Common misconceptions and mistakes
- •
Believing that somnolence makes a trial of bilevel positive pressure ventilation (BiPAP) unsafe
- •
Believing that any hemoptysis, regardless of the volume or context, makes a trial of BiPAP unsafe
- •
Starting BiPAP for respiratory failure using inadequate pressure settings (ie, 12/4)
- •
Ordering BiPAP like a nebulizer treatment (ie, not being at the bedside when initiating BiPAP for respiratory failure)
- •
Sedating a patient for anxiety/agitation related respiratory failure while using BiPAP
Noninvasive ventilatory support
- •
Patients in need of ventilatory assistance can be managed either noninvasively with positive pressure applied to the nose and mouth via face mask, or invasively with positive pressure applied directly to the lungs via an endotracheal tube (gold standard)
- •
Most arousable patients in need of ventilatory support, or improved oxygenation despite 100% Fi o 2 , deserve a trial of noninvasive BiPAP before intubation, assuming:
- •
They have the ability to wear a mask (ie, no preclusive facial or scalp wounds) and
- •
Do not require continual oral clearance (ie, emesis, copious pulmonary secretions, massive hemoptysis)
- •
- •
BiPAP:
- •
Allows for differential setting of inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP), a.k.a. positive end expiratory pressure (PEEP)
- •
The driving pressure for ventilation comes from the difference between the IPAP and the EPAP
- •
Minimum driving pressure (IPAP − EPAP) appropriate for acute respiratory failure = 10 cm H 2 O
- •
Isolated increases in IPAP will increase driving pressure and may further decrease the work of breathing
- •
- •
Minimum EPAP (PEEP) = 5 cm H 2 O (physiologic)
- •
Increasing EPAP (a.k.a. PEEP) may provide additional support in two settings:
- •
Patients with obstructive lung disease, suffering dynamic hyperinflation (ie, breath stacking) and significant intrinsic PEEP (a.k.a. auto-PEEP), typically “tripoding” on the edge of the with and pursed-lip breathing
- •
Increasing EPAP can match intrinsic PEEP, making the initiation of inhalation easier, decreasing the work of breathing
- •
- •
Patients with cardiogenic pulmonary edema and hypoxemia
- •
Increasing EPAP can redistribute fluid in the alveolar space and improve oxygenation
- •
- •
- •
A high EPAP is uncomfortable for patients
- •
EPAP should be increased slowly (increments of 2 cm H 2 O) to avoid precipitating intolerance
- •
Feedback regarding comfort must be solicited
- •
Successfully matching intrinsic PEEP should provide the patient instantaneous improvement
- •
- •
- •
- •
- •
Initiation of bilevel positive airway pressure ( Fig. 20.1 )
- •
Respiratory failure represents an unstable situation requiring immediate action to avoid respiratory arrest
- •
The definitive therapy for respiratory failure is invasive endotracheal intubation and mechanical ventilation
- •
In the absence of contraindications, use of BiPAP to prevent intubation is appropriate, but requires care and vigilance to ensure that respiratory arrest does not ensue if BiPAP fails (or is not tolerated)
- •
Initiation of BiPAP for acute respiratory failure requires a physician to be at the bedside to ensure initial tolerance and efficacy
- •
Intolerance of the mask and/or sudden worsening of respiratory status should prompt immediate rapid sequence intubation (RSI)
- •
- •
BiPAP has its greatest efficacy in assisting ventilation (unloading the diaphragm and decreasing the work of breathing), but it may also improve oxygenation in hypoxemic respiratory failure, by increasing mean airway pressure, which:
- •
Facilitates recruitment
- •
Redistributes fluid to the edge of the alveolus
- •
Decreases preload (helpful in cardiogenic edema)
- •
- •
The contraindications to BiPAP are:
- •
Obtundation (unarousable)
- •
BiPAP requires that a patient have sufficient oral-pharyngeal reflexes to clear oral secretions and protect their airway from aspiration (generally absent in the obtunded)
- •
- •
Facial or scalp wounds (eg, surgical flap) precluding the use of a mask and securing straps
- •
The need for continual oral clearance (not possible with a mask strapped to your face), as seen with:
- •
Copious respiratory secretions (phlegm)
- •
Ongoing emesis
- •
Massive hemoptysis
- •
- •
