3 - Noninvasive Respiratory Support

benefits of high-flow nasal cannula (HFNC)

• precise F_iO₂

• dead space clearance

• reduced upper airway resistance

• increased pharyngeal pressure and lung volume

• heated humidity

indications for HFNC

• acute hypoxemic respiratory failure

• risk of post-extubation hypoxemic respiratory failure

• COPD

• asthma

• cardiogenic pulmonary edema

ROX index

• calculation that predicts HFNC success

• formula: (S_pO₂ ÷ F_iO₂) ÷ RR

  • > 4.88 = likely success

  • < 3.85 = possible need for invasive ventilation

flow rate for HFNC with mouth closed

~1 cmH₂O for each 10 L/min flow

interfaces for CPAP & NIV

• common interfaces

  • nasal mask

  • oronasal (full face) masks

  • nasal pillows

  • total face masks

  • helmets

• antiasphyxia = apparatus on mask that allows for breathing in case of machine failure

• vented = exhaled CO₂ (single limb)

• standard = dual limb

CPAP

• allows for lung expansion (pressure above atmospheric level)

• treatment

  • acute cardiogenic (decreases preload/afterload, shunt)

  • acute respiratory failure (prevent post-op atelectasis, shunt)

• threshold resistors

• OSA

  • ramp/delay feature

  • 4-5 hours

  • bilevel to help with exhaling discomfort

  • auto-positive airway pressure

noninvasive positive pressure ventilation (NPPV)

• critical care ventilators

  • dual limb

  • bilevel (IPAP/EPAP)

  • rise time

    • fast (inspiratory pressure reached quickly)

• modes

  • pressure control (PC)

  • volume control (VC)

  • bilevel

  • average volume-assured pressure support (AVAPS)

physiologic effects of NIV and CPAP

• improved oxygenation

• decreased work of breathing

• alveoli recruitment

• reduction of airway resistance

• enhanced CO₂ elimination (slight)

• decreased left ventricular afterload

• prevention of intubation

noninvasive ventilation (pressure support)

ventilation that is similar to NIV/CPAP but improves ventilation (IPAP, PS)

NIV application

1. Select patients for __ who will benefit.

2. Choose ventilator.

3. Choose correct interface; avoid mask that is too large.

4. Explain therapy to patient.

5. Silence alarms; choose low settings.

6. Initiate NIV while holding mask in place.

7. Secure mask.

8. Titrate inspiratory pressure to patient comfort.

9. Titrate F_iO₂ to SpO₂ > 90%.

10. Avoid inspiratory pressure per trigger effort and SpO₂.

11. Continue to coach and reassure patient; make adjustments to improve patient compliance.

CPAP settings

• IPAP

• EPAP

• F_iO₂

• rate

• i-time

• rise time

complications of noninvasive ventilatory support

• leaks

• facial skin breakdown

• mask discomfort

• eye irritation

• sinus congestion

• oropharyngeal drying

• patient-ventilator asynchrony

• gastric insufflation

• barotrauma

• hemodynamic compromise

contraindications of noninvasive ventilatory support

relative

• anxiety

• patient inability to cooperate

• obesity

• copious secretions

• swallowing

• impairment

• multiple organ failure

• need for continuous ventilatory assistance

absolute

• respiratory arrest

• unstable cardiopulmonary status

• decreased level of consciousness that results in inability to protect airway

• facial/esophageal lesions

• craniofacial trauma/burns

• severe failure