Non-Invasive Ventilation in Adults with Acute Hypercapnic Respiratory Failure

Acute Hypercapnic Respiratory Failure (AHRF) refers to respiratory failure resulting in acute respiratory acidosis, with a PC02 > 6.5 kPa and H+ >45 (pH < 7.35). 

ARHF results from an inability of the respiratory pump, in concert with the lungs, to provide sufficient alveolar ventilation to maintain a normal arterial PC02.¹

Non-Invasive Ventilation (NIV) refers to the provision of ventilatory support through the patient's upper airway using a mask or similar device². In the context of AHRF a full-face mask is recommended.¹

In this document, NIV refers to non-invasive bi-level positive pressure ventilation.

Background Information

NIV is a non-invasive method of augmenting spontaneous respiratory efforts. When a patient initiates a breath, the ventilator delivers air until a preset pressure is reached (Inspiratory positive airway pressure – IPAP). The ventilator will maintain this pressure until the patient breathes out.  As the patient exhales, the ventilator provides an expiratory positive airway pressure (EPAP) within the lungs - the background pressure during expiration. 

The assistance of inhalation with inspiratory positive airway pressure (IPAP) improves gas exchange within the lungs, as it will increase the volume of air into and out of the patient's lungs with each breath (Improved alveolar ventilation). This will in turn help to expire alveolar carbon dioxide.

End expiratory positive pressure (EPAP) will expand the alveoli in the lungs, helping to improve the capacity of the lungs and increase the area available for gas exchange. (Improved Functional Residual Capacity). NIV will also reduce the effort the patient has to make to achieve a satisfactory oxygen level and help rest the muscles required for breathing.

Terminologies

The terminology used for pressure-targeted ventilation can cause confusion and some acronyms/terms can be used interchangeably. In bi-level ventilation, one pressure is set for inspiration (IPAP) and a second pressure for expiration (EPAP). This mode is most commonly used for NIV. 

The difference between IPAP and EPAP is the level of ventilatory assistance or pressure support (PS). 

IPAP – EPAP = PS

EPAP is also known as PEEP (positive end expiratory pressure). CPAP (continuous positive airway pressure) is a form of non-invasive assisted ventilation which delivers a single pressure throughout the respiratory cycle, hence maintaining a PEEP (positive end expiratory pressure)/EPAP (expiratory positive airway pressure) during both inspiration and expiration. 

The term ‘CPAP with Pressure Support’ can be used to describe a mode of bi-level invasive ventilation and/or non-invasive ventilation on some ventilators eg Draeger Savina. The operator sets an incremental pressure support (PS) above the PEEP/EPAP setting rather than setting an absolute level of inspiratory pressure (IPAP). 

Hence IPAP = PEEP + PS

Acute NIV should only be used for the treatment of hypercapneic respiratory failure with a respiratory acidosis.  NIV has been shown to reduce length of stay, reduce requirement for intubation and decrease mortality in patients with Type 2 respiratory failure.The majority of evidence for acute NIV exists in patients with COPD. Other underlying conditions with AHRF that would benefit from NIV include obesity hypoventilation syndrome, chest wall deformities egkyphoscoliosis,and neuromusculardiseaseseg muscular dystrophies. Some conditions may overlap eg COPD and Obesity hypoventilation.

COPD

Patients with exacerbation of COPD with respiratory acidosis should receive an hour of optimised medical therapy. This includes controlled oxygen therapy to maintain target saturations 88-92%, steroids, nebulisers andantibiotics. NIV should be considered if a repeat ABG still shows H+ >45 (pH<7.35),PaCO2 >6.5kPA.

Obesity Hypoventilation

Patients with obesity hypoventilation often presents with acute on chronic respiratory failure. Medical treatment includes treatment of reversible triggers eg infection; controlled oxygen therapy to maintain target saturation 88-92%; and diuresis. NIV is indicated in presence of AHRF H+ >45 (pH <7.35) and pCO2 >6.5.  NIV can also be considered when the daytime pCO2>6.0 with or without acidosis if patient is somnolent. This should be discussed with respiratory team. 

Obese patients have reduced chest wall compliance and often have coexistent upper airways obstruction, particularly at night. They would need higher IPAP and EPAP. These patients may benefit from referral to home ventilation service upon discharge.

Chest Wall Deformities and Neuromuscular Diseases

Patients with chest wall deformity or neuromuscular disease may develop acute hypercapnic respiratory acidosis and benefit from acute NIV. Medical treatment would include treating underlying infections and controlled oxygen therapy to maintain target saturation 88-92%. NIV should also be considered in the context of respiratory illness if RR>20 if their usual Vital Capacity is <1L, even in the absence of hypercapnoea or acidosis (pCO2 <6.5, H+ <45).  This should be discussed with respiratory team.

Patients with neuromuscular weakness are often very sensitive to inspiratory pressures in NIV and can become hypocapnic if excessive pressures are utilised. These patients require lower starting pressures and gentle up-titration. 

Patients with chest wall deformity due to poor chest wall compliance, by contrast, often require higher IPAP pressures of 20-30 cmH20.

These patients may benefit from referral to home ventilation service upon discharge.

Absolute:

Facial burns/trauma/surgery

Fixed upper airway obstruction

Relative:

Life threatening hypoxaemia

Vomiting

Severe comorbidities

Confusion/agitation

Inability to protect airway

Haemodynamically unstable

Copious secretions

Undrained pneumothorax

All patients must have a chest x-ray reviewed prior to starting NIV to exclude a pneumothorax. NIV should not be delayed if the patient is severely acidotic, but a chest X-ray must be obtained and reviewed urgently. A patient with an acute pneumothorax must have a functioning intercostal chest drain before NIV is commenced. Again if the patient is severely acidotic the drain can be inserted simultaneously to NIV being started. 

All other relative contraindications do not normally preclude use of NIV but if present does increase risk of NIV failure. These patients would need closer monitoring in appropriate areas eg High Dependency Unit.

Decision Regarding Treatment Escalation Plan

PRIOR to initiation of NIV, a decision regarding treatment escalation plan should be clearly documented in notes with NHSL TEP/DNACPR filled as appropriate. Decision should be communicated to all staff in case of treatment failure. 

Care decision, as discussed with senior clinician or Intensive care where appropriate (1&2), should follow the RCP 2008 stratification³: 

1. Requires immediate intubation + ventilation 
2. Suitable for NIV and escalation to ITU/intubation 
3. Suitable for NIV, but not ITU/intubation 
4. Not suitable for NIV, but for full active medical treatment 
5. Palliative care

Consent

Treatment should be explained to patient with verbal/written consent obtained prior to commencement of NIV. In instances where patients are unable to consent, decision of treatment should be communicated to next of kin and AWI filled in.

Requirements/Equipment

Appropriate area 

Appropriately designated area for NIV according to site protocol eg A&E, Medical HDU, ITU

Trained member of staff to set up NIV and monitoring 

NIV machine (Draeger Savina) 

Tubing, facemask, filter, exhalation port 

Oxygen supply, suction facilities 

SaO2 and ECG monitoring equipment 

Acute NIV Patient Care Plan and Prescription chart (available in HDU/For download on Firstport link).

This must be completed by middle grade/senior medical staff prior to commencement.  Setting changes, observations and blood gases must be documented on the NIV Monitoring Chart (add appendix).

Initial Set Up

1. Select appropriate mask using the sizing tool. 
2. Ensure exhalation port, filter/water trap, tubing, bacteria filter and oxygen tubing are connected. 
3. Turn on machine and wait for self-check to finish. 
4. Ensure oxygen is connected. 
5. Select settings for Draeger Savina

Mode Spon-CPAP-PS (CPAP with Pressure Support)

Dial PEEP (EPAP)

Dial PS (Pressure support).

PEEP + PS = IPAP 

Dial FiO2 to achieve target saturation 88-92%

Please refer to NIV Flow Chart for initial starting pressure depending on indications.

6. Encourage the patient to breath in and out whilst holding the mask close to face to allow acclimatisation. Once the patient is comfortable, adjust the head gear with straps to ensure minimal leak. Care needs to be taken to ensure the mask is not fitted too tightly to reduce pressure sores. 
7. Titrate Pressure Support (PS) in 2-4cmH2O increments every 5-10 minutes interval (1cmH2O every 10 minutes for Neuromuscular) as tolerated to achieve good chest/abdominal movement and reduced respiratory rate. Titrate FiO2 to achieve target saturation. Refer to flowchart for titration of pressures depending on indications.

Monitoring

Arterial blood gas (ABG)

Perform ABG 1 hour post initiation of NIV, and at 4-6 hour intervals. ABGs should be done 1 hour after any change in ventilator settings. 

Vital signs

Continuous SPO2 monitoring

Monitor RR, HR, BP every 15 mins for first hour then hourly

Check patient comfort, air leak/mask leak and synchronisation.

Signs of improvement would include: 

Reducing H⁺ and pCO2

Improved PaO2 (Aiming for target saturation 88-92%)

Reduced respiratory rate

Good patient synchronisation

If there is no improvement after one hour, consider discussing patient with ITU unless NIV is the ceiling of treatment.

If there is no response after 6 hours of optimal ventilatory support, the likelihood of subsequent success is small and other management should be considered.

If patient is improving, aim to maximise use of NIV in the first 24-48 hours to optimise outcome. 

Allow short breaks for nutrition, medications, nebulisers and comfort as required. 

Taper NIV during the day over the following 2-4 days before discontinuing overnight use. NIV can be discontinued once acidosis resolved and pCO2 reduced and stabilised. 

Duration of treatment may differ in individual patients.

For further information the following documents can be found in the Clinical Records on FirstPort:

• NIV Setting and Blood Gas Monitoring.
• Acute Non-Invasive Ventilation (NIV) Patient Care Plan and Prescription.

1. British Thoracic Society, Intensive Care Society (2016). Guideline for the ventilatory management of acute hypercapnic respiratory failure in adults. Thorax 2016;71:ii1-ii35.
2. British Thoracic Society, Standards of Care Committee (2002). Non-invasive ventilation in acute respiratory failure. Thorax 2002; 57:192- 211.
3. British Thoracic Society, Royal College of Physicians London and Intensive Care Society (BTS/RCP/ICS) (2008). The use of non-invasive ventilation in patients with chronic obstructive pulmonary disease admitted to hospital with acute type II respiratory failure (with particular reference to BiLevel positive pressure ventilation).
4. British Thoracic Society, Scottish Intercollegiate Guidelines Network (BTS/SIGN) (2003). British guideline on the management of asthma: A national clinical guideline. Revised edition July2019.
5. British Thoracic Society (2009). Guidelines for the management of community acquired pneumonia in adults: update 2009. Thorax 2009;64(Suppl III):iii1–iii55.