Acute Respiratory Failure - question?


So, I feel like I know my acid-base imbalance stuff pretty well, but every once in a while there's something that makes me feel stupid. For example this question from the Uworld test bank.

An elderly client is becoming increasingly restless. Respirations are 28/min and shallow. Which ABG results best indicate that the client is in ARF and needs immediate intervention?

>>The answer is PaO2 of 49 and PaCO2 of 60.

I feel like there is something easy I'm missing, and I'd appreciate if someone could point it out for me. Hyperventilation means more CO2 exhaled - which usually means resp alkalosis, right? And there are two types of Respiratory failure - hypoxemic and hypercapnic - right? So shouldn't the CO2 be low and the oxygen be closer to normal (but still low)?

I know I'm probably overthinking this, making a dumb mistake, or just plain wrong, but I'd appreciate someone dumbing it down for me if they can!

vanilla bean

861 Posts

If the breaths are too shallow (low tidal volume), then it is possible for very little of the breath to make it to areas where gas exchange can take place. Most of the breath may only move through areas of "dead space" where gas exchange does not take place.

You are correct in thinking that a RR of 28 could lead to hyperventilation (hypocapnea), but that is if the patient has normal or greater than normal tidal volumes without underlying lung disease or conditions interfering with normal gas exchange.

Has 1 years experience.

I'm a respiratory therapist now in nursing school. I see what you are thinking in regards to this question.

So, yes, you are correct that there are two types of respiratory failure. Type 1 is hypoxemic respiratory failure, meaning the PO2 result on the blood gas are 45. This is a problem with ventilation or breathing.

So, you would think that if a patient is in respiratory distress type 1 with low oxygen levels, breathing at an increased rate, that the patient's CO2 would go down due to blowing off CO2. This seems logical. But the key to the question is that the patient is said to be breathing *SHALLOW* which means they are not taking in an adequate amount of air per breath. As a respiratory therapist, we talk of Tidal Volumes (Vt - the volume of air inhaled and exhaled in a single breath). If the patient is not getting enough Vt to meet their body's demands, they can start to retain CO2. In fact, many CO2 retainers are people with obstructive pulmonary disorders, like COPD (chronic bronchitis, emphysema, asthma). Obstructive disorders can get air in but have a hard time exhaling it out ("barrel chest" or widening of the intercostal spaces on a chest xray).

So, sometimes type 1 and type 2 resp failure can coincide with each other (and in real life much of the time they do). It's easy to determine the primary cause of the respiratory failure. If you take the patient in question and provide him with oxygen (in this case maybe a Non-rebreather mask on 10-15L) and follow up with another ABG in 30-60 mins, you should see his PO2 levels rise and his CO2 levels decrease. If not, then perhaps it is type 2 causing the type 1. So, my next step in real life would be to assist his ventilation with either CPAP or Bipap depending on what else is happening with the patient.

For school, it's probably fine to think of respiratory failure as 2 separate problems (either oxygenation or ventilation) but in real life the two often go hand in hand like a seesaw. You can't treat one without effecting the other, and one can't break down without affect the other.

In the respiratory world, we are either treating/supporting oxygenation (using oxygen therapy, secretion clearance devices or CPAP) or ventilation (Bipap, IPPB, EZPAP).

I hope this helps!