Comment
Author: Admin | 2025-04-28
Respiratory acidosis rapidly by increasing ventilation; this is because CO2 easily crosses the blood brain barrier to stimulate the respiratory control centre in the medulla. However, at a certain level of CO2, the respiratory drive will be abolished and narcosis will set it; this is what we see with significant respiratory acidosis in, for example, an exacerbation of COPD. Metabolic Acid-Base BalanceThankfully, respiratory acid-base changes are explained simply enough using our well known carbonic acid dissociation equation as above. Metabolic acid-base disturbance is more complex and contested. During the Traditional era, two useful concepts were introduced to help address this black-box of metabolic acid-base interpretation:Base excess and the anion gap.Base ExcessBase excess is available on a blood gas as a number. The normal is zero, with a physiologic range of -2 to +2. What is it?The number given represents the amount of excess or deficit of base in the blood. A positive base excess implies an excess of base (metabolic alkalosis), whereas if it is negative, this suggests a deficit of base (and a metabolic acidosis, given that base is being used up to buffer protons). Base excess (BE) is an aggregate measure of metabolic changes, that considers all buffering capacity; this includes HCO3- and non-bicarbonate buffers (haemoglobin, plasma proteins such as albumin, and phosphates). As such, it is a more sensitive measure of metabolic disturbance than HCO3 alone, as it accounts for all buffer bases, not just HCO3. Importantly, BE is unaffected by respiratory acidosis/alkalosis, as it is calculated
Add Comment