Combined effects of elevated body position on gastroesophageal reflux and intra-abdominal pressure in mechanical ventilated patients

Abstract

To investigate the combined effects of elevated body position on gastroesophageal reflux and intra-abdominal pressure (IAP) in patients undergoing mechanical ventilation (MV) who were receiving enteral nutrition, and to find out their proper height of head of bed. The continuous pH-impedance and bladder pressure (reflecting IAP) at different body positions (0 degree angle, 20 degree angle, 30 degree angle, 45 degree angle) in 6 hours were monitored in 41 MV and enteral nutrition supported patients. The patients who did not have previous gastroesophageal reflux disease (GERD) were admitted to intensive care unit (ICU) of Peking University Third Hospital from March 2010 to December 2010 were included in the study. (1)The most common fluid reflux were weak acid and non-acid reflux. Acid reflux was rare. When elevating the body position from 0 degree to 30 degree angle, the accumulated numbers of these 3 kinds of reflux were declined significantly, and the percentage of high esophageal reflux decreased significantly (numbers of reflux: 0 degree angle: 20 degree angle: 30 degree angle: acid 3.0: 2.0: 1.0, weak acid 13.0: 9.0: 6.0, non-acid 4.0: 3.0: 2.0; percentage of high esophageal reflux: 0 degree angle: 20 degree angle: 30 degree angle: acid 16.00%: 9.00%: 7.84%; weak acid 68.40%: 47.40%: 46.69%; non-acid 15.61%: 9.82%: 8.89%, P<0.05 or P<0.01). But when elevating the body position from 30 degree angle to 45 degree angle, no more significant changes in the numbers of reflux were found, instead, the percentage of high esophageal reflux increased (numbers of reflux 30 degree angle: 45 degree angle: acid 1.0: 1.0, weak acid 6.0: 5.0, non-acid 2.0: 2.0, all P>0.05; percentage of high esophageal reflux 30 degree angle: 45 degree angle: acid 7.84%: 12.00%, weak acid 46.69%: 52.29%, non-acid 8.89%: 17.58%, all P<0.05).(2) Four of the 41 patients (9.76%, 4/41) were found to have intra-abdominal hypertension (IAH) at 0 degree angle body position, with one patient at IV degree (IAH>25 mm Hg, 1 mm Hg= 0.133 kPa). With the patients' body position elevated, the IAP appeared to be further increased [the IAP (mm Hg) at 0 degree angle, 20 degree angle, 30 degree angle, 45 degree position were 10.32±3.48, 11.33±3.71, 13.55±3.58 and 18.25±3.82, respectively P<0.01]; With each level of elevation of the body position, the increasing rate was enhanced markedly [the increasing rate of IAP from 0 degree angle to 20 degree angle, 20 degree angle to 30 degree angle and 30 degree to 45 degree were (9.74±3.05)%, ( 19.60±5.67 )% and (34.73±7.67)%, respectively, the difference between any two groups was significant, all P<0.01]. When elevating the body position from 30 degree to 45 degree angle, the numbers of patients with different levels of IAH were increased significantly too (30 degree angle: 45 degree angle: leveI: 5: 8; leveII: 2: 5; level III: 3: 5; level IV: 2: 3, P<0.05 or P<0.01). Although elevation of the body position of MV patients can reduce gastroesophageal reflux, it also increase the IAP. When the body position is elevated to 45 degree angle, the number of reflux is not reduced effectively, while the rate of high esophageal reflux and the patients' IAP are increased significantly, indicating that 30 degree might be the proper body position for the MV patients receiving enteral nutrition.