Dr. A is sitting at home enjoying dinner when the phone rings. The caller is Mr. B, an acquaintance. He is distraught. He asks how much air must be injected into an intravenous line to cause a person to die. When asked why he wants to know, he explains that his 72-year-old father, currently a patient in a local hospital, has end-stage metastatic lung cancer and is in excruciating pain. Mr. B cannot bear to see his father in such pain and wants to end his suffering by means of an air embolism.

Mr. C, a 68-year-old man with a 100 pack-per-year history of smoking and known chronic obstructive pulmonary disease, presents to the emergency department with pneumonia and respiratory failure. He has been intubated four times before for respiratory failure. He uses oxygen at home and is dyspneic at rest. He has hypoxemia, hypercapnia, and is delirious. The emergency physician, Dr. D, tries to stabilize his condition with oxygen, bronchodilators, steroids, and non-invasive ventilation, but Mr. C's respiratory status worsens. Dr. D cannot locate Mr. C's family. She calls Mr. C's family physician and respirologist to find out whether they have ever discussed re-intubation, but unfortunately neither has done so. Although she is uncomfortable with this situation because of the uncertainty about the patient's wishes, Dr. D decides to perform the intubation.