NPPV Notes

Noninvasive Positive-Pressure Ventilation (NPPV)

Overview

  • NPPV involves delivering positive-pressure ventilator support without an endotracheal tube.
  • It's used for managing both acute and chronic respiratory failure.
  • NPPV offers benefits of mechanical ventilation without intubation risks in specific patient groups.
  • Clinicians should understand patient selection, equipment, and ventilator settings.
  • The term NPPV commonly refers to Bilevel Positive Airway Pressure (BPAP).
  • In BPAP, the ventilator alternates between Expiratory Positive Airway Pressure (EPAP) and Inspiratory Positive-Airway Pressure (IPAP).
  • The difference between IPAP and EPAP supports tidal volumes, increasing ventilation.
  • Tidal volume correlates with IPAP/EPAP difference, inspiratory time, patient effort, and airway/lung mechanics.
  • Continuous Positive Airway Pressure (CPAP) delivers constant airway pressure throughout the respiratory cycle.
  • Some ventilators reduce pressure during expiration to enhance comfort with CPAP.
  • CPAP doesn't directly support ventilation but can improve it indirectly, such as through alveolar recruitment.

Indications

  • Consider BPAP for patients showing respiratory distress.
  • Clinical signs include dyspnea, tachypnea, and using accessory respiratory muscles.
  • Arterial blood gas measurements may reveal:
    • Acidemia: arterial pH < 7.35
    • Hypercapnia: partial pressure of carbon dioxide (PaCO₂) > 45 mm Hg
    • Hypoxemia: ratio of partial pressure of arterial oxygen (PaO₂) to fraction of inspired oxygen (FIO₂) < 200
  • Trials confirm BPAP benefits for hypercapnic respiratory failure from acute COPD exacerbation.
  • Both BPAP and CPAP benefit patients with cardiogenic pulmonary edema (without shock or ischemia).
  • BPAP benefits patients with immune compromise, fever, and pulmonary infiltrates who have acute hypoxemic respiratory failure.
  • BPAP facilitates the shift from invasive ventilation to spontaneous breathing in COPD patients.
  • Insufficient evidence supports BPAP for severe asthma exacerbations, pneumonia, ARDS, postoperative respiratory failure, respiratory failure with "do not intubate" orders, and palliation in terminally ill, but these areas are being studied.

Contraindications

  • Absolute contraindications for BPAP and CPAP include cardiac arrest and respiratory arrest.
  • Relative contraindications:
    • Mask discomfort unresolved with adjustments.
    • High aspiration risk due to impaired mental status (unless from hypercapnia).
    • Large secretion volume, recurrent vomiting, recent upper-airway or GI surgery.

Equipment

Interface
  • The interface is the defining feature, providing noninvasive airway access between the patient and ventilator.
  • Masks are the most common interface.
  • Oronasal masks are commonly used in urgent situations; they seal around the nose and mouth.
  • If oronasal masks are too tight, they can cause discomfort and skin abrasion on the nose bridge.
  • Alternatives: total-face masks, nasal masks, and nasal pillows.
  • Total-face masks cover the entire face, avoiding nose abrasion but potentially causing claustrophobia.
  • Nasal masks and nasal pillows generally cause less claustrophobia, but the mouth must stay closed to prevent air leaks.
Ventilators
  • Inpatient noninvasive ventilators offer various settings, alarms, and modes (BPAP or CPAP).
  • They display real-time patient breathing information in numeric and graphic formats (respiratory cycle phase, rate, tidal volume, minute ventilation, peak inspiratory pressure, air leak volume).
  • Available settings depend on the mode.
  • CPAP mode settings: CPAP level and FiO₂.
  • BPAP mode settings: IPAP, EPAP, and FiO₂.
  • BPAP often uses Spontaneous/Timed (S/T) mode, including minimum respiratory rate and inspiratory time (I-time).
  • If the patient's respiratory rate is slower than the set minimum, the ventilator delivers additional breaths at regular intervals, providing IPAP for the I-time duration.
  • If the patient's respiratory rate is faster than the minimum, the patient triggers all breaths, and the ventilator delivers IPAP when spontaneous inspiration is detected.
  • The ventilator cycles between EPAP and IPAP based on the patient's spontaneous breathing or a set time interval.

Procedure

  • For patients showing respiratory distress, provide initial support and involve a trained respiratory therapist for ventilator setup and troubleshooting.
  • If possible, get a baseline arterial blood gas measurement.
  • Explain BPAP's essential features to the patient to reduce anxiety and improve tolerance.
  • To prepare the ventilator, select the appropriate mode.
  • BPAP is suitable for hypercapnic respiratory failure due to COPD.
  • CPAP or BPAP can be used for cardiogenic pulmonary edema without shock or ischemia, as both provide positive end-expiratory pressure beneficial for ventricular dysfunction. However, BPAP is more appropriate if hypercapnia is present.
  • Enter initial settings, starting with low pressures, and adjust upwards as needed.
  • When using BPAP, set initial inspiratory and expiratory pressures to 10 cm and 5 cm of water, respectively.
  • Secure the mask on the patient, ensuring the straps are snug but not overly tight; two fingers should fit between the straps and the patient's head.
  • The mask should fit comfortably over the nose and mouth without extending beyond the chin.
  • Adjust alarms based on the clinical scenario and ventilator settings, and assess the patient whenever an alarm sounds.
  • Monitor patient symptoms and vital signs closely, and address any ventilator-related complications as needed.
  • Adjust FiO₂ to achieve the desired oxygen saturation.
  • Re-measure arterial blood gases after 30 minutes to determine if further adjustments are necessary.
  • For persistent hypercapnia, increase minute ventilation by changing tidal volume or respiratory rate.
  • Increase tidal volume by increasing the difference between IPAP and EPAP.
  • Increasing the minimum respiratory rate affects ventilation only if the patient's spontaneous breathing rate is slower than this rate.
  • If there is persistent hypoxemia, increase either the fraction of inspired oxygen or the EPAP.
  • If EPAP is increased, IPAP should also be increased proportionally to maintain the pressure support level.
  • If the patient has persistent respiratory distress despite ventilator adjustments or develops a contraindication to BPAP (e.g., vomiting), perform endotracheal intubation immediately.
  • If respiratory failure improves with BPAP, reduce ventilatory support until the patient can attempt spontaneous breathing.

Summary

  • NPPV can stabilize patients with acute respiratory failure and prevent intubation.
  • Patients who are most likely to benefit are those with acute hypercapnic respiratory failure caused by a COPD exacerbation and those with cardiogenic pulmonary edema in the absence of shock or ischemia.