[Applause] [Music] this is Eric strong again and I will be talking to you today about how to identify simple acid-based disorders here are the learning objectives of this lecture first to understand the difference between acidemia and an acidosis and between alkalemia and an alkalosis second to know the four basic categories of acid-based disorders and the last to be able to identify simple acid-based disorders I'll start with the frequently misused terms acidemia and acidosis and alkalemia and alkalosis the words acidemia and alkalemia referred to a physiologic state dependent solely upon arterial pH acidemia is present if the pH is less than 7.35 while alkalemia is present if the pH is greater than 7.45 acidosis and alkalosis on the other hand refer to the individual processes which tend to drive the pH towards acidemia and alkalemia respectively a patient can be acidemic or alkalic but not both however a patient can have one or more acidosis and one or more alkalosis which can directly offset one another in some cases this may even result in an overall normal pH now I will discuss the four basic categories of acid-based disorders which you may have already inferred from the last lecture disorders can be either respiratory or metabolic resp disorders are those pathologic processes which disrupt acidbase balance due to their effect on the lungs specifically these disorders alter Alvar ventilation a respiratory acidosis occurs when the pco2 is too high that is the patient is hypoventilating a respiratory alkalosis occurs when the pco2 is too low that is the patient is hyperventilating metabolic disorders are those pathologic processes which disrupt acidbase balance due to their effects on anything other than the lungs this almost always refers to the kidneys GI tract or cellular respiration in general a metabolic acidosis is present when the serium bicarbonate concentration is too low a metabolic alkalosis is present when the bicarb is too high this chart will need to become second nature to you before you are able to master abgs you may remember back to the first lecture on this series on the ABG that the five primary values given by the ABG are as follows the pH the P2 the pao2 the bicarbonate concentration and the O2 saturation since we are talking just about the acidbase status for now we will set aside the pa2 and the O2 sat and just focus on the the remaining three values a quick note about the PAC CO2 there is a distinction between P little a CO2 and P big a CO2 just like there is a distinction between P little A2 and P big ao2 when the a is lowercase it is referring to the partial pressure of the relevant gas in arterial blood when the a is uppercase it is referring to the partial pressure of the relevant gas in the alveol space this distinction will be much more important when we talk about a patient's oxygenation status in future lectures in common usage however if someone simply States P CO2 without specifying little or big a it is assumed to be little a that is the partial pressure of carbon dioxide in arterial blood I will frequently use this shortcut in the remaining lectures another quick word about notation concern turns the serum bicarbonate level you may encounter square brackets around the bicarbon level like this and I will intermittently use them during this course the brackets denote that we are talking about the concentration of bicarbonate ion these are frequently neglected in informal discussions and even when I leave them out I will still be referring to the bar carb concentration in serum unless otherwise specified so let's get started with actually analyzing the ABG now this may seem obvious but the first step to analyzing the acid-based status of a patient is always to start with a pH if the pH is less than 7.35 the patient has acidemia and at least one acidosis whereas if the pH is greater than 7.45 the patient has alkalemia and at least one alkalosis let's look at a quick example here the pH is 7.25 as this is less than 7.35 this patient has an acidemia that's very straightforward next to step two check the pco2 if the pco2 is deranged in the same direction as the pH the acidbase disorder is metabolic in origin if the pco2 is deranged in the opposite direction as the pH the acid based disorder is respiratory in origin with this example the pco2 is 60 this is higher than the normal pco2 of 40 since the ph and the pco2 are deranged in opposite directions the disorder presence is respiratory thus this patient has a respiratory acidosis that is the patient has a pathologic process of the respiratory system that is driving the pH to be lower than normal let's take a quick look at three more examples in example one we have a patient with a pH of 7.50 a pco2 of 45 and a bicarb of 34 step one look at the pH 7.50 is greater than 7.45 thus there is an alkalemia step two look at the pco2 both the ph and the pco2 are higher than normal therefore the disorder is metabolic that is this patient has a metabolic alkalosis here is example two pH is 7.16 pco2 is 35 and bicarb is 12 step one the pH is low therefore the patient has an acidemia step two the pco2 is also low the same direction as as the pH therefore the disorder is metabolic and we have a metabolic acidosis Here's the final example first the pH is very low so there's an acidemia while the pH is lower than normal the pco2 is higher than normal therefore the cause of the disorder is respiratory therefore the patient has a respiratory acidosis identifying simple acid-based disorders really is that simple in the next lecture I'll discuss further the phenomenon of compensation and how that allows us to identify the presence of more than one acid-based disorder simultaneously [Music]