Reflux resistant cannula and system for chronic delivery of therapeutic agents using convection-enhanced delivery

1. A reflux-resistant cannula for chronic convection-enhanced delivery of substances to the brain; the cannula comprising:

a tubular body having a proximal end and a distal end and having a central lumen between said proximal and distal ends, wherein the proximal portion of said tubular body is non-rigid; and

an infusion tube positioned in said central lumen and extending beyond said proximal and distal ends of said tubular body, wherein the portion of said infusion tube extending beyond said distal end of said tubular body forms a rigid delivery tip of fixed length and having a smaller diameter than the distal end of said tubular body, and wherein the portion of said infusion tube extending beyond said proximal end of said tubular body is non-rigid;

wherein during convection-enhanced delivery of substances into tissue in the brain said cannula shows no backflow beyond said delivery tip at flow rates up to 10 μl/min.

2. A cannula as recited in claim 1 , wherein the distal end of said infusion tube is fused silica.

3. A system for reflux-resistant chronic convection-enhanced delivery of substances to the brain, comprising:

a cannula according to claim 1 ; and

a tubular delivery sheath having an outer surface, a proximal end and a distal end;

said delivery sheath having a central lumen extending from said distal end toward said proximal end;

said delivery sheath having a longitudinal passageway which communicates between said central lumen and said outer surface wherein said delivery sheath includes a plurality of opening adjacent said passageway configured for receiving sutures;

wherein said passageway is configured for insertion of said cannula into said delivery sheath and through said central lumen.

4. A system as recited in claim 3 , wherein the distal end of the infusion tube is fused silica.

5. A system as recited in claim 3 , wherein at least a portion of said delivery sheath is non-rigid.

6. A system as recited in claim 3 , wherein said tubular body has a substantially uniform inner diameter of approximately 0.33 mm.

7. The system as recited in claim 3 , wherein said rigid delivery tip is approximately 1 mm to 10 mm in length.

8. The cannula of claim 1 , wherein the inner diameter of said tubular body approximately matches the outer diameter of said delivery tip.

9. The cannula of claim 1 , wherein said delivery tip is decreased in diameter from 0.31 to 1.77 mm relative to said tubular body.

10. The cannula of claim 1 , wherein said delivery tip is decreased in diameter approximately 0.31 mm relative to said tubular body.

11. The cannula of claim 1 , wherein the outer diameter of said tubular body is non-uniform and decreases from the proximal end to the distal end.

12. The cannula as recited in claim 11 , wherein said tubular body comprises a first segment having a length of approximately 40 mm and an outer diameter of approximately 5 mm, a second segment having a length of approximately 124 mm and an outer diameter of approximately 2.1 mm, and a third segment having a length of approximately 10 mm and an outer diameter of approximately 0.64 mm; and

wherein said infusion tube extends beyond said third segment by approximately 10 mm to form said delivery tip and has an outer diameter of approximately 0.33 mm.

13. The cannula as recited in claim 1 , further comprising a tubing fabricated from a flexible biocompatible material coupled to the proximal end of said tubular body.

14. The cannula as recited in claim 1 , wherein said rigid delivery tip is approximately 1 mm to 10 mm in length.