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Assessment :: Assessment Step 2 :: Respiratory vs. Metabolic

    Step Two: Once you have determined the pH, you can move on to determine the 'primary' problem, or which system, respiratory or metabolic is the prime messenger. Let's look at the two systems and understand the rationale behind determination of the 'primary' problem.

    Respiratory System

    If you keep in mind that carbon dioxide acts as the ‘acid’ of the human body, you will be able to determine if the primary acid-base imbalance is respiratory. Chemically speaking, there is an equilibrium between carbonic acid and bicarbonate. Therefore, just remember that an increased PaCO2 (greater than 45mmHg) along with an acidosis (pH less than 7.35) represents a RESPIRATORY ACIDOSIS. If you have a situation where there is a decreased PaCO2 (less than 35mmHg) and an alkalosis (pH greater than 7.45) you will have a RESPIRATORY ALKALOSIS! Easy. Right?

    Metabolic System

    Keep in mind that HCO3 represents a ‘base’ situation, and if there is an increased HCO3 (greater than 26 mEq/L) in an alkalotic environment (pH greater than 7.45) there is a METABOLIC ALKALOSIS. On the opposite side of the coin, if there is a decreased HCO3 (less than 22 mEq/L) in an acidic environment (pH less than 7.35) this will be representative of METABOLIC ACIDOSIS.

    If you need to review the above steps, that is OK. If you understand the above material, let's move on to COMPENSATION!

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