Anatomy Chapter 1: Circulatory System

Anatomy of the Heart

• The heart is a cone-shaped organ located in the middle of the chest, between the lungs, in the middle mediastinum.
• The heart has four chambers: right and left atria, and right and left ventricles.
• The heart has four one-way valves to direct blood flow through the chambers.
• The upper chambers, the right and left atria, are divided by the atrial septum.
• The lower chambers, the right and left ventricles, are divided by the ventricular septum.

Heart Walls

• The heart has a protective covering called the pericardium, which allows the heart to move with minimal friction.
• The pericardium has two layers: the fibrous layer and the serous pericardium.
• The serous pericardium is further divided into the parietal and visceral layers.
• There are three layers of the heart wall: epicardium, myocardium, and endocardium.

Right Heart

• The right heart receives deoxygenated blood from the upper body through the superior vena cava and from the lower body through the inferior vena cava.
• The right atrium is the site of venous cannulation for cardiopulmonary bypass (CPB).
• The blood moves from the right atrium through the tricuspid valve into the right ventricle.
• The right ventricle pumps blood through the pulmonary valve into the pulmonary artery.

Left Heart

• The left heart receives oxygenated blood from the lungs through four pulmonary veins.
• The left atrium is slightly larger than the right atrium.
• The blood moves from the left atrium through the mitral valve into the left ventricle.
• The left ventricle pumps blood through the aortic valve into the aorta.

Coronary Arteries

• The coronary arteries supply oxygenated blood to the heart muscle.
• The coronary arteries come from the aorta and branch into smaller arteries.
• The left main coronary artery supplies the myocardium of the left ventricle.
• The right coronary artery supplies the myocardium of the right ventricle.

Coronary Veins

• The coronary sinus system and the anterior cardiac system make up the venous drainage of the heart.
• The coronary sinus is a large vessel that allows blood from the superficial veins to enter the right atrium.
• The coronary veins mirror the coronary arteries to some extent.

Arteries and Veins

• Arteries are muscular, elastic tubes that carry oxygenated blood away from the heart.
• Veins are thin-walled, low-pressure vessels that carry deoxygenated blood back to the heart.
• Arteries have three layers: intima, media, and adventitia.
• Veins have valves that prevent backflow of blood.

Aortic Arch Vessels

• The aortic arch is the curved part of the aorta that gives rise to the innominate, left common carotid, and left subclavian arteries.
• The innominate artery divides into the right carotid and right subclavian arteries.
• The left common carotid artery supplies the brain and eyes.
• The left subclavian artery supplies the left arm and hand.

Arteries of the Upper and Lower Extremities

• The subclavian artery supplies the upper extremity.
• The axillary artery becomes the brachial artery in the upper arm.
• The brachial artery divides into the radial and ulnar arteries.
• The radial and ulnar arteries supply the arm and hand.
• The abdominal aorta gives rise to the celiac, mesenteric, and renal arteries.
• The renal arteries supply the kidneys.
• The abdominal aorta bifurcates to form the right and left common iliac arteries.
• The common iliac arteries divide into the internal and external iliac arteries.
• The external iliac artery becomes the femoral artery at the inguinal ligament.
• The femoral artery supplies the leg.
• The popliteal artery divides into the peroneal, anterior, and posterior tibial arteries.
• The anterior and posterior tibial arteries supply the lower leg and foot.### Venous System
• The venous system parallels the arterial system in structure and function
• Veins return blood to the heart through the superior and inferior vena cavae
• The blood then passes through the right atrium, ventricle, and pulmonary artery to the lungs
• In the lungs, oxygen is absorbed, and carbon dioxide is removed
• The oxygen-rich blood returns to the left heart and enters the arterial system

Veins of the Head

• Veins of the brain drain into the venous sinuses of the brain
• The sagittal and transverse sinus veins drain the veins of the brain
• Diploic veins connect the veins outside the skull to the sinuses inside the skull
• The venous blood from the head enters the external and internal jugular veins
• The external jugular vein is the largest vein in the neck and drains the face and scalp
• The internal jugular vein runs alongside the carotid artery on both sides of the neck

Veins of the Upper Extremities

• The upper extremities have deep and superficial veins
• The subclavian vein drains the axillary vein from the arm
• The brachial and basilic veins combine to drain into the axillary vein
• The cephalic vein runs in the arm up to the shoulder and drains into the subclavian vein
• Fingers are drained by digital veins that converge into the palmar arch
• The palmar arch joins with the radial vein that runs alongside the radial artery

Large Veins

• The gastroepiploic veins drain the stomach and enter the inferior vena cava
• The splenic vein is formed from five or six branches that return blood from the spleen
• The splenic vein and mesenteric veins combine to form the portal vein
• The superior and inferior mesenteric veins drain the small intestine and colon, respectively
• The renal veins empty into the inferior vena cava

Veins of the Lower Extremities

• The lower extremities are drained by superficial and deep veins
• The superficial veins include the greater and lesser saphenous veins
• The deep veins include the femoral and popliteal veins
• The femoral vein runs up the inner thigh alongside the femoral artery
• The popliteal vein receives blood from the anterior and posterior tibial veins

Blood Gases

• Blood gases are used to assess oxygenation and acid-base status
• Oxygen content, capacity, and consumption are dependent on hemoglobin
• The hemoglobin oxygen dissociation curve represents the relationship between hemoglobin and oxygen in the blood
• Shifts in the curve reflect changes in oxygen affinity
• P50 is a reflection of the enzyme effect on hemoglobin affinity for oxygen
• Oxygen calculations include formulas for oxygen carrying capacity, content, and saturation

Carbon Dioxide

• The arterial pCO2 affects the pH of the blood
• Carbon dioxide is transported by hemoglobin and dissolved in the plasma
• The Bohr effect describes the release of oxygen from hemoglobin in response to increased CO2
• The Haldane effect describes the release of CO2 from hemoglobin in response to increased O2

pH

• pH indicates the blood's acidity or basicity
• Normal pH range is 7.35-7.45
• Acidosis is present when the pH is below 7.35, and alkalosis is present when the pH is above 7.45
• Buffer systems resist changes in pH
• The bicarbonate system is the major buffer system in the body
• The kidneys play a role in regulating pH through the excretion of bicarbonate ions

Acid-Base Balance

• Acidosis can be caused by respiratory or metabolic factors
• Respiratory acidosis is caused by too little CO2 being removed from the lungs
• Metabolic acidosis is caused by inadequate oxygenation of the tissues
• Alkalosis is caused by excessive removal of CO2 or excessive administration of alkaline solutions
• Correction of acidosis or alkalosis may involve administering sodium bicarbonate or adjusting ventilatory support### Blood Gases
• Signs of shunting:
  • High venous pO2
  • Low systemic arterial blood pressure
  • Decreased A-V pO2 difference
• Atmospheric gases at sea level:
  • Oxygen: 20.84% of total, 159 mmHg partial pressure
  • Nitrogen: 78.62% of total, 597 mmHg partial pressure
  • Carbon dioxide: 0.04% of total, 15 mmHg partial pressure
  • Water: 5% of total, 385 mmHg partial pressure
• Alveolar air:
  • Oxygen: 13.6% of total, 104 mmHg partial pressure
  • Nitrogen: 74.9% of total, 569 mmHg partial pressure
  • Carbon dioxide: 5.3% of total, 40 mmHg partial pressure
  • Water: 6.2% of total, 47 mmHg partial pressure

Corrective Actions for Abnormal Blood Gas Results

• Respiratory alkalosis:
  • Corrective action: Decrease sweep gas, raise pO2 by increasing FIO2 percentage
  • Increase pump flow to expose more blood to oxygen or cool slightly
• Respiratory acidosis:
  • Corrective action: Increase sweep gas, raise pO2 by increasing FIO2 or increasing blood flow
• Metabolic acidosis:
  • Corrective action: Ensure adequate tissue perfusion, give sodium bicarbonate

Alpha-Stat and pH-Stat

• Alpha-stat and pH-stat are methods of calculating blood gas values
• pH-stat method: values are corrected for blood temperature
• Alpha-stat method: values are not temperature corrected

Conduct of Perfusion

• Pre-bypass:
  • Review procedure and patient's chart
  • Calculate necessary blood flow and determine if blood or other products are needed
  • Prime the pump and determine cannula sizes
  • Consult with surgeon regarding cannula sizes
• Predicted hematocrits:
  • Calculate the hematocrit that will result from the dilution of the volume used in priming the CPB oxygenator and circuit
• Pre-bypass checklist:
  • Review patient's chart and procedure
  • Check oxygenator holder, pump circuit tubing, and Luer connections
  • Check gas lines, oxygen supply, and purge lines
  • Check power cords, backup power, and handcranks
  • Check water lines, temperature probes, and level detector
  • Check bubble detector, pressure warning devices, and in-line sensors

Initiation of Bypass

• Heparin administration:
  • Administered by surgeon or anesthesiologist
  • ACT started to determine adequate anticoagulation
• Cannulation:
  • Place cannulae with purse string sutures
  • Test transfusion through arterial cannula
• Initiation of bypass:
  • Start oxygen flow and remove arterial clamp
  • Begin pump flow slowly and observe arterial line pressure
  • Check for any obstructions or cannula malfunction
• Checks after bypass is initiated:
  • Blood flow at proper rate
  • Arterial line pressure is normal
  • Oxygen started at proper flow and concentration
  • Oxygen saturations normal
  • Patient's arterial pressure 50-90 mmHg
  • Temperature appropriate
  • Coagulation status acceptable
  • Vaporizer turned on at appropriate level