Clinical application of a prognostic model for severe community-acquired pneumonia.

Ungar RG, et al. Mouth leak with nasal continuous positive airway pressure increases nasal airway resistance. I thank Dr. Winck and colleagues for their interesting letter on the objective salutary effect of warming nasal continuous positive airway pressure (CPAP) air on their patient's nasal symptoms. They raise the interesting question of whether nasal symptoms are the result of the low temperature, the low relative humidity (rH), or both. Unfortunately, published studies on this subject do not currently provide the answer, since none specifically address the condition of warm air and low humidity. For instance, Richards and colleagues 1 examined nasal airway resistance in patients with mouth leaks using nasal CPAP air conditioned in a variety of ways. This included the following: cold dry air (tem-and body temperature humidified air (temperature, 37°C; rH, 97 to 100%). They demonstrated that most of the fall in nasal resistance from baseline occurred when rH was increased even if the air remained cool, while further heating of the air while maintaining the same, almost fully saturated, humidity did not result in much additional benefit. Unfortunately, they did not test the condition of heated, relatively dry air as suggested by Winck and coworkers. Togias and colleagues 2 have outlined a mechanism by which nasal mucosal drying could cause an inflammatory response resulting in nasal symptoms. They challenged subjects with cold dry air and measured the osmolality of nasal secretions, nasal symptoms, and the concentration of inflammatory mediators. They were able to demonstrate that osmolality correlated with the level of inflammatory mediators in those subjects who developed nasal symptoms in response to the challenge. Other workers have demonstrated that isolated mast cells exposed to a hyperosmolar medium will release inflammatory mediators. 3,4 Finally, a large body of evidence has emerged suggesting that a similar phenomenon, that of exercise-induced asthma, is the result of water loss from the respiratory mucosa rather than heat loss, although this is still somewhat controversial. 5,6 While I applaud the results obtained by Winck and colleagues in treating their patient with warmed, but not humidified, CPAP air, I remain skeptical that this method will be universally applicable. Certainly, there is no harm in asking patients complaining of nasal symptoms from their CPAP to take the simple measure of placing the circuit under the bedclothes; this procedure is, in fact, commonly recommended by durable medical equipment suppliers in our area. However, if symptoms do …