O2 Therapy Flashcards
O2 therapy is:
the administration of oxygen at concentrations greater than those found in ambient air in order to treat or prevent hypoxaemia. When used as a medical treatment, oxygen is regarded as a drug and must be prescribed according to a target saturation range
The patient is monitored to:
ensure that the oxygen therapy administered keeps them within the target saturation range. For most patients, a target of 94-98% is appropriate. For those at risk of carbon dioxide retention (hypercapnia), a target of 88-92% ensures safe levels of oxygenation and minimises risk of respiratory acidosis
O2 therapy will improve:
oxygenation but it does not treat the underlying cause of hypoxaemia which must be diagnosed and treated as a matter of urgency
Indications for O2 Therapy:
- Documented hypoxemia as evidenced by: 1) PaO2 < 8Kpa or SaO2 < 90-92% on room air 2) PaO2 or SaO2 below desirable range for a specific clinical situation
- Acute care situations in which hypoxaemia is suspected
- Severe trauma
- Acute myocardial infarction
- Short term therapy (Post anaesthesia recovery)
- Decrease the symptoms associated with chronic hypoxaemia in pts who are not CO2 retainers
- Decrease the workload hypoxaemia imposes on the cardiopulmonary system, i.e. increased CO and redistribution to vital organs
Strong indicator for oxygen therapy is:
PaO2 < 9 kPa is a strong indicator for oxygen therapy
Early signs of hypoxemia include:
PaO2 8-10 kPa: Cold, clammy extremities/restless
Late signs of hypoxemia include:
Symptoms if PaO2 <8 kPa: Cyanosis (peripheral and central), tachycardia (increased HR), dyspnoea (SOB)
Symptoms of PaO2 <6kPa: Mental deficiency, memory loss, arrhythmia, confusion, loss of co-ordination (ataxic)
Symptoms of PaO2 <4kPa: Bradycardia (reduced HR), cardiac arrest, hypotension
Complications of O2 therapy are:
- Oxygen toxicity: increased free radicals results in fibrotic changes. Occurs from prolonged exposure. Seen as tremors, twitching, convulsions
- Depression of ventilation: Those with hypoxic drive are at risk of slowing RR leading to cardiac arrest. Require Non-Invasive Ventilator (NIV) to blow off CO2
- Retinopathy of Prematurity: premature babies ocular system affected results in visual changes
- Absorption atelectasis: increased O2 concentration levels at detriment of normal N2 levels in lungs that maintain alveoli to stay open thus alveoli will begin to collapse
- Fire hazard: smoking
Guidelines procedure in starting and monitoring O2 therapy include:
Oxygen should be prescribed prior to administration (except in an emergency)
Oxygen therapy is started using an appropriate delivery system and flow rate
Oxygen saturations should be observed for first 5 mins after a change to oxygen therapy
Oxygen therapy is titrated to maintain target saturation
Patients requiring >28% oxygen for more than 24 hours can have oxygen delivered via a humidification system for comfort and to avoid the drying of secretions
Oxygen saturation is documented with the oxygen device, FiO2 (concentration) and flow rate
Signs of Respiratory Deterioration:
Increased RR (especially if >30)
Decreased SpO2
Increase in O2 dose needed to keep SpO2 in target range
Increase in NEWS score
Patients require prompt medical review and further assessment including monitoring of arterial blood gas
Signs of CO2 retention:
Drowsiness, headache, flushed face, flapping tremor
Those at risk of hypercapnia are:
Chronic obstructive pulmonary disease (emphysema); Neuromuscular and chest wall disorders; Cystic fibrosis; Morbid obesity.
Assessment techniques for suitability of O2 therapy include:
Pulse Oximetry: 1st port of call, Non-invasive, Measures SpO2 and HR only (no information on pH, PaCO2, haemoglobin levels)
Arterial Blood Gases: ‘Gold Standard Test’ for assessing respiratory failure, Measures PaO2, pH, PaCO2, HCO3, SaO2, Invasive
Oxygen Delivery Methods include:
Variable-Performance Devices (estimated oxygen delivery): Nasal Cannula (Reservoir Cannula), Simple Face Mask, Reservoir Mask (Partial re-breath mask, Non-rebreathe)
Fixed-Performance Devices: Venturi Mask (fixed FiO2 model, variable FiO2 model)
Other: Nasal Catheter, Transtracheal Catheter, Oxygen tent, Hyperbaric chamber
Indications for nasal cannula
Low to mod O2 requirement: 2-4 l min-1 (28-36%); < 2 L/min(child)
No or mild respiratory distress: Mild hypoxaemia on air (9-10 Kpa)
Long term O2 therapy
Indications for simple face mask
· mod O2 requirement: 5-8 litres /min (30-60%), > 5L/min to prevent CO2 rebreathing
· mild to mod respiratory distress: Mild hypoxaemia on air (9-10 Kpa), Moderate hypoxaemia <8Kpa (type I failure)
· Increased O2 delivery for short period (<12h)
Indications for non-rebreath mask
· High O2 requirement and/or emergency care: 8-15l min-1 (60-80%), Flow > 8L/min: The bag should remain inflated to ensure the highest FiO2 and to prevent CO2 rebreathing
Moderate hypoxaemia <8Kpa (type I failure)
Indications for Venturi system
· Desire to delivery exact FiO2: in monitoring those at risk hypercapnia
Contraindications/precautions for nasal cannula
· Poor respiratory efforts, apnoea, severe hypoxia
· Mouth breathing
Contraindications/ Precautions for simple face mask
· Poor respiratory efforts, apnoea, severe hypoxia
Contraindications/ Precautions for non-rebreath mask
· Poor respiratory efforts, apnoea, severe hypoxia
· O2 flow into mask must be sufficient to prevent collapse of reservoir (12l/min)
· To ensure highest O2 concentration given, reservoir needs inflating before placing on patient
Contraindications/ precautions for Venturi system
· Poor respiratory efforts, apnoea, severe hypoxia
· FiO2 depends on flow rate so must be set at correct level
Advantages of nasal cannula
Less expensive
Comfortable, well tolerated
Able to eat, drink and talk
Advantages of simple face mask
Less expensive
Can be a mouth breather
Advantages of non-rebreath mask
Highest possible O2 without being intubated
Suitable for severely hypoxic patients who are still spontaneously breathing
A one-way valve prevents exhaled air entering the bag
Advantages of Venturi system
Fine precise control of FiO2 at fixed flow ensuring an accurate concentration of oxygen delivery regardless of inspiratory volumes and rate
High flow comes from air, reducing O2 cost
Can be used for low and mod FiO2
Helps in deciding if O2 requirement is changing
Disadvantages of nasal cannula
· Doesn’t deliver high FiO2: Flow rates > 4 l/min can cause considerable drying of nasal mucosa and are more difficult to tolerate
· Irritation to nasal cavity (nose bleeds)
· Less FiO2 with nasal obstruction
· FiO2varies with inspiratory effort
Disadvantages of simple face mask
· Requires tight seal, Uncomfortable, Difficult to keep in position for long, Can cause skin breakdown
· Doesn’t deliver high FiO2
· FiO2varies with inspiratory effort
· Interfere with eating, drinking and communication
· CO2 Rebreathing (if input flow is less than 5 L/min)
Disadvantages of non-rebreath mask
· Expensive
· Increases WOB
· Require tight seal so uncomfortable
· Interfere with eating, drinking and communication
· Not suitable for long term use
· Malfunction or incorrect use can cause CO2 build up, suffocation
Disadvantages of Venturi system
· Uncomfortable
· Expensive
· Can’t deliver high FiO2
· Interferes with eating, drinking and communication
What is the difference between a non rebreather and partial rebreather mask?
Non Rebreather: one way valve
Partial Rebreather: not one way valve
An alternative to nasal cannula is:
Reservoir cannula - nasal or pendant reservoir
Advantages of reservoir cannula:
Lower O2 use and cost
Increased mobility
Less discomfort because of lower flow
Disadvantages of reservoir cannula:
Poor compliance due to unattractive
Must be regularly replaced (3 weekly)
Breathing pattern affects performance (must exhale through nose to reopen reservoir membrane)
In variable-performance devices the amount of oxygen delivered is dependent on:
Oxygen flow rate, Patient’s inspiratory volume, Respiratory rate
What are the alternative delivery methods if there is facial devices are inappropriate:
Nasal Catheter
Transtracheal Catheter: Fixed-performance device between cartilage in throat via fine needle surgery. For those that have facial trauma but do not need tracheostomy. Increased risk of infection.
Oxygen tent
Hyperbaric chamber (less common; expensive): above atmospheric pressure of O2 (21%) therefore O2 more readily absorbed.
