To the Editor:—  It was interesting to read the case report by Fleck et al.  1suggesting an appropriate duration of cerebrospinal fluid drainage after thoracoabdominal aneurysm repair. However, toward the end of their discussion, the authors mention that draining 1,700 ml cerebrospinal fluid over 24 h is seven times greater than the normal 250 ml cerebrospinal fluid that is produced in the same period. Although it may be a minor point, cerebrospinal fluid is actually formed at the rate of 500–550 ml/24 h and not 250 ml, as mentioned by the authors. 2–5 

1.
Fleck TM, Koinig H, Hutschala D, Wolner E, Grabenwoger M: Cerebrospinal fluid drainage after thoracoabdominal aortic aneurysm repair. Anesthesiology 2003; 99:1019–20
2.
Guyton AC, Hall JE: Cerebral blood flow, the cerebrospinal fluid, and brain metabolism, Textbook of Medical Physiology, 10th edition. Edited by Guyton AC, Hall JE. Orlando, Florida, Harcourt, 2000, pp 709–17
3.
Ganong WF: Circulation through special regions, Review of Medical Physiology, 20th edition. Edited by Ganong WF. Boston, McGraw Hill, 2002, pp 588–606
4.
Sherwood L: The central nervous system, Human Physiology from Cells to Systems, 4th edition. Edited by Sherwood L. Australia, Brooks/Cale Thompson Learning, 2001, pp 122–72
5.
Drummond JC, Patel PM: Cerebral physiology and the effects of anesthetics and techniques, Anesthesia, 5th edition. Editing by Miller RD. Philadelphia, Churchill Livingstone, 2000, pp 695–733