Mr Cantrall is a 72-year-old man with no known pulmonary history admitted to the hospital with E. coli sepsis due to cholecystitis. He receives antibiotics, fluids, and narcotic analgesia. On hospital day 3, he gets out of bed to go to the bathroom and becomes “winded.” When you arrive to see him, he is sitting on the edge of his bed with his elbows on his knees, breathing at 30 breaths/min. He states he cannot catch his breath. His pulse ox registers an SaO2 of 87%.
1. What is your differential diagnosis for Mr Cantrall's acute respiratory failure (ARF)?
There are quite a few entities that could explain Mr Cantrall's acute dyspnea and hypoxia. Since he is in the postoperative period, a DVT with pulmonary embolism should be on your differential, as should a hospital-acquired or aspiration-type pneumonia. Cardiac causes include fluid overload or CHF (patients commonly exhibit reduced ejection fractions after sepsis). In patients with kyphoscoliosis, which is relatively common in the geriatric population, the addition of narcotic analgesia can result in a reduction of their vital capacity to the point where normal activity causes hypoxia. Another problem that could cause shallow ventilation would be the development of peritonitis from his infected gallbladder.
Acute Respiratory Failure
ARF is defined as a sudden (minutes to hours) inability of the lungs to maintain normal respiratory function, resulting in abnormal arterial oxygen or carbon dioxide levels. Whether classified as Type 1 (hypoxemic) or Type 2 (hypercarbic), ARF represents a major immediate threat to homeostasis and is a medical emergency. Work to diagnose the initiating problem as well as augmentation of the patient's ability to exchange gases must proceed quickly, and in parallel. An initial workup including a cardiac and pulmonary examination, chest x-ray, ABG, and EKG should point you in the right direction by helping to classify the ARF and generate a differential diagnosis as to the cause.
Patients with Type 1 ARF have hypoxemia as their predominant blood gas abnormality. Typically, these patients are anxious and intensely focused on relieving their dyspnea. When you attempt to obtain their history, they may not be able to cooperate, repeating phrases like “I can't breathe” or “Help me.” You may note use of accessory muscles of respiration and, in severe cases, cyanosis. The patient may exhibit unstable vital signs as well. Your differential should include parenchymal and interstitial disease (pneumonia, aspiration, COPD or CHF exacerbation, ARDS) as well as diseases that can cause an acute right-to-left shunt (pulmonary embolism).
Patients with Type 2 ARF have high pCO2 levels as their predominant blood gas problem. They may be hypoxemic as well. These patients can exhibit a “narcosis,” appearing confused, intoxicated, or unresponsive. On physical examination, you may find a tremor or asterixis, peripheral vasodilation ...