EP1251898A1

EP1251898A1 - Venous return cannula with enhanced drainage

Info

Publication number: EP1251898A1
Application number: EP00978424A
Authority: EP
Inventors: Delos M. Cosgrove; Scott H. Davis
Original assignee: Edwards Lifesciences Corp
Current assignee: Edwards Lifesciences Corp
Priority date: 1999-11-11
Filing date: 2000-11-07
Publication date: 2002-10-30
Also published as: AU1589001A; JP2009148602A; JP2003534828A; CA2391214A1; AU784413B2; CA2391214C; WO2001034237A1

Abstract

An improved venous drainage cannula having enhanced drainage for minimally invasive surgeries involving vacuum-assisted venous drainage. The cannula includes more than two discrete segments in which suction holes are provided. There may be a distal segment with suction holes and two segments spaced proximally therefrom with suction holes. The tubular cannula body terminates in a tapered tip and the distal suction segment extends proximally therefrom. Between a first proximal suction segment and a distal suction segment, the cannula is reinforced. Likewise, the cannula is reinforced between the first proximal suction segment and the next suction segment. The reinforcement may be a helical wire molded into the wall of the cannula. The proximal suction segments are designed to reside within the right atrium during venous drainage. If one of the atrial suction segments becomes occluded by contact with the atrial wall, the other atrial suction segment maintains adequate flow from the right atrium.

Description

VENOUS RETURN CANNULA WITH ENHANCED DRAINAGE

Field of the Invention The present invention relates to cannulas used in draining venous blood for surgical procedures requiring cardiopulmonary bypass. More particularly, the present invention is directed to a venous return cannula adapted for use in draining blood from the right atrium and the vena cavae with enhanced drainage for minimally invasive surgery.

Background of the Invention

It is a routine requirement of a variety of surgical procedures to utilize extracorporeal cardiopulmonary bypass in order to mechanically perform the functions normally conducted by the heart and lungs. Venous blood depleted in oxygen and rich in carbon dioxide is removed from the patient and pumped to an oxygenating apparatus in order to oxygenate the blood and remove excess carbon dioxide. The blood is then returned to the patient's arterial system.

It is exceedingly important that adequate volumes of blood be drained from the patient during cardiopulmonary bypass so that the extracorporeal life support equipment can keep up with the patient's need for oxygen and can adequately remove excess carbon dioxide. Insufficient quantities of oxygen can lead to serious tissue damage. Inadequate removal of carbon dioxide leads to a condition known as "acidosis," which can result in serious consequences caused by the alternation in normal metabolic functioning of critical enzymes. Either condition can result in serious injury to the patient.

It will be appreciated that many factors affect the ability to drain adequate volumes of blood from a patient during cardiopulmonary bypass. Two such factors are the design and placement techniques of a drainage cannula used to remove the venous blood from the patient for extracorporeal treatment. Numerous cannula designs and placement techniques have been devised and tested, and various cannula designs and cannulation techniques have been recognized as safe and effective for venous drainage during cardiopulmonary bypass.

One such technique involves placement of a pair of cannulas, one into the superior vena cava, and another into the inferior vena cava, in order to collect venous blood returned to the patient's right atrium. This technique is extremely reliable but suffers from the disadvantage that it takes time to surgically place two cannulas, and then to suture the insertion locations when the cannulas are removed following bypass. Nevertheless, because of problems experienced in connection with conventional single cannula designs discussed below, some physicians continue to utilize a two cannula technique.

A second general technique involves placement of a single cannula. Many physicians prefer a single cannula technique over a two cannula technique because only one incision is required, thereby simplifying and shortening the cannulation procedure both at the time of insertion and at the time of removal. It is also helpful to reduce the number of cannulas that a surgeon must work around as he conducts surgery on the patient.

One variation of the single cannula technique involves placement of a cannula so that its distal tip lies in the right atrium. Such a placement permits the cannula to collect blood draining into the right atrium from the inferior vena cava and from the superior vena cava. While this procedure is capable of achieving adequate venous drainage, on occasion the cannula tip is overinserted or otherwise inadvertently manipulated so that the drainage openings in the cannula are pressed against tissue within the right atrium, thereby reducing or even interrupting blood flow into the cannula. This can be extremely dangerous to the patient. Because of these dangers, only a relatively small number of physicians utilize this procedure.

A second variation of the single cannula technique is a hybrid of the two cannula and single cannula techniques described above. Thus, a single cannula is provided having drainage openings not only at the distal end, but also along its length proximal to the distal end. Such a cannula, sometimes referred to as a "dual drainage" cannula, is then inserted through the right atrium and into either the inferior vena cava or the superior vena cava, with the proximal drainage openings positioned within the right atrium. This placement permits blood to be drained simultaneously from the vena cava in which the dual drainage cannula is placed and from the right atrium.

Due to the presence of multiple drainage openings along a portion of the length of a dual drainage cannula, blood flow is less likely to become dangerously reduced when utilizing this type of cannula than when utilizing a simple single cannula. However, conventional dual drainage cannula designs still suffer from some significant disadvantages.

Commonly, conventional dual drainage cannulas have a multi-diameter structure, with a relatively small diameter distal cannula portion (e.g., 36 French) and a larger diameter proximal portion (e.g., 51 French). Such cannulas are typically constructed by forming a molded reducer having elongate slots therein, and then affixing suitable lengths of 36 French and 51 French tubing to opposite sides of the reducer. Optimally, the distal portion of the cannula is inserted only partially into one of the vena cavae so that the proximal drainage openings remain substantially centered within the right atrium. Sometimes, however, the cannula is overinserted, occasionally so much so that the proximal drainage openings are partially occluded at the entrance to the vena cava, or are actually inserted into the vena cava so that both distal and proximal drainage openings drain from the vena cava, and none drain the right atrium. This results in a substantial reduction in venous drainage.

Another common difficulty is inherent in the most common dual drainage cannula placement technique. Most often, a dual drainage cannula is used by inserting it through the right atrial appendage and then into the inferior vena cava. Since the inferior vena cava is not directly opposite the right atrial appendage, placement of a cannula using this conventional placement technique results in a bend of about 30 degrees in the distal portion of the cannula.

Normally, this causes no problems. Some surgical procedures, however, require manipulation or movement of the heart. Since the inferior vena cava is substantially anchored in place, manipulation of the heart frequently increases the angle of bend in the portion of the cannula situated at the juncture between the inferior vena cava and the right atrium. Not uncommonly the increased degree of bending causes the cannula to become kinked. This, of course, restricts or even interrupts blood drainage from the inferior vena cava, and hence reduces overall blood drainage.

Until recently, conventional bypass surgery involved gravity-assisted venous drainage. That is, the venous return cannula is positioned within the venous return side of heart, and connected with a venous reservoir that is placed below the level of the operating table. Through a siphoning action, venous blood is removed from a patient and circulated through the bypass system. Several years ago the institutional bias against using a negative pressure to assist in the venous drainage process was overcome with the successful introduction of vacuum- assisted drainage systems. Such systems typically include a hard-shelled venous reservoir to which a source of vacuum is connected, and into which the venous return cannula terminates. A negative pressure within the hard-shelled reservoir is transmitted along the venous return cannula to produce a suction at the distal tip apertures. Various benefits are realized by vacuum-assisted venous drainage, including the potential for reduced tubing and prime volume because the venous reservoir no longer needs to be positioned below the operating table to establish a pressure head. In addition, smaller cannulas can be utilized because of the active suction of the venous blood. Gravity-assisted drainage requires relatively large bore cannulas for adequate flow. The option of reducing the cannula bore size when using vacuum-assisted drainage facilitates moderate minimally invasive procedures, in which all of the components entering the heart through small passages are desirably reduced in size.

One solution to the problems of inadequate drainage and kinking is shown in USPN 4,639,252, to Kelly, et al. the entire disclosure of which is incorporated herein by reference. This patent discloses a venous return cannula having a first diameter distal portion suitable for insertion in a vena cava, a second, larger diameter proximal portion, and a transition portion forming a smooth transition between the first and second diameter portions. Drainage openings are provided in both the proximal and distal cannula portions. The cannula is also provided with wire reinforcement. Although the cannula disclosed in the Kelly patent is suitable for conventional gravity-assisted open heart surgeries in which the heart remains relatively stationary, there is a need for increased drainage during procedures in which the heart is substantially manipulated by the surgeon.

Figure 1 illustrates a venous drainage cannula 20 of the prior art positioned within the right atrium (RA) and inferior vena cava (IVC) of the heart of a patient. The cannula passes through an aperture 22 created in the right atrial appendage (RAA) that is sealed around the cannula using purse string sutures 24. For the sake of orientation, the superior vena cava (SVC) extends upward from the RA, and the main pumping chambers of the heart (the left and right ventricles, LV and RV) are located to the right of the RA, as seen from the front of the heart.

The cannula 20 extends from a proximal end 30 to a tapered distal tip 32 having a distal port 34. The body of the cannula 20 is tubular and may be of a relatively constant diameter, or may have a stepped diameter. A plurality of suction holes is provided through the wall of cannula 20 for venous drainage. More particularly, a plurality of distal suction holes 36 are provided in a segment adjacent the distal tip 32. The suction holes 36 are entirely positioned within the IVC. Additionally, a plurality of atrial suction holes 38 are grouped together in a short segment of the cannula 20 that is positioned within the RA. In one embodiment, there are eight such suction holes 38 positioned in atrium.

In between the segment of the cannula 20 having the atrial suction holes 38, and the segment having the distal suction holes 36, is a distal reinforcement segment 40. Furthermore, a proximal reinforcement segment 42 begins just proximal to the atrial suction holes 38 and extends almost to the proximal end 30. The body of the cannula 20 is made of relatively soft polymer material, and the reinforcements 40 and 42 may be provided by a helically coiled wire, preferably stainless steel, molded within the wall of the cannula. A connector portion 44 on a proximal end of the cannula provides a coupling to a venous return line extending to a venous reservoir (not shown).

The venous drainage cannula 20 is shown in operation during a vacuum- assisted procedure. The right side of the cannula 20 in the region of the distal suction holes 36 is shown in contact with the wall of the IVC at 46. Likewise, the left side of the cannula 20 in the region of the atrial suction holes 38 is shown in contact with the wall of the RA at 48. In both of these regions, the suction created by the negative pressure within the cannula 20 tends to draw the soft tissue adjacent the suction holes 36, 38 against the cannula body so that the holes are occluded. Although some of these suction holes 36, 38 remain unoccluded, the reduction in flow capacity may be detrimental to the procedure. Furthermore, the increase in pressure drop by the occlusion of a number of the suction holes 36, 38 may impact the flow rate. Moreover, the occlusion of a number of either the distal suction holes 36 or atrial suction holes 38 may preclude drainage from one of the right atrium or vena cava. An alternative technique for introducing the venous drainage cannula 20 is to enter through the IVC and extend the distal tip 32 upward into the SVC. The same problems of occlusion of the suction holes 36, 38 tend to occur, except that the distal suction holes 36 are occluded by the wall of the SVC. In both cannula introduction techniques, the occlusion of the suction holes during vacuum-assisted surgeries is more of a problem when heart is substantially manipulated. During minimally invasive procedures, the heart may need to be shifted around by the surgeon to gain access to otherwise hard to reach locations. For instance, repair or replacement of the mitral or aortic valve, or repair or bypass of the circumflex artery around the backside of heart, requires the surgeon to move the heart muscle around in order to deliver instruments and/or implants to the operating site. This manipulation of the heart may cause mis-alignment between the SVC, RA, and IVC. Mis-alignment means the cannula 20 traverses a severely curved or bent path within the RA and respective vena cava, and inevitably brings the suction holes into close proximity with the surrounding soft tissue.

Because of the drawbacks associated with prior venous return cannulas, there is a need for improved venous drainage, especially when the heart will be substantially manipulated.

Summary of the Invention The present invention comprises a kink-resistant venous return cannula having enhanced drainage for vacuum-assisted minimally invasive surgery. In one aspect of the present invention, the cannula includes an elongate, flexible tubular body having a proximal end and a distal tip. A distal drainage segment adjacent the distal tip has at least one drainage hole through the tubular body and a first axial length. A first reinforced or otherwise strengthened segment is located proximal to the distal drainage segment and has a second axial length. A first atrial suction segment with a plurality of drainage holes therein is located proximal to the first reinforced segment and has a third axial length. A second reinforced segment is located proximal to the first atrial suction segment and has a fourth axial length. A second atrial suction segment with a plurality of drainage holes therein is located proximal to the second reinforced segment and has a fifth axial length. A proximal reinforced segment is located proximal to the second atrial suction segment and may extend substantially along the rest of the cannula into proximity with the proximal end.

In another aspect, the present invention provides a venous cannula, comprising an elongate tubular body having a proximal end and a distal tip. Three discrete suction segments are formed in the tubular body each having a plurality of drainage holes therein. Preferably, at least two of the segments are located closer to the distal tip than to the proximal end of the tubular body. Furthermore, the lengths of the two reinforced segments relative to lengths of said discrete suction segments and the number and size of the drainage holes are sufficient to avoid kinking of the cannula. There are at least two reinforced segments along the tubular body extending intermediate the three suction segments. Each of the reinforced segments has an axial length that is preferably equal or longer than each of two of the suction segments.

In a preferred embodiment, an insertion indicator line is provided on the tubular body proximal to the proximally-most located suction segment, wherein an insertion length is defined between the distal tip and the indicator line. The three suction segments desirably comprise a distal segment adjacent the distal tip and first and second atrial suction segments located in series proximally with respect to the distal segment. The first atrial suction segment desirably commences at a point that is about 30-50% (preferably between 38-46%) of the insertion length from the distal tip. Further, the second atrial suction segment may be spaced from the first atrial suction segment a distance between about 10-20% (preferably between 14- 17%) of the insertion length. A further understanding of the nature advantages of the invention will become apparent by reference to the remaining portions of the specification and drawings.

Brief Description of the Drawings Figure 1 is a perspective cutaway view of the heart of a patient showing a venous return cannula of the prior art positioned for venous drainage within the right atrium and inferior vena cava;

Figure 2 is a perspective cutaway view of the heart of a patient showing an exemplary venous return cannula of the present invention positioned for venous drainage within the right atrium and inferior vena cava and illustrating the enhanced drainage capabilities of the cannula;

Figure 3 is a perspective cutaway view of the heart of a patient showing an exemplary venous return cannula of the present invention positioned for venous drainage within the right atrium and inferior vena cava and further illustrating the enhanced drainage capabilities of the cannula;

Figure 4A is a plan view of one embodiment of a venous return cannula of the present invention; and

Figure 4B is an elevational view of the venous return cannula of Figure 4A.

Description of the Prefeπed Embodiments

Figures 2 and 3 illustrate a cannula 50 of the present invention positioned within the right atrium (RA) and inferior vena cava (IVC). The cannula 50 is shown in more detail in Figures 4A and 4B and includes a tubular cannula body that extends from a proximal end 52 to a tapered distal tip 54 having a distal aperture 56. In contrast to the cannula 20 seen in Figure 1, the cannula 50 of the present invention includes two discrete segments 58a and 58b having atrial suction holes 60a and 60b in addition to the distal segment 62 having distal suction aperture 56, and preferably a plurality of distal suction holes 64. A first reinforcement segment 66 extends between the distal segment 62 and the first atrial suction segment 58a, a second reinforcement segment 68 extends between the first and second atrial suction segments 58a, 58b, and a proximal, elongated reinforcement segment 70 may extend from the second atrial suction segment 58b at least and up to a proximal connector portion 72.

Preferably, the first reinforcement segment 66 extends at least up to the end of the length of the cannula that is inserted in the body vessel, however, it may extend substantially along the rest of the cannula into proximity with its proximal end. The three reinforcement segments 66, 68, 70 are dimensioned such that two of them are preferably longer than the two suction segments 58a, 58b.

As with the prior art, the reinforcement segments 66, 68, and 70, are desirably formed by molding a helically coiled stainless steel wire in the body of the cannula 50. Of course, other means for reinforcing or strengthening the cannula body between the segments having suction holes are possible, including, but not limited to, segments with thicker walls, different materials, molded ribs, attached ribs, embedded fibers, mat or rings, or other suitable expedients.

The cannula 50 further includes one or more indicator lines for gauging the depth of insertion of the cannula. Specifically, as seen in Figure 4A, the cannula 50 may include a single proximal indicator line 80 spaced proximally from the second atrial suction segment 58b. Additionally, a pair of distal indicator lines 82 are spaced proximally from the indicator line 80.

Figures 2 and 3 illustrate the cannula 50 inserted through an aperture 90 formed in the right atrial appendage (RAA) and secured therein using purse string sutures 92. The cannula 50 is inserted into the right atrium (RA) so that the distal segment 62 having the distal suction holes 64 is located within the inferior vena cava (IVC). Both the first and second proximal suction segments 58a and 58b are located within the RA.

This positioning of the cannula is insured by the surgeon by advancing the cannula until the aperture 90 is between the distal indicator line 80 and the proximal indicator lines 82. The axial spacing of the distal tip and suction holes of the cannula 50 relative to the indicator lines 80, 82 is designed to position the cannula in most adult patients as illustrated in Figure 2. Of course, if the patient is small in stature, or is an infant or neonate, a different relative axial spacing can be used. Desirably, the surgeon can select from an array of sizes or cannulas 50 with different relative axial spacing, all of which are generally proportional to the spacing shown and described herein.

With both the first and second suction segments 58a and 58b positioned within the RA, there is less chance of occlusion of any of the suction holes 60a or 60b. That is, the spacing between the suction segments 58a, 58b helps prevent simultaneous occlusion of the holes 60a and 60b. Therefore, Figure 2 shows the first suction segment 58a against the left wall of the RAA, such as might occur when a vacuum is drawn through the cannula 50 and the heart is manipulated, thus occluding some of the suction holes 60a. At the same time, the second suction segment 58b is shown distanced from the suπounding tissue walls so that all of the suction holes 60b are open and available for draining blood. Conversely, as seen in Figure 3, the first suction segment 58a is shown in the middle of the RA, and not in contact with the suπounding tissue walls so that all of the suction holes 60a are open. At the same time, the second suction segment 58b is shown in contact with the left wall of the RA so that some of the suction holes 60b are occluded.

Of course, in use, both of the suction segments 58a and 58b may be out of contact with the suπounding tissue walls so that all of the suction holes 60a, 60b remain open. The illustrations in Figures 2 and 3 are believed to represent the worst-case scenario with the cannula 50 of the present invention. This performance has been verified by numerous clinical trials.

For optimum performance of the cannula 50, the lengths of the respective suction and reinforcement segments are preferably as seen in the exemplary embodiment of Figures 4A and 4B. It should be emphasized, however, that these dimensions and/or proportions are exemplary only, and should not limit the claims. Essentially, the cannula 50 of the present invention better hole distribution and less chance of occlusion than the prior art without creating a structure that would be prone to kinking. That is, there is a balance between improved suction performance and kink-resistance provided by exemplary embodiments of the present invention.

For example, in the embodiment of Figure 4a, the distal suction segment 62 desirably extends from the distal tip 54 a distance A of about 1.75 inches. The first reinforcement segment 66 extends an axial distance B of about 1.25 inches. The first and second atrial suction segments 58a and 58b may extend similar distances C and C of about 1.15 inches. The second reinforcement segment 68 has an axial length D of about 1.15 inches. The distance E between the second atrial suction segment 58b and proximal indicator line 80 is about 1.18 inches. The distance F from the distal tip 54 to the proximal indicator line 80 is about 6.53 inches, while the distance G from the distal tip 54 to the distal indicator lines 82 is about 8.0 inches.

As mentioned above, these dimensions may differ based on the estimated size of the patient's heart, though the proportions will desirably remain approximately the same. That is, the distance B between the distal suction segment 62 and the first atrial suction segment 58a is less than, and preferably about 70% of, the length A of the distal suction segment. Additionally, the lengths C and C of both the first and second atrial suction segments 58a, 58b may be different, but are preferably equal, and are both less than length A (and preferably less than about 50% of length A). The spacing D between the first and second atrial suction segments 58a, 58b is desirably less than distance B, and preferably about 92 percent of distance B. The distance from the second atrial suction segment 58b to the proximal indicator line 80 is desirably about the same as spacing D, and more preferably slightly greater than spacing D. Viewed another way, the length F from the distal tip 54 to the proximal indicator line 80 is the minimum extent of the cannula 50 inserted into the heart, and the length G is the maximum extent of the cannula inserted in the heart. Along this range of inserted cannula length, the distal segment 62 makes up between 20- 30% (preferably between 22-27%), the first reinforcement portion 66 makes up between 15-20% (preferably between 16-19%), the first and second atrial suction segments 58a, 58b each make up between 5-10% (preferably between 7-9%), and the second reinforcement portion 68 makes up between 15-20% (preferably between 14-17%).

Additionally, the first atrial suction segment 58a preferably commences at a point about 30-50% (more preferably about 38-46%) along the length of the inserted portion (length range F to G) from the distal tip 54, and the second atrial suction segment 58b preferably commences at a point about 55-75% (more preferably about 59-73%) along the inserted portion from the distal tip 54. Finally, the discrete first and second atrial suction segments 58a and 58b are desirably spaced apart between about 10-20% (more preferably about 14-18%) of the length of the inserted portion (length range F to G) of the cannula 50, or between about 0.9 and 2.0 inches. To emphasize once again, the aforementioned dimensional relationships provide an optimum spacing between the discrete segments of suction holes, while also providing rigidity to the cannula 50 to prevent kinking. That is, between each of the segments having suction holes the cannula 50 is reinforced with, for example, a helically wound wire. Although more segments having suction holes may be provided, there is an attendant increased tendency of the cannula body to kink in the un-reinforced suction segments. Therefore, the aforementioned placement and length of suction segments is believed to provide an optimum compromise between adequate drainage and strength.

The particular number and size of the various suction holes is also significant to ensure adequate drainage through the cannula 50. Of course, the hole size, spacing, and configuration may depend on the cannula bore, which in the exemplary embodiment is about 0.38 inches. In a prefeπed embodiment, more suction holes 64 are provided in the distal suction segment 62, than in either of the first or second atrial suction segments 58a or 58b. As illustrated, there are six circular suction holes, and two oval-shaped suction holes to complement the distal aperture 56 in the distal suction segment 62. The circular holes preferably have a diameter of about 0.15 inches, and oval-shaped holes have a minor dimension of 0.13 inches and a major dimension of 0.38 inches. In all of the suction segments, the holes are distributed circumferentially around the tubular body to minimize the proportion of holes occluded at any one time.

In the exemplary embodiment, there are six suction holes 60a, 60b for each of the atrial suction segments 58a and 58b. The suction holes 60a, 60b preferably have a diameter of about 0.15 inches. Of course, more or less holes may be provided in any of the suction segments, and the size of each may be modified according to the drainage requirements. Importantly, enough holes of sufficient size must be provided in each of the suction segments to accommodate adequate venous flow in case one or the other of the suction segments is in contact with tissue so that some of the suction holes are occluded. On the other hand, there is a practical maximum number of suction holes 60a, 60b beyond which the cannula 50 would be unduly prone to kinking in its expected use, such as in minimally invasive surgery where the cannula may be severely manipulated and bending stresses will be experienced. The present invention contemplates several ways to quantify this balance between an increased number of holes/segments and a sufficient strength. For example, the number of holes per inch of cannula could be used. Alternatively, the number of holes per suction segment, and the maximum number of segments could be specified. Or, the total area of the suction holes in relation to the cannula length affected could be set. Finally, a chart of flow rates against different suction pressures (assuming no obstruction to flow) could be provided and optimized with the bending strength of the cannula. Those of skill in the art will therefore recognize that there are a number of ways to determine the practical maximum number of suction holes that can be effectively used, and the present invention is intended to cover the various formulations. For instance, a cannula as described herein having the particular diameter, suction hole size, segment size and placement, and reinforcement segment size and placement may have more than the six (6) suction holes per suction segment as illustrated. One example is to provide eight (8) suction holes per suction segment, assuming all other parameters remain the same. Therefore, the number of holes per inch of cannula, the number of holes per segment using only two segments, and the total area of the suction holes relative to the affected cannula length can be calculated from the exemplary specifications given above. Likewise, the actual flow rates at different suction pressures could be determined using conventional measurement techniques and coπelated with cannulas of different bending strengths. Therefore, those of skill in the art will realize that the flow rate can be maximized for any particular cannula while retaining kink-resistance within predetermined bending stress limits, which limits can be empirically determined with strain gauges and the like in the surgical field, or in training mock-ups of the heart. While the foregoing is a complete description of the prefeπed embodiments of the invention, various alternatives, modifications, and equivalents may be used. For example, a different type of reinforcement may be used, or the number, size and/or shape of the various suction holes may be modified. Moreover, it will be obvious that certain other modifications may be practiced within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A kink-resistant venous return cannula having enhanced drainage, comprising: an elongate, flexible tubular body having a proximal end and a distal 5 tip; a distal drainage segment adjacent the distal tip having at least one drainage hole through the tubular body; a first reinforced segment located proximal to the distal drainage segment; o a first atrial suction segment with a plurality of drainage holes therein and located proximal to the first reinforced segment; a second reinforced segment located proximal to the first atrial suction segment; a second atrial suction segment with a plurality of drainage holes 5 therein and located proximal to the second reinforced segment; and a proximal reinforced segment located proximal to the second atrial suction segment.

2. The cannula of claim 1 , wherein the tubular body is made of a polymer material, and the reinforced segments comprise helical metallic members 0 embedded in the tubular body.

3. The cannula of claim 1 , wherein an insertion length along the cannula is defined between the distal tip and a location proximal to the second atrial suction segment, the cannula being designed to be inserted into a body cavity at least up to the insertion length. 5

4. The cannula of claim 3, wherein the first and second atrial suction segments each have an axial length that is between 7-9% of the insertion length.

5. The cannula of claim 3, wherein the first atrial suction segment commences at a point that is about 30-50% of the insertion length from the distal tip. 0

6. The cannula of claim 5, wherein the second atrial suction segment is spaced from the first atrial suction segment a distance between about 10-20% of the insertion length.

7. The cannula of claim 3, wherein the second atrial suction segment commences at a point that is about 55-75% of the insertion length from the distal tip.

8. The cannula of claim 3, wherein the distal drainage segment has a first axial length between about 20-30% of the insertion length, and the first and the second atrial suction segments have third and fifth axial lengths coπespondingly which are less than the first axial length.

9. The cannula of claim 3, wherein the insertion length is between about 6.5 and 8.0 inches and the proximal reinforced segment extends at least to the end of the insertion length.

10. The cannula of claim 3, further including an insertion indicator line provided on the tubular body proximal to the second atrial suction segment wherein the insertion length is defined between the distal tip and the indicator line.

11. The cannula of claim 1 , wherein the first and second reinforced segments have a second and a fourth axial lengths coπespondingly and both the second and fourth axial lengths are greater than either of the third and fifth axial lengths.

12. The cannula of claim 1 , wherein the first atrial suction segment is approximately the same length as the second atrial suction segment.

13. A venous cannula, comprising: an elongate tubular body having a proximal end and a distal tip; three discrete suction segments formed in the tubular body each having a plurality of drainage holes therein, at least two of the suction segments being located closer to the distal tip than to the proximal end of the tubular body; and at least two reinforced segments along the tubular body extending intermediate the three suction segments wherein the lengths of the two reinforced segments relative to lengths of said discrete suction segments and the number and size of the drainage holes are sufficient to avoid kinking of the cannula.

14. The cannula of claim 13 wherein there are three discrete reinforced segments located proximal to the distally-most located suction segment.

15. The cannula of claim 13, further including an insertion indicator line provided on the tubular body proximal to the proximally-most located suction segment, wherein an insertion length is defined between the distal tip and the indicator line.

16. The cannula of claim 15, wherein the three suction segments comprise a distal segment adjacent the distal tip and first and second atrial suction segments located in series proximally with respect to the distal segment.

17. The cannula of claim 16, wherein the first atrial suction segment commences at a point that is about 30-50% of the insertion length from the distal tip.

18. The cannula of claim 17, wherein the second atrial suction segment is spaced from the first atrial suction segment a distance between about 10-20% of the insertion length.

19. The cannula of claim 16, wherein the second atrial suction segment commences at a point that is about 55-75% of the insertion length from the distal tip.

20. The cannula of claim 16, wherein the two atrial suction segments each has an axial length that is between 5-10% of the insertion length.

21. The cannula of claim 13, wherein said two reinforced segments are longer than the two of said three suction segments that are located closer to the proximal end of the cannula.

22. The cannula of claim 13, wherein three suction segments each include at least six holes distributed circumferentially around the tubular body, and the reinforced segments include a helical wire embedded in the tubular body.