Effect of body mass index in acute respiratory distress syndrome.

BACKGROUND: Obesity is associated in healthy subjects with a great reduction in functional residual capacity and with a stiffening of lung and chest wall elastance, which promote alveolar collapse and hypoxaemia. Likewise, obese patients with acute respiratory distress syndrome (ARDS) could present greater derangements of respiratory mechanics than patients of normal weight. METHODS: One hundred and one ARDS patients were enrolled. Partitioned respiratory mechanics and gas exchange were measured at 5 and 15 cm H2O of PEEP with a tidal volume of 6-8 ml kg(-1) of predicted body weight. At 5 and 45 cm H2O of PEEP, two lung computed tomography scans were performed. RESULTS: Patients were divided as follows according to BMI: normal weight (BMI≤25 kg m(-2)), overweight (BMI between 25 and 30 kg m(-2)), and obese (BMI>30 kg m(-2)). Obese, overweight, and normal-weight groups presented a similar lung elastance (median [interquartile range], respectively: 17.7 [14.2-24.8], 20.9 [16.1-30.2], and 20.5 [15.2-23.6] cm H2O litre(-1) at 5 cm H2O of PEEP and 19.3 [15.5-26.3], 21.1 [17.4-29.2], and 17.1 [13.4-20.4] cm H2O litre(-1) at 15 cm H2O of PEEP) and chest elastance (respectively: 4.9 [3.1-8.8], 5.9 [3.8-8.7], and 7.8 [3.9-9.8] cm H2O litre(-1) at 5 cm H2O of PEEP and 6.5 [4.5-9.6], 6.6 [4.2-9.2], and 4.9 [2.4-7.6] cm H2O litre(-1) at 15 cm H2O of PEEP). Lung recruitability was not affected by the body weight (15.6 [6.3-23.4], 15.7 [9.8-22.2], and 11.3 [6.2-15.6]% for normal-weight, overweight, and obese groups, respectively). Lung gas volume was significantly lower whereas total superimposed pressure was significantly higher in the obese compared with the normal-weight group (1148 [680-1815] vs 827 [686-1213] ml and 17.4 [15.8-19.3] vs 19.3 [18.6-21.7] cm H2O, respectively). CONCLUSIONS: Obese ARDS patients do not present higher chest wall elastance and lung recruitability.

Time to reach a new steady state after changes of positive end expiratory pressure.

PURPOSE: To assess the time interval required to reach a new steady state of oxygenation-, ventilation-, respiratory mechanics- and hemodynamics-related variables after decreasing/increasing positive end expiratory pressure (PEEP). METHODS: In 23 patients (group 1) with acute respiratory distress syndrome (ARDS), PEEP was decreased from 10 to 5 cmH2O and, after 60', it was increased from 5 to 15 cmH2O. In 21 other ARDS patients (group 2), PEEP was increased from 10 to 15 cmH2O and, after 60', decreased from 15 to 5 cmH2O. Oxygenation, ventilation, respiratory mechanics and hemodynamic variables were recorded at time 5', 15', 30' and 60' after each PEEP change. RESULTS: When PEEP was decreased, PaO2, PaO2/FiO2, venous admixture and arterial oxygen saturation reached their equilibrium after 5'. In contrast, when PEEP was increased, the equilibrium was not reached even after 60'. The ventilation-related variables did not change significantly with PEEP. The respiratory system compliance, when PEEP was decreased, significantly worsened only after 60'. Hemodynamics did not change significantly with PEEP. In the individual patients the change of oxygenation-related variables and of respiratory system compliance observed after 5' could predict the changes recorded after 60'. This was not possible for PaCO2. CONCLUSIONS: We could not find a unique equilibration time for all the considered variables. However, in general, a decremental PEEP test requires far lower equilibrium time than an incremental PEEP test, suggesting a different time course for derecruitment and recruitment patterns.

A validation study of a new nasogastric polyfunctional catheter.

PURPOSE: Pleural and abdominal pressure are clinically estimated by measuring the esophageal and bladder or intragastric pressure (IGP), respectively. A new nasogastric polyfunctional catheter is now commercially available, equipped with two balloons in the lower and distal part; this catheter allows simultaneous esophageal pressure (Pes) and IGP measurements and can be also used to feed the patient. We compared the Pes and IGP measured using this new device with those obtained with a standard balloon catheter taken as gold standard. METHODS: Twenty-four intubated patients requiring ventilator support (mean age 64.3 ± 16.8 years, body mass index 25.3 ± 3.0 kg/m(2), and PaO(2)/FiO(2) 280.8 ± 123.4 mmHg) were enrolled. Esophageal pressure and IGP were measured with the new nasogastric polyfunctional catheter (Nutrivent, Sidam, Italy) and with a standard balloon catheter (Smart Cath Viasys, USA). The Smart Cath was first inserted in the stomach and then retracted to the esophagus to measure IGP and Pes, respectively. In each patient two paired measurements were averaged. RESULTS: In the Bland-Altman analysis, the bias and agreement bands for Pes, ΔPes (computed as the difference of esophageal pressure between end-inspiration and expiration), and IGP were -0.25 (-2.65 to +2.15), 0.0 (-0.9 to +0.9), and -0.45 (-2.85 to + 1.95) cmH(2)O, respectively. No side effects or complications were recorded. CONCLUSIONS: The new polyfunctional catheter showed a clinically acceptable validity in recording esophageal and intragastric pressure. This device should help physicians to better individualize the clinical patient management.