pH homeostasis/ Respiratory Role/Blood gas analysis

Normal pH range of systemic arterial blood

7.35-7.45

Acidosis

Blood pH below 7.35

Alkalosis

Blood pH above 7.45

Effect of acidosis

CNS depression (coma)

Effect of alkalosis

Overexcitability of PNS then CNS (spasms and convulsions)

Sources of Acid

Carbonic acid
Protein metabolism
Lactic acid

pH Regulation

CO2 regulated by Lungs
H+ and HCO3- regulated by Kidneys

A patient has diarrhea - does HCO3- or PCO2 change? Does their pH rise or fall?

Falls

Cause of Respiratory acidosis

High PaCO2 due to decrease gaseous exchange.

Response of kidney to respiratory acidosis

Increased H+ secretion and increased level of bicarb ions.

Central cause of respiratory acidosis

Drugs

Airway obstruction cause of respirotry acidosis

COPD

Neuromuscular cause of respiratory acidosis

Myasthenia gravis

Cause of respiratory alkalosis

Low PaCO2 due to alveolar hyperventilation.

Response of kidneys to respiratory alkalosis

Decrease in excretion of H+ and increased excretion of HCO3-

CNS cause of Respiratory alkalosis

Pain

Tissue hypoxia cause of respiratory alkalosis

Pneumonia

Metabolic acidosis clinical example

Diarrhea

Metabolic alkalosis clinical example

Gastric vomiting

[H+] at normal pH 7.4

40nmol/L

PaCO2 normal level

4.6-6.4kPa

[HCO3-] normal range

22-26mmol/L

Type 2 respiratory failure

elevated PaCO2, acidosis, normal oxygen