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CHANGES IN LIVER FUNCTION AND SIZE AFTER A SEVERE THERMAL INJURY

Jeschke, Marc G.*†; Micak, Ronald P.*; Finnerty, Celeste C.*†; Herndon, David N.*†

doi: 10.1097/shk.0b013e318047b9e2
Clinical Aspects
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Hepatic homeostasis and metabolism are essential for survival in critically ill and severely burned patients. There is evidence that the liver undergoes hypertrophy after burn. However, the extension and the duration of liver enlargement are not known. The aim of the present study was to determine the changes in liver size, weight, and hepatic protein synthesis in a large prospective clinical trial throughout acute hospitalization and up to 12 months after burn. Liver size was measured by means of ultrasound, and liver weight was calculated weekly during short-term hospital stay and at 6, 9, and 12 months after burn. The liver size was then compared with the predicted liver size for each individual. The levels of hepatic proteins and enzymes were determined by using standard laboratory techniques. One hundred two children were included in the study, with 58% ± 2% total body surface area and 45% ± 2% third-degree burn. Liver size and weight significantly increased during the first week after burn (mean ± SEM, 85% ± 5%), peeked at 2 weeks after burn (mean ± SEM, 126% ± 19%), and, at discharge, increased by 89% ± 10%. At 6, 9, and 12 months, the liver weight increased by 40% to 50% compared with the predicted liver weight. The hepatic protein synthesis was affected up to 9 months after burn. The liver demonstrates a significant enlargement during short-term hospitalization, accompanied with impairment in the hepatic protein synthesis. The treatment to prevent liver enlargement and the improved impaired function may result in a reduction of complications accompanied with liver hypertrophy and failure.

*Shriners Hospitals for Children and University of Texas Medical Branch, Galveston, Texas

Received 13 Nov 2006; first review completed 1 Dec 2006; accepted in final form 21 Dec 2006

Address reprint requests to Marc G. Jeschke, MD, PhD, Shriners Hospitals for Children, Galveston Burns Unit, 815 Market Street, Galveston, TX 77550. E-mail: majeschk@utmb.edu.

This study was supported by the Shriners Hospitals for Children (grants 8660, 8760, and 9145), National Institutes of Health (grants R01-GM56687, T32 GM008256, and P50 GM60338), and National Institute on Disability and Rehabilitation Research (grant H133A020102).

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INTRODUCTION

The liver has been shown to play a pivotal role after a thermal injury (1, 2). After burn, the liver interacts with the site of injury and modulates the immune functions, the inflammatory processes, and the acute-phase response (1-4). Previous studies indicated that thermal injury affects liver morphology by decreasing protein and DNA concentration (1, 5, 6). We suggest that liver homeostasis is necessary for survival and clinical outcome after a thermal injury. After a thermal injury, a variable degree of liver injury usually related to the severity of the thermal injury is present (3, 4). Immediately after burn, the damage of the liver may be associated with an increased hepatic edema formation. In a burn rat model, we have shown that the liver weight and the liver-to-body weight ratio significantly increased 2 to 7 days after burn compared with controls (1). Because hepatic protein concentration was significantly decreased in burned rats, we suggested that the liver weight gain is caused by the increased edema formation rather than by the increases in the number of hepatocytes or protein levels. An increase in edema formation may lead to cell damage with the release of the hepatic enzymes (2). In addition, fatty changes occur (7, 8). Fatty changes, a very common finding, per se are reversible, and their significance depends on the cause and the severity of accumulation. However, the autopsies of burned children showed that fatty liver infiltration was associated with increased bacterial translocation, liver failure, and endotoxemia, delineating the crucial role of the liver during the postburn response (7).

There is strong evidence that the liver undergoes hypertrophy after burn (9, 10). The extent and duration of liver enlargement and the associated functional changes, however, are not known. The aim of this study was to determine the changes in liver size and weight and the associated functional changes in a large prospective clinical trial throughout short-term hospitalization and up to 12 months after burn.

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MATERIALS AND METHODS

This study was approved by the University of Texas Medical Branch institutional review board. Informed written consent was obtained from each patient's guardian before enrollment in the study. The inclusion criteria were as follows: children younger than 18 years with total body surface area (TBSA) of burns greater than 40%. From 1996 to 2005, severely burned patients who did not receive any anabolic agent or study drug treatment were included in the study. At the Shriners Hospital, we admit burn patients aged 1 week to 18 years, but most of the children in our series are approximately 8 years. None of the older children were excluded from this study.

In this prospective study, all patients received the same standard acute-burn care. Within 48 h of admission, each patient underwent total burn wound excision and grafting with autograft skin and allograft. The patients returned to the operating room when the autograft donor sites healed and became available for reharvest (usually 6 to 8 days from the last operation). Sequential staged surgical procedures for repeat excision and grafting were undertaken until the wounds were healed. Each patient received enteral nutrition via a nasoduodenal tube using Vivonex (Sandoz Nutrition Corporation, Minneapolis, Minn) TEN. The composition of Vivonex is 82% carbohydrate, 15% protein, and 3% fat. The daily energy intake was administered at a rate calculated to deliver 1,500 kcal/m2 TBSA burned + 1,500 kcal/m2 TBSA. This feeding regimen was started at admission and continued at a constant rate until the wounds were healed. The energy intake remained constant throughout the study periods.

An Emtek (Eclipsys; Rockville, Md) vital signs tracking system was connected to the burn patients using standard electrocardiogram leads. Heart rate was measured hourly and was verified by each patient's nurse. The average heart rate for each entire 24-h period was determined throughout the hospital stay.

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Liver size

The ultrasound measurements in this study were performed using the HP Sonos 100 CF (Hewlett-Packard Imaging Systems, Andover, Mass) echocardiogram. The liver was scanned using an Escoline B-scanner, a modified HP diagnostic sounder 7214 A, and a modified 3.5-MHz transducer probe. To obtain the ultrasound liver weight, a 3.5-MHz transducer was placed directly below the midline of the rib cage on the right upper quadrant in a vertical line running through the right nipple, with the patient in the supine position. When the liver was visualized, measurements were performed by scanning in a plane perpendicular to the base of the liver. The base of the liver and the free edge hepatic dome was marked on the display screen; then, the distance between these two points was automatically measured.

The formula used for estimating liver weight from the single longitudinal scan along the right nipple line was WT = (1.15l)3d, where l3 represents the volume of a cube cut in half diagonally to visualize the approximate shape of the healthy liver in situ. A factor of 1.15 was used to correct for the portion of the liver (15%) lateral to the left nipple line and representing the most inferior point of the liver. This correction was estimated from the liver at autopsy. The density (d) of the liver was measured on several sections by water displacement. Determining the right nipple line was not problematic unless the nipple was obliterated by a severe burn to the thorax. In this case, an approximation was made and recorded as such. The actual size was then compared with the predicted size (10).

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Hepatic enzymes and acute-phase and constitutive proteins

The levels of hepatic enzymes and acute-phase and constitutive proteins were determined throughout the study period using standard laboratory techniques.

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Statistical analysis

One-way analysis of variance, with Bonferroni post hoc correction, and paired and unpaired Student t tests were used to compare the two groups. Data are expressed as percentages or mean ± SEM, where appropriate. Significance was accepted at P < 0.05.

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RESULTS

Demographics

One hundred two severely burned pediatric patients were included in the present study. Forty-one were girls and 61 were boys. The mean burn size was 58% (SEM, ±2%), with a third-degree burn component of 45% ± 2%. The average age was 8 years (SEM, ±1 year). None of the patients received anabolic agents and no patient died. Further demographic data are shown in Table 1.

Table 1

Table 1

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Liver changes

Immediately after burn, the liver length increases by approximately 1 cm and remains increased up to the time of discharge. The liver length decreases during the 6- to 12-month period (Fig. 1A). Based on the ultrasound measurements, liver weight increases immediately after burn from approximately 800 g to 1,500 to 1,800 g (P < 0.05). The liver weight remains significantly greater compared with controls throughout the entire study period (Fig. 1B). When the change in liver weight was determined, we found that the liver size increased by 180% to 230% at 2 weeks after burn. The liver weight and size approached the predicted physiological weight and size at 12 months after burn (Fig. 1C).

Fig. 1

Fig. 1

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Hepatic protein panel and enzymes

The level of serum albumin, a constitutive hepatic protein, drastically decreased twofold to threefold immediately after burn (P < 0.05) (Fig. 2A). Despite the clinical replacement of albumin, the levels significantly decreased up to 6 months after burn. By 12 months after burn, the serum albumin levels approached the reference range. The serum prealbumin followed in a similar pattern as albumin. The prealbumin levels dropped fourfold immediately after burn and remained significantly low up to the time of discharge (P < 0.05). By 6 months, the prealbumin levels approached the reference range (Fig. 2B). The level of serum transferrin, another constitutive hepatic protein, decreased threefold immediately after burn. It took 9 months for the transferrin levels to increase and reach the reference levels (P < 0.05) (Fig. 2C).

Fig. 2

Fig. 2

Acute-phase proteins were significantly increased after burn, and increased levels were found up to 6 to 9 months after burn. The serum C-reactive protein (CRP) level demonstrated a rapid rise and increased by 1,500% immediately after burn and remained significantly elevated until the time of discharge of the patient (P < 0.05) (Fig. 3A). Serum haptoglobin level increased threefold to fourfold, but the peak occurred at discharge (range, 3-4 months after burn), indicating that haptoglobin is a slower acute-phase protein. Haptoglobin levels remained significantly elevated up to 9 months after burn (P < 0.05) (Fig. 3B). The serum C3-complement level increased above reference levels at discharge and at 6 months after burn, with levels approaching the reference level at 12 months (P < 0.05) (Fig. 3C).

Fig. 3

Fig. 3

In contrast to acute-phase protein levels, the levels of the hepatic enzymes serum aspartate aminotransferase (AST), serum alanine aminotransferase (ALT), and serum bilirubin were increased during the acute postburn phase. The serum AST level increased fourfold immediately after burn, with levels approaching the reference range at discharge (P < 0.05) (Fig. 4A). Compared with the reference levels, the serum ALT level only increased at 1 and 2 weeks after burn (P < 0.05) (Fig. 4B). The serum bilirubin level increased at 1 and 2 weeks after burn and returned to reference levels at 4 weeks after burn (P < 0.05) (Fig. 4C).

Fig. 4

Fig. 4

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DISCUSSION

After a thermal injury, a variable degree of liver injury, usually related to the severity of the thermal injury, is present. Fatty changes, a very common finding, per se are reversible, and their significance depends on the cause and the severity of accumulation (1, 2, 7, 8, 11, 12). Autopsies of burned children showed that fatty liver infiltration was associated with increased bacterial translocation, liver failure, and endotoxemia, thus delineating the crucial role of the liver during the postburn response (7).

In the present study of the cases of 102 children, we found that liver size and weight significantly increased during the first week after burn, peeked at 2 weeks after burn, and remained increased at 6, 9, and 12 months after burn. In addition, the liver protein synthesis was impaired during a 6-month period with a shift from constitutive hepatic proteins to acute-phase proteins. The liver enzymes were significantly elevated during the first 3 weeks after burn, normalizing over time. These findings are in agreement with those of another study from our institute in which we determined the extent and the duration of the hepatic acute-phase response during the acute-phase postburn (9). The extent of the liver dysfunction and morphological changes is correlated to the burn size, which means that the larger the burn, the bigger the dysfunction and the increase in size (unpublished observations).

Immediately after burn, the damage of the liver may be associated with an increased hepatic edema formation (1, 12). In a rat burn model, we have shown that the liver weight and the liver-to-body weight ratio significantly increased 2 to 7 days after burn compared with controls. Because hepatic protein concentration was significantly decreased in burned rats, we suggest that the liver weight gain is caused by the increased edema formation rather than by the increases in the number of hepatocytes or protein levels. An increase in edema formation may lead to cell damage with the release of the hepatic enzymes (2). The enzymes that achieve abnormal serum levels in hepatic disease and have been studied widely are the serums AST and ALT. In the present study, we showed that AST and ALT are increased and released into the serum for a period of 4 to 6 weeks, indicating that liver damage is present immediately after burn. Serum bilirubin level was only increased for 2 weeks after burn, indicating that bilirubin level during the postburn response is not an important marker as in other pathophysiological states, such as sepsis. In sepsis, an intrahepatic cholestasis occurs frequently without demonstrable extrahepatic obstruction. This phenomenon has been described in association with a number of processes, such as hypoxia, drug toxicity, or total parenteral nutrition (13). The mechanisms of intrahepatic cholestasis seem associated with an impairment of basolateral and canalicular hepatocyte transport of bile acids and organic anions (14). This is most likely caused by decreased transporter protein and RNA expression. We (16) and Bolder et al. (14, 15) have shown that decreased transporter expression is associated with decreased bile acid output, leading to increased intrahepatic bile concentration.

Liver damage has been associated with increased hepatocyte cell death, which is caused by increased hepatocyte apoptosis and necrosis (1, 5, 8, 12, 17). Pathological studies found that 10% to 15% of thermally injured patients have liver necrosis at autopsy, but we have shown that a cutaneous thermal injury also induces liver cell apoptosis (1, 7, 10, 18). This increase in hepatic programmed cell death is compensated by an increase in hepatic cell proliferation, suggesting that the liver attempts to maintain homeostasis (1). Despite the attempt to compensate for the increased apoptosis by increased hepatocyte proliferation, the liver cannot regain hepatic mass and protein concentration, as suggested by a significant decrease in hepatic protein concentration we found in burned rats. The mechanisms whereby a cutaneous burn induces programmed cell death in hepatocytes are not defined. In burns, it has been suggested that hypoperfusion or ischemia-reperfusion lead to apoptosis (19). In addition, ischemia-reperfusion has been shown to induce gut apoptosis (1, 19, 20). After a thermal injury, the blood flow rate to the bowel decreases by nearly 60% of baseline and stays decreased for approximately 4 h (19). It can be surmised that the hepatic blood flow rate also decreases, thus causing programmed cell death. In addition, proinflammatory cytokines, such as interleukin 1 and tumor necrosis factor, have been described as an apoptotic signal (21-24). Severe burn is associated with increased cytokine levels in the serum and in the liver; we therefore suggest that two possible mechanisms are involved in the induction of hepatocyte apoptosis: (1) hypoperfusion of the splanchnic system and (2) elevation of proinflammatory cytokines (6, 25-27).

The significance of the present study is that the liver undergoes massive enlargement during a period of 12 months and the hepatic acute-phase proteins are predominantly produced for 6 to 9 months after burn, whereas the amount of constitutive hepatic proteins is decreased for the same period. Liver damage, as indicated by elevated enzymes, is present for 4 weeks after burn, after which the liver returns to normal condition. These data suggest that after a severe burn, liver damage occurs, the hepatocytes undergo apoptosis and necrosis, and the constitutive hepatic protein synthesis and hepatic metabolism are impaired. These events last 4 to 6 weeks; then, liver regeneration is complete and damage is not detectable anymore. However, acute-phase protein synthesis and metabolic impairment persists for almost 12 months, and the need for hepatic protein synthesis and metabolism leads to a massive liver enlargement. Because the fluid overload of resuscitation is only present for approximately 7 days after burn, hepatic edema is not caused by fluid overload. In a recent study, our group characterized liver composition at autopsy and found that liver enlargement is mainly caused by the increased amount of intrahepatic fat and hepatocyte hypertrophy (11). Hypertrophy is mainly caused by increased intrahepatic edema (11). On the basis of these findings, we suggest that the treatment to prevent liver enlargement and the improved impaired function may result in a reduction of complications accompanied with liver hypertrophy and failure (e.g., the use of insulin (25-27), insulinlike growth factor 1 (28-30), hepatocyte growth factor, (31) propranolol (32)).

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Keywords:

Hepatomegaly; liver enzymes; pediatrics; thermal injury

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