IV Catheter Physics & Clinical Complications

What happens
after you insert.

Four interactive modules on the forces, failures, and physics that govern what moves through your peripheral IV catheter — and what goes wrong when they go wrong. From pressure gradients to barotrauma, from reflux to medication surges.

← Vol. I: The Vascular Lab ← Vol. II: The Ultrasound Lab
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Reflux
Blood flowing backward into catheter and tubing when pressure gradients reverse
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Blood Draw
Drawing samples through existing IV catheters — hemolysis, deadspace, technique
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Med Surge
Concentration spikes when bolus medications flush through deadspace into circulation
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Barotrauma
Pressure-induced tissue injury from infiltration, extravasation, and compartment pressure
ΔP = P_venous − P_IV
Reflux Threshold
Q = πr⁴ΔP / 8ηL
Draw Rate (Poiseuille)
τ = 4ηQ / πr³
Hemolysis Shear Stress
C_surge = C_drug × V_dead / V_flush
Surge Concentration
P_comp = F / A
Compartment Pressure
V_inj = P × C / K
Extravasation Volume
Four Modules
01
Catheter Reflux
Pressure Reversal
& Blood Reflux
When venous pressure exceeds IV line pressure, blood flows backward — silently occluding catheters, seeding clots, and creating the conditions for catheter failure. Understand the physics of the gradient that keeps your line patent.
Pressure GradientClot FormationCoughing/Valsalva1950s
Open module →
02
Blood Draw
Drawing Through
an Existing IV
Using peripheral IV catheters for blood collection — the hemolysis risk, negative pressure shear stress, gauge limitations, and the discard volume problem. Where Navi fits in the story of needle-free blood collection.
HemolysisShear StressNavi DeviceSample Integrity
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03
Medication Surge
The Deadspace
Bolus Problem
When you flush an IV line, concentrated medication sitting in deadspace reaches the bloodstream as a bolus surge — before dilution. Understand why saline flushes can be as dangerous as the drug itself in critical care.
Deadspace VolumeConcentration SpikeFlush PhysicsICU Safety
Open module →
04
Barotrauma
Pressure Injury
& Extravasation
The physics of fluid pressure in soft tissue — infiltration, extravasation, compartment syndrome, and vesicant injury. What pressure thresholds trigger irreversible damage, and how flow rate determines the window between a safe infusion and a surgical emergency.
Compartment PressureVesicantsExtravasation30 mmHg Rule
Open module →
Historical Timeline — IV Catheter Medicine
1628
Harvey Describes Circulation
Pressure gradients as the engine of blood movement — the precondition for all IV therapy
1656
First IV Injection (Wren)
Christopher Wren injects opium into a dog's vein using a quill and bladder — first deliberate IV access
1832
Saline IV in Cholera
Thomas Latta uses IV saline in cholera patients — first therapeutic IV infusion in humans
1945
Rochester Needle (Massa)
First plastic-over-needle catheter — enables dwell times beyond a single injection
1950s
Reflux Recognition
Blood reflux into IV tubing identified as cause of catheter occlusion and clot seeding
1960s
Heparin Lock Era
Heparin flushes adopted to prevent reflux clotting — saline-vs-heparin debate continues to present day
1973
Extravasation Literature
First systematic descriptions of chemotherapy extravasation injury — barotrauma formally classified
1985
INS Standards Published
Infusion Nurses Society formalizes pressure limits, flush volumes, catheter gauges — evidence-based IV practice begins
2000s
Needleless Connectors
Positive-displacement connectors reduce reflux without heparin — but create deadspace and surge problems
2024
Navi (Venocare)
FDA 510(k) K244047 — needle-free blood collection via existing peripheral IV catheters
The Unifying Insight
Every catheter complication is a physics problem with a biological consequence.

Reflux is a pressure gradient problem. Hemolysis is a shear stress problem. Medication surge is a fluid dynamics and deadspace problem. Barotrauma is a pressure-area problem. The biology — clots, lysed cells, arrhythmias, tissue necrosis — is just what happens when the physics goes wrong at the wrong place.

Reflux Threshold
ΔP < 0 → blood flows in
Hemolysis Risk
τ > 150 Pa → RBC rupture
Surge Window
V_dead / V_flush × C_drug
Compartment Danger
P > 30 mmHg → ischemia