Effects of Phenylephrine on Cardiac Preload

The Dynamic Effects of Phenylephrine on Preload and Cardiac Output in Patients Under General Anaesthesia

In patients under general anesthesia, episodes of hypotension are often treated with phenylephrine. The effect of phenylephrine is conventionally attributed to afterload increase. The aim of the study is to describe the time course of the effects of phenylephrine on the cardiac preload and cardiac output, and to evaluate whether phenylephrine, as an exclusive alpha-mimetic, could be beneficial for preload optimisation.

In consecutive patients scheduled for laparoscopic sigmoidectomy, all hemodynamic and respiratory variables are recorded electronically for subsequent offline analysis. All patients are ventilated in volume control mode with a tidal volume of 8 ml/kg ideal body weight. During steady-state Target Controlled Infusion (TCI) propofol/remifentanil anesthesia, when the Mean Arterial Blood Pressure (MAP) dropped below 80% of the awake state for at least 5 minutes, a phenylephrine bolus of 2 μg/kg is administered. If necessary this is repeated, or a continuous administration of phenylephrine is started at a rate of 10-30 μg/kg/u. All patient manipulations during the procedure are electronically recorded and time stamped for subsequent off-line data analysis. The first episode in each patient where phenylephrine is administered and in a period of at least 10 minutes when minimal or absent patient manipulation occurred, the hemodynamic variables are analysed to describe the effects of phenylephrine administration on the dynamic preload parameters and macro-hemodynamics.

Inclusion Criteria: Adult necessity for arterial blood pressure monitoring necessity for central venous blood pressure monitoring Exclusion Criteria: unwilling or unable to grant written informed consent cardiac arrythmia contra-indication for phenylephrine contra-indications for atropine contra-indication for Total Intravenous Anesthesia