The pre-placement catheter length measured through the body surface was greater than the actual length. Therefore, 2 cm was subtracted from the pre-puncture point to the ipsilateral sternoclavicular joint to calculate the effective catheter pre-placement length.

The pre-placement length of the catheter was measured by subtracting 3-4 cm from the distance between the puncture point and ipsilateral midclavicular line. This adjustment was intended to prevent the catheter tip from entering the subclavian vein.

The measurement method of catheter pre-placement length was as follows: in cases where the catheter was punctured from the basilic and brachial veins, the distance from the pre-puncture point to the intermuscular sulcus of the ipsilateral deltoid muscle and pectoralis major muscle was measured (not surpassing the intermuscular sulcus and not reaching the axilla); however, the distance from the pre-puncture point to the ipsilateral sub shoulder or axilla was measured.

The procedures ① evaluation and selection of blood vessels: select the puncture vein in the middle of the patient's upper arm, ② Skin disinfection and towel laying: take the supine position, extend the upper limb to be punctured 45 ~ 90 °, disinfect the pre punctured upper limb with 75% alcohol and 5% povidone iodine. ③ Puncture vein: tie a tourniquet to fill the vein. Before puncture, use 0.2 ~ 0.4 ml of 2% lidocaine for local anesthesia. Under the guidance of ultrasound, use the puncture needle in the improved sedinger assembly for puncture. After successful puncture, insert the guide wire. ④ Delivery and confirmation of catheter position: after successful puncture, insert the dilator catheter sheath assembly, withdraw the setinger guide wire, deliver the catheter, after catheter placement, flush and seal the catheter with normal saline, and fix the catheter with sterile dressing.

Prolonged veins appear red, swollen, hot, and painful, with severe cord-like changes and indurations when touching. Mechanical phlebitis, infectious phlebitis, and thrombophlebitis are collected as phlebitis data

The PICC-related thrombosis in this study refers only to symptomatic thrombi, excluding asymptomatic thrombi. Catheter-related venous thrombosis was diagnosed by color Doppler ultrasound examination when the clinical manifestations were related symptoms such as swelling and pain in the upper arm of the catheterization side.

According to the degree, it is divided into complete occlusion and incomplete occlusion. When there is resistance or difficulty in flushing the tube, poor blood withdrawal or even no blood return can indicate that the catheter is incompletely occlusion; if it is difficult to flush the tube and draw blood, it can indicate that the catheter is completely occlusion.

Including local infection of the puncture site and catheter-related blood stream infection (Catheter-Related Blood stream Infection, CRBSI). Local infection refers to redness, swelling and pain around the puncture point, or even pus; Catheter-associated bloodstream infection: refers to patients with indwelling catheters who develop bacteremia and draw blood cultures through peripheral veins for at least one positive result, accompanied by fever (> 380C), chills, or hypotension. Other clear sources of bloodstream infection.

Time from tube insertion to extubation, in days

Ultrasound examination of the vascular intima before catheterization and within 24 hours after extubation was performed. No abnormality in the intimal smoothness was negative, and abnormalities in the intimal smoothness and hyperplasia were positive.