The indications for central venous catheters (CVCs) include invasive hemodynamic monitoring, transvenous cardiac pacing, hemodialysis, lack of peripheral venous access, administration of vasopressors, nutritional support, and in some texts…. volume resuscitation. It’s this last one that bothers me. Yes, some CVCs like multi-lumen access catheters (MAC) can be wonderful for massive resuscitation, but the traditional CVC is horrible compared to large bore peripheral intravenous (PIV) catheters. Let’s look at this in terms of catheter flow rates.
Poiseuille’s Law describes the dynamics of laminar fluid movement through a pipe much longer than its diameter and is given below.
Q = (ΔP*π*r4) / (8*η*l)
where Q = flow rate, P = pressure gradient, r = tube radius, η = fluid viscosity, and l = tube length
In essence, as our catheter’s length increases (think of 20 cm CVCs compared to ~ 3 cm PIVs), flow will be reduced. More importantly, as the catheter’s radius increases (lower gauge sizes, higher French sizes), the flow rate increases by a power of 4. Clearly, this is the most important factor in determining overall flow.
Pictured, you see 16G, 18G, 20G, and 22G Terumo PIV catheters with flow rates of 198 cc/min, 100 cc/min, 60 cc/min, and 35 cc/min, respectively. In comparison (and depending on what you read), a central line which includes a 16G lumen has a rate of approximately 70 cc/min. This is substantially different from the almost 200 cc/min we get with a 16G PIV.
Manufacturers often list flow rates through their catheters, but in general, I’ve found large bore PIVs to be superior to most central lines for volume administration. I’ll never forget a case where I placed two 14 gauge PIVs for a patient with known placenta accreta, a case where copious bleeding is anticipated. Those lines ran like fire hoses! 🙂
Next time you place a central line for “volume resuscitation”, look at the actual packaging and consider how the length of the catheter, lumens, and even IV tubing (extensions, stopcocks, adapters) will affect your overall flow rate. We’re usually better off avoiding the risks of CVCs (pneumothorax, arterial injury, air embolism, catheter-related bloodstream infections, etc.) and placing large bore PIVs instead. 🙂