System for collection of blood without damage

Details System for collection of blood without damage System for collection of blood without damage

2002-01-09

2003-12-16

Lo, Weilun (Department: 3761)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C604S004010, C604S119000, C604S323000, C604S902000, C600S378000, C600S379000, C417S038000

Reexamination Certificate

active

06663586

ABSTRACT:

TECHNICAL FIELD
This invention relates to the art of systems for recovery of physiological fluids, such as blood. In the preferred embodiment, the invention relates to a system for collection of blood during surgery and for returning the collected blood to the patient.
BACKGROUND
Systems for collection of blood during surgery for the purpose of returning the blood to the patient are known. These systems typically are vacuum systems that rely on sources of low pressure existing in the hospitals to create the suction required for collecting the blood. The collected blood may be washed by any of several known cell washing devices prior to providing the collected blood back to the patient.
Because blood cells are very fragile, they are frequently damaged during the collection process, which makes them unavailable for return to the patient. For example, cells will be damaged if subjected to excessive physical contact, such as turbulence or compression. For example, collection systems that use roller pumps cause excessive physical damage. Similarly cells subjected to pressure differentials that are too great will be damaged. Thus, blood cells subjected during vacuuming operations to exterior pressures that are too low will burst and not be available for return to the patient.
Although the use of vacuum is well known in the art, conventional systems use high vacuum (in excess of 250 mmHg), which is throttled by simple mechanical regulators. These systems do not employ a “feed-back loop” or other sensing circuits to monitor vacuum parameters. Such systems are not optimal for collecting shed blood and are known to cause significant damage to collected red cells.
Mechanically regulating vacuum to −100-150 mmHg(dead end) can reduce the red cell damage greatly, but significant red cell damage occurs nevertheless and the problem is compounded by lack of understanding by the user of correct adjustment technique.
Systems that rely on the source of vacuum pressure typically used in hospitals frequently subject the cells to very low pressures, which severely damages the cells. Standard surgical suckers have an opening at the tip of about 0.125 to 0.150 inch, and the standard surgical suction tubing is usually 0.25 inch, (inside diameter), but may be as large as 0.281 inch (inside diameter). The connections between these components or to a standard collection chamber may incorporate substantial changes in diameter and possibly have reduced diameters at the connection points. The vacuum levels for suction collection of shed blood for return to a patient are recommended in the prior art (Autotransfusion Standards, American Association of Blood Banks) to be in the range of from −100 mmHg to −150 mmHg. This standard assumes the use of the above standard sucker and suction tubing.
Thus, there is a need for methods and apparatus that rapidly collect shed blood in surgery and trauma and do not damage the blood during collection. A need also exists for systems that safely collect shed blood that has formed into small, shallow pools in the surgical site, a process known as “skimming.” A further need exists for a suction (vacuum) system that does not exert large pressures on tissues in the surgical area while the blood is collected. Such systems are known as atraumatic systems.
Although portable suction devices for various application are known in the art, there has never been a blood collection system with all parameters optimized which can collect blood at high flow rates, allow skimming, and not subject cells and tissues to trauma.
SUMMARY OF THE INVENTION
In accordance with the invention a portable, electrically-powered blood collection system collects blood substantially without damage to the blood cells. The collected fluids are filtered and placed in a flexible bag to facilitate their return to the patient. The system is self-contained and requires only external electric power in one version and no external power in a second version. Minimal damage to the collected blood is obtained by optimization of the physical characteristics of the system. Further, the system conditions the collected blood and maintains it in a safe condition until a volume has been collected that is sufficient to warrant returning the blood to the patient. The system immediately and effectively packages the collected blood for convenient return to the patient by conventional IV administration techniques.
The blood collection system of the invention uses an electronically-controlled pump to create a low pressure flow of air to aspirate shed blood. An electronic circuit increases and decreases the vacuum parameters, such as pressure and flow rate, according to need, by sensing no load, low load and high load situations. Under a no load condition, e.g., air flow only, and a low load condition, e.g., surface suctioning air mixed with mostly foam, the system maintains a very low vacuum of about 20 mmHg and a correspondingly small rate of air flow. Under high load conditions, e.g., where the tip of the aspiration tool is immersed in a pool of blood or is occluded, the system instantaneously increases the vacuum to about −100 mmHg. Because the flow in the high load condition is almost all liquid, the flow velocity through the aspiration path is low (Poiselle-Hagen Law). In this system, the blood being collected is never exposed to the high vacuum or velocity that would damage the cells, and laboratory testing using these control parameters has shown insignificant levels of blood damage.
The collection/suction tube of the invention preferably has a thin wall, whereby it is lightweight and easy to use. Because the vacuum level is controlled and small, however, there is little danger that the tube wall will collapse when the tip is occluded.
The system of the invention preferably includes a large-bore sucker, the opening at the tip having a diameter of between 0.285 and 0.500 inch. The bore of the sucker continues unreduced to its connection with the suction tubing, which has a nearly equal diameter, and the two components are connected by a coupler that provides an unrestricted, smooth transition between them. The large bore sucker and tubing are connected to a collection chamber equipped with an equally large bore fitting. A suitable coupler is employed to allow an unrestricted and smooth transition between the tubing and chamber fitting.
The sucker assembly described above is connected to a vacuum source capable of regulating the vacuum at very low levels. The preferred embodiment of the system regulates the vacuum between −10 mmHg and −100 mmHg. The particular level of the vacuum is based on the demand and is governed by feedback through the sucker, tubing and collection chamber to the vacuum source. The pressure differential across a mechanical resistor in the vacuum line is sensed by pressure transducers and resulting signals are fed to a suitable electronic regulating source, which, in turn, operates the vacuum source in a pulsed mode, alternating between on and off conditions as required to maintain the desired vacuum for the particular demand condition.
With an open suction line (carrying no liquid) the resistance across the mechanical resistor is minimal and the vacuum is reduced to the minimum level. During skimming, there is increased resistance through the tubing and across the mechanical resistor, so the vacuum is slightly increased. With the collection of some pooled liquid there will be further resistance, so the vacuum level will further increase proportionately. With full immersion of the sucker tip in liquid, the vacuum resistance through the system will be at a maximum level, and the vacuum will then be controlled to be the largest level of −100 mmHg.
A general observation of fluid mechanics is that the rate of fluid flow through a tube is a function of the 4
th
power of the radius of the tube. Thus, a slight increase in the internal diameter of a tube results in a significant increase in the flow rate, all other conditions being equal. Recognizing this relationship, the

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