Assuring safer surgeries--
catheter removes dangerous air
The possibility of potentially deadly air bubbles forming in the veins is probably not high on a surgical candidateís list of concerns. And when a special catheter invented by scientists in the Health Science Centerís anesthesiology department is used during the procedure, that worry can continue to be absent from the list.
We take for granted that under normal circumstances the air we breathe will enter our systems through the respiratory tract, that oxygen will be extracted, and that nitrogen and carbon dioxide will be exhaled through the lungs. However, if air enters the circulation through an open blood vessel or because of an infection, the bubbles form air emboli.
Air bubbles in the veins, called venous air emboli, have been described since the 17th century when Francisco Redi produced death in an animal by blowing air into one of its neck veins. Since that time, many physicians and scientists have discussed the diagnosis, prevention and treatment of air emboli, which can cause fatal complications.
Leonid Bunegin, BS, assistant professor of anesthesiology, and Maurice S. Albin, MD, clinical professor of anesthesiology, are modern pioneers in the study of how air emboli affect the body. In 1974, these two scientist-inventors began working on a life-saving catheter capable of removing dangerous air emboli during surgery. They completed the project in 1980.
"When a surgical procedure requires the patient to be in a position where the heart lies below the level of the operated site, such as in some neurosurgical, urological or obstetrical cases, a relatively high negative pressure develops," Dr. Albin said. "Air could then enter the circulatory system by a suction effect and substantial amounts of air in the circulation may form large bubbles that, due to surface tension, impede the return of blood flow to the heart, causing an airlock.
"Hypotension (low blood pressure) and cardiac arrhythmias (irregular heartbeats) may develop, leading to cardiac arrest," Dr. Albin continued, "or air that has entered the right heart chamber may enter the left heart chamber and then the brain, the coronary sinuses, the ascending and descending aorta and the arterial tree."
In order to detect these emboli, an ultrasonic Doppler probe is placed on the chest over the heart area. A metallic chirping sound is emitted when even the tiniest air bubble passes through the ultrasonic field.
Bunegin and Dr. Albin also have carried out pioneering work using similar Doppler technology to track the passage of air bubbles into the brain during and following open heart surgery. They embarked on a series of studies to find the optimal method of withdrawing air bubbles from the heart, using a special plastic catheter. The two scientists first developed a heart model that was indistinguishable from the human heart in terms of size, pumping functions and pressures in the chambers. Once their model was perfected, the inventors injected air into the model heart and tested aspiration percentages with different catheters while the heart was placed at different positions.
"Our technique isnít new," Bunegin said. "We adapted a tool that has been mentioned in medical literature since the early 1800s. We took a catheter with a single opening and after many years and much testing, we found that a catheter with multiple orifices gave the best results."
"Our catheter is threaded through a vein into the heart," Dr. Albin explained, "and can be used to suction out the air and also to measure venous blood pressure."
"When an embolus is detected by the ultrasonic Doppler monitor, the catheter is aspirated and the air is removed," Bunegin added.
The ability of the Bunegin-Albin catheter to remove embolic air from the heart has been confirmed by work from other laboratories and has been used in tens of thousands of clinical cases. The universal application of this multi-orificed air aspiration catheter was noted during a visit by Dr. Albin to a small Japanese hospital where neurosurgery was to be performed.
"Our translator was not present in the operating room, and I didnít understand what the Japanese anesthesiologist was trying to tell me," Dr. Albin recounted. "Finally our Japanese colleague put on a pair of sterile gloves and, all smiles, went to a sterile table, pulled out our multi-orificed catheter and excitedly waved it in the air."
"This catheter was developed in the neuroanesthesia laboratories of the department of anesthesiology at the Health Science Center," Bunegin and Dr. Albin commented. "We are proud of that, but we are even prouder that it has helped make surgery and anesthesia safer for patients everywhere."
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