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Anesthesiology:
doi: 10.1097/ALN.0000000000000166
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Cerebral and Renal Blood Flow Autoregulation

Schwartz, Arthur E. M.D.

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To the Editor:

I was delighted to see our work cited in the recent editorial, “Intraoperative hypotension and patient outcome: Does one size fit all?”.1,2 Unfortunately, the authors made unsupported claims about the differences between renal and cerebral blood flow autoregulation. Indeed, the editorial’s conclusion that cerebral blood flow is determined by cerebral perfusion pressure and independent of changes in cardiac output is confirmed by our laboratory studies in nonhuman primates.3–5 In our laboratory model, cardiopulmonary bypass flow was varied by adjusting pump output, whereas arterial blood pressure was independently manipulated by administration of intrathecal lidocaine. Furthermore, this finding that cerebral perfusion is dependent on mean arterial pressure and not dependent on cardiac output is strongly supported by the clinical data in cardiac surgery patients.6
In stark contrast, the editorial claim that, “the kidney can be hypoperfused at normal mean arterial pressure if cardiac output is compromised,” is not supported by the cited reference.7 In that study’s piglet model, renal blood flow decreased during hemorrhagic hypotension. Although cardiac output was not measured at all, one would presume that the hemorrhage resulted in both decreased cardiac output and decreased arterial blood pressure. That decrease in renal blood flow may have been a consequence of hypotension, low cardiac output, or both. Whether or not changes in cardiac output, independent of arterial blood pressure, alter renal blood flow remains largely an open question.
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Competing Interests

The author declares no competing interests.
Arthur E. Schwartz, M.D.
, The Mount Sinai School of Medicine, New York, New York. arthur.schwartz@mountsinai.org
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References

1. Brady K, Hogue CW. Intraoperative hypotension and patient outcome: Does “one size fit all?”. ANESTHESIOLOGY. 2013;119:495–7

2. Michler RE, Sandhu AA, Young WL, Schwartz AE. Low-flow cardiopulmonary bypass: Importance of blood pressure in maintaining cerebral blood flow. Ann Thorac Surg. 1995;60(6 suppl):S525–8

3. Schwartz AE, Kaplon RJ, Young WL, Sistino JJ, Kwiatkowski P, Michler RE. Cerebral blood flow during low-flow hypothermic cardiopulmonary bypass in baboons. ANESTHESIOLOGY. 1994;81:959–64

4. Schwartz AE, Sandhu AA, Kaplon RJ, Young WL, Jonassen AE, Adams DC, Edwards NM, Sistino JJ, Kwiatkowski P, Michler RE. Cerebral blood flow is determined by arterial pressure and not cardiopulmonary bypass flow rate. Ann Thorac Surg. 1995;60:165–9; discussion 169–70

5. Schwartz AE, Minanov O, Stone JG, Adams DC, Sandhu AA, Pearson ME, Kwiatkowski P, Young WL, Michler RE. Phenylephrine increases cerebral blood flow during low-flow hypothermic cardiopulmonary bypass in baboons. ANESTHESIOLOGY. 1996;85:380–4

6. Rogers AT, Prough DS, Roy RC, Gravlee GP, Stump DA, Cordell AR, Phipps J, Taylor CL. Cerebrovascular and cerebral metabolic effects of alterations in perfusion flow rate during hypothermic cardiopulmonary bypass in man. J Thorac Cardiovasc Surg. 1992;103:363–8

7. Rhee CJ, Kibler KK, Easley RB, Andropoulos DB, Czosnyka M, Smielewski P, Brady KM. Renovascular reactivity measured by near-infrared spectroscopy. J Appl Physiol. 2012;113:307–14

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