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Arterial blood gas analysis is a test most frequently performed on critically ill patients in the emergency room, recovery room and intensive care unit by nursing staff. One of the main purposes of the test is assessment of acid-base status, which is often disturbed during critical illness.
This article is intended to provide an introduction to the physiology of acid-base balance and the many pathological conditions that are associated with disturbance of that balance. It provides nurses and other health professionals, who are less than familiar with the topic, with a basis for understanding how the results of arterial blood gas analysis are applied in the investigation of patients whose acid-base balance is disturbed.
Normal cell metabolism depends on the maintenance of blood pH within very narrow limits (7.35-7.45).
Even relatively mild excursions outside this normal pH range can have deleterious effects, including reduced oxygen delivery to tissues, electrolyte disturbances and changes in heart muscle contractility; survival is rare if blood pH falls below 6.8 or rises above 7.8.
The problem for the body is that normal metabolism is associated with continuous production of hydrogen ions (H+) and carbon dioxide (CO2), both of which tend to reduce pH. The mechanism which overcomes this problem and serves to maintain normal blood pH (i.e. preserve acid-base homeostasis) is a complex synergy of action involving chemical buffers in blood, the red cells (erythrocytes), which circulate in blood, and the function of three organs: lungs, kidneys and brain.
Before explaining how these five elements contribute to the overall maintenance of blood pH, it would be helpful to quickly review some basic concepts.
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This article is intended to provide an introduction to the physiology of acid-base balance and the many pathological conditions that are associated with disturbance of that balance. It provides nurses and other health professionals, who are less than familiar with the topic, with a basis for understanding how the results of arterial blood gas analysis are applied in the investigation of patients whose acid-base balance is disturbed.
Normal cell metabolism depends on the maintenance of blood pH within very narrow limits (7.35-7.45).
Even relatively mild excursions outside this normal pH range can have deleterious effects, including reduced oxygen delivery to tissues, electrolyte disturbances and changes in heart muscle contractility; survival is rare if blood pH falls below 6.8 or rises above 7.8.
The problem for the body is that normal metabolism is associated with continuous production of hydrogen ions (H+) and carbon dioxide (CO2), both of which tend to reduce pH. The mechanism which overcomes this problem and serves to maintain normal blood pH (i.e. preserve acid-base homeostasis) is a complex synergy of action involving chemical buffers in blood, the red cells (erythrocytes), which circulate in blood, and the function of three organs: lungs, kidneys and brain.
Before explaining how these five elements contribute to the overall maintenance of blood pH, it would be helpful to quickly review some basic concepts.