On 2014 Mar 20, Patrice Brassard commented:

We have posted this comment also on the Journal website (http://bja.oxfordjournals.org/content/108/4/623/reply).

Editor - We read with interest the manuscript published by Tang et al. regarding the possible correlation between cerebral oxygen desaturations during single lung ventilation and postoperative cognitive dysfunction in patients undergoing thoracic surgery. The authors reported cerebral oxygen desaturations in an important number of patients during single lung ventilation in thoracic surgery. One-third of patients showed impairment of early postoperative cognitive function, with 90% of these patients normalizing their cognitive function at 24 hour after surgery. These results are potentially clinically important. However, we would like to highlight important missing information and one methodological issue that need to be discussed to fully appreciate the conclusion of this study.

The first issue relates to the use of vasopressors during thoracic surgery. Did the investigators keep blood pressure within a given range with vasopressors during surgery? Administration of local anesthetics through a peridural catheter is frequently associated with perioperative hypotension. Looking at Fig 3, mean arterial pressure was relatively constant throughout surgery. It would be surprising that vasopressors were not used to maintain or restore mean arterial pressure when using peridural analgesia during general anesthesia. This is of importance since recent evidence suggests that the use of phenylephrine (1-3) and norepinephrine (4) is associated with reduced cerebral oxygenation. Cerebral oxygen desaturations reported in this study during thoracic surgery could thus be partly explained by the administration of vasopressor agents used to restore or maintain blood pressure during the procedure.

The other issue pertains to the baseline cerebral oxygenation measure. Why was baseline cerebral oxygenation only monitored with patients breathing 100% oxygen and not also room air? Evidence suggests that patients can respond to supplemental oxygen (i.e. cerebral oxygenation will increase) while others will not respond (5). Breathing 100% oxygen could have increased baseline cerebral oxygenation in responder subjects and thus, artificially widen the difference between baseline cerebral oxygenation and the lowest cerebral oxygenation value monitored during the surgical procedure. Future studies interested in relative changes in cerebral oxygenation during surgical procedure in relation to postoperative cognitive function should present baseline cerebral oxygenation with patients breathing room air and hyperoxic gas.

Jean S. Bussieres, MD, FRCPC (1,3), Philippe Desjardins, R5 (1), Patrice Brassard, PhD (2,3)

(1) Department of Anesthesiology, Faculty of Medicine, Laval University, Quebec, Canada, (2) Department of Kinesiology, Faculty of Medicine, Laval University, Quebec, Canada, (3) Institut universitaire de cardiologie et de pneumologie de Quebec, Canada.

References

1.Brassard P, Seifert T, Wissenberg M, Jensen PM, Hansen CK, Secher NH. Phenylephrine decreases frontal lobe oxygenation at rest but not during moderately intense exercise. J Appl Physiol. 2010;108:1472-1478

2.Meng L, Cannesson M, Alexander BS, Yu Z, Kain ZN, Cerussi AE, Tromberg BJ, Mantulin WW. Effect of phenylephrine and ephedrine bolus treatment on cerebral oxygenation in anaesthetized patients. Br J Anaesth. 2011;107:209-217

3.Nissen P, Brassard P, Jorgensen TB, Secher NH. Phenylephrine but not ephedrine reduces frontal lobe oxygenation following anesthesia- induced hypotension. Neurocrit Care. 2010;12:17-23

4.Brassard P, Seifert T, Secher NH. Is cerebral oxygenation negatively affected by infusion of norepinephrine in healthy subjects? Br J Anaesth. 2009;102:800-805

5.Heringlake M, Garbers C, Kabler JH, Anderson I, Heinze H, Schon J, Berger KU, Dibbelt L, Sievers HH, Hanke T. Preoperative cerebral oxygen saturation and clinical outcomes in cardiac surgery. Anesthesiology. 2011;114:58-69

On 2014 Mar 20, Patrice Brassard commented:

We have posted this comment also on the Journal website (http://bja.oxfordjournals.org/content/108/4/623/reply).

Editor - We read with interest the manuscript published by Tang et al. regarding the possible correlation between cerebral oxygen desaturations during single lung ventilation and postoperative cognitive dysfunction in patients undergoing thoracic surgery. The authors reported cerebral oxygen desaturations in an important number of patients during single lung ventilation in thoracic surgery. One-third of patients showed impairment of early postoperative cognitive function, with 90% of these patients normalizing their cognitive function at 24 hour after surgery. These results are potentially clinically important. However, we would like to highlight important missing information and one methodological issue that need to be discussed to fully appreciate the conclusion of this study.

The first issue relates to the use of vasopressors during thoracic surgery. Did the investigators keep blood pressure within a given range with vasopressors during surgery? Administration of local anesthetics through a peridural catheter is frequently associated with perioperative hypotension. Looking at Fig 3, mean arterial pressure was relatively constant throughout surgery. It would be surprising that vasopressors were not used to maintain or restore mean arterial pressure when using peridural analgesia during general anesthesia. This is of importance since recent evidence suggests that the use of phenylephrine (1-3) and norepinephrine (4) is associated with reduced cerebral oxygenation. Cerebral oxygen desaturations reported in this study during thoracic surgery could thus be partly explained by the administration of vasopressor agents used to restore or maintain blood pressure during the procedure.

The other issue pertains to the baseline cerebral oxygenation measure. Why was baseline cerebral oxygenation only monitored with patients breathing 100% oxygen and not also room air? Evidence suggests that patients can respond to supplemental oxygen (i.e. cerebral oxygenation will increase) while others will not respond (5). Breathing 100% oxygen could have increased baseline cerebral oxygenation in responder subjects and thus, artificially widen the difference between baseline cerebral oxygenation and the lowest cerebral oxygenation value monitored during the surgical procedure. Future studies interested in relative changes in cerebral oxygenation during surgical procedure in relation to postoperative cognitive function should present baseline cerebral oxygenation with patients breathing room air and hyperoxic gas.

Jean S. Bussieres, MD, FRCPC (1,3), Philippe Desjardins, R5 (1), Patrice Brassard, PhD (2,3)

(1) Department of Anesthesiology, Faculty of Medicine, Laval University, Quebec, Canada, (2) Department of Kinesiology, Faculty of Medicine, Laval University, Quebec, Canada, (3) Institut universitaire de cardiologie et de pneumologie de Quebec, Canada.

References

1.Brassard P, Seifert T, Wissenberg M, Jensen PM, Hansen CK, Secher NH. Phenylephrine decreases frontal lobe oxygenation at rest but not during moderately intense exercise. J Appl Physiol. 2010;108:1472-1478

2.Meng L, Cannesson M, Alexander BS, Yu Z, Kain ZN, Cerussi AE, Tromberg BJ, Mantulin WW. Effect of phenylephrine and ephedrine bolus treatment on cerebral oxygenation in anaesthetized patients. Br J Anaesth. 2011;107:209-217

3.Nissen P, Brassard P, Jorgensen TB, Secher NH. Phenylephrine but not ephedrine reduces frontal lobe oxygenation following anesthesia- induced hypotension. Neurocrit Care. 2010;12:17-23

4.Brassard P, Seifert T, Secher NH. Is cerebral oxygenation negatively affected by infusion of norepinephrine in healthy subjects? Br J Anaesth. 2009;102:800-805

5.Heringlake M, Garbers C, Kabler JH, Anderson I, Heinze H, Schon J, Berger KU, Dibbelt L, Sievers HH, Hanke T. Preoperative cerebral oxygen saturation and clinical outcomes in cardiac surgery. Anesthesiology. 2011;114:58-69