Several considerations can enhance the likelihood of successful noninvasive ventilation (NIV). In addition to these factors, the experience and expertise of front-line health care providers, specifically nursing and respiratory therapy staff, cannot be underestimated. This is not a concern in hospitals where noninvasive ventilation is well established, but it is an important factor in facilities where noninvasive ventilation has been infrequently administered or not used at all. It can be used in the ICU, especially if there is the possibility of intubation. It can be used in a step-down unit (lower severity of illness), as follows:
It can be used in the ward setting (not recommended if intubation is a consideration), as follows:
In its simplest terms, noninvasive ventilation differs from invasive ventilation by the interface between the patient and the ventilator. Invasive ventilatory support is provided via either an endotracheal tube or tracheostomy tube. Noninvasive ventilatory support uses a variety of interfaces, and these have continued to evolve with modifications based on patient comfort and efficacy. Many of the interfaces or masks were initially used in patients with obstructive sleep apnea before they were adapted for use in patients to provide noninvasive ventilatory support. Nasal masks and orofacial masks were the earliest interfaces, with subsequent development and use of full face masks, mouthpieces, nasal pillows, and helmets. Nasal masks and orofacial masks are still the most commonly used interfaces. Orofacial masks are used almost twice as frequently as nasal masks. Both have advantages and disadvantages in the application of noninvasive ventilation. Note the images below.
Proper fitting of the mask or other interface is another key component to successful noninvasive ventilation. The mask or interface may be held in place (without straps applied) by the patient or therapist to familiarize the patient with the mask and ventilator. Typically, the smallest mask providing a proper fit is the most effective. Straps hold the mask in place, with care to minimize excess pressure on the face or nose. Leaks are the bane of all of the interfaces, but excess pressure applied with the straps increases the risk of pressure necrosis and skin breakdown. Straps should be tight enough to prevent leaks, but with enough slack to allow passage of one or two fingers between the face and the straps. The nasal and orofacial masks may be first-line and second-line options, specifically in patients who may have prior familiarity with these interfaces or in those who may have had difficulty with orofacial or nasal masks. Clinical trials have not demonstrated the superiority of any interface, although the nasal mask may be more effective in patients with a lower severity of illness. [4] In patients with a higher severity of illness, the orofacial mask and total face mask appear to result in comparable outcomes. The main considerations regarding the choice of an orofacial mask or nasal mask are outlined below. Orofacial mask general advantages are as follows:
Orofacial mask cautions and disadvantages are as follows:
Nasal mask general advantages are as follows:
Nasal mask cautions and disadvantages are as follows:
While orofacial masks and nasal masks are the most commonly used interfaces, other patient ventilator interfaces through which noninvasive ventilation can be applied include mouthpieces, nasal pillows, total face masks, and even a helmet device, which encompasses the entire head. Experience with helmet devices is limited but increasing, and it has been successful in patients who are unable to tolerate the nasal or orofacial devices. The choice of ventilators available to provide noninvasive ventilatory support has continued to expand. Early noninvasive ventilatory support was applied using either large bedside critical care volume ventilators or smaller volume or pressure specialty ventilators devoted to noninvasive ventilation. While the critical care ventilators had more options, they were also less tolerant of leaks. The specialty ventilators had fewer options and range, but they were more leak tolerant. Many critical care ventilators currently in use also have a noninvasive ventilation option, either as part of the original device or available as an upgrade option. The ideal device is dependent on a number of factors, including familiarity by staff and available options. The differences between the bedside critical care ventilator and specialty noninvasive ventilator continue to diminish as differences related to ventilator options, range of support, and leak tolerance are corrected in both devices. The distinction in function and capability has blurred, and there are devices that are capable of providing both invasive and noninvasive ventilation with a mere switch of ventilator settings. Nevertheless, most hospitals continue to provide noninvasive support with the specialty ventilator. Choosing the initial mode of ventilation is based in part on past experience, in part on the capability of ventilators available to provide support, and in part on the condition being treated. Most patients who are provided noninvasive ventilation are provided support with pressure ventilation, with continuous positive airway pressure (CPAP), which is the most basic level of support. CPAP may be especially useful in patients with congestive heart failure or obstructive sleep apnea. Bilevel positive airway pressure (BiPAP) is probably the most common mode noninvasive positive pressure ventilation and requires provisions for inspiratory positive airway pressure (IPAP) and expiratory positive airway pressure (EPAP). The difference between IPAP and EPAP is a reflection of the amount of pressure support ventilation provided to the patient, and EPAP is synonymous with positive end-expiratory pressure (PEEP). Some noninvasive ventilation is provided using proportional-assist ventilation (PAV), which provides flow and volume assistance with each breath. Clinical trials have not demonstrated a significant difference between PAV and pressure-support ventilation with BiPAP. [5, 6] However, BiPAP is the most commonly available and more frequently used modality for noninvasive ventilation. PAV remains available on many ventilator models, but use is much less common than BiPAP. While volume ventilators can be used to provide noninvasive ventilatory support, the previously described modes are preferred because they provide better patient comfort and synchrony and are more tolerant of the leaks that accompany all noninvasive ventilatory interfaces. Adequate ventilation and oxygenation, correction of respiratory failure, and adequate patient tolerance and comfort are the primary goals of noninvasive ventilation, and adjustments are made to achieve these endpoints. Initial settings focus on achieving adequate tidal volumes, usually in the range of 5-7 mL/kg. Additional support is provided to reduce the respiratory rate to less than 25 breaths/minute. Oxygen is adjusted to achieve adequate oxygenation, with a pulse oximetry goal of greater than 90%. Serial arterial blood gas measurements are essential to monitor the response to therapy and to guide further adjustments in the ventilator. The following provides some guidance on titration of ventilator settings in patients with respiratory distress and who have never been placed on noninvasive ventilation. In those patient who may have chronic noninvasive support, the initial values should be based on prior support levels. The listed levels may be inadequate and would thus increase the likelihood of intolerance or failure. If there is uncertainty, it is important to perform a bedside titration with increasing levels based on patient comfort or exhaled tidal volumes. These adjustments can be made within minutes and can be done without obtaining blood gases. Initial IPAP/EPAP settings are as follows:
Subsequent adjustments based on arterial blood gas values are as follows:
The above considerations and approach to adjustment are best suited for those with COPD or chronic heart failure as the primary cause of their hypercapnia or hypoxemic respiratory distress and failure. Patients with neuromuscular disorders (amyotrophic lateral sclerosis, postpolio syndrome, muscular dystrophy) or thoracic cage disorders (severe kyphoscoliosis) may fare better with other ventilatory modalities. The most current noninvasive ventilators have PC or average AVAPS options. In PC ventilation, both the inspiratory pressure and the inspiratory time are set and fixed. This differs from BiPAP in which the patient controls the inspiratory time. This modality may be useful in the neuromuscular disease patient who does not have the respiratory muscle strength to generate an adequate inspiratory time. Setting an increased inspiratory time may increase the tidal volume provided, but it may also increase patient-ventilator dyssynchrony if the set inspiratory time is longer than the patient's desired inspiratory time. AVAPS is another option in these neuromuscular disease patients and has also been used in those with severe obesity-hypoventilation syndrome. It should be noted that AVAPS is not generally used for those patients with acute respiratory distress and is better suited for management as they recover or have recovered from their acute decompensated state. Although most experience with AVAPS in COPD is with chronic respiratory failure, some investigators have noted favorable outcomes when used in acutely decompensated COPD patients. [7] As with any pressure-cycled mode, the dependent variable is volume and it may vary widely if there is patient dyssynchrony, changes in lung compliance, or changes in resistance that can occur with changes in body position that occurs in the very morbidly obese. [8] A fixed pressure support setting will not compensate for these changes, and, as a result, delivered tidal volume will fall. AVAPS allows a target tidal volume to be identified with a range of pressure support settings that fluctuate to meet the target tidal volume. AVAPS uses an internal algorithm to make changes in the pressure support supplied to achieve the target volume, but these changes are small and occur over minutes (typically 1-2.5 cm water per minute). That is why rapidly changing, acute respiratory conditions are not suited for AVAPS as the ventilator adjustments may not be timely enough to meet the patient's requirements. Typically, the pressure support required to produce the target volume during bedside titration is used to identify the minimal pressure with the set minimal pressure (min P), typically 2-3 cm water lower to allow flexibility for adjustment in the AVAPS mode. The maximal pressure (max P) is typically set in the 20-25 cm water range as higher pressures are not well tolerated. The min P is at least 8 cm water and usually higher. Additional parameters that are part of AVAPS setting are the target tidal volume, respiratory rate, EPAP, and inspiratory time. Importantly, recognize that certain parameters may predict successful noninvasive ventilation or failure of noninvasive ventilation, so that patients are not subjected to continued treatment when optimal treatment requires intubation and mechanical ventilation. This includes changes during a trial of noninvasive ventilation. The changes, in turn, are a reflection of the patient's ability to cooperate with noninvasive ventilation, patient-ventilatory synchrony, and noninvasive ventilation effectiveness. Trials of noninvasive ventilation are usually 1-2 hours in length and are useful to determine if a patient can be treated with noninvasive ventilation. Extended trials without significant improvement are not recommended because this only delays intubation and mechanical ventilation (unless patients are do-not-intubate status). Predictors of success, with a response to a trial of NIV (1-2 h), are as follows:
Predictors of failure are as follows:
Late admission predictors of failure (>48 h after initiation of noninvasive ventilation) are as follows:
Certain patients may benefit from a trial of therapy; however, limiting trials is important to avoid delays in definitive therapy. Trials may be as short as a few minutes, in patients with immediate failure, and probably should not exceed 2 hours if patients fail to improve. Objective criteria for discontinuation are important to limit trials in patients in whom noninvasive ventilation ultimately fails. This specifically refers to intubation criteria, which carry a subjective element but have been defined in the literature in investigational studies. All these criteria are subject to some degree of interpretation in the context of the patient's clinical status. Importantly, recognize the following as guidelines to assist with the decision to intubate a patient. Most patients who meet these criteria are candidates for intubation, but a few may be able to be managed with continued noninvasive ventilation. Although the focus has been on noninvasive ventilation (NIV), there has been increasing use of high-flow nasal cannula (HFNC) oxygen in clinical situations where NIV had previously been used. This also warrants objective measures that may identify patients in whom HFNC oxygen support fails and who require intubation. This is important, as delayed intubation of patients with progressive hypoxemic respiratory failure has been associated with increased mortality. This led to the identification of the ROX index, defined as the ratio of pulse oximetry oxygen saturation and fraction of inspired oxygen to respiratory rate [(SpO2/FIO2)/RR]. In an inception and validation cohort of patients with pneumonia and on HFNC oxygen, values of the ROX index greater than 4.88 measured at 2, 6, and 12 hours, 18 and 24 hours after initiation of HFNC were found to identify those patients who would not need intubation. [9] Lower ROX index scores not only identified those requiring intubation, but was also associated with poor outcomes, specifically mortality. The authors identified the hours between the 12th and 24th hours as the most vulnerable in their cohort, with an increased risk of failure in those with ROX index scores lower than 3.85. Major criteria (any one of the following) are as follows [10, 11] :
Minor criteria (two of the following) are as follows:
Any one of the following [12] :
Two or more of the following in the context of respiratory distress:
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When there are two rescuers to dedicate to the airway the most appropriate device to use on a Nonbreathing patient would be?
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