Oxygen

Chemical

Oxygen → chemical element, O = O, atomic number 8

Use

  1. Treat hypoxia
  2. CO poisoning
  3. Decompression sickness
  4. Resorption of PTX

Presentation

  • As a gas in black cylinders with white shoulders
  • Stored at 137 BAR @ 15°C
  • Colourless, tasteless, odourless gas
  • Supports combustion

Route/Dose

FiO2 21 – 100% via inhalation

MoA

O2 is reduced via a series of electron transfers in the presence of cytochrome oxidase → Energy is released → used to form ATP

PD

CNS – cerebral VC → ↓CBF

CVS – ↓HR, ↑coronary BF, ↓PVR

Resp – ↓vent drive (↓sensitivity of resp centre to CO2)

Metabolic – allows oxidative phosphorylation for the generation of ATP

PK

A

Freely permeates BGB

D

Bound to Hb (majority) + dissolved

M

In mitochondria → CO2 + H2O

E

CO2 (exhaled) & H2O (urine, faeces, sweat)

Adverse Effects

Safety: supports combustion

  • O2 toxicity occurs due to excess production of O2 free radicals
  • At ↑PO2 → free radical production > scavenging mechanism

FiO2 safety:

  • 100% 12hrs
  • 80% 24hrs
  • 60% 36hrs

Toxicity depends on alveolar PAO2, not PaO­2

 CNS

  • >2 ATM
  • Probability ↑with ↑time at ↑PaO2
  • N&V, numbness, twitching, dizziness
  • Seizures “Paul Bert effect”

Lungs

  • Free radicals damage capillary membrane
  • Tracheobronchitis 2° abnormal ciliary transport
  • Absorption atelectasis
  • ARDS
  • Loss of hypoxic drive

Neonate

  • Premature (<36weeks) at greatest risk
  • Vascularisation of foetal retina not until term
  • Constricts terminal vessels