Many mini-invasive devices to monitor cardiac output (CO) have been introduced and among them the Pressure Recording Analytical Method (PRAM). The aim of this study is to assess the agreement of PRAM with the intermittent transpulmonary thermodilution (ThD) and continuous pulmonary ThD in measuring CO in hemodynamically unstable patients.

Hemodynamic monitoring is important in critically ill patients. It is often used to assess a cardiovascular derangements, to help diagnosing the causes and to monitor the response to therapy.

Pulmonary thermodilution (ThD) is still considered the gold standard reference method for cardiac output (CO) measurement [1]. Its invasiveness, however, often limits or delays its application [2, 3]. In the last decades new less invasive hemodynamic monitoring systems have been developed. The majority of such new devices allows for continuous monitoring of CO and other hemodynamic variables [4].

Among the various less invasive techniques, the PiCCO (Pulse-induced Contour Cardiac Output) relies on the concept of the "pulse contour methodology" for providing beat-to-beat CO assessment. This method needs transpulmonary ThD calibration. This is a well validated dilution technique [5]. Another minimally invasive system is the Pressure Recording Analytical Method (PRAM). Unlike other systems with pulse contour analysis, the PRAM does not need external or internal calibration factors since it analyzes the pressure waveform at a frequency of 1000 Hz and computes the patient's cardiovascular system impedance using a mathematical algorithm based on the physical theory of perturbations. It only requires a connection to a femoral or radial artery catheter for the acquisition and analysis of the arterial pressure traces [6]. This new method has been validated under different experimental and clinical settings [6-9]. Limited data are available under conditions of hemodynamic instability [10-12]. So far, its accuracy and reliability in assessing CO in hemodynamically unstable patients needs yet to be clarified.

Inclusion Criteria:

Hemodynamic instability in:

• septic shock
• pneumonia
• polytrauma
• chronic obstructive pulmonary disease
• heart failure
• post operative cardiosurgical patients

Exclusion Criteria:

• Atrial fibrillation
• Pacemaker or implantable cardiac defibrillator
• Aortic or mitral valve disease
• Intra-aortic balloon pump

hemodynamic instability