Maintaining water and electrolyte balance and internal environmental stability is a fundamental part of critical burn treatment, especially when combined with severe inhalation injury, pulmonary infection or cardiac or renal insufficiency, it is crucial to maintain a more accurate volume balance. The main feature that distinguishes burn patients from general patients is the continuous exudation before the trauma is effectively covered, which makes it difficult to maintain the balance of inlet and outlet volume in burn patients compared with general patients. The amount of fluid loss has a great influence. Therefore, it is of great clinical significance to establish an empirical understanding of the balance of inlet and outlet volume in patients with severe burns and to discover its changing pattern for the treatment of critically ill patients. Li Feng, Department of Burns and Plastic Surgery, The First Affiliated Hospital of the General Hospital of the Chinese People’s Liberation Army 1. Materials and methods 1.1 Clinical data 28 adult patients with inpatient burns ≥70% TBSA and complete data during the 5 years from 2005 to 2009 were reviewed and divided into the surviving and deceased groups. Patients were admitted to the hospital in suspension beds, routinely treated with fluid rehydration and anti-shock therapy, and underwent scab cutting, autologous particulate skin grafting, and large allograft skin coverage on the extremities and trunk 3-5 days after the injury, and were converted to a turning bed 2 to 3 days after the first scab cutting and skin grafting, with intermittent skin grafting to close the residual trauma after allografting. During the treatment, the room temperature or local temperature was maintained at about 26-30℃, and the room humidity was not specially adjusted. There were 17 cases in the survival group, 10 males and 7 females; age ranged from 21 to 64 years old, with an average of (35.6±10.9) years; burn area ranged from 80% to 99% TBSA, with an average of 91.3%±7.4% TBSA; among them, third-degree burns ranged from 40% to 85% TBSA, with an average of 67.3%±20.4%. There were 11 cases in the death group, 10 males and 1 female; age ranged from 19 to 52 years, with a mean of (34.3±11.7) years; burn area ranged from 90% to 100% TBSA, with a mean of 95.6%±3.5% TBSA; among them, third-degree burns ranged from 45% to 99% TBSA, with a mean of 79.0%±22.8%. There was no statistically significant difference in age, burn area and third-degree burn area between the two groups. Patients’ intake, discharge and difference of intake and discharge from day 1 to day 7, day 10, 13, 16, 19, 22, 25, 28, 31, 34, 37 and 40 of hospital admission were recorded. 1.2 Statistical methods The t-test was performed on stata 7.0 statistical software, and P < 0.05 was considered statistically different. The results were expressed as X±S. 2. Results 2.1 Comparison of intake between the surviving group and the deceased group: There was no statistical difference between the two groups in terms of intake at each time point. 2.2 Comparison between the surviving group and the deceased group: except for days 1 to 5 and 10, the volume of the surviving group was significantly greater than that of the deceased group. 2.3 Comparison of the difference between the outgoing and incoming volumes in the survivor group and the death group: on days 6, 7, 13, 22, 25, 28, 31, and 40, the difference between the outgoing and incoming volumes in the survivor group was significantly smaller than that in the death group. Discussion After large burns, the body's water and electrolyte metabolism is significantly imbalanced due to fluid exudation. In the early post-injury period, the increase in vascular permeability causes a large amount of plasma components to be transferred to the tissue interstitial space, which is still in the body but outside the circulatory system, and can cause a huge difference in the volume of intake and output; for a long period after the shock period, the loss of skin barrier function and the evaporation of water from the trauma surface cause a large increase in unobtrusive water loss, which, together with the occurrence of capillary leakage when combined with complications such as sepsis, can still cause the difference in the volume of intake and output This increases the difficulty of maintaining fluid balance in patients with severe burns, especially when combined with cardiac, pulmonary, renal and other organ complications, which require strict restriction of intake and output, often made more difficult by the difficulty of estimating traumatic water loss. After the shock period, unobtrusive water loss caused by traumatic exudation is an important factor affecting the balance of intake and output, so in previous studies, the measurement of traumatic exudation per unit area was mostly used as the main purpose of the study. However, this method, which is based on a more accurate estimation of trauma area, has considerable limitations in practical application because of the many factors that affect the amount of trauma exudate, including ambient temperature, humidity, depth of trauma, type of trauma (fresh trauma or granulation trauma), whether the trauma is covered or the type of covering [2, 3, 4]; secondly, it is relatively easy to estimate the trauma area in the early post-injury period, while in the mid- to late-stage, there are great differences in the viability of skin fragments at different times after skin grafting, especially after allograft skin covers the trauma, and the effect of covering the trauma and reducing exudation will certainly vary accordingly. Therefore, if further calculation of the trauma non-significant water loss is based on the accurate estimation of the existing trauma area, there is bound to be considerable subjectivity and it cannot include the water transfer caused by vascular leakage caused by infection factors, thus limiting its application in clinical practice; on the contrary, if statistical analysis of the balance of the inlet and outlet of patients with large burns at different stages in the course of the disease is carried out as a whole to discover its On the contrary, if the statistical analysis of the balance of intake and output of patients with large burns at different stages of the disease course is conducted as a whole, to discover the pattern and significance of changes and to establish empirical understanding, it is more likely to provide intuitive reference for clinical treatment. In the present study, the difference between the inlet and outlet volume of patients in the early post-injury period could exceed 10,000 ml, and then rapidly decreased. After 6 days post-injury, the difference between the inlet and outlet volume of the surviving group was mostly around 2,500 ml, while that of the dead group was around 4,500 ml, and the surviving group was significantly smaller than the dead group. We believe that the large difference in volume in the early stage is caused by hypovolemic shock and massive fluid resuscitation, while the difference in volume in the later stage mainly depends on the vascular leakage and evaporation of trauma caused by the combined sepsis and other complications. Significant positive fluid balance can also be observed in those who die from sepsis and traumatic shock [5, 6]; and the main difference between patients with large burns and those with general trauma and sepsis is the persistence of trauma, and in addition to inflammatory exudation, fluid loss through trauma exudation is an important factor affecting the balance of access. According to previous studies, the amount of evaporation from wounds covered with allograft skin can be reduced by about 3/4 compared with that from exposed wounds, which is very close to the evaporation from normal skin, and the study of Youth et al. also proved that allograft skin coverage can significantly reduce evaporation from wounds. The effect of allograft skin coverage on exudation is evident at 8 hours postoperatively, not after the establishment of hematopoiesis by the allograft skin. In the present study, the difference in volume between the surviving group and the dead group was significantly smaller at most of the observed time points, and we believe that the reason for this phenomenon, in addition to the amount of residual trauma that did not receive an implant, is more important than whether the allograft skin formed an "effective" coverage of the trauma, if it was not completely removed due to hematoma, infection, basal necrotic tissue, or If the allograft is not completely removed due to hematoma, infection, basal necrotic tissue, or poor viability of the allograft itself, it will not help the allograft to form an effective coverage of the trauma and will not prevent the continued loss of plasma components from the trauma, which will also easily cause complications such as sepsis and further aggravate the inflammatory exudate, thus expanding the positive fluid balance. In conclusion, this study observed the changing pattern of the difference between the inlet and outlet volume of patients with large burns at different periods after injury, which can provide an empirical basis for maintaining the fluid balance of patients; it was found that the difference between the inlet and outlet volume of the surviving group was significantly smaller than that of the dead group, the reason for which is still unclear and may be related to the smaller trauma surface that did not receive effective coverage.