Absolute contraindications
Coma (not attributed to CO2 narcosis)
Cardiac arrest
Respiratory arrest (apnea or agonal respirations)
Any other condition requiring immediate intubation
Relative contraindications (exception should be reviewed on a case-by-case basis)
Cardiac instability (shock, vasopressor requirements, cardiac instability due to dysrhythmias, complicated myocardial infarction)
Gastrointestinal bleeding (hemodynamic instability, hematemesis)
Potential upper airway obstruction (head and neck tumor, angioedema)
Inability to protect airway due to depressed sensorium, inability to cough or clear secretions (cerebrovascular accident, advanced neuromuscular disease, severe drug overdose)
Status epilepticus
Once it is determined that the patient does not require immediate intubation, careful consideration should be made of the underlying disease causing respiratory failure. The vast majority of success with NIV has been accumulated in patients with exacerbations of COPD, and these patients remain the best suited for NIV. Cardiogenic pulmonary edema is another condition that readily responds to NIV. Although these are the two best-suited conditions for NIV, there has been expansion of NIV use into other causes of respiratory failure and in circumstances where NIV has not been traditionally applied (Table 97.2).
Table 2
Clinical conditions suitable for management with noninvasive ventilation
Established efficacy (for most patients, multiple studies) |
Chronic obstructive pulmonary disease (COPD) exacerbations |
Cardiogenic pulmonary edema (CPE) |
Efficacy in selected patients (effective in subgroups or experience limited) |
Asthma |
Post-extubation, following discontinuation of mechanical ventilation (COPD and hypercapnia) |
Community acquired pneumonia (and COPD) |
Immunocompromised state and infiltrates (known cause of infiltrates) |
Solid organ transplants |
Febrile neutropenic patients |
Postoperative respiratory distress and respiratory failure |
Atelectasis |
Postoperative lung resection |
Rib fractures |
Trauma with nonpenetrating chest injury; flail chest |
Decompensated obstructive sleep apnea/cor pulmonale |
Efficacy promising or limited (limited reports) |
Acute respiratory distress syndrome (ARDS) |
Do not intubate status |
Cystic fibrosis |
Interstitial lung disease |
Neuromuscular respiratory failure (better in chronic than acute respiratory failure); best to avoid if upper airway issues |
Kyphoscoliosis |
Muscular dystrophy |
Post-polio syndrome |
Severe acute respiratory distress syndrome (SARS) |
Mild Pneumocystis jiroveci pneumonia |
The next step in patient selection is to determine the severity of their respiratory illness because this may influence their ability to be managed with NIV. This has been most extensively studied in patients with COPD exacerbations. NIV is best suited for those with decompensated COPD who have a moderate to moderately severe illness, defined by the severity of hypercapnic respiratory acidosis starting with a pH < 7.35. Those with a pH ≥ 7.35 have not been demonstrated to derive any benefit from the addition of NIV to standard therapy. However, increasing respiratory acidosis does increase the possibility of intubation as it falls below 7.25 and especially below 7.20. The lowest threshold of effectiveness is not well defined inasmuch as comatose patients with severe hypercapnic respiratory acidosis, CO2 narcosis, and pH as low as 6.93 have been successfully treated with NIV. Although hypoxemia is one of the hallmarks of cardiogenic pulmonary edema, those who also have a hypercapnic respiratory acidosis may represent a group most responsive to management with NIV. These and other factors used in patient selection are presented in Table 97.3. None of these values are absolute contraindications to NIV, but should be factored into the decision to institute NIV, as well as determining failure of therapy and need for endotracheal intubation. Some have identified a combination of factors, including severity of illness (Acute Physiology and Chronic Health Evaluation (APACHE) II), neurologic status (Glasgow Coma Score), and respiratory rate as predictive of failure and, therefore, patients who may be poorly suited for NIV [6
].
Table 3
Predictors or response to NIV
Severity of illness (moderate to severe) |
Hypercapnic respiratory acidosis (pH 7.20—7.34); lower limit of effectiveness not known |
*APACHE II score <25 |
*Glasgow Coma Scale >11 |
*Respiratory rate ≤35 |
*combination may further identify poor candidates |
Trial of therapy (response to 1–2 h trial) |
Improvement in respiratory parameters (respiratory rate, oxygenation, dyspnea) |
Improvement in pH (increase by ≥0.06) |
Improvement in PaCO2 (decline by ≥8 mmHg) |
97.2 Location of Therapy
NIV was restricted to the intensive care unit (ICU) when first used to treat patients with respiratory failure. There was a learning curve that required frequent monitoring by nursing and respiratory staff and the ventilator devices initially used for NIV were not well suited for this application. There was also concern for possible respiratory failure requiring intubation and, therefore, NIV was best administered in a location where there would be rapid transition to invasive mechanical ventilation. However, with staff education, experience, and smaller NIV dedicated ventilators, it became evident that NIV could be provided in an unmonitored ward setting with staff specially trained in the nuances of NIV. In the ensuing years, the location of NIV has become less of an issue as NIV is routinely provided for patients in a step-down unit setting, emergency room, and even an unmonitored ward. The ward still represents a third or fourth-line option for its applications (behind the ICU, step-down unit, and emergency department), but this is changing as providers gain experience and are more comfortable with NIV in a ward setting [7].
97.3 Trial of Therapy
The other approach that has been used to determine the utility of NIV has been a time-limited trial of therapy. Most patients who are treated with NIV are able to tolerate a trial of therapy. However, some patients fail NIV in minutes or within an hour of initiation. This group represents about 15 % of all patients treated with NIV. For the remainder, the response to a short 1–2 h trial of therapy is often predictive of successful treatment. This is often clinically evident at the bedside, manifested as a reduction in respiratory rate and accessory muscle use. Arterial blood gases before and after the trial provide further evidence of efficacy with decreasing PaCO2 and increasing pH, objective markers that reflect effective patient synchrony and ventilation. A short trial is useful to identify not only those effectively treated with NIV but also to identify those with a poor response to NIV, thereby invoking consideration for intubation and mechanical ventilation [6, 8]. Extended trials without significant improvement only delay intubation and mechanical ventilation with a risk of other adverse events at the time of intubation. Failure of NIV usually occurs early, within 4–12 h of initiation, but there are those that fail after 24–48 h and others with late failure, after 48 h of NIV, some in spite of initial response to therapy. Failure to improve sensorium or respiratory acidosis after 24 h of NIV is another marker of eventual failure. Although this experience has been mostly accumulated in COPD patients, this clinical experience should hold for other conditions treated with NIV.
97.4 Health-Care Staff
Staff experience is another factor that can influence utilization of NIV. As with any therapy, there is a learning curve for staff whenever NIV is introduced into use, and this involves physicians, nurses, and respiratory therapists. Early experience with NIV was tempered by some nursing and respiratory therapy staff who experienced difficulties in its application, thereby limiting its effectiveness. These issues dissipated with increasing staff education and experience, and NIV generally does not require significantly more time for initiation and maintenance than invasive ventilation using an endotracheal or tracheostomy tube. When surveyed, the vast majority spend <30 min with initiation and maintenance of NIV, a good portion reported <15 min, but, of course, some patients may require an hour of time for satisfactory NIV. As may be expected, larger centers with more patients have more frequent use of NIV and also report greater success rates. It is difficult to discern whether patient volume or operator expertise best explains the differences in institutional utilization and outcomes, as both factors are inexorably related. Prior education and experience with NIV also influences its utilization, which may partially explain some of the global differences in utilization between Europe and North America. NIV utilization is much higher in Europe, where there has been long-standing experience with NIV.
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