BYANAESTHESIOLOGY UNIT

♦ What is oxygen?♦ Hypoxia /Hypoxemia♦ Indications for oxygen therapy♦ Oxygen delivery systems♦ Complications of oxygen therapy♦ Conclusions

♦ Oxygen is a gas with chemical formula of O2♦ Colourless, odorless, tasteless♦ Boiling point -183 C♦ Melting point –216.6C♦ Critical temp. –118.4C , Critical pressure

736.9psi♦ Constitutes about 20.95% of atmosphere♦ Used at cellular level as the final electron acceptor

in the electron transport chain in the mitochondria of cell

Inadequate delivery of O2 to the tissueType of hypoxia1. Hypoxic hypoxia ( decrease diffusion of O2 across the

alveolar-capillary membrane -low inspired FiO2 -V/Q inequalities -increased shunt(eg cardiac anomalies)2. Stagnant hypoxia (decreased cardiac output resulting in

increased systemic transit time -Shock -Vasoconstrictio3. Anaemic hypoxia ( decreased O2 carrying capacity in the

blood) -Anaemia

-Carbon monoxide poisoning4. Histotoxic hypoxia ( inability the tissue utilize available O2) - Cyanide poisoning

Reduced O2 concentration/tension in the bloodPaO2<80mmhg.

Should be determined through evaluation of the patient(clinical assessment and blood gas result)In general the indication are:-4. Hypoxemia/hypoxia5. Excessive work of breathing6. Excessive myocardial work7. Improvement of oxygenation in patient with decreased

O2 carrying capacity ( anaemia)8. Promotion of absorption of air in the body cavity

THIS PERSON NEED O2 ????????

Many devices for administering supplemental O2 are available

ClassificationLow-Flow Systems/Variable performanceDefinition: Do not provide all gases

necessary to meet the patient minute ventilation

- Nasal canula - Face mask - Partial rebreathing mask - Nonrebreathing mask

High-Flow Systems/Fixed performanceDefinition : Flow sufficient to meet all of patient Mv and ensure patient receive constant inspired O2 concentration - Venturi masks - Head box - Semi closed/closed anaesthetic circuit

Nasal canula♦ Capable to deliver an FiO2 ranging from 0.24-0.44

depending on the amount of flow♦ Maximum of 6LPM Why? causes crusting of the secretion, drying of the nasal

mucosa and epistaxis♦ Advantages –inexpensive,well tolerated, comfortable patient can eat and drink♦ Disadvantages – pressure sore, irritant to the mucosal Flow FiO2 1LPM 0.24 2LPM 0.28 3LPM 0.32 4LPM 0.36 5LPM 0.40 6LPM 0.44

Simple face mask♦ Increases the O2 reservoir- higher FiO2♦ O2 flow must be more than 5LPM Why? - To prevent rebreathing

Flow FiO2 5-6LPM 0.40 6-7LPM 0.50 7-8LPM 0.60 >10LPM ?

♦ Advantages – simple, light, deliver higher FiO2♦ Disadvantages – need to remove for eat, drink, speak - uncomfortable for facial trauma

Partial rebreathing and Non rebreathing mask♦ Similar to simple mask with addition of the O2 reservoir to increase FiO2 greater than 0.60♦ Non rebreathing mask – one way valve to prevent

rebreathingPartial rebreathing Flow FiO2 7LPM 0.65 8-15LPM 0.70-0.80Non rebreathing Flow FiO2 Set to prevent collapse of bag 0.85-1.0

Venturi mask♦ Operate on Bernoulli principle - As gas flow under pressure at rapid flow rate an area of

pressure develops lateral to the small opening and lead to entrainment of room air through the side port.

♦ Advantages – delivery of very predictable FiO2 - may use in COAD patient♦ Disadvantages – same like face mask Flow FiO2 4 0.24 6 0.28 8 0.35-0.40 12 0.60

Hypoventilation and Carbon Dioxide NarcosisHypoventilation and Carbon Dioxide Narcosis- the increased PO2 decreased and eliminates the hypoxic

drive ( esp. in pt. with chronic CO2 retention )- Under this circumstances O2 must be given at low

concentration <30%

Absorption AtelectasisAbsorption Atelectasis- Nitrogen a relatively insoluble and exists 80% by volume

of the alveolar gas.N2 assists in maintaining alveolar stability.O2 therapy replaced N2. Once O2 absorb into the blood the alveolar will collapse esp. in alveolar distal to the obstruction.

Pulmonary Oxygen ToxicityPulmonary Oxygen Toxicity- The exposure of the high O2 and for prolonged period can lead to parenchymal changes- In general FiO2 > 50% for prolonged period shows

increased O2 toxicity- Pulmonary changes mimic ARDS (Exudative changes and

proliferative changes.)- Sx –cough, burning discomfort, nausea and vomiting,

headache, malaise and etc

Retrolental FibroplasiaRetrolental Fibroplasia- Excessive O2 to pre-mature infants may result in

constriction of immature retinal vessels, endothelial damage, retinal detachment and possible blindness

- Recommended that PO2 be maintained between 60-90 mmHg range in neonate

FireO2 support combustionDo not smoke while receiving O2 therapy

Patient on Chemotherapy Patient on chemotherapy especially bleomycin

will develop pulmonary fibrosis if get excessive O2 therapy

O2 can be store either1)Cylinder Oxygen can be stored under pressure in

cylinders made of molybdenum steel. Cylinders are black with white shoulders. The pressure inside at 15°C is 137 bar. 2)Oxygen concentrators An oxygen concentrator is a device which

extracts oxygen from atmospheric air using canisters

Nitrogen is filtered out and oxygen produced. 3)Vacuum Insulated Evaporator (VIE). Designed to store liquid oxygen. It consists of two layers, where the outer carbon

steel shell is separated by a vacuum from an inner stainless steel shell, which contains the oxygen

The oxygen temperature is -170 C at 10.5 atm. The VIE system is used in large hospitals which

have a pipeline system, and where liquid oxygen can be supplied by road tanker

♦ O2 therapy is the delivery of any O2 conc. Greater then 21%

♦ The need for O2 should be determined through the thorough evaluation

♦ One must consider advantages and disadvantages when choosing the appropriate technique

♦ No procedure without complication