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What are they?

Acidosis and alkalosis are terms used to describe the abnormal conditions when a patient’s blood pH does not fall within the healthy range. Measuring the pH of blood is a way of determining how acidic or basic (alkaline) the blood is. Normal blood pH must be maintained within a narrow range of 7.35 - 7.45 to ensure that metabolic processes function properly and the right amount of blood is delivered to the tissues. Many diseases or situations can cause a patient’s blood pH to fall outside of these limits.

In the human body, normal metabolism generates large quantities of acids that must be eliminated to maintain a normal pH balance. Most of the acid is carbonic acid which is produced when carbon dioxide (CO2) combines with water in the body. Lesser quantities of lactic acid, ketoacids and other organic acids are also produced. This balance can be disrupted by a build-up of an acid or a base (alkali) or by an increased loss of an acid or a base (see Figure 1, below).

Acidosis occurs when blood pH falls below 7.35

Alkalosis occurs when blood pH rises above 7.45

Both of these conditions act as an alarm to the body; they trigger actions intended to restore the pH balance and return the blood pH to its normal range.

The major organs involved in regulating blood pH are the lungs and the kidneys. The lungs flush acid out of the body by exhaling CO2 (carbon dioxide). Within physical limits, the body can raise and lower the rate of breathing to alter the amount of CO2 that is breathed out. This can affect blood pH within seconds or minutes. The kidneys excrete some acids in the urine, and they produce and regulate the retention of HCO3- (bicarbonate), a base that increases the blood’s pH or alkalinity. Changes in HCO3- concentration occur more slowly than changes in CO2, taking hours or days. Often, both of these processes proceed at the same time, and they continue until the balance is restored or the body’s ability to compensate is exhausted or overwhelmed. Diseases that affect either the lungs or the kidneys as well as other metabolic conditions, can interfere with the regulation of blood pH.

Illstration of Acid-Base Balance

Figure 1: Taps and drains

  • The blood’s pH must remain between 7.35 and 7.45.
  • The body’s goal is to maitain a constant balance between incoming/produced acids and bases (tap on) and eliminated acids and bases (drain open).
  • Imbalances lead to acidosis (acid sink overflow) or alkalosis (base sink overflow).
  • Balance can be restored by increasing elimination (faster draining) and/or by decreasing flow (slowing down the dripping tap).

Acidosis or alkalosis can be an acute condition or it may be a chronic condition. Acidosis may not cause any symptoms or it may be associated with nonspecific symptoms such as fatigue, nausea and vomiting. Acute acidosis may also cause an increased rate and depth of breathing, confusion and headaches, and it can lead to seizures, coma, and in some cases death. Symptoms of alkalosis are often due to associated potassium (K+) loss and may include irritability, weakness and cramping.

Acid-base disorders are divided into two broad categories. Those that affect respiration and cause changes in CO2 concentration are called respiratory acidosis (low pH) or respiratory alkalosis (high pH). Respiratory acid-base disorders are commonly due to lung diseases or conditions that affect normal breathing. Disorders that affect HCO3- concentration are called metabolic acidosis (low pH) and metabolic alkalosis (high pH). Metabolic acid-base disorders may be due to kidney disease and a variety of other conditions. There are also known genetic abnormalities prevent normal metabolic pathways from functioning perfectly and can cause acid-base imbalance, usually acidosis. These are called inborn errors of metabolism (or genetic-metabolic disorders), and the acid-base effect is due to deficiencies or build-ups of different compounds, many of which are acidic in nature. Other disorders that can cause metabolic (non-respiratory) acid-base disorders include diabetes (diabetic ketoacidosis), severe vomiting and severe diarrhoea.


Last Review Date: April 5, 2017