Non Invasive Ventilation

Definitions

• CPAP
  • Maintains alveolar recruitment and improves pulmonary shunting
  • Improves predominantly oxygenation and therefore indicated in type 1 respiratory failure
• BiPAP
  • S/T mode refers to spontaneous and timed mode and therefore has a backup rate
    • The use of ventilator-triggered breaths in acute respiratory failure while on NIV is questionable; if the patient doesn’t have a good respiratory rate perhaps they should be intubated
  • S mode refers to spontaneous (only)

$$\text{Pressure support (PS)}\approx \text{IPAP}-\text{EPAP}$$

Indications

• Acute hypercapnic respiratory failure secondary to COPD exacerbation, neuromuscular disease, obesity hypoventilation syndrome
  • Patients with COPD and a pH < 7.26 or a reduced level of consciousness are at greater risk of failing NIV and require closer monitoring
• Acute Pulmonary Oedema
• Immunocompromised patients with acute respiratory failure
• Acute pneumonitis (including COVID-19) with acute respiratory failure with $P_{\text{a}}\mathrm{O}{}_2$/$F_{\text{i}}\mathrm{O}{}_2$ > 150 mmHg
  • In moderate-to-severe hypoxaemia with $P_{\text{a}}\mathrm{O}{}_2$/$F_{\text{i}}\mathrm{O}{}_2$ ≤ 150 mmHg, delayed intubation can increase mortality and so NIV should only be applied in context of the ability to closely monitor
• Weaning high-risk patients from mechanical ventilation
• Post extubation management
• Post-operative acute respiratory failure
• Trauma
• Widely used for asthma, but this remains controversial¹

Contraindications

• Absolute
  • Immediate need for tracheal intubation
  • Imminent cardiorespiratory arrest
  • Anatomically fixed upper airway obstruction
  • Facial burns
  • Decreased level of consciousness in the setting of severe acute traumatic brain injury
• Relative
  • Haemodynamic instability
  • Impaired consciousness with inability to protect the airway
  • Altered level of consciousness due to hypercapnia
  • Recent upper airway surgery (requires discussion with surgeon)
  • Copious secretions or vomiting
  • Pneumothorax
  • Facial injuries, including fractured base of skull
  • Recent upper gastrointestinal surgery (requires discussion with surgeon)
  • Following immediate transsphenoidal resection of a pituitary tumour (requires discussion with neurosurgeon)

Initial NIV Settings

Fraction of Inspired Oxygen ($F_{\text{i}}\mathrm{O}{}_2$)

• Titrate to achieve target saturation of 88-92% in patients with chronic respiratory failure
• In other medical conditions (including neuromuscular disease and chest wall deformity), target $S_{\text{p}}\mathrm{O}{}_2$ range of 92-96%
• In acute coronary syndromes, target $S_{\text{p}}\mathrm{O}{}_2$ > 93%
• In heart failure, target $S_{\text{p}}\mathrm{O}{}_2$ > 90%

Settings for Congestive Heart Failure

• The goal is to have a relatively high EPAP setting to maintain high intrathoracic pressures throughout the respiratory cycle
• Example:
  • Start at 10 cm $\mathrm{H}{}_2\mathrm{O}$ IPAP / 5 cm $\mathrm{H}{}_2\mathrm{O}$ EPAP to allow the patient to get used to the mask
  • Increase to 15 cm $\mathrm{H}{}_2\mathrm{O}$ IPAP / 10 cm $\mathrm{H}{}_2\mathrm{O}$ EPAP
  • Increase to 18 cm $\mathrm{H}{}_2\mathrm{O}$ IPAP / 15 cm $\mathrm{H}{}_2\mathrm{O}$ EPAP
• CPAP is also perfectly fine and is equally effective

Settings for COPD and Restrictive Diseases

• Initial settings
  • S/T mode – spontaneously triggered with a timed backup respiratory rate
  • IPAP 14 cm $\mathrm{H}{}_2\mathrm{O}$
  • EPAP 4 cm $\mathrm{H}{}_2\mathrm{O}$
  • Rise time 0.2 seconds
  • Back-up respiratory rate (BRR) 12-16 breaths per minute
  • Inspiratory time 1.0-1.4 seconds
• Increase IPAP by 2 cm $\mathrm{H}{}_2\mathrm{O}$ increments every few minutes until maximum tolerance or target tidal volume of 8-10 mL/kg ideal body weight is achieved
  • An IPAP of 20-25 cm $\mathrm{H}{}_2\mathrm{O}$ may be required for adequate alveolar ventilation²
• Do not increase EPAP in the absence of obesity or obstructive sleep apnoea
• Adjust mask to minimise leaks
• Minimise $F_{\text{i}}\mathrm{O}{}_2$ to maintain $S_{\text{p}}\mathrm{O}{}_2$ 88-92%

Settings for Obesity Hypoventilation Syndrome

• The goal is to increase the driving pressure which provides mechanical support
• Initial settings
  • S/T mode – spontaneously triggered with a timed backup respiratory rate
  • IPAP 20 cm $\mathrm{H}{}_2\mathrm{O}$
  • EPAP 8-10 cm $\mathrm{H}{}_2\mathrm{O}$
  • Rise time 0.3 seconds
  • BRR 12-16 breaths per minute
  • Inspiratory time 1.4 seconds
• Increase IPAP by 2 cm $\mathrm{H}{}_2\mathrm{O}$ increments every few minutes until maximum tolerance or target tidal volume of 8-10 mL/kg ideal body weight is achieved
  • An IPAP of 20-30 cm $\mathrm{H}{}_2\mathrm{O}$ is often required to effectively treat alveolar hypoventilation during sleep
• EPAP needs to be sufficient to overcome upper airway resistance and extrapulmonary restriction
• Adjust mask to minimise leaks
• Minimise $F_{\text{i}}\mathrm{O}{}_2$ to maintain $S_{\text{p}}\mathrm{O}{}_2$ 88-92%

Settings for Neuromuscular Disorders

• Initial settings
  • S/T mode – spontaneously triggered with a timed backup respiratory rate
  • IPAP 8 cm $\mathrm{H}{}_2\mathrm{O}$
  • EPAP 4 cm $\mathrm{H}{}_2\mathrm{O}$
  • Rise time 0.3 seconds
  • BRR 12-16 breaths per minute
  • Inspiratory time 1.4 seconds
• Increase IPAP in 1 cm $\mathrm{H}{}_2\mathrm{O}$ increments, until maximum tolerance or target tidal volume of 6-8 mL/kg ideal body weight is achieved
  • An IPAP of 12-16 cm $\mathrm{H}{}_2\mathrm{O}$ is often sufficient
• A slightly higher EPAP may be required in bulbar disease or obesity (although generally minimal EPAP required)
• Adjust mask to minimise leaks
• Minimise $F_{\text{i}}\mathrm{O}{}_2$ to maintain $S_{\text{p}}\mathrm{O}{}_2$ 88-92%

Sedation

• Demedetomidine remains as one of the first line agents to allow tolerance of BiPAP however it has limited availability outside the ICU setting and can cause bradycardia and hypotension
• Alternatives include IV droperidol, haloperidol, ketamine, fentanyl
• Benzodiazepines are unfortuantely widley used but are probably not the best agents

Sources

• Non-Invasive Positive Pressure Ventilation (NIPPV) — ICU One Pager
• aci.health.nsw.gov.au/__data/assets/pdf_file/0004/820372/ACI-Non-invasive-ventilation-for-patients-with-acute-respiratory-failure.pdf
• Non-Invasive Ventilation (NIV) SID • LITFL • CCC Respiratory
• Noninvasive Respiratory Support - EMCrit Project

Footnotes

1. See Non-invasive ventilation (NIV) and asthma • LITFL for more information ↩

2. Noninvasive Respiratory Support - EMCrit Project suggests to avoid inspiratory pressures above 20 cm $\mathrm{H}{}_2\mathrm{O}$ as it increases the risk of aspiration and gas inssuflation ↩