Question

Respiratory Case Histories

Charles returned home to his apartment at 5 PM in the evening and turned on his old kerosene-fueled space heater. It had been a cold day in late spring and his third floor apartment was chilly. After spending an hour fixing dinner, he ate while watching the evening news on TV. He noticed that his vision became progressively blurred. When he got up to go to the kitchen, he felt lightheaded and unsteady. Entering the kitchen, he became very disoriented and passed out. The next thing he remembered was waking up in the intensive care unit of the hospital. Some friends who had stopped by about 7 PM had found Charles unconscious on the kitchen floor. They had called an ambulance, which had rushed Charles, still unconscious, to the hospital.

At the hospital, an arterial blood sample was drawn and showed the following values:

(Assume the patient lives at sea level, and normal values are + or –10 mm Hg.)

Partial pressure of N2= 573 mm Hg

Partial pressure of O2= 95 mm Hg

Partial pressure of CO2= 40 mm Hg

Partial pressure of CO = 0.4 mm Hg

1) From the case information given, what is the most likely explanation for the blood gas values given? Type answer as 1 or 2 short sentences

2) Would you expect the % Saturation/ O2 Sat. to be: normal, high or low?

3) Would you expect the Oxygen-Hemoglobin Dissociation Curve to be: normal; shifted right or shifted left?

4) Would you expect Charles to have chemoreceptor-mediate hyperventilation: yes or no?

5) Would you expect pulmonary ventilation to be the primary respiratory issue for Charles: yes or no?

Answer 1

The partial pressure of CO is 0.4 mm of Hg.

Normally CO (carbon monoxide) is not present in the blood.

CO has much higher affinity for hemoglobin than oxygen.So in the presence of carbon monoxide, hemoglobin is preferentially bound to carbon monoxide and not oxygen.

1) Charles turned on his kerosene fuelled space heater.This produces CO and since the doors and windows would have been kept closed because of the chilly weather, there is increase in the CO concentration in the air leading to CO poisoning.

2)The O2 saturation will increase because when the hemoglobin is bound to CO ,it increases the affinity of the hemoglobin for oxygen molecule. So less oxygen is released and hence the saturation with oxygen remains high.

3)The oxygen dissociation curve is shifted to the left also because of the same reason that CO increases affinity of hemoglobin for oxygenated and hence less O2 is released.

4) No chemorecepor mediated hyperventilation does not occur because the PO2 is normal (95 mm of Hg).

5)No pulmonary ventilation is not the issue for Charles because the respiratory gas values are almost normal .So pulmonary exchange is normal.The issue is decreased release of oxygen in the tissues.