Compressibility in lattice Boltzmann on standard stencils: effects of deviation from reference temperature.

With growing interest in the simulation of compressible flows using the lattice Boltzmann (LB) method, a number of different approaches have been developed. These methods can be classified as pertaining to one of two major categories: (i) solvers relying on high-order stencils recovering the Navier-Stokes-Fourier equations, and (ii) approaches relying on classical first-neighbour stencils for the compressible Navier-Stokes equations coupled to an additional (LB-based or classical) solver for the energy balance equation. In most cases, the latter relies on a thermal Hermite expansion of the continuous equilibrium distribution function (EDF) to allow for compressibility. Even though recovering the correct equation of state at the Euler level, it has been observed that deviations of local flow temperature from the reference can result in instabilities and/or over-dissipation. The aim of the present study is to evaluate the stability domain of different EDFs, different collision models, with and without the correction terms for the third-order moments. The study is first based on a linear von Neumann analysis. The correction term for the space- and time-discretized equations is derived via a Chapman-Enskog analysis and further corroborated through spectral dispersion-dissipation curves. Finally, a number of numerical simulations are performed to illustrate the proposed theoretical study. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.

Decrease in pulse pressure and stroke volume variations after mini-fluid challenge accurately predicts fluid responsiveness†.

BACKGROUND: Dynamic indices, such as pulse pressure variation (PPV), are inaccurate predictors of fluid responsiveness in mechanically ventilated patients with low tidal volume. This study aimed to test whether changes in continuous cardiac index (CCI), PPV, and stroke volume variation (SVV) after a mini-fluid challenge (100 ml of fluid during 1 min) could predict fluid responsiveness in these patients. METHODS: We prospectively studied 49 critically ill, deeply sedated, and mechanically ventilated patients (tidal volume <8 ml kg(-1) of ideal body weight) without cardiac arrhythmias, in whom a fluid challenge was indicated because of circulatory failure. The CCI, SVV (PiCCO™; Pulsion), and PPV (MP70™; Philips) were measured before and after 100 ml of colloid infusion during 1 min, and then after the additional infusion of 400 ml during 14 min. Responders were defined as subjects with a ≥15% increase in cardiac index (transpulmonary thermodilution) after the full (500 ml) fluid challenge. Areas under the receiver operating characteristic curves (AUCs) and the grey zones were determined for changes in CCI (ΔCCI100), SVV (ΔSVV100), and PPV (ΔPPV100) after 100 ml fluid challenge. RESULTS: Twenty-two subjects were responders. The ΔCCI100 predicted fluid responsiveness with an AUC of 0.78. The grey zone was large and included 67% of subjects. The ΔSVV100 and ΔPPV100 predicted fluid responsiveness with AUCs of 0.91 and 0.92, respectively. Grey zones were small, including ≤12% of subjects for both indices. CONCLUSIONS: The ΔSVV100 and ΔPPV100 predict fluid responsiveness accurately and better than ΔCCI100 (PiCCO™; Pulsion) in patients with circulatory failure and ventilated with low volumes.

Theoretical and numerical analysis of the lattice kinetic scheme for complex-flow simulations.

The lattice kinetic scheme (LKS) is a modified version of the classical single relaxation time lattice Boltzmann method. Although used for many applications, especially when large variations in viscosity are involved, a thorough analysis of the scheme has not been provided yet. In the context of this work, the macroscopic behavior of this scheme is evaluated through the Chapman-Enskog analysis. It is shown that the additional degree of freedom provided in the scheme allows for an independent control of higher-order moments. These results are further corroborated by numerical simulations. The behavior of this numerical scheme is studied for selected external and internal flows to clarify the effect of the free parameter on the different moments of the distribution function. It is shown that it is more stable than SRT (single relaxation time) when confronted to fully periodic under-resolved simulations (especially for λ≈1). It can also help minimize the error coming from the viscosity-dependence of the wall position when combined with the bounce-back approach; although still present, viscosity-dependence of the wall position is reduced. Furthermore, as shown through the multiscale analysis, specific choices of the free parameter can cancel out the leading-order error. Overall, the LKS is shown to be a useful and efficient alternative to the SRT method for simulating numerically complex flows.

Stability of the lattice kinetic scheme and choice of the free relaxation parameter.

The lattice kinetic scheme (LKS), a modified version of the classical single relaxation time (SRT) lattice Boltzmann method, was initially developed as a suitable numerical approach for non-Newtonian flow simulations and a way to reduce memory consumption of the original SRT approach. The better performances observed for non-Newtonian flows are mainly due to the additional degree of freedom allowing an independent control over the relaxation of higher-order moments, independently from the fluid viscosity. Although widely applied to fluid flow simulations, no theoretical analysis of LKS has been performed. The present work focuses on a systematic von Neumann analysis of the linearized collision operator. Thanks to this analysis, the effects of the modified collision operator on the stability domain and spectral behavior of the scheme are clarified. Results obtained in this study show that correct choices of the "second relaxation coefficient" lead, to a certain extent, to a more consistent dispersion and dissipation for large values of the first relaxation coefficient. Furthermore, appropriate values of this parameter can lead to a larger linear stability domain. At moderate and low values of viscosity, larger values of the free parameter are observed to increase dissipation of kinetic modes, while leaving the acoustic modes untouched and having a less pronounced effect on the convective mode. This increased dissipation leads in general to less pronounced sources of nonlinear instability, thus improving the stability of the LKS.

Extensive analysis of the lattice Boltzmann method on shifted stencils.

Standard lattice Boltzmann methods (LBMs) are based on a symmetric discretization of the phase space, which amounts to study the evolution of particle distribution functions (PDFs) in a reference frame at rest. This choice induces a number of limitations when the simulated flow speed gets closer to the sound speed, such as velocity-dependent transport coefficients. The latter issue is usually referred to as a Galilean invariance defect. To restore the Galilean invariance of LBMs, it was proposed to study the evolution of PDFs in a comoving reference frame by relying on asymmetric shifted lattices [N. Frapolli, S. S. Chikatamarla, and I. V. Karlin, Phys. Rev. Lett. 117, 010604 (2016)].PRLTAO0031-900710.1103/PhysRevLett.117.010604 From the numerical viewpoint, this corresponds to overcoming the rather restrictive Courant-Friedrichs-Lewy conditions on standard LBMs and modeling compressible flows while keeping memory consumption and processing costs to a minimum (therefore using the standard first-neighbor stencils). In the present work systematic physical error evaluations and stability analyses are conducted for different discrete equilibrium distribution functions (EDFs) and collision models. Thanks to them, it is possible to (1) better understand the effect of this solution on both physics and stability, (2) assess its viability as a way to extend the validity range of LBMs, and (3) quantify the importance of the reference state as compared to other parameters such as the equilibrium state and equilibration path. The results clearly show that, in theory, the concept of shifted lattices allows the scheme to deal with arbitrarily high values of the nondimensional velocity. Furthermore, just like the zero-Mach flow for the standard stencils, it is observed that setting the shift velocity to the fluid velocity results in optimal physical and numerical properties. In addition, a detailed analysis of the obtained results shows that the properties of different collision models and EDFs remain unchanged under the shift of stencil. In other words, by introducing a velocity shift in the stencil, the optimal operating point, in terms of physics and numerics, will also be shifted by the same vector regardless of the EDF or collision model considered. Eventually, while limited to the D2Q9 stencil with the nine possible first-neighbor shifts, the present study and corresponding conclusions can be extended to other stencils and velocity shifts in a straightforward manner.

The obesity supine death syndrome (OSDS).

The obesity supine death syndrome refers to a catastrophic cascade of cardiorespiratory complications resulting from the supine positioning of a morbidly obese subject which can ultimately lead to death. It was first described in 1977 in two massively obese patients who were forced to lie down for medical procedures. But surprisingly, despite the current worldwide epidemic of obesity, very few cases have been reported yet. It can be assumed that the syndrome is poorly recognized in clinical practice and may participate in the high rate of unexplained death in morbidly obese patients. Based on the previously published cases and on those we met, this review aims at helping clinicians to early detect at-risk patients, to correctly diagnose this dramatic syndrome and to understand the underlying pathophysiology. More importantly, the main objective is to convince the attending clinicians that they have to do everything in their power to prevent obesity supine death syndrome occurrence by maintaining morbidly obese patients in the sitting or upright position whenever possible. When the syndrome unfortunately occurs, the best therapeutic approach is based on the immediate return to sitting position.

A novel type of semi-active jet turbulence grid.

This article describes a novel approach to generate increased turbulence levels in an incoming flow. It relies on a cost-effective and robust semi-active jet grid, equipped with flexible tubes as moving elements attached onto tube connections placed at the intersections of a fixed, regular grid. For the present study, these flexible tubes are oriented in counter-flow direction in a wind tunnel. Tube motion is governed by multiple interactions between the main flow and the jets exiting the tubes, resulting in chaotic velocity fluctuations and high turbulence intensities in the test section. After describing the structure of the turbulence generator, the turbulent properties of the airflow downstream of the grid in both passive and active modes are measured by hot-wire anemometry and compared with one another. When activating the turbulence generator, turbulence intensity, turbulent kinetic energy, and the Taylor Reynolds number are noticeably increased in comparison with the passive mode (corresponding to simple grid turbulence). Furthermore, the inertial subrange of the turbulent energy spectrum becomes wider and closely follows Kolmogorov's -5/3 law. These results show that the semi-active grid, in contrast to passive systems, is capable of producing high turbulence levels, even at low incoming flow velocity. Compared to alternatives based on actuators driven by servo-motors, the production and operation costs of the semi-active grid are very moderate and its robustness is much higher.

Neuodevelopmental outcomes for children transplanted under the age of 3 years.

UNLABELLED: Our previous investigations on neurodevelopmental outcomes for intestinal transplanted infants revealed that while some children were able to achieve a normal developmental outcomes, most children suffered from significant motor delays and several experienced severe cognitive delays. In our current investigation, we were especially interested in children who are transplanted before the age of 3 years because the impact of the chronic illness and nutrition impairment on the infant's developing brain may be more severe than those children who receive a liver transplant. METHODS: We evaluated 34 infants using the Bayley Scales of Infant Development. Twenty-seven children received a liver/intestine or multivisceral transplant and seven received a liver transplant. RESULTS: Comparison of the two groups revealed that children receiving an intestine/multivisceral transplant have much poorer outcomes. Seventy-four percent of these children were significantly delayed mentally compared to only 57.14% of the liver transplant infants. Furthermore, 42.86% of the liver-transplanted infants were actually functioning in the normal range posttransplant. The intestinal/multivisceral transplant infants' motor development shows the most striking difference, with 96.3% being severely delayed as compared to liver transplant infants in whom only 71% experienced serious delays. The neurodevelopmental impact of organ failure and transplant before the age of 3 years may depending on the type of organ transplant. Our study found that it may be more likely to expect a good outcome for liver transplant patients than for intestinal and multivisceral transplanted infants. This difference maybe due to the overall severity of the disease and the possible impact of nutritional deficits early in infancy.

Neurodevelopmental outcomes of infant multivisceral transplant recipients: a longitudinal study.

UNLABELLED: This longitudinal investigation compares cognitive and physical capabilities of transplant recipients, both before and after receiving an intestinal transplant. METHODS: Using the Bayley Scales of Infant Development, we conducted pretransplant and posttransplant assessments on nine children (4 males, 5 females) who received either an isolated intestine, combined intestine and liver, or multivisceral transplants, with a mean age at transplant of 18 months (range 8-29) and a mean time posttransplant of 2 months (range 1-4 months). RESULTS: Scores on the Mental Developmental Index reflected that a majority (55.6%) of patients who scored in the significantly delayed range prior to transplant remained in the significantly delayed classification after receiving a transplant. In addition, 33.3% showed a decrease in their mental classification; either from "mildly delayed" to "significantly delayed" or from "within normal limits" to "mildly delayed". Results on the Motor Developmental Index demonstrated that 78% of recipients had significant delays both before and after receiving a transplant, while 11.1% fell one standard deviation after transplantation. We found that the majority of children who experience developmental delays prior to transplant are still experiencing delays when they are discharged from inpatient care. In addition, those children receiving multivisceral transplantations, as opposed to an isolated bowel, may be at a much greater risk of developing and retaining both cognitive and physical delays. Early neurodevelopmental evaluations of these patients is essential for early parental education and compliance with early intervention services to maximize potential recovery and ability to obtain normal development.

Fluid-Structure Simulations of a Ruptured Intracranial Aneurysm: Constant versus Patient-Specific Wall Thickness.

Computational Fluid Dynamics is intensively used to deepen the understanding of aneurysm growth and rupture in order to support physicians during therapy planning. However, numerous studies considering only the hemodynamics within the vessel lumen found no satisfactory criteria for rupture risk assessment. To improve available simulation models, the rigid vessel wall assumption has been discarded in this work and patient-specific wall thickness is considered within the simulation. For this purpose, a ruptured intracranial aneurysm was prepared ex vivo, followed by the acquisition of local wall thickness using µCT. The segmented inner and outer vessel surfaces served as solid domain for the fluid-structure interaction (FSI) simulation. To compare wall stress distributions within the aneurysm wall and at the rupture site, FSI computations are repeated in a virtual model using a constant wall thickness approach. Although the wall stresses obtained by the two approaches-when averaged over the complete aneurysm sac-are in very good agreement, strong differences occur in their distribution. Accounting for the real wall thickness distribution, the rupture site exhibits much higher stress values compared to the configuration with constant wall thickness. The study reveals the importance of geometry reconstruction and accurate description of wall thickness in FSI simulations.

Multivariate analysis of prognostic factors in acute myeloid leukemia: value of clonogenic leukemic cell properties.

The initial clinical and biological parameters, including clonogenic leukemic cell (CFU-L) assay, were reviewed for their prognostic significance in a cohort of 188 adult patients with newly diagnosed untreated acute myeloid leukemia (AML). Almost all patients received induction therapy with daunorubicin (DNR) and cytarabine (Ara-C) according to the European Organization for Research and Treatment of Cancer (EORTC) AML 5 to AML 9 trials. Bone marrow samples from 116 representative patients were obtained for CFU-L assay with an efficiency percentage of 89.6%; 76 patients had a measurement of the CFU-L self-renewal capacity (second plating efficiency [PE2]) and 91 patients had CFU-L inhibition test after exposure to DNR and/or Ara-C. The prognostic significance of parameters such as age, hematological antecedent, WBC count, liver enlargement, and Auer rods is confirmed in the present study. Moreover, high platelet and polymorphonuclear counts appeared to be related to resistance to induction course. However, through multivariate analysis, CFU-L sensitivity to drugs and self-renewal capacity appeared to be major independent prognostic factors in AML. A low CFU-L inhibition in the presence of the DNR and Ara-C combination correlates with a poorer complete remission (CR) rate, but not with CR duration. Patients with the lower PE2 values experienced both higher CR rate and longer CR duration. The practical interest of CFU-L study remains to be defined but, at least, PE2 measurement could be considered in the future as a major variable in determining therapeutic aggressiveness.

Prognostic value of clonogenic assay for induction and duration of complete remission in acute myelogenous leukemia.

The validity of an in vitro clonogenic drug sensitivity assay to predict the induction and the duration of complete remission was evaluated in a group of 81 patients with acute myelogenous leukemia treated with chemotherapy including an anthracycline drug (daunorubicin or adriamycin) and cytosine arabinoside (Ara-C). The inhibition of bone marrow clonogenic leukemic cells by in vitro exposure to anthracyclines 10(-5) and 10(-6) M, Ara-C 10(-5) M, and daunorubicin 10(-6) M + Ara-C 10(-7) M was significantly correlated with the achievement of a complete remission, but not with the duration of remission. A high second plating efficiency was correlated with short duration of complete remission, reflecting the poor prognosis of a high self-renewal capacity.

In vitro sensitivity of normal and leukemic myeloid clonogenic cells to hyperthermia: absence of selective effect.

The in vitro heat sensitivity of myeloid clonogenic cells was tested in 22 normal marrows (granulo-monocytic progenitors) and in 40 marrows of patients with acute myelogenous leukemia (leukemic progenitors). Cells were treated for 1 h at 42 degrees, 43 degrees, 44 degrees, or 45 degrees C prior to plating. A temperature-dependent inhibition of growth was seen without a selective effect on the two kinds of progenitors. Because these two kinds of progenitors have the same heat sensitivity, hyperthermia should not be used alone as a technique for in vitro depletion of residual myeloid leukemic cells.

In vitro effect of P-glycoprotein (P-gp) modulators on drug sensitivity of leukemic progenitors (CFU-L) in acute myelogenous leukemia (AML).

Cyclosporine A (CyA), a potent reversant of multidrug resistance (mdr), was studied for its effects on the sensitivity of leukemic progenitors (leukemia colony-forming units, CFU-L) to daunorubicin (DNR) and mitoxantrone. CyA was first compared to verapamil and cefoperazone for reversion of mdr in the mdr1+ cell line K562/DOX. A dramatic increase of sensitivity to 10(-6) M DNR was noted with CyA (0.5 and 1 microgram/ml) and verapamil (1 and 5 micrograms/ml), but not for cefoperazone (0.3 and 0.6 mg/ml). The sensitivity of K562/DOX to 10(-6) M mitoxantrone was also slightly enhanced by CyA. The change in CFU-L drug sensitivity in the presence of CyA was then tested in 12 relapsing/resisting patients and in 3 untreated patients with acute myelogenous leukemia (AML). No change in CFU-L sensitivity to DNR was noted, despite the presence of a subset of P-glycoprotein positive (P-gp+) cells in three out of the ten evaluable cases. Among the six evaluable cases tested with mitoxantrone and CyA, an increase of 50% in CFU-L sensitivity to mitoxantrone was noted in one (of three) P-gp+ patient. These data suggest that the CFU-L in AML rarely expressed the P-gp and that other mechanisms of drug resistance could be involved in AML.

Comparison of in vitro inhibition of etoposide (VP16) on leukemic and normal myeloid, erythroid clonogenic cells.

We have compared in various clonogenic assays the in vitro sensitivity to etoposide (VP16) of 1) human leukemic precursors (leukemia colony-forming units; L-CFU), 2) normal erythroid progenitors (erythroid burst-forming units; BFU-E, and 3) normal committed myeloid progenitors (granulocyte-macrophage colony-forming units; CFU-GM and more primitive hemopoietic precursors (PPC) that adhere to cultured marrow stromal cells. Bone marrow samples were obtained from 15 normal subjects and 16 leukemic patients: 9 in the acute phase of acute nonlymphoblastic leukemia (ANLL) and 7 in complete remission. VP16 was tested at concentrations ranging from 10(-8) to 10(-3) M. The median recoveries at 10(-3) M VP16 were respectively 0%, 0.5%, 0%, and 0% for leukemic progenitors, CFU-GM from leukemic patients in complete remission, normal CFU-GM, and BFU-E, and 23% for PPC. This indicates that CFU-GM, BFU-E, and L-CFU are highly sensitive to VP16, whereas PPC, more primitive myeloid precursors, are spared. These results suggest that VP16 may be used as an "ex vivo" purging agent for autologous bone marrow.

Prognostic value of in vitro uptake and retention of cytosine arabinoside in acute myelogenous leukemia.

In vitro uptake and retention of 3H-cytosine arabinoside (ara-C) was studied in 68 acute myelogenous leukemia (AML) patients (ten were studied twice) treated with a regimen containing conventional (54 patients) or high doses (24) of ara-C. Drug uptake and retention after four hours were measured following 30 minutes exposure to 1 and 50 micrograms/mL of ara-C. A good correlation was observed between high uptake in the acid soluble (AS) fraction (P less than .01), or high retention in the acid insoluble (Al) fraction (P less than .03) of 1 microgram, but not 50 micrograms, of the drug and obtainment of complete remission (CR) in patients treated with conventional doses of ara-C. Patients with a high percentage of ara-C retained in the AS fraction (greater than 26%) have a significantly longer CR duration than patients with a lower level of retention (P less than .02). In 17 patients who achieved a CR in spite of a low tritiated ara-C uptake, the clonogenic leukemic (CFU-L) cells were especially sensitive to drugs (15 of 17 v three of 11 among resisting patients).

PHA-induced blast colonies and kinetic parameters in acute myeloid leukemia.

The in vitro leukemic colony-forming ability of 30 acute myeloid leukemias tested after PHA stimulation was analyzed by comparing the CFU-GM growth pattern, the myeloblast [3H]thymidine index and the response to treatment. PHA-induced leukemic colonies were obtained in 15 out of 30 cases. No correlation was found between the FAB classification, the CFU-GM growth pattern and the PHA-induced colony growth. A significant correlation was observed between PHA-induced colony growth and [3H]thymidine labeling index (p less than 0.001). A correction was also noted between the presence of leukemic growth and the failure of the induction treatment (p less than 0.02). The proliferation of the clonogenic blastic subpopulation selected by this technique seems to be linked to a poor prognosis.

DNA ligases in human leukemia.

Following partial purification on sucrose gradient and/or phosphocellulose chromatography, DNA ligase was tested in peripheral white blood and bone marrow cells of nearly 100 patients with various kinds of leukemias, mainly acute leukemias. Terminal deoxynucleotidyl transferase (TdT) was tested in parallel. DNA ligase of acute myeloblastic leukemia (AML) was extracted with the same sedimentation coefficient (5.5S) on sucrose gradient, and eluted with the same KCl molarity (0.3 M) than the one extracted from normal lymphocytes. Acute lymphoblastic leukemias (ALL) were characterized by no detectable DNA ligase activity--in most T or non T-non B-ALL, or a low activity in pre-B and B (Burkitt type) ALL, with levels similar to the one observed in chronic lymphocytic leukemia (CLL). An inverse relationship was observed between DNA-ligase and TdT in ALL, ligase being undetectable in cells positive for TdT and being present in some T or non T-non B, and in all pre-B and B-ALL negative for TdT. AML and chronic myelocytic leukemia (CML) were characterized by a markedly higher DNA-ligase activity. This activity was higher in the most differentiated subtypes--M2, M3 and M4 subtypes of FAB classification--and in CML. Moreover a high degree of correlation was observed in AML between the DNA ligase activity and the S phase fraction measured by 3 H-thymidine autoradiography or flow cytophotometry on the total cell sampling. Besides their clinical interest, these results are discussed in relation with the role of DNA-ligase in DNA replication and repair.

Simplified prediction rule for prognosis of patients with severe community-acquired pneumonia in ICUs.

STUDY OBJECTIVES: To develop a simplified prognostic prediction rule for patients admitted to ICUs for severe community-acquired pneumonia (CAP). SETTING: Six ICUs in the north of France. PATIENTS: Five hundred five patients admitted to ICUs over a 9-year period (from 1987 to 1995) for severe CAP. INTERVENTIONS: Retrospective prognosis analysis and multivariate analysis using a credit scoring technique. MEASUREMENTS: The primary outcome measure was ICU mortality. RESULTS: Among the 505 patients, 472 were eligible for the prognosis study. The ICU mortality rate was 22.9%. Multivariate analysis identified, on the basis of the patient's medical history and initial examination on ICU admission, six independent predictors of mortality: age > or = 40 years, anticipated death within 5 years, nonaspiration pneumonia, chest radiograph involvement > 1 lobe, acute respiratory failure requiring mechanical ventilation, and septic shock. An initial risk score based on these factors classified patients into three risk classes of increasing mortality: 4% in class I, 25% in class II, and 60% in class III. Multivariate analysis of events occurring during ICU stay identified three independent predictors of mortality: hospital-acquired lower respiratory tract superinfections, nonspecific CAP-related complications, and sepsis-related complications. An adjustment risk score based on these factors was essential to accurately predict the final outcome of patients in the initial risk class II. CONCLUSIONS: As an aid to clinicians in stratifying the prognosis of patients with severe CAP, the simplified prediction rule used in this study could be useful for therapeutic decisions and appropriate care.

Community-acquired pneumonia in the intensive care unit: epidemiological and prognosis data in older people.

OBJECTIVES: To compare epidemiological data, etiology, and prognosis of severe community-acquired pneumonia (CAP) in the intensive care unit (ICU) according to age (< or > or = 65 years) and to determine prognostic factors of CAP in older people. DESIGN: A retrospective (1987-1992) and prospective (1993-95) multicenter study. SETTING: Six ICUs in the north of France. PATIENTS: Five hundred five patients admitted to an ICU for severe CAP. MEASUREMENTS: Patient characteristics were compared with regard to age. Prognosis of CAP in older patients was studied by stepwise discriminant analysis. RESULTS: Two hundred seventy-eight patients (55%) were aged 65 years or older. Comparison of epidemiological data between older and younger patients revealed a higher prevalence of women (38% vs 29%), more severe underlying comorbidities (anticipated death within 5 years: 59% vs 26%), and more frequent chronic respiratory insufficiency (48% vs 33%) in the older patients. In this study group, 224 organisms were isolated from 172 patients (62%); those identified most frequently were Gram-negative bacilli (34%), S. pneumoniae (32%), and Staphylococcus sp. (19%). Compared with younger patients, no significant differences in bacteriological data were observed. However, crude and attributable mortality rates were significantly higher in the older patients (33% vs 21% and 30% vs 19%, respectively). Prognosis analysis identified four independent predictors of mortality in the older patients: initial septic shock (relative risk (RR) = 3), sepsis-related complications (RR = 4.3), hospital-acquired lower respiratory tract superinfections (RR = 2), and nonspecific pneumonia-related complications (RR = 2.8). CONCLUSION: The bacterial etiology provides some approaches to empirical therapy for older patients with severe community-acquired pneumonia. In addition, the inappropriateness of withholding intensive care for reasons of age alone is emphasized.