Noninvasive positive-pressure ventilation (NIPPV) provides positive-pressure airway support through a face or nasal mask without the use of an endotracheal tube or other airway device. NIPPV is an initial noninvasive airway management strategy. In adults, NIPPV includes continuous positive airway pressure (CPAP) and bilevel positive airway pressure (BiPAP).
NIPPV helps to augment spontaneous respirations. Ideal patients for NIPPV are cooperative, have protective airway reflexes, and have intact ventilatory efforts. NIPPV is not appropriate in patients who have absent or agonal respiratory effort, impaired or absent gag reflex, altered mental status, severe maxillofacial trauma, potential basilar skull fracture, life-threatening epistaxis, or bullous lung disease. Use NIPPV with caution in hypotensive patients because any volume depletion can be worsened from the positive pressure, triggering more hypotension (Table 5).
NIPPV reduces work of breathing through multiple mechanisms.7,8 NIPPV improves pulmonary compliance and recruits and stabilizes collapsed alveoli, improving alveoli aeration and ventilation-perfusion mismatches.1 NIPPV increases both intrathoracic and hydrostatic pressure, shifting pulmonary edema into the vasculature. Increased intrathoracic pressure can also decrease venous return, transmural pressure, and afterload, leading to improved cardiac function. NIPPV also increases tidal volume and minute ventilation, leading to increased PaO2 and reduction in PaCO2. NIPPV reduces work of breathing by 60% and dyspnea scores by 29% to 67%, while improving inspiratory muscle endurance by 14% to 95% over spontaneous respirations.1 The ability of NIPPV to improve pulmonary function such as forced expiratory volume and forced vital capacity is unclear.9-11
CPAP delivers a constant positive pressure throughout the respiratory cycle. BiPAP provides different levels of positive airway pressure during inspiration (inspiratory positive airway pressure [IPAP]) and expiration (expiratory positive airway pressure [EPAP]). Although the terms EPAP and positive end-expiratory pressure are often used interchangeably, positive end-expiratory pressure is specific to the end of the respiratory cycle whereas EPAP refers to the pressure administered via the BiPAP machine during the entire expiratory phase. Both CPAP and BiPAP can be used in a variety of patient populations with limited data directly comparing the two methods.
Be aware that different NIPPV devices exist with differing operating mechanisms. Many standard ventilators can provide NIPPV, although in these devices, the inspiratory and expiratory pressures are additive. For example, if the IPAP is set at 5 cm H2O and the IPAP is set at 15 cm H2O, the total delivered IPAP may be 20 cm H2O (5 + 15). There are standalone NIPPV units that can provide both CPAP and BiPAP, allowing for independent setting of inspiratory and expiratory pressures. For example, if the IPAP is set at 5 cm H2O and the IPAP is set at 15 cm H2O, the total delivered IPAP will be 15 cm H2O. Specialized adapters that connect directly to oxygen tanks and wall-mounted oxygen units may provide CPAP for a brief period of time. These devices have a limited range of settings and should be used on a temporary basis.
Initiating and Titrating NIPPV
Select the mask for NIPPV to create a tight seal while preserving patient comfort. Base the initial settings on the patient's condition and type of respiratory failure. Typical starting settings for CPAP are 5 to 15 cm H2O. Typical starting setting for BiPAP include "spontaneous" mode with IPAP set to 8 to 10 cm H2O and EPAP set to 3 to 5 cm H2O. Be cautious when using NIPPV at pressures >15 cm H2O because this may increase the intrathoracic pressure, leading to barotrauma along with decreased venous return, decreased preload and afterload, and eventually decreased cardiac output.
NIPPV requires frequent assessment for work of breathing, heart rate, respiratory rate, oxygen saturation, and blood pressure. Arterial blood gas analysis can aid in titrating NIPPV but is not mandatory. EPAP can help open and stabilize collapsed alveoli and reverse hypoxemia. In patients in whom ventilation is an issue, adjust the IPAP settings to help decrease the work of breathing and improve ventilation.
If the patient is not tolerating NIPPV, the first potential cause is an air leak. NIPPV is a flow-limited, pressure support system, and therefore, leaks prevent the machine from reaching the preprogrammed flow rate for a set pressure. As a result, the inspiratory time may be prolonged, making each breath cycle less comfortable for the patient. Potential solutions for air leaks include programming the machine to limit the inspiratory time or selecting alternative modes of ventilation including proportional assist ventilation.1 Proportional assist ventilation is a form of synchronized ventilatory support where the NIPPV machine generates pressure in proportion to the patient's instantaneous effort such that as the patient generates a greater inspiratory effort, the machine generates greater IPAP. This allows the machine to adjust to air leaks that may impair ventilation and oxygenation with other modes (CPAP and BiPAP). Although proportional assist ventilation has not been shown to improve clinical outcomes, it is better tolerated by some patients.12
If the patient is not improving with NIPPV, consider endotracheal intubation and ventilation.
The most common use of NIPPV is for cardiogenic pulmonary edema where NIPPV may reduce rates of endotracheal intubation, hospital length of stay, and mortality.13-20 In patients with chronic obstructive pulmonary disease, NIPPV is helpful in those with respiratory acidosis.21 NIPPV may similarly benefit patients with moderate to severe asthma exacerbations, although data on effectiveness are limited.22 Because of the bronchospastic nature of chronic obstructive pulmonary disease and asthma, be vigilant for air trapping and subsequent barotrauma when using NIPPV.
NIPPV may reduce the rate of intubation and in-hospital death in patients with pneumonia.23-25 Exercise caution in this patient group because hypovolemia may coexist, with resultant NIPPV-induced hypotension.
There are reports of NIPPV use in blunt chest wall trauma, including flail chest, although it does not yet clearly decrease mortality or hospital length of stay.26-28 NIPPV is also reported in burn patients. Do not use NIPPV in patients with suspected or confirmed high esophageal or tracheal injuries, maxillofacial or basilar skull fractures, or severe facial burns.29,30
Prehospital NIPPV in patients with cardiogenic pulmonary edema and chronic obstructive pulmonary disease decreases the rate of subsequent intubation and mortality.31-34 When such patients arrive in the ED, assess the response to NIPPV and determine whether to discontinue NIPPV, adjust the NIPPV settings, or change to invasive airway strategies.
Complications of NIPPV include difficulty with mask seal, patient discomfort, aspiration (rare), air trapping, pulmonary barotrauma including pneumothorax, and increased intrathoracic pressure leading to decreased cardiac output and hypotension. Monitor patients carefully to determine NIPPV effectiveness and to identify the need to further secure the airway with intubation. Aspiration risk can be minimized by proper patient selection35; make sure patients have a gag reflex and do not have altered mental status. Gastric distension and increased intragastric pressure can lead to abdominal compartment syndrome, resulting in oliguria, hypoxia, hypercarbia, high peak inspiratory pressures, and even renal failure. A nasogastric tube can decompress the stomach and relieve this syndrome.36 Although complications are uncommon, evaluate patients frequently to identify any of these complications early.
Occasionally, patients develop anxiety and agitation during NIPPV treatment due to the claustrophobic feeling of the mask or the discomfort of positive-pressure ventilation. Anxiety and agitation can increase the work of breathing and result in NIPPV asynchrony. Although often relieved with encouragement, verbal support, or hand restraints, anxiety and agitation may require the administration of sedatives or anxiolytics. There are no systematic studies of sedation during NIPPV, and sedation practices are typically based on physician preference.35,37 Avoid agents or doses that cause excess sedation or respiratory depression. Dexmedetomidine, a centrally acting α2 agent, can provide sedation without decreasing respiratory drive, but its expense and availability limit general use.38 Benzodiazepines and opiates are commonly used but can be difficult to titrate and may cause respiratory depression.35,37,38 Haloperidol in low doses may accomplish anxiolysis with less respiratory depression than opiates or benzodiazepines.37