Experimental Study Of Continuous Blood Purification In The Traumatic Pulmonary Fat Embolism

Fat embolism syndrome(FES) is a serious complication of orthopedic surgery and trauma . Classically, it causes pulmonary fat embolism (PFE). It is reported systemic inflammatory response syndrome may be occurred in FES and the therapy of continuous blood purification(CBP) may be effective on it.Objective: To investigate the changes of hemodynamics, cytokines and arterial blood gases in pulmonary fat embolism caused by femoral intramedullary operation, as well as the influence of continuous blood purification on it.Methods: Measurements were made in 14 healthy male outbreed dogs. They were randomly divided into three groups: A group (intramedullary reaming and bone cement injection , n=6) ,B group (intramedullary reaming , bone cement injection and CBP, n=6) and C group (only the surgical approach was made without opening the medullary cavity, n=2) . Each dog was anesthetized with pentobarbital given intravenously (30mg/kg) and mechanically ventilated during the experiment. The changes of the intramedullary pressure were observed. The mean arterial pressure (MAP), heart rate (HR) , central venous pressure(CVP), mean pulmonary arterial pressure (MPAP), pulmonary capillary wedge pressure (PCWP) , cardiac index (CI) ,extravascular lung water(EVLW) ,intrathoracic blood volume(ITBV) and global end diastolic volume(GEDV) were monitored and recorded on different times including T0 (pre-operation) ,T1 (pre-unilateral medullary reaming),T2(post-the first unilateral medullary reaming),T3 (post-the second unilateral medullary reaming) ,T4 (post-the third unilateral medullary reaming) ,T5 (pre-unilateral bone cement injection) ,T6 (five minutes after unilateral bone cement injection) ,T7 (post-operation of unilateral femur) ,T8 (post-operation of bilateral femur) ,T9 (60 minutes after the operation of bilateral femur) and T10 (120 minutes after the operation of bilateral femur) . Blood samples were collected at related time points for arterial blood gas and cytokines (TNF-α, IL-1β,IL-6).The X-ray of chest (preoperation,post-operation) were also observed. The postmortem pulmonary tissues were studed by pathological examination.Results: 1 The intramedullary pressure showed a rapid increase during the first intramedullary reaming,while the increase of the intramedullary pressure decreaseed gradually during the second and the third intramedullary reaming.There were no significant differences on the changes of the intramedullary pressure between left and right femur (P>0.05) .2 There were no significant differences on chest X- ray of each group between pre-operation and post-operation. No fat embolics were found in any lung sections of C group. There were significant differences between the A and B groups in relation to the number of dogs showing pulmonary fat emboli stained by Oil Red O (18.13±6.25 of A group versus 4.17±1.99 of B group) (P<0.05).3 The hemodynamics such as HR, MPAP, PCWP, CVP, CI and MAP were stable during the operation in B group.There were no significant differences on different times (P>0.05 ) . In A group, HR ,CVP,MPAP,PCWP and EVLW increased while MAP and CI decreased immediately after the reaming and bone cement infusion. There were significant differences between T4 and T0 in increased HR (140.17±13.53 /min), CVP(9.17±2.40mmHg), MPAP(18.32±3.20 mmHg), PCWP(9.15±1.72 mmHg),EVLW (15.83±2.14 ml/kg) and decreased MAP(72.84±11.91mmHg), CI(2.34±0.31 L/min/m²)(P<0.05) .4 The HR, CVP, MPAP and PCWP decreased while MAP and CI increased in A group gradually on T5. There were no significant differences between T5 and TO (P>0.05), but there were significant differences on EVLW (P< 0.05).After bone cement injected ,the HR, CVP, MPAP, PCWP and EVLW increased while MAP and CI decreased again . There were significant differences between T6 and T1 in increased HR (142.34±9.12/min), CVP(9.66±2.42 mmHg) , MPAP(20.16±2.23mmHg) , PCWP(10.18±1.83mmHg),EVLW (16.33±2.66 ml/kg) and decreased MAP(69.17±12.07 mmHg) , CI(2.30±0.37L/min/m²)(P<0.05) .Thereafter, there was a decrease in HR and a increase in MAP gradually. The HR(112.32±12.11 /min) decreased while MAP(95.16±15.32 mmHg) increased on T7 significantly compared with those on T6 (P <0. 05),but there were no significant differences between T7 and T1 (P>0.05) .5 In the animals of A group, there were no significant differences on decreased CVP, MPAP, PCWP and increased CI between T8 and T7 (P>0.05) , whereas EVLW(15.67±2.66ml/kg) remained high on T8 , which were significant differences between T8 and T0(P<0.05) . In the animals of B group, EVLW remained relatively stable over time during CBP.The EVLW were 11.67±2.80 ml/kg on T9 and 11.17±2.64 ml/kg on T10,which were significant differences compared with those in the animals of A group (P <0. 05).6 The ITBV was 475.68±78.49 ml/m2 and the GEDV was 380.17±62.49ml/m2 on T6,which were significant decreased compared with those on T6 in the animals of A group (P <0. 05).And there were no significant differences on the other times. But the ITBV and GEDV remained relatively stable over time during CBP in the animals of B group.7 In the animals of A group, there was a decrease in pH and PaO₂ and an increase in PaCO₂ on T8, which were significant differences compared with those on TO (P <0. 05). Although there was an amendment in pH and PaO₂, the PaCO₂(47.8±7.3 mmHg) was still high , which was significant difference compared with that on T0(P<0.05). The variance tendency of EVLW was correlated with those of pH, PaO₂ and PaCO₂ (P<0.05) .Whereas, there were no significant changes in pH, PaO₂ and PaCO₂ on different times during the operation in the animals of B group ,which were no significant differences compared with those on T0(P>0.05) .8 After the operation , the serumal TNF-αincreased from 0.80±0.23ng/ml to 1.41±0.36ng/ml, while the serumal IL-1βincreased from 0.48±0.14 ng/ml to 0.80±0.31 ng/ml and the serumal IL-6 increased from 114.93±21.96 pg/ml to 136.99±14.19 pg/ml, respectively. Compared with those on T0,there were significant differences in TNF-αon T8 and T10, as well as in IL-1βon T8 and IL-6 on T10 (P<0.05). The serumal TNF-α, IL-1βand IL-6 were decreased after CBP. Compared with those on A group,there were significant difference in TNF-a on T10,as well as in IL-1βand IL-6 on T8 and T10 (P<0.05).Conclusions: 1 The PFE model analoguing the features of fernoralintramedullary operation was more coincident with actual physiological functions than the other model injected by fat drop or medullary fat.2 Pulmonary fat embolism and the changes of hemodynamics could be elicited during femoral intramedullary operation . After pulmonary fat embolism happened, cardiopulmonary effects included increased HR, CVP, MPAP, PCWP and EVLW accompanying a decrease in MAP and CI. Meanwhile there was a decrease in PaO₂ and an increase in PaCO₂ during the operation.3 Although the changes of the hemodynamics and respiratory function caused by femoral intramedullary operation could be amended gradually after the operation,the serumal TNF-α, IL-1β,IL-6 and the EVLW were still higher than those on pre-operation. The variance tendency of EVLW was correlated with those of pH,PaO₂ and PaCO₂, which could be a risk factor of FES.4 There was remarkable amendment in respiratory function in B group. Early CBP could decrease the level of the TNF-α,IL-1β, IL-6 and EVLW . The hemodynamics were stable during the operation in B group.There were no significant changes in pH,PaO₂ and PaCO₂ on different times.5 The total positive Oil Red O stainings performed on sections of the lungs on both A and B groups showed a higher incidence of PFE caused by femoral intramedullary operation,which could be the other risk factor of FES. Earlier CBP could reduce pulmonary fat emboli and decrease the incidence of PFE caused by femoral intramedullary operation.