Respiratory & Ventilatory Failure and theories of positive pressure Flashcards
Aims
- Describe the concept, underlying pathophysiology, impairments and clinical presentations of type I and type II respiratory failure
- Justify an evidence-based treatment plan for the management of a patient with type I and type II respiratory failure
- Describe and explain the physiology, and relevant precautions and contraindications for using continuous positive airways pressure (CPAP), non-invasive positive pressure ventilation (NIV) and intermittent positive pressure breathing (IPPB)
- Select and critically evaluate appropriate research evidence that explore the use of NIV in patients with COPD
Define respiratory failure?
aka type 1
- Failure to maintain adequate gas exchange and is characterised by abnormalities of arterial blood gas tension.
- Decreased PO2
- Decreased or normal PCO2
What is Acute hypercapnic respiratory failure?
aka type 2
- AHRF results from an inability of the respiratory pump, in concert with the lungs, to provide sufficient alveolar ventilation to maintain a normal arterial PCO2.
- Co-existent hypoxaemia is usually mild and easily corrected.
- PCO2 > 6.5 kPa and pH < 7.35
Which respiratory components can fail, in respiratory failure?
Associated with both the lungs and the respiratory muscle pump. So anything that effects the; Load, capacity or drive.
So that could be;
- The lung itself.
- Damage to pleura or the chest wall.
- Nerve damage e.g. phrenic nerve.
- NMJ via diseases such as Myasthenia Gravis.
- Weak respiratory muscles.
What are the normal values for the following?
- pH
- PaO₂
- PaCO₂
- HCO₃¯
- BE
- pH 7.35 - 7.43
- PaO₂ 10.7 - 13.3 kPa
- PaCO₂ 4.7 - 6.0 kPa
- HCO₃¯ 22 - 26 mmol
- BE -2 - +2
What is the process and end result of untreated respiratory failure.
(Its the same for type 1 and 2, and describe in a flowchart like manor)
- O₂ is fuel for tissue respiration / metabolism.
- Lack of O₂ = hypoxemia
- -> anaerobic metabolism
- -> metabolic acidosis
- -> Neurological and cardiovascular deterioration.
- -> Cell hypoxia
- -> Cell death.
Summarise type 1 respiratory failure (Hypoxemic)
- Decrease in O₂ (<8kPa)
- CO₂ normal or low
- pH normal
Oxygenation failure (V/Q mismatch or diffusion impairment)
Summarise type 2 respiratory failure
Hypercapnic
- Decrease in O₂ (<8kPa)
- Increase in CO₂ (>6KpA)
- Decrease in pH
Ventilatory failure (Failure with the respiratory pump)
What type of reparatory failure am I?
- pH 7.43
- PaCO₂ 7.5
- PaCO₂ 5.5
- HCO₃¯ 24
- BE 0.5
Type 1
What type of reparatory failure am I?
- pH 7.29
- PaO₂ 7.6
- PaCO₂ 8.1
- HCO₃¯ 23
- BE -1
Type 2 acute
What type of reparatory failure am I?
- pH 7.36
- PaO₂ 8.1
- PaCO₂ 7.3
- HCO₃¯ 31
- BE +3
Type 2 chronic
What can cause type 1 respiratory failure?
- Secretion retention.
- Acute lobar collapse.
- Fluid - Pleural effusion / Pulmonary oedema
- Pneumonia
What can cause type 2 respiratory failure?
- Decreased respiratory drive e.g., opiate overdose
- impaired inspiratory muscle strength e.g. Neuromuscular disease.
- Increased demand on system e.g. Acute ex COPD or COVID -19 pneumonia
What are the signs of Type 1 respiratory failure?
- Tachypnoea (abnormally rapid breathing)
- Tachycardia (abnormally rapid bpm)
- Accessory muscle use
- Cyanosis (peripheral v’s central)
- Clammy
- Altered mental state
- Breathlessness.
What are the signs of Type 2 respiratory failure?
Same as type 1 plus;
- Confusion
- Headache
- Bounding pulse
- Vasodilation
- Decreasing consciousness
- Breathlessness
What are treatment aims for management of respiratory failure?
Treatment aims;
- Increase capacity of system.
- Reduce load on the system.
- Optimise drive.
What type of management would be appropriate for type 1 respiratory failure?
- O₂ therapy
- Humidification
- Positioning (decrease load and increase capacity)
- ## Non-invasive ventilation
What type of management would be appropriate for type 2 respiratory failure?
- O₂ therapy
- Aim PO₂, SpO₂ 88-92%
- Provides adequate tissue oxygenation without further increasing CO₂ retention.
- Increase Capacity: Increase lung volumes - positioning, pain relief, secretion clearance, ventilatory support.
- Decrease load: Decrease WOB - positioning, secretion clearance, ventilatory support.
- Drive: Respiratory stimulants, remove respiratory depressants.
What are the 3 types of PP (positive pressure) breathing?
- Intermittent (IPPB)
- Continuous (CPAP)
- Non-invasive ventilation (NIV)
What are the basic principles of Positive pressure breathing
- Air pushed into the lungs during inspiration.
- Intrathoracic pressure becomes positive.
- Increases lung volumes/ tidal volume.
- Offloads respiratory muscles.
- Cardiovascular effects
- decrease venous return.
- decrease CO
- decrease BP
- Decrease organ perfusion.
What are the principals of IPPB (Intermittent positive pressure breathing)?
What’s it used for?
What does it do?
- Mainly used now to increase VT, and aid secretion clearance.
- non-invasive
- patient triggered
- pressure cycled
- passive expiration
Can control the rate and depth of breath delivered by machine, settings adjusted for each patient.
How does IPPB (Intermittent positive pressure breathing) work?
FYI the device is aka “The Bird”
- Increases VT
- Mobilises secretions using collateral ventilation.
- Reduces WOB
- Ventilates uppermost areas (not a good thing as usually its the distal pathways which are least ventilated, so this is a weakness of the device)
What patients are best suited to IPPB (Intermittent positive pressure breathing)?
Patients who have/ are;
- reduced VT
- Sputum retention
- Lobar collapse
- Increase WOB
- fatigued
- Weak cough
What is the effect of IPPB on lung volumes; VT, FRC?
- Increases VT.
- No effect on FRC.
Continuous positive airway pressure (CPAP), what is it, what does it do?
- Positive pressure applied throughout inspiration and expiration during spontaneous breathing.
- Non-invasive
- Splints open alveoli
- Patient determines own RR and VT
What is the effect of CPAP on lung volumes?
FRC
VT
- FRC increases
- no effect on VT
How does CPAP work?
- Increase in intrathoracic pressure - splinting open alveoli
- Increase in FRC
- Improves oxygenation
- Decreases WOB
- A CON: can be noisy, uncomfortable, cause abdominal distention and reduce BP
Which patients are best suited to CPAP?
suitable problems
- Atelectasis (lungs collapse partially or completely).
- Decreased FRC
- Hypoxemia despite high FiO₂ levels
- Type 1 respiratory failure
- NOT type 2 RF if using high flow O₂ if concerns regarding O₂ sensitivity.
Just a little note/fact regarding COVID-19
- CPAP is the preferred form of non-invasive ventilatory support in the management of the hypoxemic COVID-19 patient. Its use does not replace invasive mechanical ventilation (IMV), but early application may provide a bridge to IMV.
- NHS Guidance 2020
What is NIV and what does it do?
- Provision of a higher inspiratory and lower expiratory pressure in time with patients breathing.
- Delivered via face or nasal mask.
- Patient triggered
- Pressure cycled
- Can set back up rate to ventilate patient.
What is the effect of NIV on lung volumes?
- FRV
- VT
- Increases both.
How does NIV work?
- Delivers an inspiratory pressure (IPAP) and provides an expiratory pressure (EPAP).
The IPAP;
- Offloads respiratory muscles
- Increases VT
- Aids elimination of CO₂
- Decreases WOB
The EPAP;
- Splints open alveoli
- Improves oxygenation
- Increases FRC.
What patients / problems is NIV suited to?
- Type 2 (hypercapnic) RF
- Patients who are fatigued
- Weaning from conventional mechanical ventilation.
It is important to monitor patients who are on Positive pressure therapy, but what would you be monitoring?
- Important to monitor effects / tolerance of treatment.
- Should include: HR, BP, RR and pattern, SpO2, ABG’s.
- Oxygen saturations alone is not enough to tell about ventilatory needs.
- Equipment settings.
- Mask fit / seal – check no leaks.
- Skin condition / integrity
What are the contraindications / precautions to Positive pressure?
Its a looooong list :(.
- Undrained pneumothorax
- Vomiting
- Severe haemoptysis
- Non-compliance of patient
- Large air leak post op
- Proximal tumour
- Emphysematous bullae
- Lung abscess
- Active TB
- Proximal airway obstruction
- Raised ICP
- haemodynamic instability
- surgical emphysema
- recent lung, oesophageal, facial surgery.
What is the Evidence for NIV?
Cochrane NIV 2017;
essentially strong supportive evidence for its effectiveness and reduced mortality rate.
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