Airway 5: Noninvasive Ventilatory Support Portal

Non-invasive ventilation (NIV), also called pressure-support ventilation (PSV) or non-invasive positive pressure ventilation (NIPPV), refers to the application of positive pressure ventilatory assistance to an alert, spontaneously breathing patient via a nasal mask or facemask. NIV works by improving lung mechanics and reducing the work of breathing. This technology is in the process of finding its niche between those patients with respiratory problems who don’t need assistance in breathing and those who need to be intubated and supported by mechanical ventilation. NIV’s success is defined as keeping patients from undergoing intubation and ventilation. However, the benefits of not intubating patients (better outcomes, less cost, lower morbidity) are closely tied to this intervention’s major complication: postponing intubation. As with most evolving critical care technologies, certain uses of NIV are controversial. At this point in time, it seems to prevent the need for mechanical ventilation in selected patients.

Not only is current use limited to certain conditions, but NIV is also labor intensive. (Nursing and respiratory staff must closely monitor these patients.) For these reasons, it behooves the provider/organization to conduct an audit of NIV-supported diseases (to derive frequency of use) and its resources before committing to its use.

Terminology

BiPAP: Bi-level Positive Airway Pressure (also a trade name for the machine). This machine gives positive airway pressure throughout the cycle, using differential pressures for the inspiration and expiration phases of the cycle: a higher IPAP and a lower EPAP. The EPAP is considered the equivalent of CPAP.
CPAP: Continuous (and Constant) Positive Airway Pressure. Functionally equivalent to PEEP in the intubated patient.
EPAP: Expiratory Positive Airway Pressure
IPAP: Inspiratory Positive Airway Pressure
PEEP: Positive End Expiratory Pressure
Pressure Support: the difference between IPAP and EPAP
PSV: Pressure Support Ventilation. A somewhat general term for NIV and BiPAP.

NIV Indications

BiPAP may be an effective adjunct for COPD exacerbations,¹ especially in management of patients unresponsive to conventional interventions.
CPAP may be an effective adjunct for patients with cardiogenic pulmonary edema without shock, especially in management of patients unresponsive to conventional interventions.² BiPAP is probably not safe in pulmonary edema as it has been associated with myocardial infarction.

Possible Uses of NIV

Asthma or pneumonia (effective use yet to be proven)
“Do Not Intubate” patients
Neutropenic patients with respiratory failure (high mortality rate with intubation)3
Cystic fibrosis patients
Sleep apneic patients who present in an emergency setting
Prehospital setting (effective use yet to be proven)

NIV Contraindications

Note that in a respiratory distress context, these are either indications to intubate and/or perform other acute interventions:

Shock/hypotension
Pneumothorax
Apneic patient
Life-threatening hypoxemia (PaO₂ < 60% on 100% O₂)
Inability to handle secretions/protect airway
Non-cooperative patient
Altered mental status
Inability to monitor/frequently re-evaluate the patient
Facial fractures
Recent upper GI/airway surgery; open tracheal stoma
Vomiting
Cardiac dysrhythmias/ischemia/AMI are relative contraindications.
BiPAP with pulmonary edema is relatively contraindicated.

NIV Techniques and Equipment

There is a steep learning curve for patients using NIV, the difficulty of which is compounded by their current respiratory distress. Instruction, coaching, and reassurance are critical for compliance. If the patient experiences improvement in the first few minutes, he or she is more likely to tolerate the procedure for a longer period of time.
Always have your airway cart nearby for rescue RSI/intubation.
Keep the NIV equipment in the ED/critical care area: early use (within minutes) has been found to be a critical success factor.⁴
The machines themselves are fairly simple. In addition, CPAP may be run from wall O₂on flush setting, utilizing a special mask with a CPAP valve. Special flow generators are also available. The BiPAP machine may also be used for CPAP.
Full face mask, nasal masks, and nasal plug/pads are effective; several types should be available for patient considerations, such as beards, edentulous patients, mouth breathers, the need to talk, etc. Sometimes a patient who cannot tolerate a full face mask will tolerate a nasal mask or vice-versa. Assure a good seal; small air leakages are acceptable.
CPAP settings: start at 5 cm H₂O and titrate upward incrementally 2 cm at a time to effect: O₂ sats > 90%, patient comfort, respiration rate < 25, exhaled tidal volume > 7 mL/kg. Maximum CPAP 15-20 cm H₂O, see BiPAP below.
BiPAP involves two settings: IPAP and EPAP, with IPAP settings always maintained higher than EPAP settings. Initial settings of 10 cm inspiratory pressure, 5 cm expiratory pressure may be used for patients whose main problem is hypoxia; patients with hypercarbia who need treatment may start with 10 cm of IPAP and 2 cm of EPAP. Titrate incrementally to effect: O₂ sats > 90%, patient comfort, respiration rate < 25, exhaled tidal volume > 7 mL/kg. Pressures may range as high as 24 cm H₂O for IPAP and 20 cm H2O for EPAP, but pressures greater than 15 cm of water may result in gastric distention since the normal esophageal sphincter will only resist pressures up to 15 cm of water. Synchronize BiPAP’s peak flow with patient effort to breathe.
Clinical signs and symptoms, O₂ sats, exhaled tidal volume, and ABGs are modalities to monitor treatment efficacy. PFTs may be monitored in COPD cases.
Sedation is used only with caution with NIV. For those few exceptions, sedation must be used sparingly, and the provider must be sure that reasons to use it (such as anxiety and agitation) are psychological and not related to the underlying disease condition(s). Generally speaking, if sedation is considered, consider RSI/intubation.

NIV Failure and Complications

Failure to improve is the most common complication. Strongly consider intubation.
Worsening conditions/patient deterioration dictates intubation and/or other interventions.
Gastric distention may occur with pressures above the resting upper esophageal sphincter, but is uncommon. Vomiting could lead to aspiration. Monitor the patient for symptoms and distention, and use an NG tube as needed.
Barotrauma—air in the thorax, mediastinum, pericardium, and other spaces—may occur whenever positive pressure is used. Be alert and manage accordingly.

References

Bach PB, Brown C, Gelfand SE, et al. American College of Physicians-American Society of Internal Medicine. American College of Chest Physicians. Management of acute exacerbations of chronic obstructive pulmonary disease: a summary and appraisal of published evidence. Ann Inter Med. 2001;134:600-620.
Pang D, Keenan SP, Cook DJ, et al. The effect of positive pressure airway support on mortality and the need for intubation in acute cardiogenic pulmonary edema. Chest. 1998;114:1185-1192.
Hilbert G, Gruson D, Vargas F, et al. Noninvasive continuous positive airway pressure in neutropenic patients with an acute respiratory failure requiring intensive care unit admission. Crit Care Med. 2000;28:3185-3190.
Calicle T, Sungur M, Ceyhan B, et al. Comparison of noninvasive positive pressure ventilation with standard medical therapy in hypercapnic acute respiratory failure. Chest. 1998;114:1636-1642.