Catheter and manufacturing method of catheter

A method of using a catheter, the method comprising:

• providing the catheter, which comprises:
• a catheter body defining:
• a first catheter portion defining a first lumen communicating with a first distal opening, and
• a second catheter portion defining a second lumen communicating with a second distal opening,
• wherein the second distal opening positioned proximal of the first distal opening,
• wherein a flow path cross-sectional area of the first lumen in at least a part of a distal region of the catheter body that is distal of the second distal opening is larger than a flow path cross-sectional area of the first lumen in a proximal region of the catheter body that is proximal of the second distal opening,
• wherein the catheter body includes a tubular body having an outer circumferential surface that is recessed radially inward to form a groove portion, and
• wherein a first part of the groove portion is covered by a covering member and a second part of the groove portion is exposed from the covering member to form the second distal opening;
• and
• positioning the catheter in a blood vessel of an individual such that the second distal opening is located at a position in an arm of the individual, and the first distal opening is located at a position at or near a central vein of the individual;
• infusing a first infusion solution into the blood vessel at the position at or near the central vein of the individual via the first distal opening;
• and
• infusing a second infusion solution into the blood vessel at the position in the arm of the individual via the second distal opening.