Arterial Blood Gasses (ABGs)

What is the primary function of the pH scale in a physiological context?

It is the measurement by which we determine the acidity or alkalinity of bodily fluids.

What is the normal, tightly regulated pH range for the human body?

The normal pH range is 7.35 to 7.45.

A blood pH value of less than 7.35 represents a state of _____.

acidosis

A blood pH value greater than 7.45 represents a state of _____.

alkalosis

Why is maintaining an average body pH of approximately 7.4 considered optimum?

This pH level is optimum for blood oxygenation, as the interaction between haemoglobin and O2 is affected by pH changes.

How does a change in pH disrupt the function of many proteins in the body?

Protons (H+ ions) bind to amino acids, which changes the protein's shape and function.

What is the pH scale actually measuring?

The concentration of hydrogen ions (H+) in a solution.

What is the maximum pH range that the human body can tolerate, and only for a short time?

The body can only tolerate a pH range between 6.9 and 7.8 for a short time.

A blood pH of less than 6.8 or greater than 7.8 is considered to be what?

It is considered incompatible with life.

What are Arterial Blood Gases (ABGs)?

They are measurements of factors that help to determine the acid-base balance of the body.

Which three ABG measurements directly contribute to determining the acid-base balance?

pH, partial pressure of carbon dioxide (PaCO2​), and concentration of bicarbonate (HCO3−​).

What does Base Excess (BE) measure in an ABG analysis?

It measures the amount of acid or base needed to restore blood pH to normal.

A positive value for Base Excess (BE) indicates an excess of what?

An excess of base.

Which two ABG measurements relate to oxygen status but do not contribute to acid-base balance?

Partial pressure of oxygen (PaO2​) and the saturation percentage of haemoglobin (SaO2​).

What is the first step in the 4-step analysis of an arterial blood gas?

Step 1 is to check the pH to identify acidosis or alkalosis.

What is the second step in the 4-step analysis of an arterial blood gas?

Step 2 is to check the partial pressure of carbon dioxide (PaCO2​).

What is the third step in the 4-step analysis of an arterial blood gas?

Step 3 is to check the bicarbonate (HCO3−​) level.

What is the fourth and final step in the 4-step analysis of an arterial blood gas?

Step 4 is to determine the compensation status.

What is the normal range for the partial pressure of carbon dioxide (PaCO2​) in arterial blood?

The normal range is 4.5 to 6.0 kPa.

What condition does a PaCO2​ level higher than 6.0 kPa indicate?

Respiratory Acidosis.

What condition does a PaCO2​ level lower than 4.5 kPa indicate?

Respiratory Alkalosis.

If bicarbonate (HCO3−​) levels are abnormal, the underlying issue is likely to be of what origin?

The underlying issue is likely to be metabolic.

What is the normal range for bicarbonate (HCO3−​) concentration in arterial blood?

The normal range is 22 to 26 mmol/L.

A bicarbonate (HCO3−​) level lower than 22 mmol/L indicates what condition?

Metabolic Acidosis.

A bicarbonate (HCO3−​) level higher than 26 mmol/L indicates what condition?

Metabolic Alkalosis.

In acid-base balance, what is meant by 'compensation'?

It is an emergency response where one system (respiratory or metabolic) tries to correct a pH change caused by an issue in the other system.

An acid-base imbalance is described as 'uncompensated' when the opposing system has done what?

The opposing system has remained within its normal range.

An acid-base imbalance is 'partially compensated' when the opposing system has changed but has not been sufficient to do what?

It has not been sufficient to bring the pH back within the normal range of 7.35-7.45.

An acid-base imbalance is 'fully compensated' when the opposing system's change is sufficient to do what?

It is sufficient to bring the pH back within the normal range.

What is the normal range for Base Excess (BE)?

The normal range is -2 to +2 mEq/L.

What is the normal range for the partial pressure of oxygen (PaO2​) in arterial blood?

The normal range is 10.7 to 13.3 kPa.

What is the normal range for the saturation percentage of haemoglobin in arterial blood (SaO2​)?

The normal range is 96% to 98%.

What is the definition of Type 1 respiratory failure?

Type 1 (hypoxemic) respiratory failure occurs when the respiratory system cannot provide enough oxygen to the body.

In Type 1 respiratory failure, the arterial partial pressure of oxygen (PaO2​) is less than _____ kPa.

8 kPa

In Type 1 respiratory failure, what is the typical level of the arterial partial pressure of carbon dioxide (PaCO2​)?

The PaCO2​ level is normal or low.

What is the definition of Type 2 respiratory failure?

Type 2 (hypercapnic) respiratory failure occurs when the respiratory system cannot remove enough carbon dioxide from the body.

In Type 2 respiratory failure, the arterial partial pressure of oxygen (PaO2​) is less than _____ kPa.

8 kPa

In Type 2 respiratory failure, the arterial partial pressure of carbon dioxide (PaCO2​) is higher than _____ kPa.

6 kPa

What two organ systems work together to restore the body's acid-base balance?

The respiratory and renal systems.

What is the reversible chemical equation for the bicarbonate buffer system in the blood?

H2​O+CO2​↔H2​CO3​↔H++HCO3−​

What physiological state, defined by reduced minute volume, causes respiratory acidosis?

Hypoventilation.

How does hypoventilation lead to respiratory acidosis?

Excess carbon dioxide accumulates, causing a build-up of hydrogen ions in the blood and a fall in pH.

What physiological state, defined by increased minute volume, causes respiratory alkalosis?

Hyperventilation.

How does hyperventilation lead to respiratory alkalosis?

Reduced carbon dioxide levels lead to a deficit of hydrogen ions in the blood, causing the pH to increase.

How is metabolic acidosis typically caused?

The body either gains non-respiratory acid or loses base, resulting in a build-up of H+ ions or a deficit of bicarbonate ions.

How is metabolic alkalosis typically caused?

The body either gains base or loses acid, resulting in a build-up of bicarbonate ions or a deficit of H+ ions.

Term: FiO2

Definition: Fraction of Inspired Oxygen, expressed as a fraction (e.g., 0.21 for 21% oxygen).

What is the approximate FiO2 of room air?

The FiO2 of room air is approximately 0.21 (or 21%).

In metabolic acidosis, excess non-respiratory acids must be buffered by 'spare' _____, causing its levels to fall.

bicarbonate

During metabolic alkalosis, the loss of H+ ions via metabolic systems causes more carbon dioxide to be converted, leading to increasing levels of what?

Bicarbonate (HCO3−​).

A patient with COPD is an example of a common cause for which type of respiratory failure?

Type 2 (hypercapnic) respiratory failure.

Pneumonia or pulmonary oedema are common causes of which type of respiratory failure?

Type 1 (hypoxemic) respiratory failure.