2(b) NIV and Acute Respiratory Failure Flashcards
When might ventilatory support be required?
Respiratory acidosis and hypercapnia
What is CPAP?
Delivery of a constant pressure during both inspiration and expiration.
- same level of pressure (above atmospheric pressure)
How does CPAP help?
CPAP does NOT actively assist inspiration.
- Provides a distending pressure.
Physiologically:
Increases FRC
Opens collapsed or underventilated alveoli
Increases PaO2
Stabilises up0per airway obstruction
(maintains an open upper airway, especially during sleep
** Positive airway pressure
How can CPAP affect cardiac output?
If it delivers too much pressure, can decrease the blood coming back to the heart (low BP)
or can increase cardiac output and help cardiac muscle contraction
How does bilevel ventilatory support work? (NIV)
Provides two levels of airway pressure
Actively assists inspiration while providing end expiratory pressure
Physiologically: - CPAP effect + increases TV & MV
Reduces WOB
When would CPAP be used?
When oxygenation is the problem or when holding the airways open is the primary goal of therapy
When is Bilevel (NIV) indicated?
When CO2 is raised
When pump failure is the problem (recognised by increased CO2)
What does Bilevel ventilatory support do during expiration and what is the effect?
EPAP - end positive airway pressure.
Pressure remaining in airway to hold them open: helps if there is airway closure
What modes does Bilevel include?
Pt triggered breaths (spontaneous)
Machine triggered breaths ( Timed)
Combined (ST)
What is IPAP/pressure supoort in bilevel?
Level of inspiratory assistance
Increases tidal volume
What will the pressure support be limited by?
What the patient finds comfortable.
If too fast, patient feels like they’ve been hit in the face with a big gust of wind. If it’s too slow, can feel like they’re suffocating
What is the rise time in bilevel?
How rapidly the machine goes from EPAP to IPAP.
Normal in:exp = 1:2
What are the goals of using bilevel
To improve gas exchange. Decrease PaCO2 and acidosis
Reduced work of breathing
Prevent the need for invasive ventilatory support
Improve clinical outcomes
What is the best evidence for bilevel?
patients with underlying hypoventilation ie raised CO2
What sort of patients could have bilevel
Lung disease eg COPD, cystic fibrosis, brochiectasis
Obesity-related hypoventilastion
Neuromusclular disease
Chest wall deformity
Benefits of Bilevel over intubation for some patients
Can be used for someone who is startng to struggle > non invasive ventilation > acoid intubation and break that cycle and avoid further respiratory decompensation.
Also for people who need to be ventilated but would not do well in ICU
Patients can be given NIV for palliation, some extra time, make them more comfortable
Clinical indications for NIV
pH 45 mmHg
Moderate to severe dyspnoea
High WOB (access mm, increased respiratory rate)
Clinical impression of deterioration
Respiratory acidosis/hypercapnia esp COPD/SDB
Clinical indications for NIV and not intubation
Respiratory deterioration but immediate intubation not required
Haemodynamically stable
Single system failure (Reversible diagnosis, cooperative/non combative)
Manageable secretions
Who is not suitable for NIV?
Need for immediate intubation - imminent respiratory arrest
Refractory hypoxaemia
GCS <80 mmHg, significant ventricular arrhythmias)
Sepsis
Recent oral, oesophageal or gastric surgery
Facial trauma/burns or surgery
Undrained pneumothorax
Vomiting or bowel obstruction
Where is the strongest evidence for the benefit of bilevel ventilation?
In patients with underlying COPD
- Reduces mortality
- Reduces need for intubation
Also some evidence for use in pulmonary oedema
Where is there growing use of NIV where there is little evidence to support it
Pneumonia Asthma Sepsis Neurologic Other
What is the outcome when NIV fails
In hospital mortality rate is higher than for patients receiving IMV without prior NIV
What is the rate of successful weaning and what does failure after extubation mean?
10-20% of all pts fail first extubation attempt
Extubation failure is assoc with poor outcomes including high mortality rates of 25-50%
What are the factors associated with extubation failure?
Age >65 *Underlying chronic cardioresp disease Rapid shallow breathing index (F/Vt) Pneumonia as the cause of intubation GCS< 8 * Excessive endotracheal secretions * Weak or absent cough Increased PaC02 > 45 mmHg or low Pa02/Fi02 during weaning trial
What are the goals of IPAP and how is it set/does it work.
Goals:
Improve gas exchange
Reduce work of breathing
Alter breathing pattern
Set to maximum tolerated
Increasing pressure or swing increases tidal volume, alters respiratory rate
What are the goals of EPAP
Offset PEEPi
Decrease WOB
Improve V/Q matching
Maintain UA patency
What are the complications and side effects of NIV therapy?
Generally few.
Skin breakdown
Eye irritation from leak
Airway drying
Gastric distension
Pulmonary barotrauma
Aspiration pneumonia
Hypotension
What is the role of the physio during NIV treatment?
Involved in the NIV team
Secretion clearance in pts on NIV
Mobilisation/early rehab of pts using NIV
Results for airway clearance during NIV in AECOPD
ACBT= dec. length of time on NIV
PEP = cleared more secretions and dec. length of weaning
CPT: reduced time on NIV and better gas exchange
Intrapulmonary percussive ventilation + dec. LOS ICU and CO2
What is mechanical in-exsufflation - cough assist, how is it applied and how does it work
Mechanically assisted cough technique
Applies positive pressure to the airways, followed by a rapid change to negative pressure.
Increases peak cough flow more than other airway clearance techniques
Applied via mask or trache tube
