For example, if the CO2 is high, and is causing the pH imbalance, then the pH must be low, since CO2 behaves as an acid. If HCO3
- level is also abnormal, then usually it will be high, to compensate for the low pH, since it is a base.)
3-Correlate the abnormal values:
Respiratory acidosis (with or without renal compensation)
• Respiratory alkalosis(with or without renal compensation)
• Metabolic acidosis (with or without respiratory compensation)
• Metabolic alkalosis (with or without respiratory compensation)
5- Suggest a possible causeFor example, a cause of chronic respiratory acidosis
is emphysema.
4- Name the disorder:
• Normal values for ABG's: pH range 7.35 - 7.45 PCO2 35 - 45 mm Hg HCO3-,
22 - 26 mEq/L
• pH is too low - acidosis; PCO2 is too high, would cause acidosis or correct
alkalosis; HCO3- is normal, neither causing nor correcting imbalance
• high PCO2 is correlated with low pH, which is consistent with patient's
report because PCO2 is causing the problem, this is respiratory acidosis;
because bicarbonate is normal, there is no compensation
Practice Problem 1ABG's:
pH 7.31 PCO2 55 mm Hg HCO3
- 22mEq/L
pH – low = acidosis
PCO2 – high = respiratory acidosis
HCO3 - high = renal compensation
Practice Problem 2 ABG's:
pH 7.31 PCO2 55 mm Hg HCO3- 35 mEq/L
pH – low = acidosis
HCO3 - low = metabolic acidosis
PCO2 – normal; no compensation
Practice Problem 3 ABG's:
pH 7.31 PCO2 35 mm Hg HCO3- 20 mEq/L
pH – low = acidosis
HCO3 - low = metabolic acidosis
PCO2 – low = respiratory compensation
Practice Problem 4 ABG's:
pH 7.31 PCO2 25 mm Hg HCO3- 20 mEq/L
pH – high = alkalosis PCO2 – low = respiratory alkalosis
HCO3 - normal; no compensation
Practice Problem 5 ABG's:
pH 7.48 PCO2 25 mm Hg HCO3- 24 mEq/L
pH – high = alkalosis
PCO2 – low = respiratory alkalosis
HCO3 - low = renal compensation
Practice Problem 6 ABG's:
pH 7.48 PCO2 25 mm Hg HCO3- 20 mEq/L
pH – high = alkalosis
HCO3 – high = metabolic alkalosis
PCO2 – normal; no compensation
Practice Problem 7 ABG's:
pH 7.48 PCO2 40 mm Hg HCO3- 33 mEq/L
pH – high = alkalosis
HCO3 – high = metabolic alkalosis
PCO2 – high = respiratory compensation
Practice Problem 8 ABG's:
pH 7.48 PCO2 55 mm Hg HCO3- 33 mEq/L