DURHAM, N.C. -- Duke anesthesiologists have found that a "Doppler" technique of using reflected sound waves to measure the heart's pumping action can better guide the administration of fluids and plasma during major surgery. They have found that the use of Doppler technology appears to reduce hospital stays and to speed patient recovery.
Additionally, according to Duke University Medical Center researchers, these patients experience less postoperative nausea and vomiting and are able to eat solid foods much earlier. The researchers say that by not allowing fluid levels to drop below normal -- which is common during surgery -- the proper functioning of the intestines are maintained and recovery is improved.
Typically, fluids such as blood, plasma or synthetic agents known as plasma expanders are administered to patients during surgery to compensate for blood loss and to maintain blood pressure. Physicians add these fluids in response to changes in blood pressure, urine output or heart rate. Instead of this reactive approach, the Duke researchers proactively used an esophageal Doppler monitor (EDM) to obtain continuous readings of cardiac output.
Use of the EDM involves placing a small ultrasound probe down the esophagus to a location adjacent to the aorta, the main artery out of the heart. By measuring the reflection of sound waves directed into the aorta, the EDM is able to measure and calculate the volumes of blood being pumped out of the heart and to the body. Such measures give the anesthesiologist a direct indication of how much fluid needs to be administered.
"The traditional reactive indicators do not always accurately reflect the status of fluids, since the changes we see tend to occur later than the actual fluid loss," said anesthesiologist Tong Joo (TJ) Gan, M.D., the lead author of the study appearing today (Oct. 2) in the October 2002 issue of the journal Anesthesiology.
"With the Doppler technology, we get continuous, real-time measurements, which allows us to maintain a patient's fluid levels at a more constant and natural state," Gan continued. "This study shows that by keeping the fluid levels from dropping, patients will recover faster and leave the hospital sooner."
Patients whose care was guided by EDM were discharged six days after surgery, compared to seven days for the control group who received conventional care, the researchers found. In terms of eating, the EDM group began tolerating solid foods three days after surgery, compared to five days for the control group. More than twice the number of patients in the control group experienced severe postoperative nausea and vomiting.
For his study, Gan enrolled 100 patients who were to undergo major non-cardiac surgeries of the prostate, colon, bladder, pancreas and liver as well as major gynecologic procedures. In these surgeries, physicians anticipated blood losses of at least 500 ml. Fifty patients had their fluid levels guided by EDM, while the other 50 received standard care.
For the EDM group, the researchers determined the optimal fluid levels for each individual patient based on such characteristics as age, height, weight and heart function. The researchers would then administer the appropriate fluids during the surgery to maintain the specific goal.
"While we traditionally monitor the heart, kidneys and brain during surgery to make sure they are getting proper blood supply, it is actually the gut that is the first to be impacted when there is a decline in blood supply," Gan explained. "In times of declining blood supply, the body redirects blood to the organs that are most susceptible to ischemia -- like the brain -- and away from less important organs, like the intestines."
However, this natural redirection of blood comes at a cost to the intestines. During these periods of low fluid volumes -- a state known as hypovolemia -- the intestines tend to "go to sleep," according to Gan. It can takes days for normal function to return, leaving patients susceptible to nausea and vomiting, as well as the inability to tolerate solid food.
"When the gut is stressed by lack of perfusion, it is also hypothesized that the bacteria that normally inhabit the gut can enter the bloodstream, which can lead to a host of additional problems, including sepsis, which tend to prolong hospital stays and can cause death," Gan said.
According to Gan, EDM technology is easy to use, and actually takes less time and discomfort to insert than traditional methods, which includes inserting a catheter into the aorta or pulmonary artery to take similar measurements.
"This study also confirms that the routinely measured standard cardiovascular variables such as blood pressure, heart rate and oxygen saturation were unreliable indicators of mild hypovolemia," Gan said.
The issue of maintaining proper fluid volumes is an area in need of more research because of its prevalence and its effects on recovery after surgery, Gan said.
"Many patients are already in a state of hypovolemia even before they get to the operating room, since it is common practice not to eat or drink anything from six to eight hours before surgery," Gan said. "Additionally, anesthetic agents can cause dehydration and there is the loss of blood during surgery."
The study was supported by Duke's department of anesthesiology and Deltex Medical Inc., Irving, Texas, one of a number of companies involved in EDM technology. Gan has no financial interest in Deltex
Members of Gan's team, from Duke, include Andrew Soppitt, M.D., Mohamed Maroof, M.D., Habib El-Moalem, Ph.D., Kerri Robertson, M.D., Eugene Moretti, M.D., and Peter Dwane, M.D. Peter Glass, M.D., University Medical Center at Stony Brook, New York, also participated.