|VACUUM ASSISTED VENOUS RETURN
WITH A VENOUS BAG
Department of Surgery,
North Shore University Hospital
Circulatory Technology Inc.,
|and James Beck,
The NY Presbyterian Hospital,
New York, NY
Supported in part by NIH NHLBI
A augmented venous return allows the perfusionist to use a venous line having a smaller inner diameter thereby reducing prime volume and allows the surgeon to use a smaller venous cannula resulting in easier insertion, better surgical view and a smaller surgical incision. Currently augmented venous return is achieved either by applying vacuum directly to a hard shell venous reservoir (vacuum augmented venous drainage, KAVD). The former does not allow use of a closed bag reservoir while the latter requires an additional pump. Therefore users that prefer the safety of venous bags and would like to augment venous return without using a venous pump are unable to do so or must compromise.
Vacuum can be applied to a soft shell venous reservoir by enclosing it within a rigid housing, see figure. Once the bag is sealed within the rigid structure, vacuum applied to the space surrounding the bag, is transmitted across the flexible wall of the bag to the blood. It is as if the vacuum is applied directly to the blood but without contacting it. Thus, whatever negative pressure is in the housing (Phousing), it is also the blood pressure in the bag (Pblood), Phousing »Pblood. A vacuum regulator controls the degree of vacuum of Phousing just as it is with a hard shell reservoir. The system allows the user the make the atmospheric pressure around the bag negative and the negative pressure in the bag provides vacuum assisted drainage.
The concept of sealing a venous bag within a rigid housing was described US patent # 6,017,493 entitled Vacuum Assisted Venous Drainage Reservoir for CPB Systems by Cambron R., Vijay F., Knight R., and Litzie K. was issued to Baxter. The authors suggest that the venous bag, preferably a Bentleys BMR-800 Gold or BMR-1900 Gold, and rigid housing be a single disposable unit. Such a system is inherently expensive (the housing must withstand a force of 200lb per 100mmHg housing pressure), prevents the user from reaching the bag (its sealed within the housing) and requires significantly greater storage space than the bag alone. It also dictates that the hardware for non-VAVD be different, resulting in redundancy and longer setup time. These drawbacks may be the reason for that no such unit is offered clinically.
We developed a new venous bag and a nondisposable rigid housing combination that allows vacuum assist venous drainage. The system is simple to use and fast to setup and breakdown. Confidentiality, that will be resolved once FDA clearance is issued, prevents us from disclosing the design of the new system. We do offer some results from bench tests used to evaluate its functionality.
Tests were conducted to determine the increase in venous flow with the new bag using a closed bench-top circuit primed with water. The circuit consisted of a venous line connecting the patient (i.e. a hard shell cardiotomy reservoir) via a venous cannula to the new venous bag placed in its rigid housing. A roller pump pumped the water from the outlet tube of the venous bag back to the patient. Venous bag inlet pressure housing pressure and venous flow were continuously monitored. The height difference between bottom of the cardiotomy reservoir (patient) and the top of the bag was 30". Pressure and flow readings were first collected without vacuum applied to the housing and then with various degrees of vacuum applied to the housing.
Figure below illustrates typical data collected under this study. It is clear that as greater vacuum as applied to the housing, greater flow is achieved for each of the cannulae used. There were no difference between the negative pressure applied to the housing and the pressure measured at the inlet to the venous bag. For each, a vacuum of -50mmHg applied to the housing, resulted in a 40% increase in flow as compared to venous flow without vacuum. The application of -100mmHg resulted in a flow that is 80% higher than without vacuum.
The results indicate that vacuum assisted venous drainage can be had with a soft shell venous reservoir.
Copyright © 1996,
The American Academy of Cardiovascular Perfusion,
All rights reserved.