[The influence of positive end-expiratory pressure on central venous pressure in patients with severe craniocerebral injury].

Objective To observe the impact of positive end-expiratory pressure ( PEEP) on central venous pressure (CVP) in mechanically ventilated patients with severe craniocerebral injury.Methods A prospective,interventional,self-control study was conducted.Thirty severe craniocerebral injury patients with central respiratory failure were enrolled.The changes in CVP,mean arterial pressure (MAP),heart rate (HR) and pulse oxygen saturation (SpO2) were monitored at different PEEP levels (0,3,6,9,12,15 cm H2O; 1 cm H2O=0.098 kPa)during mechanical ventilation and after weaning of mechanical ventilation.The influences of PEEP and its discontinuance on haemodynamics and oxygenation were analyzed.Results The values of CVP (cm H2O) were increased when PEEP increased (from 7.9 ± 3.1 to 13.1 ± 3.7 ),a linear correlation was found (R=0.509,P=0.000),and linear regression equation was CVP (cm H2O)=7.774 + 0.368 × PEEP (cm H2O); CVP was elevated about 0.368 cm H2O when PEEP increased 1 cm H2O.CVP values significantly decreased during discontinuance of mechanical ventilation,as compared to those measured at different PEEP levels during mechanical ventilation ( F=24.429,P=0.000).The values of MAP,H R and SpO2 showed no significant change with increase of PEEP levels [MAP (mm Hg,1 mm Hg=0.133 kPa):from 81.6 ± 10.4 to 85.6 ± 10.6; HR (heats per minute):from 79.9 ± 13.5 to 88.1 ± 15.4;SpO2:from 0.968 ± 0.036 to 0.975 ± 0.033,all P＞0.05]in mechanically ventilated patients,but discontinuance of mechanical ventilation could significantly increase the levels of MAP and HR ( 95.3 ± 8.4 and 94.9 ± 10.3.respectively )and lower SpO2 levels (0.928±0.036,all P=0.0(00).Conclusions CVP values were overestimated during an increase in PEEP in mechanically ventilated patients with severe craniocerebral injury.CVP was increased about 0.368 cm H2O following an increase of PEEP of 1 cm H2O,whereas the values of MAP,HR and SpO2 showed no significant change with increase in PEEP levels.This study could offer a theoretical base in the correct assessment of CVP values at different PEEP levels without discontinuation of mechanical ventilation. Key words: Positive end-expiratory pressure; Central venous pressure; Severe craniocerebral injury; Mechanical ventilation