Description #
This unit is designed to review the various oxygen delivery systems. This unit will be administered online followed by a pre and post quiz. Accumulated knowledge from all of the units will be practiced and evaluated via case scenarios using the simulated patient.
Learning Objectives #
At the completion of this module the student will be able to:
1. Understand the role of the respiratory therapist.
2. Understand hospital policies regarding the delivery of Oxygen.
3. Understand the basics of oxygen titration.
4. Describe basic oxygen delivery systems.
Introduction #
Introduction to Oxygen Therapy (1) (2) (3) (4) :
Oxygen is a requirement to life. Despite the relaxed attitude to Oxygen of the majority of Health Professionals, it has always and still remains a controlled drug. It needs to be prescribed by a Physician, and care should be taken to avoid possible complications, such as over oxygenation, or under oxygenation.
All physician orders for oxygen therapy must have a specified oxygen saturation to be maintained, unless the oxygen delivery system is specified by the physician (6).
Too little causes Hypoxia/Hypoxaemia resulting in increased cardiovascular demand thereby inducing ischemia and tissue damage which can lead to cell death or ultimately, physical death. Too much oxygen can damage the sensitive epithelia of the lungs; suppress respiratory drive in certain diseases; can cause cell damage in infants/children (retrolental fibroplasia); and cause Oxygen toxicity which produces ARDS like symptoms of pulmonary oedema, inflammatory changes, and subsequent fibrosis. Whenever able FiO2 >0.5-0.6 should be restricted to <72 hours to reduce risk of developing negative effects from Oxygen Toxicity (1). An FiO2 of >0.6 has also been shown to reduce vital capacity (2). Thus in the hospital setting, it is vital to patient health to ensure adequate and appropriate oxygenation.
The amount of oxygen in ones blood can be easily measured via pulse oximeter, during the routine measurement of patients’ vitals, or in the acutely ill patients by an arterial stab which provides details about the patients’ blood-gas buffer. Oxygen molecules bind to Haemoglobin in the lungs and are transported around the body. Normally 4 Oxygen ions bind to each Haemoglobin with increasing affinity after the first ion binds (cooperative bonding) forming Oxy-Haemoglobin. Once at the appropriate tissue, Oxygen ions are exchanged for CO2 which has a higher affinity for Haemoglobin at the tissue level, thus forming deOxy-Haemoglobin (or CarbAmino-Haemoglobin).
Oxygen saturation levels depend on the amount of Oxy-Haemoglobin in the blood. Certain conditions can affect the amount of oxygen that binds to Haemoglobin. These include PO2, pH, Temperature, CO/CO2 levels and metabolic activity. Normal Oxygen Saturation levels are >93% in people with healthy Lungs. In diseased lungs (COPD/emphysema) the normal accepted range is usually lower (88-92%).
Oxygen in the hospital setting is an extremely dry gas. Therefore when being administered to patients it is important to note if there are complaints about dryness, cracking mucosa, epistaxis, runny nose, pain in oral/nasal cavity with breathing. This dryness can also impair gas exchange, reducing the effect of added oxygen into the patients system. Usually if a patient is requiring oxygen of >40% for prolonged period it will be humidified. This serves to increase comfort, compliance and also improve oxygen transfer into the circulatory system. Note that Nasal Cannula (with flow rate of 1-5lpm) are not routinely humidified.
The American College of Chest Physicians recommends instituting oxygen therapy in the following situations (8):
Cardiac and respiratory arrest
Hypoxemia (PaO2 < 60mmHg, SaO2 <90%)
Hypotension (systolic blood pressure <100mmHg)
Low cardiac output and metabolic acidosis (bicarbonate <18 mmol/l)
Respiratory distress (repsiratory rate >24/min)
Once the oxygen delivery system is set up, it should be monitored regularly to ensure adequate oxygenation of the recipient. This includes regular observation of the SpO2, RR, and HR, whilst also watching for signs of dyspnoea. Checking that the desired flow rate of oxygen is being delivered helps to minimise any accidental changes to the system.
Role of the Respiratory Therapist:
For the purpose of this module the physiotherapist should be aware of the VCH Patient Care Guideline PCG 0-120 that states an Respiratory Therapist (RT) should be contacted for the assessment of any patient with the following :
1. An Order of Oxygen >40%
2. An Oxygen Saturation of <93%
3. Acute Respiratory Distress
4. Transport with Oxygen Therapy concentration of >40%
5. Presence of an Artificial Airway (i.e. tracheotomy)
Of course, it goes without saying, that a physiotherapist could also assess any patient with the above issues.
Oxygen Titration Guidelines:
Current VCH guidelines for Oxygen Titration (6) state:
1. Patients should be at rest and not have received any bronchodilators for at least 20 minutes prior to titration
2. Changes in Oxygen percentage should be made in 5-10% increments/decrements
3. Changes in flow rate should be made in 1-2lpm increments/decrements
4. Any change should be followed by the assessment of the oxygen saturation 5 minutes following the change
5. If Oxygen saturation is less than the ordered oxygen saturation and oxygen percentage >40% call the RT
6. Follow the specific physician order for the levels of oxygen saturation for each patient
7. Nasal Cannula flow rate should not be >6lpm
8. Simple mask flow rate should not be <6lpm
Low Flow Oxygen Delivery Systems:
Low Flow Oxygen delivery systems are systems in which the devices flow rate is less than the patients inspiratory flow rate. A normal healthy person has a peak inspiratory flow rate of between 35-40 litres per minute.
In a Low Flow delivery system the flow rate delivered by the device is less than that of the patients peak inspiratory flow rate.
As a result of this the delivered oxygen is diluted with room air as the patient breathes. This leads to unpredictable and variable FiO2 values. The final concentration is determined by the amount of room air mixed with the oxygen on inspiration.
The following systems are examples of low flow delivery systems:
- Nasal Prongs
- Simple Face Mask
- Non-Rebreathing Mask
Nasal Prongs #
Advantages:
- Comfortable for Patient
- Ideal for patients requiring small amounts of oxygen or Home Oxygen Therapy
- Allow patient to communicate easily, and eat freely
- Can be humidified if required
Disadvantages:
- Max. FiO2 estimated to be FiO2 =0.40-0.44
- Not appropriate for Respiratory Distress
- Need orders in Litres Per Minute (lpm)
- Flows rates of up to only 6 lpm
- Flow rates greater than 4lpm associated with dryness, epistaxis, headaches
- High Minute Ventilation (VE) rates lower the delivered FiO2 significantly
Note: High Flow Nasal Cannula (up to 15lpm) are available and occasionally used for patients unable to tolerate a mask. They also provide the ability for patients to maintain Oxygen Therapy whilst eating/drinking/talk easily without having to take off mask to do so.
Rule of Thumb of Nasal Cannula FiO2
- Room Air = 0.21
- 1 lpm = 0.24
- 2 lpm = 0.28
- 3 lpm = 0.32
- 4 lpm = 0.36
- 5 lpm = 0.40
- 6 lpm = 0.44
Simple Mask #
Advantages:
- Quick and easy to set up and apply
- Often found at head of bed in emergency equipment
- PCG states that if patient experiencing chest pain, a facemask with flow of 6 lpm should be applied
Disadvantages:
- Non-specific FiO2 that is largely dependent on patient VE
- Maximum FiO2 = 0.50-0.60 at 8-10 lpm (higher flow rates do not significantly increase FiO2 due to entraining of room air)
- Minimum flow rate of 5 lpm required ensure expired gas washed out of mask and prevent rebreathing of CO2
- Not intended for long term use
- Patients often find uncomfortable and claustrophobic
Non Rebreather Mask #
Advantages:
- Quick and easy setup
- Able to deliver high levels of FiO2
- Useful in emergency situations and for transporting patients requiring High levels of FiO2/High flow oxygen therapy
Disadvantages:
- Requires tight seal to work effectively
- Theoretically designed to deliver a fixed FiO2 of about 1.0 if reservoir remains inflated
- Low flow rates can increase hypoxia rather than reduce it, therefore should set up with as high flow rate as possible.
- In reality FiO2 is extremely variable. Flow into reservoir must be enough to prevent collapse during inspiration. Without a tight seal room air will be entrained and decrease FiO2. The higher the VE the lower the FiO2. Actual FiO2 is closer to 0.60-0.80.
- Intended for short term use only. Patient should be changed to a High Flow Device at earliest
High Flow Oxygen Delivery Systems:
High Flow Oxygen Delivery Systems are systems or circuits that provides a constant FiO2. This is achieved by providing a flow rate higher than the patients’ peak inspiratory flow rate, thereby being unaffected by changes in ventilatory pattern. High Flow Oxygen Delivery Systems exceed the peak inspiratory flow rate of the patient and therefore completely satisfy the patients inspiratory demand.
As a result there is no additional room air being entrained around the mask and the FiO2 can be measured very accurately. High Flow Oxygen Delivery Systems can be single or double flow and are generaly humidified. There is an air entrainment port that can be opened to increase the amount of room air entrained into the system. Using this method the FiO2 can be accurately set.
Examples of High Flow Oxygen Delivery Systems include the following:
- Venturi Mask
- Aerosol Face Mask
- Tracheostomy Mask
- Face Tent
Venturi Mask #
Advantages:
- Administers specific FiO2 (ideal for COPD exacerbation or chronic CO2 retainers)
- Quiet
- Overall flow rate to patient exceeds Minute Ventilation (0.28 = 44 lpm, 0.40 = 40 lpm)
Disadvantages:
- Only specific FiO2 available depending on Venturi Valve (0.24, 0.28, 0.31, 0.35, 0.40 and 0.50)
- Air entrainment ports need to be open and clear of bed linen etc, as can significantly alter both FiO2 and overall flow rate
- Humidification should NOT be used as will alter the FiO2 and cause backpressure in the circuit diverting oxygen away from patient (if humidification needed, then change system to Aerosol mask)
- Colour coded Venture Valves are not universal, different companies use different colours.
Aerosol Face Mask #
Advantages:
- Administers specific FiO2 determined by the Venturi Valve on the nebulizer
- High humidity output improves patient comfort and gas exchange
Disadvantages:
- Nebulizer is noisy
- Total gas flow reaching patient decreases as FiO2 approaches 0.50, at >0.50 special set up is required to guarantee specific FiO2 whilst continuing to exceed patients VE (Double Flow)
- Constant ‘rain out’ of humidification fluid in tubing can alter FiO2, circuit should have catchment reservoir to prevent occlusion by fluid build up, still needs close monitoring to check nebulizer fluid level and empty catchment reservoir
- Temptation to reduce noise by reducing flow rate or covering air entrainment ports on nebulizer can lead to potentially dangerous alterations in FiO2
Tracheotomy Mask #
Advantages:
- Designed for patients with tracheotomy
- Allows humidification of air, as well as Oxygen
- Uses same set up as Aerosol mask therefore can set FiO2 to specific levels
Disadvantages:
- Similar comments as the Aerosol mask due to the humidification system being the same
- The Mask can require frequent cleaning/replacement if patient is coughing up sputum
Face Tent #
Advantages:
- Designed for persons unable to wear mask or nasal prongs (e.g. facial surgery, trauma, delirious/non compliant, claustrophobic).
Disadvantages:
- Bulky and cumbersome
- Difficult to administer specific FiO2 due to lack of seal and entrainment of room air, therefore high flow set up most effective, but still unreliable
- Refer to Aerosol Face Mask
Optiflow #
References #
1. Bongard, FS and Sue, DY. Critical Care Diagnosis and Treatment. Second Edition. New York : McGraw-Hill Professional, 2002.
2. Marino, PL. The ICU Book. Third Edition. USA : Lippincot Williams & Wilkins, 2007.
3. Nunn, JF. Applied Respiratory Physiology. Third Edition. Boston : Butterworths, 1987.
4. Shapiro, Harrison and Walton. Clinical Application of Blood Gases. Third Edition. Chicago : Year Book Medical Publishers Inc., 1982.
5. Dobkowski, L and Simeone, L. Oxygen Delivery Devices.
6. VCH Policy Net – http://policynet.vch.ca/index.cfm – PCG O-120
7. Oxygen and Respiratory Care Reference Manual – http://policynet.vch.ca/Docs/O-130-Feb0402TherpyandRespManual.pdf
8. Bateman, NT and Leach, RM. BMJ 1998; 317:798-801