Oxygen
21/11/10
Part I Notes
Class - a gaseous inorganic element
Mechanism of Action
- essential role in process of oxidative phosphorlyation -> production of energy for a
multitude of biological processes.
- combined with H+ via mitochondrial cytochrome oxidase -> production of ATP
Pharmaceutics
-
compressed gas cylinders (137 bar @ 15 C)
black with white shoulders
available in six sizes
also available in liquid form (1 volume -> 840 volumes of O2)
colourless, odourless, tasteless gas
supports combustion
specific gravity of 1.1
critical temperature -118 C
critical pressure 51 atm
melting point -218 C
atomic weight 18
INH
Dose – titrated to PaO2 and SpO2
Indications
(1)
(2)
(3)
(4)
(5)
(6)
all forms of hypoxia (except histotoxic)
shock
CO poisoning
pnematosis coli
decompression sickness
anaerobic infections
Adverse Effects
-
coronary after vasoconstriction
decrease in Q
de-nitrogenation -> atelectasis
cerebrovascular vasoconstriction
PK
Absorption - freely permeable through normal alveolar tissue
Jeremy Fernando (2010)
Distribution - transported in Hb & dissolved
Metabolism - within mitochondria -> CO2 + H2O
Elimination - CO2 exhaled & water metabolized
Toxicity
- loss of hypoxic drive in patients with CO2 retension
- retrolental fibroplasia (corneal)
- acute O2 toxicity with hyperbaric 100% O2 -> altered mood, vertigo, LOC, convulsions.
- > 60% O2 -> tracheal irritation, sore throat, substernal pain, pulmonary congestion,
atelectasis & decreased VC.
- prolonged exposure to 100% O2 -> interferance with RBC formation
- dry nose and mouth
- oxygen toxicity (pulmonary, CNS, CVS)
- denitrogenation -> atelectasis
- obtunding of hypoxic respiratory drive
- ? increase in infarct size in MI
- ? increase in mortality post cardiac arrest
Manufacturing
Photosynthesis!
- plants convert photoenergy from the sun to convert CO2 -> O2
Fractional distilliation of air
- O2 can be obtained from the atmosphere by liquefication & fractional distillation of air
- liquid air is a mixture of liquid nitrogen (BP -196 C) and liquid O2 (BP - 183 C)
- nitrogen is more volatile and boils off first during evapouration
- some of the O2 evapourates with nitrogen, so separation of the two gases is bought about
by fractionation -> letting the evolved gas mixture bubble through liquid air rich in O2 in a
tall rectifying column
- the O2 in the gas mixture condenses an almost pure nitrogen gas leaves the top of the
column leaving almost pure liquid O2 which is then evapourated to give O2 gas.
- O2 gas is distributed as compressed gas in high pressure cylinders
O2 concentrators
- device for extracting O2 from atmospheric air
- air passed under pressure through a column of zeolite (molecular sieve) -> traps nitrogen &
H2O vapour whilst leaving O2 and trace gases.
- nitrogen removed by depressurising the column
- produces a continuous supply of over 90% O2
- can range from small (individual) or large (supplying hospitals)
Evidence
Jeremy Fernando (2010)
Jeremy Fernando (2010)