Oxygen
Oxygen is a drug and should be prescribed with target saturations (scale 1 or 2), except in an emergency situation where someone is critically unwell.
Indications for oxygen
- Hypoxia
- Hypoxaemia
- Target sats
What is hypoxia
Hypoxia is reduced oxygen at tissue level measured as SpO2
Hypoxia is caused by
- Hypoxaemia
- Reduced cardiac output e.g. Myocardial Infarction (Ml or heart attack)
- Reduced oxygen carrying capacity of the blood e.g. anaemia, sickle cell disease
- Reduced blood flow e.g. haemorrhage, peripheral vascular disease
- Disrupted blood flow e.g. multi-system failure
- Reduced ability of tissues to extract oxygen e.g. septic shock
What is hypoxaemia
Hypoxaemia- is reduced oxygen in arterial blood measured as PaO2
Hypoxaemia is Caused by:
- V/Q mismatch due to wasted perfusion e.g. atelectasis, consolidation
- V/Q mismatch due to wasted ventilation e.g. pulmonary embolism (PE — blood clot in the lungs)
- Hypoventilation
- Diffusion Problem e.g. pulmonary oedema, fibrosis
- Reduced Fi02 e.g. fire entrapment, high altitude, inadequate oxygen therapy
Target sats
Who has scale 1 - 94-98%
- Pneumonia HAP/CAP
- Post surgical patients
- Asthma
- Bronchiectasis
- ILD interstitial lung disease
- 92-96% COVID positive patients
Who has Scale 2- 88-92% = pt at risk of CO2 retention
Severe chronic hypoxic lung disease
* COPD, severe chronic asthma, bronchiectasis & CF
Chest wall disease
* Kypho-scoliosis - cant ventilate properly due to anatomy not allowing expansion of chest wall
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Neuromuscular disease
* Motor neuron diseases, Spinal muscular atrophy, muscular dystrophy
Obesity hypoventilation
In emergency situations
- When a patient is critically unwell OR has SpO2 <85%
- Once stable, aim for SpO2 94-98% or patient-specific target range (scale 2)
- COPD patients who are critically ill should have the same oxygen therapy until blood gases have been obtained.
- Administer 1.5L/min via reservoir mask
- Hypoxia more dangerous than hypercapnia
High O2 is harmful too
- Absorption Atelectasis.
- High concentrations may impair the respiratory drive of hypercapnic COPD patients.(reasoning for scale 2)
- Excess oxygen depletes protective anti-oxidants, causing oxygen toxicity.
- Affects on the CV system.
Variable vs fixed rate devices
Variable
* Increase % of oxygen by increasing flowrate
* Fi02 = Sp02
* Increased Sp02 can reduced RR
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Fixed
* Fixed devices require specific flow rate (you can not increase the Fi02 by increasing the flow, unless you change the device)
* Increased Flow rate alone = reduced RR
Nasal Cannula
Nasal cannula
* Deliver up to 6L, as a rule maximum of 4 before switch to something else
- Recommended for most patients.
- 1-6L/min flow rate gives 24-50% Fi02 (Fi02 depends on: oxygen flow rate, patient’s minute volume and inspiratory flow and pattern of breathing).
o However, 1-4L are optimal for patient comfort
- + Comfortable and easily tolerated
- + No re-breathing of expired air
- + Patient can eat and drink and communicate freely
- + Low cost product
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BUT note higher flow rates can quickly dry out the nasal mucosa and consider whether appropriate in patients with high RR who are mouth breathing.
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Setting up:
1. Connects directly to the oxygen flow meter.
2. Turn the dial on the flow meter to the required flow rate.
Venturi mask
Venturi mask
* fixed rate device - change the flow of O2 change the colour of the valve attached to the simple face mask
24-60%
- The minimum oxygen flow is displayed on each valve
- With TACHYPNOEA (RR >30/min) the oxygen flow should be increased by 50%
- Increasing flow does not increase oxygen concentration as it is a fixed dose device
- Good device for patients with raised C02 (patients with a target of 88-92%) as it delivers more accurate oxygen concentrations.
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BUT can be drying and not as easy to eat and drink.
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Setting up:
1. Connect the appropriate valve that gives the desired Fi02 to a simple face mask.
2. Connect oxygen tubing to the bottom of the valve.
3. Connect the other end of the tubing to the oxygen flow meter.
4. Turn the dial on the flow meter to the required flow rate as shown on the valve. (Remember always set the minimum flow shown, but this can be increased if the patient has a high RR).
5. As you want to change Fi02, you change valves to the appropriate one as described above
Simple face mask
Simple face mask
* after surgery, up to 8L variable flow rate device, not very accurate.
- Delivers variable 02 concentration between 5-10 L/min flow rate which gives approx. 35% - 60% Fi02
- Flow must be at least 5 L/min to avoid C02 build up and resistance to breathing
- Low cost product
- Often used for brief periods of time e.g. post-op
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BUT can be drying and not as easy to eat and drink etc.
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Setting up:
1. Connect oxygen tubing to the mask.
2. Connect the other end of the tubing to the oxygen flow meter.
3. Turn the dial on the flow meter to the required flow rate.
Non-rebreathe
Non-rebreathe
* up to 15L, as close to 100% of oxygen as possible. Make sure the valves are open and bag is filled
- Needs flow of 15L to maintain inflation of bag
- Delivers 02 concentrations between 80%-100% at 15L of flow
- Effective for short term treatment and often used in emergency situations
- Two different on-way valve systems in the mask prevent:
- Entrainment of room air during inspiration
- Retention of exhaled gases during exhalation
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BUT high flows are very drying.
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Setting up:
1. Connect the oxygen tubing to the mask
2. Connect the other end of the tubing to the flow meter on the wall
3. Set flow to 15L/min
4. Occlude the valve at the base of the mask allowing the reservoir bag to inflate
5. Once the bag is fully inflated it can be put on the patient
Nasal high flow
- High flow and percentage of oxygen 60L
- Heated humidified oxygen gold standard
- Paediatrics less than 60L
- Sterile water provides humidity
- Delivers adequately heated and humidified medical gas at up to 60 L/min of flow and from 21% (RA) - 100% oxygen.
- Provides respiratory support (through reduction of anatomical dead space and delivery of dynamic positive airway pressure)
- Dead space is reduced due to clearance of air in the upper airways, which reduces the re-breathing of gas high in C02 and depleted of 02 by creating a reservoir with high Fi02 in the nasal cavity.
- Creates PEEP - High flow reduces inspiratory resistance making inspiration easier and increases expiratory resistance prolonging expiration, promoting a slow deep breath which increases alveolar ventilation. Can therefore help reduce RR and WOB.
- Provides airway hydration — the oxygen is passed through a humidifier which heats it to body temperature to achieve optimal humidity emulating the natural balance of heat and moisture in healthy lungs.
- This can help maintain the function of the mucociliary escalator to aid sputum clearance.
- Enables comfortable delivery of high flows
- Patient comfort
- More tolerable interface in the form of nasal prongs, which can be more comfortable than a mask
- Allow eating and drinking
- Patients can communicate more easily
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Setting up
1. Oxygen flow meter allows 02 to be added and controlled.
2. Specialised tubing connecting the heated humidifier to the specialist nasal cannula.
3. Humidifier and control panel — to turn on/off and adjust the temp and flow. Can also view Fi02.
In both cases, the humidifier will also have a bag of sterile water attached. This needs to be replaced when it runs out so these systems need to be checked regularly.
Humidified oxygen
Humidified oxygen
* cold water humidified oxygen- goes to a simple face mask
- Can be cold or warm
- Can be used for patient comfort
- Often set-up or recommended by PTS as part of treatment e.g. if sputum retention is identified as a problem or potential problem.
- Should be considered in: Tracheostomy, bronchiectasis, CF, long term ventilation.
Setting up:
1. Lots of different systems but all comes as separate parts!
2. The white connector at the top screws directly into the oxygen port
3. Sterile water then needs to be screwed into the bottom of the oxygen delivery system (sometimes there is a reservoir that needs filling with sterile water)
4. Elephant tubing connects to the wide bore port at the side
5. The other end of the elephant tubing is connected to a simple face mask
6. Use the dial to set the required Fi02
7. Turn the dial on the flow meter to set the appropriate flow for the required Fi02 as show on the device.
Tracheostomy mask
Tracheostomy mask
* pts with tracheostomy or laryngectomy to fit their neck, as their neck is their airway
Titrating up or down
- Increase oxygen if SpO2 is lower than target range
- Decrease oxygen if SpO2 is higher than target range
- Monitor SpO2 for 5 mins at every change
- If oxygen therapy is increased, medical assessment is needed.
- ABG is needed after 30-60mins in patients with target SpO2 88-92% who have an increase in O2.
- Ensure any change is documented in the patient record
Mask escalator
- 1L nasal cannula = 24% venturi blue
- 2L nasal cannula = 28% venturi white
- 4L nasal cannula = 35% venturi yellow
Anything above 4L oxygen you wouldn’t use a nasal cannula and would switch to something else
Nasal cannulae or simple face mask 5-6L/min = 40% venturi
Simple face mask 7-10L/min = 15 l/min
Clinical signs of of Hypoxemia
- Cyanosis
- Tachypnoea
- Tachycardia
- Peripheral vasoconstriction
- Altered mental state/drowsiness
- Increase WOB
PRECAUTIONS:
- Established hypoxic drive
HYPOXIC DRIVE:
- Normal respiratory drive is initiated by rising C02. In individuals that constantly retain C02 they lose their sensitivity to it and therefore low 02 becomes the trigger.
- Caution with these patients but remember hypoxia will ultimately lead to death
ASSESSMENT OF EFFICACY
Observations:
- Improved Sp02(saturation of Hb) measured using pulse oximeter
- Improved Pa02 (oxygen dissolved in plasma) measured using ABGs
- RR
- Reduced WOB
- Patient colour
- HR and BP
- Consider potential for errors in pulse oximetry e.g. poorly perfused peripheries.
Tracheostomy masks
- Used to deliver oxygen to patients with either a laryngectomy or a tracheostomy - “neck breathing patients”
- Ideally they should receive heated humidified oxygen if required (similar set-up to the with the humidifier unit and tubing to the patient).
- For safety, it should be clear which patients on a ward have a tracheostomy or laryngectomy, so they have appropriate equipment available and can be managed appropriately in an emergency situation.
- Also shows the importance of a thorough A-E assessment, to ensure A and B are assessed and managed appropriately.
