Thermodilution cardiac output measurement is a reliable method, but it is an invasive one. PiCCO device requires cannulation of central vein and peripheral artery. Impedance method requires only attachment of special electrodes. Non-invasive methods are less accurate. Aim of study is to assess accuracy and reliability of impedance method ( using NICCOMO device) in comparison of thermodilution method ( using PiCCO device) at different PEEP levels.

Echocardiography is performed prior to measurement to exclude patients with heart valve abnormalities.

Patients without spontaneous ventilation ( deeply unconscious, sedated or sedated and paralysed), ventilated with controlled mechanical ventilation mode with tidal volume 6-8 ml/ideal body weight, resulting in EtCO2 35-45 mmHg, with PiCCO catheters implemented have additionally NICCOMO device attached. Fraction of inspired oxygen (FiO2) is set to achieve saturation >96% at positive end expiratory pressure (PEEP) 0 cmH2O.

Measurement of cardiac output are performed on expiration at PEEP 0, 5, 10, 15 20 cmH2O and at optimal PEEP (obtained from P-V curve). Simultaneously CO value from impedance device is noted. Other haemodynamic parameters, calculated by both devices are also noted - stroke volume (SV), stroke volume variation (SVV), Cardiac index (CI), systemic vascular resistance (SVR), systemic vascular resistance index (SVRI).

Inclusion Criteria:

• critically ill patients
• patients on mechanical ventilation
• circulatory insufficiency (present or in the past) monitored with with PiCCO device

Exclusion Criteria:

• morbid obesity,
• short neck,
• severe pneumonia,
• inability to NICCOMO electrodes attachment,
• massive tissue oedema,
• non-sinus cardiac rhythm,
• tachycardia,
• low cardiac output,
• septic shock,
• heart valve pathologies,
• severe atherosclerosis,
• aortic prosthesis,
• severe hypertension,
• extremes of height and weight,
• intraaortic pump

patients treated in intensive therapy unit, mechanically ventilated, haemodynamics monitored with PiCCO technique