Influence of fluid loading in patients at different stages of septic shock: a prospective study

Abstract

To explore the influence of fluid loading at different stages in patients with septic shock. A prospective study was conducted. Forty-two mechanically ventilated patients in septic shock were enrolled in the Department of Critical Care Medicine of the Fourth People's Hospital of Shenyang from March 2010 to March 2014. Fluid loading was performed at 0, 24, 48 and 72 hours after the diagnosis of septic shock. The hemodynamic parameters including cardiac output ( CO ), stroke volume ( SV ), and extravascular lung water index ( EVLWI ) were measured by pulse indicator continuous cardiac output ( PiCCO ), and arterial partial pressure ( PaO2 ) was determined. Positive responders were defined as SV increased by more than 15% after fluid loading. Increase of lung water was defined as EVLWI increased after fluid loading and its value was more than 7 mL/kg. Oxygenation descend was defined when oxygenation index ( PaO2/FiO2 ) lowered. Fluid responsiveness, extravascular lung water, and oxygenation were analyzed and recorded at different stages in patients with septic shock. Fluid loading test was conducted for a total of 168 times in 42 patients. Compared with those before fluid loading test, the heart rate ( HR ) was lowered, and mean arterial pressure ( MAP ), CO, and SV were increased after fluid loading at 0, 24, 48 hours ( all P<0.01),unchanged at 72 hours. EVLWI levels at all time points were increased including an increase of EVLWI less than 7 mL/kg at 0 hour and 24 hours, and higher than 7 mL/kg at 48 hours and 72 hours [ EVLWI ( mL/kg ) at 0 hour: 6.0±1.5 vs. 4.7±1.5, t = -4.183, P = 0.000; 24 hours: 6.5±1.5 vs. 5.6±1.3, t = -6.000, P = 0.000; 48 hours: 8.1±2.2 vs. 6.1±1.7, t = -7.246, P = 0.000; 72 hours: 9.0±2.4 vs. 6.2±1.5, t = -7.524, P = 0.000 ]. After fluid loading, PaO2/FiO2 was increased remarkably at 0 hour and 24 hours, unchanged at 48 hours, and decreased significantly at 72 hours [ PaO2/FiO2 ( mmHg, 1 mmHg = 0.133 kPa ) at 0 hour: 189.6±34.5 vs. 183.2±36.6, t = -3.644, P = 0.002; 24 hours: 194.6±35.7 vs. 190.7±37.5, t = -4.594, P = 0.000; 48 hours: 201.8±30.2 vs. 200.8±33.0, t = -0.793, P=0.437; 72 hours: 201.7±24.8 vs. 206.2±26.9, t = 2.243, P = 0.036 ]. The rate of positive response gradually decreased: 85.7%, 80.9%, 42.8%, 28.6% at 0, 24, 48, and 72 hours, the rate of lung water increased was gradually elevated: 9.8%, 14.3%, 42.8%, 61.9% at 0, 24, 48, and 72 hours, and there was an increase of rate of lowering oxygenation with elapse of time ( 9.5%, 11.9%, 19.0%, 33.3% at 0, 24, 48 and 72 hours ). Compared with 0 hour, the rate of positive response decreased and rate of lung water increased were increased from 48 hours on ( P<0.05 or P<0.01 ), and rate of lowering oxygenation was increased at 72 hours ( P<0.01 ). 48 to 72 hours might be the crucial period of occurrence of volume overload in patients with septic shock. Curtailing fluid infusion during this period might reduce the occurrence of pulmonary edema.