Osmetech Opti R Critical Care Analyzer, Model GD7044

pH

The pH value of the blood, serum or plasma may be the single most valuable factor in the evaluation of the acid-base status of a patient. The pH value is an indicator of the balance between the buffer (blood), renal (kidney) and respiratory (lung) systems, and one of the most tightly controlled parameters in the body. The causes of abnormal blood pH values are generally classified as:

a) primary bicarbonate deficit - metabolic acidosis

b) primary bicarbonate excess - metabolic alkalosis

c) primary hypoventilation - respiratory acidosis

d) primary hyperventilation - respiratory alkalosis

An increase in blood, serum or plasma pH (alkalemia) may be due to increased plasma bicarbonate, or a feature of respiratory alkalosis due to an increased elimination of CO2, due to hyperventilation.

A decreased pH value (acidemia) in blood, serum or plasma may occur due to an increased formation of organic acids, an increased excretion of H+ions in certain renal disorders, an increased acid intake such as in salicylate poisoning or loss of alkaline body fluids. Respiratory acidosis is the result of a decreased alveolar ventilation and may be acute; as the result of pulmonary edema, airway obstruction or medication, or may be chronic; as the result of obstructive or restrictive respiratory diseases.

PC02

The PCO2 value of arterial blood is used to assess how well the body eliminates carbon dioxide, a byproduct of metabolism. A PCO2 value below the normal range is termed respiratory alkalosis and indicates hypocapnia, a condition caused by increased alveolar ventilation such as hyperventilation.

An arterial PCO2 above the normal range is termed respiratory acidosis and indicates hypercapnia,a sign of ventilatory hypoventilation and failure, resulting from cardiac arrest, chronic obstructive lung disease, drug overdose, or chronic metabolic acid-base disturbances.

P02

The P0 2 value of arterial blood is used to assess how well the body is able to absorb oxygen in the lungs. Values below the normal arterial P0 2 (arterialhypoxeinia) are usually caused by pulmonary, circulatory, or respiratory abnormalities (e.g. bronchial obstruction, vascular problems, decrease in cardiac output, increased oxygen demand, anatomical heart defect, low inspired 02 content). Generally, 02 levels above 100 mmHg do not contribute significantly to the oxygen content since, with normal hemoglobin concentrations, 80 - 100 mmHg, P02 provides a 97% saturation level, and a level greater than 100% cannot be achieved.

Sodium

Sodium is the major cation of extracellular fluid. Its primary functions in the body are to chemically maintain osmotic pressure and acid-base balance and to transmit nerve impulses. Sodium functions at the cell membrane level by creating an electrical potential between different cell membranes causing the transmission of nerve impulses and neuromuscular excitability to be maintained. Sodium is involved in sonic enzyme catalyzed reactions as a cofactor. The body has a strong tendency to maintain a total base content, and only slight changes are found even under pathologic conditions.

Low sodium values, hyponatremia, usually reflect a relative excess of body water rather than a low total body sodium. Reduced sodium levels may be associated with: low sodium intake; sodium losses due to vomiting or diarrhea with adequate water and inadequate salt replacement, diuretics abuse, or salt-losing nephropathy; osmotic diuresis, metabolic acidosis; adrenocortical insufficiency; congenital adrenal hyperplasia; dilution type due to edema, cardiac failure, hepatic failure; and hypothyroidism.

Elevated sodium values, hypernatremia,are associated with conditions with water loss in excess of salt loss through profuse sweating, prolonged hyperpnea, severe vomiting or diarrhea, diabetes insipidus or diabetic acidosis; increased renal sodium conservation in hyperaldosteronism, Cushing's syndrome; inadequate water intake because of coma or hypothalamic diseases; dehydration; or excessive saline therapy.

The sodium value obtained may be used in the diagnosis or monitoring of all disturbances of the water balance, infusion therapies, vomiting, diarrhea, burns, heart and kidney insufficiencies, central or renal diabetes insipidus, endocrine disturbances and primary or secondary cortex insufficiency of the adrenal gland or other diseases involving electrolyte imbalance.

Potassium

Potassium is the major cation in the intracellular fluid and functions as the primary buffer within the cell itself. Ninety percent of potassium is concentrated within the cell, and damaged cells release potassium into the blood. Potassium plays an important role in nerve conduction, muscle function, and helps maintain acid-base balance and osmotic pressure.

Elevated potassium levels, hyperkalemia, can be found in oligouria, anemia, urinary obstruction, renal failure due to nephritis or shock, metabolic or respiratory acidosis, renal tubular acidosis with the K/H, exchange and hemolysis of the blood. Low potassium levels, hypokalenzia, can be found in excessive loss of potassium through diarrhea or vomiting, inadequate intake of potassium, malabsorption, severe burns and increased secretion of aldosterone. High or low potassium levels may cause changes in muscle irritability, respiration and myocardial function.

The potassium value obtained may be used to monitor electrolyte imbalance in the diagnosis and treatment of infusion therapies, shock, heart or circulatory insufficiency, acid-base imbalance, therapy with diuretics, all kinds of kidney problems, diarrhea, hyper- and hypo-function of adrenal cortex and other diseases involving electrolyte imbalance.

Ionized Calcium

Calcium in blood is distributed as free calcium ions (50%); bound to protein, mostly albumin (40%); and 10% bound to anions such as bicarbonate, citrate, phosphate and lactate. However, only ionized calcium can be Used by the body in such vital processes as muscular contraction, cardiac function, transmission of nerve impulses and blood clotting. The OPTI R measures the ionized portion of the total calcium. In certain disorders such as pancreatitis and hyperparathyroidism, ionized calcium is a better indicator for diagnosis than total calcium.

Elevated calcium, hypercalcemia, may be present in various types of malignancy, and calcium measurements may serve as biochemical markers. In general, while ionized calciuImmay be slightly more sensitive, either ionized or total calcium measurements have about equal utility in the detection of occult malignancy. H-ypercalcernia occurs commonly in critically ill patients with abnormalities in acid-base regulation and losses of protein and albumin, which gives a clear advantage to monitoring calcium status by ionized calcium measurements.

Patients with renal disease caused by glomnerular failure often have altered concentrations of calcium, phosphate, albumin, magnesium and pH. Since these cohditions tend to change ionized calcium independently of total calcium, ionized calcium is the preferred method of accurately monitoring calcilum status in renal disease.

Ionized calcium is important for diagnosis or monitoring of. hypertension management, parathyroidismn, renal diseases, malnutrition, kidney stones, multiple rmyelonma and diabetes Mellitus.

total Hemoglobin concentration (ctHb)

Hemoglobin is the main component of erythrocytes. It serves as the vehicle for transportation of oxygen within the bloodstream and each gram of hemoglobin canl carry 1.39 mL of oxygen. The oxygen combining capacity of the blood is directly proportional to the ]hemoglobin concentration rather than to the number of red blood cells (RBC), because some red cells contain more hemoglobin than others,

Although oxygen transport is the main function of hemoglobin, it also serves as anl important buffer in thle extracellular fluid. Decreases in the amount of hemoglobin canl come about as a result of a decreased concentration of hemoglobin in the erythrocytes, or a decreased number of erythrocytes that contain a normal concentration of hemoglobin.

Decreased levels are found in anemia states, hyperthyroidism, severe hemorrhage and hemolytic reactions due to transfusions of incompatible blood, reaction to chemical, infectious and physical agents as xvell as various systemlic diseases. Increased levels are found in hiemoconcentration of the blood, chronic obstructive pulmonary disease and congestive heart failure.

ctHb gives valuable information in anl emergency situation if interpreted not inl an isolated fashion but in con~junction with other pertinent laboratory data.

ctHb is used to screen for disease associated xvith anemia, to determine the severity of anemia, to follow the response to treatment for anemia and to evaluate polycythemnia.

Hemoglobin Oxygen Saturation (S02%)

When each heme group of the hemoglobin molecule is associated with one molecule of oxygen, tie hemoglobin is referred to as oxyhemoglobin (O2Hb). The amount of oxyhemoglobin, expressed as a fraction of the total functional hemoglobin (able to hind oxygen), is termed hemoglobin oxygen saturation (S02%). The largest portion (about 98%) of blood oxygen content is the oxygen bound to hemoglobin. The reference interval for arterial blood from healthy adults is typically 94 to 98%.

Decrease in S02 below the critical level necessary for tissue oxygen saturation is a grave clinical situation. Low oxygen saturation may be caused by many of the same factors responsible for arterial hypoxemnic. Low fractional oxyhemoglobin (FO2Hb), defined as a fraction of total available hemoglobin, may also be caused by unusually large aMOunlts of non-functional hemoglobins, high concentrations of deoxyliemoglobin, chemically altered hemoglobin or factors affecting the affinity of hemoglobin for oxygen, including: temperature, pH, PCO2, 2,3-DPG concentration and type of hemoglobin.