Lecture 6: O2 therapy and sleep apnoea Flashcards
What are the four main sources of O2?
Oxygen Cylinders
Wall Supply
Oxygen Concentrators
Liquid Oxygen
How is O2 delivered (units)?
Litres per minute
OR
Percentage inspired oxygen
Describe oxygen cylinders.
Widely available (home & institutional)
Various sizes
Limited length of supply
Suitable for limited/short duration treatment
Relatively expensive
Supply 100% oxygen
Describe wall supply.
In hospital only
Central supply piped in to clinical areas
May not be available in all clinical areas (clinic rooms)
Supply 100% oxygen
Describe O2 concentrators.
Mains operated machine
Molecular sieve- removes nitrogen
Oxygen predominant gas >90% concentration
Use in the home or when out
Regional suppliers with franchise for installation & support
Describe liquid O2.
More highly compressed
Larger gaseous volume per cylinder volume
Allow higher flow rates
Well developed in US & parts of Europe
What are the 3 ways to administer O2 (patient interfaces)?
Nasal cannulae
Uncontrolled masks (hudson, non-rebreathe)
Controlled (fixed percentage - venturi) masks
Describe nasal cannulae.
Usually well tolerated
Accepts flow rates 1-4L/min
Delivers 24-40% O2
(= FiO2 of 0.24-0.4)
% delivered depends on multiple factors
Uses: mild hypoxaemia, not critically ill
What are the advantages and disadvantages of nasal cannulae?
Advantages:
- Means they can still eat/drink
- Less claustrophobic
- Can talk
Disadvantages:
- Limited flow rate
- Uncomfortable (can get breakdown of the skin, drying out
Describe uncontrolled masks.
Simple face mask
Hudson mask
Delivers 30-60% O2
Flow rate 5-10L/min
Mixing of O2, room air & exhaled air in mask
Used less often - used when first arrive (during triage then change)
Describe uncontrolled masks.
Non-rebreathe mask
Delivers 85-90% oxygen with 15L flow rate
One-way valve stops:
- mixing with room air
- patient rebreathing expired air
Use: acutely unwell patients
Step down as soon as possible
Describe venturi mask.
Controlled Oxygen
Venturi valve allows delivery of a fixed concentration of oxygen
Used for patients with COPD (where worried about chronic hypoxia)
When is O2 treatment indicated?
Oxygen is a treatment for hypoxaemia, not breathlessness.
- Acutely hypoxaemic patients
- Chronically hypoxaemic COPD patients with acute exacerbation
- Chronically hypoxaemic COPD patients who are stable
- Palliative use in advanced malignancy
(sats <90% and breathless, though often multifactorial)
Why might a patient have low O2?
Chest infections (pneumonia) Pneumothorax Emphysema Asthma CO poisoning Shock Pulmonary embolism
What are the target O2 sats?
Normal young adult average = 96-98%
Over 70yrs age = 94-98%
Target in most patients = 94-98%
Balance of what is normal and what is safe
Target in those at risk of hypercapnic (high PaCO2) respiratory failure = 88-92%
(may be lower for some)
Who is at risk of hypercapnia (CO2 retention) if given high dose oxygen?
Chronic hypoxic lung disease (COPD, bronchiectasis, cystic fibrosis)
Chest wall disease (kyphoscoliosis, thoracoplasty)
Neuromuscular disease
Obesity related hypoventilation
Why are some people at risk of hypercapnia (CO2 retention) if given high dose oxygen?
They often rely on their hypoxaemic drive
if you over-correct their pO2 you may switch off their respiratory drive
leading to:
- further CO2 retention
- worsening acidosis
- narcosis - reduced level of consciousness
(& death)
You can kill the patient with oxygen
Hypoxaemia may still be a risk to them
What three things need to be stated when prescribing O2?
Target oxygen saturation range - depends on the clinical scenario
Delivery device - controlled vs uncontrolled (venturi or nasal cannulae)
“Dose” – flow rate or percentage of inspired oxygen
What are the indications for COPD patients to receive LTOT?
COPD patients with pO2 < 7.3 kPa
OR
COPD patients with pO2 7.3 < 8 kPa AND:
- secondary polycythaemia
- nocturnal hypoxaemia
- peripheral oedema/evidence of right ventricular failure
- evidence of pulmonary hypertension
What is LTOT?
Provided from an oxygen concentrator
Regional concentrator supply service
O2 treatment for ≥15 hours per day
What are the benefits of LTOT?
Improved long term survival
Prevention of deterioration in pulmonary hypertension
Reduction of polycythaemia (raised Hb)
Improved sleep quality
Increased renal blood flow
Reduction in cardiac arryhthmias
Improved quality of life
What is apnoea?
“Cessation of Airflow” for 10 seconds or longer
What is central apnoea?
Respiratory Control Centre - no respiratory effort
What is obstructive apnoea?
Collapse of pharyngeal airway during sleep (continuation of respiratory effort)
What is obstructive sleep apnoea?
5 or more obstructive apnoeas per hour
What is hypopnoea?
Reduction in airflow by 50% accompanied by desaturation of 4% and/or arousal from sleep
What are the risk factors for sleep apnoea?
- Male sex
- Obesity
- Neck circumference greater than 43 cm (41cm women)
- Family history of OSAHS
- Smoking
- Alcohol/sedative use
- Craniofacial abnormalities (e.g retrognathia)
- Pharyngeal abnormalities (e.g. tonsillar enlargement)
- Some medical conditions (hypothryroidism, acromegaly, pregnancy)
- Sleeping supine
What are the three regions of the pharynx?
Nasopharynx
Oropharynx
Laryngopharynx
What pharyngeal abnormalities may increase risk of apnoea?
Nasal pathology (polyps, deviated septum)
Enlarged tonsils
Increased soft tissue (obesity, hypothyroidism)
Abnormal chin (micrognathia, retrognathia)
What causes the pharynx to collapse?
↓ UA neuromuscular tone
↓ UA caliber
↑ UA resistance
↑ pharyngeal compliance
What are the clinical features of sleep apnoea?
- Snoring (Hx often from partner)
- Nocturnal choking/waking with a “start”
- Unrefreshing/restless sleep
- Morning dry mouth
- Morning headaches
- Excessive daytime sleepiness
- Difficulty concentrating
- Irritability/Mood changes
- Sleeping at inappropriate times
- Nocturia
What are the possible complications of sleep apnoea?
Cor pulmonale - right heart failure secondary respiratory disease
Secondary Polycythaemia - excess of red blood cells
What can be used to assess sleep apnoea?
Epworth Sleepiness Scale
Sleep Studies
- Nocturnal oximetry (measure o2 and pulse over night)
- Video studies
- Polysomnography (detailed measurements of nasal flow and movement of the chest)
How do you diagnose sleep apnoea?
AHI = apnoeas + hypopnoeas / total sleep time in hours
Mild: AHI 5–14per hour (+ symptoms/signs)
Moderate: AHI 15–30per hour
Severe: AHI more than 30per hour
What are the consequences of OSA?
Hypertension Type 2 diabetes Ischaemic heart disease Heart failure Cerebrovascular disease/stroke Cardiac arrhythmias Death
Increased risk of accidents
How can you treat OSA?
Mandibular advancement devices
- hold soft tissues of oropharynx forward
- mild-mod OSA, patient preference, failed CPAP
Surgery
- most effective if severe, correctable, obstructing lesion
- tonsillar or adenoid hypertrophy, craniofacial abnormalities
Continuous Positive Airway Pressure (CPAP)
What is CPAP?
Device generates airflow
Positive pressure delivered to airway via mask
Intraluminal pharyngeal pressure > surrounding pressure
Pharynx stays open
What are the benefits of CPAP?
Symptoms resolve ↓ apnoea/hypopnoea ↓ daytime sleepiness ↓ risk road accidents ↑ quality of life Normalises BP
What are the problems with CPAP?
- Adherence an issue
- Airway drying/irritation
- Can humidify
- Mask problems
- Air leak
- Comfort
- Normally life long treatment
