DOPPLER 'RADAR' KEEPS BLOOD FLOWING AT ITS BEST DURING SURGERY
T. J. Gan, M.D. ASA ANNUAL MEETING
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DALLAS -- The same technology metereologists use to predict the weather could help anesthesiologists predict potentially hazardous conditions during major surgery.
Doppler radar uses ultrasound to map changes in radio frequencies and track the direction and speed of winds. The same ultrasound technique can now help anesthesiologists track changes in a patient's cardiac output and fluid volume -- critical indicators of how well the heart is transporting blood and oxygen to the organs during surgery, T.J. Gan, M.D., reported at the American Society of Anesthesiologists annual meeting.
Blood carries oxygen throughout the body, but anesthesiologists often must administer other fluids during surgery to aid this process. "The anesthesiologist's careful monitoring and management of fluid volume during surgery helps patients recover quicker and with fewer complications," Dr. Gan said.
Cardiac output -- the amount of blood pumped by the heart with each beat multiplied by the number of beats per minute -- offers a reliable but indirect measure of the amount of fluid in the cardiovascular system. Fluid volume is important because too much or too little can lead to organ failure, shock and death.
Current methods of monitoring cardiac output and fluid volume, however, require anesthesiologists to insert a catheter (tube) in a vein. This invasive and highly technical procedure poses some risks and requires anesthesiologists to periodically administer a small amount of fluid to measure cardiac output each time they need a new reading.
Researchers at Duke University substituted the catheter with a flexible, pencil-sized Doppler ultrasound probe. After the patient is unconscious, the probe is placed in the esophagus near the heart. It then provides displays of cardiac output and fluid volume in continuous numerical values and tracings on a monitor.
"The probe makes it easier to know when and how much fluid is needed because it provides continuous feedback," Dr. Gan said. "It also offers an attractive alternative to catheterization because it is less invasive."
In a study of 100 patients having major surgery, 50 had surgery with the Doppler probe and 50 in a "control" group had surgery with routine monitoring.
The patients in the probe group went home an average of two days earlier than the control group. The probe patients stayed in the hospital an average of five days, while the control group stayed an average of seven, Dr. Gan said.
The study also revealed a two-day difference between the two groups in their ability to tolerate solid food, which is a key factor in determining length of hospital stay. Patients in the probe group began eating solids within three days, while the control group began in five, Dr. Gan said.
These differences occurred regardless of the type of surgery. "By managing fluid optimally during surgery, we've shown it is possible to reduce length of hospital stay -- a difference that translates into considerable cost savings," Dr. Gan said.
Although the Doppler ultrasound probe has been used in the United Kingdom for patients undergoing hip replacement and cardiac surgery, this was the first study of the probe's effectiveness in the United States. The researchers at Duke University plan to study its usefulness for other types of surgery.
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