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Postoperative Pulmonary Complications
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Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
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IN RESPONSE:
Measurement of oxygenation, purely numerically, as a surrogate, without clear linkage to clinically important outcomes, may not advance the science or art of patient care and research in perioperative pulmonary risk management. Data from a large trial of pulse oximetry in the operating room and postanesthesia care unit suggest that there is more measurable hypoxemia than there are important clinical sequelae of it (1). Mild hypoxemia, which probably has little clinical significance as a postoperative pulmonary complication, should not be considered as such in the same league as pneumonia.
There may be other reasons to care about oxygenation besides pulmonary complications. Dr. Ramsay cites two reports from a multicenter trial of patients having colorectal surgery who were randomly assigned to receive 30% (standard care) or 80% supplemental oxygen intraoperatively and 2 hours postoperatively (2, 3). Eighty percent supplemental oxygen was associated with less postoperative nausea and vomiting and fewer wound infections (2, 3). Both reports state that oxygen saturation was maintained at greater than 92% to at least 95% in all patients.
Dr. Ramsay's mention of “subtle tissue ischemia” provides additional perspective. The definition of clinically important hypoxemia may vary among tissues. In the study of wound infection (3), mean arterial oxygen saturation was 98.7% and 99.7% in the 30% and 80% oxygen groups, respectively. The difference between these groups was statistically significant (P < 0.001), but would anyone argue that it is clinically important? Yet clinical meaning is less clear for the similarly statistically significant differences between groups for more sophisticated measures of intraoperative tissue oxygenation: mean subcutaneous oxygen tension (59 mm Hg vs. 109 mm Hg), muscle oxygen tension (25 mm Hg vs. 40 mm Hg), and partial pressure of arterial oxygen (121 mm Hg vs. 348 mm Hg). Do the latter measures validly lower the bar for “clinical” hypoxemia, or are they irrelevant surrogate measures? It takes well-designed research that defines the link between surrogate measures and clinical outcomes to answer these questions.
Valerie A. Lawrence, MD
South Texas Veterans Health Care System
University of Texas Health Science Center at San Antonio
San Antonio, TX 78229-3900
The Editors welcome submissions for possible publication in the Letters section. Authors of letters should:
•Include no more than 300 words of text, three authors, and five references
•Type with double-spacing
•Send three copies of the letter, an authors' form signed by all authors, and a cover letter describing any conflicts of interest related to the contents of the letter.
Letters commenting on an Annals article will be considered if they are received within 6 weeks of the time the article was published. Only some of the letters received can be published. Published letters are edited and may be shortened; tables and figures are included only selectively. Authors will be notified that the letter has been received. If the letter is selected for publication, the author will be notified about 3 weeks before the publication date. Unpublished letters cannot be returned.
Annals welcomes electronically submitted letters.
- Copyright ©2004 by the American College of Physicians
