In study session III you have learnt
- Blood is a cell containing fluids that circulates through the heart, arteries, veins and capillaries carrying nourishments, electrolyte, hormones, vitamins, antibodies, heat and oxygen to the tissues and taking away waste materials and carboondioxide
- The major function of red blood cell is to trans-port hemoglobin, which in turn carries oxygen from the lungs to the tissues. The red cells are produced in the red marrow from a nucleated cell called the erythroblast. The red cell count is 5 million/mm3.
- The hematocrit (or PCV - packed cell volume) is the percentage of red blood cells in whole blood.
- The leukocytes, also called white blood cells, are the mobile units of the body's protective system. The normal WBC count is 4000 - 11000/mm3.
- Platelets or thrombocytes play a major role in coagulation of the blood and in hemostasis.
- They are formed in the bone marrow from giant cells (megakaryocytes).
- The heart is the motor of the circulation it pumps blood to maintain a steady blood flow throughout the body. The heart is composed of four chambers, left atrium and ventricle and right atrium and ventricle. The atria and ventricles are separated by the atrioventricular (AV) valves, mitral on the left and tricuspid on the right.
- The vascular system are comprised of arteries, arterioles, capillaries, venules and veins, conventionally described in progressive order leaving from the left side of the heart and returning to the right. The arterial side of the circulation carries oxygenated blood.
- The cardiac cycle refers to the mechanical events that occur during the contraction (systole) and relaxation (diastole) of the ventricular muscle.
- Systole is the period of ventricular contraction. Diastole is the period of ventricular relaxation.
- Under normal resting conditions, heart rate is approximately 70 beats/min and each cardiac cycle therefore takes approximately 0.85 sec. Systole lasts 0.3 sec and diastole lasts 0.55 sec, most of the time being taken up by ventricular filling.
- Myocardial blood supply is from the right and left coronary arteries, which run over the surface of the heart giving branches to the endocardium. Myocardial oxygen consumption is higher than in skeletal muscle.
- Cardiac output is defined as the volume of blood ejected by each ventricle per minute and is the product of the stroke volume and heart rate it is expressed in litres/min. Cardiac output varies widely with the level of activity of the body, the basic level of body metabolism, whether the person is exercising, the person's age, and size of the body.
- Venous return is the quantity of blood flowing from the veins into the right atrium each minute.
- Preload is end-diastolic volume, which is generally dependent on ventricular filling, which in turn depends mainly by venous return. The afterload of the ventricle is the pressure in the artery leading from the ventricle.
- The heart rate and contractility can be increased or decreased by the activity of the autonomic nervous system through a number of nerve reflexes which detect and respond rapidly to changes in arterial blood pressure. The heart rate is controlled predominantly by a change in sympathetic or vagal tone
- The peripheral resistance is the resistance to blood flow at the level of the peripheral arterioles and depends on arteriolar diameter and viscosity of blood
- Induction and maintenance of anesthesia is usually accompanied by a fall in the patient's blood pressure; cardiac output falls due to decreased preload and myocardial contractility and the reduced afterload decreases systemic vascular resistance. The anesthetics also depress the medulla reducing the sympathetic response to the fall in blood pressure.
- Spinal anesthesia results in vasodilatation proportional to the height of the block. As the local anaesthetic drug spreads cranially, there is an increasing block of the sympathetic nerves leaving the spinal cord (the sympathetic chain) that supply the vascular beds.
- Cardiovascular assessment is an extension of general preanesthetic assessment. History of the patient, physical examination and laboratory studies should be reviewed from the patient chart. Consultation to different medical specialty or physician is vital importance for understanding patient status.
- Blood pressure, character of pulse, cardiac reserve, ECG, palpation and auscultation of the heart should be done.
- Cardiac abnormal findings or suspicions needs communication with the operating physician and if possible consultation of the appropriate discipline.
Last modified: Wednesday, 16 November 2016, 9:23 AM