Review Note
Last Update: 03/30/2025 10:20 PM
Current Deck: ACG Part 2::Plastic Surgery and Burns
New Card (Unpublished)Currently Published Content
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Front
Commit #312104
SS_PB 1.1 Describe the physiological principles relevant to optimising blood flow to tissue flaps, including
∙ Resistance and redistribution of blood volume
∙ Resistance and redistribution of blood volume
Back
Commit #312104Resistance : determined by the Hagen-Poiseuille equation
- Flow = ΔP×πr4/ 8nl
- Vessel radius most critical factor
- Vasoconstriction (SNS activation, hypothermia, pain, excessive vasopressor use) reduces flap perfusion by increasing systemic vascular resistance (SVR) and local arteriolar resistance.
- Vasodilation (regional anaesthesia, normothermia, inhalational anaesthetics, metabolic autoregulation) improves blood flow to tissue flaps.
Arterial vs Venous Resistance in Flap Perfusion
- Arteriolar resistance controls inflow and is influenced by myogenic, metabolic, and neurohumoral factors.
- Venous resistance is equally important—venous congestion impairs outflow, leading to tissue oedema, hypoxia, and potential flap failure.
- Systemic factors (e.g., hypovolaemia, anaesthesia, sympathetic tone) alter blood volume distribution between central and peripheral compartments.
- Venous capacitance vessels (veins/venules) store ~70% of total blood volume. SNS stimulation (e.g., stress, pain) causes venoconstriction, increasing preload but reducing blood available for peripheral tissues like flaps.