Y khoa, y dược - Chapter 4: Blood and the cardiovascular system

Chapter 4Blood and the Cardiovascular System The HeartProvides the pump that ejects both deoxygenated blood to the lung and simultaneously oxygenated blood to the systemic circulation Weighs around 300grams Is positioned in the thoracic cavity in the mediastinum, resting between the right and left lungs. Figure 4.1 The heart and its relationship with the blood and the lymphatic systemCardiovascular FunctionFigure 4.1 demonstrates an overall picture of the function of the cardiovascular system. Optimum function requires several key components working in unison.The heart is an extremely muscular organ necessary for its principle action of providing the individual with a lifetimes supply of blood. Identifying the ApexAnatomy & Physiology in ActionThe cardiac cycle reflects the flow of blood through the heart during one heartbeatDepolarisation = dischargingRepolarisation = rechargingSystole = the contraction phaseDiastole = the relaxation phase (filling) phaseThe atria contract and force blood down into the ventricles, in contrast the ventricles need to exert a pumping force to reach their targets. The contraction of the atria can result in between 20-30% more blood entering the ventricles, in disease states such as atrial fibrillation where the atria fail to adequately contract the individual can lose this amount of their cardiac output resulting in haemodynamic collapse. What Makes the Heart Pump?A combination of internal components result in the rate, force of contraction and rhythm of each heart beat (know as the rate, rhythm & depth).These are the: MechanicsNervous stimulationElectrical activation Neurologic (involuntary control over the heart) Various neurologic factors regulate heart function; the most predominant is the autonomic nervous system. The heart is innervated via the cardiac centres in the brain by both sympathetic and parasympathetic fibres. Electrophysiological (the conduction system) The cardiac conduction system controls the route and pace or timing of electrical stimulation through the heart muscle. The four chambers are coordinated to work in coordinated sequence The MechanicsThe heart is a powerful, muscle rich pump.Each ventricle has a specific job: The right pumps deoxygenated blood to the lungs for oxygenation.The left pumps oxygenated blood around the body (the systemic circulation)The amount of blood that the heart circulates is referred to as the cardiac output.The Cardiac OutputThe cardiac output can be defined as the amount of blood ejected from the heart by each ventricle in each minute. Anatomy & Physiology in Practice Cardiac Output (average under normal conditions) Stroke volume (SV) = 70mlsHeart rate (HR) = 70bpmCardiac output = SV x HR = 4900mls The stroke volume can be defined as the amount of blood in the ventricles immediately before they contract (preload).Cardiac output is the product of the heart rate multiplied by the stroke volume.It represents the efficiency with which the heart circulates the blood throughout the body. Each minute the entire blood supply in pumped through each side of the heart. The Affects of Aging Chronic wear and tear affects the heart and its ability to function in several ways: Arteriosclerosis - degenerative process affecting the arteries; the walls of the vessel calcify and harden resulting in a loss of elasticity, causing an increased blood pressure.Degeneration of the valves within the heart.Degeneration of the electrics - leading to conditions such as atrial fibrillation and heart blocks.Atheromatous deposits - cause an increase in blood pressure and the potential for varying degrees of thrombus/clot formation.ScenarioJames Collins a 56-year-old Caucasian male is admitted to the emergency department after suffering severe chest pain and shortness of breath for the last 25 minutes. On arrival he appears grey, sweaty and clammy. He is still experiencing chest pain and has vomited in the ambulance.On arrival his vital signs are recorded as:Airway - clear patient is talking AVPU = ABreathing - Respiratory rate 24Circulation - Pulse 102Blood pressure 149/94PMH: Hypertension. Mr Collins also smokes 20 cigarettes per day and is grossly obese. Scenario AnalysisDivide into small groups and each answer one the following questions:Identify the main points within the scenarioWhat are the main risk factors for developing coronary heart disease?Which risk factors does Mr Collins present with?What are the initial nursing priorities?Developing & Delivering Expert Care Clinical Signs Associated with AMI Chest pain - commonly central & radiating into the neck, arms or jawSweaty clammy or ashen grey appearanceNausea or Vomiting Chest pain can be masked by diabetic neuropathy Sudden collapse of unknown causeShortness of breath/DyspnoeaCrushing sensation to central chestThe early identification of these signs can prove life saving. Heart Disease – The Facts Cardiovascular disease (CVD) is the collective name given to diseases affecting the heart and circulatory system. Diseases related to the cardiovascular system were responsible for in excess of 216,000 deaths in the UK in 2004. Coronary heart disease (CHD) claimed the lives of 137,000 individuals. Cardiovascular disease is the leading cause of premature death, with more than one in three people dieing from it (BHF, 2006). Pathophysiology Atherosclerosis is the term used to describe the deposition of lipid and cholesterol rich atheromatous plaques within the arterial walls. The inner lumen becomes increasingly clogged, resulting in a reduced distal blood flow. These atheromatous plaques have a serious risk of dislodgement, leading to thrombus formation in a narrower part of the lumen and the complete occlusion of blood to that area of the heart.The Acute Coronary SyndromesThe end result of this insidious disease process is various degrees of ischaemia; these ischaemic episodes are referred to as the acute coronary syndromes (ACS).The ACS reflect a disease continuum comprising three distinct but interchangeable stages of disease progression.The immediate treatment options depend on the extent of damage to the heart. Developing & Delivering Expert Care The Three Stages of Acute Myocardial Infarction Development         Ischaemic – tissue damage caused by a lack of oxygen. Early administration of O2 therapy can salvage the potential damage        Injury – greater degree of damage, but still salvageable with the early instigation of treatment        Infarction – necrotic/dead tissue depending on timescale damage can be limited or cardiac arrest preventedThe early administration of oxygen can prevent further deterioration and potentially reduce mortality and morbidity rates. Acute Coronary SyndromesPlaque disruption or erosionThrombus formation with or without embolisationAcute cardiac ischaemiaAbsence of S-T elevationS-T elevation presentMarkers of myocardial necrosis not elevated Elevated markers of myocardial necrosisElevated markers of myocardial necrosisUnstable anginaNon S-T elevation Myocardial infarctionS-T elevation myocardial infarctionDeveloping & Delivering Expert Care MONA MorphineOxygenNitratesAnti-Platelet agentsThis is an excellent tool for curtailing AMI developmentAMI and the TreatmentsIn March 2000 the Department of Health published the National Service Framework (NSF) for CHD. The traditional treatment for AMI centres on delivering an intravenous drug to decompose the thrombus, or clot, referred to as a thrombolytic. Newer therapies involving directly accessing the occluded vessel and either removing or squashing the thrombus, or inserting a stent have proven to be increasingly effective (ESC 2005). These forms of treatment are called percutaneous coronary interventions. The Obesity Epidemic & Cardiovascular Disease Obesity and the associated long-term increase to both morbidity and mortality have lead to this condition being the number one public health issue in the developing world. The clinical consequences primarily include;heart diseasetype two diabetesObesity – The FactsIn 2003, within the UK 22% of men and 23% of women were clinically obese.The Department of Health have constructed a National Service Framework focusing on reducing clinical obesity, a phenomena which is escalating at a prolific rate (DoH 2006). Anatomy & Physiology in ActionThe Cardiac Conducting System Under normal physiology the sinoatrial (SA) node is the heart’s pacemaker, meaning an impulse from this collection of conducting fibres instigates myocardial contraction. The SA node sets the pace because it initiates a faster intrinsic rate of fire than other areas within the heart. The rate ranges between 60-100bpm, depending on the particular requirement of the body via the autonomic nervous system.If there is a failure of the SA node to conduct an impulse to the atrioventricular node (AV), the AV node will itself instigate the impulse and become the pacemaker with a rate between 40-60bpm. If this back-up mechanism also fails impulses can be generated further down the conduction system this includes the bundle of His and Purkinje fibres, these rates vary between 15-40bpm but are notoriously unreliable.By understanding the rate/origin the clinician can make an informed guess at the possible origin of heart blocks (although this provides a good rule of thumb it is not always correct). PathophysiologyThe conduction sequence and its relationship to heart function are commonly affected by disease.These diseases can either result in a slow heart rate, a fast heart rate or a rhythm incompatible with life such as ventricular tachycardia.Cardiac ArrestActions aimed at curtailing cardiac arrest centre on prevention rather than cure (RC(UK) 2006).The underpinning philosophy of both basic and advanced life support centres on the chain of survival. Developing & Delivering Expert CareThe Chain of SurvivalActRationale·  Early recognition of associated signs and call for help·  Early cardiopulmonary resuscitation (CPR)·  Early defibrillation  ·  Post resuscitation care·  Prevention is better than cure ·  Cerebral oxygenation whist buying time·  To restart organised electrical activity and cardiac output ·  To maintain adequate circulation ·  Prevent further arrests ·  To restore quality of life  The BloodThe blood can be viewed as a fluid and mobile connective tissue. This tissue is composed of two prime components cells plasmaThe components of blood are bathed and transported in the plasma. Plasma constitutes 55% of the blood volume. The Composition of Blood Cells The Blood CellsErythrocytes(Red blood cells/RBCs)Leucocytes(White blood cells/WBCs)Thrombocytes(Platelets)· These biconcave cells do not contain a nucleus· They are produced in the red bone marrow and contain haemoglobin which absorbs oxygen providing blood with its distinctive red colour· These cells averagely circulate for 120 days when they are broken down by the spleen and iron recycled by the liverGranular and non granular leucocytes·  These irregularly shaped cells are the largest in blood·  Actively prevent infection and repair damaged areas·  Can proliferate dramatically through mitosis when confronted by infection·  Small and easily damaged cell with no nucleus·  Thrombocytes are the instigators to blood clotting·  Produced within the red bone marrowAnaemia – The Facts Anaemia is a collective term used to describe the end result of many disease processes in which the blood cannot carry enough oxygen, either resulting from a decrease in the number of RBCs or because each RBC is unable to carry sufficient oxygen due to the depletion of essential components, such as haemoglobin. PainPain is a complex phenomenon consisting of physiological, psychological and social elements.The ability of a nurse to conduct a structured assessment of an individuals pain, implement a plan of care and evaluate its effectiveness are essential parts of nursing practice.There are many tools or structures used to assess pain; the categorical rating scale for acute pain provides the user with a direct correlation between the identified level of pain and an appropriate pain killer.Developing and Delivering Expert Care Categorical Rating Scale for Acute Pain Pain Score Appropriate analgesia0 = No Pain1 = Mild pain 2 = Moderate Pain3 = Severe pain 4 = Very SevereNone indicated Non opioid analgesiaWeak opioids combinationsStrong opioid combinationOpioids titrated to pain Blood TransfusionEach year thousands of patients require a blood transfusion for a multitude of clinical conditions ranging from chronic anaemia to acute trauma and massive blood loss. The consequences of transfusing a patient with the wrong blood type can be devastating. Despite continued improvements in the processes involved there continues to be errors, resulting in morbidity and mortality to those affected (McClelland 2007). Good practice Good practice centres on following a few basic guiding principles:Right bloodRight patientRight timeRight place Each healthcare Trust will have specific guidelines on the process of obtaining blood and the actual transfusion. Blood TransfusionThere are several different blood types, with many being incompatible with each other. When administering blood and undertaking physical observations there are two important factors to consider, first, what changes to the patient’s vital signs are normal and second what needs to be done if things go wrong.Administering incompatible blood to a patient can result in an anaphylactic type reaction. If a patient’s renal function is compromised or there heart is unable to pump effectively they may not be able to physically cope with the increased blood volume and may start to exhibit signs of cardiac failure and pulmonary oedema.Anatomy & Physiology in ActionBlood GroupAntigenAntibodyONoneAnti A Anti BAA Anti BBBAnti AABABNoneRhesus PositiveDNoneRhesus NegativeDNoneIt is essential to learn and follow local guidelines on blood administration. For further reading McClelland (2007) is highly recommended. ConclusionGaining a solid understanding of the cardiovascular system and the fluid it carries is essential to delivering expert care. Regardless of the setting in which a nurse works he, or she, will encounter patients with both chronic conditions related to these systems, and acute episodes that may be acute exacerbations of established disease or may be truly acute.With the current trend towards obesity escalating, heart disease and its prevention will play a prominent role in the future; therefore, the knowledge gained in this chapter will assist in developing a solid and dynamic approach to patient care.