Arterial Blood Gases Flashcards
What is PO2?
the partial pressure of oxygen: This variable indicates how much oxygen is dissolved in the arterial blood, and if it is particularly low it can suggest inadequate gas exchange in the lungs
What is PCO2?
the partial pressure of carbon dioxide: This variable indicates how much CO2 is dissolved in arterial blood, and if it is particularly high it can suggest inadequate gas exchange in the lungs
What is pH?
the ‘power of hydrogen’: This variable describes the acidity, neutrality or alkalinity of the blood. The pH of arterial blood is finely tuned and small deviations can affect oxygen transport and delivery
What is HCO3?
plasma bicarbonate: This variable describes the concentration of bicarbonate dissolved in arterial blood. If plasma bicarbonate is higher or lower than normal, this could be evidence of gas exchange imbalance
What is base excess (BE)?
This variable describes the concentration of bases (predominantly bicarbonate) compared with the ‘expected concentration’. An exact match is 0, an excess of base is positive and a base deficit is negative
More digestible way of presenting bicarbonate
What is the PO2 when blood is first pumped into the systemic systems?
Oxygen enters RBCs
Oxygenated blood is pumped into systemic system
At start as PO2 greater than 10 kPa
What is the PO2 when blood is in the venous system?
Between 4-5.3 kPa
What is pulmonary transit time?
How long the RBCs are close enough to the respiratory exchange system to exchange gases
What is a point of care test?
Analyser very close to the patient
Not sent of to the blood
How do you convert a proton concentration to pH?
𝑝𝐻= - 𝑙𝑜g 10 [𝐻^+]
As proton concentration increases, pH decreases
The body produces a signifcant amount of acid how much is respiratory and how much is metabollic?
99% is Respiratory
What is CO2 flux?
Measures CO2 before and after the tissues
e.g. for every decilitre of blood that passes through, 4ml of CO2 is produced
200ml per minute of CO2 produced in an average adult male
300L of acid and cleared by the lung in a day
What happens if there is an imbalance
Blood has an enormous buffering capacity that can react almost immediately to imbalances
What is corrective compensation?
Changes in ventilation can stimulate a RAPID compensatory response to change CO2 elimination and therefore alter pH
What is different between corrective compensation in the lungs and in the kidney?
Changes in HCO3- and H+ retention/secretion in the kidneys can stimulate a SLOW compensatory response to increase/decrease pH
RAPID in the lungs
