CHEST VOLUME 67/ NUMBER 3/ MARCH, 1975
EDITORIALS
based upon an assumed exponential decline in arterial Po 2 • It was calculated from the time required for the arterial POI! to decrease to one-hall of its initial value-the exponential portion of the wash out curve. Sherter and colleagues made no comparable computation for their pulmonary patients. We took the liberty of doing so from their data and found comparable values for the time required for the arterial POI! to fall to one-half the starting value. o But, thereafter, over the lower hall of the washout curve, marked differences were found, as would be expected in view of the grossly irregular gas wash.n and washout known to occur in patients with chronic obstructive pulmonary diseases. Patient number 17 in the report by Howe and associates had very low arterial POI! values during oxygen breathing and a negligible change upon switching to room air. Patient number 2 in Sherter's paper differed considerably from the others in that he had an extraordinarily rapid change in arterial Po 2 • Because he had only one lung, it was presumed that its gas composition changed very rapidly. Thus, there were exceptions to the expected findings-in both directions. How long does it take for the blood oxygen to return to baseline values when the patient is switched from breathing oxygen to room air? Five minutes or less in patients with cardiac disease (and no concomitant obstructive lung diseases), say Howe et al; 20 to 25 minutes in patients with obstructive lung disease, say Sherter et al; but you had better check your patients with additional arterial blood samples just to be sure, say I! David W. Cugell, M.D., F.C.C.P. 00 Chicago
How Long Should You Wait? hen a patient is switched from breathing W gen to breathing room air, how long an
o~y 10-
terval is required before arterial oxygen stabilizes at the lower level? This common clinical problem is the subject of two reports in this issue. Their simultaneous appearance is not fortuitous; it was overtly contrived by the undersigned. In the first of these manuscripts, submitted by Howe (see page 256) and colleagues, results in 21 patients with cardiac disease are described. Although this paper was enthusiastically endorsed by our reviewers. they urged the addition of appropriate words of caution because, in patients with pulmonary diseases, the results would, in all likelihood, be markedly different. A member of the editorial board of Chest and a long-time friend of the College, Dr. Gordon Snider, agreed to provide the necessary data so that the reviewers' concerns might have a basis in fact. The accompanying article by Sherter and associates (see page 259) is the result. There are important differences in the manner in which these two studies were conducted, dictated in part by the different nature of the patients' diseases. Oxygen was administered to the cardiac patients via a face mask at a flow of 5 liters per minute. The maximum arterial POI! value achieved thereby was 330 mm Hg, with an average for all 21 subjects of only 229 mm Hg. For the study of the patients with lung diseases a demand valve, mouthpiece, and nose clip were used. The lowest arterial POI! in these patients was 310 mm Hg, with an average of 478 mm Hg. Thus, the time required for the patients to achieve their customary arterial P02 values while breathing room air, after being switched from oxygen back to air, was based upon quite different initial blood P0 2 values. Howe et al calculated a "decay constant-( K )"
°Computations perfonned by Mr. Gary Slutsky, B.S.E., Northwestern University Medical Center-Pulmonary Section. °°Bazley Professor of Medicine, Northwestern University Medical School.
253
EDITORIALS
based upon an assumed exponential decline in arterial Po 2 • It was calculated from the time required for the arterial POI! to decrease to one-hall of its initial value-the exponential portion of the wash out curve. Sherter and colleagues made no comparable computation for their pulmonary patients. We took the liberty of doing so from their data and found comparable values for the time required for the arterial POI! to fall to one-half the starting value. o But, thereafter, over the lower hall of the washout curve, marked differences were found, as would be expected in view of the grossly irregular gas wash.n and washout known to occur in patients with chronic obstructive pulmonary diseases. Patient number 17 in the report by Howe and associates had very low arterial POI! values during oxygen breathing and a negligible change upon switching to room air. Patient number 2 in Sherter's paper differed considerably from the others in that he had an extraordinarily rapid change in arterial Po 2 • Because he had only one lung, it was presumed that its gas composition changed very rapidly. Thus, there were exceptions to the expected findings-in both directions. How long does it take for the blood oxygen to return to baseline values when the patient is switched from breathing oxygen to room air? Five minutes or less in patients with cardiac disease (and no concomitant obstructive lung diseases), say Howe et al; 20 to 25 minutes in patients with obstructive lung disease, say Sherter et al; but you had better check your patients with additional arterial blood samples just to be sure, say I! David W. Cugell, M.D., F.C.C.P. 00 Chicago
How Long Should You Wait? hen a patient is switched from breathing W gen to breathing room air, how long an
o~y 10-
terval is required before arterial oxygen stabilizes at the lower level? This common clinical problem is the subject of two reports in this issue. Their simultaneous appearance is not fortuitous; it was overtly contrived by the undersigned. In the first of these manuscripts, submitted by Howe (see page 256) and colleagues, results in 21 patients with cardiac disease are described. Although this paper was enthusiastically endorsed by our reviewers. they urged the addition of appropriate words of caution because, in patients with pulmonary diseases, the results would, in all likelihood, be markedly different. A member of the editorial board of Chest and a long-time friend of the College, Dr. Gordon Snider, agreed to provide the necessary data so that the reviewers' concerns might have a basis in fact. The accompanying article by Sherter and associates (see page 259) is the result. There are important differences in the manner in which these two studies were conducted, dictated in part by the different nature of the patients' diseases. Oxygen was administered to the cardiac patients via a face mask at a flow of 5 liters per minute. The maximum arterial POI! value achieved thereby was 330 mm Hg, with an average for all 21 subjects of only 229 mm Hg. For the study of the patients with lung diseases a demand valve, mouthpiece, and nose clip were used. The lowest arterial POI! in these patients was 310 mm Hg, with an average of 478 mm Hg. Thus, the time required for the patients to achieve their customary arterial P02 values while breathing room air, after being switched from oxygen back to air, was based upon quite different initial blood P0 2 values. Howe et al calculated a "decay constant-( K )"
°Computations perfonned by Mr. Gary Slutsky, B.S.E., Northwestern University Medical Center-Pulmonary Section. °°Bazley Professor of Medicine, Northwestern University Medical School.
253
