217 Body Fluid-Related Diseases and Disorders
Acidosis
Acidosis describes increased acidity in the blood and other tissues, usually measured as arterial pH below 7.35.
Learning Objectives
Describe acidosis ans its medical implications
Key Takeaways
Key Points
- Acidemia is the state of low blood pH; acidosis is the process leading to the state of acidemia.
- The normal pH of arterial blood is between 7.35 and 7.45.
- Metabolic acidosis may occur as a result of increased metabolic acids, either from increased production of metabolic acids, or decreased excretion of acids by the kidneys. The lungs compensate for metabolic acidosis by increasing the exhalation of CO2.
- Blood pH is calculated using the Henderson-Hasselbach equation, appropriate here because blood is a buffer solution.
- Respiratory acidosis occurs from an increased concentration of carbon dioxide in the blood, usually due to hypoventilation resulting from pulmonary problems. In respiratory acidosis, carbon dioxide concentration rises, but bicarbonate is normal or increased.
Key Terms
- Henderson-Hasselbalch equation: In chemistry, the Henderson–Hasselbalch equation describes the derivation of pH as a measure of acidity (using pKa, the negative log of the acid dissociation constant) in biological and chemical systems. The equation is also useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions (it is widely used to calculate the isoelectric point of proteins).
- respiratory acidosis: Respiratory acidosis is a medical condition in which decreased ventilation (hypoventilation) causes increased blood carbon dioxide concentration and decreased pH (a condition generally called acidosis).
- metabolic acidosis: In medicine, metabolic acidosis is a condition that occurs when the body produces too much acid or when the kidneys are not removing enough acid from the body.
Acidosis is an increased acidity in the blood and other body tissue (i.e., an increased hydrogen ion concentration). If not further qualified, it usually refers to acidity of the blood plasma.
Acidosis is said to occur when arterial pH falls below 7.35, while its counterpart ( alkalosis ) occurs at a pH over 7.45. Arterial blood gas analysis and other tests are required to separate the main causes.
The term “acidemia” describes the state of low blood pH, while acidosis is used to describe the processes leading to these states. Nevertheless, the terms are sometimes used interchangeably. The distinction may be relevant where a patient has factors causing both acidosis and alkalosis, wherein the relative severity of both determines whether the result is a high or a low pH.
The rate of cellular metabolic activity affects and, at the same time, is affected by the pH of the body fluids. In humans, the normal pH of arterial blood lies between 7.35 and 7.45. Blood pH values compatible with life in all mammals are limited to a pH range between 6.8 and 7.8. Changes in the pH of arterial blood (and therefore the extracellular fluid) outside this range result in irreversible cell damage.
Types of Acidosis
Metabolic acidosis may result from increased production of metabolic acids or disturbances in the ability to excrete acid via the kidneys. Renal acidosis is associated with an accumulation of urea and creatinine as well as metabolic acid residues of protein catabolism.
A rise in lactate out of proportion to the level of pyruvate is termed “excess lactate,” and may be an indicator of fermentation due to anaerobic metabolism occurring in muscle cells, as seen during strenuous exercise. Once oxygenation is restored, the acidosis clears quickly. Another example of increased production of acids occurs in starvation and diabetic acidosis. It is due to the accumulation of ketoacids (ketosis) and reflects a severe shift from glycolysis to lipolysis for energy needs.
Metabolic Acidosis
Metabolic acidosis is compensated for in the lungs, as increased exhalation of carbon dioxide promptly shifts the buffering equation to reduce metabolic acid. This is a result of stimulation to chemoreceptors, which increases alveolar ventilation, leading to respiratory compensation, otherwise known as Kussmaul breathing (a specific type of hyperventilation). Should this situation persist, the patient is at risk for exhaustion leading to respiratory failure.
The Henderson-Hasselbalch equation is useful for calculating blood pH, because blood is a buffer solution. The amount of metabolic acid accumulating can also be quantitated by using buffer base deviation, a derivative estimate of the metabolic as opposed to the respiratory component. In hypovolemic shock for example, approximately 50% of the metabolic acid accumulation is lactic acid, which disappears as blood flow and oxygen debt are corrected.
Treatment of uncompensated metabolic acidosis is focused upon correcting the underlying problem. When metabolic acidosis is severe and can no longer be compensated for adequately by the lungs, neutralizing the acidosis with infusions of bicarbonate may be required.
Respiratory Acidosis
Respiratory acidosis results from a build-up of CO2 in the blood (hypercapnia) due to hypoventilation. It is most often caused by pulmonary problems, although head injuries, drugs (especially anesthetics and sedatives), and brain tumors can cause this acidemia. Pneumothorax, emphysema, chronic bronchitis, asthma, severe pneumonia, and aspiration are among the most frequent causes. It can also occur as a compensatory response to chronic metabolic alkalosis.
One key to distinguish between respiratory and metabolic acidosis is that in respiratory acidosis, the CO2 is increased while the bicarbonate is either normal (uncompensated) or increased (compensated). Compensation occurs if respiratory acidosis is present, and a chronic phase is entered with partial buffering of the acidosis through renal bicarbonate retention.
However, in cases where chronic illnesses that compromise pulmonary function persist, such as late-stage emphysema and certain types of muscular dystrophy, compensatory mechanisms will be unable to reverse this acidotic condition. As metabolic bicarbonate production becomes exhausted, and extraneous bicarbonate infusion can no longer reverse the extreme buildup of carbon dioxide associated with uncompensated respiratory acidosis, mechanical ventilation will usually be applied.
Symptoms of Acidosis: General symptoms of acidosis are described in relation to their location on the body. These symptoms usually accompany symptoms of another primary defect (respiratory or metabolic).
Alkalosis
Alkalosis is the increased alkalinity of blood and other tissues, generally occurring when the blood pH is above 7.45.
Learning Objectives
Describe the medical conditions caused by alkalosis
Key Takeaways
Key Points
- Alkalosis may be respiratory or metabolic.
- Respiratory alkalosis may be caused by hyperventilation, which causes a loss of carbon dioxide.
- Metabolic alkalosis may be caused by prolonged vomiting, which reduces the amount of hydrochloric acid in the stomach, diuretics, dehydration, endocrine disorders, or consumption of alkali.
- Metabolic alkalosis typically occurs with disturbed muscle function such as weakness, pain, cramps, and spasms, and may also cause hypocalcemia.
- Respiratory alkalosis may be acute or chronic. Acute respiratory alkalosis occurs rapidly, and the patient may lose consciousness and return to normal ventilation. Chronic respiratory alkalosis is maintained by metabolic compensation, where bicarbonate ion concentrations are reduced to compensate for decreased levels of carbon dioxide in the blood.
- Metabolic alkalosis may be chloride-responsive or chloride-resistant.
Key Terms
- alkalosis: An abnormally increased alkalinity in the blood.
- metabolic alkalosis: Metabolic alkalosis is a metabolic condition in which the pH of tissue is elevated beyond the normal range ( 7.35–7.45 ). This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations.
- respiratory alkalosis: Respiratory alkalosis is a medical condition in which increased respiration (hyperventilation) elevates the blood pH (a condition generally called alkalosis).
Alkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma (alkalemia). Generally, alkalosis is said to occur when pH of the blood exceeds 7.45. The opposite condition is acidosis (when pH falls below 7.35).
Alkalosis can refer to respiratory alkalosis or metabolic alkalosis. The main cause of respiratory alkalosis is hyperventilation, resulting in a loss of carbon dioxide. Compensatory mechanisms for this would include increased dissociation of the carbonic acid buffering intermediate into hydrogen ions, and the related excretion of bicarbonate, both of which lower blood pH.
Metabolic Alkalosis
Metabolic alkalosis is a metabolic condition in which the pH of tissue is elevated beyond the normal range (7.35–7.45 ). This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate or alternatively a direct result of increased bicarbonate concentrations. Metabolic alkalosis can be caused by prolonged vomiting, resulting in a loss of hydrochloric acid with the stomach content. Severe dehydration and the consumption of alkali are other causes. It can also be caused by administration of diuretics and endocrine disorders such as Cushing’s syndrome. Compensatory mechanism for metabolic alkalosis involves slowed breathing by the lungs to increase serum carbon dioxide, a condition leaning toward respiratory acidosis. As respiratory acidosis often accompanies the compensation for metabolic alkalosis, and vice versa, a delicate balance is created between these two conditions.
Metabolic alkalosis is usually accompanied with hypokalemia, causing, e.g., muscular weakness, myalgia, and muscle cramps (owing to disturbed function of the skeletal muscles), and muscle spasms (from disturbed function of smooth muscles). It may also cause hypocalcemia. As the pH of blood increases, the protein in the blood becomes more ionized into anions. This causes the free calcium present in blood to bind strongly with protein. If severe, it may cause tetany (alkalotic tetany).
Davenport Diagram: A Davenport Diagram, as shown, is a graphical tool developed by Allan Jones Davenport that allows a clinician or investigator to describe blood bicarbonate concentrations and blood pH following a respiratory and/or metabolic acid-base disturbance.
Edema
Edema is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling.
Learning Objectives
Evaluate factors involved in edema
Key Takeaways
Key Points
- During edema, there is either increased secretion of fluid into the interstitium or impaired removal of this fluid from the interstitium, resulting in fluid accumulation.
- Cutaneous edema is considered pitting edema when pressure applied to an area leaves an indentation that persists for some time after release.
- Edema may also occur as a result of cardiac failure due to the rise in hydrostatic pressure. A fall in osmotic pressure occurs in nephrotic syndrome and liver failure, and may cause edema.
Key Terms
- edema: An excessive accumulation of serum in tissue spaces or a body cavity
- interstitium: An interstitial space within a tissue or organ.
- cutaneous edema: Edema, formerly known as dropsy or hydropsy, is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling.
Examples
Causes of edema which are generalized to the whole body can cause edema in multiple organs and peripherally. For example, severe heart failure can cause pulmonary edema, pleural effusions, ascites, and peripheral edema.
Edema is an abnormal accumulation of fluid beneath the skin or in one or more cavities of the body that produces swelling. Edema is caused by increased secretion of fluid into the interstitium or impaired removal of this fluid.
Peripheral pitting edema: Peripheral pitting edema results from water retention. It can be caused by systemic diseases, pregnancy in some women, and as a result of heart failure or varicose veins.
Cutaneous edema is referred to as pitting when, after pressure is applied to a small area, the indentation persists for some time after the release of the pressure. Peripheral pitting edema, as shown in, is the more common type, resulting from water retention. It can be caused by systemic diseases, pregnancy in some women, either directly or as a result of heart failure, or local conditions such as varicose veins, thrombophlebitis, insect bites, and dermatitis. Non-pitting edema is observed when the indentation does not persist. It is associated with such conditions as lymphedema, lipoedema, and myxedema.
Edema may also occur as a result of cardiac failure due to the rise in hydrostatic pressure. A fall in osmotic pressure occurs in nephrotic syndrome and liver failure, and may cause edema.
Causes
Causes of edema which are generalized to the whole body can cause edema in multiple organs and peripherally. For example, severe heart failure can cause pulmonary edema, pleural effusions, ascites, and peripheral edema.
As well as the previously mentioned conditions, edemas often occur during the late stages of pregnancy in some women. Edema is more common with those of a history of pulmonary problems or poor circulation, and may be affected by the presence of arthritis. Edemas that occur during pregnancy are usually found in the lower part of the leg, usually from the calf down.
Edema will occur in specific organs as part of inflammations, tendinitis, or pancreatitis, for instance. Certain organs develop edema through tissue specific mechanisms. Examples of edema in specific organs include cerebral edema, pulmonary edema, periorbital edema (eye puffiness), and cutaneous edema due to mosquito bites, spider bites, bee stings, or contact dermatitis). Another cutaneous form of edema is myxedema, which is caused by increased deposition of connective tissue. In myxedema edema is caused by an increased tendency of the tissue to hold water within its extracellular space. In myxedema this is because of an increase in hydrophilic carbohydrate-rich molecules (perhaps mostly hyaluronan) deposited in the tissue matrix.
