Metabolic alkalosis - causes, symptoms, diagnosis, treatment, pathology

Summary

Metabolic alkalosis occurs when blood pH rises above 7.45 due to increased bicarbonate concentration. It can result from loss of hydrogen ions through vomiting or excess aldosterone, or from primary bicarbonate gain via kidney reabsorption or antacid ingestion. Hypokalemia often accompanies it, affecting the body's compensatory mechanisms, including cellular ion transport and respiratory rate adjustments. The kidneys eventually correct the imbalance by retaining hydrogen ions and reducing bicarbonate reabsorption.

Takeaways

• 📝 Metabolic alkalosis is a condition where blood pH rises above 7.45 due to an increase in bicarbonate (HCO3-) concentration.
• 📝 Blood pH is maintained between 7.35 and 7.45, and deviations indicate an imbalance in the body's acid-base regulation.
• 📝 The condition can arise from two main causes: loss of hydrogen ions or gain of bicarbonate ions, often a combination of both.
• 📝 Loss of hydrogen ions can occur through the gastrointestinal tract, such as during vomiting, or through the kidneys.
• 📝 Excess aldosterone, possibly due to an adrenal tumor, can lead to increased reabsorption of bicarbonate and loss of hydrogen ions in the urine.
• 📝 Primary gain of bicarbonate can be caused by increased reabsorption from the kidneys, stimulated by factors like volume contraction or hypokalemia.
• 📝 Hypokalemia, or low potassium levels, can trigger the renin-angiotensin-aldosterone mechanism, leading to metabolic alkalosis.
• 📝 Excess bicarbonate ions can also come from external sources, such as the ingestion of large amounts of antacids like sodium bicarbonate.
• 📝 Metabolic alkalosis often leads to hypokalemia, as the body tries to maintain pH balance by shifting potassium and hydrogen ions.
• 📝 The body compensates for increased bicarbonate levels by using ion transporters in cells and adjusting respiratory rates.
• 📝 If not caused by renal issues, the kidneys can eventually correct the imbalance by retaining hydrogen ions and reabsorbing less bicarbonate.

Q & A

What is metabolic alkalosis?

Metabolic alkalosis is a condition where blood pH is raised above 7.45 due to an increase in bicarbonate (HCO3-) concentration in the blood.

What is the normal range for blood pH?

The normal range for blood pH is between 7.35 and 7.45.

How can loss of hydrogen ions lead to metabolic alkalosis?

Loss of hydrogen ions, which can occur from the gastrointestinal tract during vomiting or through the kidneys due to excess aldosterone, leads to a relative increase in bicarbonate ions, thus causing metabolic alkalosis.

Why does vomiting lead to loss of hydrogen ions?

Vomiting leads to loss of hydrogen ions because gastric secretions, which are acidic and rich in hydrogen ions, are expelled from the body. Additionally, the pancreas may not secrete bicarbonate to neutralize the acid in the intestines, leading to a buildup of bicarbonate in the blood.

How does aldosterone contribute to the loss of hydrogen ions?

Aldosterone stimulates the kidneys to excrete more hydrogen ions and reabsorb more bicarbonate, leading to a more acidic urine and a more basic blood pH.

What is the role of diuretics in causing metabolic alkalosis?

Diuretics, especially loop and thiazide diuretics, can cause volume contraction and excessive loss of extracellular fluid, which can stimulate the kidneys to reabsorb more bicarbonate, leading to metabolic alkalosis.

How does hypokalemia (low potassium levels) relate to metabolic alkalosis?

Hypokalemia can trigger the renin-angiotensin-aldosterone mechanism, leading to increased reabsorption of bicarbonate by the kidneys and thus contributing to metabolic alkalosis.

What is contraction alkalosis?

Contraction alkalosis is a type of metabolic alkalosis that occurs due to volume contraction or excessive loss of extracellular fluid, often as a result of diuretic use or severe dehydration.

How do antacids contribute to metabolic alkalosis?

Antacids, such as sodium bicarbonate, are used to neutralize stomach acid. Excessive use can lead to an excess of bicarbonate ions being absorbed into the blood, increasing the blood pH.

What are the body's mechanisms to counteract metabolic alkalosis?

The body counters metabolic alkalosis through cellular ion transporters that exchange hydrogen for potassium ions, respiratory adjustments that retain carbon dioxide, and renal mechanisms that retain hydrogen ions and reduce bicarbonate reabsorption.

How does hypokalemia act as both a cause and a result of metabolic alkalosis?

Hypokalemia can be both a cause, by triggering increased bicarbonate reabsorption, and a result of metabolic alkalosis, as aldosterone can cause potassium excretion in the urine.

Outlines

00:00

🌡️ Metabolic Alkalosis Explained

Metabolic alkalosis is a condition where blood pH rises above 7.45 due to an increase in bicarbonate (HCO3-) concentration. It can occur from loss of hydrogen ions or gain of bicarbonate ions. Loss of hydrogen ions typically happens through vomiting, which leads to a lack of stomach acid and reduced bicarbonate secretion by the pancreas, or through increased aldosterone levels, which can be caused by adrenal tumors. Gain of bicarbonate ions can be due to increased reabsorption by the kidneys in response to volume contraction or hypokalemia. Hypokalemia can be both a cause and a result of metabolic alkalosis. The body responds by using ion transporters to move hydrogen ions into the blood and potassium ions into cells, which can contribute to hypokalemia. Another response is the respiratory system's adjustment to decrease the respiratory rate and depth, leading to a buildup of carbon dioxide and a decrease in pH.

05:01

💨 Respiratory Response to Metabolic Alkalosis

The respiratory system plays a crucial role in managing metabolic alkalosis. Chemoreceptors in the carotid arteries and aortic arch detect increased pH and signal the brain stem to reduce the respiratory rate and depth. This results in decreased minute ventilation, slowing the expulsion of carbon dioxide and increasing its partial pressure, which in turn lowers the pH. If metabolic alkalosis is not due to renal issues like diuretic use or volume contraction, the kidneys can correct the imbalance over several days by retaining hydrogen ions and reabsorbing less bicarbonate, facilitating its excretion in urine. The paragraph concludes with a recap that metabolic alkalosis is caused by an elevated bicarbonate ion concentration, leading to a pH above 7.45, and is most commonly due to loss of hydrogen ions from vomiting or adrenal tumors, or less commonly from bicarbonate gain due to antacids or volume contractions.

Keywords

💡Metabolic Alkalosis

Metabolic alkalosis is a condition characterized by an increase in blood pH above 7.45, caused by an excess of bicarbonate ions (HCO3-) in the blood. This term is central to the video's theme as it is the main subject discussed. The video explains that metabolic alkalosis can occur due to loss of hydrogen ions or gain of bicarbonate ions, often a combination of both.

💡Bicarbonate

Bicarbonate, or HCO3-, is a base that plays a crucial role in maintaining the body's acid-base balance. In the context of the video, an increase in bicarbonate concentration in the blood leads to metabolic alkalosis. The video mentions that bicarbonate can increase due to various factors such as loss from the gastrointestinal tract or increased reabsorption by the kidneys.

💡pH

pH is a scale used to measure the acidity or alkalinity of a solution. In the video, the normal blood pH range is given as 7.35 to 7.45. The video discusses how metabolic alkalosis disrupts this balance by raising the blood pH above the normal range, indicating an overly alkaline state.

💡Hydrogen Ions

Hydrogen ions are particles that contribute to the acidity of a solution. The video explains that the loss of hydrogen ions, which can occur through vomiting or kidney function, can lead to metabolic alkalosis. The loss of these ions from the body results in a higher pH, thus creating an alkaline condition.

💡Aldosterone

Aldosterone is a hormone produced by the adrenal glands that regulates electrolyte balance and blood pressure. The video discusses how excess aldosterone, potentially caused by an adrenal tumor, can lead to the loss of hydrogen ions through the urine, contributing to metabolic alkalosis.

💡Vomiting

Vomiting is mentioned in the video as a common cause of metabolic alkalosis. When a person vomits, they lose stomach acid, which is rich in hydrogen ions. Additionally, the pancreas normally neutralizes this acid with bicarbonate, but during vomiting, this bicarbonate is not secreted into the intestines and instead builds up in the blood, leading to alkalosis.

💡Diuretics

Diuretics are medications that increase the amount of urine produced and excreted, which can lead to volume contraction and metabolic alkalosis. The video explains that certain types of diuretics, like loop and thiazide diuretics, can cause excessive loss of extracellular fluid, stimulating the kidneys to reabsorb more bicarbonate and leading to alkalosis.

💡Hypokalaemia

Hypokalaemia refers to low levels of potassium in the blood. The video describes how hypokalaemia can both cause and result from metabolic alkalosis. Low potassium levels can trigger mechanisms that increase bicarbonate reabsorption by the kidneys, contributing to alkalosis.

💡Renin-Angiotensin-Aldosterone System

The renin-angiotensin-aldosterone system is a hormonal system that regulates blood pressure and fluid balance. The video explains that hypokalaemia can trigger this system, leading to increased levels of angiotensin II and aldosterone, which in turn cause the kidneys to retain water and reabsorb more bicarbonate, contributing to metabolic alkalosis.

💡Antacids

Antacids are substances that neutralize stomach acid and are used to relieve indigestion. The video mentions that antacids containing bicarbonate, like sodium bicarbonate, can be a cause of metabolic alkalosis if used excessively. This is because they can introduce more bicarbonate ions into the stomach and bloodstream than can be balanced by hydrogen ions.

💡Respiratory Compensation

Respiratory compensation refers to the body's response to changes in blood pH by adjusting the respiratory rate. The video explains that in response to metabolic alkalosis, the respiratory system may decrease the rate and depth of breathing, leading to a buildup of carbon dioxide and a subsequent decrease in pH to compensate for the alkaline state.

Highlights

Metabolic alkalosis is a condition where blood pH rises above 7.45 due to an increase in bicarbonate concentration.

Blood pH is normally maintained between 7.35 and 7.45, balancing bases and acids.

Metabolic alkalosis can occur from loss of hydrogen ions or gain of bicarbonate ions.

Vomiting can lead to loss of hydrogen ions as stomach acid is expelled and bicarbonate is not secreted by the pancreas.

Excess aldosterone from adrenal tumors can cause loss of hydrogen ions through urine.

Primary gain of bicarbonate is often due to increased reabsorption by the kidneys.

Volume contraction or excessive loss of extracellular fluid can stimulate kidneys to reabsorb more bicarbonate, leading to alkalosis.

Hypokalemia, or low blood potassium, can trigger renin-angiotensin-aldosterone mechanism, increasing bicarbonate reabsorption.

Excess bicarbonate intake from antacids can also cause metabolic alkalosis.

Hypokalemia can be both a cause and a result of metabolic alkalosis.

The body compensates for increased bicarbonate by shifting hydrogen ions into the blood and potassium into cells.

Respiratory system responds to alkalosis by decreasing respiratory rate and depth, retaining carbon dioxide.

Kidneys can correct metabolic alkalosis by retaining hydrogen ions and reabsorbing less bicarbonate if not caused by renal problems.

Metabolic alkalosis is frequently caused by vomiting or adrenal tumors, and less commonly by antacids or volume contractions.

Transcripts

with metabolic alkalosis alkalosis

refers to a process that raises blood pH

above 7.45

and metabolic refers to the fact that

it's caused by an increase in the

concentration of bicarbonate or hco3

minus in the blood

normally blood pH depends on the balance

or ratio between the concentration of

bases mainly bicarbonate which increases

the ph and acids which decrease the pH

the blood pH needs to be constantly

between 7.35 and 7.45

now metabolic alkalosis can typically

happen from two main causes

loss of hydrogen ions and gain of

bicarbonate ions or most often a

combination of these two

loss of hydrogen ions can happen either

from the gastrointestinal tract or from

the kidneys

the first case most commonly happens

during vomiting because the gastric

secretions are very acidic meaning that

they have lots of hydrogen ions

on top of that normally as gastric

secretions flow into the pancreas

they're met with bicarbonate secretions

which neutralize the acid so that the

various pancreatic enzymes like trypsin

and chymotrypsin can work effectively

so during vomiting not only is the

stomach acid lost but in addition the

pancreas doesn't secrete bicarbonate

into the intestines and so it builds up

in the blood instead

another way that hydrogen ions can be

lost is through the urine in the context

of having too much of the hormone

aldosterone

this can happen when there's an adrenal

tumor that secretes excess aldosterone

the aldosterone makes the alpha

intercalated cells to the distal

convoluted tubule and collecting duct

dump out hydrogen ions and reabsorb more

bicarbonate

the result is that the urine becomes

more acidic and the blood becomes more

basic

now the second cause a primary gain of

bicarbonate is usually caused by an

increased reabsorption of bicarbonate

from the kidneys

there are various things that could

stimulate the kidneys to do this one of

them is volume contraction or excessive

loss of extracellular fluid which can

happen with Loop Diuretics and thiazide

diuretics as well as in cases of severe

dehydration

the resulting alkalosis is called a

contraction alkalosis

sometimes dehydration happens in

combination with other causes of

metabolic alkalosis like prolonged

vomiting

another stimulus is hypokalemia or

decreased levels of potassium in the

blood which can be due to excessive loss

from the gastrointestinal tract like in

diarrhea or from the kidneys due to

diuretic use

in any case When there's less volume or

less potassium in the extracellular

space it triggers the renin Angiotensin

aldosterone mechanism

as a result Angiotensin II and

aldosterone levels rise and the kidneys

start to retain water and reabsorb more

bicarbonate in the proximal convoluted

tubule

in addition the alpha intercalated cells

of the distal convoluted tubule and the

collecting ducts secrete more hydrogen

ions into the urine but most importantly

they also make new bicarbonate ions

which will again get reabsorbed

now in other cases excess bicarbonate

ions don't come from within our bodies

at all but are ingested in large amounts

usually in the form of antacids like

sodium bicarbonate

these are typically used to neutralize

stomach acid and relieve indigestion

excess use of antacids though can result

in more bicarbonate ions than hydrogen

ions in the stomach and the excess

bicarbonate ions can get absorbed into

the blood

all these processes have a net result of

increasing the bicarbonate ion

concentration in the blood which

increases blood pH

but in addition there's often a

hypokalemia

in vomiting for example potassium ions

in the gastric secretions are lost

in other situations there's an increase

in aldosterone like during a contraction

alkalosis or when there's an adrenal

tumor

the aldosterone can affect principal

cells which line the distal convoluted

tubule and collecting ducts making them

excrete potassium into the urine

so essentially hypokalemia can be both a

cause and a result of metabolic

alkalosis

now if there's an increase in the

bicarbonate concentration in the blood

the body has a few important mechanisms

to help keep the pH in balance

first cells throughout the body have a

special type of ion transporter that

exchanges hydrogen ions for potassium

ions across the cell membrane

using this transporter the cells can

shift hydrogen ions out of the cells and

into the blood and in exchange pull

potassium ions out of the blood and into

the cells

and this can contribute to the

hypokalemia

another mechanism involves a respiratory

system and starts with chemoreceptors

that are located in the walls of the

carotid arteries and in the wall of the

aortic Arch

these chemoreceptors fire less often

when the pH Rises and that notifies the

respiratory centers in the brain stem

that they need to decrease the

respiratory rate and depth of breathing

as the breathing becomes slow and

shallow the minute ventilation decreases

and that's the volume of air that moves

in and out of the lungs in a minute

the decreased ventilation slows down how

much carbon dioxide leaves the body

increasing the partial pressure of

carbon dioxide in the body which

decreases the pH

a final mechanism is that of metabolic

alkalosis isn't caused by some renal

problem like the use of diuretics or

extracellular fluid volume contraction

then several days later the kidneys

usually correct the imbalance

the kidneys retain more hydrogen ions

while also reabsorbing less bicarbonate

ions so that it's more easily dumped

into the urine

alright as a quick recap metabolic

alkalosis is caused by an increased

bicarbonate ion concentration in the

blood

that elevates blood pH above 7.45

this most frequently results in loss of

hydrogen ions due to vomiting or adrenal

tumors

and less commonly from a gain of

bicarbonate ions from antacids or volume

contractions