Oxygen Therapy
Key Points
Key Points
Fraction of inspired oxygen (FiO2) is the fraction or percentage of oxygen in the air that is inspired in lungs. Medical patients experiencing difficulty breathing are provided with oxygen-enriched air, which means a higher-than-atmospheric FiO2. Natural air includes 21% oxygen, which is equivalent to FiO2 of 0.21. Oxygen-enriched air has a higher FiO2 than 0.21; up to 1.00 which means 100% oxygen. FiO2 is typically maintained below 0.5 even with mechanical ventilation, to avoid oxygen toxicity.
Formula :FiO2 = 20% + (4 x Oxygen flow rate)
Eg: 1 liters = 24%
2 liters =28 % etc
NASAL CANNULA:
Flow rate – 2-6 litres per min
24-45 percentage
Advantage – light weight, comfortable, inexpensive and continuous
use with meals and activity.
Disadvantage – nasal mucosa drying
Oropharyngeal catheter
Flow rate – 1-6 Litres
Deliver 22-44 %
Adv – inexpensive and no need for tracheostomy
Dis adv – mucosal drying, catheter should be changed frequently to both nostrils.
Simple face mask
Flow rate – 6-8 Litres
Deliver 40-60%
Adv – inexpensive and simple to use
Dis adv – mucosal drying poor fitting
Partial rebreather mask
Flow rate – 8-11 Litres
Deliver 50-75 %
Adv – moderate oxygen concentration
Dis adv – mucosal drying ,poorly fitting, must remove to eat.
Non rebreather mask
Flow rate – 10-12 Litres
Deliver 80-100 %
Adv – High oxygen concentration
Dis adv – poorly fitting ,must remove to eat
Trans tracheal catheter
Flow rate – 4 Litres/min
Deliver 60=100 %
Adv – more comfortable, concealed by clothings, less O2 is needed to achieve 100% saturation
Dis adv – requires frequent and regular cleaning and needs surgical intervention
Venturi mask
Flow rate – 4-6 l/min
Deliver 24-40 %
Ady – precise Fio, and additional humidity available
Dis adv – must be removed to eat
Trans tracheal catheter
Flow rate – 4 Litres/min
Deliver 60=100 %
Adv – more comfortable , concealed by clothings, less O, is needed to achieve 100% saturation
Dis adv – requires frequent and regular cleaning and needs surgical intervention
Aerosol mask
Flow rate – 8-10 Litres/min
Deliver 21- 100% FiO2 based on nebulizer setting
Adv – good humidity and accurate FiO2
Dis adv – uncomfortable for some
Tracheostomy collar
Flow rate – 8-10 Litres/min
Deliver 30- 100%
Adv – good humidity, comfortable ,fairly accurate FiO2
Dis adv – requires surgical intervention
High Flow Oxygen Delivery Calculation
In order to compute the ratio of O2 to air required for delivering a particular FiO2 through high-flow system a simple aid referred to as “magic-box’ (figure 1) is often used. To use this aid draw a box and place 20 (room ait) at the top left and 100 at the bottom left. Then place the desired O2 percentage in the middle of the box (in this case 70). Next, subtract diagonally from lower left to upper right (disregard the sign). Then subtract diagonally again from upper left to lower right (disregard sign). The resulting numerator (30) is the value for air, with denominator (50) being the value for oxygen. Air to oxygen ratio, by convention, is always expressed with denominator liters of oxygen) set to 1
The total output flow is the sum of Oz input and air entrained. Thus the air-to-oxygen ratio parts are added. The flow rate of O, required to maintain a minute volume (i.e. total output flow) of 60 LPM is thus easily calculated.
T-piece
Flow rate – 8-10 Litres/min
Deliver 60=100 %
Adv-good humidity, comfortable, fairly accurate FiO2
Dis adv – heavy with tubings
Face tent
Flow rate – 8-10 Litres/min
Deliver 30- 100%
Adv-good humidity, comfortable, fairly accurate FiO2
Dis adv – bulky and cumbersome
