Case Studies

The following are examples of clinical situations and the ABGs that may result, as well as causes and solutions for ABG abnormalities.

Case 1

Mrs. Puffer is a 35-year-old single mother, just getting off the night shift. She reports to the ED in the early morning with shortness of breath. She has cyanosis of the lips. She has had a productive cough for 2 weeks. Her temperature is 102.2, blood pressure 110/76, heart rate 108, respirations 32, rapid and shallow. Breath sounds are diminished in both bases, with coarse rhonchi in the upper lobes. Chest X-ray indicates bilateral pneumonia.

• ABG results are:
  • pH= 7.44
  • PaCO2= 28
  • HCO3= 24
  • PaO2= 54

Problems:

• PaCO2 is low.
• pH is on the high side of normal, therefore compensated respiratory alkalosis.
• Also, PaO2 is low, probably due to mucous displacing air in the alveoli affected by the pneumonia (see Shunting).

Solutions:

• Mrs. Puffer most likely has ARDS along with her pneumonia.
• The alkalosis need not be treated directly. Mrs. Puffer is hyperventilating to increase oxygenation, which is incidentally blowing off CO2. Improve PaO2 and a normal respiratory rate should normalize the pH.
• High FiO2 can help, but if she has interstitial lung fluid, she may need intubation and PEEP, or a BiPAP to raise her PaO2. (Click here to compare BiPAP to other respiratory treatments.)
• Expect orders for antibiotics, and possibly steroidal anti-inflammatory agents.
• Chest physiotherapy and vigorous coughing or suctioning will help the patient clear her airways of excess mucous and increase the number of functioning alveoli.

Case 2

Mr. Worried is a 52-year-old widow. He is retired and living alone. He enters the ED complaining of shortness of breath and tingling in fingers. His breathing is shallow and rapid. He denies diabetes; blood sugar is normal. There are no EKG changes. He has no significant respiratory or cardiac history. He takes several antianxiety medications. He says he has had anxiety attacks before. While being worked up for chest pain an ABG is done:

• ABG results are:
  • pH= 7.48
  • PaCO2= 28
  • HCO3= 22
  • PaO2= 85

Problem:

• pH is high,
• PaCO2 is low
• respiratory alkalosis.

Solution:

• If he is hyperventilating from an anxiety attack, the simplest solution is to have him breathe into a paper bag. He will rebreathe some exhaled CO2.This will increase PaCO2 and trigger his normal respiratory drive to take over breathing control.
• * Please note this will not work on a person with chronic CO2 retention, such as a COPD patient. These people develop a hypoxic drive, and do not respond to CO2 changes.

Case 3

You are the critical care nurse about to receive Mr. Sweet, a 24-year-old DKA (diabetic ketoacidosis) patient from the ED. The medical diagnosis tells you to expect acidosis. In report you learn that his blood glucose on arrival was 780. He has been started on an insulin drip and has received one amp of bicarb. You will be doing finger stick blood sugars every hour.

• ABG results are:
  • pH= 7.33
  • PaCO2= 25
  • HCO3=12
  • PaO2= 89

Problem:

• The pH is acidotic,
• PaCO2 is 25 (low) which should create alkalosis.
• This is a respiratory compensation for the metabolic acidosis.
• The underlying problem is, of course, a metabolic acidosis.

Solution:

• Insulin, so the body can use the sugar in the blood and stop making ketones, which are an acidic by-product of protein metabolism.
• In the mean time, pH should be maintained near normal so that oxygenation is not compromised (see Oxyhemoglobin Dissociation Curve).

© RnCeus.com