OXYGENATION

Chapter 38 OXYGENATION




KEY TERMS/CONCEPTS






























CHAPTER FOCUS


The role of the cardiac and respiratory systems is to supply the body’s oxygen demands. Cardiopulmonary physiology involves delivery of oxygenated blood from the lungs to the left side of the heart and thence to the tissues, and deoxygenated blood from the tissues to the right side of the heart and thence to the pulmonary circulation for re-oxygenation. Blood is oxygenated through ventilation, perfusion and transport of respiratory gases.


The overall function of the cardiovascular system, which includes the lymphatic system, is to move blood around the body. Blood is circulated by the heart through blood vessels to transport oxygen, nutrients and other substances to the cells and to transport wastes away from the cells. Blood also assists in protecting the body against infection and distributing heat evenly throughout the body, and prevents its own loss by means of a built-in clotting mechanism. The respiratory system provides the body with the ability to absorb oxygen and excrete carbon dioxide and other waste products from the body. The two systems work in conjunction to maintain homeostasis.


Every cell in the body requires a constant supply of nutrients and oxygen, and every cell must rid itself of waste products. The cardiovascular, lymphatic and respiratory systems are the means by which these activities are achieved. The overall function of the circulatory system is transportation of substances to and from the cells.


The respiratory system is the means by which oxygen from the atmosphere is delivered to the bloodstream and carbon dioxide is diffused out from the bloodstream. This is achieved through the capillary alveoli membrane in the lungs. Ventilation is the method of delivering air into and out of the lungs. Respiration, which is the intake and use of oxygen and the elimination of carbon dioxide to the atmosphere, is achieved by the respiratory system and the cardiovascular system.


An adequate supply of blood is necessary for the normal function of every cell. Cells temporarily deprived of blood or oxygen will not function normally, and continued disruption of blood supply causes irreversible damage or cell death. Any disorder that interferes with the distribution or delivery of blood to tissues or the uptake or excretion of gases in respiration is a potential harm to body cells and may have permanent effects on a part, or all, of the body. The most common complication of a respiratory disorder is carbon dioxide retention. This can be a result of alveolar hypoventilation, or a cardiovascular disorder altering the ventilation or the perfusion of the lungs and other tissues.


Homeostasis depends on the ability of the heart to adequately circulate the required volume of blood and oxygen to the tissues. One of the most important aspects of nursing care is the maintenance or restoration of a clear airway, which includes measures directed at removing secretions by the use of suction via the nasal, oropharyngeal or endotracheal routes or by tracheostomy. Education is essential to promote exercise, which maintains optimal circulation of blood, and deep breathing and coughing exercises are encouraged to minimise the retention of secretions and secondary infections. Circulation can be assisted by changes in diet, fluid, exercise, medications and positioning. The patency of airways can be assisted by the use of humidification, nebulisation and physiotherapy using isotonic or hypotonic solutions or certain medications.


Although disorders of the cardiovascular and the respiratory system are common in most communities, the incidence of cardiac and respiratory disease is controlled to some extent by: legislation to minimise airborne irritants; immunisation programs; and health education regarding risks such as bad diet, smoking, hypertension and environmental pollution.





STRUCTURE OF THE RESPIRATORY SYSTEM


The function of the respiratory system (Figure 38.1) is to deliver oxygen from the atmosphere to the bloodstream and to deliver carbon dioxide from the bloodstream to the atmosphere. The structures that make up the respiratory tract constitute the means by which this exchange of gases occurs. The respiratory system consists of cavities and conducting airways that begin at the nasal and oral cavity and end at the alveoli, the functional unit of the respiratory system. The larger airways are composed of cartilage and smooth muscle that maintain their patency, and are gradually replaced with smooth muscle in the terminal airways, which allow alterations in airway diameter and ventilation. The two lungs are located in the thoracic cavity, encased by a double membrane known as the pleura, and are separated by the mediastinal cavity that contains the heart and great vessels. The thoracic cavity has ribs that aid in ventilation and protect the lungs from damage. The diaphragm and the internal and external intercostal regions are composed of skeletal muscle and constitute the main muscles of ventilation; other muscles are used when required for more forceful inhalation or expiration.






THE LARYNX


The larynx is situated in the upper region of the neck and extends from the pharynx above to the trachea below. It is composed of pieces of cartilage connected by membranes and provides a passageway for air between the pharynx and trachea. As air passes through, it is further moistened, warmed and filtered. The main cartilages that form the larynx are:





The larynx is lined with mucous membrane, which becomes ciliated in the lower part. In the upper part, two folds of membrane containing embedded fibrous and elastic tissue form the vocal cords. The vocal cords extend from the anterior wall to the posterior wall of the larynx to form the glottis, or voice box, which produce sounds. The nerve supply to the larynx is from the laryngeal and recurrent laryngeal nerves, which are branches of the vagus nerve.











SCIENTIFIC PRINCIPLES RELATED TO THE RESPIRATORY SYSTEM


Air is moved into and out of the lung by alterations in pressures in different areas in relation to the atmosphere. An understanding of pressure relationships and laws concerning gases will assist in the understanding of ventilation and respiration discussed later in this chapter.




ATMOSPHERIC PRESSURE


Atmospheric pressure arises by virtue of the weight of the air above the earth. Atmospheric pressure decreases as altitude increases because of the reduced amount of air above. Even at a particular altitude, atmospheric pressure is not constant, but varies according to atmospheric conditions. The total pressure exerted by the atmosphere is about 6.8 kg per 25 mm2 of surface area at sea level. The atmosphere consists principally of nitrogen (N2) 79.03%, oxygen (O2) 20.93%, and carbon dioxide (CO2) 0.0004%, which totals 99.9604%. Other gases such as carbon monoxide (CO) are present in minute quantities. Oxygen, a colourless and odourless gas, is essential in sustaining most forms of life.


Water vapour and gases in the atmosphere have weight and, at sea level, exert a pressure defined as 1 atmosphere of pressure (‘atmospheric pressure’) equivalent to 760 mmHg. The terms negative and positive pressure are used to compare a pressure to normal atmospheric pressure at sea level. Any pressure above normal atmospheric pressure is regarded as a positive pressure, and any pressure below normal atmospheric pressure is regarded as a negative pressure.


The following three laws of physics define the characteristics of gases:





The combined effects of atmospheric pressure and the application of the gas laws above provide the basis for the operation of many common devices, and also of the lungs. Boyle’s law refers to pressure differentials and is able to be applied to the process of breathing. By changing the volume of the thoracic cavity, the air pressure in the lungs can be made lower or higher than atmospheric pressure, leading to inhalation or exhalation, respectively.



REGULATION OF VENTILATION








VENTILATION AND RESPIRATION


Respiration is the term used to describe an interchange of gases. The main purpose of respiration is to supply the body with oxygen and dispose of carbon dioxide. The four processes involved are:







Ventilation


Ventilation has two phases: inhalation and exhalation (Figure 38.4).






Respiration







STRUCTURE OF THE CARDIOVASCULAR SYSTEM


The structures that make up the cardiovascular system are the:







BLOOD


Blood, which is classed as a connective tissue, constitutes about one-twelfth of the weight of the body. It is a viscous substance composed of a fluid portion (plasma) and formed elements (cells and cell fragments). Depending on the weight of the individual, the average total volume of blood is about 5–6 L. Blood varies in colour, from bright red when it has a high oxygen content, to dark red when the oxygen content is low. Arterial blood normally has a pH range of 7.35 to 7.45.




Constituents of blood


Plasma and formed elements make up the components of blood. Plasma, the fluid part of blood, is a straw-coloured watery fluid in which blood cells are suspended. Plasma forms about 55% of the blood volume and contains:












Blood group types


Human blood is grouped into four classifications based on immune reactivity. The groups are O, A, B, AB. The Rhesus factor (either negative or positive) is also determined. Eighty-five percent of the population has Rh antibodies on the surface of the red blood cell (that is RH positive). Generally speaking the blood of any one group is incompatible with the blood group of another. Therefore blood transfusions should be an exact match to the client’s blood group and Rh factor. When blood transfusions occur with mismatched blood a haemolytic reaction can occur (refer to Table 38.4 Preparing and monitoring a client undergoing a blood transfusion) (Tollefson 2004).


TABLE 38.4 PREPARING AND MONITORING A CLIENT UNDERGOING A BLOOD TRANSFUSION






Review and carry out the steps in Appendix 1  















































































Action Rationale
Check medical orders to ascertain type, frequency and amount of fluid to be administered, and time prepared Ensures correct quantities are given to client
Explain procedure to client Reduced anxiety/apprehension and gains client’s trust and cooperation
Measure and record blood pressure and vital signs Provides a baseline of the client’s haemodynamic health status
Prepare equipment  
Wash and dry hands Prevents cross infection and contamination of blood and tubing
Don appropriate equipment and clothing as per infection control guidelines  
Gather equipment including:



Ensures all equipment is at
Establish an IV infusion with normal saline IV access is established by a doctor or accredited Registered Nurse (RN). Normal saline is the solution used during a blood transfusion because it is compatible with blood and does not cause red blood cell lysis
Identify the client and the blood product according to policy Group and type of blood product matches on the order and the product
Two nurses check the:



 
The blood transfusion must be initiated within 15 minutes of arrival to the ward Minimises risk of bacterial infection





Ensures cells and plasma are mixed
Initiate the transfusion slowly Most reactions occur within the first 10 minutes. Beginning the transfusion slowly reduces the amount of blood for the system to react against reducing the severity of the reaction
Monitor the client Vital signs are taken as per facility guidelines. Most are generally taken every 15 minutes for the first hour of the infusion then hourly for the remainder of the infusion
Observe for reactions such as: Signs of a febrile reaction. Slow infusion rate

 
Observe for reactions such as:  




Observe for reactions such as: Signs of a haemolytic reaction




Complete the transfusion Ensures client receives the entire transfusion
Dispose of the blood unit as per facility guidelines Some facilities require all blood units (including the giving set) to be returned to blood bank and kept for 24 hours in case of a delayed reaction
Monitor client Clients can have a delayed reaction to the blood product for up to 24 hours
Vital signs are often recorded hourly for 4 hours then 4 hourly for 24 hours
Report and document the procedure and any complications Most blood products have a peel off identification tag that is identical to the blood unit ID number, grouping and Rh factor so that errors in transcription are avoided. This tab should be removed and placed in the


BLOOD CELLS


The blood cells and fragments are suspended in the plasma and are called formed elements. The three types of blood cells or fragments of cells are erythrocytes, leucocytes and thrombocytes.


Erythrocytes (red cells) are biconcave non-nucleated discs measuring about 7 microns in diameter. In adults, erythrocytes are produced in the red bone marrow of cancellous bone tissue, where they pass through several stages of development. They begin as large nucleated cells but when mature (after they have produced haemoglobin) they lose the nucleus and are liberated into the circulation. Haemoglobin is a complex protein composed of four different ‘haem’ chains, each containing a central atom of iron and a globulin protein. It has a strong affinity for both oxygen and carbon monoxide and gives the blood its colour. The normal haemoglobin level is about 14–16 g/100 mL of blood.


The number of erythrocytes is about 5 000 000/mm3 of blood, and their average life span is 100–120 days. As their nucleus is absent, they are unable to repair damage and become worn out in circulation, and are destroyed in the spleen and liver. The haemoglobin is split; its iron is stored by the liver for future use, and the pigment is used by the liver in the production of bile. The primary function of erythrocytes is to carry oxygen. In the lungs, oxygen combines with haemoglobin to form oxyhaemoglobin, making the blood bright red in colour. As blood circulates through the tissues, the oxygen is released, forming deoxyhaemoglobin, and the blood becomes dark red in colour.


Leucocytes (white cells) measure about 10 microns in diameter. They differ from erythrocytes in that they are larger, possess a nucleus and are less numerous. They also have the power of independent movement, known as diapedis, or emigration, which erythrocytes do not possess. There are two main types of leucocytes: granulocytes and agranular leucocytes. Granulocytes contain granules of enzymes and are classified as neutrophils, basophils or eosinophils. Neutrophils are the most numerous of the leucocytes and are important to the body in defence against bacteria, as they have the ability to engulf phagocytose and digest them. Neutrophils also play an important part in the inflammatory response. Injured tissues, and other leucocytes, secrete substances that stimulate the bone marrow to release increased numbers of neutrophils. Basophils release substances in infected tissue that are toxic to many microorganisms. They also play a part in the allergic response and act to limit the inflammatory response. Eosinophils are also involved in phagocytosis, as they ingest antigen–antibody complexes and parasites. They also play a role in clot retraction.


Agranular leucocytes lack granules of enzymes and are classified as monocytes or lymphocytes. Monocytes have the ability to move into the tissues, where they become macrophages and are capable of phagocytosis. They also secrete a variety of substances involved in the body’s defence, and play a role in the immune response. Lymphocytes are either T lymphocytes or B lymphocytes, both of which divide when stimulated by antigens. T lymphocytes are responsible for cellular immunity, and adhere to cells identified as foreign to the body. They secrete cytotoxic substances that kill the foreign cells. B lymphocytes are involved in humoral immunity, as they produce antibodies and are also responsible for immunoglobulin production. While the life span for granular leucocytes is only about 21 days, lymphocytes may survive for up to 100 days.


The total number of leucocytes is about 8000–10 000/mm3 of blood, but this number increases considerably (leucocytosis) when there is any infection in the body. The life span of a leucocyte is variable and depends to some extent on the degree of activity.


Thrombocytes (platelets) are colourless microscopic fragments of the megakaryocyte cell. Measuring about 3 microns in diameter, they do not possess a nucleus. Thrombocytes are produced in the red bone marrow, which is present in cancellous bone tissue. The number of thrombocytes is about 250 000–300 000/mm3 of blood, and the average life span of a thrombocyte is 5–9 days. The function of thrombocytes is to play a major role in the clotting of blood to reduce blood loss when a vessel wall is injured. The process involves many substances (clotting factors) which are produced by the liver and circulate in the plasma, as well as some substances released by the platelets and injured tissues. Normally a blood clot will form within 2–6 minutes after a blood vessel wall has been damaged.


The mechanism of clotting (haemostasis) involves three phases: vasoconstriction, formation of a temporary platelet plug and formation of a clot. When a small vessel becomes damaged:








The clotting mechanism is a complex one that will not occur if any of the necessary elements are reduced, defective or missing.



BLOOD VESSELS


Blood is circulated throughout the body within vessels that form a closed continuous system (Figure 38.6). The walls of blood vessels have three layers: an outer coat of fibrous tissue, a thick middle layer of involuntary muscle with elastic fibrous tissue and an inner lining of endothelium to form a smooth surface for contact with blood (Figure 38.7). Blood vessels include the arteries, veins and capillaries (Figure 38.8).









THE HEART


The heart is a hollow, conical muscular organ situated obliquely in the thoracic cavity between the lungs and behind the sternum. One third of the heart lies to the right, and two thirds lie to the left of the median plane. Its base is uppermost and points towards the right shoulder, and its apex is below, pointing to the left. The adult heart is about 12 cm × 8 cm × 6 cm, and weighs about 300 g.


Feb 12, 2017 | Posted by in NURSING | Comments Off on OXYGENATION
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