EFFECT OF A NASOGASTRIC TUBE ON ESOPHAGEAL PRESSURE MEASUREMENT IN NORMAL ADULTS

We studied the correspondence between fluctuations of esophageal press ure measured before and after placement of a nasogastric (NG) tube in six normal volunteers. Flow, airway pressure,' and esophageal pressure data from at least 20 breaths were recorded in seven ventilatory cond itions in two body postures: 0 degrees (supine) and 60 degrees (uprigh t). The conditions studied included normal quiet breathing, added resi stance, reduced compliance, increased frequency, increased tidal volum e, continuous positive airway pressure, and volume-cycled ventilation with positive pressure, During recording with the NG tube in place, th e subject targeted the same tidal volume (VT), respiratory rate, and i nspiratory time fraction (TI/ TTOT) recorded before NG tube placement. A computer program selected for analysis only those recorded breaths with and without an NG tube that were ''matched'' within 5 percent for both VT and TI. We calculated average VT, TI, and esophageal pressure fluctuation (Delta Pes) for the matched breaths from each subject dur ing every condition. The Delta Pes values with and without NG tube wer e not statistically different in any tested condition (p > 0.05). Our data indicate that the presence of an NG tube does not invalidate the accuracy of Delta Pes measurements made using a well-positioned balloo n catheter in the tested conditions.