Noninvasive Ventilation in Acute Respiratory Failure: Practical Tips for Success
August 1, 1999 8 minutes read
Special Feature
Noninvasive Ventilation in Acute Respiratory Failure: Practical Tips for Success
By Robert M. Kacmarek, PhD, RRT, FCCM, FCCP, FAARC
Undeniably, noninvasive positive pressure ventilation (NIPPV) has become the standard of care in the initial management of the COPD patient with acute respiratory failure. In this setting, NIPPV decreases the frequency of intubation, the duration of mechanical ventilation, the length of ICU stay, mortality, and the cost of care.1 Data from dozens of studies define a NIPPV success rate of about 70%.2 In addition, others have proposed the use of NIPPV in acute respiratory failure of almost any etiology3,4,5 and as a bridge to weaning in COPD patients.6 However, when the average institution attempts to translate the high success rate of NIPPV in the literature into practice at that institution there is frequently disappointment in the initial results. The inability to achieve the success rate defined in the literature is multifactorial (see Table). Many of the primary reasons can be grouped into the following areas: inadequate training, inadequate time to initiate treatment, inappropriate selection or availability of equipment, and inappropriate initial application. This brief essay addresses these common pitfalls and offers practical tips for avoiding them.
Staff Training
The application of NIPPV is different from the management of the endotracheally intubated, mechanically ventilated patient. The average respiratory therapist and nurse generally finds conventional mechanical ventilation easy to manage. The patient is sedated and intubated, with the ventilator easily adjusted to provide the gas exchange and patient effort considered appropriate.
With NIPPV, the situation is not so simple. Staff must realize that the patient must be involved in the process. If the patient is uncomfortable they will not tolerate NIPPV and failure is likely. Although small doses of intermittently administered sedatives are acceptable, heavy sedation is unacceptable. As a result, patient cooperation and approval are generally necessary for successful application.
In addition to staff members needing to approach patients more from the perspective of a rehabilitation clinician, caregivers need to be well educated on the benefits of NIPPV. If staff do not understand the benefits of NIPPV they are unlikely to appropriately encourage patients who appear uncomfortable to continue with NIPPV. In addition, attending physicians and housestaff must fully understand the difficulties and problems associated with the application of NIPPV. The better the staff understands all of the issues and idiosyncrasies associated with application of NIPPV, the greater the likelihood of a successful program.
Available Time
The initial application of NIPPV is time consuming and demands the undivided attention of a respiratory therapist or other clinician at the bedside if it is to be successful. In many institutions the reason for failure of an NIPPV program is the assumption that the initiation of NIPPV on an emergent basis can be easily fit into the daily activities of the respiratory therapist without appropriate allocation of time.
In general, it requires about 90-120 minutes from the time of reception of an order for NIPPV to its successful application and the stabilization of the patient. If time is not taken to properly select the correct equipment, to carefully apply NIPPV, and to monitor its application, the likelihood for success is minimal. After initial application, ongoing monitoring of the patient requires the same time commitment from nurses and respiratory therapists as conventional mechanical ventilation. It must always be remembered that if NIPPV were not being applied, the patient would be intubated and invasively mechanically ventilated.
Equipment
The availability of the correct equipment is a critical factor in a successful NIPPV program. Specifically, a wide selection of mask types and sizes as well as appropriate ventilators is essential.
Selecting the Right Mask
It should not require excessive force to keep a mask (whether nasal or full face mask) on a patient’s face during NIPPV! The most common mistake here is the selection of a mask that is too large. Ideally, mask size should be chosen using a sizing template that can be placed on the patient’s face. In all settings, the smallest mask size that fits over the patient’s nose or nose and mouth is best.
The most common location for leaks from a mask is at the top of the mask. This is almost always a result of using too large a mask that rides above the bridge of the nose. With all masks the top of the mask should be about 1 cm from the top of the nose and closely contoured to the lateral wall of the nose. With nasal masks, the bottom of the mask should fit snugly above the upper lip, and with most full-face masks the lower border should be just below the lower lip. Masks tend to be too large: I have never used the medium- or large-sized masks of some manufacturers!
| Table Components of a Successful NIPPV Program |
Training Respiratory therapists Nurses Physicians Available Time Initiation of NIPPV Ongoing monitoring Equipment Available Masks Ventilators Initial Application Setting the ventilator Response to the ventilator
In addition to a variety of mask sizes, a number of different mask types should always be available. Generally, I find the mask with a free inner lip that is compressed to the face during inspiration preferable to those with an inflatable tube or cushion. However, depending on the patient’s facial anatomy, a mask that is undesirable in one patient may be useful in another. My advice is to assemble a "tackle box," with multiple nasal and full-face masks of different sizes from different manufacturers, along with their sizing templates that can be taken to the bedside whenever NIPPV is being started. It should be noted that it is impossible to eliminate all leaks with either nasal or full-face masks, and that this is also unnecessary! The problem of minor leakage can be handled by the ventilator.
Regarding my preference for full vs. nasal masks, in the setting of acute respiratory failure I prefer to begin with a full-face mask and only attempt to use a nasal mask if the patient will not tolerate the full-face mask. However, for elective applications or after stabilization during acute application (> 24-48 hrs.), a nasal mask is appropriate.
In many elderly patients or in patients with poor peripheral perfusion, it is useful to apply an artificial skin cover (such as Duoderm or a similar product) to the bridge of the patient’s nose, and in some instances also to the facial surface in contact with the lateral border of the mask. Application of these products prior to or early in the use of NIPPV can dramatically reduce skin breakdown.
Finally, the mask straps should never be tightly applied to the patient’s face. These are only designed to snugly secure the mask. It should be possible to place two fingers between the mask straps and the patient’s face. As I already indicated, some leakage will always be present.
The Ventilator
Theoretically, any ventilator manufactured is capable of providing NIPPV. However, most ventilators are not as responsive as is necessary to match the patient’s ventilatory pattern, are unable to compensate for leaks, and are inappropriately alarmed. The ventilator used for the application of NIPPV for patients with acute respiratory failure should be able to provide an accurate and constant oxygen concentration, monitor the patient’s ventilatory pattern, and alarm if it becomes disconnected or if the ventilatory pattern becomes inappropriate. As with invasive assisted ventilation, synchrony with the patient is critical. Ideally, airway pressure and flow waveforms should be available to evaluate synchrony. At the least, an airway pressure manometer should be available.
For these reasons an ICU ventilator is preferred over most bilevel pressure ventilators for acute applications. However, a number of new bilevel pressure and portable home care ventilators, either currently available or soon to be introduced to the market, allow for evaluation of synchrony. Unfortunately, with the original bilevel pressure ventilators it is impossible to ensure that the patient is breathing in synchrony and not fighting the ventilator.
The major problem with the use of ICU ventilators in this setting is that they do not compensate for leaks in the pressure support mode. Even those newer ventilators with the ability to adjust inspiratory termination in pressure support cannot compensate for variation in leak on a breath-to-breath basis. When leaks around the mask are a problem with ICU ventilators, the pressure assist/control mode should be used. Gas delivery during pressure assist/control is the same as during pressure support, except that inspiration is cycled by time (as in volume assist/control) rather than by flow. The setting of an inspiratory time consistent with the patient’s own inspiratory time (e.g., 0.7-1.0 sec) during pressure assist/control dramatically improves synchrony.
A final potential concern with all bilevel pressure ventilators that do not incorporate a true exhalation valve is CO2 rebreathing. Unless positive end-expiratory pressure (PEEP) is set higher than 5 cm H2O, because of the low internal resistance of these machines exhaled gas easily moves retrograde up the single gas delivery tube. As a result, regardless of the type of mask used, with all bilevel pressure ventilators a non-rebreathing valve should be added as close as possible to the patient’s mask to prevent CO2 rebreathing.
Initial Application
Many patients fail NIPPV before the device is given a chance for success! If the ventilator is set at 15 cm H2O of pressure support with 5 cm H2O of PEEP and the mask simply strapped to the face of a dyspneic, frightened, and probably claustrophobic patient, failure is inevitable. Time must be taken to carefully explain what NIPPV is, why NIPPV is being performed, and what the alternative is!
The mask should be applied first without ventilation. This should be done by the therapist holding the mask so it can be rapidly removed if needed. The mask should not be strapped until the patient has fully accepted the therapy. Pressure should be applied slowly with discussion with the patient regarding comfort. For the vast majority of patients, 4-6 cm H2O PEEP, along with 8-12 cm H2O of pressure support or pressure assist/control, is all that is required.
As long as total pressure does not exceed 20 cm H2O we find it unnecessary to use a nasogastric tube. In fact, in my institution it is an extreme rarity that a nasogastric tube is ever used at these pressure settings. It is only when pressure exceeds 20 cm H2O and clinically significant gastric distension is present that such a tube is required. We have found that the use of a nasogastric tube reduces the likelihood of success.
Conclusion
The clinician’s learning curve for proper application of NIPPV in patients with acute respiratory failure can be long, and it is unlikely that the success rate in the nonresearch setting will rapidly approach what is achieved in the research setting, where personnel, equipment, and time are not of concern. However, it is reasonable to expect that with time the success rate of NIPPV in the acute setting will exceed 50%.
References
1. Keenan SP, et al. Effect of noninvasive positive pressure ventilation on mortality in patients admitted with acute respiratory failure: A meta-analysis. Crit Care Med 1997;25:1685-1692.
2. Abou-Shala N, Meduri U. Noninvasive mechanical ventilation in patients with acute respiratory failure. Crit Care Med 1996;24:705-715.
3. Meduri GU, et al. Noninvasive positive pressure ventilation in status asthmaticus. Chest 1996;110:767-774.
4. Gozal D. Nocturnal ventilatory support in patients with cystic fibrosis: Comparison with supplemental oxygen. Eur Respir J 1997;10:1999-2003.
5. Antonelli M, et al. A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure. N Engl J Med 1998:339:429-435.
6. Nava S, et al. Noninvasive mechanical ventilation in the weaning of patients with respiratory failure due to chronic obstructive pulmonary disease. Ann Intern Med 1998;128:721-728.
Which of the following is not an essential aspect of a successful program for managing acute respiratory failure with NIPPV?
a. Adequate training
b. Proper ventilator
c. Proper mask size
d. Physical presence of physician
e. Careful monitoring
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