Acid base disorder

ACID BASE DISORDER

DEFINITION

• Changes in the ECF bicarbonate concentration that commonly occur because of a build-up or loss of hydrogen ion.

Acid Base Balance

• Several mechanism helps maintain the pH of systemic arterial blood between 7.35 & 7.45

• The removal of H+ from the body depend on the following 3 major mechanism:

a) Buffer system

act quickly to temporarily bind H+, removing the highly reactive excess H+, and raising the pH.

b) Exhalation of CO2

By increasing the rate and depth of breathing, more CO2 can be exhaled. Within minutes this reduces the level of carbonic acid in blood, which raises the blood pH ( blood H+ level).

c) Kidney excretion of H+

the slowest mechanism, but the only way to eliminate acids, through urine.

Acidosis & Alkalosis

• A change in blood pH that leads to acidosis or alkalosis may be encountered by compensation which response to acid base imbalance.

• If a person has altered blood pH due to metabolic causes, hyperventilation of hypoventilation can help bring the blood pH back to normal. This form of compensation, occurs within minutes and reaches its maximum within hours.

Respiratory acid-base imbalance

• If a person altered blood pH due to respiratory causes, then renal compensation –changes in secretion of H+ and reabsorption of HCO3- by the kidney tubules –can help reverse the change.

• Renal compensation may begin in minutes, but it takes days to reach maximum effectiveness.

• Both respiratory acidosis and alkalosis are disorders resulting from changes in partial pressure of CO2 (PCO2) in systemic arterial blood (35-45 mmHg).

• By contrast, both metabolic acidosis and alkalosis are disorders resulting from changes in HCO3- concentration (22-26 mEq/L) in systemic arterial blood.

Respiratory Acidosis

• PCO2 level (>45mmHg).• pH (7.35) if there is no compensation.

Common causes:• Hypoventilation due to emphysema,

pulmonary edema, trauma to respiratory center, airway obstruction or dysfunction of muscles of respiration.

Compensatory mechanism:• Renal:

excretion of H+

reabsorption of HCO3-

Aim of treatment:• Exhalation of CO2 by providing ventilation

therapy. In addition IV HCO3- administration may be helpful.

Respiratory Alkalosis

• PCO2 level (<35mmHg).• pH (7.45) if there is no compensation.

Common Cause:• Hyperventilation due to oxygen deficiency,

pulmonary, pulmonary disease, cerebrovascular accident (CVA), or severe anxiety.

Compensatory mechanism:• Renal:

excretion of H+

reabsorption of HCO3-

Aim of treatment:• Is aimed at increasing level of CO2 in the

body. One simple treatment is to have the person inhale and exhale into a paper bag for a short period.

Metabolic Acidosis

• HCO3- (<22mEq/L).• pH (<7.35) if there is no compensation.

Common Cause:• Loss of bicarbonate ions due to diarrhea,

accumulation of acid (ketosis), renal dysfunction.

Compensatory mechanism:

• Respiratory:

hyperventilation, which increases the loss of CO2

Aim of treatment:• If the problem is not too severe,

hyperventilation can help bring blood pH into the normal range. Treatment consists of administering IV solution of sodium bicarbonate and correcting the cause of acidosis.

Metabolic Alkalosis

• HCO3- (>26mEq/L).• pH (>7.45) if there is no compensation.

Common Cause:• Loss of acid due to vomiting, gastric

suctioning or use of certain diuretics, excessive intake of alkaline drugs.

Compensatory mechanism:

• Respiratory:

hypoventilation, which increases the loss of CO2

Aim of treatment:• If the problem is not too severe, hyperventilation

can help bring blood pH into the normal range. Treatment consists of administering IV solution of sodium bicarbonate and correcting the cause of acidosis.

Diagnosis

• Evaluation of 3 factors in a sample of systemic arterial blood:-pH, [HCO3-], PCO2

• Examined in the following 4 step sequence:1. Note whether the pH is high (alkalosis) or low(acidosis).

2. Then check whether which value PCO2 or HCO3- is out of the normal range and could be the cause of the pH change. For example, elevated pH could be caused by low PCO2 or high HCO3-.

3. If the cause is a change in pH PCO2, the problem is respiratory; if the case is a change in HCO3-, the problem is metabolic.

Homework

• Summarize respiratory and metabolic acidosis and alkalosis (in form of table).

• *note: definition, common cause and compensatory mechanism

• Question 1

A patient was admitted at the A&E department in hospital due to ethylene glycol poisoning. Following are the arterial blood diagnosis:

Laboratory findings Patient Normal

pH 5.3 7.4 + 0.05

pCO2 40 mmHg 40mmHg

HCO3 15mmHg 20mmHg

  What is the diagnosis for the above condition? (1m)

What is the compensatory action occurs in the body of the above patient? (1m)

Explain on one of the common cause of the above condition. (1m)

• Question 2

A patient was admitted at the A&E department in hospital. Following are the arterial blood diagnosis:

Laboratory findings Patient Normal

pH 7.85 7.4 + 0.05

pCO2 20mmHg 40mmHg

  What is the diagnosis for the above condition? (1m)

What is the 2 compensatory action occurs in the body of the above patient? (2m)

Explain on one of the common cause of the above condition. (1m)

• Question 3

A patient was presented at the A&E department in hospital with the symptoms of vomiting.

Estimate the probable arterial blood diagnosis. (2m)

What is the diagnosis for the above condition? (1m)

Write down the pathophysiology that lead to the above condition starting from the ABG test. (2m)

  What is the compensatory action occurs in the body of the above patient? (1m)

What are the other common cause that lead to the above condition. (2m)

• Question 4

A patient was admitted at the A&E department in hospital. Following are the arterial blood diagnosis:

Laboratory findings Patient Normal

pH 7.2 7.4 + 0.05

pCO2 60mmHg 40mmHg

  Justify the above condition? (2m)

What is the 2 compensatory action occurs in the body of the above patient? (2m)

Explain on one of the common cause of the above condition. (1m)

• Question 5HCO3- level is decreased, the compensatory mechanism shows high PCO2

What would be the probable value of pH? (1m)Interpret the above value and how does it lead to the above condition? (2m)Suggest one possible clinical condition that lead to the above disorder. (1m)

• Question 6PCO2 increased, the compensatory mechanism shows increased HCO3- What would be the probable value of pH? (1m)Where does the compensatory action took place? (1m)What is another result of compensatory action? (1m)Suggest one possible clinical condition that lead to the above disorder. (1m)

• Question 7PCO2 decreased, the compensatory mechanism shows decreased HCO3- What would be the probable value of pH? (1m)Where does the compensatory action took place? (1m)What is another result of compensatory action? (1m)Suggest one possible clinical condition that lead to the above disorder. (1m)

• Question 8

A patient was presented at the A&E department in hospital diagnosed with hypoxia or raised intracranial pressure.

Estimate the probable arterial blood diagnosis. (2m)

What is the diagnosis for the above condition? (1m)

Explain the compensatory mechanism. (2m)

Where does the compensatory action took place? (1m)

• Question 9

A patient was presented at the A&E department in hospital diagnosed with acute exacerbation asthma.

Estimate the probable arterial blood diagnosis. (2m)

What is the diagnosis for the above condition? (1m)

Explain the compensatory mechanism. (2m)

Where does the compensatory action took place? (1m)

• Question 10

A patient was presented at the A&E department in hospital diagnosed with renal failure with bicarbonate being lost in the urine.

Estimate the probable arterial blood diagnosis. (2m)

What is the diagnosis for the above condition? (1m)

Explain the compensatory mechanism. (2m)

Where does the compensatory action took place? (1m)

• Question 11

A patient was presented at the A&E department in hospital diagnosed with extremely high ingestion of sodium bicarbonate.

Estimate the probable arterial blood diagnosis. (2m)

What is the diagnosis for the above condition? (1m)

Explain the compensatory mechanism. (2m)

Where does the compensatory action took place? (1m)

• Blood gas syringes