Modified cannula

Details Modified cannula Modified cannula

1997-06-13

1999-12-07

Coggins, Wynn Wood

Surgery

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

Treating material introduced into or removed from body...

604507, A61M 500

Patent

active

059975164

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention is concerned with a modified cannula and is especially applicable to cannulae adapted for use in connecting a heart lung machine to a patient's aorta during open-heart surgery.
Cannulae are devices which connect items of hardware or drainage vessels to a patient's body. During heart surgery, for example, a patient's blood is oxygenated and circulated by an artificial heart lung machine. A surgical incision is made into the patient's aorta wherein a cannula is surgically secured such that the outlet end is directed into and along the route of the aorta.
The present invention finds application with cannulae generally, but specifically it is well suited to the modification of cannulae adapted to supply blood from a heart lung machine.
With conventional such cannulae there have been flow problems associated with the relatively high velocity of blood into the aorta. There are also concerns over the possible dislodgement of fatty tissue from the vicinity of the aorta and its potentially serious implications.
Problems can arise during aortic perfusion associated with cardiopulmonary bypass surgery. Specifically, there is concern that blood emerging at high velocity from cannulae could damage the aortic wall and/or dislodge atheromatous plaque and hence cause embolic phenomena. A secondary concern is that high velocities (and related high impact pressures) might disturb the distribution of flow to the great vessels originating from the arch.
For cannula of the heart lung machine type, there is sometimes a bend in the tubing for the surgeon's convenience whilst simultaneously permitting flow of blood along the general route of the aorta. Commercially produced cannulae, e.g. of the type 3M Sarns Healthcare `soft flow` and `D4` cannulae, incorporate such a planar bend.
A feature of both Soft Flow and D4 cannulae is a sharp planar bend near the tip. It has been found that such a bend causes skewing of the velocity profile, with high velocities at the outer wall of curvature and low velocities (and possibly flow separation and flow reversal) at the inner wall of curvature.
Accordingly, it has been considered desirable to develop a new and improved cannula which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.


SUMMARY OF THE INVENTION

In an effort to reduce the flow velocity of blood which exits from the cannula and minimise the force of impact on and around the internal surfaces of the aorta, the profile of the outlet of the cannula has been subjected to various modifications. One of these modifications is shown in FIG. 2 herein.
A consideration of the conventional design of cannulae for heart lung machines and their shortcomings has led to the development of the present invention. It has surprisingly been found that modification of the flow velocity profile in a particular way before the flow encounters the bend, reduces the severity of the impact forces on the interior of the aorta wall and helps to alleviate other difficulties associated with the design of conventional such cannulae.
Accordingly, the inventors proposed that, if there was to be modification of the cannulae with preservation of the bend, the flow should be made non-planar in type. Non-planar-type flow has been found to be characterised by swirling predominantly in one sense, strong mixing, and a relatively uniform distribution circumferentially of near-wall velocity. As a means of achieving such a flow, a twisted strip can be introduced into the cannulae, immediately upstream of the planar bend, the strip having a helical twist. Alternatively (or additionally) a swirling flow can be provided both in `soft flow` and `D4` cannulae by rendering the curvature non-planar e.g. introduce a bend in a plane different from the plane of the existing bend.
According to this invention we provide a surgical cannula comprising a generally hollow inlet portion which can receive a fluid flow and an angled outlet portion connected in fluid communication with

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