Current issues of ACP Journal Club are published in Annals of Internal Medicine


Letters

Increased oxygen delivery for high-risk surgery

ACP J Club. 1994 Nov-Dec;121:84. doi:10.7326/ACPJC-1994-121-3-085

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Increased oxygen delivery for high-risk surgery



To the Editor

The commentary on the article by Boyd and colleagues provided by Ventura and Mehra (1) made sweeping recommendations about the clinical applications of the results. These recommendations are not warranted by the findings of the study nor by the literature as a whole.

Boyd and colleagues correctly conclude from their findings that "dopexamine hydrochloride significantly reduces mortality and morbidity in high-risk surgical patients." The commentators, however, generalized this conclusion to include other methods of increasing oxygen delivery (fluids, dopamine, and dobutamine) not studied by Boyd and colleagues. The literature provides little justification for this conclusion based on the results of a prospective study by Tuchschmidt and colleagues (2) that failed to show a survival benefit from this treatment. Even if one considers the study cited by the commentators (3), the literature is, at best, inconclusive. A recent study by Hayes and colleagues (4) [seeBoosting oxygen delivery was not effective in critically ill patients] has provided further evidence that some methods used to increase oxygen delivery (dobutamine) may even be detrimental.

The statement by the commentators that "the fundamental physiologic event that results in organ failure and death in critically ill patients is tissue hypoxia" may be true. It may, however, just as easily be false. The hypothesis of tissue hypoxia has been based on measurements of increased serum lactate concentrations. Experimental studies, however, have shown other mechanisms for increased lactate and no evidence of tissue hypoxia (5). The work by Boyd and colleagues is important because it contributes to our understanding of the potential benefits of a new drug, dopexamine hydrochloride. Their results should not be interpreted as evidence of mechanism nor as proof that hyper-resuscitation is beneficial.

John A. Kellum, MD
University of Pittsburgh School of Medicine
Pittsburgh, Pennsylvania

In response

Dr. Kellum's comments are unduly critical and even misleading. As clearly stated in our commentary, our comments were strictly intended for high-risk surgical patients and are not "sweeping generalizations." These should not have been construed as applicable to other critically ill patients (e.g., adult respiratory distress syndrome and septic shock).

Dr. Kellum cites 2 studies to support his conclusion that there is little justification for the methods used to optimize oxygen delivery. Tuchschmidt and colleagues (1) studied patients with septic shock, not high-risk surgical patients; they used dobutamine, dopamine, and fluid resuscitation to achieve target hemodynamic goals and, thus, supranormal oxygen delivery; and, contrary to Dr. Kellum's assertion, this study shows a survival benefit in (optimal treatment) patients who achieved "supranormal oxygen delivery" (74% mortality in the normal treatment group vs. 40% mortality in the optimal treatment group; P < 0.05).

The second study by Hayes and colleagues (2) analyzed elevations of systemic oxygen delivery with dobutamine in the treatment of critically ill patients. The conclusion is heralded by Dr. Kellum as evidence of adverse effects. But as Hayes and colleagues state: "The contrast between our results and those reported in previous studies may be due to differences in the patient populations, as well as in the timing of therapy and the doses of inotropic agents used."

Differences between the study by Hayes and colleagues and the ones by Boyd and colleagues (3) and Shoemaker and colleagues (4) include the facts that the populations were clinically different (high-risk surgical patients in the studies of Boyd and Shoemaker); the timing of targeted treatment was different (presurgical in the studies of Boyd and Shoemaker compared with postsurgical in the Hayes study); and the therapy to obtain maximal oxygen delivery was started after complications occurred in the Hayes study (2) but much earlier in the other 2 studies.

The relevant studies to date support the use of supranormal oxygen delivery in high-risk surgical patients.

H. Ventura
M. Mehra
Ochsner Transplant Center
New Orleans, Louisiana


References

1. Ventura HO, Mehra MR.Increased Oxygen Delivery for High-Risk Surgery ACP J Club. 1994 May-June:76 (Ann Intern Med. vol 120, suppl 3).

2. Tuchschmidt J, Fried J, Astiz M, Rackow E. Elevation of cardiac output and oxygen delivery improves outcome in septic shock. Chest. 1992;102:216-20.

3. Shoemaker WC, Appel PL, Kram HB, Waxman K, Leet TS. Prospective trial of supranormal values of survivors as therapeutic goals in high-risk surgical patients. Chest. 1988;94:1176-86.

4. Hayes MA, Timmins AC, Yau EH, et al. Elevation of systemic oxygen delivery in the treatment of critically ill patients. N Engl J Med. 1994;330:1717-22.

5. Hotchkiss RS, Rust RS, Dence CS, et al. Evaluation of the role of cellular hypoxia in sepsis by the hypoxic marker [18F]fluoromisonidazole. Am J Physiol. 1991;261:R965-72.

1. Tuchschmidt J, Fried J, Astiz M, Racknow E. Elevation of cardiac output and oxygen delivery improves outcome in septic shock. Chest. 1992;102:216-20.

2. Hayes MA, Timmins AC, Yau EH, et al. Elevation of systemic oxygen delivery in the treatment of critically ill patients. N Engl J Med. 1994;330:1717-22.

3. Boyd O, Grounds RM, Bennett ED. A randomized clinical trial of the effect of deliberate perioperative increase of oxygen delivery on mortality in high-risk surgical patients. JAMA. 1993;270:2699-707.

4. Shoemaker WC, Appel PL, Kram HB, Waxman K, Leet TS. Prospective trial of supranormal values of survivors as therapeutic goals in high-risk surgical patients. Chest. 1988;94:1176-86.