RESUMO
BACKGROUND: Maintenance of volume status and treatment of hypovolemia constitute an important component of anesthetic management. A Pulse oxymeter providing a continuous display of the pulse waveform offers a new method of estimating relative volume status during positive pressure ventilation. This study was undertaken to use the pulse wave variance of a plethysmographic signal measured from a pulse oximeter as a useful tool in the assessment of volume status. METHODS: Forty patients underwent general anesthesia with controlled positive pressure ventilation. After induction, the fluid infusion rate was 100 cc/hr until the dura was opened. During the operation, fluid losses were not replaced until hemodynamic variables were printed out. In addition to standard monitoring,the arterial pressure was monitored with a radial artery catheter. Systolic pressure variation (SPV) was defined as the maximum variation in peak systolic pressure during the respiratory cycle and measured in mmHg. Plethysmographic pulse wave variation (PWV) was defined as the maximum variation in the waveform peaks during the respiratory cycle and measured in millimeters from the printed output of the pulse oximeter. SPV and PWV were printed out right after induction and right before dura opening. In addition to SPV and PWV, other hemodynamic variables (HR, MAP, CVP) were obtained. RESULTS: Heart rate, SPV and PWV increased before the dura opening compared with those after induction. PWV correlated well with SPV after fluid losses CONCLUSIONS: A Pulse oximeter which is a standard monitor in anesthesia provides a useful, noninvasive and inexpensive adjunct to the more invasive estimators of volume status.