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Gainesville, FL
Rome, Italy
Dr. Gabrielli is Assistant Professor of Anesthesiology and Surgery, Dr. Caruso is Assistant Professor of Anesthesiology, and Dr. Layon is Professor Anesthesiology, Surgery, and Medicine, University of Florida College of Medicine. Dr. Antonelli is Professor, Instituto di Anestesiologia e Reanimazione, Universita Cattolica del Sacro Cuore.
Correspondence to: A. Joseph Layon, MD, FCCP, Department of Anesthesiology, PO Box 100254, Gainesville, FL 32610-0254; e-mail: layon{at}ufl.edu
Liesching and colleagues, in this month’s issue of CHEST (see page 699), have nicely reviewed the acute applications of noninvasive positive-pressure ventilation (NPPV). This is neither the first review of this type, nor is NPPV a particularly new manner of delivering positive-pressure therapy. So what is of interest here?
COPD
Liesching and colleagues comment on the efficacy of NPPV. The most studied application is in acute exacerbations of COPD. The authors comment that the extant data support the contention that NPPV is effective in acute exacerbations of COPD, bringing about rapid symptomatic and physiologic improvement, and decreasing the need for intubation. We suspect that this is correct, and NPPV may well reduce the number of intubations in patients with acute exacerbations of COPD. However, there are some caveats. Brochard and colleagues1 compared NPPV delivered with a mask to standard therapy. Whether the improvement in the NPPV group was related to the noninvasive ventilation per se or to the use of pressure support ventilation used in the NPPV group is not clear. The use of pressure support ventilation would likely reduce the work of breathing (WOB),2 and this may be responsible for at least some of the improvement seen. A second trial, carried out by our Turkish colleagues Çelikel et al,3 noted a 93% success rate for NPPV in preventing endotracheal intubation. This high rate of success makes one wonder whether these patients were ill enough to have required mechanical ventilation. Despite these concerns, there is a large body of literature suggesting that NPPV may be considered the first-line intervention for acute exacerbations of COPD. Patients chosen for this method of ventilation should, however, be carefully selected based on their risk factors.
Cardiogenic Pulmonary Edema
In patients with cardiogenic pulmonary edema (CPE), the administration of positive pressure increases pericardial pressure, reduces transmural pressure, and thus decreases afterload. Additionally, the increase in intrathoracic pressure decreases preload, thereby improving mechanics in an overloaded ventricle. Thus, therapy with NPPV may be beneficial in patients with systolic dysfunction. However, in patients with diastolic dysfunction requiring a relatively high filling pressure, as well as in those patients who are relatively hypovolemic, the hemodynamic effect of therapy with positive pressure may compromise venous return, resulting in the deterioration of hemodynamics and the need for further fluid administration.
As expected, the effect of positive pressure on hemodynamics is determined by pulmonary mechanics. The higher the compliance, for example in COPD patients, the more pressure is transmitted and the more one expects venous return to be decreased. Lin and Chiang4 have shown that there is no difference in mortality rate whether or not continuous positive airway pressure (CPAP) is used in the treatment of patients with CPE. This is not unexpected, as outcome in CPE patients is likely to be related not to effective ventilation, but to cardiovascular performance. Masip and colleagues5 have reported that the application of NPPV to patients with CPE led to rapid improvement of the clinical picture, with a reduction in the intubation rate with respect to those patients treated with oxygen therapy delivered via Venturi mask and aggressive medical therapy, even though the final outcome was not different.
Is there a difference between therapy with CPAP and NPPV in patients with CPE? NPPV is thought to decrease WOB more than therapy with CPAP. Any effect of CPAP on WOB is likely to be secondary to its ability to bring the pulmonary compliance curve to a more advantageous position such that a higher tidal volume is generated at the same pressure change. We think that it is likely that both CPAP and NPPV are useful in the treatment of CPE, but no randomized controlled trial has compared the two techniques thus far.
Severe Community-Acquired Pneumonia
Liesching and colleagues note that the use of NPPV in selected COPD patients with pneumonia is appropriate. However, the usefulness of NPPV in patients with pneumonia without COPD is less clear.6 It may be that when pulmonary secretions are a major issue and the oxygenation is severely compromised, as in a patient with pneumonia, noninvasive ventilation is a poor choice. Data regarding the use of NPPV in patients with pneumonia are, at the moment, not definitive and do not support the safe and extensive application of NPPV for patients with severe community-acquired pneumonia.
ARDS
Great caution is advised in the use of NPPV in patients with ARDS. Antonelli and colleagues7 have pointed out, in their large multicenter study of predictors of failure in patients with acute hypoxemic respiratory failure treated with NPPV, that failure rates in ARDS range from about 6 to 54%. This is compared to a failure rate of about 10% in patients with CPE. We believe that if NPPV is to be used at all in patients with ARDS, it must be applied in hemodynamically stable patients who can be closely monitored and for whom endotracheal intubation is immediately available. At this time, no randomized controlled trials exist on the use of NPPV in patients with ARDS/acute lung injury. All extant data have come from subgroup analyses of larger studies on hypoxemic acute respiratory failure, from studies of the immunocompromised patients, or from case report series. The promising results published to date should not be interpreted as supporting the extensive use of NPPV in patients with ARDS, but rather provide suggestions for future randomized controls trials.8 9
One is also somewhat concerned about the use of NPPV as compliance deteriorates, as this might lead to gastric distension, resulting from high airway pressures.
Facilitation of Weaning and Extubation
Commonly used extubation criteria, such as negative inspiratory force, FVC, and the presence of a leak around the deflated endotracheal tube cuff, are relatively poor predictors of successful extubation. As, on occasion, work imposed by the endotracheal tube and ventilator circuit (ie, imposed WOB [IWOB]) may result in difficult weaning, removal of the endotracheal tube and a switch to noninvasive ventilation might speed recovery from mechanical ventilation.10 11 Although speculative, the measurement of IWOB before extubating these patients, and having NPPV available for all appropriate patients, might clarify which patients require endotracheal intubation and ventilatory support, as opposed to those whose IWOB is elevated simply because of the presence of the endotracheal tube.
Personnel Time Consumption and Financial Considerations
There are significant problems in resource consumption for NPPV. One study12 has noted that nurses must be at the bedside 91% of the time when patients are receiving noninvasive ventilation. This means, at least theoretically, that the nurse/patient ratio should be 1:1 and that the patient likely should be housed in the ICU, a not inexpensive requirement. After the first hour of NPPV, the time spent at the bedside may not differ from that required for intubated patients. Additionally, respiratory therapist resources are required, fairly intensively, for the first 48 h of NPPV use.13
Finally, we note that, in the United States, the insurance and governmental reimbursement of NPPV is lower than expected, especially given the rather intense resource use required to make this method of ventilation safe and effective. Interestingly, the European situation with regard to reimbursement is different, and, at least in Italy, NPPV is included in the diagnosis-related groups (DRGs). This may be one of the reasons why this technique is more popular and widely used among our European colleagues. In the United States, the DRG code (not the International Classification of Diseases, ninth revision, code) for mechanical ventilation specifically excludes mechanical ventilation administered via a mask, even though NPPV may be safer and may result in fewer complications.
For example, a patient is admitted to the hospital with pneumonia and ultimately develops respiratory failure, requiring mechanical ventilation. If the mechanical ventilation is delivered via an endotracheal tube, the DRG coding would be as follows. Respiratory failure with mechanical ventilation using an endotracheal tube codes to DRG 475, with a weight of 3.6632, which equals a hospital reimbursement (not physician reimbursement) of $24,574.98 (in US dollars). The coding is different if this same patient has the mechanical ventilation delivered by any of the following methods: bilevel airway pressure; continuous negative-pressure ventilation; intermittent positive-pressure breathing; face mask; nasal cannula; or nasal catheter. The code properly used is DRG 91, with a weight of 0.7034. This leads to a hospital reimbursement of $4,718.84. There is an illogical inconsistency in this manner of reimbursement that could, quite logically, lead hospitals to minimize the use of NPPV in favor of the more invasive ventilation delivered by endotracheal tube.
In summary, NPPV is a useful tool for delivering positive-pressure ventilation in the ICU. Several points should be remembered regarding this method of ventilation:
References
This article has been cited by other articles:
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  P. T. Macklem Con: Greater Funding of Cell and Molecular Biology Has Not Delivered What Was Promised to Respiratory Medicine Am. J. Respir. Crit. Care Med., February 15, 2004; 169(4): 438 - 439. [Full Text] [PDF]
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