IV TherapyAnatomy & Physiology

Dr Manjit George Anaesthetics

Anatomy

Upper limb veins

• Basilic vein• Cephalic vein • Median cubital vein

Lower limb veins• Femoral vein• Saphenous vein

Anatomy

ARTERY ARTERIOLES CAPILLARY THE HEART VEIN VENULE

Structure of vessels

• Arteries- smooth muscles

Clinical application- cold, nerve blocks

• Arterioles- tiny branches of arteries that lead to capillaries

Controlled by Sympathetic Nervous System

constrict & dilate to regulate blood flow

Structure of vessels

• Veins- Walls consist of 3 layers of tissues thinner and less elastic than the corresponding layers of arteries

• Valves aid return of blood to the heart by preventing blood flowing in the reverse direction

Structure of vessels

• Capillaries- tiny blood vessels(approx 5-20 microns in diameter)

Walls are only one cell thick

permits exchanges of material between them & the surrounding tissue

• Venules- minute vessels that drain blood from capillaries into veins

Many venules unite to form a vein

Artery v/s Vein

• Away from heart

• Oxgenated blood

• Narrow lumen

• More muscle/elastic

tissue

• High pressure

• Towards the heart

• Deoxygenated blood

• Wide lumen

• Less muscle /elastic

tissue

• Low pressure

Physiology

• Superficial veins are not paired with an artery unlike deep veins

• Superficial veins are important physiologically for cooling of the body

• Not as important as deep veins as they carry less blood

Physiology

Poiseuille’s Law

Flow rate F = P1 – P2 __ _____ = R

(pressure difference) (radius)4

_______________________8(viscosity) (length)

Determinants of flow rate

• Viscosity of infusing fluid• Length of the plastic cannula tube• The diameter of the tube (gauge size)• size 24 - 19mm long, 0.7 diam,flow rate -22ml/min

size 14 - 50mm long, 2.2 diam, flow rate 343ml/min• Pressure of infusion (pressure bags)• Blood pressure of the patient

Clinical patho physiology

• Varicose veins

• Venous ulcers

• Arterialisation of veins – AV fistula

A “good” vein

• One that is not kinked

• One that is clearly visible

• One that is easily palpable

• “Forked” veins where 2 tributaries come together

Unsuitable veins

• Tortuous veins• Flexor aspect of the wrist (risk of radial.n damage)• Veins above the elbow joint- median cubital vein• Veins over bony prominences• Dorsum of hand in the elderly except when they are

prominent & well filled• Avoid patients dominant arm, if possible• Areas over mobile joints/ areas of flexion• Limbs with fractures/ a-v shunts

Difficult venous access

• Obese

• Extremes of age

• Grossly oedematous states- hypoalbuminemia

• Burns

• IV Drug Abusers

• Malignancy- Oncology patients

• Sickle cell anaemia

Practical issues

• Indication ?• Site ?• Rate of infusion ?• Choice of cannula size ?• Duration ?• Protocols ?

Venflons- infusion rates

• 14 G- 343ml/min• 16 G- 220 ml/ min• 18 G- 120 ml/min• 20 G- 80ml/min• 22 G- 40 ml/min• 24 G- 22ml/min

Complications

• Pain/ fear

• Bruising/ Haematoma

• Thrombophlebitis

• Injury to nerve/artery

• Subcutaneous infiltration

• Cellulitis

Practical tips

• Visual / tactile senses, good lighting • Start distally• Dependant position (below heart level)• Tourniquet/ BP cuff inflated to 70-80 mm Hg• Tapping/ opening and closing of fist• Local application of warmth/ warm towel• Correct size of venflon• Hair/ sweat• EMLA cream(1 hour), Ametop (20 mins), Lignocaine 1%