2.4.1 Interpreting Arterial Blood Gases Flashcards
What is the expected change in pH for a chronic respiratory disturbance?
0.03 X (measured PaCO2-40)/10
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 is the primary alteration in respiratory disorders?
pCO2
- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


What are the two organ systems that could lead to an acid-base disorder?
Kidneys and Lungs
- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


Metabolic disorders lead to irregularities in which value?
Bicarbonate
Metabolic acidosis (HCO3 retention/overproduction); Metabolic alkalosis (HCO3 depletion)
- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


What is the expected change in pH for an acute respiratory disturbance?
0.08 x (measured PaCO2-40)/10
What are some causes of respiratory acidosis?
CNS depression
Neuromuscular disorder
Thoracic cage limitation
Acute obstruction
Chronic obstruction
Ventilator Malfunction
What is the equation for anion gap? What is a normal value?
AG = Na+ - (Cl- + HCO3-)
Normal is 12 or less
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})
- 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?


What two tests are needing for diagnosing an acid-base disorder?
Blood chemistry (electrolytes) and arterial blood gases
What is the Henderson-Hasselbach equation?
pH = pKa + log [HCO3-]/ PCO2
What is acidemia? alkalemia?
Acidemia: pH < 7.35-7.45
Alkalemia: pH > 7.35-7.45
What is the Kassirer-Bleich equation?
[H+] = 24 X PCO2/[HCO3-]
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 are the two types of metabolic acidosis?
Anion gap
Non-anion gap (hypercholeremic)
- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


What formula is used to determine respiratory compensation?
The Winter Formula
expected pCO2 = (1.5 X [HCO3-]) + 8 +/- 2
- Is there a gap?
- Is the pCO2 appropriate?
- What are the problems?


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


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
Put the normal values into the KB equation.
[H+] = 24 x 40/24
[H+] = 40 = pH of 7.4
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 are some causes of respiratory alkalosis?
Anxiety
CNS Disorders
Drugs - Salicylates, analeptics
Fever, sepsis
Pregnancy
Liver insufficiency
Hyperthyroidism