Novel influenza A H1N1 testing was performed in each institution, or centralized in a reference laboratory when not available. A confirmed case was defined as an acute respiratory illness with laboratory-confirmed pandemic H1N1 virus infection identified by Abiraterone RT-PCR or viral culture [10]. Only confirmed cases were included in the current study.Community-acquired respiratory coinfection (CARC) was defined as any infection diagnosed within the first 2 days of hospitalization. Infections occurring later were considered nosocomial [11]. Patients who presented healthcare-associated pneumonia were excluded from the present study [12]. Patients were admitted to the ICU either because they were potential candidates for mechanical ventilation and/or because they were judged to be in an unstable condition requiring intensive medical or nursing care [13,14].

Oseltamivir was administered orally in accordance with CDC recommendations, and the regimen (150 mg per 24 hours or 300 mg per 24 hours) was chosen by the attending physician [15]. The ICU admission criteria and treatment decisions for all patients, including determination of the need for intubation, the dosage of RRT and the type of antibiotic and antiviral therapy administered were not standardized and were decided by the attending physician.The AKI stages in critically ill patients with H1N1 virus infection were diagnosed according to the glomerular filtration rate criteria of the current AKIN definitions [6]. Information in regard to urine output was not used in the present manuscript.

Diagnostic criteria for AKI were an abrupt (within 48 hours) reduction in kidney function, currently defined as an absolute increase in serum CK level of ��0.3 mg/dl, a percentage increase in serum CK level of ��50% (1.5-fold greater than baseline) or a reduction in urine output (documented oliguria of <0.5 ml/kg/hour for more than 6 hours) [6]. The severity of AKI was classified as stage I (serum CK increase of >150% to 200% (1.5- to twofold increase) or ��0.3 mg/dl), stage II (serum CK increase of >200% to 300% (more than two- to threefold)) and stage III (serum CK increase of >300% (more than threefold) or the need for RRT). Alternatively, stage III was defined by an increase of serum CK 0.5 mg/dl from baseline serum CK values of 4.0 mg/dl. The CK criteria describe changes in renal function without specifying the direction of change.

We performed an analysis of the maximum AKI severity stage reached. RRT in the course of AKI was always initiated when needed for the following indications: pulmonary edema, oliguria (defined as urine output <0.5 ml/kg body weight per hour for >6 hours), metabolic acidosis or hyperkalemia Brefeldin_A not responding to conventional treatment and uremia defined as urea nitrogen of >100 mg/dl.