Pulmonology E1: ABGs

Normal pH

7.38-7.44

Normal PaCO2

38-42 mmHg

Normal PaO2

75-100 mmHg

Normal HCO3-

23-26 mEq/L

Acids derived from CO2

Volatile

Acids derived from sources other than CO2

Non-volatile

Non-volatile acids are excreted by the ______

Kidneys

A weak (protonated) acid + a conjugate (unprotonated) base that minimizes changes in H+ when adding an acid or base

Buffer

What receptors are sensitive to pCO2 and pH?

Chemoreceptors in the medulla

Hypoventilation results in a _____ pH

Decreased

Hyperventilation results in a ______ pH

Increased

What is sensitive to arterial pO2?

Carotid bodies and aortic arch

What level of pO2 is required to cause an increase in the respiratory rate?

< 60 mmHg

Who would need to have an ABG done?

- Patients on ventilators
- Critically ill patients
- Monitor O2 flow rate
- Diagnose and treat significant metabolic and respiratory disorders

Relative or Absolute Contraindication for an ABG:
No pulse or poor collateral circulation

Absolute Contraindication

Relative or Absolute Contraindication for an ABG:
Cellulitis or local infection

Absolute Contraindication

Relative or Absolute Contraindication for an ABG:
Aneurysm at puncture sit

Absolute Contraindication

Relative or Absolute Contraindication for an ABG:
AV fistula or graft above puncture site

Absolute Contraindication

Relative or Absolute Contraindication for an ABG:
Active Raynaud's syndrome radial site

Absolute Contraindication

Relative or Absolute Contraindication for an ABG:
Chronic renal disease patient

Relative Contraindication

Relative or Absolute Contraindication for an ABG:
Presence of arterial disease

Relative Contraindication

Relative or Absolute Contraindication for an ABG:
Bleeding disorders; Anticoagulant Rx

Relative Contraindication

What is the most common location where an ABG is taken?

Radial artery

What is the effect of respiratory acidosis on potassium levels?

Hyperkalemia

What are some causes of respiratory acidosis?

Obstructive pulmonary disease, neuromuscular disorders (spinal cord injury), sedative/narcotics, anesthesia, tumor/trauma/stroke, obesity (Pickwickian syndrome)

What is the effect of respiratory alkalosis on potassium levels?

Hypokalemia

What are some causes of respiratory alkalosis?

- Stimulation of the brainstem respiratory center: fever, salicylate and sepsis
- Mechanical overventilation
- Cardiac disease: mild CHF --> pulmonary edema

Severe CHF can lead to _____

Hypoperfusion --> lactic acidosis --> metabolic acidosis

What is the effect of metabolic acidosis on potassium levels?

Hyperkalemia

If there is metabolic acidosis with a normal anion gap, what electrolyte imbalance occurs?

Hyperchloremia

High anion gap metabolic acidosis differentials

MUDPILES
Methanol
Uremia
DKA
Propylene glycol
Iron & Isoniazid
Lactic acidosis
Ethanol & Ethylene glycol
Salicylates & Starvation

In what conditions does lactic acidosis occur?

In conditions with impaired tissue perfusion

Conditions with impaired tissue perfusion

Shock, hypotension, septicemia, hypoxia, anemia

Causes of ketoacidosis

Diabetes, starvation, alcoholism --> decreased insulin

Normal anion gap metabolic acidosis differentials

HARDUPS
Hyperalimentation
Acetazolamide
Renal tubular acidosis
Diarrhea
Uretero-pelvic shunt
Post-hypocapnia
Spironolactone

What is the most common cause of normal anion gap metabolic acidosis?

Diarrhea

What is the effect of metabolic alkalosis on potassium levels?

Hypokalemia

What are causes of metabolic alkalosis?

Vomiting, diuretics, Conn's syndrome, Cushing's syndrome

Increased aldosterone

Conn's syndrome

Increased Cortisol

Cushing's syndrome

Respiratory compensation occurs over _______

Minutes to hours

Metabolic compensation occurs over _______

Days