Oxygen measurements Flashcards
What is the maximum quanity of O2 that can combine with haemoglobin in a unit volume of blood?
1g haemoglobin can combine with 1.34 ml O2
What are normal Hb levels?
male-160g/litre
female- 135g/litre
what is the O2 saturation equation?
O2 saturation = O2 bound to Hb (ml/l) / O2 capaciity (ml/l)
x100
what does spO2 stand for?
peripheral oxygen saturation (measured using pulse oximetry)
What does SaO2 stand for?
arterial oxygen saturation
define oxygen content/ CaO2
the total volume of oxygen carried in a litre of blood
what are the units of oxygen content?
mls per litre of blood
What is the equation for oxygen content?
oxygen content= oxygen carried by Hb + oxygen in solution
(1.34 xHB x spo2/100) +(0.225 x paO2)
What factors does the oxygen content of arterial blood depend on?
1- partial pressure of inspired oxygen
2-the adequacy of ventilation and gas exchange
3-haemoglobin level and affinity of Hb for oxygen
what does PaO2 determine?
the oxygen saturation of haemoglobin (the oxygen dissociation curve)
Does anemia affect PO2 or oxygen saturation?
No
Define hypoxaemia
lack of oxygen in the blood (PaO2 is below normal)
Define Hypoxia
reduced oxygen supply to the tissues
Define cyanosis
Blue coloration of the skin and mucus membranes resulting from raised levels of deoxyhaemoglobin caused by hypoxaemia
What causes hypoxaemia?
1-hypoventilation
(causes hypercapnia which raises CO2 in the blood)
2-diffusion limitaion
(more effect on O2 as CO2 is 20 times more soluble)
3-shunt
4-V/Q mismatch or inequality
Why does a shunt cause hypoxaemia?
arterial blood which has not passed through ventilation areas of the lung
what is a V/Q inequality/
ventilation and perfusion are not matched
PH blood range
7.35-7.45
PCO2 blood gas range
4.8-6.0
PO2 blood gas range
10.0-13.5
Sa02 blood gas range
95.0-98.0
HCO3 blood gas range
22.0-26.0
units of PCO2 and Po2
KPa
SaO2 units
%
HCO3 units
mmol/L
When does respiratory failure occur?
when insufficent oxygen passes from the air in the alveoli into the blood
What are the oxygen levels in the blood of someone with hypoxaemia?
10KPa
How is respiratory failure defined?
PaO2 < 8KPa
What are the two types of respiratory failure?
type 1- oxygenation
tyoe 2- ventilation
What is type 1 respiratory failure?
-oxygenation
-low levels of oxygen in the blood (hypoxaemia) with a normal or reduced arterial partial pressure of CO2
-PaCo2<6KPa
What is type 2 respiratory failure?
-ventilation
hypoxaemia with raised CO2
-PaCO2> 6KPa
define oxygen capacity
is the maximum quantity of oxygen which can combine with haemoglobin in a unit volume of blood.
