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TABLE 3.1Flow Relationship Defined by the Poiseuille Equation

  • Determinants of flow rate:

    • - Catheter radius (larger radius → larger area → higher flows)

      • Small changes in radius have relatively large impacts on flow rates

      • Measured as French (Fr) vs. gauge

        • - Two scales that reflect the diameter and therefore size of the lumen

          • Fr: Larger Fr catheters (i.e., higher number) have LARGER diameters

          • Gauge: Larger gauge catheters (i.e., higher numbers) have SMALLER diameters

    • - Length of catheter (shorter catheter → higher flows)

    • - Number of lumens (fewer lumens → higher flows)

    • - Pressure difference (larger changes in pressure → higher flows)

      • Augment by using pressure bags, manually squeezing the bag, or increasing vertical distance between the fluid bag and the patient

    • - Viscosity: More viscous products (i.e., blood) will flow more slowly

  • Venous site selection:

    • - Internal jugular (most common)

      • Pros: High placement success rate, low risk of pneumothorax with ultrasound guidance

      • Cons: Possible higher rate of bloodstream infections compared to subclavian

    • - Subclavian

      • Pros: Likely lowest rates of bloodstream infections of the three sites

      • Cons: Highest rate of pneumothorax, decreased placement success rate with less experienced providers

    • - Femoral

      • Pros: High placement success rate, no pneumothorax risk. Often used in trauma or codes given site is away from intubation or CPR

      • Cons: Possible higher rate of bloodstream infections given location, limits patient mobility

  • Vascular access options for common patient scenarios:

    • - Most patients in the ICU and medical wards:

      • Angiocath for peripheral venous access: Various sizes, including 14G, 16G, 18G, 20G, 22G

    • - ICU patient with septic shock requiring vasopressors, multiple IV antibiotics, and other medications:

      • Triple-lumen central venous catheter: Contains three lumens which are 1 × 16G and 2 × 18G; catheter length from 15–30 cm selected based on patient size and insertion location

    • - Gastrointestinal bleed requiring aggressive and rapid transfusion of multiple blood products:

      • MULTIPLE large-bore (often 16G or 18G) peripheral IVs

      • Alternative is an introducer or cordis, which are short catheters with large diameters, most commonly 8 Fr

    • - Code blue → PEA arrest in a patient without IV access:

      • Intraosseous (IO) access into a long bone (often tibia) with a 15G tibial needle enabling rapid infusions; short-term use until other access can be obtained

    • - Patient with endocarditis or osteomyelitis requiring long-term administration of antibiotics:

      • Peripherally inserted central catheter (PICC): Long catheters ranging from 30–60 cm in length; single-, double-, or triple-lumen options, with lumens being 4–5 Fr or 18G


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