Resp ABG Flashcards
What are measured ABG units
PH
P02
Pc02
Lactate
What are derived ABG units?
Hc03
Base excess
What is a normal PH
7.35-7.45
What is a buffer
A substance that has an ability to minimise changes to PH when acid or base added
Carbonic acid / bicarbonate buffer equation
C02 + h20 = h2c03 = H* + hc03
Normal paC02 measurement
4.7 - 6 KPA
Normal HC03 measurement
22 - 26 MMOL
Normal pa02
Pa02 should be about 10 kpa less than % inspired concentration
EG
>11kpa on air (fio2 21%)
5 step approach to ABG interpretation
- How is the pt
- Assess oxygenation
- Determine the PH
- Determine respiratory component
- Determine metabolic component
Normal base excess
-2 ~ +2
Anion gap calculation
(Na+ + K+) - (Cl- + HC03-) =
(Sodium + potassium) - (chloride + bicarb) =
(Normal 4-12)
Name cations
Sodium (Na+) and potassium (K+)
Name anions (negatively charged)
Chloride (Cl-) and Bicarbonate (HC03)
And
Misc (albumin etc)
When to check anion gap?
Metabolic acidosis
Causes of low chloride - hypochloremia
Dehydration
Kidney disease
Respiratory acidosis
Cancer treatment
Drugs - steroids, diuretics, laxatives
Causes of high anion gap
DKA
Salicylate toxicity (aspirin)
Uremia (renal failure)
Starvation ketosis
Toxic ingestion - methanol, ethylene glycol (anti freeze)
Renal / Heart failure
Causes of respiratory acidosis
COPD, OSA, CNS depression
Neuromuscular (obesity, GBS, myasthenia gravis)
Causes of respiratory alkalosis
Anxiety
Pain
Hypoxia
Most common cause of metabolic alkalosis
Chloride loss due to gastric loss or renal loss
Causes of lactic acidosis
Type A - all types of shock (ischemia)
Type B - not related to hypoxia or poor perfusion
A-a gradient
Alveolar - arterial gradient
Difference between fi02 and pa02
Etc02 and paC02 gradient
Awareness
