Pulse pressure variation shows a direct linear correlation with tidal volume in anesthetized healthy patients

Abstract

Background: The settings of mechanical ventilation, like tidal volume (VT), occasionally need to be adjusted in the process of anesthesia for some special reasons. The aim of this study was therefore to assess the relationship between pulse pressure variations (PPVs) in different settings of VT in anesthetized healthy patients under mechanical ventilation.

Methods: Sixty nine ASA I-II patients scheduled for gastrointestinal surgery under general anesthesia were included in this prospective study. All the patients were ventilated at a VT of 6, 8 or 10 ml/kg (predicted body weight) with no positive end expiratory pressure (PEEP) in a random order after intubation. PPV, mean arterial blood pressure, and other hemodynamic and respiratory parameters were recorded in each VT setting respectively after Partial Pressure of End-Tidal Expiration Carbon Dioxide (PetCO2) maintained between 30 mmHg and 40 mmHg by changing Respiratory Rate (RR) before incision.

Results: The values of PPV at different settings of VT showed a tight correlation between each other (6 vs. 8 ml/kg: r = 0.97, P < 0.0001; 6 vs.10 ml/kg: r = 0.95, P < 0.0001; 8 vs. 10 ml/kg: r = 0.98, P < 0.0001, respectively).

Conclusion: There is a direct linear correlation between PPVs at different tidal volumes in anesthetized ASA I-II patients. PPV in any of the 3 VT settings (6, 8 or 10 ml/kg) can deduce that in any other 2 settings. Further studies are needed to explore the effect of intraoperative confounders for this knowledge to be clinically applied.

Trial registration: NCT01950949 , www.clinicaltrials.gov , July 26, 2013.

Keywords: Blood pressure; Mechanical ventilation; Pulse pressure variation; Tidal volume; Volume.

Fig. 1

Respiratory parameters in three setting of VT. ^# - significant difference 8 ml/kg vs. 6 ml/kg group; ^$ - significant difference 10 ml/kg vs. 8 ml/kg group; ^* - significant difference 10 ml/kg vs. 6 ml/kg group RR: respiratory rate; Ppeak: peak airway pressure; Pmean: mean airway pressure; PetCO2: End-tidal carbon dioxide partial pressure

Fig. 2

Hemodynamic parameters in three setting of VT. ^# - significant difference 8 ml/kg vs. 6 ml/kg group; ^$ - significant difference 10 ml/kg vs. 8 ml/kg group; ^* - significant difference 10 ml/kg vs. 6 ml/kg group. HR: heart rate; MAP: mean arterial pressure; PPV: pulse pressure variation

Fig. 3

Linear relationship between PPVs under the VT of 6, 8 and 10 ml/kg before volume expansion. PPV6: pulse pressure variation at a VT of 6 ml/kg; PPV8: pulse pressure variation at a VT of 8 ml/kg; PPV10: pulse pressure variation at a VT of 10 ml/kg. Equation (a) represented the linear correlation between PPV6 and PPV 8. Equation (b) represented the linear correlation between PPV8 and PPV 10. Equation (c) represented the linear correlation between PPV6 and PPV10

Fig. 4

Linear relationship between PPVs under the VT of 6, 8 and 10 ml/kg after volume expansion. PPV6: pulse pressure variation at a VT of 6 ml/kg; PPV8: pulse pressure variation at a VT of 8 ml/kg; PPV10: pulse pressure variation at a VT of 10 ml/kg. Equation (a) represented the linear correlation between PPV6 and PPV 8. Equation (b) represented the linear correlation between PPV6 and PPV 10. Equation (c) represented the linear correlation between PPV8 and PPV10.

Fig. 5

Relationship between PPVs in different VT settings. PPV6, pulse pressure variation at a VT of 6 ml/kg; PPV8, pulse pressure variation at a VT of 8 ml/kg; PPV10, pulse pressure variation at a VT of 10 ml/kg