Acid-base Balance Values In Different Conditions:

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× MENU Acid-base Balance:- Part 5 – Bicarbonate Level (HCO3-) March 16, 2025Chemical pathologyLab Tests Bicarbonate Level (HCO3–)

What sample is needed for Bicarbonate Level (HCO3–)?

It is done on the patient’s serum or plasma (plasma arterial or venous can be used).
- The best anticoagulant is heparin.
The test should be done as soon as possible, and the time interval between taking and analyzing a sample should be minimized.
Collect samples anaerobically, and heparin is the preferred anticoagulant.

What are the indications for Bicarbonate Level (HCO3–)?

It assists in evaluating the pH of the patient.
It also assists in evaluating electrolyte balance.
The bicarbonate ion measures a metabolic (renal) component of the acid-base equilibrium.

How will you define Bicarbonate Level (HCO3–)?

This is the second most plasma anion after chloride.
As an index bicarbonate ions concentration, this measures the total CO2 in the blood (serum).
>90% of blood CO2 exists in the ionized HCO3– form, which is converted to CO2 by adding a standard amount of acid in the serum.
Arterial blood has less CO2 than venous blood.
For the result’s uniformity, total CO2 is done on venous blood serum where the normal range is 19 to 25 meq/L.
The CO2 contents measure H2CO3, dissolved CO2, and the HCO3– anions.
1. H2CO3 and dissolved CO2 contents in the blood are so small that CO2 contents are an indirect measure of HCO3– anions.
HCO3– Play a major role in the acid-base balance.

Bicarbonate level (HCO3-): HCO3- ECF ICF distribution

How will you discuss the pathophysiology of Bicarbonate Level (HCO3–)?

Bicarbonate is the most important buffer system in the blood, maintaining the pH (acid-base balance).
H+ + HCO3 –↔ H2O + CO2
1. Buffer pair = HCO3– / H2CO3
2. The ratio = HCO3– / H2CO3 = 20:1
  1. HCO3– = 24 meq/L (ECF)
  2. HCO3– = 12 meq/L (ICF)
  3. Carbonic acid = 1.2 meq/L
  4. Normal pH = 7.4
Correction occurs when the values for both components of the buffer pair (HCO3 / H2CO3) return to normal.
Bicarbonate measures a metabolic (Kidney) component of acid-base balance.
The kidney easily regulates bicarbonate, which excretes excess and retains it when needed.
This buffer pair (HCO3–/H2CO3) operates in the kidneys and the lungs and is the major extracellular buffer.
Most of the CO2 in the body is in the form of HCO3-, so the CO2 level in the blood measures HCO3–.
1. The CO2 contents measure H2CO3, dissolved CO2, and the bicarbonate (HCO3–) ions present in the blood.

How will CO2 be carried in the blood?

Dissolved in the plasma (pCO2).
As bicarbonate (HCO3–).
Carbamino compound.

Bicarbonate metabolism

Various respiratory and metabolic disturbances affect the bicarbonate level, affecting acid-base balance.
1. HCO3– ion measures the metabolic kidney part of the acid-base balance.
HCO3– is exchanged for other ions like Chloride and Phosphate to maintain electroneutrality.

Bicarbonate (HCO3-) regulation in kidney

Bicarbonate (HCO3-) regulation in the kidney

Bicarbonate metabolism and absorption

When the HCO3 level increases, the pH also increases.

What is the role of the Kidney in acid-base balance?

Kidneys play an important role in the balance of the acid-base system (compensation).
Kidneys compensate by producing more acidic or alkaline urine.
In respiratory acidosis, the kidney compensates by increased reabsorption of HCO3–.
In respiratory alkalosis, the kidney compensates by increased excretion of HCO3–.

Bicarbonate (HCO3-) and kidney role for acid-base balance

What is the role of Lungs in acid-base balance?

Lungs compensate by increased or decreased blow-off of CO2, and this will change the pH.

Acid-base balance: CO2 role for pH by the lungs

What is the normal Bicarbonate Level (HCO3–)?

Arterial blood = 21 to 28 meq/L
Venous blood = 22 to 29 meq/L
- Peritoneal fluid = 24 to 29 meq/L
- Duodenal fluid = 4 to 21 meq/L
- Pancreatic fluid = 66 to 127 meq/L
For SI, the unit multiplication factor is 1, which will be in mmol/L

What are the causes of decreased Bicarbonate (HCO3-) levels?

Addison disease
Diarrhea
Ethylene glycol poisoning
Ketoacidosis
Kidney disease
Lactic acidosis
Metabolic acidosis
Starvation.
diabetic ketoacidosis.
Methanol poisoning
Salicylate toxicity (such as aspirin overdose)
Liver disease

What are the causes of increased Bicarbonate (HCO3-) levels?

Breathing disorders (compensated respiratory acidosis)
Cushing syndrome
Excessive vomiting
Hyperaldosteronism
Ingestion of excessive amounts of antacids, diuretics, and steroids
Severe vomiting.

What are the conditions that may alter bicarbonate (HCO3–) levels?

Alkalosis
Delirium
Dementia
Renal tubular acidosis, distal.
Renal tubular acidosis, proximal.

Acid-base balance and HCO3– level

Acidemia means arterial blood pH <7.4.
- Acidosis means a systemic increase in H+ ions.
Alkalemia means arterial blood pH >7.4.
- Alkalosis means a systemic decrease in H+ ions.

Respiratory acidosis:

An absolute CO2 excess results in decreased pH, increased pCO2, and a base deficit.

Acid-base Respiratory acidosis

Respiratory alkalosis:

There is an absolute CO2 deficit that results in increased pH and decreases pCO2 and base excess.

Respiratory alkalosis

Acid-base Respiratory alkalosis compensatory mechanism

Metabolic acidosis:

There is an absolute HCO3 deficit, resulting in decreased pH and HCO3.

Metabolic acidosis

Acid-base metabolic acidosis compensatory

Metabolic alkalosis:

There is absolute HCO3 excess, resulting in increased pH and HCO3 levels.

Metabolic alkalosis

Acid-base metabolic alkalosis compensatory mechanism

Acid-base summary

What are the Acid-base balance values in different conditions?

HCO3	pCO2	pH	Etiology
Normal values	22 to 26 meq/L	35 to 45 mm Hg	7.35 to 7.45
Metabolic alkalosis	Increased	Normal	Increased	Prolonged vomiting Nasogastric drainage NaHCO3 overdose
Metabolic acidosis	Decreased	Normal	Decreased	Diabetes Intestinal fistula kidney disease
Respiratory alkalosis	Decreased	Decreased	Increased	Hyperventilation
Respiratory acidosis	Increased	Increased	Decreased	Drugs causing respiratory depression

What are the Panic values?

Clinical parameter	Panic value
pH	<7.25 or >7.55
pO2	<50 mm Hg
pCO2	>60 mm Hg

What parameters are needed for acid-base balance?

Lab test	Importance
pH	This will tell: Increased pH value indicates alkalosis A decreased value of pH indicates acidosis
pCO2	This is the partial pressure of CO2, and it will tell: The respiration modulates this pCO2 This is the index of ventilation
pO2	This is the partial pressure of the O2 in the arterial blood and tells: Low values indicate hypoxia pO2 is the indirect measure of O2 contents of arterial blood.

Questions and answers:

Question 1: What is the panic value of pH?Show answer pH panic values are <7.25 and >7.55. Question 2: What is the role of lungs in acid-base balance?Show answer Increase or decrease in the respiration changes the pH. Possible References Used Go Back to Chemical pathology

Comments

Jabbarkhan Reply May 16, 2022

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Dr. Riaz Reply May 16, 2022

The topic is upgraded. Thanks for your remarks.