Blood gas analysis PDF

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Lecture notes on blood gas analysis ...

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Blood gas analysis Acid-base balance • pH = -log10[H+]" • Chemical buffers, respiratory and renal systems all act to maintain the normal pH of the blood" • Chemicals such phosphates, proteins and bicarbonate all reversibly bind H+ ions in order impede any pH changes "

Acid base disturbances 1. Metabolic acidosis: " - Increased acid production " - e.g diabetes" 2. Metabolic alkalosis: " - Acid loss" - e.g shock " 3. Respiratory acidosis:" - Increase in minute volume and hyperventilation" 4. Respiratory alkalosis:" - Decrease in minute volume and hypoventilation " Base excess • This is the amount of acid required to titrate 1L of blood to a pH of 7.4 at 37 degrees and a PaCo2 of 40mmHg " • Can be positive (metabolic acidosis) or negative (metabolic alkalosis)" Anion gap • • • • •

Normally 15-25 mmol/L" Increased = lactic acidosis or ketoacidosis " Normal = GI barcyrbonate loss " Decreased = hypoproteinaemia " [Na+] + [K+] + [UC+] = [Cl-] + [HCO-] + [UA-]"

Oxygenation • Measuring arterial oxygen concentration is more accurate " • The curve can be effected by pH and temperature" Examples

pH is increased so therefore is alkalaemia

respiratory alkalosis as pCo2 is decreased. This suggests that the patient is undergoing hypoventilation

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31/10/18

pH is decreased so therefore acidaemia

respiratory acidosis as pCo2 is increased. Place on a ventilator to manage Co2 levels

Metabolic acidosis suggests that this patient is in shock. IVFT should be started in order to perfuse the kidneys in order to rebalance acidbase disturbances...