Blood Gas Analysis

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Questions and Answers

What is the approximate linear range of PCO2 in arterial blood?

10-20 kPa

40-80 mmHg

20-40 mmHg

10-40 kPa (correct)

What is the normal blood pH range?

7.45-7.55

7.35-7.45 (correct)

7.20-7.30

7.25-7.45

What is the effect of an increase in alveolar ventilation on PCO2 levels?

Decreases PCO2 levels (correct)

Increases PCO2 levels

Has no effect on PCO2 levels

Causes respiratory acidosis

What is the solubility of CO2 in blood (in mmol/dl/kPa)?

0.23 Signup and view all the answers

What is the ratio of [HCO3-] / [CO2] in the Henderson-Hasselbach equation?

20 Signup and view all the answers

What is the dissociation constant of H2CO3 (pKa)?

6.1 Signup and view all the answers

What is the effect of decreasing ventilation on PCO2 levels?

Increases PCO2 levels Signup and view all the answers

What is the amount of CO2 produced by tissues for every 100 ml of blood passing through?

4 ml Signup and view all the answers

What is the primary effect of anaemia on oxygen carriage?

Reduced oxygen carrying capacity Signup and view all the answers

What is the purpose of the Bohr shift in oxygen unloading?

To decrease oxygen binding to haemoglobin Signup and view all the answers

What is the effect of 2,3 DPG on oxygen binding to haemoglobin?

Decreases oxygen binding affinity Signup and view all the answers

What is the relationship between pH and oxygen binding to haemoglobin?

Increased pH decreases oxygen binding affinity Signup and view all the answers

What is the effect of fetal haemoglobin on oxygen carriage?

Increases oxygen binding affinity Signup and view all the answers

What is the unit of measurement for PO2 in the graph?

mmHg Signup and view all the answers

What does dead space ventilation refer to in the context of respiration?

The volume of air that does not participate in gas exchange Signup and view all the answers

What is the formula to calculate alveolar ventilation?

Minute ventilation - dead space ventilation Signup and view all the answers

What is the normal oxygen uptake in the alveoli?

250 ml/min Signup and view all the answers

What is the respiratory quotient (RQ) in the context of respiration?

The ratio of CO2 produced to O2 utilised Signup and view all the answers

What is the result of hyperventilation?

A decrease in arterial PCO2 Signup and view all the answers

What is the formula to calculate O2 consumption using the Fick principle?

Cardiac output x (arterial - venous O2 content) Signup and view all the answers

What is the result of hypoventilation?

An increase in arterial PCO2 Signup and view all the answers

What is the normal CO2 production in the tissues?

200 ml/min Signup and view all the answers

What is the primary reason for the difference in oxygen affinity between HbA and HbF?

The different globin subunits in HbF Signup and view all the answers

What is the result of the differences in oxygen affinity between HbA and HbF?

Favours O2 moving from mother's blood to fetal blood across the placenta Signup and view all the answers

What is the cause of peripheral cyanosis?

Reduced blood flow to a region Signup and view all the answers

What is the best site to spot central cyanosis?

Buccal mucosa and lips Signup and view all the answers

What is the definition of cyanosis?

A condition where the oxygen supply to the tissues is deficient Signup and view all the answers

What is the result of hypoxia on the tissue capillaries?

Increased de-oxyHb content in the tissue capillaries Signup and view all the answers

What is the difference between peripheral and central cyanosis?

Peripheral cyanosis is caused by reduced blood flow, while central cyanosis is caused by arterial hypoxaemia Signup and view all the answers

What is the effect of low temperature on the body?

Reduced blood flow to the extremities Signup and view all the answers

What is the primary difference between increased ventilation during exercise and hyperventilation?

Increased ventilation during exercise is closely matched to the increase in metabolic rate Signup and view all the answers

What is the effect of low PCO2 on the concentration of H+ ions?

It decreases the concentration of H+ ions Signup and view all the answers

What is a possible consequence of hyperventilation on excitable cells?

Increased excitability due to increased plasma free [Ca2+] Signup and view all the answers

What is a potential cause of metabolic acidosis that can lead to hyperventilation?

Renal failure Signup and view all the answers

What is the effect of high PCO2 due to hypoventilation on CNS function?

It depresses CNS function Signup and view all the answers

What is the normal range for arterial PCO2 in kPa?

5.3-6 kPa Signup and view all the answers

What is a consequence of high PCO2 due to hypoventilation on peripheral vasculature?

Peripheral vasodilation Signup and view all the answers

What is a possible cause of hyperventilation?

Anxiety Signup and view all the answers

Study Notes

Oxygen Carriage and Anaemia

Anaemia is a condition where there is a reduced content of functional haemoglobin in the blood, leading to a reduction in O2 carrying capacity.
Defects in haemoglobin production or red cell numbers can cause anaemia, with various underlying causes such as defects in Hb synthesis, mutations in genes, or production or loss of red cells.
The effects of anaemia on O2 carriage can be seen in the O2 dissociation curve, where the curve shifts to the right, indicating a decrease in O2 binding affinity.

Fetal Haemoglobin

Fetal haemoglobin (HbF) has a different globin structure, with 2a and 2g globin subunits, which increases the affinity of the haem group for O2.
HbF binds DPG less, favouring O2 movement from the mother's blood to the fetal blood across the placenta.

Cyanosis

Cyanosis occurs when the supply of O2 to the tissues is deficient, causing an increase in de-oxyHb in tissue capillaries, which has a blueish tinge, leading to discolouration of the tissues.
There are two types of cyanosis: peripheral and central.
Peripheral cyanosis occurs due to reduced blood flow to a region, resulting in hypoxic tissue and a bluish grey tinge in extremities.
Causes of peripheral cyanosis include cardiovascular shock, low temperature, reduced cardiac output, and poor arterial supply.
Central cyanosis occurs due to arterial hypoxaemia, characterized by a reduction in O2 content, and can be seen in the conjunctiva, ear lobes, buccal mucosa, and lips.

CO2 and pH Regulation

The Haldane effect states that for a given PCO2, there is more CO2 content in venous than arterial blood.
At rest, tissues produce 4 ml of CO2 for 100 ml of blood passing through.
The Henderson-Hasselbach equation defines the relationship between pH, PCO2, and HCO3-.
The normal blood pH range is 7.35-7.45, and the ratio of HCO3- to CO2 is 20, resulting in a pH of 7.4.

Ventilation and Alveolar PCO2

Alveolar PCO2 is inversely proportional to alveolar ventilation, such that an increase in ventilation will decrease PCO2 levels and increase pH.
Conversely, decreasing ventilation will increase PCO2 levels and decrease pH.
Alveolar ventilation is the volume of air that reaches the alveoli where gas exchange can occur, and is calculated by subtracting dead space ventilation from minute ventilation.

Ventilation and Metabolic Rates

Normally, O2 uptake in the alveoli equals O2 utilised by the tissues, which is approximately 250 ml/min.
CO2 produced in the tissues is equal to the amount removed in the alveoli, which is approximately 200 ml/min.
The respiratory quotient (RQ) is the ratio of CO2 produced to O2 utilised, and is dependent on the diet.

Mismatching of Ventilation and Metabolic Requirement

Hyperventilation occurs when ventilation is greater than metabolic requirement, leading to a lowering of arterial PCO2 below normal values.
Hypoventilation occurs when ventilation is less than metabolic requirement, resulting in higher arterial PCO2 levels.
Hyperventilation can lead to respiratory alkalosis, cerebral vasoconstriction, and cerebral hypoxia, while hypoventilation can lead to respiratory acidosis, peripheral vasodilation, and depressed CNS function.

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Description

This quiz covers the analysis of blood gas parameters, including pH, PCO2, and temperature, in relation to 2,3 DPG levels and various medical conditions.