Clinical Reasoning about Patients with Asthma:
Examination: The nurse auscultates the patient's chest in all the lung fields. The underlying breath sounds are "distant" because sound does not travel through air as well as it does through healthy, normally aerated tissues, or liquid. The sounds are distant also because the patient is just not moving much air. The underlying breaths have a markedly prolonged expiratory phase... because airways naturally collapse a bit with expiration... but with CG's very inflamed, constricted airways, this tendency is magnified. This too is a key indicator of increased airway resistance. And the nurse can semi-quantify the severity of obstruction (the expiration is 3 times as long as the inspiration.) The nurse also hears wheezes. A wheeze is (of course) always abnormal and heard, most commonly,during the expiratory phase of respiration. They are usually absent because airflow in healthy lungs is laminar (straight and smooth). When the airways are tight, airflow is turbulent... a situation that promotes wheezes.
Labs - Chemistries: CG's serum sodium, BUN and Creatinine indicate she is somewhat dehydrated. This is not unusual with an acutely ill asthmatic. They struggle to breathe, they have a fast respiratory rate, and their insensible fluid loss goes way up. If they arrive in the ER hours into their attack (as we see with CG) they tend to be "dry". Add to that, they may not be drinking fluids... they are too busy trying to breathe! The truly disturbing number in these values is the lower than normal bicarbonate. Whenever this is less than normal it means some fixed acid is consuming bicarbonate ions (the major buffer of body fluids.) In this case... as we suspected earlier, CG is not oxygenating her tissues well and some cells and mitochondria are operating anaerobically, producing lactic acid as a by-product. This is a very bad sign.
ABG's: The PaO2 and %sat appear pretty normal. But that's only because C.G. is breathing 4L/min O2. The pH is bad. We know she is acidotic. But is it a respiratory acidosis? or a metabolic acidosis? It's BOTH! It's respiratory acidosis because her PaCO2 is elevated. It's a metabolic acidosis because her serum bicarbonate is low. A quick aside: Most of the time asthmatics will manifest a lower than normal PaCO2 and a respiratory alkalosis. Why? It's true they aren't moving air well... but CO2 diffuses 20 times more readily than oxygen. The asthma attack is driving the patients to breathe harder. Thus they actually blow-off CO2. When an asthmatic has a "normal" PaCO2... that is a bad sign. They are beginning to fatigue and fail.
Labs - Chemistries: CG's serum sodium, BUN and Creatinine indicate she is somewhat dehydrated. This is not unusual with an acutely ill asthmatic. They struggle to breathe, they have a fast respiratory rate, and their insensible fluid loss goes way up. If they arrive in the ER hours into their attack (as we see with CG) they tend to be "dry". Add to that, they may not be drinking fluids... they are too busy trying to breathe! The truly disturbing number in these values is the lower than normal bicarbonate. Whenever this is less than normal it means some fixed acid is consuming bicarbonate ions (the major buffer of body fluids.) In this case... as we suspected earlier, CG is not oxygenating her tissues well and some cells and mitochondria are operating anaerobically, producing lactic acid as a by-product. This is a very bad sign.
ABG's: The PaO2 and %sat appear pretty normal. But that's only because C.G. is breathing 4L/min O2. The pH is bad. We know she is acidotic. But is it a respiratory acidosis? or a metabolic acidosis? It's BOTH! It's respiratory acidosis because her PaCO2 is elevated. It's a metabolic acidosis because her serum bicarbonate is low. A quick aside: Most of the time asthmatics will manifest a lower than normal PaCO2 and a respiratory alkalosis. Why? It's true they aren't moving air well... but CO2 diffuses 20 times more readily than oxygen. The asthma attack is driving the patients to breathe harder. Thus they actually blow-off CO2. When an asthmatic has a "normal" PaCO2... that is a bad sign. They are beginning to fatigue and fail.