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Ms Golden is a 64-year-old chronic smoker hospitalized for a knee replacement. As part of the orthopedic care protocol, she receives 2 L O2 per nasal cannula and a patient-controlled analgesia pump with morphine postoperatively. Although she initially does well, a rapid response call is made on her on her second postoperative day when the nurses find her unresponsive. Vital signs are normal, as is a blood glucose check done at bedside.

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1. What would be your next evaluative step?

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Answer

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  1. You should obtain an arterial blood gas in order to evaluate this patient's ability to ventilate and exchange gases adequately. Her history suggests that she could have chronic COPD and undiagnosed chronic, mild hypoxia. With the addition of sedating analgesics, her ventilatory capacity could be reduced and cause her to retain CO2, accounting for her unresponsive state. Alternatively in a patient with undiagnosed COPD, the addition of supplemental oxygen could have reduced her hypoxic drive leading to CO2 retention and unresponsiveness.

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Acute Respiratory Failure

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Diagnosis

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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.

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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).

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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 with pink nail beds, and significant bradycardia or sinus pauses. Your differential should include disease states that can induce a shallow or inadequate respiratory effort such as asthma or COPD exacerbation in a patient who has “tired out,” neuromuscular issues ...

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