Gastric Intramucosal pH is Stable During Titration of Positive End-Expiratory Pressure to Improve Oxygenation In Acute Respiratory Distress Syndrome

Ibrahim Ozkan Akinci, Nahit Çakar, Gökhan Mehmet Mutlu, Simru Tugrul, Perihan Ergin Ozcan, Musa Gitmez, Figen Esen Lutfi Telci

Disclosures

Crit Care. 2003;7(3) 

In This Article

Method

The study protocol was approved by the Institutional Ethics Committee of Istanbul University Hospital. Written informed consent was obtained from each patient or the patient's next of kin. We consecutively enrolled 17 patients with ARDS admitted to the multidisciplinary intensive care unit at Istanbul University Hospital. The criteria for eligibility were a diagnosis of ARDS (based on a consensus report[10]), age older than 18 years and mean arterial pressure (MAP) greater than 60 mmHg with no haemodynamic support. All patients were enrolled within the first 24 hours following the diagnosis of ARDS. Patients with known cardiac dysfunction or pre-existing liver disease were not included in the trial.

All patients were ventilated using a Servo 300 Siemens ventilator (Siemens Elema, Uppsala, Sweden) using the pressure-regulated volume control mode with a tidal volume of 8-10 ml/kg (based on ideal body weight), frequency of 12 breaths/min, fraction of inspired oxygen of 1.0, and inspiratory:expiratory ratio of 1:2. Patients were sedated with midazolam (Dormicum; Hoffmann LaRoche, Basel, Switzerland) at 4 mg/hour and paralyzed with 0.1 mg/kg vecuronium (Norcuron; Organon, Oss, The Netherlands) infusion during the study. In addition to employing a radial arterial catheter for blood pressure measurement, a pulmonary artery catheter (Abbot labs, North Chicago, IL, USA) was placed in all patients for haemodynamic monitoring. No patients received any therapeutic intervention to improve haemodynamics (i.e. fluid resuscitation or catecholamine infusion) throughout the study.

Baseline PEEP (PEEPbaseline) was set at 5 cmH2O and titrated at 2 cmH2O increments until the partial arterial oxygen tension (PaO2) reached at least 300 mmHg, peak airway pressure was 45 cmH2O or greater, or MAP dropped by 20% or more from the baseline value. Criteria for overinflation of lung (and therefore for discontinuation of further titration of PEEP) were reduction in PaO2 of 10% or more and an increase in arterial carbon dioxide tension of 10% or more. Optimal PEEP (PEEPopt) was defined as the PEEP that achieved the best oxygenation, whereas maximum PEEP (PEEPmax) was the greatest level of PEEP achieved during titration in each patient.

A nasogastric catheter (TRIP Catheter; Tonometrics Division, Instrumentarium Corp., Helsinki, Finland) was inserted into the stomach to measure pHi. Correct placement of the TRIP catheter was confirmed by radiography. Enteral nutrition was withheld throughout the study, and all patients received ranitidine 50 mg intravenously. In order to allow for equilibration, pHi was measured 45 min after injection of 2.5 ml isotonic saline into the semipermeable balloon of the TRIP catheter. Partial pressure of carbon dioxide in saline solution and bicarbonate level in arterial blood were measured simultaneously using a blood gas analyzer (ABL-500; Radiometer, Copenhagen, Denmark) immediately after sampling[11] and were corrected for the equilibration time.[12] The pHi was calculated using the Henderson-Hassel-bach equation.

All measurements, including respiratory, haemodynamic parameters, arterial and mixed venous blood gas analyses, and gastric pHi, were taken at baseline and following ventilation for 45 min at each level of PEEP. Haemodynamic parameters were monitored continuously using an Horizon XL monitor (Mennen Medical Inc., New York, NY, USA). Cardiac output was measured in triplicate by thermodilution technique using 10 ml saline solution at room temperature. Cardiac index, shunt fraction, oxygen delivery (DO2) and oxygen consumption were calculated at baseline and at all PEEP levels.

Paired analysis of variance tests were used to analyze the differences between measurements. P < 0.05 was considered statistically significant. All values are presented as mean ± standard deviation.

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