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G. Patrick Clagett (Dallas, Tex). What was the temporal relationship between operation and intracranial hemorrhage? Did patients develop hemorrhage during operation or later in the postoperative period? Was the spinal drain in place at the time of hemorrhage and were there technical problems such as draining too much CSF [cerebrospinal fluid] too fast?

Dr Matthew Mell. Most of the occurrences of bloody spinal fluid drainage occurred during the procedure or shortly thereafter. All patients had a functioning drain in place. No patients had excessive fluid drained or exceedingly low pressures, as the drainage was performed manually, and therefore did not rely on a passive drainage system.

Dr Starros Kakkos (Detroit, Mich). I have a couple of questions. What is the mechanism of developing intracerebral hematoma? Also, how much heparin do you give during the procedure?

Dr Mell. The mechanism of bleeding is not completely understood, but it is thought to be due to the effect of pressure changes on the dural sinuses or the cortical veins, which cross the subdural space. These veins become engorged as the CSF pressure decreases, increasing the risk for disruption and bleeding. There may also be an effect of the rate of pressure change, with sudden drops in the CSF pressure further increasing that risk.

With regard to heparinization, we perform open TAAA [thoracoabdominal aortic aneurysm] repair without CPB [cardiopulmonary bypass], and patients in this group were not routinely heparinized. The patients undergoing endovascular repair did receive a standard dose of heparin; for these patients we have adjusted our protocol, aiming for a higher target CSF pressure.

Dr William Jordan (Birmingham, Ala). We have had some challenges at our institution with collaboration from other services. Specifically, the anesthesia team has hesitation that placing the drain may create a spinal hematoma, or epidural hematoma, leading to the neurologic problem we are trying to avoid. You have demonstrated a wonderful series where you had none, is that correct, you had no spinal drain complications in that series?

Additionally, our neurosurgeons have great concern about the intracranial pathology that might create complications, as you demonstrated. You have elucidated some of the factors that you would consider high risk. Would you then consider scanning everyone with a CT prior to placing a drain, to pick up any of these intracranial pathologies?

Dr Mell. To answer your first question, there were no spinal hematomas in our series. We are very fortunate to work in very close collaboration with anesthesiologists dedicated to optimal operative anesthetic management during these complex cases, which includes expertise in placement and monitoring of the CSF drain. This dedication has been instrumental in the success of our TAAA program.

Optimal preoperative imaging for identifying intracranial pathology is a difficult question to answer. The incidence of asymptomatic subdural hematoma in the population increases with age, although it remains quite uncommon even in elderly patients. While it is true that some patients will have unrecognized intracranial pathology at the time of surgery, we have not adopted an approach of routine preoperative imaging. Rather, we have selectively imaged patients considered to be at higher risk for intracranial pathology. These may include patients with mild dementia, a history of traumatic brain injury, alcohol abuse, and so forth.

Dr Richard Cambria (Boston, Mass). I have always been impressed at the great variability in volume of CSF drainage when you set that bag at a passive 10 cm of water. So isn't controlling the volume just a question of what pressure threshold you will accept? I think it is particularly important postoperatively.

Dr Mell. Thank you for your comments. We do not use a technique of passive drainage with a preset pop-off valve, but instead drain manually in 5-ml increments to achieve our target CSF pressure. This technique controls both the volume and rate of CSF drainage, factors we think are important to prevent bleeding. With this approach, our average drainage is much lower than that of other studies looking at CSF volume and bleeding complications. Of course, we rely on the anesthesiologists to pay strict attention to operative drain management. Additionally, the newer drain is able to more precisely regulate the CSF pressure, enabling the anesthesiologists to time the drainage so that the target CSF pressure is reached just when we are ready to cross-clamp. This ability to regulate has allowed us to minimize the amount of drainage before the cross-clamp to about 80 ml. Postoperatively, the ICU [intensive care unit] nurses have been trained to continue the manual drainage until the patient is awake with normal leg strength. These are some of the techniques that we have been able to use control the amount and rate of CSF drainage for these procedures.