pertaining to a center; located at the midpoint.
central cord syndrome
injury to the central portion of the cervical spinal cord resulting in disproportionately more weakness or paralysis in the upper extremities than in the lower; pathological change is caused by hemorrhage or edema.
Central cord syndrome. From Ignatavicius and Workman, 2002.
central fever sustained fever resulting from damage to the thermoregulatory centers of the hypothalamus.
central venous catheterization
insertion of an indwelling catheter into a central vein for administering fluid and medications and for measuring central venous pressure
. The most common sites of insertion are the jugular and subclavian veins; however, such large peripheral veins as the saphenous and femoral veins can be used in an emergency even though they offer some disadvantages. The procedure is performed under sterile conditions and placement of the catheter is verified by x-rays before fluids are administered or central venous pressure measurements are made.
Selection of a large central vein in preference to a smaller peripheral vein for the administration of therapeutic agents is based on the nature and amount of fluid to be injected. Central veins are able to accommodate large amounts of fluid when shock or hemorrhage demands rapid replacement. The larger veins are less susceptible to irritation from caustic drugs and from hypertonic nutrient solutions administered during parenteral nutrition
Patient Care. Patients who have central venous lines are subject to a variety of complications. Air embolism is most likely to occur at the time a newly inserted catheter is connected to the intravenous tubing. Introduction of air into the system can be avoided by having the patient hold his breath and contract the abdominal muscles while the catheter and tubing are being connected. This maneuver increases intrathoracic pressure; if the patient is not able to cooperate, the connection should be made at the end of exhalation.
Sepsis is a potential complication of any intravenous therapy. It is especially dangerous for patients with central venous lines because they are seriously ill and less able to ward off infections. Careful cleansing of the insertion site, sterile technique during insertion, periodic changing of tubing and catheter, and firmly anchoring the catheter to prevent movement and irritation are all essential for the prevention of sepsis.
Formation of a clot at the tip of the catheter is indicated if the rate of flow of intravenous fluids decreases measurably or if there is no fluctuation of fluid in the fluid column. Preventive measures include maintaining a constant flow of intravenous fluids by IV pump or controller, periodic flushing of the catheter, heparin as prescribed, and looping and securing the catheter carefully to avoid kinks that impede the flow of fluids. Cardiac arrhythmias can occur if the tip of the catheter comes into contact with the atrial or ventricular wall. Changing the patient's position may eliminate the problem, but if ectopic rhythm persists, additional interventions are warranted.
central venous pressure
(CVP) the pressure of blood in the right atrium. Measurement of central venous pressure is made possible by the insertion of a catheter through the median cubital vein to the superior vena cava. The distal end of the catheter is attached to a manometer (or transducer and monitor) on which can be read the amount of pressure being exerted by the blood inside the right atrium or the vena cava. The manometer is positioned at the bedside so that the zero point is at the level of the right atrium. Each time the patient's position is changed the zero point on the manometer must be reset. For a multilumen catheter the distal port is used to measure central venous pressure; for a pulmonary artery catheter the proximal port is used.
An arterial line can also be used to monitor the central venous pressure. The waveform for a tracing of the pressure reflects contraction of the right atrium and the concurrent effect of the ventricles and surrounding major vessels. It consists of a, c, and v ascending (or positive) waves and x and y descending (or negative) waves. Since systolic atrial pressure (a) and diastolic (v) pressure are almost the same, the reading is taken as an average or mean of the two.
The normal range for CVP is 0 to 5 mm H2
O. A reading of 15 to 20 mm usually indicates inability of the right atrium to accommodate the current blood volume
. However, the trend of response to rapid administration of fluid is more significant than the specific level of pressure. Normally the right heart can circulate additional fluids without an increase in central venous pressure. If the pressure is elevated in response to rapid administration of a small amount of fluid, there is indication that the patient is hypervolemic in relation to the pumping action of the right heart. Thus, CVP is used as a guide to the safe administration of replacement fluids intravenously, particularly in patients who are subject to pulmonary edema
. Central venous pressure indirectly indicates the efficiency of the heart's pumping action; however, pulmonary artery pressure is more accurate for this purpose.
A high venous pressure may indicate congestive heart failure
, cardiac tamponade
in which the heart is unable to fill, or vasoconstriction
, which affects the heart's ability to empty its chambers. Conversely, a low venous pressure indicates hypovolemia
and possibly a need to increase fluid intake.
1. a set or series of interconnected or interdependent parts or entities (objects, organs, or organisms) that act together in a common purpose or produce results impossible by action of one alone.
an organized set of principles or ideas. adj., adj
The parts of a system can be referred to as its elements or components; the environment of the system is defined as all of the factors that affect the system and are affected by it. A living system is capable of taking in matter, energy, and information from its environment (input), processing them in some way, and returning matter, energy, and information to its environment as output.
system is one in which there is an exchange of matter, energy, and information with the environment; in a closed
system there is no such exchange. A living system cannot survive without this exchange, but in order to survive it must maintain pattern and organization in the midst of constant change. Control of self-regulation of an open system is achieved by dynamic interactions among its elements or components. The result of self-regulation is referred to as the steady state; that is, a state of equilibrium. homeostasis
is an assemblage of organic regulations that act to maintain steady states of a living organism.
A system can be divided hierarchically into subsystems, which can be further subdivided into sub-subsystems and components. A system and its environment could be considered as a unified whole for purposes of study, or a subsystem could be studied as a system. For example, the collection of glands in the endocrine system can be thought of as a system, each endocrine gland could be viewed as a system, or even specific cells of a single gland could be studied as a system. It is also possible to think of the human body as a living system and the endocrine system as a subsystem. The division of a system into a subsystem and its environment is dependent on the perspective chosen by the person studying a particular phenomenon.
Systems, subsystems, and suprasystems. Within the environment there are suprasystems, such as human society, and systems within the suprasystem, such as the educational and industrial systems and the health care delivery system. Within the health care delivery system are subsystems, such as the patient, family members, the nurse, the physician, and allied health care professionals and paraprofessionals.
in the behavioral system model
of nursing, the patterned, repetitive, and purposeful behaviors of an individual.
the heart and blood vessels, by which blood is pumped and circulated through the body; see also circulatory system
) a system for classifying cell-surface markers
expressed by lymphocytes based on a computer analysis of monoclonal antibodies
against hla antigens
, with antibodies having similar specificity characteristics being grouped together and assigned a number (CD1, CD2, CD3, etc.); these CD numbers are also applied to the specific antigens recognized by the various groups of monoclonal antibodies
. See also CD antigen
(CGS) (cgs) a system of measurements in which the units are based on the centimeter
as the unit of length
, the gram
as the unit of mass
, and the second
as the unit of time
the neurons in the central core of the brainstem
from the thalamus to the medulla oblongata, connecting the cerebral hemispheres
conduction system (conductive system (of heart)) the system of atypical cardiac muscle fibers, comprising the sinoatrial and atrioventricular nodes, internodal tracts, atrioventricular bundle, bundle branch, and terminal ramifications into the Purkinje network.
Emergency Medical Services (EMS) system a comprehensive program designed to provide services to the patient in the prehospital setting. The system is activated when a call is made to the EMS operator, who then dispatches an ambulance to the patient. The patient receives critical interventions and is stabilized at the scene. A communication system allows the health care workers at the scene to contact a trauma center for information regarding further treatment and disposition of the patient, followed by transportation of the patient to the most appropriate facility for treatment.
the system of ductless glands and other structures that produce internal secretions (hormones
) that are released directly into the circulatory system, influencing metabolism and other body processes; see endocrine glands
expert system a set of computer programs designed to serve as an aid in decision making.
gateway system a software interface between an online searcher and one or more search systems, facilitating the use of the system by searchers who are unfamiliar with it, or with online retrieval in general.
a haversian canal
and its concentrically arranged lamellae, constituting the basic unit of structure in compact bone (osteon
Haversian system: Structures of compact and spongy bone with the central haversian canal surrounded by the lamellae. From Applegate, 2000.
heterogeneous system a system or structure made up of mechanically separable parts, as an emulsion or suspension.
His-Purkinje system the intraventricular conduction system from the bundle of His to the distal Purkinje fibers, which carries the impulse to the ventricles.
Home Health Care Classification system see home health care classification system.
homogeneous system a system or structure made up of parts that cannot be mechanically separated, as a solution.
) (hypothalamo-hypophysial portal system
) the venules connecting the hypothalamus
with the sinusoidal capillaries of the anterior lobe of the pituitary gland
; they carry releasing substances to the pituitary.
lay health system a system comprising an informal referral network and sources of treatment outside the formal biomedical sources of health care; it includes individual consultation and information-seeking through significant others and peers concerning health behaviors, symptoms, and evaluation of treatment before, during, and after consultation with health care professionals.
in the omaha system
, anything connected with law or its administration; it includes legal aid, attorney, courts, or Child Protective Services (CPS), and many other agencies and officials.
limbic system a system of brain structures common to the brains of all mammals, comprising the phylogenetically old cortex (archipallium and paleopallium) and its primarily related nuclei. It is associated with olfaction, autonomic functions, and certain aspects of emotion and behavior.
lymphoid system the lymphoid tissue of the body, collectively; it consists of primary (or central) lymphoid tissues, the bone marrow, and thymus, and secondary (or peripheral) tissues, the lymph nodes, spleen, and gut-associated lymphoid tissue (tonsils, Peyer's patches).
mononuclear phagocyte system
the group of highly phagocytic cells that have a common origin from stem cells of the bone marrow and develop circulating monocytes and tissue macrophages, which develop from monocytes that have migrated to connective tissue of the liver (kupffer's cells
), lung, spleen, and lymph nodes. The term has been proposed to replace reticuloendothelial system
, which includes some cells of different origin and does not include all macrophages.
in the self-care model
of nursing, all the actions and interactions of nurses and patients in nursing practice situations; nursing systems fall into three categories: wholly compensatory, partly compensatory, and supportive-educative.
oxygen delivery system a device that delivers oxygen through the upper airways to the lungs at concentrations above that of ambient air. There are two general types: the fixed performance or high flow type, which can supply all of the needs of a patient for inspired gas at a given fractional inspired oxygen; and the variable performance or low flow type, which cannot supply all of the patient's needs for oxygen and delivers fractional inspired oxygen that varies with ventilatory demand.
peripheral nervous system
the portion of the nervous system
consisting of the nerves and ganglia outside the brain and spinal cord.
an arrangement by which blood collected from one set of capillaries passes through a large vessel or vessels and another set of capillaries before returning to the systemic circulation, as in the pituitary gland (the hypothalamo-hypophysial portal system
) or the liver (the hepatic portal circulation).
the group of specialized organs whose specific function is to provide for the transfer of oxygen from the air to the blood and of waste carbon dioxide from the blood to the air. The organs of the system include the nose
, the pharynx
, the larynx
, the trachea
, the bronchi
, and the lungs
. See also respiration
and Plates 7 and 8.
in the general systems framework and theory of goal attainment
, an organized boundary system of social roles, behaviors, and practices developed to maintain balance for growth, development, and performance, which involves an exchange of energy and information between the person and the environment for regulation and control of stressors.
in the omaha system
, the circle of friends, family, and associates that provide love, care, and need gratification; it may include church, school, workplace, or other groupings.
unit dose system a method of delivery of patient medications directly to the patient care unit. Following review by a nurse, a copy of the physician's original order is sent to the pharmacy, where the pharmacist reviews it again. The pharmacist then fills the order and delivers the medication to the patient care unit, usually in a 24-hour supply. Each patient has an individual supply of medications prepared and labeled by the pharmacist.
the system formed in the body by the kidneys
, urinary bladder
, and urethra
, the organs concerned in the production and excretion of urine
vasomotor system the part of the nervous system that controls the caliber of the blood vessels.