Anesthesia Student Survival Guide.pdf - Index of

230 ● AnesthesiA student survivAl Guide
Intravenous (IV) Lines
Relevant Anatomy
The extremity veins are very thin-walled. They have an endothelium, a thin
muscle layer capable of contracting and constricting the lumen of the vein, and
are supported by an adventitia of thin connective tissue. The latter makes them
sometimes difficult to puncture because they are hard to fix in space by the
penetrating catheter stylet tip. In some body areas, they are valveless, but in others,
like the extremities, they have valves, bends, angles, and dead ends. These
factors may make catheter threading difficult. Veins usually run anatomically
in neurovascular bundles with the accompanying arteries and nerves, making
nerve injury and arterial puncture potential complications of venipuncture.
A useful mnemonic for remembering the position of these structures is NAVEL
– denoting from lateral to medial: Nerve, Artery, Vein, Empty space, Lymphatic.
This is important to visualize when cannulating the femoral artery or vein.
Physiology of Veins
Veins have smooth muscle in their walls, which may contract after the stimulus
of puncture, making it harder to cannulate in subsequent attempts. The pressure
of veins is low (27–31 mm Hg) but that of surrounding tissues is even lower,
making hematomas likely after unsuccessful puncture – unless firm pressure
is applied at the site for 30–45 s. Veins have sensory and motor (sympathetic)
innervation and may cause pain if the infused fluids are cold, hypotonic, or
contain certain irritating electrolytes, such as potassium chloride, or emulsions,
such as intralipid, for TPN. The repair mechanism of the punctured vein first
involves thrombus formation on denuded or injured endothelium. Therefore,
the way to keep a catheter patent is to keep a slow flow of intravenous fluid
entering the vein.
Technique of Peripheral Cannulation
One should begin by taking time to look and feel by gentle palpation for a
vein at a favorable site for insertion. If you do not find a promising vessel in
the first site you examine, consider moving to a different extremity. Frequently,
the patient’s skin and subcutaneous tissues will not allow one to see the veins
beneath the surface but they may often be felt. The vein in an extremity with a
tourniquet applied feels bouncy or rubbery to the finger tip, distinct from the
surrounding soft tissue. Injecting lidocaine around the vein will anesthetize
the overlying skin as well as inhibit venospasm. The intracatheter (14–24 g)