Acid-Base Balance

By

M.H.Farjoo M.D. , Ph.D.Shahid Beheshti University of Medical Science

M.H.Farjoo

Acid-Base Balance

Introduction Determining the Disturbance Respiratory Acidosis Metabolic Acidosis Respiratory Alkalosis Metabolic Alkalosis Exercise

M.H.Farjoo

Introduction

pH: This measures hydrogen ions, Normal pH = 7.35-7.45.

pCO2 : Partial Pressure of CO2: is the concentration of CO2 in the blood. A high pCO2 indicates acidosis and vise versa.

HCO3 or Bicarbonate: measures the concentration of HCO3 ion only. High values indicate alkalosis and vise versa.

CO2 : Carbon Dioxide Content: is a measure of both carbon dioxide dissolved and bicarbonate ions and is an older test.

M.H.Farjoo

Introduction (Cont’d)

The lungs regulate the amount of Co2 in the blood and the kidneys regulate the bicarbonate.

Both acidosis and alkalosis can be of two different types: respiratory and metabolic.

Respiratory disturbances are caused by various malfunctions of the lungs.

Metabolic disturbances are caused by metabolic disorders which result in an excessive build up or loss of acids or bases.

M.H.Farjoo

Determining the Disturbance

To Determine about acidosis or alkalosis: look at the pH value.

To Determine about metabolic or respiratory: look at the pCO2 and bicarbonate ion value.

To Determine Whether the Condition is Compensated or not: look at the H+, HCO3- and CO2 values.

Try to get the best match of values for the above conditions.

Finally check all Lab. results to see if they are consistent.

M.H.Farjoo

Respiratory Acidosis

Example: pH =7.2, pCO2 = 60, CO2 = 24. pH = 7.2: acidosis pCO2 = 60: respiratory CO2 = 24: uncompensated

So it is: uncompensated respiratory acidosis.

M.H.Farjoo

Metabolic Acidosis

Example: pH =7.1, pCO2 = 42, HCO3- = 12. pH =7.1: acidosis HCO3- = 12: metabolic pCO2 = 42: Uncompensated

So it is: Uncompensated metabolic acidosis.

M.H.Farjoo

Metabolic Acidosis (Cont’d)

Metabolic Acidosis with a Normal Anion Gap: Longstanding diarrhea (bicarbonate loss) Uretero-sigmoidostomy Pancreatic fistula Renal Tubular Acidosis Intoxication (ammonium chloride, acetazolamide,

bile acid sequestrants) Renal failure

M.H.Farjoo

Metabolic Acidosis (Cont’d)

Metabolic acidosis with an elevated anion gap: Lactic acidosis ketoacidosis Chronic renal failure (accumulation of sulfates,

phosphates, uric acid) Intoxication (salicylates, ethanol, methanol,

formaldehyde, ethylene glycol, paraldehyde, INH, toluene, sulfates, metformin).

Rhabdomyolysis

M.H.Farjoo

Respiratory Alkalosis

Example: pH =7.58, pCO2 = 27, HCO3= 24. pH =7.58: alkalosis pCO2 = 27: respiratory HCO3 = 24: uncompensated

So it is: Uncompensated respiratory alkalosis.

M.H.Farjoo

Metabolic Alkalosis

Primary Metabolic alkalosis may occur from various causes including: Loss of acid via the urine, stools or vomiting Transfer of hydrogen ions into the cells Excessive bicarbonate administration (alkali given

to patients with renal failure) Contraction of the extracellular space due to

excessive diuretic treatment

M.H.Farjoo

Metabolic Alkalosis (Cont’d)

Prolonged metabolic alkalosis may be caused by a number of different mechanisms: Decrease in renal perfusion stimulates the renin-angiotensis

system which increases sodium reabsorption. Chloride Depletion (vomiting, use of loop diiuretics) which

enhances bicarbonate reabsorption with associated hydrogen ion loss.

Metabolic alkalosis may be associated with hypokalemia which maintains metabolic alkalosis by various mechanisms.

M.H.Farjoo

Exercise

Use the following lab results to determine the patient condition: CO2 = 39; pCO2 = 40; pH = 7.6; K = 3.0 and the patient has been vomiting.

pH = 7.6 and K = 3.0 both indicate alkalosis. The pCO2 = 40 is normal and indicates a metabolic

condition. The CO2= 39 value is measuring HCO3 and indicates

an uncompensated condition. Therefore it is Uncompensated metabolic alkalosis.

SummaryIn English

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