Intrathoracic Blood Volume Index In The End Of Shock Stage Predicting ARDS In Fluid Reabsorption Stage Among Severely Burned Patients:A Retrospective Study

BackgroundDeveloping precision resuscitation of early burn shock is the key of improving outcome and decreasing mortality of severely burned patients.Choosing and setting a rational resuscitation goal is an important process of precision resuscitation.Pulse contour cardiac output technology can monitor hemodynamic parameters,heart function,extravascular lung water index?EVLWI?and many other parameters.As a parameter reflecting cardiac preload,intrathoracic blood volume index?ITBVI?is treated as an ideal goal guiding fluid resuscitation.However,the exact value of ITBVI that guiding fluid resuscitation in severely burned patients remains unclear,thus precision resuscitation is not widely used in clinical practice.Precision resuscitation of burn injury is not only to treat ischemia-hypoxia and shock caused by severe burn but to avoid complications caused by fluid overloading,including osteofascial compartment syndrome,organ edema and so on.Acute respiratory distress syndrome?ARDS?is a common respiratory system complication in severely burned patients,which usually happens in fluid resuscitation.We previously found that the high morbidity of ARDS in the fluid reabsorption stage probably results from the abnormal elevation of EVLWI,the risk factor of which is ITBVI.Based on this,we perform this study to find how ITBVI predicts and prevents ARDS happened in fluid reabsorption stage and provide some information for further development of severe burn precision resuscitation.There were two parts of this study.First,analyze the clinical features and risk factors of ARDS happened in severely burned patients according to the medical records.Second,case-control study was performed based on the first part to find how ITBVI in the end of burn shock stage predicts ARDS happened in fluid reabsorption stage and to put forward an ITBVI goal which is beneficial to precision resuscitation among severely burned patients received PiCCO monitoring.MethodsThere were two parts of this study.The first part is a retrospective study.We enrolled168 severely burned patients who admitted to Southwest Hospital between May 2012 and December 2014.The data we collected included demographic information,physical exam,records about burn injury,mechanical ventilation,and outcome.The second part is a retrospective case-control study.The case group enrolled 65 severely burned patients who developed ARDS in fluid reabsorption stage and admitted to Southwest Hospital between January 2015 and August 2018.The control group was matched according to age and full thickness burn size by 1:1 ratio.Except for the data collected in the first part,we also recorded PiCCO parameters in 48 hours after burn injury,including EVLWI,pulmonary vascular permeability index,ITBVI,central venous pressure,left ventricular systolic index,stroke volume index,systemic vascular resistance index.The data were analyzed using the SPSS 20.0.Continuous variables were presented as means±standard deviations and were analyzed using Student t test or Mann-Whitney test as appropriate.Categorical data were analyzed using chi-squared test.To compare the difference of the demographic variables of patients with different ARDS severity,one-way ANOVA with the post hoc LSD test were performed.Logistic regression analysis was performed to determine the influence factors of ARDS in severely burned patients.We calculated odds ratio of ARDS in patients with different ITBVI level.A P-value less than0.05 was considered significant.ResultsPart one:Clinical features and risk factors of ARDS happened in severely burned patients1.Clinical features of ARDS happened in severely burned patientsAmong the enrolled patients,63 developed ARDS,the morbidity is 37.5%.Compared with patients who did not developed ARDS,patients with ARDS was older,with larger total burn size and larger full thickness burn size?age:P=0.036,total burn size:P=0.037,full thickness burn size:P=0.013?.Patients who developed ARDS had higher mortality than other patients?38.1%vs.17.1%,P=0.002?.There existed no significant difference in other data between the two groups.Among the patients developed ARDS,there were 27 with mild ARDS,30 with moderate ARDS and 6 with severe ARDS.There existed significant difference in full thickness burn size among the three groups?P<0.001?.The death rate of patients with mild,moderate and severe ARDS was18.5%,50.0%,and 66.7%,respectively.There existed significant difference in mortality between the three groups.There existed no significant difference in other data between the three groups.The timing of ARDS onset was 1-18 days postburn,with an average value of 5.86±3.48 days and an median value of 5 days postburn.There existed no significant difference in mortality between patients developed ARDS in different stages??²=0.745,P=0.689?.2.Risk factors of ARDS happened in severely burned patientsAfter analyzing demographic data and medical records of the enrolled patients,age and full thickness burn size were determined as two important influence factors of ARDS.With one unit increasement of age and full thickness burn size,the risk of developing ARDS increase 4.0%and 2.6%,respectively.Part two:Intrathoracic blood volume index in the end of burn shock stage predicting ARDS in fluid reabsorption stage among severely burned patients:a case-control study1.Comparison of PiCCO parameters in 48 hours postburn between the case group and the control groupParameters reflecting lung function:EVLWI of the two groups increased after burn injury,and there were no differences in EVLWI between the two groups.Besides,PVPI in the two groups increased after burn injury,PVPI in case group was significantly higher than in control group 40 hours postburn?3.15±0.46 vs.2.96±0.47,P=0.019?.Parameters reflecting cardiac preload:ITBVI of the two groups increased after burn injury,and was lower than the lower limit of the normal range in the whole burn shock stage.ITBVI in case group was significantly higher than in control group after 24 hours postburn.CVP of the case group first decreased then increased after burn injury,no differences were found in CVP between the two groups.Parameters reflecting cardiac function:CI,dPmax and SVI of the two groups all increased after burn injury,no differences were found in these three parameters between the two groups.Parameters reflecting cardiac afterload:SVRI of the two groups all decreased after burn injury,SVRI decreased to normal range on 40 hours postburn.No differences were found in SVRI between the two groups.2.Relationship between ITBVI in the end of burn shock stage and ARDS developed in fluid reabsorption stageRegarded ITBVI?650 ml/m² as the lowest explore level,patients with 750ml/m²<ITBVI?850 ml/m² were 9.50 times easier to develop ARDS in fluid reabsorption stage than patients with ITBVI?650 ml/m²[?²_0.01?3?=7.81,?²=11.05>7.81,P<0.01],and patients with ITBV?850 ml/m² were 11.50 times easier to develop ARDS in fluid reabsorption stage than patients with ITBVI?650 ml/m²[?²_0.005?3?=12.84,?²=13.16>12.84,P<0.005].Patients with ITBVI>750 ml/m² were more likely to develop ARDS in fluid reabsorption stage than patients with ITBVI?750 ml/m²?OR=10.3,95%CI:4.4-23.6,P<0.001?.Conclusion:1.ARDS happened in severely burned patients mainly developed in fluid reabsorption stage with a mild or moderate severity and had a high morbidity and mortality.2.Age and full thickness burn size were important influence factors for ARDS development in severely burned patients.3.On the condition that all patients were well resuscitated and age and full thickness burn size were matched,patients with higher ITBVI in the end of burn shock stage were more likely to develop ARDS in fluid reabsorption stage.4.On the condition that all patients were well resuscitated and age and full thickness burn size were matched,patients with ITBVI higher than 750ml/m² in the end of burn shock stage were more likely to develop ARDS in fluid reabsorption stage than other patients.This result revealed that setting the ITBVI goal lower than 750ml/m² can not only maintained tissue perfusion but was also beneficial for reducing ARDS in fluid reabsorption stage.5.Our study provided a practical resuscitation goal in the end of burn shock stage to help developing severe burns precision resuscitation and reducing complications in fluid reabsorption stage.