WEEK 1: Acid – Base Balance Flashcards
State the importance of acid-base balance.
- Necessary to sustain life
- The pH determines
*Properties of proteins: enzyme activity
part of the cell structure
*Permeability of membranes: distribution of electrolytes
State the Consequences of fluctuations in pH.
*Changes in excitability of nerve and muscle cells
*Marked influence on enzyme activity
*Changes influence K+ levels in body
What is the normal pH kept at?
State the pH levels not compatible to life.
pH is kept between 7.35 and 7.45.
pH levels <7.0 or> 7.8 are not compatible with life.
The free hydrogen ion (H+) concentration in body fluids is regulated exquisitely around _____________.
H+flux through the body greatly exceeds this magnitude.
In a 70-kg human being at a basal state, normal metabolic and dietary acid production rate is about 50 to 70 mmoles/d and respiratory volatile acid production at the basal state is around 15,000 mmoles/d, with peak production at maximal exercise reaching 200 mmoles/min.
The flux of H+through the organism over 24 hours is __orders of magnitude greater than the total pool of free H+in total body water (<2μmoles).
The free hydrogen ion (H+) concentration in body fluids is regulated exquisitely around 40 nmol/L (pH 7.40)
H+flux through the body greatly exceeds this magnitude.
In a 70-kg human being at a basal state, normal metabolic and dietary acid production rate is about 50 to 70 mmoles/d and respiratory volatile acid production at the basal state is around 15,000 mmoles/d, with peak production at maximal exercise reaching 200 mmoles/min.
The flux of H+through the organism over 24 hours is 8 orders of magnitude greater than the total pool of free H+in total body water (<2μmoles).
What is an electrolyte?
An electrolyte is a substance which develops an electrical charge in the presence of water.
-Cation
-Anion
What is an acid?
Electrolyte that forms a hydrogen cation and any anion in the presence of water.
Sources of H+ in the body.
*Carbonic acid formation
*Inorganic acids produced during breakdown of nutrients (e.g., HCl, nitric acid)
*Organic acids resulting from intermediary metabolism (e.g., lactic acid, acetic acid)
Define a strong and weak acid with examples.
- Weak acid
partially ionizes in water.
H2CO3, lactic acid, citric acid, ketones, aminoacids, fatty acids, uric acid - Strong acid
Totally ionizes in water.
HCl, sufuric, nitric, phosphoric,
What is a base?
A substance that can accept hydrogen ions.
Define weak and strong base with examples.
- Weak base
do not bind well with hydrogen.
HCO3- - Strong base
binds well with hydrogen.
OH-
What is pH?
Designation used to express the concentration of H+
On a typical Western diet, approximately 15,000 mmol of carbon dioxide and 50 to 100 mEq of nonvolatile acid (mostly sulfuric acid derived from the metabolism of sulfur-containing amino acids) are produced each day.
State two important sulfur-containing amino acids found in proteins.
Two important sulfur-containing amino acids found in proteins are methionine and cysteine.
State the different mechanisms in the body that maintain acid-base balance.
What exerts a pivotal role in the excretion of nonvolatile acid and base loads?
Acid-base balance is accomplished by concerted efforts of
1. extracellular and intracellular buffers,
2. highly efficient ventilatory responses,
3. metabolic functions of the liver, and
4. renal ammoniagenic and solute transport mechanisms.
For excretion of nonvolatile acid and base loads, the kidney assumes the pivotal role.
State the range of pH.
State the neutral pH.
State the physiologic pH.
Ranges from 0 - 14
Neutral pH (7) (physiological 7.4)
Physiological pH (7.4)
Define acidosis and alkalosis.
Acidosis refers to a pH less than 7.35.
Alkalosis refers to a pH greater than 7.45.
Which blood is used to determine acid-base status?
NB! Arterial blood is used to determine acid-base status. Normal arterial pH=7.4
What are volatile acids?
Can be eliminated as CO2 gas.
State the only physiological volatile acid.
What are the others?
Carbonic acid is the only physiological.
Others (Acetic acid formic acid, succinic acid, butyric acid and propionic acid)
State the 2 elements that carbonic acid dissociates into.
Which part of the body are volatile acids eliminated?
Carbonic acid dissociates to CO2 and H20.
Volatile acids are eliminated through the lungs.
What is a non-volatile acid?
An acid that cannot be eliminated as CO2 gas.
State examples of non-volatile acids.
Example
*Lactic acid
*Ketoacids
-Acetoacetate
-3hydroxybutyrate
-acetone
What is a buffer?
A buffer is an aqueous solution made of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.
Its pH changes very little when a small amount of strong acid or base is added.
It is used to prevent any change in the pH of a solution.
State the 3 functions of buffers.
*Control pH
*Converts a strong acid into a weak one
*Converts a strong base into a weak one
What is the Henderson-Hasselbalch equation?
The Henderson-Hasselbalch equation is a mathematical expression that describes the relationship between the pH of a solution, the pKa (acid dissociation constant) of a weak acid, and the concentrations of the weak acid and its conjugate base. The equation is as follows:
pH=pKa+log([A-] / [HA])
pH is the negative logarithm (base 10) of the hydrogen ion concentration in a solution.
pKa is the negative logarithm (base 10) of the acid dissociation constant (Ka) of the weak acid.
[A^-] is the concentration of the conjugate base of the weak acid.
[HA] is the concentration of the weak acid.
State the most important buffer which operates both in the lung and the kidney.
Bicarbonate buffer
State the components which make the bicarbonate buffer.
Consists of:
*H2CO3 and HCO3-
CO2 is excreted or retained as needed.
HCO3 is excreted or retained as needed.
Describe how the Protein Buffer System work.
Proteins carry a negative charge.
They can combine with H+.
Hemoglobin is an example of the protein buffering system.
Describe how it works.
- As tissues metabolize, they produce carbon dioxide (CO2) as a byproduct. Carbon dioxide can combine with water to form carbonic acid (H2CO3) through the action of an enzyme called carbonic anhydrase.
2.The carbonic acid (H2CO3) formed rapidly dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+).
- Hemoglobin plays a crucial role in buffering the increased hydrogen ions (H+) generated during this process. Hemoglobin can bind to hydrogen ions.
The reaction with hemoglobin looks like this:
HHb (deoxyhemoglobin) + H+⇌H2O + Hb (oxygenated hemoglobin)
When hemoglobin binds to hydrogen ions, it prevents the accumulation of excessive protons in the blood, helping to resist changes in pH.
- In the lungs, where oxygen levels are higher, hemoglobin releases the bound hydrogen ions, and the bicarbonate ion is converted back to carbon dioxide.
The overall reaction in the lungs is the reverse of the initial reaction:
HCO3- + H+ ⇌ H2CO3 → CO2 + H2O
Describe how the Phosphate buffer system works.
It involves the presence of dihydrogen phosphate (H2PO4-) and hydrogen phosphate (HPO4^2-) ions, which act as weak acids and bases, respectively.
Dibasic phosphate HPO4-2 filtered freely at glomerulus, 75% is reabsorbed.
- HPO4-2 combines with H + to form monobasic phosphate H2PO4-
- Bicarbonate is reabsorbed as needed
Describe the role of the liver in acid-base balance.
Detoxification of ammonia (NH3) in the liver is done via two ways (ammonia is produced during deamination of amino acids.
- Urea Synthesis:
The liver plays a role in the synthesis of urea through the urea cycle. Urea is a nitrogenous waste product formed from the breakdown of proteins and amino acids. The removal of nitrogen in the form of urea helps eliminate excess acids from the body, contributing to acid-base balance.
- Synthesis of Glutamine:
The liver can also detoxify ammonia by incorporating it into the amino acid glutamine.
Glutamine synthesis involves the combination of ammonia with glutamate in a reaction catalyzed by the enzyme glutamine synthetase.
The resulting glutamine is a relatively non-toxic form of ammonia.
Glutamine can be transported to other tissues, such as the kidneys, where it releases ammonia to be used in various metabolic processes or excreted.
Describe how the Renal buffer system works.
Kidneys regulate pH via 3 ways.
- Reabsorption of filtered HCO3-
- Generating consumed HCO3-by secreting protons(renal acidification)
- formation of titrable acid of
H2PO4- / HPO4–2 - Excretion of ammonia in Urine (as ammonium)
Describe the kidney role in ABB.
*Third line of defense
*Kidneys require hours to days to compensate for changes in body-fluid pH
Control pH of body fluids by adjusting
H+ excretion
HCO3- excretion (during alkalosis)
Ammonia (NH3) secretion (during acidosis)
Describe the Cellular Shifts in Buffer System during acidosis and alkalosis.
Acidosis
*Potassium leaves the cell
*Hydrogen ion enters the cell
Alkalosis
*Hydrogen leaves the cell
*Potassium enters the cell
State the time taken by the following to regulate pH.
1. Buffering system
2. Respiratory system
3. Renal system
- Buffering system
within seconds - Respiratory system
20-30 minutes - Renal system
several days
Describe the respiratory control of pH.
- Acidosis
respiratory rate increases - Alkalosis
respiratory rate decreases
Response time
20-30 minutes
Increased hydrogen ions
Decreased bicarbonate ions.
Decreased pH.
Name the phenomena described above.
Acidosis.
Decreased hydrogen ion concentration.
Increased bicarbonate concentration
Increased pH
Name the phenomena described above.
Alkalosis
State the normal values for the following.
pH
pCO2
HCO3-
Base Excess
pO2
Saturation O2
pH 7.4 (7.35 - 7.45)
pCO2 40 (35-45) mmHg
HCO3- 24 (22-26) mEq/L
Base Excess 0 (-2 to +2 mEq/L)
pO2 (75-100 mmHg)
Saturation O2 98 %
Define anion gap.
Difference between cations and anions.
State the formula for calculating anion gap.
Anion Gap= (Sodium− (Chloride + Bicarbonate))
In this equation:
*Sodium (Na) represents the concentration of sodium ions in the blood.
*Chloride (Cl) represents the concentration of chloride ions in the blood.
*Bicarbonate (HCO₃⁻) represents the concentration of bicarbonate ions in the blood.
State the units for anion gap.
The anion gap is usually expressed in milliequivalents per liter (mEq/L) or millimoles per liter (mmol/L).
What is the normal anion gap?
Normal Value
10 to 12 mEq/L
Calculate the anion gap.
Na = 145 mEq/L
Cl = 104 mEq/L
HCO3 = 26 mEq/L
Anion gap = 145 – (104 +26) => AG = 15 mEq/L
Describe the anion gap when there is hypoalbuminemia.
Hypoalbuminemia will show low Anion Gap than normal!
What Does Anion Gap Tell You?
Anion gap represents the remaining unmeasurable anions in the ECF.
phosphates
sulfates
ketone
pyruvate
lactate
What does an elevated anion gap represent?
Elevated anion gap represents metabolic acidosis.
If the anion gap is significantly elevated, it may indicate the presence of unmeasured anions, which could be due to conditions like lactic acidosis, diabetic ketoacidosis, or renal failure.
Define oxygen saturation.
State the normal oxygen saturation.
What is the oxygen saturation dependent on?
Oxygen saturation (SaO2) is a measure of the percentage of hemoglobin (Hb) molecules in the blood that are bound to oxygen.
Oxygen Saturation (greater than 95%)
Dependent on SAO2
Which delivers more oxygen to the tissue?
Sat 87% Hgb 15 gm/dl
Sat 95% Hgb 10 gm/dl
Interpretation of Arterial Blood Gases.
State the pH for the following.
normal
acidosis
alkalosis
Look at the pH.
normal 7.35 - 7.45
acidosis <7.35
alkalosis >7.45
Can arise from either respiratory dysfunction or metabolic disturbances.
State the Deviations divided into four general categories.
Respiratory acidosis
Respiratory alkalosis
Metabolic acidosis
Metabolic alkalosis
How does respiratory disturbance result in Acid-Base Imbalances?
Respiratory disturbance= retention or removal of CO2
Look at the respiratory component.
normal pCO2?
increased pCO2 –>?
decreased pCO2 –>?
Look at the respiratory component.
normal pCO2 (35 - 45 mm Hg)
increased pCO2 –> respiratory acidosis
decreased pCO2 –> respiratory alkalosis.
Look at the metabolic component.
normal HCO3-?
Increased HCO3-?
Decreased HCO3-?
Look at the metabolic component
normal HCO3- (22 - 26 mm HG)
Increased HCO3- metabolic alkalosis
Decreased HCO3- metabolic acidosis
What is respiratory acidosis?
Result of abnormal CO2 retention arising from hypoventilation,
(therefore ↑PCO2 observed)
Describe respiratory acidosis under the following:
*Ventilation
*CO2
*H2CO3
*H+
Hypoventilation
increased CO2
increased H2CO3
increased H+
State the following Laboratory Values for respiratory acidosis.
*pH
*pCO2
*HCO3-
Laboratory Values
pH < 7.35
pCO2 > 45 mm Hg
HCO3- unchanged
State the 4 main causes of respiratory acidosis.
Etiologies
*Obstructive Lung Diseases
*Restrictive Lung Diseases
*Hypoventilation
*Depression of respiratory center by drugs or disease
-narcotics
-inappropriate ventilator settings
State the 5 main signs and symptoms of respiratory acidosis.
Signs and symptoms
*Cyanosis
*Shallow breathing
*Dyspnea: Dyspnea is a term used to describe the sensation of difficult or labored breathing, often referred to as shortness of breath or breathlessness.
*Confusion
*Cardiac dysrhythmias: refer to abnormal heart rhythms or irregularities in the heart’s electrical activity.
What is respiratory alkalosis?
Primarily due to excessive loss of CO2 from body as result of hyperventilation (therefore ↓PCO2 observed)
State the 3 aspects of the mechanism of respiratory alkalosis.
Mechanism
-Hyperventilation
-Low carbonic acid level
-Low CO2
State the following Laboratory Values for respiratory alkalosis.
*pH
*pCO2
*HCO3-
Laboratory Values
pH > 7.45
pCO2 < 35 mm Hg
HCO3- unchanged
State the 2 main causes of respiratory alkalosis.
*Hyperventilation
-anxiety
-panic attacks
*Increased respiratory center activity
-fever
Which part of the tubule and specific cells is involved H+ retention & HCO3- excretion? (Respiratory alkalosis)
During respiratory alkalosis, the type B intercalated cells in the distal convoluted tubule and connecting tubule of the renal tubule play a key role in H+ retention and HCO3- excretion to help maintain acid-base balance in response to changes in respiratory conditions.
State the 5 main signs and symptoms of respiratory alkalosis.
Signs and Symptoms
-Light headedness
-Paresthesia’s
-Twitching
-Chvostek’s sign
-Trousseau’s sign
Lightheadedness:
Hypocalcemia can affect the nervous system, leading to symptoms such as lightheadedness or dizziness.
Paresthesia’s:
Hypocalcemia may cause tingling sensations or numbness, known as paresthesia’s. This can occur around the mouth, in the hands, and in the feet.
Twitching:
Muscle twitching or spasms (fasciculations) can be a symptom of hypocalcemia. Calcium plays a crucial role in muscle contraction, and low levels may lead to increased neuromuscular excitability.
Chvostek’s Sign:
Chvostek’s sign is a clinical sign of hypocalcemia. It is elicited by tapping the facial nerve in the region of the parotid gland, resulting in twitching of the facial muscles, particularly the muscles around the mouth. This response is due to increased neuromuscular excitability.
Trousseau’s Sign:
Trousseau’s sign is another clinical sign of hypocalcemia. It is elicited by inflating a blood pressure cuff on the arm above systolic pressure for a few minutes. This can lead to carpal spasm, where the hand and fingers go into a characteristic position due to increased neuromuscular excitability.
State the 2 aspects of Mechanism of metabolic acidosis.
Retention of nonvolatile acids
Excessive loss of base
What happens to the following during metabolic acidosis?
Laboratory: HCO3-, pH,
Laboratory : HCO3-, pH: decreases
Why does paCO2 decrease later in metabolic acidosis?
In metabolic acidosis, the primary disturbance is a decrease in bicarbonate ions (HCO3-) in the blood, leading to an acidic pH.
To compensate for this acidotic state, the respiratory system responds by increasing the respiratory rate, a compensatory mechanism aimed at reducing the concentration of carbon dioxide (CO2) in the blood.
The increase in respiratory rate results in hyperventilation, which, over time, leads to a decrease in the partial pressure of carbon dioxide (PaCO2).
State the 3 main causes of metabolic acidosis with increased AG.
Metabolic acidosis with an increased anion gap (AG) occurs when there is an excess of acid in the body, leading to a decrease in blood pH.
- Lactic acidosis
hypoxia, reduced lactic acid degradation. - Ketoacidosis
diabetes, starvation, alcoholism… - Renal acidosis
Accumulation of sulphates
- Intoxications
State the 4 main causes of metabolic acidosis without increased anion gap.
- Diarrhea and other losses from the GIT
- Renal tubular acidosis; HCO3-resorption disorders in renal tubule
- Dilution acidosis
administration of large quantities infusion without buffer system? (constant pCO2, HCO3-is quickly diluted) - NH4Cl overdose: This type of metabolic acidosis is often termed “hyperchloremic metabolic acidosis” because of the elevated chloride levels. It is characterized by a decrease in bicarbonate concentration without a corresponding increase in the anion gap.
State the 2 aspects of the mechanisms for metabolic alkalosis.
Increased levels of HCO3-
Decreased levels of H+
State the following laboratory values for metabolic acidosis.
Laboratory Values
pH
HCO3-
Laboratory Values
pH > 7.45
HCO3- > 26 mEq/L
What happens to the following during metabolic alkalosis?
Laboratory: HCO3-, BBs, BE, pH
NB
*Base Excess (BE):
*Buffer Bases (BBs):
Laboratory: HCO3-, BBs, BE, pH
Base Excess (BE):
Base excess is a measure of the amount of excess or deficit of base (primarily bicarbonate) in the blood. It indicates the degree of metabolic acidosis or alkalosis.
A negative base excess suggests metabolic acidosis, while a positive base excess suggests metabolic alkalosis.
Buffer Bases (BBs):
Buffer bases, also known as total buffer base, represent the total concentration of buffers in the blood that can accept or donate protons.
It reflects the blood’s ability to resist changes in pH. Changes in buffer bases are related to changes in bicarbonate levels and can provide additional information about acid-base status.
Why does paCO2 increase later in metabolic alkalosis?
In metabolic alkalosis, the primary disturbance is an excess of bicarbonate (HCO3-) in the blood, leading to an elevated pH. The respiratory system compensates for this alkalosis by decreasing the respiratory drive, resulting in hypoventilation. However, this hypoventilation doesn’t lead to an increase in arterial carbon dioxide (PaCO2); rather, it tends to normalize or decrease PaCO2.
The reason for this is that, in metabolic alkalosis, the decrease in respiratory rate is a compensatory mechanism aimed at reducing the loss of carbon dioxide (CO2) through ventilation. By hypoventilating, the body retains more CO2, which helps counteract the alkaline shift in pH.
State 5 causes of metabolic alkalosis.
*Ingestion of large amounts of sodium bicarbonate
*Parenteral administration of NaHCO3
*Vomiting of gastric contents
*Nasogastric suctioning
*Potassium wasting diuretics
-thiazide diuretics
-loop diuretics
Describe the Potassium Imbalancesin Acidosis
at the kidneys.
Kidney
In acidosis there is an excess of H+
In acidosis the kidneys preferentially eliminate H+
When a H+ is eliminated a K+ is retained.
Increased K+ retention leads to hyperkalemia
Describe the Potassium Imbalancesin Acidosis
at the cellular.
Cellular
In acidosis H+ is buffered in the cell
As H+ moves into the cell, K+ moves out of the cell.
Increased K+ in the ECF produces hyperkalemia.
Describe the Potassium Imbalancesin Alkalosis
at the kidneys.
Kidney
Alkalosis is related to decreased H+ concentration or increased base.
In alkalosis the kidneys preferentially retain H+.
When H+ is retained, a K+ is excreted.
Increased excretion of K+ leads to hypokalemia.
Describe the Potassium Imbalancesin Alkalosis
at the cellular.
Cellular
H+ moves from the cell to the extracellular fluid.
When H+ moves from the cell, it is replaced by a K+.
The result is hypokalemia.
Describe Calcium Imbalancesin Acidosis.
Causes increased release of Ca++ from plasma proteins.
Hypercalcemia
Describe Calcium Imbalancesin Alkalosis.
Causes increased binding of Ca++ to plasma proteins.
Hypocalcemia
Describe the Compensationfor Respiratory Acidosis.
- Chemical buffers immediately take up additional H+
Which one (s)? - The kidneys are the major compensatory mechanism for respiratory acidosis.
-The kidneys retain increased HCO3-
-Serum HCO3- rises above 26 mEq/L
-pH returns to normal
Which chemical buffers compensate for respiratory acidosis?
Describe the Compensationfor Respiratory Alkalosis.
*The kidneys are the major compensatory mechanism for respiratory alkalosis.
*The kidneys excrete more bicarbonate.
*The HCO3+ falls below 22 mEq/L
*This balances the acid-base ratio.
Describe the Compensationfor Metabolic Acidosis.
*The respiratory system is the major compensatory mechanism for metabolic acidosis.
*Hyperventilation occurs
*CO2 is blown off.
*pH returns to normal
Describe the Compensationfor Metabolic Alkalosis.
*The respiratory system is the major compensatory mechanism for metabolic alkalosis.
*Hypoventilation
*pH returns to normal.
