Raymond Harrison, a 64 year old male, was admitted to the hospital with fever (101.8 F), shaking chills, a nonproductive cough, and chest pains.  A chest X-ray revealed extensive accumulation of fluid in both lungs.  The patient had mild hypertension (high blood pressure) of 150/90 (normal would be 120/80) and a smoking history of 275 packs per year. The patient was cyanotic (looked blue) and in respiratory distress.  The patient’s heart rate was elevated at 100 beats per min (normal would be 60-80 ppm).

An arterial blood gas test was performed, and the oxygen saturation of the atrial blood was 72% (normal would be 90-100%).  The blood test also revealed an elevated white blood cell count.  Initial treatment consisted of antibiotics and bronchodilators.

1. An atrial “blood gas test” was performed to measure oxygen levels.  Explain why the blood was taken from an artery and not a vein.
2. In the blood gas test, the oxygen measurement is reported as saturation.  How is the oxygen carried in the blood, and what exactly is being saturated with oxygen.
3. Why does this patient have low oxygen saturation? What is preventing him from having saturation in the normal range?
4. How does the abnormal oxygen saturation value relate to the patient’s cyanotic (blue) appearance?
5. How does the abnormal oxygen saturation value related to the patient’s elevated heart rate?