Understanding Perfusion and Hemorrhage

• Inability to adequately oxygenate tissues at the capillary level is altered perfusion
• Factors that could alter perfusion include ventilation-perfusion mismatch, impaired circulation, inadequate cardiac output, and excessive perfusion demands

Ventilation-Perfusion Mismatching

• The most common cause of hypoxemia is a problem with the ventilation-perfusion ratio
• Inadequate ventilation in well perfused areas of the lungs may be caused by asthma, pneumonia, or pulmonary edema
• Inadequate perfusion in well-ventilated areas of the lungs is caused by vascular obstructive processes in the lung, such as with a pulmonary embolus

Impaired Circulation

• Problems include inadequate or excess blood flow to tissues or organs
• Includes impaired circulatory patency and functioning
• This can be caused by injury to the vessels, obstructive processes, inadequate movement of blood, or inadequate blood volume
• Loss of vessel integrity and loss of blood (haemorrhage) occurs

Impaired Circulation Injury

• Other causes of hemorrhage include aneurysms, coagulation disorders, or degradation of the vessel by neoplasms

Impaired Circulation Obstruction

• Blocks free movement of blood through the circulatory system
• Occluded arteries don't allow oxygenated blood to reach peripheral tissues
• Occluded veins restrict venous return, leading to circulatory congestion
• Common obstructions include a thrombus (blood clot)
• Response to injury: blood clot formation is an essential part of wound healing
• Undesired thrombi can form in arteries or veins

Virchow's Triad (Impaired circulation)

• Three major factors are responsible for thrombus formation
• Includes vessel wall damage (vasculature), excessive clotting (blood) and alterations in blood flow (turbulence or sluggish blood movement) (flow)
• Injury to vessel endothelium resulting in the formation of atherosclerosis: the most common cause of thrombus formation (in arteries)
• Occurs and contributing to venous thrombosis

Impaired Circulation Vasculature

• Atherosclerosis is a condition of irregularly distributed lipid deposits in the inner lining (intima) of large or medium arteries
• Atherosclerosis may eventually occlude the artery

Impaired Circulation Flow

• Turbulent or stagnant blood flow contributes to thrombus formation
• Common sites of altered blood flow are bifurcations (region where vessel branches) and aneurysms (local outpouchings in the vessel wall due to weakness)
• Areas of venous stasis (a condition of slow blood flow in the veins)

Impaired Circulation Blood

• Hypercoagulability (excess clotting): unregulated formation of thrombi throughout the body
• Genetic mutations - excess coagulant factors or deficient anticoagulant mechanisms
• Acquired due to autoimmune mechanisms that activate platelets or alter coagulation factors
• certain types of cancer, or myeloproliferative disorders, such as thrombocythemia (excess platelets)
• Sickle cell anemia, Polycythemia vera (too many RBCs are produced)
• Use of oral contraceptives, vascular changes in the late stage of pregnancy

Thrombus formation outcomes

• Continues to grow and occlude the vessel completely
• Degraded by enzymes and decreases in size

Embolus

• Any plug of material that travels in the circulation and can obstruct the lumen of a vessel
• Can consist of thrombi, air/foreign material, neoplasm, microorganisms, or amniotic fluid
• Thromboembolus breaks off and travels

Emboli continued

• Venous thromboemboli originate in the deep veins of the legs; break off, travel along the vein; lodge in the pulmonary arteries where vessels narrow and bifurcate
• Arterial thromboemboli originate in the heart as atherosclerotic plaques and travel to the legs, brain, intestines, lower extremities, or kidneys

Impaired circulation

• An infarct is an area of necrosis resulting from a sudden insufficiency of blood supply due to vessel obstruction
• Loss of blood supply, necrosis formation, and loss of function of the affected tissue may occur
• The severity of the infarction is dependent on the size and location of the emboli
• Small emboli: small and less significant areas of necrosis; areas with collateral circulation are capable of perfusing tissue around the obstructed vessel
• Larger emboli: occlude large vessels and their tributaries, causing sudden death

Inadequate Cardiac Output

• The heart is unable to successfully eject the necessary amount of blood to the pulmonary and systemic circulation
• Occurs due to changes in blood volume, composition, or viscosity, impaired ventricular pumping, or structural heart defects (such as valve defects that allow leaking or regurgitation of blood)
• Additionally, conduction defects leading to an unresponsive heart rate and rhythm, and excessive or significantly reduced peripheral vascular resistance

Inadequate Cardiac Output - Changes in blood

• Volume and viscosity is altered, caused by dehydration, haemorrhage, or hypercoagulation (disseminated intravascular coagulation (DIC))
• Composition is altered due to anemia
• Altered oxygen transport, not enough red blood cells to carry oxygen
• The heart tries to move the small number of cells at a faster heart rate and becomes overtaxed

Inadequate Cardiac Output - Impaired Ventricle

• Loss of muscle activity leads to the inability to move blood effectively forward through the arterial circulation
• Leads to congestion of venous blood and impaired venous return
• Heart failure may be caused by impaired ventricular pumping and venous insufficiency
• Failure of one ventricle increases the workload on the other
• Increased workload often leads to failure

Inadequate Cardiac Output - Valvular Defects

• Can be congenital or acquired via infection, inflammation, trauma, and degeneration
• Stenosis (narrowing of the valve) or regurgitation (incompetence of the valve)
• Most often affects bicuspid (mitral) and aortic valves, causes valves to open or close improperly

Inadequate Cardiac Output - Conduction Defects

• Alters an optimal heart rate and rhythm
• Cardiac dysrhythmias are indicative of problems with maintaining an efficient heart rhythm
• SA node, AV node, cardiac cells that join the SA and AV nodes, and conduction systems in the atria or ventricles may be affected
• The heart is unable to perfuse body tissues well without a regular, productive, efficient heart rhythm

Excessive Perfusion Demands

• Altered perfusion from lack of meeting this excessive demand leads to excessive demands/tissue metabolism
• All other aspects of ventilation and diffusion are functioning optimally
• Tissue demands are too much, and perfusion is not able to supply
• Common causes include extreme and prolonged exertion, metabolic alterations (hyperthyroidism), and anemia

General Manifestations of Altered Perfusion

• Depend on the cause; impaired cardiac output causes cyanosis, edema, shortness of breath, impaired growth, tachycardia, tachypnea, and fatigue
• Changes in blood volume or peripheral vascular resistance may cause hypotension or hypertension
• Obstructive processes, such as myocardial or cerebral infarction, generally result in loss of the function of the affected organ because of ischemia, pain, and edema
• Deep vein thrombosis symptoms are tenderness in the calf, especially with dorsiflexion of the foot Total occlusion of veins may lead to edema, coolness, pallor, and cyanosis of the lower extremity

General Manifestations - Hemorrhage

• Leads to altered perfusion
• Skin manifestations of haemorrhage: ecchymoses (bruises from superficial bleeding into the skin), petechiae (pinpoint hemorrhages), purpura (diffuse hemorrhages of the skin or mucous membranes), hematoma (larger accumulations of blood in the tissue)

General Manifestations - Heart

• Two sounds (lub-dup) associated with closing of heart valves, including the first as AV valves close with the beginning of systole
• Second as SL valves close with the beginning of ventricular diastole
• Heart murmurs are abnormal heart sounds that usually indicate incompetent or stenotic valves

Select Diagnostic Aids to Detect Altered Perfusion

• Echocardiography (cardiac ultrasound) provides an ultrasound picture of cardiac structures and great vessels to detect cardiovascular and valvular lesions, changes in heart size/position, and wall motion abnormalities
• Cardiac catheterization involves inserting a catheter (small tube) that is passed into the heart from a vein or artery
• The catheter is used to withdraw blood samples, measure pressures, or inject contrast media to detect functional and structural defects (coronary angiography)
• A chest radiograph provides a radiographic picture of the chest, showing heart borders and detecting changes in heart size and position
• Detects pulmonary congestion and pleural effusion An electrocardiography (ECG) measures electrical impulses in the heart to detect disturbances in cardiac conduction and increases in chamber size and ischemia or myocardial infarction
• A Holter monitor is a portable device that records 24-hour ECG activity as a patient performs their usual daily activities Pressure measurements determine hypotension/hypertension
• Cardiac catheterization to measure pressure in the arteries, veins, and heart chambers
• A stress test involves the use of treadmill or bicycle exercise in conjunction with ECG, blood pressure monitoring, or other imaging studies to elicit chest pain, ECG changes, or signs of myocardial ischemia
• Cardiac nuclear scanning uses intravenous radioactive compounds, which collect in the heart, and a gamma camera to produce diagnostic images

Treatment Measures

Lifestyle modifications, such as:

• reduction of risks or modification of lifestyle: weight reduction, blood pressure management, stress reduction, smoking cessation, exercise, healthy nutrition, and diabetes management
• Pharmacologic
• Large group of various medications: to dilate blood vessels, reduce or increase blood pressure, control the heart rate/rhythm, increase myocardial contractility, reduce myocardial workload, or improve cardiac output
• ASA (aspirin) therapy: to reduce platelet aggregation and clot formation
• Thrombolytic agents: to break through an obstruction and revascularize myocardial tissue
• Pain medications: acute myocardial infarction
• Oxygen therapy: reduce hypoxemia Intravenous
• Fluid volume or blood replacement with severe hemorrhage or dehydration, administration of blood or fluids
• Surgery: to repair valve defects, remove varicose veins, and drain excess fluid from the pericardial cavity Pacemaker placement: a pacemaker may be placed to mechanically control heart rate and rhythm

Test your knowledge of factors affecting perfusion and hemorrhage, including ventilation, circulatory patency, and Virchow's triad. Questions cover causes, consequences, and mechanisms underlying these conditions, with a focus on pulmonary and peripheral tissues.