ABG TEST CASE

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

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. 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

Case4: A 21 year old man is brought in by his father with a one week history of vomiting. He has not been able to keep any food down. He has been diagnosed with Hashimoto’s thyroiditis by his local doctor 4 months previously. Today his blood pressure is 90/48 and pulse rate 104. These are his venous blood gas results: pH  7.31 pCO2  39 pO2  25 HCO3- 19 BE -7 Na 108 K 6.2 Cl 72 Glc 3.3

SOLUTION Is it acidosis or alkalosis?     ACIDOSIS What is the primary cause? Given the low HCO3 and the not so high pCO2 it is METABOLIC ACIDOSIS. Is there adequate compensation? Expected pCO2 is [(1.5xHCO3) +8]+2  i.e.., [(~30) + 8]+2 = 38-39 so there is adequate compensation What is the Anion Gap? Na -(Cl + HCO3) = 108-(72 + 19) = 17 so raised anion gap metabolic acidosis. (reference is 8-16) Is there any other process going on? Look at the delta gap. change in AG/change in HCO3 = 17-12(use 12 as the expected AG)/24-19(24 is the expected HCO3) = 5/5 = 1 so this is a pure anion gap metabolic acidosis. ( Given what I say below, I might have also expected a normal anion gap metabolic acidosis) If we comment on the Na and K:

The Na is very low and the corrected K is (6. 2 + 0. 5) 6. 7 The Na is very low and the corrected K is (6.2 + 0.5) 6.7. This is indicative of Addison’s disease. The patient was initially treated with 1L of normal saline stat. There was also a concern that there may have been an adrenal crisis occurring and he was given hydrocortisone IV, after which the blood pressure increase. He was admitted for slow correction of his hyponatremia and further investigation of his underlying condition.

Case 5 : A 68 yo woman with known COPD, on home oxygen, presents a little drowsy. Her initial Co2 on venous gases was 84mmHg. She is placed on a short course of CPAP and is soon sitting out of bed eating sandwiches. The medical registrar looks at the venous gases and doesn’t want to take the patient to the ward because of the CO2. What do you think? pH         7.25 pCO2    74 mmHg pO2      17 mmHg HCO3  33 mmol/L

SOLUTION Solving gases like this is relatively simple. FIRST THING TO SAY IS: This patient should not be going to ICU anyway, as she is on home oxygen. The only question to ask is; is she OKAY to leave the ED and go to the ward?  I say yes! My suspicion in this patient, is that she normally is compensated for a high CO2. Lets see if that is correct. Using the 7 Step System for gas interpretation( we only need the first 2 steps here): Step 1: Acidosis or Alkalosis?This is an ACIDOSIS What is it due to primarily? Given that the CO2 is very raised in comparison to the HCO3, this is a RESPIRATORY ACIDOSIS

Step 2: Is there adequate compensation Step 2: Is there adequate compensation?I use the 1234 rule for calculating compensation in respiratory primary causes. In the acute phase we would expect the HCO3 to increase by 1 mmol/L for every 10mmHg rise in CO2(above 45) Let’s take the baseline of the HCO3 as 24 we know that CO2 has risen by 29- lets say 30mmHg. In acute compensation the HCO3 would be expected to be 24(baseline to use) + (3 x 1) = 27  In chronic compensation we would expect the HCO3 to increase by 3mmol/L for every 10mmHg increase in CO2 Therefore the HCO3 would increase by 24 + (3 x 3) =33 The bicarb is in fact 33mmol/L. This indicates that this patient may normally be sitting at around this CO2 level. That’s why she is sitting out of bed, looking better and eating sandwiches. She can go to the ward.