Brain MRI Findings in Patients in the Intensive Care Unit with COVID-19 Infection.

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Metabolic changes and factors influencing base deficit in infants undergoing craniosynostosis surgery: a retrospective study.

BACKGROUND: Corrective craniosynostosis surgery is often associated with a large amount of blood loss and metabolic disturbances. In the present study, we investigated the severity, duration of metabolic disturbances, and causal risk factors in infants. METHODS: A retrospective analysis was performed of 36 infants who underwent craniosynostosis surgery. We analyzed the following: demographics, duration of surgery, intraoperative blood loss, RBC, FFP and fluids transfused, urine output, hemodynamic parameters, and electrolyte and base deficit (BD) values. The lowest intraoperative BD value and time required (period I: <6 h; period II: 6-12 h; period III: >12 h) for BD values to return to normal (-4 to +2) in the postoperative period were determined. In addition, we recorded the postoperative length of stay in the ICU and hospital, postoperative blood loss, and early complications. RESULTS: We detected that 88% of the patients had subnormal BD levels and 22% had metabolic acidosis. The lowest average BD measured during the operation was -8.4 ± 2.6 mmol/l. We carried out a multiple regression analysis, which revealed that lower BD values were associated with a longer duration of hypotension (p = 0.002, R(2) = 0.453) and greater intraoperative blood loss (p = 0.002, R(2) = 0.674). We examined the amount of intraoperative blood loss and found that that there were fewer blood product transfusions in period I patients and longer hypotensive episodes in period III patients. Also, a negative correlation was detected between the lowest intraoperative BD value with ICU duration (p = 0.004, r = -0.466) and hospital stay (p < 0.001, r = -0.764). CONCLUSION: Almost all patients developed intraoperative negative BD, which was prolonged in the postoperative period. The most important risk factors for developing negative BD are the amount of blood loss and duration of hypotension.

The Relationship Between Decreased CD-8 T-Cells and Mortality in Patients with COVID-19 Pneumonia in the Intensive Care Unit, A Retrospective Study.

Objective: CD-8 T-cells are responsible for the clearance of virally infected cells. In patients with Coronavirus disease-2019 (COVID-19) pneumonia, there are quantitative reductions and functional impairments in T-cells. Low CD-8 T-cell levels cause worse clinical situations. In this study, the relationship between decreased CD-8 T-cells and mortality in patients with COVID-19 pneumonia in the intensive care unit (ICU) was investigated. Methods: In this multicenter retrospective study, 277 patients were analyzed. Demographic data, ICU admission scores, blood gas levels, laboratory samples, and outcomes were recorded. Statistical Package for the Social Sciences version 28 was used for statistical analysis. Results: Two hundred forty of 277 patients were included in the study. The mortality rate was 43.3%. In non-survivors, median values of age, Charlson comorbidity index, Acute Physiology and Chronic Health Evaluation II (APACHE-II), procalcitonin, leukocyte count, neutrophil count, neutrophil-lymphocyte count ratio, and duration of invasive mechanical ventilation were significantly higher, whereas median values of PaO2-FiO2 ratio, lymphocyte count, CD-4, and CD-8 T-cells were significantly lower than those in survivors. In the multivariate Cox regression model, the risk of mortality increased 1.04-fold (1.02-1.06) and 1.05-fold (1.01-10.8) by every one unit increase in age and APACHE-II, respectively, whereas it decreased 0.71-fold (0.58-0.87) by every hundred increase in CD-8 T-cells P < 0.001, P=0.007 and P=0.001 respectively. Conclusion: According to our findings, age, APACHE-II, and CD-8 T-cell levels seem to be independent risk factors for mortality in patients with COVID-19 pneumonia in the ICU.

Base-excess chloride; the best approach to evaluate the effect of chloride on the acid-base status: A retrospective study.

To practically determine the effect of chloride (Cl) on the acid-base status, four approaches are currently used: accepted ranges of serum Cl values; Cl corrections; the serum Cl/Na ratio; and the serum Na-Cl difference. However, these approaches are governed by different concepts. Our aim is to investigate which approach to the evaluation of the effect of Cl is the best. In this retrospective cohort study, 2529 critically ill patients who were admitted to the tertiary care unit between 2011 and 2018 were retrospectively evaluated. The effects of Cl on the acid-base status according to each evaluative approach were validated by the standard base excess (SBE) and apparent strong ion difference (SIDa). To clearly demonstrate only the effects of Cl on the acid-base status, a subgroup that included patients with normal lactate, albumin and SIG values was created. To compare approaches, kappa and a linear regression model for all patients and Bland-Altman test for a subgroup were used. In both the entire cohort and the subgroup, correlations among BECl, SIDa and SBE were stronger than those for other approaches (r = 0.94 r = 0.98 and r = 0.96 respectively). Only BECl had acceptable limits of agreement with SBE in the subgroup (bias: 0.5 mmol L-1) In the linear regression model, only BECl in all the Cl evaluation approaches was significantly related to the SBE. For the evaluation of the effect of chloride on the acid-base status, BECl is a better approach than accepted ranges of serum Cl values, Cl corrections and the Cl/Na ratio.

The treatment of acute liver failure with fractionated plasma separation and adsorption system: Experience in 85 applications.

INTRODUCTION: Artificial liver support systems represent a potential useful option for the treatment of liver failure. The outcomes of patients treated with the fractionated plasma separation and adsorption (FPSA) system are presented. PATIENTS AND METHODS: FPSA was performed 85 times for 27 patients (median 3 treatments/patient) with liver failure [85.2% acute liver failure (ALF) and 14.8% acute-on-chronic liver failure] using the Prometheus 4008H (Fresenius Medical Care) unit. Citrate was used for anticoagulation. A variety of clinical and biochemical parameters were assessed. Comparisons between pretreatment and post-treatment data were performed using paired t-test. RESULTS: The 85 sessions had a mean duration of 6 h. There were significant decreases in total bilirubin (13.18 +/- 9.46 mg/dL vs. 9.76 +/- 7.05 mg/dL; P < 0.0001), ammonia (167.6 +/- 75 mg/dL vs. 120 +/- 43.8 mg/dL; P < 0.0001), blood urea nitrogen (BUN; 12.55 +/- 13.03 mg/dL vs. 8.18 +/- 8.15 mg/dL; P < 0.0001), creatinine (0.54 +/- 0.47 mg/dL vs. 0.46 +/- 0.37 mg/dL; P = 0.0022) levels, and in pH (7.48 +/- 0.05 vs. 7.44 +/- 0.08; P = 0.0045). Four patients (14.8%) received liver transplantation after the treatments; in nine patients, transplantation was not necessary anymore (33%); the remaining 14 patients did not receive a transplantation because they were either not appropriate candidates or no organ was available. Overall survival was 48.1% (4 transplanted and 9 treated patients). No hematological complications related to FPSA were observed. CONCLUSIONS: FPSA system is a safe and effective detoxification method for patients with liver dysfunction, including ALF. The system is useful as a symptomatic treatment before liver transplantation; in up to 1/3 of the cases, it can even be used as a sole method of treatment.

The effects of airway pressure and inspiratory time on bacterial translocation.

BACKGROUND: Mechanical ventilation with high peak inspiratory pressure (PIP) induces lung injury and bacterial translocation from the lung into the systemic circulation. We investigated the effects of increased inspiratory time on translocation of intratracheally inoculated bacteria during mechanical ventilation with and without extrinsic positive end-expiratory pressure (PEEP). METHODS: Rats were ventilated in pressure-controlled mode with 14 cm H2O PIP, 0 cm H2O PEEP, I:E ratio 1/2, and Fio2 1.0. Subsequently, 0.5 mL of 10(5) cfu/mL Pseudomonas aeruginosa was inoculated through tracheostomy and rats were randomly assigned to six groups; two low-pressure groups (LP)1/2, 14 cm H2O PIP, 0 cm H2O PEEP, I:E = 1/2, and LP2/1 14 cm H2O PIP, 0 cm H2O PEEP, I:E = 2/1; two high-pressure groups (HP)1/2, 30 cm H2O PIP, 0 cm H2O PEEP, I:E = 1/2, and HP2/1, 30 cm H2O PIP, 0 cm H2O PEEP, I:E = 2/1; two HP PEEP groups (HPP)1/2, 30 cm H2O PIP, 10 cm H2O PEEP, I:E = 1/2, and HPP2/1, 30 cm H2O PIP, 10 cm H2O PEEP, I:E = 2/1. Blood cultures were obtained every 30 min. The rats were killed and their lungs were processed. RESULTS: When compared with baseline values, Pao2 decreased in the LP1/2, LP2/1, HP1/2, and HP2/1 groups at the last time point, but the decline in Pao2 reached statistical significance in only the HP1/2 group. The bacterial translocation rate was greater in group HPP2/1 than group HPP1/2 (P = 0.01). CONCLUSIONS: We found that high PIP, with or without prolonged inspiratory time, increased the rate of bacterial dissemination. PEEP prevented bacterial translocation in the high PIP group. However, the protective effect of PEEP was lost when inspiratory time was prolonged.

A Case of Biotinidase Deficiency in an Adult with Respiratory Failure in the Intensive Care Unit.

BACKGROUND: Biotinidase deficiency (BD) is a rare, inherited autosomal recessive disorder that is treatable within childhood. We present a patient with pneumonia and respiratory acidosis who was not diagnosed with any systemic disorders; the patient was finally diagnosed as BD. CASE REPORT: A thirty-year-old woman was admitted to the emergency department with respiratory failure that had persisted for a few days and progressively weakening over the previous six months. Then, the patient was admitted to the intensive care unit with marked respiratory acidosis, respiratory failure and alterations in consciousness. At the follow-up, the patient was not diagnosed with a systematic disorder. Rather, the patient's historical clinical findings suggested a metabolic disorder. Finally, the patient was diagnosed with biotinidase deficiency. CONCLUSION: Even though biotinidase deficiency is not frequently seen in the intensive care unit, metabolic syndromes such as biotinidase deficiency should be considered. Patients should be evaluated holistically with attention to medical history, family history and clinical findings.

Effects of different recruitment maneuvers on bacterial translocation and ventilator- induced lung injury.

BACKGROUND: Investigated in the present study were the effects of various recruitment maneuvers (RMs) using the same inflation pressure-time product on bacterial translocation from lung to blood, and ventilator-induced lung injury (VILI). METHODS: Tracheotomy was performed on anesthetized rats, and ventilation was initiated using pressure-controlled mode. Subsequently, Pseudomonas aeruginosa was inoculated through the tracheotomy tube and ventilated for 30 minutes before rats were randomly separated into 4 groups. Group 1 underwent sustained inflation (SI), Group 2 underwent low-pressure SI, Group 3 underwent modified sigh, and Group 4 was a control group. Blood cultures were taken at baseline, 15 minutes after randomization (after each RM for the first hour), and finally at 75 minutes after the last RM. The rats were euthanized and the lungs were extirpated. The left lung was taken for measurement of wet:dry weight ratio, and the right lung was used for pathologic evaluation. RESULTS: Positive blood cultures were found to be higher in Group 3 at early study periods. Total pathological scores were also higher in Group 3. CONCLUSION: Higher severity of ventilator-induced lung injury occurred in the modified sigh group, evidenced by bacterial translocation and results of histopathological evaluation.

Effect of magnesium sulfate administration on blood-brain barrier in a rat model of intraperitoneal sepsis: a randomized controlled experimental study.

INTRODUCTION: Permeability changes in the blood-brain barrier (BBB) and their possible contribution to brain edema formation have a crucial role in the pathophysiology of septic encephalopathy. Magnesium sulfate has been shown to have a protective effect on BBB integrity in multiple experimental models. In this study we determine whether magnesium sulfate administration could have any protective effects on BBB derangement in a rat model of sepsis. METHODS: This randomized controlled experimental study was performed on adult male Sprague-Dawley rats. Intraperitoneal sepsis was induced by using the infected fibrin-thrombin clot model. To examine the effect of magnesium in septic and sham-operated rats, a dose of 750 micromol/kg magnesium sulfate was given intramuscularly immediately after surgery. Control groups for both infected and sham-operated rats were injected with equal volume of saline. Those rats surviving for 24 hours were anesthetized and decapitated for the investigation of brain tissue specific gravity and BBB integrity by the spectrophotometric assay of Evans blue dye extravasations. Another set of experiments was performed for hemodynamic measurements and plasma magnesium level analysis. Rats were allocated into four parallel groups undergoing identical procedures. RESULTS: Sepsis significantly increased BBB permeability to Evans blue. The dye content of each hemisphere was significantly lower in the magnesium-treated septic rats (left hemisphere, 0.00218 +/- 0.0005; right hemisphere, 0.00199 +/- 0.0007 [all results are means +/- standard deviation]) than in control septic animals (left hemisphere, 0.00466 +/- 0.0002; right hemisphere, 0.00641 +/- 0.0003). In septic animals treated with magnesium sulfate, specific gravity was higher (left hemisphere, 1.0438 +/- 0.0007; right hemisphere, 1.0439 +/- 0.0004) than in the untreated septic animals (left hemisphere, 1.0429 +/- 0.0009; right hemisphere, 1.0424 +/- 0.0012), indicating less edema formation with the administration of magnesium. A significant decrease in plasma magnesium levels was observed 24 hours after the induction of sepsis. The dose of magnesium that we used maintained the baseline plasma magnesium levels in magnesium-treated septic rats. CONCLUSIONS: Magnesium administration attenuated the increased BBB permeability defect and caused a reduction in brain edema formation in our rat model of intraperitoneal sepsis.

Effects of body temperature on ventilator-induced lung injury.

PURPOSE: To evaluate the effects of body temperature on ventilator-induced lung injury. MATERIAL AND METHODS: Thirty-four male Sprague-Dawley rats were randomized into 6 groups based on their body temperature (normothermia, 37 +/- 1 degrees C; hypothermia, 31 +/- 1 degrees C; hyperthermia, 41 +/- 1 degrees C). Ventilator-induced lung injury was achieved by ventilating for 1 hour with pressure-controlled ventilation mode set at peak inspiratory pressure (PIP) of 30 cmH2O (high pressure, or HP) and positive end-expiratory pressure (PEEP) of 0 cmH2O. In control subjects, PIP was set at 14 cmH2O (low pressure, or LP) and PEEP set at 0 cmH2O. Systemic chemokine and cytokine (tumor necrosis factor alpha , interleukin 1 beta , interleukin 6, and monocyte chemoattractant protein 1) levels were measured. The lungs were assessed for histological changes. RESULTS: Serum chemokines and cytokines were significantly elevated in the hyperthermia HP group compared with all 3 groups, LP (control), normothermia HP, and hypothermia HP. Oxygenation was better but not statistically significant in hypothermia HP compared with other HP groups. Cumulative mean histology scores were higher in hyperthermia HP and normothermia HP groups compared with control and normothermia HP groups. CONCLUSIONS: Concomitant hyperthermia increased systemic inflammatory response during HP ventilation. Although hypothermia decreased local inflammation in the lung, it did not completely attenuate systemic inflammatory response associated with HP ventilation.

Effects of magnesium administration on brain edema and blood-brain barrier breakdown after experimental traumatic brain injury in rats.

In this study, we examined the effects of magnesium sulfate administration on brain edema and blood-brain barrier breakdown after experimental traumatic brain injury in rats. Seventy-one adult male Sprague-Dawley rats were anesthetized, and experimental closed head trauma was induced by allowing a 450-g weight to fall from a 2-m height onto a metallic disk fixed to the intact skull. Sixty-eight surviving rats were randomly assigned to receive an intraperitoneal bolus of either 750 micromol/kg magnesium sulfate (group 4; n = 30) or 1 mL of saline (group 2; n = 30) 30 minutes after induction of traumatic brain injury; 39 nontraumatized animals received saline (group 1; n = 21) or magnesium sulfate (group 3; n = 18) with an identical protocol of administration. Brain water content and brain tissue specific gravity, as indicators of brain edema, were measured 24 hours after traumatic brain injury. Blood-brain barrier integrity was evaluated quantitatively 24 hours after injury by spectrophotometric assay of Evans blue dye extravasations. In the magnesium-treated injured group, brain water content was significantly reduced (left hemisphere: group 2, 83.2 +/- 0.8; group 4, 78.4 +/- 0.7 [P <.05]; right hemisphere: group 2, 83.1 +/- 0.7; group 4, 78.4 +/- 0.5. [P <.05]) and brain tissue specific gravity was significantly increased (left hemisphere: group 2, 1.0391 +/- 0.0008; group 4, 1.0437 +/- 0.001 [P <.05]; right hemisphere, group 2, 1.0384 +/- 0.001; group 4, 1.0442 +/- 0.005 [P <.05]) compared with the saline-treated injured group. Evans blue dye content in the brain tissue was significantly decreased in the magnesium-treated injured group (left hemisphere: group 2, 0.0204 +/- 0.03; group 4, 0.0013 +/- 0.0002 [P <.05]; right hemisphere: group 2, 0.0064 +/- 0.0009; group 4, 0.0013 +/- 0.0003 [P <.05]) compared with the saline-treated injured group. The findings of the present study support that beneficial effects of magnesium sulfate exist after severe traumatic brain injury in rats. These results also indicate that a blood-brain barrier permeability defect occurs after this model of diffuse traumatic brain injury, and magnesium seems to attenuate this defect.

Comparison of Different Induction Doses of Rocuronium and Vecuronium in Neuroanaesthesia Practice.

OBJECTIVE: To evaluate the efficiency of use of rocuronium and vecuronium in different dose regimens in neuroanaesthesia practice in terms of intubation time and first additional dose requirement. METHODS: Sixty-eight neurosurgery patients with intracranial mass that were operated on were included in our study. Patients were randomly divided into 4 groups according to the induction dose of neuromuscular blocker (NMB) as: Group 1: Vecuronium 0.1 mg kg(-1), Group 2: Priming, 20% of total vecuronium (0.1 mg kg(-1)) needed for induction injected 5 minutes before induction and then the rest used for induction, Group 3: Rocuronium group: 0.6 mg kg(-1), Group 4: Rocuronium with rapid-sequence induction dose (RSID) (1.2 mg kg(-1)). TOF (Train of four) test was used to decide on intubation and an additional NMB dose during surgery. Intubation quality, time from induction to intubation, time until the first additional NMB dose and subsequent NMB dose intervals were recorded. RESULTS: The RSID of rocuronium provided a significantly shorter time period for intubation against the other groups. Also, the time period from induction to first additional NMB requirement was significantly longer in the RSID group than the others. There were no statistically significant differences between the groups' in terms of time period for monitorisation, positioning and start of surgery. CONCLUSION: With the use of RSID of rocuronium, it was seen that excellent intubation quality is provided at around 1 minute and, with its longer duration of action until a first additional dose, it covers the time period for monitorisation, positioning and start of surgery. Because of these effects, we think that RSID of rocuronium may be a better choice of dose regimen for neuroanaesthesia practice.

[Late presentation of posttraumatic pulmonary arteriovenous fistulea occlusion with septal occluder device]. / Travma sonrasi geç prezente olmus pulmoner arteriyovenöz fistülün septal tikayici cihaz ile kapatilmasi

Posttraumatic pulmonary arteriovenous fistula is a rare complication of penetrating injury. Cases may remain asymptomatic for years prior to diagnosis. We present a case of pulmonary arteriovenous fistula related to a penetrating injury of the thorax 6 years previously that was occluded with a septal occluder device. Consistent use of CT or conventional catheter pulmonary angiography following penetrating injury to the thorax is essential to the early diagnosis of pulmonary arteriovenous fistula during the asymptomatic stage. Modern occlude devices facilitate the transcatheter approach as a viable alternative to surgery for the closure large, high pressure defects.

Recruitment Maneuver Does not Increase the Risk of Ventilator Induced Lung Injury.

BACKGROUND: Mechanical ventilation (MV) may induce lung injury. AIMS: To assess and evaluate the role of different mechanical ventilation strategies on ventilator-induced lung injury (VILI) in comparison to a strategy which includes recruitment manoeuvre (RM). STUDY DESIGN: Randomized animal experiment. METHODS: Thirty male Sprague-Dawley rats were anaesthetised, tracheostomised and divided into 5 groups randomly according to driving pressures; these were mechanically ventilated with following peak alveolar opening (Pao) and positive end-expiratory pressures (PEEP) for 1 hour: Group 15-0: 15 cmH2O Pao and 0 cmH2O PEEP; Group 30-10: 30 cmH2O Pao and 10 cmH2O PEEP; Group 30-5: 30 cmH2O Pao and 5 cmH2O PEEP; Group 30-5&RM: 30 cmH2O Pao and 5 cmH2O PEEP with additional 45 cmH2O CPAP for 30 seconds in every 15 minutes; Group 45-0: 45 cmH2O Pao and 0 cmH2O PEEP Before rats were sacrificed, blood samples were obtained for the evaluation of cytokine and chemokine levels; then, the lungs were subsequently processed for morphologic evaluation. RESULTS: Oxygenation results were similar in all groups; however, the groups were lined as follows according to the increasing severity of morphometric evaluation parameters: Group 15-0: (0±0.009) < Group 30-10: (0±0.14) < Group 30-5&RM: (1±0.12) < Group 30-5: (1±0.16) < Group 45-0: (2±0.16). Besides, inflammatory responses were the lowest in 30-5&RM group compared to all other groups. TNF-α, IL-1ß, IL-6, MCP-1 levels were significantly different between group 30-5&RM and group 15-0 vs. group 45-0 in each group. CONCLUSION: RM with low PEEP reduces the risk of ventilator-induced lung injury with a lower release of systemic inflammatory mediators in response to mechanical ventilation.

Effects of prone and jackknife positioning on lumbar disc herniation surgery.

BACKGROUND: Intra-abdominal hypertension due to surgical position increases bleeding at the surgical site. In this study, we evaluated the impact of prone and jackknife position on intra-abdominal pressure (IAP), lung mechanics, blood loss at the surgical site, and duration of the surgical procedure on lumbar disc operations. METHODS: Forty patients operated for single-space lumber disc herniation were included in our study. All patients were ASA I-II and 18 to 70 years old. Patients who had undergone previous spinal surgery, were on anticoagulant or anti-aggregant therapy, had hypertension, cardiac, respiratory, liver, or renal disorders, and were obese (Body Mass Index >35 kg/m²) were excluded. Patients were randomly assigned to either the prone or the jackknife position for surgery. Differences in lung mechanics, IAP, and surgical-site blood loss were calculated in both patient groups. Changes in pulmonary and abdominal pressure levels were measured both in face-up and down positions. RESULTS: Bleeding at the surgical site (prone: 180.0±100.0 mL, jackknife: 100.0±63.6 mL, P=0.018) and IAP (prone: 11.0±3.0 mm Hg, jackknife: 8.0±2.0 mm Hg, P=0.006) were significantly reduced when patients were in the jackknife position. Operating time was approximately 40 minutes shorter in the jackknife position group, although this difference was not significant. CONCLUSIONS: The jackknife position causes less IAP elevation and less surgical site bleeding compared with the prone position. The jackknife position is the preferred choice for single-level lumbar disc surgery in healthy, nonobese patients.

Role of magnesium sulfate in postoperative pain management for patients undergoing thoracotomy.

OBJECTIVE: The purpose of this study was to investigate the effect of magnesium sulfate on pain management for post-thoracotomy patients. DESIGN: A prospective, randomized, controlled clinical study. SETTING: University hospital. PARTICIPANTS: Twenty-four patients undergoing thoracotomy. INTERVENTIONS: After thoracotomy operations, patients were assigned to 2 groups. The control group received intravenous morphine (0.5 mg/h infusion, 0.3 mg patient-controlled anesthesia dose, 15-minute lockout time) via patient-controlled analgesia, and the magnesium group received magnesium sulfate (30-mg/kg bolus, 10 mg/kg/h infusion for 48 hours) plus the same patient-controlled analgesia protocol. MEASUREMENTS AND MAIN RESULTS: Visual analog scale for pain score, sedation score, mean arterial pressure, heart rate, and valid and invalid analgesic demand were recorded. Serum magnesium levels were determined at postanesthesia care unit admission, at 24 hours, and at 48 hours. Side effects were also recorded. There were no significant differences between groups with respect to demographics, sedation score, and pain score. Cumulative mean morphine consumption was found to be higher in the control group compared with the magnesium group at 4, 8, and 48 hours (5.6 +/- 1 mg v 3.2 +/- 0.6 mg [p < 0.0001], 10.2 +/- 1.8 mg v 7.2 +/- 1.6 mg [p = 0.0003), and 40.2 +/- 4.5 mg v 34.8 +/- 6.3 mg [p = 0.02], respectively). CONCLUSION: Postoperative use of magnesium sulfate reduced opioid consumption for pain after thoracotomy operations.

Time required for equilibration of arterial oxygen pressure after setting optimal positive end-expiratory pressure in acute respiratory distress syndrome.

OBJECTIVE: To evaluate the time course of Pao2 change following the setting of optimal positive end-expiratory pressure (PEEP) in patients with acute respiratory distress syndrome (ARDS). DESIGN: Prospective clinical study. SETTING: Multidisciplinary intensive care unit of a university hospital. PATIENTS: Twenty-five consecutive patients with ARDS. INTERVENTIONS: ARDS was diagnosed during pressure-regulated volume control ventilation with tidal volume of 7 mL/kg actual body weight, respiratory rate of 12 breaths/min, inspiratory/expiratory ratio of 1:2, Fio2 of 1, and PEEP of 5 cm H2O. A critical care attending physician obtained pressure volume curves and determined the lower inflection point. Following a rest period of 30 mins with initial ventilation variables, PEEP was set at 2 cm H2O above the lower inflection point, and serial blood samples were collected during 1-hr ventilation with optimal PEEP. Arterial blood gas analyses were performed at 1, 3, 5, 7, 9, 11, 15, 20, 30, 45, and 60 mins. MEASUREMENTS AND MAIN RESULTS: Twenty-five patients were found eligible for the study. Three patients were excluded due to deterioration of oxygen saturation and hemodynamic instability following the initiation of optimal PEEP. Eight cases (36%) were considered to be of pulmonary origin and 14 cases (64%) of extrapulmonary origin. Optimal PEEP levels were 14 +/- 3 cm H2O and 14 +/- 4 cm H2O in pulmonary and extrapulmonary ARDS, respectively. Pao2 demonstrated a 130 +/- 101% increase at the end of 1-hr period in total study population. This improvement did not differ significantly between pulmonary and extrapulmonary forms of ARDS (135 +/- 118% vs. 127 +/- 95%, p = .8). Mean 90% oxygenation time was found to be 20 +/- 19 mins. In the subset of patients with ARDS of pulmonary origin, 90% oxygenation time was 25 +/- 26 mins, whereas it was 17 +/- 15 mins in patients with ARDS of extrapulmonary origin (p = .8). CONCLUSIONS: Our data showed that 20 mins would be adequate for obtaining a blood gas sample in ARDS patients with pulmonary and extrapulmonary origin after application of optimal PEEP 2 cm H2O above the lower inflection point.