Question

Explain how the anion gap measurement would differ if acidosis were caused by respiratory versus metabolic illness. Hint: think about what happens to the bicarbonate in each

Answer 1

Answer ;

The anion gap (AG) is a calculated parameter derived from messuered serum/ plasma electrolyet concentrations. Both increased and reduced anion gap have clinical significance, but the deviation from normal that has most clinical significance is increased anion gap associated with metabolic acidosis. This reflects the main clinical utility of the anion gap, which is to helps in elucidating disturbances of acid-base balance.

Calculation of anion gap : Serum anion gap = Na+ _ (Cl- + HCO3 - ). The normal value for the serum anion gap is approximately 3 to 10 mEq / L , but may vary according to lab.

High anion gap metabolic acidosis :

It is a form of metabolic acidosis charecterized by a high anion gap (a medical value based on the concentrations of ions in patient's serum). Metabolic acidosis occurs when the body produces too much acids, or when the kidneys are not removing enough acid from the body.

Metabolic acidosis is primary reduction in bicarbonate (HCO3 -), typically with compensatory reduction in carbondioxide partial pressure(Pco2) ; pH markedly low or slightly subnormal. Metabolic acidosis are categorized as high or normal anion gap based on the presence or absence of unmeasured anion in serum. Causes include accumulation of ketones and lactic acid,renal failure and drug or toxin ingestion ( high anion gap) and GI or renal HCO3 - loss (normal anion gap).

Signs and syptoms :

• nausea and vomiting
• lethargy
• hyperpnea.

Diagnosis is clinical and with arterial blood gas(ABG) and serum electrolyte meassurement. The cause is treated with IV sodium bicarbonatemay be indicated when pH is very low.

Here some pulmonary compensation occurs by removal of CO2 . In cituations with normal kidney compensation occurs by removal of H+ ions through urine and weak organic acids, ultimately there is decreased CO2 ,decreased HCO3- and pH returns towards normal.

Respiratory acidosis :

It occurs due to retention of CO2 owing to decreased VA or decreased DLCO2-  initially ther is increased PCO2  slight increase of [ HCO3- ] and fall of pH. (Rise of [ HCO3- ] is due to hydration of some of the excess CO2 ; CO2 + H2O H+ + HCO3- ).

Here compensation is not possible by the lungs as the defect lies there. Kidneys increase HCO3- recovery, so that the HCO3- / CO2 , ratio returns towards its normal value and after some days , if high PCO2  is maintained , there is rise of [ HCO3- ] with pH returing towards normal.