Acid-base disorders and blood gas analysis (Proceedings)
Nov 01, 2010
CVC IN SAN DIEGO PROCEEDINGS
Blood gas analysis provides information about respiratory function and acid/base status. This information is vital in determining and monitoring treatment of patients with primary or secondary respiratory disease and/or metabolic disturbances. Blood gas (BG) can be assessed on arterial (ABG) or venous (VBG) samples, although oxygenation assessment is made on arterial blood only. Specifically, ABG assessment describes the degree of hypoxemia and hyper or hypocapnea associated with respiratory disease. These assessments may be used to determine the need for oxygen supplementation or mechanical ventilation. Evaluation of arterial or venous blood gases also determines whether the patient suffers from any of the acid/bas disturbances. Hydrogen ion concentration determines acid/base status and is described by blood pH. The body's major regulation of pH is performed by the lungs which regulate carbon dioxide (CO2) and the kidneys which regulate bicarbonate (HCO3). Disturbances in lung function may result in respiratory acidosis or alkalosis. Disturbances in kidney function may result in metabolic acidosis or alkalosis. Since both organ systems work in concert to regulate blood pH, it is common to see respiratory abnormalities to compensate for metabolic disturbances and visa versa.
Respiratory Acidosis is caused by an increase in carbon dioxide (CO2). Hypercapnea may be due to CNS disease, anesthesia, respiratory muscle weakness, etc.
SIMPLE 5 STEP BLOOD GAS ANALYSIS
5 steps of basic ABG interpretation:
A pH in the normal range does not necessarily indicate the absence of acidosis or alkalosis, as an abnormal PCO2 or HCO3 may be due to compensatory mechanisms or multiple simultaneous pathologies which "balance" each other. The clinician must therefore be vigilant in reading the entire blood gas. Lastly, many blood gas analyzers have the capability to measure electrolytes and lactate. These values are also imperative in evaluating and understanding the acid-base abnormality or severity of hypoperfusion (lactate). Please see proceedings specific for lactate analysis for further information.