2.4.1 Interpreting Arterial Blood Gases Flashcards
What are the two organ systems that could lead to an acid-base disorder?
Kidneys and Lungs
What two tests are needing for diagnosing an acid-base disorder?
Blood chemistry (electrolytes) and arterial blood gases
What are the normal values for pH, PCO2, and PO2?
pH: 7.4 (7.38-7.42)
PCO2: 40 (38-42)
PO2: 80, depends on age (104 - 0.27{age})
What is the Henderson-Hasselbach equation?
pH = pKa + log [HCO3-]/ PCO2
What is the Kassirer-Bleich equation?
[H+] = 24 X PCO2/[HCO3-]
What is acidemia? alkalemia?
Acidemia: pH < 7.35-7.45
Alkalemia: pH > 7.35-7.45
Put the normal values into the KB equation.
[H+] = 24 x 40/24
[H+] = 40 = pH of 7.4
What are the two types of metabolic acidosis?
Anion gap
Non-anion gap (hypercholeremic)
Metabolic disorders lead to irregularities in which value?
Bicarbonate
Metabolic acidosis (HCO3 retention/overproduction); Metabolic alkalosis (HCO3 depletion)
What are some causes of metabolic alkalosis?
Nasogastric suctioning, vomiting
Diuretic therapy
Cushing Syndrome - ACTH excess
Hyperaldosteronism - Addison’s Dz
Exogenous therapy
Licorice ingestion
Alkali ingestion
What are some causes of anion gap metabolic acidosis? (there is a neumonic)
MUDPILES
Methanol
Uremia
DKA
Paraldehyde
INH/Iron
Lactic Acidosis
Ethylene Glycol
Salicylates/Starvation
What are some of the causes of non-anion gap metabolic acidosis?
HARD-UP
Hyperailmentation
Acetazolamide and other carbonic anhydrase inhibitors
Renal tubular acidosis
Diarrhea
Ureteroenteric fistula
Pancreaticoduodenal fistula
What formula is used to determine respiratory compensation?
The Winter Formula
expected pCO2 = (1.5 X [HCO3-]) + 8 +/- 2
What is the primary alteration in respiratory disorders?
pCO2
What are some causes of respiratory acidosis?
CNS depression
Neuromuscular disorder
Thoracic cage limitation
Acute obstruction
Chronic obstruction
Ventilator Malfunction
What are some causes of respiratory alkalosis?
Anxiety
CNS Disorders
Drugs - Salicylates, analeptics
Fever, sepsis
Pregnancy
Liver insufficiency
Hyperthyroidism
What is the standard approach for understanding an acid-base disorder?
- Evaluate pt history
- Review ABG
- What is the pH? Acidemic or alkalemic?
- Primarily respiratory or metabolic disorder?
- Look at arterial PaCO2 and serum bicarbonate level
- If respiratory: acute or chronic disturbance?
- If metabolic: anion gap or non-anion gap?
- Use Winter’s formula to determine appropriate respiratory compensation (for metabolic acidosis)
What is the expected change in pH for an acute respiratory disturbance?
0.08 x (measured PaCO2-40)/10
What is the expected change in pH for a chronic respiratory disturbance?
0.03 X (measured PaCO2-40)/10
What is the equation for anion gap? What is a normal value?
AG = Na+ - (Cl- + HCO3-)
Normal is 12 or less
- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?

