The aim of the study is to evaluate whether fluid responsiveness of the critically ill patient can be assessed by analysing the PEEP-induced hemodynamic effects to systolic blood pressure, pulse pressure, aortic blood flow, aortic time-velocity integral and left ventricular end diastolic area measured with transesophageal echocardiography (PEEP-test). The chances are compared to increase of CI after volume expansion (gold standard). In clinical practise, it would be especially relevant if PEEP-induced changes in arterial pressure variations could be used in evaluation of volume status and fluid responsiveness. However, as ECHO-derived variables are used in greater extent to guide the treatment with inappropriate evidence, the simultaneous registration of ECHO-derived hemodynamic measurements is essential in the study design.

Inclusion Criteria:• Written informed consent by patient or relative

• Time in ICU < 48 hours
• Septic shock
• Pulmonary artery catheter and radial arterial catheter
• Age 18 - 75 years
• Sinus rhythm
• Need for norepinephrine over 0.1 ug/kg/min but otherwise hemodynamically stable i.e no need to change the dose over the last 15min period before the study
• Mechanical ventilation with sedation
• Pwcp <18 mmHg

Exclusion Criteria:

• Contraindication to elevation of PEEP ( elevated intracranial pressure, pulmonary hypertension or other contraindication )
• Contraindication to fluid challenge
• Contraindication to TEE
• Previous heart failure, heart valve stenosis of insufficiency