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The performance of viscoelastic coagulation monitor (VCM) compared with TEG 5000 (TEG) is unknown. In this multicenter study, the authors evaluated the agreement among VCM/TEG parameters and their relationship with standard coagulation tests in critically ill patients. Viscoelastic coagulation monitor, TEG, and laboratory samples were analyzed simultaneously. Viscoelastic coagulation monitor/TEG agreement was computed by Bland and Altman's plots, association with laboratory parameters was studied with Spearman's correlation coefficient and random-intercept linear models. One-hundred and twenty-seven patients enrolled, 320 paired observations: 210 (65.6%) under unfractioned heparin (UFH), 94 (29.4%) under low molecular weight heparin (LMWH), 16 (5.0%) no heparin. Under UFH prolonged clot formation times and reduced the amplitude of viscoelastic tracings on both devices, especially on TEG. The type of heparin affected the agreement between VCM/TEG homolog parameters. Reaction time (TEG-R) resulted 23.1 min longer than the homolog clotting time (VCM-CT) under UFH; maximum amplitude (TEG-MA) resulted 29.5 mm higher than maximum clot firmness (VCM-MCF) under LMWH. Weak correlation was observed between VCM-CT/TEG-R and activated partial thromboplastin time (aPTT)/anti-Xa; no correlation was found between VCM-alpha/TEG-angle and fibrinogen concentration. Viscoelastic coagulation monitor-MCF showed strong (LWMH) to moderate (UFH) correlation with platelet count, while TEG-MA only showed lower correlation. Viscoelastic coagulation monitor and TEG are differently affected by heparin. The platelet count is well represented by VCM-MCF even during UFH administration., Competing Interests: Disclosure: The authors have no conflicts of interest to report., (Copyright © ASAIO 2023.)

Objectives: To determine the prevalence and outcomes associated with hemorrhage, disseminated intravascular coagulopathy, and thrombosis (HECTOR) complications in ICU patients with COVID-19., Design: Prospective, observational study., Setting: Two hundred twenty-nine ICUs across 32 countries., Patients: Adult patients (≥ 16 yr) admitted to participating ICUs for severe COVID-19 from January 1, 2020, to December 31, 2021., Interventions: None., Measurements and Main Results: HECTOR complications occurred in 1,732 of 11,969 study eligible patients (14%). Acute thrombosis occurred in 1,249 patients (10%), including 712 (57%) with pulmonary embolism, 413 (33%) with myocardial ischemia, 93 (7.4%) with deep vein thrombosis, and 49 (3.9%) with ischemic strokes. Hemorrhagic complications were reported in 579 patients (4.8%), including 276 (48%) with gastrointestinal hemorrhage, 83 (14%) with hemorrhagic stroke, 77 (13%) with pulmonary hemorrhage, and 68 (12%) with hemorrhage associated with extracorporeal membrane oxygenation (ECMO) cannula site. Disseminated intravascular coagulation occurred in 11 patients (0.09%). Univariate analysis showed that diabetes, cardiac and kidney diseases, and ECMO use were risk factors for HECTOR. Among survivors, ICU stay was longer (median days 19 vs 12; p < 0.001) for patients with versus without HECTOR, but the hazard of ICU mortality was similar (hazard ratio [HR] 1.01; 95% CI 0.92-1.12; p = 0.784) overall, although this hazard was identified when non-ECMO patients were considered (HR 1.13; 95% CI 1.02-1.25; p = 0.015). Hemorrhagic complications were associated with an increased hazard of ICU mortality compared to patients without HECTOR complications (HR 1.26; 95% CI 1.09-1.45; p = 0.002), whereas thrombosis complications were associated with reduced hazard (HR 0.88; 95% CI 0.79-0.99, p = 0.03)., Conclusions: HECTOR events are frequent complications of severe COVID-19 in ICU patients. Patients receiving ECMO are at particular risk of hemorrhagic complications. Hemorrhagic, but not thrombotic complications, are associated with increased ICU mortality., Competing Interests: Dr. J. P. Fanning received funding from the Australian-American Fulbright Commission and Metro North Clinical Research Fellowship, Queensland Government, Australia. Drs. Suen, Li Bassi, and Fraser received support for article research from the Bill and Melinda Gates Foundation. Dr. Cho is funded by National Heart, Lung, and Blood Institute 1K23HL157610. Dr. Rando received funding from the American Heart Association. Dr. Whitman disclosed that he is 50% owner of a patent for a medical device for GWBN, LLC and that he received funding from Cellphire/Avania as principal investigator for a national study. Dr. Arora received funding from Edwards LifeSciences and Avir Pharma. Dr. Grasselli received funding from Getinge, Fisher & Paykel, Draeger Medical, Merck Sharp and Dohme, Cook Medical, and GlaxoSmithKline. Dr. Usman received support for article research from the National Institutes of Health. Drs. Suen’s and Li Bassi’s institutions received funding from The Bill and Melinda Gates Foundation. Dr. Suen is funded by the Advance Queensland fellowship program, Queensland Government, Australia. Dr. Li Bassi’s institution received funding from Fisher & Paykel. Dr. Li Bassi is a recipient of the Biomedical international training research programme for excellent clinician-scientists (BITRECS) fellowship; the “BITRECS” project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 754550 and from the “La Caixa” Foundation (ID 100010434), under the agreement LCF/PR/GN18/50310006. Dr. Dalton received funding from extracorporeal membrane oxygenation concepts, entegrion, and hemocue. The remaining authors have disclosed that they do not have any potential conflicts of interest., (Copyright © 2023 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Society of Critical Care Medicine and Wolters Kluwer Health, Inc.)

Competing Interests: The authors have disclosed that they do not have any potential conflicts of interest.

Purpose of Review: We conducted a systematic literature review to summarize the available evidence regarding the incidence, risk factors, and clinical characteristics of ventilator-associated pneumonia (VAP) in patients undergoing mechanical ventilation because of acute respiratory distress syndrome secondary to SARS-CoV-2 infection (C-ARDS)., Recent Findings: Sixteen studies (6484 patients) were identified. Bacterial coinfection was uncommon at baseline (<15%) but a high proportion of patients developed positive bacterial cultures thereafter leading to a VAP diagnosis (range 21-64%, weighted average 50%). Diagnostic criteria varied between studies but most signs of VAP have substantial overlap with the signs of C-ARDS making it difficult to differentiate between bacterial colonization versus superinfection. Most episodes of VAP were associated with Gram-negative bacteria. Occasional cases were also attributed to herpes virus reactivations and pulmonary aspergillosis. Potential factors driving high VAP incidence rates include immunoparalysis, prolonged ventilation, exposure to immunosuppressants, understaffing, lapses in prevention processes, and overdiagnosis., Summary: Covid-19 patients who require mechanical ventilation for ARDS have a high risk (>50%) of developing VAP, most commonly because of Gram-negative bacteria. Further work is needed to elucidate the disease-specific risk factors for VAP, strategies for prevention, and how best to differentiate between bacterial colonization versus superinfection., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Extracorporeal membrane oxygenation (ECMO) bridge to lung transplantation (LuTX) exposes the patients to a high risk of perioperative bleeding secondary to systemic anticoagulation and coagulation factors deficiency. With this case series, we propose innovative "no-heparin" management of ECMO-bridge support during LuTX, based upon 1) control heparin resistance with antithrombin III in the preoperative period; 2) relying upon a fully functional, brand new heparinized ECMO circuit; 3) completely avoiding perioperative heparin; 4) hampering fibrinolysis with tranexamic acid; and 5) limiting venoarterial (VA) ECMO escalation, and the following need for full anticoagulation. Following the application of this new approach, we carried out three challenging clinical cases of bilateral ECMO-bridged LuTX effectively, with limited intraoperative blood requirement and no major postoperative bleeding or thromboembolic events. Of note, two of them had an extremely high risk for hemorrhage due to complete right lung anatomic derangement in case number 2 and surgical adhesion following first LuTX in case number 3, while for the case number 1, no blood products were administered during surgery. Despite the limited patient population, such an approach relies on a strong rationale and may be beneficial for managing ECMO bridging to LuTX. Prospective studies are necessary to confirm the validity of our strategy., Competing Interests: Disclosure: Dr. Pesenti received payment for lectures and service on speaker bureau from Maquet and Novalung; he received consulting honorarium from Maquet and Novalung. Dr. Grasselli received payment for lectures from Thermo Fisher and Pfizer Pharmaceuticals and travel-accommodation-congress registration support from Biotest (all these relationships are unrelated with the present work). The other authors have no conflicts of interest to report., (Copyright © ASAIO 2021.)

Viscoelastic coagulation monitor (VCM) is a portable device developed to evaluate the viscoelastic properties of whole blood activated by contact with glass. In this study, VCM was employed to analyze the viscoelastic profiles of 36 COVID-19 intensive care patients. Full anticoagulant dose heparin (unfractionated [UFH]; low molecular weight [LMWH]) was administrated to all patients. The association between VCM and laboratory parameters was retrospectively analyzed. The administration of UFH-influenced VCM parameters prolonging clotting time (CT) and clot formation time (CFT) and reducing angle (alpha) and amplitudes of the VCM tracings (A10, A20, and maximum clot firmness [MCF]) compared with LMWH therapy. A tendency toward hypercoagulation was observed by short CT and CFT in patients receiving LMWH. Clotting time was correlated with UFH dose (Spearman's rho = 0.48, p ≤ 0.001), and no correlation was found between CT and LMWH. All VCM tracings failed to show lysis at 30 and 45 minutes, indicating the absence of fibrinolysis. A10, A20, and MCF exhibited very-good to good diagnostic accuracy for detecting platelet count and fibrinogen above the upper reference limit of the laboratory. In conclusion, VCM provided reliable results in COVID-19 patients and was easy to perform with minimal training at the bedside., Competing Interests: Disclosure: Dr. Dalton is a consultant for Innovative ECMO Concepts. The other authors have no conflicts of interest to report., (Copyright © ASAIO 2020.)

Objectives: Supplementation of antithrombin might decrease the amount of heparin needed to achieve a given anticoagulation target during extracorporeal membrane oxygenation. However, exogenous antithrombin itself may increase the risk of bleeding. We conceived a study to evaluate the effect of antithrombin supplementation in adult patients requiring venovenous extracorporeal membrane oxygenation for respiratory failure on heparin dose, adequacy of anticoagulation, and safety., Design: Prospective randomized controlled trial., Setting: ICUs of two Italian referral extracorporeal membrane oxygenation centers., Patients: Adult patients requiring venovenous extracorporeal membrane oxygenation for severe respiratory failure and unfractionated heparin for systemic anticoagulation., Interventions: Before extracorporeal membrane oxygenation start, patients were randomized to either receive antithrombin concentrate to maintain a plasmatic level 80-120% (treatment) or not (control) during the extracorporeal membrane oxygenation course., Measurements and Main Results: The primary outcome was the total amount of heparin required to maintain activated partial thromboplastin time ratio 1.5-2. Secondary outcomes were anti-factor Xa, the incidence of hemorrhagic and thrombotic events, and the amount of blood products transfused. Twenty-four patients in the treatment group and 24 in the control group were included in the intention-to-treat analysis. Antithrombin was 109.5% (93.0-123.0%) in the treatment group and 84.0% (68.5-98.0%) in the control group (p = 0.001). Supplementation of antithrombin did not decrease heparin dose (13.5 international units/kg/hr [9.6-17.9 international units/kg/hr] vs 15.1 international units/kg/hr [10.7-18.3 international units/kg/hr] in the treatment and control group, respectively; p = 0.33) and anti-Factor Xa levels (0.4 international units/mL [0.3-0.5 international units/mL] vs 0.3 international units/mL [0.2-0.5 international units/mL] in the treatment group and control group respectively; p = 0.65). Bleeding, blood product transfusions, and thrombosis were not different in the two groups., Conclusions: Antithrombin supplementation may not decrease heparin requirement nor diminish the incidence of bleeding and/or thrombosis in adult patients on venovenous extracorporeal membrane oxygenation.

In patients undergoing extracorporeal membrane oxygenation (ECMO) for acute respiratory distress syndrome (ARDS), it is unknown which clinical physiologic variables should be monitored to follow the evolution of lung injury and extrapulmonary organ dysfunction and to differentiate patients according to their course. We analyzed the time-course of prospectively collected clinical physiologic variables in 83 consecutive ARDS patients undergoing ECMO at a single referral center. Selected variables-including ventilator settings, respiratory system compliance, intrapulmonary shunt, arterial blood gases, central hemodynamics, and sequential organ failure assessment (SOFA) score-were compared according to outcome at time-points corresponding to 0%, 25%, 50%, 75%, and 100% of the entire ECMO duration and daily during the first 7 days. A logistic regression analysis was performed to identify changes between ECMO start and end that independently predicted hospital mortality. Tidal volume, intrapulmonary shunt, arterial lactate, and SOFA score differentiated survivors and nonsurvivors early during the first 7 days and over the entire ECMO duration. Respiratory system compliance, PaO2/FiO2 ratio, arterial pH, and mean pulmonary arterial pressure showed distinct temporal course according to outcome over the entire ECMO duration. Lack of improvement of SOFA score independently predicted hospital mortality. In ARDS patients on ECMO, temporal trends of specific physiologic parameters differentiate survivors from non-survivors and could be used to monitor the evolution of lung injury. Progressive worsening of extrapulmonary organ dysfunction is associated with worse outcome.

Background: There is a lack of consensus on how to manage anticoagulation during veno-venous extracorporeal membrane oxygenation, including antithrombin monitoring and supplementation. The authors' aim was to determine current practice in a large number of extracorporeal membrane oxygenation centers around the world., Methods: This was an electronic survey disseminated in 2018 to directors and coordinators of extracorporeal membrane oxygenation centers as well as to extracorporeal membrane oxygenation experts. Participating centers were classified according to some covariates that may affect practice, including 2017 gross national income per capita, primary patient population, and annual extracorporeal membrane oxygenation patient volume., Results: The authors analyzed 273 unique responses from 50 countries. Systemic anticoagulation was routinely prescribed in 264 (96.7%) centers, with unfractionated heparin being the drug of choice in 255 (96.6%) of them. The preferred method to monitor anticoagulation was activated partial thromboplastin time in 114 (41.8%) centers, activated clotting time in 82 (30.0%) centers, and anti-factor Xa activity in 62 (22.7%) centers. Circulating antithrombin activity was routinely monitored in 133 (48.7%) centers. Antithrombin supplementation was routinely prescribed in 104 (38.1%) centers. At multivariable analyzes, routine antithrombin supplementation was associated with national income, being less likely in lower- than in higher-income countries (odds ratio, 0.099 [95% CI, 0.022 to 0.45]; P = 0.003); with primary patient population being more frequent in mixed (odds ratio, 2.73 [1.23 to 6.0]; P = 0.013) and pediatric-only centers (odds ratio, 6.3 [2.98 to 13.2]; P < 0.001) than in adult-only centers; but not with annual volume of extracorporeal membrane oxygenation cases, being similarly common in smaller and larger centers (odds ratio, 1.00 [0.48 to 2.08]; P = 0.997)., Conclusions: There is large practice variation among institutions regarding anticoagulation management and antithrombin supplementation during veno-venous extracorporeal membrane oxygenation. The paucity of prospective studies and differences across institutions based on national income and primary patient population may contribute to these findings.

The impact of antithrombin replacement during extracorporeal membrane oxygenation (ECMO) in adults remains unclear. This work comprises a survey, showing that antithrombin is routinely supplemented in many Italian ECMO-Centers, and a retrospective analysis on 66 adults treated with veno-venous ECMO and unfractionated heparin at our Institution. Twenty-four to 72 h after the beginning of ECMO, antithrombin activity was ≤70% in 47/66 subjects and activated partial thromboplastin time (aPTT) ratio was <1.5 in 20/66 subjects. Activated partial thromboplastin time ratio <1.5 was associated not with lower antithrombin activity (61 ± 17 vs. 63 ± 22%; p = 0.983) but with higher circulating level of C-reactive protein (23 ± 8 vs. 11 ± 9 mg/dl; p < 0.001). In 34 subjects who received antithrombin concentrate, antithrombin activity increased (from 54 ± 9 to 84 ± 13%; p < 0.001); the proportion of subjects with aPTT ratio ≥1.5 increased (from 21/34 [62%] to 31/34 [91%]; p = 0.004); heparin dosage remained constant (from 19 ± 7 to 19 ± 6 IU/kg/h; p = 0.543); and C-reactive protein decreased (from 17 ± 10 to 13 ± 9 mg/dl; p = 0.013). Among those with aPTT ratio <1.5, aPTT ratio remained <1.5 in 3 out of 13 subjects. Antithrombin is frequently supplemented during veno-venous ECMO although low antithrombin activity does not constantly impede, and antithrombin replacement does not constantly ensure, reaching the target aPTT ratio. Inflammation possibly affects the individual response to heparin.

Objective: Thrombocytopenia is the most common hemostatic disorder during sepsis and is associated with high mortality. We examined whether fibrinolytic changes precede incident thrombocytopenia and predict outcome in patients with severe sepsis., Design: Nested study from the multicenter, randomized, controlled trial on the efficacy of albumin replacement in severe sepsis or septic shock (the Albumin Italian Outcome Sepsis trial)., Setting: Forty ICUs in Italy., Patients: Three groups of patients were selected: 1) patients with platelet count less than or equal to 50 × 10/L at study entry (n = 85); 2) patients with baseline platelet count greater than or equal to 100 × 10/L who developed thrombocytopenia (≤ 50 × 10/L) within 28 days (n = 100); 3) patients with platelet count always more than or equal to 100 × 10/L (n = 95)., Interventions: Fibrinolytic variables, including fibrinolysis inhibitors and in vivo markers of plasmin generation, were measured on day 1., Measurements and Main Results: Patients with early thrombocytopenia (group 1) and those who developed it later (group 2) had similar illness severity and 90-day mortality, whereas patients without thrombocytopenia (group 3) had milder disease and lower mortality. Fibrinolysis was markedly (and similarly) depressed in groups 1 and 2 as compared with group 3. Major fibrinolytic changes included increased levels of plasminogen activator inhibitor 1 and extensive activation/consumption of thrombin activatable fibrinolysis inhibitor. Most fibrinolytic variables were significantly associated with mortality in univariate models. However, only thrombin activatable fibrinolysis inhibitor level and in vivo markers of fibrinolysis activation, namely plasmin-antiplasmin complex, and D-dimer, were independently associated with mortality after adjustment for Simplified Acute Physiology Score-II score, sex, and platelet count. Furthermore, the coexistence of impaired fibrinolysis and low platelets was associated with an even greater mortality., Conclusions: Impaired fibrinolysis, mainly driven by plasminogen activator inhibitor-1 increase and thrombin activatable fibrinolysis inhibitor activation, is an early manifestation of sepsis and may precede the development of thrombocytopenia. Thrombin activatable fibrinolysis inhibitor level, in particular, proved to be an independent predictor of mortality, which may improve risk stratification of patients with severe sepsis.

We evaluated the prevalence of a thromboelastography reaction time (R time) >90 min ("flat-line") reversible with heparinase during extracorporeal membrane oxygenation (ECMO). We evaluated the association between "flat-line" thromboelastography, other coagulation tests, and risk of bleeding during ECMO. Thirty-two consecutive patients on ECMO were included. Anticoagulation was provided by continuous infusion of unfractionated heparin to maintain an activated partial thromboplastin time (aPTT) ratio between 1.5 and 2.0. Activated clotting times (ACTs) thromboelastography without and with heparinase were measured. Occurrence of bleeding was recorded. Median heparin infusion rate was 16 (12-20) IU/kg/h, aPTT ratio was 1.67 (1.48-1.96), and ACT was 173 (161-184) sec. One hundred forty-five (46%) of 316 paired thromboelastography samples were "flat lines" all reversed with heparinase. Patients with "flat-line" thromboelastography received more heparin (p = 0.001) but had similar platelet count (p = 0.164) and fibrinogen level (p = 0.952) than those without. Activated partial thromboplastin time, ACT, and R time without heparinase weakly correlated between each other (Spearman correlation ≤0.36) with poor agreement (Cohen's κ ≤0.10). Major bleeding occurred in seven (22%) patients. Bleeding during ECMO was not predicted by any of the used test. In conclusion, adjusting heparin infusion to maintain aPTT ratio between 1.5 and 2.0 frequently resulted in "flat-line" thromboelastography.

On November 2009, the Italian health authorities set up a network of selected intensive care unit (ICU) centers (ECMOnet) to prepare for the treatment of the sickest patients of influenza A (H1N1) by means of extracorporeal membrane oxygenation (ECMO).To quickly and efficaciously train all the physicians working in the ICUs of the ECMOnet on ECMO use, we decided to take advantages of the opportunity provided by simulation technology.Simulation proved efficacious in providing adequate training and education to participants as confirmed by the survival results obtained by the group of ICUs of the ECMOnet.Our experience supports the use of simulation as a valuable alternative to animal laboratory sessions proposed by traditional ECMO training programs providing participants with cognitive, technical, and behavioral skills and allowing a proficient transfer of those skills to the real medical domain.

Objective: Continuous aspiration of subglottic secretions (CASS) is believed to lower the incidence of ventilator-associated pneumonia. Animal studies to establish safety and efficacy of CASS have not been conducted., Design: Prospective randomized animal study., Setting: Animal-research facility at the U.S. National Institutes of Health., Subjects: Twenty-two sheep., Interventions: Sheep were randomized into three groups. In group C (control), eight sheep were kept prone, intubated with a standard endotracheal tube (ETT), and mechanically ventilated for 72 hrs with head and ETT elevated at an angle of 30 degrees. In group CASS-HU (CASS, head up), seven sheep were managed as group C and intubated with a Hi-Lo Evac, Mallinckrodt ETT (CASS suction kept at < or =20 mm Hg). In group CASS-HD (CASS, head down), seven sheep were kept prone with CASS, and the ETT and trachea were horizontal to promote spontaneous drainage of mucus from the ETT., Measurements and Results: The lower respiratory tract in the CASS-HU group was heavily colonized in all seven sheep (median 4.6 x 10(9), range, 1.5 x 10(8) to 7.9 x 10(9) colony-forming units/g), with a reduction of lung bacterial colonization compared with the C group (p = .05). In group CASS-HD, the lower respiratory tract was not colonized in six of seven sheep. One sheep showed low levels of bacterial growth (median, 0; range, 0-2.2 x 10(5)). At autopsy, in all 14 sheep with CASS, we found tracheal mucosal injury of different degrees of severity at the level of the suction port of the ETT., Conclusions: In group CASS-HU, regardless of finding a marginal decrease of the bacterial colonization of the lower airways, there was pervasive trachea-bronchial-lung bacterial colonization. Second, there was minimal, or absent, bacterial colonization when the orientation of the CASS ETT was at, or just below, horizontal. Third, there was widespread injury to tracheal mucosa/submucosa from the use of CASS. Note that results of studies conducted in an animal model are always difficult to extrapolate to the clinical practice due to anatomical and functional differences.

Objective: To explore the role of the horizontal orientation of endotracheal tube and neck on bacterial colonization of the respiratory tract in anesthetized sheep on mechanical ventilation, without use of antibiotics., Design: Prospective animal study., Setting: National Institutes of Health research laboratory., Subjects: Anesthetized, paralyzed, and ventilated sheep., Interventions: Sheep were randomized into five groups and managed as follows: Group IS contained sheep that were not intubated and were immediately killed. Group HU4 contained six sheep that were mechanically ventilated for 4 hrs, with head and endotracheal tube elevated 30 degrees from horizontal. Group HU72 contained seven sheep that were prone, mechanically ventilated for 72 hrs, and managed the same as group HU4. Groups G and Gf each contained seven sheep that were prone on a lateral body rotation device, mechanically ventilated for 72 hrs, with neck and endotracheal tube horizontal. Group Gf received nasogastric enteral feeding., Measurements and Main Results: At the end of the study, sheep were examined postmortem, and a total of 11 tissue samples were taken from the trachea, the five lobar bronchi, and the five lobar parenchyma, for qualitative and quantitative culture. Group HU72 had significant decrease in Pao2/Fio2 and heavy bacterial colonization in all sheep. Groups G and Gf retained excellent lung function; lung bacterial colonization was no different from the IS group., Conclusions: The horizontal orientation of the endotracheal tube and neck, through lateral body rotation, showed no altered airway colonization and maintained excellent gas exchange and lung function in our animal model.

Background: Morbidly obese patients, during anesthesia and paralysis, experience more severe impairment of respiratory mechanics and gas exchange than normal subjects. The authors hypothesized that positive end-expiratory pressure (PEEP) induces different responses in normal subjects (n = 9; body mass index < 25 kg/m2) versus obese patients (n = 9; body mass index > 40 kg/m2)., Methods: The authors measured lung volumes (helium technique), the elastances of the respiratory system, lung, and chest wall, the pressure-volume curves (occlusion technique and esophageal balloon), and the intraabdominal pressure (intrabladder catheter) at PEEP 0 and 10 cm H2O in paralyzed, anesthetized postoperative patients in the intensive care unit or operating room after abdominal surgery., Results: At PEEP 0 cm H2O, obese patients had lower lung volume (0.59 +/- 0.17 vs. 2.15 +/- 0.58 l [mean +/- SD], P < 0.01); higher elastances of the respiratory system (26.8 +/- 4.2 vs. 16.4 +/- 3.6 cm H2O/l, P < 0.01), lung (17.4 +/- 4.5 vs. 10.3 +/- 3.2 cm H2O/l, P < 0.01), and chest wall (9.4 +/- 3.0 vs. 6.1 +/- 1.4 cm H2O/l, P < 0.01); and higher intraabdominal pressure (18.8 +/-7.8 vs. 9.0 +/- 2.4 cm H2O, P < 0.01) than normal subjects. The arterial oxygen tension was significantly lower (110 +/- 30 vs. 218 +/- 47 mmHg, P < 0.01; inspired oxygen fraction = 50%), and the arterial carbon dioxide tension significantly higher (37.8 +/- 6.8 vs. 28.4 +/- 3.1, P < 0.01) in obese patients compared with normal subjects. Increasing PEEP to 10 cm H2O significantly reduced elastances of the respiratory system, lung, and chest wall in obese patients but not in normal subjects. The pressure-volume curves were shifted upward and to the left in obese patients but were unchanged in normal subjects. The oxygenation increased with PEEP in obese patients (from 110 +/-30 to 130 +/- 28 mmHg, P < 0.01) but was unchanged in normal subjects. The oxygenation changes were significantly correlated with alveolar recruitment (r = 0.81, P < 0.01)., Conclusions: During anesthesia and paralysis, PEEP improves respiratory function in morbidly obese patients but not in normal subjects.