The prevention of catheter-related complications is nowadays an important topic of research. Flushing the catheters is considered an important clinical procedure in preventing malfunction and several complications such as phlebitis or infection. Considering the latest guidelines of the Infusion Nurses Society, the flushing involves a pre and post-drug administration, requiring different syringes (with associated overall increased times of preparation/administration of intravenous medication by nurses, also increasing the need for manipulation of the venous catheter).

A multi-centre, two-arm randomised controlled trial with partially blinded outcome assessment, of 146 adult patients. After eligibility analysis and informed consent, participants will receive usual intravenous administration of drugs with subsequent flushing procedures, with the double-chamber syringe (arm A) or with the classical syringes (arm B). The outcomes assessment will be performed on a daily basis by the unblind research team, with the same procedures in both groups. Some main outcomes, such as phlebitis and infiltration, will also be evaluated by nurses from a blind research team and registered once a day.

Inclusion Criteria:

• Patients with 18 years or above, admitted to the orthopaedic department;
• Patients with the ability to fully communicate in Portuguese;
• Patients able to consent;
• Prescribed PIVC for intravenous therapeutic administration;
• PIVC expected to remain for at least 24 hours;
• PIVC inserted at the orthopaedic department;
• PIVC size 18 gauge (G) or 20 G;
• Anatomical insertion site in arm, forearm, or back of the hand;
• PIVC secured with a transparent, semi-permeable polyurethane film dressing.

Exclusion Criteria:

• - Patients with a known infectious disease;
• Patients with leucocytosis, defined as ≥1200 leukocytes/mm3;
• Patients with anaemia, with haemoglobin levels <13g/dl for men, and <12g/dl for women;
• Patients receiving immunosuppressive treatment within 6 months prior to hospital admission;
• Patients receiving chemotherapy or radiotherapy within 6 months prior to hospital admission;
• Patients with body mass index below 16 kg/m2 or above 39 kg/m2;
• Anatomical insertion site in flexion areas (e.g. cubital fossa region) or lower members;
• Skin lesions at the insertion site (e.g. previous infiltration, dermatitis, burns) and skin alterations such as tattoos;
• Peripheral venous alterations resulting from previous hospital admissions.

No individual participant data will be shared with other researchers.

Patients and clinical staff will not be entirely blind after group allocation due to the nature of the interventions. Despite this, participants will not be directly informed of their group allocation in terms of usual care or intervention, and the nurses in the clinical staff will only be informed about the broad purposes of the research [41] - the study of a new double-chamber syringe for intravenous administration and flushing. In contrast, research nurses from the team outside the orthopaedic department will be blinded when rating some of the main outcomes such as phlebitis and infiltration.