Tables & Figures


Figure 3 - POQI.png
Figure 3. Arterial input pressure and flow. A. Theoretical relationship between pressure and flow (black line) showing the autoregulation of vascular tone to sustain a constant blood flow despite varying arterial input pressures. The orange dashed lines illustrate how changes in vascular tone alter the relationship between instantaneous arterial input pressure and blood flow subject to autoregulation. The point at which arterioles spontaneously collapse (zero blood flow) limiting arterial pressure drop is referred to as the critical closing pressure (Pcc), which also varies with changes in vasomotor tone. B. Theoretical vascular pressure profile throughout the circulatory tree. Mean arterial pressure (MAP) is constant for most of the arterial tree since larger arteries serve mainly as vascular capacitors holding stored blood under pressure. By contrast, vascular pressure drops rapidly once blood reaches smaller arteries that branch into arterioles and precapillary sphincters. The vascular waterfall is approximated by the critical closing pressure (Pcc) mirroring how water flowing over a waterfall is unaffected by how far it falls once over the edge. Thus, the decline in pressure from arterioles to venules, or changes in downstream venous pressure, does not influence either arterial pressure or blood flow. Mean systemic filling pressure (Pmsf) represents the upstream pressure driving venous return against a downstream central venous pressure (CVP).
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Figure 4 - POQI Can Ince.jpg
Figure 4. Microcirculation and arterial pressure. Microcirculatory conditions where control of arterial blood pressure under conditions of hypo or hypertension impairing tissue perfusion, is not effective in improving microcirculatory perfusion. Such conditions occurs when there is a loss of hemodynamic coherence characterized by normalized systemic hemodynamic variables but persistent microcirculatory dysfunction leading to a lack of oxygen availability in tissue (as indicated by blue cells). Four distinct aetiologies of hemodynamic incoherence leading to microcirculatory shock can be considered. Type 1: heterogeneous perfusion of the microcirculation as seen in septic patients with obstructed capillaries next to perfused capillaries resulting in a heterogeneous oxygenation of the tissue cells. Type 2: haemodilution with the dilution of microcirculatory blood resulting in the loss of erythrocyte-filled capillaries and increasing diffusion distance between RBCs in the capillaries and the tissue cells. Type 3: stasis of microcirculatory erythrocyte flow induced by altered systemic variables (e.g. increased arterial vascular resistance (R) and or increased venous pressures caused by tamponade). Type 4: alterations involve oedema caused by capillary leak syndrome and which results in increased diffusion distances from the red blood cells to the tissues and reduced ability of the oxygen to reach the tissue cells.
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Figure 2 - Cecconi..png
Figure 2. Autoregulation of blood flow. Schematic diagram showing altered relationship between flow and arterial pressure in normotensive and hypertensive individuals. Autoregulation allows optimal blood flow to be maintained for a wide range of BP values. Autoregulation is present also in hypertensive individuals, but the lower limit for BP is higher and the curve is shifted to the right compared to healthy subjects. Blood flow outside the autoregulation areas leads to either excessive vasoconstriction and impaired microcirculation, or to low blood flow and hypoperfusion.
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Figure 1 - POQI.png
Figure 1. Variation in arterial pressure by site of measurement. Simultaneously measured arterial pressure waveforms from the radial artery, femoral artery and ascending aorta. While diastolic and mean arterial pressures are similar regardless of the site at which arterial pressure is measured, systolic pressure increases as the monitoring site is further away from the ascending aorta.
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Preop Infographic.png
Infographic demonstrating the consensus recommendations from the preoperative blood pressure group
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