36 Terms Metabolic acidosis with respiratory compensation. An Arterial Blood Gas, or ABG for short, is a test that measures the blood levels of oxygen (PaO2), carbon dioxide (PaCO2), and acid-base balance (pH) in the body.It’s a test that is used to assess how well oxygen is being distributed throughout the body and how well carbon dioxide is being removed. A respiratory alkalosis would have the following characteristics on an ABG: Causes of respiratory alkalosis include: ³. Usefulness. It only addresses acid-base balance and considers just 3 values. They mostly come from collected results of volunteers or study subjects who appear to have uncompromised lungs and gas exchange. Where do these normal values come from? ABG Quick Interpretation Parameter Acidosis Normal Alkalosis Reflects pH < 7.35 7.35-7.45 > 7.45 Acid/Base Status of Body pCO2 > 45 35-45 < 35 Respiratory Component HCO3 < 22 22-26 > 26 Metabolic Component Facts: Body will not overcompensate when it … These disorders are termed complex acid-base or mixed disorders. Alveolar-arterial gradient = partial pressure of oxygen in airways (PAO ) – partial pressure of oxygen in artery (PaO. Based on the given ABG values, PaCO2 is above 45, so it is considered ACIDOSIS. Piecing this information together with the HCO3– we can complete the picture: You may note that in each of these tables HCO3– and CO2 are both included, as it is important to look at each in the context of the other. If the cause of the pH imbalance is from the respiratory system, the body can adjust the HCO3– to counterbalance the pH abnormality bringing it closer to the normal range. See whether pH is within normal range or not. CO. 3 ↔ HCO-+ H + STEP 1 – Oxygenation . PATIENT 1 A 68-year-old woman is admitted with abdominal pain, which is later found to be due to a pelvic abscess causing sepsis. Case A. Simple face masks can deliver a maximum FiO2 of approximately 40%-60% at a flow rate of 15L/min. If not, then: a. Investigations such as arterial blood gases […] The use of Venous Blood Gasses is becoming more widespread, especially in the emergency department. Note that despite the low pH the pCO2 is also high. A FOUR STEP METHOD FOR INTERPRETATION OF ABGS. The severity of the metabolic acidosis is masked by the respiratory system’s attempt at compensating via reduced CO2 levels. In these circumstances, the CO2 and HCO3– will be moving in opposite directions (e.g. If Normal, the blood gas is compensated or not. Explanation & Examples on Solving ABGs Problems. Learn how your comment data is processed. Which step? A patient is brought back to the floor from the operating room on a patient controlled analgesia (PCA) pump with hydromorphone. ST-Elevated MI. It occurs as a result of ventilation/perfusion (V/Q) mismatch; the volume of air flowing in and out of the lungs is not matched with the flow of blood to the lung tissue. covers the basic for an undergraduate. The drop in pH represents the normal mechanisms of compensation being over whelmed. For these ABG values, pH is NORMAL but slightly acidic and lines up with PACO2 which is METABOLIC. The traditional mnemonic for the causes of a metabolic acidosis with raised anion gap is ‘MUDPILES’: Copyright 2013-2019 Oxford Medical Education Ltd. It is the dedication of healthcare workers that will lead us through this crisis. We now know that the patient has a metabolic acidosis and therefore we can look back at the CO2 to see if the respiratory system is attempting to compensate for the metabolic derangement. excessive mechanical ventilation), Iatrogenic (e.g. As a result, if you see evidence of metabolic compensation for a respiratory disorder (e.g. The normal anion gap varies with different assays but is typically between 4 to 12 mmol/L. Her ABG is as follows: See relevant pages in the respiratory section for further information. It’s worth mentioning that it is possible to have a mixed acidosis or alkalosis (e.g. HCO3– is low, which is in keeping with a metabolic acidosis. Respiratory acidosis is caused by inadequate alveolar ventilation leading to CO2 retention. Normal PaCO2 Interpretation Normal ABG (acid base is balanced; there are no pH changes, so if the respiratory acid is normal, the metabolic base cannot be causing changes either.) Below is a quick reference guide, providing some approximate values for the various oxygen delivery devices and flow rates you’ll come across in practice.2, As with all oxygen delivery devices, there is a significant amount of variability depending on the patient’s breathing rate, depth and how well the oxygen delivery device is fitted. Subscribe to Resus. Acid Base Balance (pH) An ABG is performed and reveals the following: A PaO2 of 14 on room air is at the upper limit of normal, so the patient is not hypoxic. These masks are most suitable for trauma and emergency use where carbon dioxide retention is unlikely. So far we have discussed how to determine what the acid-base disturbance is, once we have this established we need to consider the underlying pathology that is driving this disturbance. You are called to see a 54 year old lady on the ward. Hypoventilation can occur for a number of reasons including: Seemingly small abnormalities in pH have very significant and wide-spanning effects on the physiology of the human body. center_focus_strong Metabolic Respiratory Combined. Respiratory alkalosis with no metabolic compensation. The changes in pH are caused by an imbalance in the CO2 (respiratory) or HCO3– (metabolic). She is three days post-cholecystectomy and has been complaining of shortness of breath. To make things simple, I will only refer to the three basic ABG values in this post. Hemodynamics. A collection of data interpretation guides to help you learn how to interpret various laboratory and radiology investigations. Examples of these situations could be hypoventilation, asphyxia, central nervous system depression, chronic obstructive pulmonary disease, infection, and drug-induced respiratory depression (Table 9). 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