History. 2. What is the Oxygenation status. 3. What is the pH? Acidemia or Alkalemia? 4. What is the primary disorder present? 5. Is there appropriate. ARTERIAL BLOOD GASES MADE EASY i This page intentionally left blank Arterial Blood Gases Made Easy Second Edition Iain A M Hennessey MBChB ( Hons). Mistakes in arterial blood gas (ABG) interpretation are common in clinical practice. The following is a simplified explanation of ABGs, including a practical.
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sO2. 70 - 75%. ABG EASY AS 1,2,3. NORMAL VALUES & DEFINITIONS 3 STEPS TO ABG INTERPRETATION made no attempt to help normalise the pH. The principles of oxygen transport and ventilation are core concepts for critical care nurses to understand in managing acutely and critically ill patients. Nurses. This nomogram has been derived using the normal range of pH (), pCO2 ( 44 mmHg), HCO3 () and the formula.
Yet most doctors struggle with interpretation of this common test. Given that this can be difficult, there is a need for a simple algorithm for systematically handling each of the numbers in turn, as discussed below.
However, I begin with a few basic points to understand. If one system is disturbed, the other tries to restore balance. Both systems are primarily concerned with keeping blood pH in the normal range. Even for the respiratory system, pH rather than oxygen is the priority.
The respiratory system — oxygenation vs pH In health, we are driven to take our next breath by the arterial partial pressure of carbon dioxide PaCO2 , which is intimately linked to pH.
This is because individuals generally live at a level of oxygenation well above that which is required to sustain life. Therefore, if, for example, a metabolic alkalosis were to develop, ventilation would fall at the expense of a small reduction in oxygenation to retain CO2 and, thus, return pH to the normal range.
Only then, will it drive ventilation to prevent harmful levels of hypoxia. Respiratory and metabolic systems — the speed of response The respiratory system can respond quickly to a metabolic derangement, with changes occurring to the blood gases within seconds to minutes.
However, the metabolic system largely regulated by the kidneys excreting or retaining acid or bicarbonate is much slower and changes can take hours to days.
Fix that fact in your mind because it will not change, no matter what the other numbers are!
If, for example, the problem is an acidosis and the PaCO2 is low, then clearly the respiratory system is attempting to compensate. Thus, one can conclude that the problem is metabolic similarly with other combinations. Therefore, after looking at only two numbers pH and PaCO2 , most of the interpretation is done.
However, they can sometimes add information about time course or provide information on additional derangements, but they will not contradict the conclusion that has already been reached.
What is perhaps surprising is that, after many years of looking at ABGs, those intelligent, enquiring minds have seemingly never once pondered that question. The problem with this measurement is that it is markedly affected by PaCO2.
It is this value that would provide a direct handle on what the metabolic system is doing. What is the base excess?
Base excess BE measures all bases, not just bicarbonate. However, because bicarbonate is the greater part of the base buffer, for most practical interpretations, BE provides essentially the same information as bicarbonate.
The major advantage of BE is that its normal range is really easy to remember. What does the base picture tell us? If one has established that problem is respiratory, then the BE can tell us something of the duration of the problem. If, for example, in a respiratory acidosis, the sHCO3 has shown no sign of responding still within the normal range , the probable explanation is that there has not yet been time to respond ie the problem is an acute respiratory acidosis.
A respiratory acidosis with a low sHCO3 would indicate a combined respiratory and metabolic -acidosis. Box 1. Open in a separate window Remember that one cannot live for long with pH outside of the normal range. An abnormal pH means there has to be an acute component to the problem.
Finally, look at the oxygen It is sometimes thought that type 2 respiratory failure is simply a more severe version of type 1. Who compensates more quickly?
Oxygen Administration Acute vs. Very essential for critical care. Flag for inappropriate content. Related titles.
Jump to Page. Search inside document. Metabolic Acidosis Way to go!! Respiratory Alkalosis Great Job!! Respiratory Acidosis You are doing a great job!!
You Are Doing Great. Metabolic Alkalosis with Partial Compensation You are doing great!! Fully Compensated Metabolic Alkalosis You have done great!! Hafiz Jaafar.
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