Non-invasive ventilation

Introduction

• Overall reduces need for intubation by 25%
• Reduces intubation-related complications
• Probably improves survival
• Reduces length of ICU stay
• Enables treatment for those not suitable for intubation

Indications for mechanical ventilatory support

• RR >30 (Type I RF) or RR >24 (Type 2 RF)
• Abdominal paradox
• Vt <5mL/kg
• VC <15mL/kg
• PEFR <1.5L/min/kg
• PaO2 <60 on FiO2 0.5 (P/F >200)
• pCO2 >60

CPAP

• Respiratory effects
  • Reduces work of breathing by:
    • Alveolar recruitment leading to reduction in elastic work
    • Increased lung compliance
    • Reducing threshold load created in presence of PEEPi
    • Increased diameter of airways to reduce resistance to airflow and promote laminar flow
  • Redistributes lung water into interstitium and away from gas exchanging surfaces
  • Reduced FiO2 requirement with less denitrogenation atelectasis and oxygen-derived free radical damage
  • Reverses hypoxia through alveolar recruitment, increased FRC, improved VQ matching and reduction of intrapulmonary shunt
• Cardiovascular effects
  • Reduction of LV transmural pressure (afterload)
    • LV pressure – Pleural pressure
    • If pleural pressure is negative, get LV pressure – (-10mmHg) for example
    • If pleural pressure positive (as in CPAP), get LV pressure – (+10mmHg)
    • Pressure gradient from intrathoracic vessels to extrathoracic vessels promotes forward flow and further reduces LV afterload
  • Reduced RV preload
  • Increased RV afterload
  • Reduction of LV preload
• Benefits
  • May avoid intubation in 90% of patients with APO
• Values >15cmH20 rarely confer benefit
• Indications
  • APO
  • Asthma
  • ARDS
  • Pneumonia
  • Chest trauma

IPAP

• Reduces elastic and resistive work of breathing
• Augments tidal volume and reduces PaCo2
• Induces pulmonary surfactant release through alveolar inflation above resting tidal volume

BiPAP

• Bilevel positive airway pressure non-invasive ventilation
• Provides positive pressure of differing levels during both inspiration and expiration
• Improves lung mechanics:
  • Stents airways open
  • Reduces atelectatic alveoli
  • Improves VQ mismatch
  • Improves pulmonary compliance
  • Reduces work of breathing

Indications for BIPAP

• Diagnoses
  • COPD
  • Neuromuscular disease
  • Obesity
  • Hypoventilation
  • APO (CPAP)
  • Asthma
  • Post-operative and post-traumatic
• Parameters
  • pH < 7.35
  • PaCO2 > 65
  • RR >23
  • Persistent hypercapnoeic respiratory failure despite bronchodilators and controlled O2 therapy

Evidence

• COPD (Cochrane review)
  • Reduced mortality by 50%
  • Reduced need for intubation by 60%
  • Reduce treatment failure by 52%
  • Rapid improvement in pH, RR and PaCO2 within 1 hour
  • NNT to avoid intubation (4) and death (10)
• APO
  • Large RCT (3CPO study) showed NIV made no difference in mortality but does reduce dyspnoea, heart rate, acidosis, hypercapnoea and need for intubation
  • Other studies have shown reduced mortality with CPAP (RR 0.64) and need to intubate (RR 0.44) with no effect on new MI
  • BiPAP has been associated with similar improvements in respiratory parameters but increased risk of MI and no benefit on mortality
• Asthma
  • No convincing evidence either way but has been used now for a long time with apparent prevention of intubation without increased risk of death 

Contraindications

• Absolute
  • Severe facial deformity
  • Facial burns
  • Fixed upper airway obstruction
  • Urgent need for intubation
  • Risk of aspiration/vomiting
• Relative
  • pH <7.15
  • GCS <8
  • Cognitive impairment/confusion
  • Excessive secretions
  • Haemodynamic instability
  • Poor patient tolerance

Settings

• Initial BiPAP settings
  • IPAP: 12-15cmH20 (maximum 25cmH2O)
  • EPAP: 4-7cmH20
  • Appropriate FiO2 for clinical state
  • Explain things to patient as very confronting
• Ongoing care
  • Titrate down or consider ketamine (WITH EXTREME CAUTION) if not tolerating
  • Failure to improve oxygenation = increase in FiO2 and EPAP (alveolar recruitment)
  • Failure to improve hypercarbia = increase in IPAP (ventilation)

Monitoring

• Increase in secretions
• Mental status changes
• Synchronicity with machine
• Air leaks
• Respiratory rate
• Tidal volume changes
• Oxygen requirements
• Blood gas

• Early predictors of success in NIV use for COAD exacerbation
  • pH and PaCO2
  • NOT the PaO2 in the first 2 hours
• Predictors of failure for NIV use in COAD
  • Mask intolerance (20-30% of patients do not tolerate)
  • Severe acidosis (pH <7.25)
  • Tachypnoea (>35)
  • Impaired conscious state
  • Poor clinical response to initial therapy

Leak

• Air leak 6-25L/min considered acceptable
• Leaks >60L/min significantly reduce function
• Late failure (>48 hours) occurs in 10-20% of patients with high mortality

Complications

• Major complications
  • Severe hypoxaemia
  • Aspiration
  • Hypotension secondary to reduced venous return
  • Mucous plugging
• Pressure-related: Sinus pain, gastric insufflation, pneumothorax, poorly tolerated, air leaks from poor mask seal, pressure sores at nasal bridge
• Airflow-related: Dryness, nasal congestion, eye irritation

BiPAP in asthma

• How it might work?
  • Bronchodilators effect
  • External PEEP offsets intrinsic PEEP i.e. negative pleural pressure not required to overcome iPEEP
  • Re-expansion of atelectasis via collateral channels
  • Improves VQ matching
  • May assist respiratory muscles
• Cochrane showed no benefit on mortality or intubation rates but reduced hospital admission, length of ICU stay and length of hospital stay
• Risk of hyperinflation if ePEEP > iPEEP
• Who to try it on?
  • Intubation not immediately called for
  • RR >25, HR >110, accessory muscle use, PaCO2 45-60 or FEV1 <50% predicted
• Initial settings
  • 15/5 with I:E ratio of 1:5
• SHOULD NOT DELAY NECESSARY INTUBATION

NIV in post-operative/post-traumatic respiratory failure

• Impaired respiratory muscle function, dependent atelectasis, impaired chest wall mechanics, poor cough, nosocomial infection, aspiration pneumonitis and non-respiratory trauma and sepsis are all seen
• Mask CPAP improves physiological parameters and may help to avoid MV
• May improve survival post-lung resection
• Superior to MV in isolated severe chest wall trauma

NIV-assisted weaning

• May allow early extubation and to treat failed or accidental extubation
• Survival benefit in COAD

HiFlow

• Heated humidified high flow nasal prong support
• Air oxygen blender generates up to FiO2 1.0 and flow of up to 60L/min
• Humidification
  • Preserves nasal mucosa
  • More comfortable
  • Enhances mucociliary function
• High FiO2
  • Permits constant oxygen delivery in intense respiratory effort
  • Washes out nasopharyngeal dead space, decreases CO2 re-breathing and provides oxygen reservoir
• CPAP effect
  • Splints nasopharynx to decrease resistance
  • Low levels of PEEP (1-5cmH20) may assist alveolar recruitment, improve compliance and decrease work of breathing

Hiflow indications

• Hypoxic respiratory failure without hypercarbia despite standard oxygen support
  • Community-acquired pneumonia
  • Viral pneumonia
  • Acute asthma
  • Cardiogenic pulmonary oedema
  • Pulmonary embolism
  • Interstitial pneumonia
  • Carbon monoxide poisoning
  • Bronchiolitis
  • Apnoea of prematurity
• Pre-oxygenation, post-extubation, weaning from mask NIV and apnoeic oxygenation

Contraindications

• Blocked nasal passages
• Choanal atresia
• Trauma/surgery to nasopharynx
• Epistaxis
• Base of skull fracture
• Obvious need for intubation

Hiflow settings

• Up to 8L/min on paediatric tubing and 60L/min on adult setup
• <10kg = 2L/kg/min (can uptitrate to this if necessary)
• >10kg = 2L/kg/min for first 10kg then 0.5L/kg/min for each kilogram above that up to 60L/min
• Start at 6L/min and uptitrate over several minutes
• FiO2 0.21-1.0 as necessary
• 37 degrees temperature

Monitoring

• Respiratory rate, heart rate, work of breathing and SpO2
• Ensure paediatric patients have NG inserted prior to initiation of HiFlow. NG should be on free drainage and aspirated q2-4h

Complications

• Gastric distention
• Pressure areas
• Blocked HFNP
• Pneumothorax
• Local trauma/discomfort
• Epistaxis
• Might cause delayed intubation and worse clinical outcomes (Kang et al. 2015)
• Patients may be thought to look more well than they actually are

Evidence

• FLORALI study showed no difference in intubation rates vs. NIV or traditional O2 delivery but significantly improved 90 day mortality
• No clear benefit of apnoeic oxygenation in terms of mortality or episodes of desaturation but also no harm found either
• Controversial as to who is most likely to benefit from this therapy

Last Updated on February 11, 2022 by Andrew Crofton