ABG interpretation

Question 1

What symptoms are associated with hypercapnia?

Answer 1

-Confusion
-Reduced consciousness level
-Asterixis
-Bounding pulse

Question 2

What can cause T2RF?

Answer 2

-Airway resistance -COPD/asthma
-Reduced breathing effort - drug effects eg opiates, brain stem lesion, extreme obesity
-Reduced area for gas exchange -chronic bronchitis
-NM problems -motor neurone disease
-Deformity -Ankylosing spondylitis

Question 3

What can cause respiratory alkalosis?

Answer 3

-Anxiety / panic attack
-Pain (–> increased RR)
-Hypoxia (altitude)
-PE
-Pneumothorax
-Iatrogenic eg excessive mechanical ventilation

Question 4

How does hyperventilation cause perioral / peripheral paraesthesia?

Answer 4

-Alkalosis causes hypocalcaemia
-H+ ions dissociate from albumin during alkalosis leading to albumin to bind to calcium instead
-Causes paraesthesia

Question 5

Why can excessive vomiting cause metabolic alkalosis?

Answer 5

-Vomiting causes loss of HCl from the stomach
-Carbonic acid is produced instead, leading to more HCO3- being transported into the blood
-Volume depletion from vomiting also increases mineralocorticoid levels which increases reabsorption of HCO3- by the kidneys

Question 6

Does metabolic compensation of a respiratory acidosis imply acute or chronic derangement?

Answer 6

-Chronic
-Metabolic system has time to compensate via generation and retention of bicarb

Question 7

How can sepsis cause metabolic acidosis?

Answer 7

-Reduced organ perfusion leads to tissue hypoxia causing increased anaerobic respiration
-Production of lactic acid causes acidosis