Acid-Base Disturbances

Summary of Acid-Base Disturbances

	pH (7.3 – 7.4)	H+	HCO3 (22-26)	pCO2 (34-45)	K+
metabolic acidosis	↓	↑	↓	↓↓↓	↑
metabolic alkalosis	↑	↓	↑	↑↑↑	↓
respiratory acidosis	↓	↑	↑↑↑	↑	↑
respiratory alkalosis	↑	↓	↓↓↓	↓	↓

Multiple arrows means it is a compensatory mechanism.

• PCo2 is usually 1.5 times the bicarb + 8, if it’s higher it’s compensated
• Gap = Sodium – (Cl + Bicarb) = normal is 6-12, greater than 12 is metabolic acidosis
• Normal respiratory rate is 12-20

Acidosis: pH < 7.38

• PCO2 < 38 – metabolic acidosis with respiratory compensation.  “Hyperventilation” compensates (blowing off carbon dioxide, which is an acid), decrease in bicarb
• PCO2 38-42 – pure metabolic acidosis
• PCO2 > 42 – primary respiratory acidosis. Need bicarb to say if primary metabolic acidosis (HCO3 < 24) or compensated respiratory acidosis (HCO3 > 28).

Alkalosis: pH < 7.42

• PCO2 <38 – primary respiratory acidosis.  Need bicarbonate to see if the patient has primary metabolic acidosis too (HC03 > 28)
• PCO2 38-42 – primary alkalosis without respiratory compensation
• PCo2 > 42 – primary metabolic acidosis with respiratory compensation

Causes of Anion Gap Acidosis:

• MUDPILES – methanol, uremia, diabetic ketoacidosis, paraldehyde, iron, isoniazid, inhalants, lactic acidosis, ethylene glycol (the propylene glycol in lorazepam can cause it too), ethanol and salicylates
• or MULEPAKS: methanol, uremia, lactic acidosis, ethylene glycol, paraldehyde, aspirin, ketoacidosis, starvation

How to work an acid-base problem:

1. Assess pH (acid or base)
2. Determine if it’s respiratory or metabolic (pCO2 and HCO3)
3. Calculate anion gap (can help determine cause).