Clinical Rationale and Indications of
Oxygen therapy
Learning Objectives
At the end of the lecture students should be able to understand;
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The concepts of oxygenation, oxygen delivery
Hypoxia, hypoxemia and anoxia and their signs and symptoms
Factors affecting delivery of oxygen to tissues
Mechanisms and Measures of Oxygenation
Indications of Oxygen therapy
Identify and understand the use of different oxygen delivery
systems
Lecture outline
Introduction
• The process of taking oxygen from the inspired air and using it to
sustain aerobic cellular metabolism throughout the body can be
conceptualized as having three steps:
– Oxygenation
– Oxygen delivery
– Oxygen consumption
Oxygenation is the process of oxygen diffusing passively from the alveolus
to the pulmonary capillary, where it binds to hemoglobin in red blood cells
or dissolves into the plasma.
Insufficient oxygenation is termed hypoxemia.
Oxygen delivery
is the rate of oxygen transport from the lungs to the peripheral
tissues
Oxygen consumption
is the rate at which oxygen is removed from the blood for use
by the tissues.
General Terminologies:
Hypoxia literally means "deficient in oxygen”, that is an abnormally low oxygen
availability to the body or an individual tissue or organ.
Hypoxemia is the reduction of oxygen specifically in the blood;
that is decreased partial pressure of oxygen in blood.
Anoxia is when there is no oxygen available at all.
Factors affecting delivery of oxygen to tissues
►Inspired oxygen concentration FIO2
►Alveolar ventilation
►Ventilation-perfusion distribution within lungs
►Haemoglobin Hb and concentrations of agents which may bind to Hb as
carbon monoxide
►Influences on the oxygen Hb dissociation curve
►Cardiac output
►Distribution of capillary blood flow within tissues
Measures of Oxygenation
►Arterial oxygen saturation (SaO2)
►Arterial oxygen tension (PaO2)
►A-a oxygen gradient
►PaO2/FiO2 ratio
►A-a oxygen ratio
►Oxygenation index
Mechanisms of Hypoxemia
►Hypoventilation
►V/Q mismatch
►Right-to-left shunt
►Diffusion limitation
►Reduced inspired oxygen tension
Note;
Hypoxemia due to ventilation perfusion mismatch, hypoventilation or
diffusion impairment is reversed by giving oxygen .
Signs and Symptoms of Hypoxemia and Hypoxia
►Dyspnea, tachypnea. Hyperventilation
►Cyanosis +/►Impaired mental performance, coma
►Seizures, brain injury
►Tachycardia/ Hypertension –
►Hypotension/ Bradycardia
►Lactic acidosis
Consequences of Hypoxemia
►Systemic hypotension
►Pulmonary hypertension which can lead to heart failure
►Polycythemia
►Tachycardia
►Cerebral involvement (from confusion to coma)
Objectives of Oxygen therapy
To overcome the reduced partial pressure and oxygen quantity in blood
To increase the quantity of oxygen carried in solution in the plasma, even
when the Hemoglobin is fully saturated.
Indications of Oxygen therapy:
Respiratory compromise
Cyanosis
Tachypnoea
Hypoxemia
Partially obstructed airway
Cardiac compromise
Chest pain
Shock
Tachycardia
Arrhythmias
Neurological deficits
Cerebrovascular accident
Spinal injuries
Coma
Types of oxygen delivery
►Nasal cannulae
►Medium concentration mask
►Fixed concentration mask
►Non-rebreather bag
►Humidified circuits
►High flow systems
Methods of Oxygen Administration
Nasal cannulas
Two prongs inserted just inside anterior nares and supported on a light
frame
Oxygen is supplied at rates of 1-4 liters/min resulting in inspired
concentrations of approx. 25-30%
Masks
Simple plastic masks fit over nose and mouth allow inspired oxygen
concentrations of upto 60% when supplied with flow rates of 6 liters/min
Some accumulation of CO2 occurs within the mask (2%),so cautious use in
patients liable to develop CO2 retention
Venturi Masks
Useful mask for delivering controlled oxygen concentrations (e.g. CO2
retainer patients) based on Venturi principle
Venturi principle:
As the oxygen enters the mask through a narrow jet, it entrains a constant
flow of air, which enters via surrounding holes.
Example: with oxygen flow of 4 liters/min, total flow (oxygen+air) of
approx, 40 liters/min is delivered to the patient. At such high flow rates,
there is negligible rebreathing of expired gas and, therefore, no CO2
accumulation
Non Rebreather bags
Reservoir bags’
Deliver FiO2 0.6 – 0.8
Flow rate must be set to 15l/min
Fill reservoir 2 thirds before applying
Useful in acute situation
Should not be worn >24hrs
Transtracheal oxygen
Delivered via a microcatheter inserted through the anterior tracheal wall
with the tip lying just above the carina
Tents
Used only for children who do not tolerate masks well.
Ventilators
Complete control over the composition of the inspired gas is available.
Patient is mechanically ventilated via endotracheal tube or tracheostomy
tube
Hyperbaric Oxygen
100% oxygen is given at an increased pressure of 3 atm.
Since normal air is 20% oxygen, pure oxygen would be 5 times more
oxygen, and at 3times normal air pressure, a patient gets 15 times more
oxygen than normal.
Indications:
►Decompression illness (the "bends")
►Carbon monoxide poisoning
►Radiation necrosis
►Reconstructive surgery
►Some infections,wounds
Domiciliary & Portable Oxygen
Advanced COPD
Advanced Interstitial Lung disease
Pulmonary Hypertension
Hazards of Oxygen Therapy
►Carbon Dioxide Retention
►Oxygen Toxicity
►Atelectasis
►Retrolental Fibroplasia