Understanding Anesthesiology - The Global Regional Anesthesia ...

Vascular Access
Peripheral venous access is the quickest, simplest and
safest method of obtaining vascular access. The upper
limb is used most commonly, either at the hand or antecubital
fossa (cephalic and basilic veins). The lower
limb can be used if necessary, the most successful site
here being the saphenous vein, located 1 cm anterior
and superior to the medial malleolus.
Flow through a tube is directly proportional to the pressure
drop across the tube and inversely proportional to
resistance.
Flow ∝ pressure drop/resistance
Resistance is directly proportional to length and inversely
proportional to radius to the fourth power.
Resistance ∝ length/radius 4
From these equations, we can understand how the anesthesiologist
achieves rapid administration of fluids.
Pressure drop is achieved by using rapid infusers that
apply a squeeze to the fluid, usually with an air-filled
bladder. A cannula that is of a greater radius makes a
significant impact on flow; to a lesser extent, a shorter
cannula allows greater flow than a longer cannula of
equivalent bore.
For example, a 16 gauge cannula will allow greater
flow (i.e. faster resuscitation) than a (smaller) 18 gauge
cannula. Likewise, a 14 gauge peripheral IV cannula
will allow greater flow than an equivalent caliber central
line, which is, by necessity, significantly longer.
From a practical perspective, a 16 gauge cannula is the
smallest size which allows rapid administration of
blood products.
Central venous access is indicated when peripheral venous
access is inadequate for fluid resuscitation, or
when central pressure monitoring is required. The internal
jugular vein is the most common site used intraoperatively.
The external jugular is also useful, but can
be technically difficult in some patients due to the presence
of valves. The subclavian site is associated with an
increased risk of pneumothorax, while the femoral site
is associated with an increased risk of infection, embolism
and thrombosis. Multiorifaced, 6 c.m., 14 gauge
catheters are the most commonly used central lines.
Wide bore “introducers” (for example, the 8.5 French
Arrow CV Introducer®) are also commonly used for
central venous access.
There are many potential complications of central venous
cannulation. They include arterial puncture, hemorrhage,
pneumothorax, thoracic duct injury, neural in-
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