Mechanical Ventilation Part II: Non-invasive Mechanical Ventilation for the Adult Hospitalized Patient
Samy S. Sidhom
Nicholas Hill
Introduction
Noninvasive ventilation (NIV) is the provision of mechanical ventilation without the need for an invasive artificial airway. NIV can be subdivided into a number of modalities with different mechanisms of action, including negative pressure ventilation that assists lung expansion by applying an intermittent negative pressure over the chest and abdomen, positive pressure ventilation that applies continuous or intermittent positive pressure to the upper airway, and abdominal displacement ventilators like pneumobelts and rocking beds that assist ventilation at least partly via the force of gravity on the abdominal contents [1,2,3]. Over the past two decades, noninvasive positive
pressure ventilation (NPPV) [4] via the nose, mouth, or combination has become the predominant mode of NIV in both the outpatient and hospital settings.
pressure ventilation (NPPV) [4] via the nose, mouth, or combination has become the predominant mode of NIV in both the outpatient and hospital settings.
In this chapter, we focus on acute applications, comparing and contrasting noninvasive and invasive approaches and describing epidemiologic trends of NIV. Next, we describe the equipment used for NPPV and discuss indications and selection of patients for NPPV in the acute care setting. We then make recommendation regarding the practical and safe application of NPPV, including selecting the proper location, appropriate monitoring, and avoiding complications. Finally, we consider the impact on global patient outcomes as well as health care and hospital quality measures.
Terminology
As used in this chapter, NIV is a generic term for a number of different noninvasive approaches to assisting ventilation, whereas NPPV refers specifically to the form that facilitates ventilation by applying a positive pressure to the upper airway. This can be continuous positive airway pressure (CPAP) that can be used to successfully treat certain forms of respiratory failure or intermittent, combining a positive end-expiratory pressure (PEEP) with pressure support (PS), the latter used to actively assist inspiration. Some ventilators are derived from portable positive pressure devices to treat sleep apnea and are commonly referred to as bilevel positive airway pressure (BPAP) devices. With these, the term expiratory positive airway pressure (EPAP) is used rather than PEEP and inspiratory positive airway pressure (IPAP) refers to the total inspiratory pressure. Thus, the difference between IPAP and EPAP equals the level of pressure support.
Why Noninvasive Mechanical Ventilation
NIV has seen increasing popularity in acute care settings throughout Europe and the United States over the past two decades [5,6]. This trend is related to a number of advantages of NPPV over invasive mechanical ventilation, but only in select patients. By averting invasion of the upper airway, NIV avoids a number of well-known complications of intubation, including aspiration of gastric contents, dental trauma, trauma to the hypopharynx, larynx, and trachea including tracheal rupture [7], hypoglossal nerve paralysis, autonomic stimulation leading to arrhythmias, and hypotension [8].
Ongoing use of invasive ventilation increases the risk of ventilator-associated pneumonia (VAP) related to disruption of airway protective mechanisms, pooling of secretions above the tube cuff that leak into the lower airways, and formation of a bacterial biofilm within the tube that is distributed peripherally with suctioning. In addition, irritation from the tube stimulates mucus secretion and interferes with normal ciliary function. The need for repeated suctioning further traumatizes the airway and promotes bleeding and mucus secretion. Following extubation, immediate complications include upper airway obstruction due to glottic swelling, negative pressure pulmonary edema, tracheal hemorrhage, and laryngospasm [9,10]. Complications of prolonged invasive ventilation (in association with tracheostomy) include a spectrum of repeated airway and parenchymal infections, vocal cord dysfunction, and tracheal stenosis and malacia [4,11,12,13,14].
In addition, NPPV is usually better tolerated than invasive ventilation, requiring less or no sedation. It usually permits short breaks that help to enhance tolerance. The avoidance of intubation-associated complications and sedation promotes more rapid weaning compared to invasive ventilation, shortening ICU stays and potentially reducing resource utilization and costs.
On the other hand, NPPV should not be considered as a replacement for invasive mechanical ventilation. When used appropriately, NPPV serves as a way to avoid intubation and its attendant complications, but it must be used selectively, avoiding patients who have contraindications (see “Selection Guidelines for NPPV in Acute Respiratory Failure” section). Appropriate candidates must be able to protect their airways and cooperate. Sometimes, NPPV is initiated in inappropriate or marginal candidates who fail to respond favorably. In this situation, it is important to intubate promptly, avoiding delays that can lead to cardiopulmonary arrest, necessitating emergency intubation and increased morbidity and mortality [15].
Utilization and Epidemiology
Rates of NPPV utilization in acute care settings are increasing in Europe and North America [16,17]. An observational study of NIV utilization for chronic obstructive pulmonary disease (COPD) and cardiogenic pulmonary edema (CPE) patients in acute respiratory failure (ARF) in a single 26-bed French intensive care unit (ICU) revealed an increase from 20% of ventilator starts in 1994 to nearly 90% in 2001 [17]. In association with this increase, the occurrence of healthcare-acquired pneumonias and ICU mortality fell from 20% and 21% to 8% and 7%, respectively. The authors speculated that increasing experience and skill with NPPV in their units contributed to the improved outcomes. In an Italian study examining outcomes of NPPV in two different time periods during the 1990s, success rates remained steady despite an increase in acuity of illness scores, suggesting sicker patients in the later time period were being managed as successfully as less ill patients in the earlier period, a trend the authors attributed to increased skill of the caregivers [16].
Sequential surveys of European (mainly French) ICUs demonstrated an increase in the use of NIV as a percentage of total ventilator starts from 16% to 23% in 1997 and 2002, respectively, with utilization in patients with COPD and CPE increasing from 50% to 66% and from 38% to 47%, respectively [6]. Esteban et al. conducted a worldwide survey in more than 20 countries that compared the trends of mechanical ventilation use and demographics between 1998 and 2004, enrolling more than 1,600 patients and showing an overall increase of about 6% (11.1% from 4.4%) in NIV use [15]. In Italy, Confalonieri et al. reported high utilization rates of NIV in specialized respiratory intensive care units (RICUs) which are similar to “intermediate” or “step-down” units in the United States, where a large proportion of patients have COPD either as an etiology of ARF or as a comorbidity. In that setting, 425 out of 586 (72.5%) patients requiring mechanical ventilation were treated initially with NIV (374 using NPPV and 51 using an “iron lung”) [18].
However, in a 2003 national audit of COPD exacerbations in the United Kingdom, NIV was unavailable in 19 of 233 hospitals and 39% of ICUs, 36% of “high-dependency units,” and 34% of hospital wards [19]. Similar results were seen in a North American survey of NIV use in 71 hospitals in Massachusetts and Rhode Island [20]. Overall use of NPPV was estimated to be 20% of all ventilator starts, but 30% of hospitals had estimated rates < 15%. Reasons for low utilization were mostly attributed to lack of physician knowledge of NPPV, inadequate equipment, and lack of staff training. Most disturbingly, estimated use of NIV for COPD exacerbations and CPE was only 29% and 39% of ventilator starts, respectively
[20]. A follow-up study in Massachusetts using data collected prospectively from 2005 to 2007 revealed an overall 38.7% NIV utilization rate, with 80% and 69% of COPD and CPE patients, respectively, receiving NIV as the initial mode [21].
[20]. A follow-up study in Massachusetts using data collected prospectively from 2005 to 2007 revealed an overall 38.7% NIV utilization rate, with 80% and 69% of COPD and CPE patients, respectively, receiving NIV as the initial mode [21].
A national survey of U.S. Department of Veterans Affairs hospitals showed that despite wide availability of NIV, its perceived use was low. Almost two-thirds of respiratory therapists responding to the survey felt that NIV was used less than half the time when it was indicated. The survey also revealed wide variations in the perception of NIV use depending on the size of the ICUs, larger ones reporting more frequent use [22]. Along these lines, a Canadian study reported that between 1998 and 2003, only 66% of patients meeting criteria for NPPV actually received it [23].
Suboptimal utilization has been reported in non-Western countries as well. A Korean survey reported that NIV was used in just 2 of 24 university hospitals and comprised only 4% of ventilator starts. A majority of the physician staff (62%) and 42% of the nurses expressed a desire for additional educational programs on NIV [24]. In an Indian survey of 648 physicians, perceived NIV use was mostly limited to the ICU (68.4%) while COPD was the most common indication for its use [25]. Findings of this survey were similar to those of the Korean, European, and North American surveys in that rates of NIV use varied widely between centers, with a substantial portion reporting low rates. These findings underline the need for NIV educational programs at individual hospitals that permit caregivers to develop the requisite expertise in administering NIV.
Indications for Acute Applications of NPPV
Indications for NPPV depend on the etiology of ARF and specific settings in which ARF occurs [i.e., do-not-intubate (DNI) patients]. As much as possible, our analysis is based on available evidence. We recommend application of NPPV for those diagnoses that are those supported by multiple randomized trials. We consider NPPV as an “option” when the application is supported by a single randomized trial, multiple historically controlled or cohort series, or sometimes conflicting evidence. Successful application of NPPV has been reported for all of these indications if applied in appropriately selected and monitored patients (Table 59.1).
Recommended Indications
Chronic Obstructive Pulmonary Disease
COPD Exacerbations
The best established acute indication for NPPV is to treat ARF due to COPD exacerbations. This is supported by a strong physiologic rationale. Studies demonstrate that the combinations of extrinsic PEEP and PS alone reduce diaphragmatic work of breathing more than either modality alone, because the expiratory pressure counterbalances intrinsic PEEP and the higher inspiratory pressure (pressure support) actively assists the inspiratory muscles [26]. In the setting of COPD exacerbations, NPPV thereby serves as a “crutch” to assist ventilation while medical therapy is given time to work.
Multiple randomized controlled trials (RCTs) and meta-analyses on COPD patients with ARF have established that NIV more rapidly reduces respiratory rate, improves dyspnea and gas exchange, reduces intubations from an average rate of 50% to 20%, and lowers mortality compared to standard therapy [5,27,28,29,30,31,32]. This evidence justifies the early use of NPPV for COPD exacerbations as a standard of care unless there are contraindications. COPD exacerbations also respond well to NPPV when complicated by pneumonia [33] or occurring in the setting of a DNI status [34,35,36], or postoperative or postextubation respiratory failure [37,38].
Table 59.1 Indications for Noninvasive Positive Pressure Ventilation As Determined By Strength of Evidence | ||
|---|---|---|
|
Facilitation of Weaning in COPD Patients
Some patients with COPD exacerbations require intubation because they are not candidates for NPPV initially or fail a trial of NPPV. Multiple controlled trials have demonstrated that NIV permits earlier extubation in such patients, even if they have failed multiple “T” piece weaning trials [39,40,41]. Early extubation to NIV increases eventual weaning rates, shortens the duration of ventilator use and hospital length of stay (LOS), reduces the occurrence of nosocomial pneumonia, and reduces mortality. This approach should be considered whenever intubated COPD patients are failing spontaneous breathing trials, but it should be used with caution—only in a patient who is otherwise an excellent candidate for NIV, can breathe without any assistance for at least 5 minutes, can tolerate levels of pressure support deliverable
by mask (i.e., inspiratory pressure < 20 cm H2O), and is not a “difficult intubation.”
by mask (i.e., inspiratory pressure < 20 cm H2O), and is not a “difficult intubation.”
Cardiogenic Pulmonary Edema
Positive airway pressure has well-known therapeutic effects in patients with acute pulmonary edema. The increased functional residual capacity opens collapsed alveoli and rapidly improves compliance and oxygenation. The increased intrathoracic pressure reduces transmyocardial pressure and has preload and afterload reducing effects, thus enhancing cardiac function in patients with left ventricular dysfunction who are afterload-dependent.
Multiple RCTs have demonstrated that noninvasive CPAP (10 to 12.5 cm H2O) alone dramatically improves dyspnea and oxygenation and lowers intubation rates in patients with acute pulmonary edema compared with standard O2 therapy [17,42,43]. Subsequent studies evaluating the efficacy of NPPV (i.e., pressure support plus PEEP or BPAP) either compared with O2 therapy or CPAP alone [44,45,46] have shown benefits similar to those previously demonstrated for CPAP. In one large RCT [47], CPAP and NPPV performed similarly, both improving dyspnea scores and pH more rapidly than oxygen alone, but neither lowered intubation nor mortality rate (the major outcome variable) compared to controls. However, the intubation rate in this study was slightly below 3% in all of the groups, including controls, suggesting that the enrolled patients were too mildly ill to manifest a significant mortality benefit.
Meta-analyses of the RCTs on CPAP or NPPV compared with O2 therapy alone have confirmed the benefits described above, even showing a significant reduction in mortality with CPAP [48,49]. Meta-analyses comparing the two modalities show equivalency of NPPV and CPAP with regard to reduction of intubation, lengths of stay, and mortality, and with no increase in the myocardial infarction rate attributable to NPPV use [50]. However, some studies have found that NPPV reduces dyspnea and improves gas exchange more rapidly than CPAP alone [44,51]. Therefore, by virtue of its greater simplicity and potentially lower cost, CPAP alone is generally regarded as the initial noninvasive modality of choice for cardiogenic edema patients, but NPPV is substituted if patients treated initially with CPAP remain dyspneic or hypercapnic. The strong evidence favoring the use of CPAP or NPPV to treat CPE establishes either one as standard therapy for initial ventilatory assistance of appropriately selected CPE patients.
The success of noninvasive positive pressure to treat CPE has encouraged its extension into the prehospital setting. An emerging trend is to provide CPAP devices on ambulances for initial therapy of CPE. The experience thus far with this practice has been favorable. Plaisance et al. [52] observed a strong trend for reduced intubation and mortality rates among 124 CPE patients randomized to “early” (started immediately on site) versus “late” (delayed by 15 minutes) CPAP (7.5 cm H2O). In another RCT, Thompson et al. observed an absolute reduction of 30% in intubation rate (17 out of 34 patients, or 50% vs. 7/35 or 20%, unadjusted OR = 0.25 and CI = 0.09 to 0.73) and 21% in mortality (OR 0.3; 95% CI 0.09 to 0.99) among CPE patients treated with CPAP compared to usual therapy with oxygen, including intubation and bag-valve-mask-ventilation if needed [53].
A pilot study by Duchateau et al. reported an improved respiratory status in 12 “do not intubate” (DNI) patients when offered NPPV out-of-hospital by emergency medical services (EMS) Respiratory rate decreased from 34 to 27 per minute, p = 0.009, and pulse oximetry improved from 86% to 94%, p < 0.01, with only one intolerant patient [54]. These studies suggest that outcomes of CPE patients can be improved by very early initiation of noninvasive positive pressure therapy in the field and adoption of this as a routine practice for EMS seems likely.
Immunodeficient Patients with Acute Respiratory Failure
Patients developing ARF with underlying immunodeficiency states such as human immunodeficiency virus and Pneumocystis pneumonia or following solid organ or bone marrow transplantation have poor outcomes when treated with invasive mechanical ventilation [55]. Nosocomial infections and fatal septicemia are common complications, and those with hematologic malignancies may encounter fatal airway hemorrhages due to upper airway trauma occurring with intubation in patients with thrombocytopenia and platelet dysfunction. NIV offers a way to avoid such complications and improve outcomes.
Randomized trials of NIV in patients with ARF who have undergone solid organ transplantation or bone marrow transplant for hematologic malignancy have demonstrated reduced intubation and mortality rates compared with controls [56,57,58,59]. NIV was begun in these patients before respiratory failure became severe, and even then the mortality rate in the NIV group in one study was 50% compared with 80% in the conventionally treated group [58]. Thus, NIV should be considered early during the development of respiratory failure in immunodeficient patients as a way to avoid intubation and its attendant morbidity and mortality [57].
Weaker Indications—Nppv Is an Option
NPPV can be used to treat ARF of other etiologies and in other settings, but the evidence to support these applications is weaker and use is optional but not necessarily recommended (Table 59.1).
Other Obstructive Diseases
Asthma Exacerbations
Retrospective cohort studies suggest that NPPV improves gas exchange and avoids intubation in patients with respiratory failure caused by asthma exacerbations [60,61]. However, there are only two randomized trials supporting the use of NPPV for this indication. In one RCT, NPPV improved FEV1 more rapidly and reduced the hospitalization rate compared with sham controls [62]. The second study [63] reported similar findings with “high” inflation pressures compared to lower pressures (IPAP and EPAP 8 and 6 cm H2O and 6 and 4 cm H2O, respectively—all lower than most other studies) or standard medical therapy. Neither study was powered to examine intubation rates or mortality.
Pollack et al. demonstrated that NPPV is an acceptable way to deliver bronchodilator aerosol, showing a greater improvement in peak expiratory flow 1 hour after administration via a “bilevel” device than a standard nebulizer [64]. These studies suggest that when NPPV is used as an early treatment for asthma exacerbations, it can potentiate the bronchodilator effect of beta-agonists. However, in most clinical situations, NPPV is reserved for patients with “status asthmaticus,” that is, those with severe airway obstruction who are not responding adequately to initial bronchodilator therapy, an application that is not yet supported by RCTs.
Cystic Fibrosis
Ideally, NPPV is initiated in patients with cystic fibrosis when they develop chronic respiratory failure before an acute crisis arises. For patients with acute exacerbations of cystic fibrosis, NPPV has been used mainly as a bridge to transplantation [65].
These patients may remain severely hypercapnic and require aggressive management of secretion retention, but NPPV permits avoidance of intubation and can sustain them for months while they await availability of donor organs.
These patients may remain severely hypercapnic and require aggressive management of secretion retention, but NPPV permits avoidance of intubation and can sustain them for months while they await availability of donor organs.
Hypoxemic Respiratory Failure
Hypoxemic respiratory failure consists of severe hypoxemia (PaO2/FIO2 < 200), severe respiratory distress, tachypnea (> 30 per minute), and a non-COPD cause of ARF such as ARDS, acute pneumonia, trauma, or acute pulmonary edema [66]. Some RCTs on hypoxemic respiratory failure have observed reductions in the need for intubation, shortened ICU lengths of stay, and even mortality in the NIV group as opposed to controls [66,67], but it is difficult to draw firm conclusions about individual diagnostic groups within this very broad category. One concern is that favorable responses in one subgroup, such as those with CPE, could obscure unfavorable responses in another, such as ARDS or pneumonia patients.
Among studies examining subcategories specifically, Jolliet et al. found very high NPPV failure rates (> 60%) in a cohort series of patients with severe community-acquired pneumonia [68]. Confalonieri et al. [33] found that NPPV reduced the need for intubation, shortened ICU LOS, and improved 90-day mortality in a RCT of patients with severe community-acquired pneumonia. However, these benefits were seen only in the COPD subgroup—not in non-COPD patients. Thus, no convincing evidence supports the use of NPPV over invasive ventilation in patients with severe community-acquired pneumonia lacking COPD, and although NPPV remains an option in such patients, it should be used only in carefully selected and monitored patients, with preparedness to intubate promptly if they are not responding well within an hour of NPPV initiation.
The situation with ARDS (which overlaps with severe community-acquired pneumonia) is quite similar, but no RCTs have been performed on the use of NPPV for ARDS per se. Small case series have suggested benefit [69], and in one interesting study that used NPPV as a “first-line” therapy for ARDS, the successful use of NPPV was associated with much lower ventilator-associated pneumonia and mortality rates than in NPPV failures [70]. The authors suggested that an initial simplified acute physiology score (SAPS) II of 34 or less and an improvement of PaO2/FIO2 to greater than 176 during the first hour of NPPV therapy could be used to identify patients likely to succeed. However, it is good to remember that this was not an RCT and that only 15% of the patients with ARDS admitted to the ICU (two thirds were intubated prior to ICU admission) actually succeeded with NPPV. Also, in a previous study on risk factors for NPPV failure in patients with hypoxemic respiratory failure, Antonelli et al. observed an odds ratio of 3.75 for ARDS and severe pneumonia [71]. Thus, as with severe pneumonia, NPPV should be used very selectively and cautiously in ARDS patients—only for those with lower acute physiology scores, hemodynamic stability, and good initial improvements in their oxygenation.
Posttrauma Respiratory Failure
Flail chest or mild acute lung injury (ALI) are conditions that are posited to respond favorably to NPPV after traumatic chest wall injuries. Support for this view comes from retrospective studies such as that by Beltrame et al. [72], in which 46 trauma patients with respiratory insufficiency were treated with NPPV and experienced rapid improvements in gas exchange and a 72% success rate, but burn patients responded poorly. More recently, a study that randomized thoracic trauma patients with PAO2/FIO2 < 200 to NPPV or high flow oxygen was stopped early after enrollment of 50 patients because of significant reductions in intubation rate (12% vs. 40%) and hospital LOS (14 vs. 21 days) in the NPPV group [73]. These results support the use of NPPV for hypoxemic respiratory failure in postthoracic trauma cases, but it is good to remember that these were carefully selected patients.
Extubation Failure
The recurrence of respiratory failure after extubation of patients initially intubated for a bout of ARF is referred to as extubation failure and is associated with a high risk of morbidity and mortality (rates exceeding 40% in some studies [74,75]). NPPV has been proposed as a way to avoid extubation failure if begun early in patients at risk for extubation failure, reducing the need for reintubation and improving outcomes. However, some earlier randomized studies [76] comparing NPPV to standard O2 therapy found no reduction in reintubation attributable to NPPV. In fact, Esteban et al. even found a significantly increased ICU mortality in the NIV group [77]. These studies were limited by low enrollment of COPD patients (only about 10% of patients), and the increased mortality was thought to be related to a 10-hour delay in reintubations in the NIV group compared with controls.
Two subsequent randomized trials [78,79] on patients deemed to be at “high risk” for extubation failure found that NIV reduced the need for reintubation and ICU mortality. Forty to fifty percent of patients in these trials had COPD or CHF and in one of the trials [78], most of the benefit was attributable to the COPD subgroup. Another recent trial focusing on patients with postextubation hypercapnia showed a significant reduction in the occurrence of postextubation respiratory failure as well as 90-day mortality in the group randomized to NPPV compared to oxygen-treated controls [80]. These studies support the use of NIV in patients at high risk of extubation failure, particularly if they have COPD, CHF, and/or hypercapnia. However, based on the Esteban study, NPPV to prevent extubation failure should be used very cautiously in at-risk patients who do not have these favorable characteristics because of the higher risk of NPPV failure and its attendant morbidity and mortality. Patients failing to improve promptly with NPPV should be reintubated without delay.
Postoperative Respiratory Failure/Insufficiency
Noninvasive positive pressure techniques, both CPAP and NPPV, have been used in postoperative patients in either of two ways: to prevent complications after high-risk surgeries or to treat frank postoperative respiratory failure. When used prophylactically after major abdominal surgery [81,82,83] or thoracoabdominal aneurysm repair [84], CPAP (10 cm H2O) reduces the incidence of hypoxemia, pneumonia, atelectasis, and intubations compared with standard treatment. In the only randomized study of NPPV in patients with postoperative respiratory failure, post–lung resection patients had reduced intubation and mortality rates if treated with NPPV compared with standard management [85]. These studies strongly support the idea that both CPAP and NPPV should be considered to prevent and treat postoperative respiratory complications and failure, but because of the variety of surgeries and positive pressure techniques evaluated, more specific recommendations cannot be made.
Patients with a Do Not Intubate Status
NIV to treat DNI and palliative care patients has been controversial. Some argue that when patients are dying of respiratory failure, there is little to lose by trying NIV. Contrariwise, others counter that this is apt to add to patient discomfort and prolong suffering in a patient’s final hours. Prospective cohort series demonstrate that many DNI patients treated with NIV actually survive the hospitalization, depending on the diagnosis [36,86]. In one series, 43% of 114 such patients survived to hospital discharge, 75% of CHF patients, and 53% of COPD patients, whereas hospital survivals for patients with pneumonia
or an underlying malignancy had hospital survivals in the range of 25% [36]. The presence of cough, awake mental status, and hypercapnia also imparted a favorable prognosis.
or an underlying malignancy had hospital survivals in the range of 25% [36]. The presence of cough, awake mental status, and hypercapnia also imparted a favorable prognosis.
Thus, it is possible to identify, on the basis of the diagnosis and some simple clinical observations, patients with a better than even chance of surviving the hospitalization, and NIV could be used in these patients as a form of life support with the hope of “bridging” them through their acute illness. NIV can also be used for palliation of patients with a poor prognosis for survival of the hospitalization, with the possible aims of alleviating dyspnea or to prolong survival slightly so that the patient has time to settle affairs or say goodbye to loved ones. As recommended by a consensus statement by a Society of Critical Care Medicine task force on NIV, it is necessary for the patient, family, and caregivers to agree on these goals and to cease promptly if NPPV seems to be adding to suffering (via mask discomfort, for example) rather than alleviating it [87].
Other Acute Applications of NPPV
Endoscopic Procedures
In separate randomized trials, CPAP alone (up to 7.5 cm H2O) or NPPV both improved oxygenation and reduced postprocedure respiratory failure in patients with severe hypoxemia undergoing bronchoscopy compared with those receiving conventional O2 supplementation [88,89]. The evidence supports the use of NIV to improve gas exchange and reduce potential complications during fiber-optic bronchoscopy, especially when the risk of intubation is deemed high such as in immunocompromised patients or in those with bleeding diatheses. However, patients must be monitored closely and the caregiver team must try to minimize the risk of aspiration and be prepared for the possible need for emergent intubation.
Preoxygenation Before Intubation
A randomized trial in critically ill patients with hypoxemic respiratory failure showed that preoxygenation with NIV before intubation improved O2 saturation during and after intubation and decreased the incidence of O2 desaturations below 80% during intubation [92]. This approach is promising but needs further evaluation before routine use can be recommended. This also begs the question whether, if NIV improves oxygenation substantially, intubation could be avoided in some of these patients.
Selection Guidelines for NPPV in Acute Respiratory Failure
Determinants of Success/Failure
Selection of appropriate patients for NPPV is critical for optimizing success and providing benefit. Knowledge of factors that predict success or failure is helpful in selecting good candidates for NPPV. Such factors, compiled from previous studies, are shown in Table 59.2. In effect, the predictors indicate that patients who are most likely to succeed with NIV have incipient, milder respiratory failure than those who fail. This suggests that there is a “window of opportunity” for implementation of NIV when success is most likely. NIV should be started when patients have evidence of acute respiratory distress and increased acute physiology and chronic health evaluation II (APACHE II) scores, but not when patients are approaching respiratory arrest, have severe acidemia, high APACHE II scores, or are unable to cooperate.
Related posts:
Full access? Get Clinical Tree
