Acute Changes in Capillary Filtration and Diffusion in Experimental Burn Injury

Hypovolemia with peripheral edema: What is wrong?

Fluid normally exchanges freely between the plasma and interstitial space and is returned primarily via the lymphatic system. This balance can be disturbed by diseases and medications. In inflammatory disease states, such as sepsis, the return flow of fluid from the interstitial space to the plasma seems to be very slow, which promotes the well-known triad of hypovolemia, hypoalbuminemia, and peripheral edema. Similarly, general anesthesia, for example, even without mechanical ventilation, increases accumulation of infused crystalloid fluid in a slowly equilibrating fraction of the extravascular compartment. Herein, we have combined data from fluid kinetic trials with previously unconnected mechanisms of inflammation, interstitial fluid physiology and lymphatic pathology to synthesize a novel explanation for common and clinically relevant examples of circulatory dysregulation. Experimental studies suggest that two key mechanisms contribute to the combination of hypovolemia, hypoalbuminemia and edema; (1) acute lowering of the interstitial pressure by inflammatory mediators such as TNFα, IL-1β, and IL-6 and, (2) nitric oxide-induced inhibition of intrinsic lymphatic pumping.

Assessment of local tissue water in breasts following breast reconstruction with an expander prosthesis or DIEP flap

The role of breast oedema in breast reconstruction is unknown. Therefore, our aim was to investigate local tissue water (LTW) and breast oedema-related symptoms in breasts reconstructed with either an expander prosthesis (EP) or with a deep inferior epigastric perforator (DIEP) flap at a minimum of one year postoperatively. Sixty-eight patients randomised to breast reconstruction with an EP or DIEP flap completed follow-up. Objective evaluation was performed at a mean of 25 (standard deviation, SD 9.5) months following breast reconstruction, and included measurements of breast volume and LTW with the MoistureMeterD® instrument. The patients completed the BREAST-Q questionnaire pre- and postoperatively. No significant differences in LTW were found when comparing EP and DIEP flap reconstructed breasts. The reconstructed breasts had an increase in LTW compared with the non-operated contralateral breasts. The BREAST-Q responses related to breast oedema symptoms were overall low and the median responses ranged from 1 to 2. A score of 1 indicated that symptoms were experienced 'None of the time'. Our findings indicate that mastectomy followed by breast reconstruction inflicts damage on the lymphatic system, shown as an increase in LTW. However, no breast oedema-related symptoms were reported in the BREAST-Q questionnaire, and therefore, we consider our objective results to be below a potential threshold for symptomatic breast oedema. A threshold for clinical indication of breast oedema remains to be defined.

Left orbital compartment syndrome and right anterior ischemic optic neuropathy in a patient with severe burns despite non-aggressive fluid resuscitation

INTRODUCTION

Ophthalmological complications such as orbital compartment syndrome (OCS) and ischemic optic neuropathy are rare complications in patients with burns and have been described in patients where aggressive fluid resuscitation was performed. While OCS requires urgent surgical intervention, no current treatment is established to treat, or prevent, ischemic optic neuropathy in patients with burns.

METHODS

The authors report a case of a 38-year-old woman with flame burns including the periorbital regions who developed OCS on the left side and anterior ischemic optic neuropathy (AION) on the right side despite non-aggressive fluid resuscitation. Immediate lateral canthotomy combined with inferior cantholysis was performed on the left side.

DISCUSSION AND CONCLUSION

OCS and AION need to be considered as potential complications even in critically ill patients with facial burns who do not receive aggressive fluid resuscitation. Whether an early surgical intervention will lower the risk of AION development is, however, speculative.

LAY SUMMARY

Ophthalmological complications such as orbital compartment syndrome and ischemic optic neuropathy are rare complications in patients with burns and have been described in patients where aggressive fluid resuscitation was performed. We present a case of a critically ill patient with severe facial burns who developed orbital compartment syndrome on the left side and anterior ischemic optic neuropathy on the right side even though our patient did not receive aggressive fluid resuscitation.Our case is particular because both of these rare complications are seen in a single patient and neither received aggressive fluid resuscitation. The fact that the patient did not develop ischemic optic neuropathy on the side where the lateral canthotomy was performed (only on the side where the patient had orbital compartment syndrome), this case might raise the discussion of whether an early surgical intervention might lower the risk of ischemic optic neuropathy development in patients with facial burns.

A Modern View of the Interstitial Space in Health and Disease

Increases in the volume of the interstitial space are readily recognized clinically as interstitial edema formation in the loose connective tissue of skin, mucosa, and lung. However, the contents and the hydrostatic pressure of this interstitial fluid can be very difficult to determine even in experimental settings. These difficulties have long obscured what we are beginning to appreciate is a dynamic milieu that is subject to both intrinsic and extrinsic regulation. This review examines current concepts regarding regulation of interstitial volume, pressure, and flow and utilizes that background to address three major topics of interest that impact IV fluid administration. The first of these started with the discovery that excess dietary salt can be stored non-osmotically in the interstitial space with minimal impact on vascular volume and pressures. This led to the hypothesis that, along with the kidney, the interstitial space plays an active role in the long-term regulation of blood pressure. Second, it now appears that hypovolemic shock leads to systemic inflammatory response syndrome principally through the entry of digestive enzymes into the intestinal interstitial space and the subsequent progression of enzymes and inflammatory agents through the mesenteric lymphatic system to the general circulation. Lastly, current evidence strongly supports the non-intuitive view that the primary factor leading to inflammatory edema formation is a decrease in interstitial hydrostatic pressure that dramatically increases microvascular filtration.

Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging

The kidneys' integrative responses to heat stress aid thermoregulation, cardiovascular control, and water and electrolyte regulation. Recent evidence suggests the kidneys are at increased risk of pathological events during heat stress, namely acute kidney injury (AKI), and that this risk is compounded by dehydration and exercise. This heat stress related AKI is believed to contribute to the epidemic of chronic kidney disease (CKD) occurring in occupational settings. It is estimated that AKI and CKD affect upwards of 45 million individuals in the global workforce. Water and electrolyte disturbances and AKI, both of which are representative of kidney-related pathology, are the two leading causes of hospitalizations during heat waves in older adults. Structural and physiological alterations in aging kidneys likely contribute to this increased risk. With this background, this comprehensive narrative review will provide the first aggregation of research into the integrative physiological response of the kidneys to heat stress. While the focus of this review is on the human kidneys, we will utilize both human and animal data to describe these responses to passive and exercise heat stress, and how they are altered with heat acclimation. Additionally, we will discuss recent studies that indicate an increased risk of AKI due to exercise in the heat. Lastly, we will introduce the emerging public health crisis of older adults during extreme heat events and how the aging kidneys may be more susceptible to injury during heat stress.

Hold the Pendulum: Rates of Acute Kidney Injury are Increased in Patients Who Receive Resuscitation Volumes Less than Predicted by the Parkland Equation

OBJECTIVE

To determine whether restrictive fluid resuscitation results in increased rates of acute kidney injury (AKI) or infectious complications.

BACKGROUND

Studies demonstrate that patients often receive volumes in excess of those predicted by the Parkland equation, with potentially detrimental sequelae. However, the consequences of under-resuscitation are not well-studied.

METHODS

Data were collected from a multicenter prospective cohort study. Adults with greater than 20% total burned surface area injury were divided into 3 groups on the basis of the pattern of resuscitation in the first 24 hours: volumes less than (restrictive), equal to, or greater than (excessive) standard resuscitation (4 to 6 cc/kg/% total burned surface area). Multivariable regression analysis was employed to determine the effect of fluid group on AKI, burn wound infections (BWIs), and pneumonia.

RESULTS

Among 330 patients, 33% received restrictive volumes, 39% received standard resuscitation volumes, and 28% received excessive volumes. The standard and excessive groups had higher mean baseline APACHE scores (24.2 vs 16, P < 0.05 and 22.3 vs 16, P < 0.05) than the restrictive group, but were similar in other characteristics. After adjustment for confounders, restrictive resuscitation was associated with greater probability of AKI [odds ratio (OR) 3.25, 95% confidence interval (95% CI) 1.18-8.94]. No difference in the probability of BWI or pneumonia among groups was found (BWI: restrictive vs standard OR 0.74, 95% CI 0.39-1.40, excessive vs standard OR 1.40, 95% CI 0.75-2.60, pneumonia: restrictive vs standard, OR 0.52, 95% CI 0.26-1.05; excessive vs standard, OR 1.12, 95% CI 0.58-2.14).

CONCLUSIONS

Restrictive resuscitation is associated with increased AKI, without changes in infectious complications.

Orbital compartment syndrome in a burn patient without aggressive fluid resuscitation

INTRODUCTION

Orbital compartment syndrome may rarely occur in the setting of burns where therapy includes aggressive fluid resuscitation.

CASE

We report a case of bilateral orbital compartment syndrome in a 13-year-old male, with superficial facial burns secondary to hydrobromic acid, who did not receive aggressive fluid resuscitation. The patient was treated successfully with bilateral lateral canthotomy and cantholysis.

COMMENT

Facial burns may lead to orbital compartment syndrome without aggressive fluid resuscitation, likely due to excessive leakage of fluid and protein into the orbit combined with an inflammatory reaction.

Transcapillary exchange: role and importance of the interstitial fluid pressure and the extracellular matrix

This review will summarize current knowledge on the role of the extracellular matrix (ECM) in general and on the interstitial fluid pressure (P(if)) in particular with regard to their importance in transcapillary exchange. The fluid volume in the interstitial space is normally regulated within narrow limits by automatic re-adjustment of the interstitial hydrostatic and colloid osmotic pressures in response to perturbations in capillary filtration and by the lymphatics. Contrary to this commonly accepted view, P(if) can become an active force and create a fluid flux across the capillaries in several inflammatory reactions and trauma situations rather than limit the changes occurring. The molecular mechanisms involved in the lowering of P(if) include the release of cellular tension exerted on the collagen and microfibril networks in the connective tissue via the collagen-binding beta(1)-integrins, thereby allowing the glycosaminoglycan ground substance, which is normally underhydrated, to expand and take up fluid. Several growth factors and cytokines, including the platelet-derived growth factor BB, are able to reverse a lowering of P(if) and restore the normal compaction of the ECM. The magnitude of the lowering of P(if) varies with the inflammatory response. In several inflammatory reactions, a lowering of P(if) to -5 to -10 mmHg is seen, which will increase capillary filtration by 10-20 times since the normal capillary filtration pressure is usually 0.5-1 mmHg (skin and skeletal muscle). Unless this lowering of P(if) is taken into account, the enhanced solute flux resulting from an inflammatory response will be ascribed to an increased capillary permeability.

Pharmacologic modification to resuscitation fluid after thermal injury--is drotrecogin alfa the answer to arrest burn depth progression?

HYPOTHESIS

The addition of drotrecogin alfa (DA), an anti-inflammatory useful in septic shock, to standard burn shock resuscitation fluids will protect burned, injured skin from further injury.

METHODS

Anesthetized animals were subjected to a standardized burn pattern by applying a branding iron to 10 different locations on the back of the rat for 1 seconds to 14 seconds, creating a range of burn depths and severities.

DESIGN

Animal burn shock and resuscitation model.

PARTICIPANTS

Thirty-one male adult Sprague-Dawley rats.

INTERVENTIONS

Control animals were resuscitated with lactated Ringer's solution (LRS) at 2 mL/kg/percent total body surface area/24 h; experimental animals received LRS plus DA 24 microg/kg/h (LRS + DA).

OUTCOME MEASURES

Perfusion to each burned area was assessed using a laser Doppler imaging technology. Punch biopsies at each burned area were stained with hematoxylin and eosin and assessed for burn depth and for inflammation using previously reported measures. Samples from 14 animals were stained for terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and caspase-3 (apoptosis markers).

RESULTS

Increasing branding iron contact times worsened perfusion, burn depth, and apoptotic ratios. There was no correlation between inflammatory markers and burn contact time. The addition of DA leads to worse perfusion, deeper burns, worse inflammation, and decreased apoptotic ratios.

CONCLUSIONS

Laser Doppler imaging is a useful technology to assess burn depth. The addition of DA to traditional resuscitation fluids for burn shock is deleterious to the injured, burned skin. Modifying the traditional burn shock resuscitation fluids, although intellectually attractive, needs to be rigorously studied.

[Immunology and sepsis syndrome in burn trauma]

Despite significant advances in burn surgery and critical care, severe burn trauma defined as injuries covering more than 25% of the total body surface area, is still associated with high mortality and morbidity. Burn trauma is a whole body injury where peripheral dermal injury rapidly results in systemic inflammation and inflammatory core organ damage. The severe disturbance of internal homeostasis involves all vital organ systems and obligates early referral to specialized burn centers. Treatment of severely burned patients is a multifaceted challenge directed by pathophysiologic events which progress from local skin destruction, disruption of physicochemical and microvascular barriers to breakdown of peripheral and central circulation, organ failure and ultimately death. While early intensive care focuses on maintenance of tissue oxygenation and perfusion, surgical treatment deals with management of the burn wounds as a source of inflammation and infection. Here wound debridement and coverage is essential to abrogate systemic effects of inflammation and limit pathogen invasion. While control of early burn stages minimizes mortality due to burn shock, subsequent burn sepsis continues to be a formidable challenge for physicians and the main cause of burn mortality.

Balance point characterization of interstitial fluid volume regulation

The individual processes involved in interstitial fluid volume and protein regulation (microvascular filtration, lymphatic return, and interstitial storage) are relatively simple, yet their interaction is exceedingly complex. There is a notable lack of a first-order, algebraic formula that relates interstitial fluid pressure and protein to critical parameters commonly used to characterize the movement of interstitial fluid and protein. Therefore, the purpose of the present study is to develop a simple, transparent, and general algebraic approach that predicts interstitial fluid pressure (P(i)) and protein concentrations (C(i)) that takes into consideration all three processes. Eight standard equations characterizing fluid and protein flux were solved simultaneously to yield algebraic equations for P(i) and C(i) as functions of parameters characterizing microvascular, interstitial, and lymphatic function. Equilibrium values of P(i) and C(i) arise as balance points from the graphical intersection of transmicrovascular and lymph flows (analogous to Guyton's classical cardiac output-venous return curves). This approach goes beyond describing interstitial fluid balance in terms of conservation of mass by introducing the concept of inflow and outflow resistances. Algebraic solutions demonstrate that P(i) and C(i) result from a ratio of the microvascular filtration coefficient (1/inflow resistance) and effective lymphatic resistance (outflow resistance), and P(i) is unaffected by interstitial compliance. These simple algebraic solutions predict P(i) and C(i) that are consistent with reported measurements. The present work therefore presents a simple, transparent, and general balance point characterization of interstitial fluid balance resulting from the interaction of microvascular, interstitial, and lymphatic function.

Apoptosis is differentially regulated by burn severity and dermal location

BACKGROUND

The cellular processes that contribute to cell death in burns are poorly understood. This study evaluated the distribution and extent of apoptosis in an established rat model of acute dermal burn injury.

MATERIALS AND METHODS

A branding iron (100 degrees C) was applied to the depilated dorsum of seven rats, creating burn contact times of 1-8, 10, 12, and 14 s. Biopsies were collected and immunohistochemistry performed for apoptosis and cell injury/necrosis by detection of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and high-mobility group box 1 (HMGB1), respectively. The slides were scored by evaluating staining in superficial, middle, and deep dermal fields. Within these, basal keratinocytes of the epidermis, mesenchymal cells, adnexal epithelia, and vasculature wall cells were morphometrically analyzed for stain detection of selected markers.

RESULTS

TUNEL staining had an inverse relationship with contact time in most fields except in deep dermal mesenchymal cells where it was increased. HMGB1 nuclear staining was significantly decreased with progressive contact time consistent with transition to cell injury/necrosis.

CONCLUSIONS

This study is the first to demonstrate that apoptosis rate is dependent on dermal location, cell type, and severity of thermal injury. Furthermore, this work suggests that for most dermal locations increased thermal injury corresponds with decreased apoptosis and increased cell injury/necrosis. Together, these findings indicate that many parameters can regulate apoptosis in burn wounds, and these results will be critical to understanding burn pathogenesis and assessing future therapies.

Atrial natriuretic peptide release associated with smoke inhalation and physiological responses to thermal injury in sheep

Markedly elevated levels of plasma atrial natriuretic peptide (ANP), which exhibit potent diuretic and vasoactive properties, has been well documented in patients with acute lung injury. We examined the physiological effects of additional smoke inhalation on plasma ANP concentrations in an ovine burn model. Seventeen sheep were instrumented to receive fluid and have physiological measurements taken. The burn group (n=8) received 40% body surface area third degree burn and the burn+smoke group (n=9) received the same burn plus 48 breaths of cotton smoke insufflation. The animals were resuscitated according to the Parkland formula with Ringer's lactate in the following 72 h period. Hemodynamic, oxygenation, fluid balance, and plasma ANP levels were serially determined. The effects of smoke inhalation manifested as deteriorated oxygenation, and increased fluid accumulation after a sustained initial shock period of more than 12 h. Plasma ANP levels in the burn+smoke group showed a biphasic elevation, whereas the burn group showed no appreciable changes throughout the whole experimental period. The initial increase in plasma ANP concentrations occurred immediately after injury (from 96+/-10 at baseline to 136+/-17 pg/mL at 3h after injury); thereafter, it decreased towards baseline value, followed by a second increase in the post resuscitation period (183+/-43 pg/mL at 72 h after injury). Decreased urine output and accentuated pulmonary vascular resistance in the combined injury group was observed between the two ANP level peaks, indicating that ANP release modified physiological responses to the burn+smoke injury.

Use of subatmospheric pressure therapy to prevent burn wound progression in human: first experiences

Thermal trauma causes two different types of injuries within the burn wound. First, an immediate and irreversible injury, and, second, a delayed and partly reversible injury. It is a very common observation in burned patients that areas that initially seemed to be partial thickness burns have to be regarded as full thickness within the next day or days. The impairment of blood flow within the zone of stasis is due to the impairment of the vascular patency at the microvascular level. This progression is closely correlated to the degree of oedema formation. The aim of the study was to demonstrate that applied, controlled subatmospheric pressure is useful to prevent the progression of partial thickness burn injuries. Therefore, seven patients (mean age, 44.2 years; S.D., 22.4 years) with bilateral partial thickness hand burns were included into this treatment protocol. The more intense injured hand was treated with controlled applied subatmospheric pressure (V.A.C. (ATS)), the other and less injured hand conservatively by use of silver sulphadiazine creme. In the V.A.C.-treated hand a massive hyperperfusion was observed, being a possible reason for the prevention of burn progression. Moreover, a noteworthy amount of fluid was removed from the burn wound and a clinically obvious oedema reduction was observed in comparison to the contralateral side. In summary, we are of the opinion, that patients with partial thickness or mixed thickness burn may benefit from the application of subatmospheric pressure by reducing oedema formation and increasing perfusion.

Trends in burn resuscitation: shifting the focus from fluids to adequate endpoint monitoring, edema control, and adjuvant therapies

Bum shock is a complex process involving a series of intertwined physiologic responses to injury that require more rigorous intervention than simply a change in fluid tonicity, fluid composition, or fluid resuscitation volume. Controversy ensues over monitoring techniques and resuscitation goals, in part because the identification of true markers of perfusion is clouded by intradependence of endpoints on other metabolic processes. The persistence of cellular hypoperfusion in patients who have been deemed adequately resuscitated by global indices supports the growing realization that failure of conventional endpoint-monitoring strategies to detect compensated bum shock can lead to significant organ injury from SIRS or MODS. Current endpoints should be interpreted in the aggregate, because none have yet been demonstrated to reflect tissue perfusion status independently and accurately. Numerous technologically advanced endpoints to predict patient outcome, which may be useful in determining futility of treatment or end-of-life decisions, are now available. Still lack-ing, however, is a reliable tool proven to improve outcome that can guide bum shock resuscitation therapies successfully. Exciting new research in tissue oxygenation and perfusion has revealed that damaging mediator cascades and irreversible microvascular changes may preclude complete resolution of bum shock solely through restoration of oxygen delivery. Because bum patients now frequently survive the early resuscitation phase. the focus should be on controlling derangements in oxygen use and correcting occult hypoperfusion to reduce later adverse patient outcomes from SIRS, sepsis, and MODS. Bum-specific research on resuscitation endpoints and monitoring strategies lags behind research in other patient populations. Present standards and monitoring guidelines for bum shock resuscitation should be critically evaluated and based on true, scientifically validated data rather than on observational studies or personal beliefs. Thus the continuing challenge for clinicians and researchers:burn centers must collaborate to perform large, multi-center studies to evaluate critically and to prove resuscitation endpoints and therapies. Future technologies targeted at microcirculatory perfusion and cellular oxygenation offer an exciting promise for less invasive, easily accessible, more accurate endpoints and treatments for bum shock resuscitation.

New and active role of the interstitium in control of interstitial fluid pressure: potential therapeutic consequences

Here we present recent data indicating that the present view of the interstitium as a passive fluid reservoir has to be revised. The connective tissue cells and extracellular matrix have a role in the control of P(if) and a fundamental role in the rapid development of edema in burns and in the initial swelling in inflammation by generating a lowering of interstitial fluid pressure. In this process, the beta1-integrin system seems to provide a common pathway by which the cells can lower as well as raise P(if). Inflammatory swelling can be reversed by endo- and exogenous substances, thereby suggesting that the connective tissue can serve as a novel target for pharmacological intervention. Furthermore, the new knowledge in interstitial physiology on means to reduce interstitial fluid pressure may be of importance for drug delivery into solid tumors, where a high P(if) limits the uptake of therapeutic agents.

PGE1 induced transcapillary transport of 51Cr-EDTA in rat skin measured by microdialysis

Interstitial fluid pressure (P(if)) is a key determinant in increasing the transcapillary driving pressure, pulling fluid from the microcirculation into the interstitial space at the onset of acute inflammatory reactions and the oedema formation associated with these. Prostaglandin E1 (PGE1) induces lowering of P(if) in rat skin which increases transcapillary transport of 51Cr-EDTA into the center of a tumor as measured by microdialysis. The aim of this study was twofold: First, to evaluate and develop the microdialysis technique thoroughly with regard to its suitability for investigating transcapillary water transport in rat skin using 51Cr-EDTA as a tracer. Secondly, to evaluate the effect of PGE1 on transcapillary transport of 51Cr-EDTA. This study demonstrates that PGE1 increases transcapillary transport of 51Cr-EDTA into skin interstitium. There were no significant differences between the experimental probe and the control probe when calculations from the entire experiment (90 min) were compared. On the other hand, significant differences were observed by examining the experiment in smaller time intervals. PGE1 increased transcapillary transport of 51Cr-EDTA during the first 15 min when administered through the microdialysis probe. This observation suggests that increased blood flow and/or permeability-surface area product are responsible for raising the transcapillary transport of 51Cr-EDTA, i.e. the transport is diffusion limited. Administration of PGE1 through the probe rather than around the probe resulted in less scatter between experiments than when PGE1 was injected subcutaneously around the probe.

Cytochalasin D induces edema formation and lowering of interstitial fluid pressure in rat dermis

The increased capillary fluid filtration required to create a rapid edema formation in acute inflammation can be generated by lowering the interstitial fluid pressure (P(IF)). The lowering of P(IF) appears to involve dynamic beta(1)-integrin-mediated interactions between dermal cells and extracellular matrix fibers. The present study specifically investigates the role of the cell cytoskeleton, i.e., the contractile apparatus of cells, in controlling P(IF) in rat skin as the integrins are linked to both the cytoskeleton and the extracellular matrix. P(IF) was measured using a micropuncture technique in the dorsal skin of the hind paw at a depth of 0.2--0.5 mm and following the induction of circulatory arrest with the intravenous injection of KCl in pentobarbital anesthesia. This procedure prevented the transcapillary flux of fluid and protein leading to edema formation in acute inflammation, which in turn can increase the P(IF) and therefore potentially mask a decrease of P(IF). Control P(IF) (n = 42) averaged -0.8 +/- 0.5 (means +/- SD) mmHg. In the first group of experiments, subdermal injection of 2 microl cytochalasin D, a microfilament-disrupting drug, lowered P(IF) to an average of -2.8 +/- 0.7 mmHg within 40 min postinjection (P < 0.05 compared with control). Subdermal injection of vehicle (10% DMSO in PBS or PBS alone) did not change the P(IF) (P > 0.05). Lowering of the P(IF) was not observed after the injection of colchicine or nocodazole, which specifically disrupts microtubuli in cultured cells. In the second group of experiments, 2 microl of cytochalasin D injected subdermally into rats with intact circulation increased the total tissue water (TTW) and albumin extravasation rate (E(ALB)) by 0.7 +/- 0.2 and 0.4 +/- 0.3 ml/g dry wt, respectively (P < 0.05 compared with vehicle). Nocodazole and colchicine did not significantly alter the TTW or E(ALB) compared with the vehicle (P > 0.05). Taken together, these findings strongly suggest that the connective tissue cells can participate in control of P(IF) via the actin filament system. In addition, the observation that subdermal injection of cytochalasin D lowered P(IF) indicates that a dynamic assembly and disassembly of actin filaments also occurs in the cells of dermal tissues in vivo.

[Systemic complications of extended burns]

Burns covering more than 10% of the total body surface area (TBSA) are responsible for systemic perturbations which, in very severe cases, can represent a vital risk and, in all cases, affect the wound evolution. Among these general perturbations, fluid volume and electrolyte changes, leading eventually to burn shock, have the most dramatic consequences. Burn shock is, still to day, a vital risk and can also, in case of inadequate early fluid resuscitation, results in secondary morbidity and mortality. Fluid replacement during the very first hours after injury represents certainly a key point of the management of severe burn cases. Estimation of resuscitation fluid needs during this period is frequently underestimated. For adult, we recommend, during the first hour, a minimum of one liter for all severe injuries and two liters if the injury exceeds 50% of TBSA. Pulmonary injuries due to smoke inhalation are frequent, about 25% of patients hospitalized in burn units, and responsible for numerous death at site of house fires. In burn units, about 25% of hospitalized patients have pulmonary injuries in relation with smoke inhalation. This population has a high mortality rate increasing with the area of the skin injury and with age. Patients with inhalation injury need more resuscitation fluids, are subject to pneumonia and necessitate frequently mechanical ventilation. Parameters of the mechanical ventilation have to be choice to avoid barotrauma. Severe burn patients are submitted to a very high metabolic level. This can leads to a deep nutritional deficit responsible for an immunological suppression. It is then of major importance to provide an adequate nutritional support. It is also necessary to fight against the stress and to put the patient in a warm environment. Finally, infection is the most frequent and the most severe complication of burn injuries. Everything have to be done to avoid bacteriological contamination including architecture, equipment's, care procedure, nutritional support, types of wound dressing and most importantly surgery. Surgical procedures have to be done as earliest as possible to excise necrosis and cover the wound.

Osmotically induced cytosolic free Ca(2+) changes in human neutrophils

Cytosolic free Ca(2+) concentration in neutrophils was measured by ratiometric fluorometry of intracellular fura2. Increasing the extracellular osmolarity, by either NaCl (300-600 mM) or sucrose (600-1200 mM), caused a rise in cytosolic free Ca(2+) (Delta(max) approximately equal to 600 nM). This was not due to cell lysis as the cytosolic free Ca(2+) concentration was reversed by restoration of isotonicity and a second rise in cytosolic free Ca(2+) could be provoked by repeating the change in extracellular osmolarity. Furthermore, the rise in cytosolic free Ca(2+) concentration occurred in the absence of extracellular Ca(2+), demonstrating that release of intracellular fura2 into the external medium did not occur. The osmotically-induced rise in cytosolic free Ca(2+) was not inhibited by either the phospholipase C-inhibitor U73122, or the microfilament inhibitor cytochalasin B, suggesting that neither signalling via inositol tris-phosphate or the cytoskeletal system were involved. However, the rise in cytosolic free Ca(2+) may have resulted from a reduction in neutrophil water volume in hyperosmotic conditions. As these rises in cytosolic Ca(2+) (Delta(max) approximately equal to 600 nM) were large enough to provoke changes in neutrophil activity, we propose that conditions which removes cell water may similarly elevate cytosolic free Ca(2+) to physiologically important levels.

High dose vitamin C counteracts the negative interstitial fluid hydrostatic pressure and early edema generation in thermally injured rats

BACKGROUND AND OBJECTIVE

edema formation after thermal injury is rapid and fulminant within the first hour after injury and increased microvascular permeability has been claimed to be the main responsible mechanism. An acute decrease in interstitial fluid hydrostatic pressure (P(if)) down to -150 mm Hg has recently been reported in dermal burns. This strong negative tissue pressure creates a 'suction' on the fluid in the capillaries. Furthermore, high dose vitamin C (VC) has been shown to reduce postburn edema and fluid requirements following major burn injuries. This led to the present study, aimed at investigating whether VC administered after thermal injury in rats, could attenuate the strongly negative P(if). Edema volume was measured by total tissue water content (TTW) and extravasation of albumin (Ealb).

STUDY DESIGN

a prospective, open experimental study.

MATERIALS AND METHODS

pentobarbital-anesthetized rats received either a full-thickness burn injury covering 10% of total body surface area, or a sham burn. The rats were given VC or equal volumes normal saline (NS) either before the burn, 5 or 30 min after the injury. VC (25 mg/ml in NS, osmolality 272 mOsm/l) was administered as a bolus (66 mg/kg) followed by infusion (33 mg/kg/h). The animals were divided into 7 groups (6 animals in each) according to the timing of VC/NS administration: (1) VC-preburn, (2) VC-5 min postburn, (3) VC-30 min postburn, (4) NS-preburn, (5) NS-5 min postburn, (6) NS-30 min postburn and (7) VC-pre sham burn group. All groups were duplicated for series I and II.

MEASUREMENTS

in series I; P(if) was measured using a sharpened glass micropipette connected to a servo-controlled counter pressure system. Measurements were averaged in the following time periods: preburn, 5-20, 21-40, 41-60 and 61-90 min postburn. In series II; Ealb and TTW were measured in burned and non-burned skin by radio-labelled albumin and wet-dry weights, respectively.

RESULTS

in the sham control group (VC-pre-sham burn), P(if) ranged between -1 and -2 mm Hg and did not change throughout the experimental period. In the NS group (placebo), P(if) fell to -46.8 +/- 10.1 (1 S.D.) mm Hg at 5-20 min after the injury and were -23.1 +/- 13.4 and -11.6 +/- 4.1 mm Hg at 21-40 and 41-60 min postburn. P(if) returned to preburn values at 61-90 min post injury. In the VC groups, there was a marked attenuation of the negative P(if) to average -10.1 +/- 11.8 mm Hg at 5-20 min, -2 +/- 1.7 and -0.6 +/- 1.2 mm Hg at 21-40 and 41-60 min after injury, respectively (all p < 0.01 compared to NS). TTW in burned skin of the NS-5 min groups was 3.12 +/- 0.28, VC5-min group was 2.57+/-0.69 and VC sham was 1.77+/-0.19 ml/g DW, respectively (p < 0.01 compared to sham control for all values). In all the VC-groups TTW values were higher than sham control and lower than in the corresponding NS-groups (p > 0.05 both ways). No statistical significant differences were found between Ealb-values in the VC- and NS-groups.

CONCLUSION

high-dose vitamin C attenuates the development of strongly negative P(if) in burned dermis and reduces the edema as measured by TTW. No significant change in Ealb was found. Vitamin C was thus found to have potential beneficial effects on the acute postburn edema generation.

Effect of alpha-trinositol on carrageenan-induced rat paw edema and lowering of interstitial fluid pressure

Alpha-trinositol attenuates edema formation and capillary albumin extravasation and lowering of interstitial fluid pressure (Pif) in several acute inflammatory reactions in rat skin or trachea. The lowering of Pif is an important driving force required to explain the rapid edema formation in acute inflammatory reactions. The lowering of Pif and edema formation are attenuated by alpha-trinositol, which is suggested to act on the cellular adhesion receptor for extracellular matrix components. This would represent a novel therapeutic strategy for acute inflammation. To further clarify the mechanisms behind the anti-inflammatory effects of alpha-trinositol, the effects of pre- and post-treatment with alpha-trinositol on edema formation and lowering of Pif were studied after subdermal injection of carrageenan in the rat. The experiments measuring Pif showed that the lowering of Pif induced by carrageenan was abolished by 10 mg alpha-trinositol when administered either prior to or after injection of 5 microl 1% (w/v) lambda carrageenan in the dorsum of the paw. Edema formation after injection of lambda carrageenan (100 microl, 1.5% w/v) into the foot pad was studied in a separate series. In control animals receiving saline vehicle, the volume of the paw injected with carrageenan increased by approximately 30% after 3-4 h. The only significant effect of infusion of 20 mg kg(-1) h(-1) alpha-trinositol was a reduction of edema to approximately 20% when treatment was started 1 h before carrageenan injection. Therefore, the plasma concentration of alpha-trinositol must already be high when carrageenan is injected in order to prevent edema in the late phase. In conclusion, the present results indicate that the mechanisms involved in the lowering of Pif in the early phase of edema development are different from those responsible for the manifest edema measured 3-4 h after carrageenan.

Microvascular permeability

This review addresses classical questions concerning microvascular permeabiltiy in the light of recent experimental work on intact microvascular beds, single perfused microvessels, and endothelial cell cultures. Analyses, based on ultrastructural data from serial sections of the clefts between the endothelial cells of microvessels with continuous walls, conform to the hypothesis that different permeabilities to water and small hydrophilic solutes in microvessels of different tissues can be accounted for by tortuous three-dimensional pathways that pass through breaks in the junctional strands. A fiber matrix ultrafilter at the luminal entrance to the clefts is essential if microvascular walls are to retain their low permeability to macromolecules. Quantitative estimates of exchange through the channels in the endothelial cell membranes suggest that these contribute little to the permeability of most but not all microvessels. The arguments against the convective transport of macromolecules through porous pathways and for the passage of macromolecules by transcytosis via mechanisms linked to the integrity of endothelial vesicles are evaluated. Finally, intracellular signaling mechanisms implicated in transient increases in venular microvessel permeability such as occur in acute inflammation are reviewed in relation to studies of the molecular mechanisms involved in signal transduction in cultured endothelial cells.

Effect of alpha-trinositol on interstitial fluid pressure, oedema generation and albumin extravasation in experimental frostbite in the rat

1. The anti-inflammatory effect of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate) on oedema formation, microvascular protein leakage and interstitial fluid pressure (Pif) in rat skin after frostbite injury, was investigated. Alpha-trinositol (40 mg kg body weight(-1)) was administered intravenously as a bolus both before and/or in the interval between freezing and thawing of the tissue. 2. Pif was measured in rat paw skin with micropipettes connected to a servo-controlled counterpressure system. Oedema formation was estimated by measuring the increase in total tissue water content (wet weight minus dry weight divided by dry weight). Albumin extravasation (i.e., the difference between the plasma equivalent space for 125I- and 131I-human serum albumin (HSA) circulating for different time intervals) was used to estimate the microvascular leakage. 3. Compared to untreated animals, alpha-trinositol given pre- and/or post-freeze reduced total tissue water and albumin extravasation as well as the fall in Pif in injured tissue significantly (P<0.05). Alpha-trinositol given only post-freeze reduced total tissue water and albumin extravasation from 4.46+/-0.93 and 2.37+/-1.12 to 2.51+/-0.29 and 0.36+/-0.18 ml g dry weight(-1), respectively (P<0.05). 4. Pif fell from -0.8+/-0.2 mmHg pre-freeze to -3.4+/-1.0 mmHg (P<0.05) at 20 min after tissue injury (circulatory arrest) and was attenuated by treatment with alpha-trinositol. 5. We conclude that alpha-trinositol exerts its anti-oedematous effect by acting on the extracellular matrix, attenuating the lowering of Pif as well as on the microvascular wall, thereby decreasing the protein extravasation.

Effect of PGE1, PGI2, and PGF2 alpha analogs on collagen gel compaction in vitro and interstitial pressure in vivo

Acute inflammation in skin is accompanied by increased negativity of interstitial fluid pressure (PIF), which will increase capillary fluid filtration and thereby potentiate edema formation. A series of studies indicates that the connective tissue cells in rat dermis are involved in the control of PIF and mediate this response. The present study describes a novel effect of prostaglandin (PG) E1 isopropyl ester, carbaprostacyclin (PGI2 analog), and latanoprost (PGF2 alpha analog) on edema formation and PIF in parallel with their action on the fibroblast-populated collagen gel contraction assay. The prostaglandins were injected subdermally in pentobarbital-anesthetized rats. PIF was measured with a servo-controlled counterpressure system after circulatory arrest had been induced with saturated potassium chloride. Circulatory arrest was induced to limit edema formation that would raise interstitial fluid volume and thereby attenuate a possible increased negativity of PIF. PGE1 (0.91 mM) and carbaprostacyclin (1.28 mM) lowered PIF from a control value of -0.8 +/- 0.4 mmHg to -3.0 +/- 0.4 (P < 0.01) and -3.7 +/- 0.9 (P < 0.01) mmHg, respectively, within 45 min in a dose-dependent manner. Edema formation was measured in separate experiments. PGE1 and carbaprostacyclin significantly increased interstitial fluid volume (extravascular 51Cr-EDTA space) at concentrations as low as 0.1 and 1.1 microM, respectively. Latanoprost had no effect on PIF or edema formation. However, latanoprost reversed, in a dose-dependent manner, an increased negativity of PIF accompanying the anaphylactic reaction to dextran. In the gel contraction assay with human diploid fibroblasts (AG 1518), a corresponding specificity was observed where PGE1 and carbaprostacyclin effectively inhibited gel contraction although latanoprost had no effect. Thus the present data demonstrate a novel effect of prostaglandins and provide further evidence for active modulation of PIF via loose connective tissue cells.

alpha-Trinositol prevents increased negativity of interstitial fluid pressure in rat skin and trachea induced by dextran anaphylaxis

The new anti-inflammatory agent alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), is suggested to act on the cellular adhesion receptor towards extracellular matrix components, the beta1-integrins, and may therefore represent a novel principle for therapy of the phenomena associated with acute inflammation. Increased negativity of interstitial fluid pressure (p(if)) is a major driving force for the rapid edema formation in trachea and skin associated with dextran anaphylaxis in the rat. We therefore used this experimental model to study the effect of alpha-trinositol in skin and trachea of pentobarbital anesthetized rats. p(if) was measured with sharpened glass capillaries (3-7 microm) connected to a servocontrolled counterpressure system. alpha-Trinositol (10 mg) was given before or after dextran. Circulatory arrest was induced 2 min after i.v. dextran to limit the increased capillary fluid filtration associated with the anaphylactic reaction. This increased filtration will otherwise raise interstitial volume and thereby p(if) and cause an underestimation of a potential increased negativity of p(if). In the trachea, p(if) was 0.0 +/- 1.0 mmHg (S.D.) and -1.4 +/- 0.5 mmHg in controls given saline vehicle and alpha-trinositol (P > 0.05), respectively, and fell to -8.5 +/- 2.7 mmHg after dextran (P < 0.01). alpha-Trinositol given 2 min prior to or after dextran resulted in p(if) of -1.7 +/- 1.2 mmHg (P > 0.05 versus control, P < 0.01 versus dextran) and -4.7 +/- 3.0 mmHg (P < 0.01 versus control and dextran), respectively. In skin, i.v. dextran caused p(if) to fall from -0.6 +/- 0.5 to -4.6 +/- 1.9 mmHg (P < 0.001). When alpha-trinositol was given prior to dextran the corresponding figures were -0.4 +/- 0.8 and -0.9 +/- 1.1 mmHg, respectively (P > 0.05). Subdermal administration of alpha-trinositol after i.v. dextran and circulatory arrest normalized p(if) in concentration of 100, 10 and partly at 1 mg/ml. Thus, alpha-trinositol prevented the increased negativity of p(if) induced by dextran anaphylaxis when administered prior to as well as after dextran showing that the alpha-trinositol also could influence an already started inflammatory reaction.

Hyperbaric oxygen therapy and piracetam decrease the early extension of deep partial-thickness burns

During the first 24 h, a progression of the burn wound in histological depth or extension is often noted. This can only partially be prevented by the routinely used protocols of fluid resuscitation and burn wound dressing. In a rat model of 5% TBSA burn, hyperbaric oxygen therapy (HBOT) and piracetam were evaluated for their ability to further prevent this early deepening of the burn wound. After infliction of the burn wound, the animals were treated with an accepted basic burn wound treatment consisting of mafenide 10% solution humid dressings. They were then randomized into three groups: a control group (n = 10), receiving no other treatment, a HBOT group (n = 17), receiving 60 min of HBOT (203 kPa) twice daily, and a piracetam group (n = 19), receiving piracetam (200 mg/kg IM) twice daily. On the third day of treatment, the entire burn wound was exised and examined histologically. It was found that both HBOT and piracetam had statistically significant effects on the preservation of epidermal basal membrane (P < 0.001 and P < 0.01, respectively). HBOT, but not piracetam, further had significant effects on the destruction of skin appendages (P < or = 0.05 and P > 0.05, respectively) and on the degree of subepidermal inflammation, as measured by leucocyte infiltration (P < 0.001 and P > 0.05, respectively). Furthermore, the HBOT group showed significantly less leucocyte infiltration than the piracetam group (P < 0.01). It was concluded that, although the clinical importance of the small effects on skin appendage and basal membrane preservation may be questionable, the effect on subepidermal leucocyte infiltration is striking and warrants further investigation of the anti-inflammatory effects of HBOT and possibly piracetam.

Pathophysiology of the burn wound and pharmacological treatment. The Rudi Hermans Lecture, 1995

The body's reaction to thermal injury is much more than an initial, local inflammatory response. The burn wound is a continuous, severe threat against the rest of the body due to invasion of infectious agents, antigen challenge and repeated additional trauma caused by wound cleaning and excision. The inflammatory mediators which control blood supply and microvascular permeability in the wound have been extensively studied and are largely understood. Attempts to suppress the inflammatory reaction by different drugs, have, however, been less successful. Extensive thermal injury and sepsis also results in immunosuppression. The defects causing immunosuppression are still very much under consideration. An understanding of these defects is essential for the development of therapies. The increasing interest in the control of the inflammatory reactions by cytokines may, in the near future, be of great importance.

A model of fluid resuscitation following burn injury: formulation and parameter estimation

A dynamic compartmental model is developed to describe the redistribution of fluid and albumin between the circulation and the intact and injured interstitia following burn injury in humans. Transcapillary fluid and albumin exchange is described by a coupled Starling mechanism, while the effect of the burn is represented by time-dependent perturbations to all three compartments. The unknown model parameters are determined for two groups of patients, having less than and greater than 25% total body surface area burns, by statistical fitting of model predictions to patient data from two sources. The parameters include the perturbations to the fluid filtration coefficients in uninjured and injured tissue, GkF,Tl and GkF,BT, respectively, the relaxation coefficient, r, which describes the exponential decay of the perturbations, and the exudation factor, EXFAC, which relates the protein concentration in the exudate to that in the injured tissue. Perturbations to other parameters, including the membrane permeability-surface area product and the albumin reflection coefficient in the injured and uninjured tissues, are determined based on interrelationships with GkF,Tl and GkF,BT. The values of GkF,BT, when corrected for tissue destruction and decreased post-injury perfusion, are in reasonable agreement with the limited experimental data available from the literature. The model and its parameters are further validated by comparing the simulated patient responses to the clinical data used in the parameter estimation as well as to data available from two additional sources.

Neurogenic inflammation in rat trachea is accompanied by increased negativity of interstitial fluid pressure

The present experiments were performed to investigate whether neurogenic inflammation in rat trachea (with edema formation and protein extravasation when the circulation is intact) induced by electrical field stimulation of neuropeptide-containing C fibers in the vagal nerve is accompanied by increased negativity of interstitial fluid pressure (P(if)). Increased negativity of P(if) in the trachea occurs in dextran anaphylaxis and mast cell degranulation and facilitates edema formation under these circumstances. Experiments were performed after circulatory arrest had been induced in pentobarbital anesthesia to prevent edema formation, which will raise P(if) and potentially cause underestimation of an increased negativity of P(if). After induction of circulatory arrest, the vagal nerve was isolated and placed in a stimulating electrode. The trachea was then exposed and covered with mineral oil, and measurement of P(if) was started as soon as possible thereafter. P(if) was measured with sharpened glass capillaries (tip diameter, 3 to 7 microns) connected to a servocontrolled counterpressure system. P(if) in the control group (n = 12) did not change throughout the observation period. Electrical stimulation of the left vagal nerve caused P(if) to fall in all experiments, from -1.1 +/- 1.1 mm Hg in the control condition to an average of -10.6 +/- 3.4 mm Hg (n = 9, P < .01). In some experiments, a continuous recording of P(if) was obtained, showing that the reduction of P(if) started within 30 seconds after onset of stimulation to reach and later remain at a stable level within a few minutes. The experimental protocol was repeated after the C fibers had been nearly depleted of neuropeptides with capsaicin.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathogenesis of edema formation in burn injuries

One of the obvious acute features of cutaneous thermal injury is the swelling of the involved tissue. This swelling is caused by a fluid shift from circulating plasma. Along with the evolution of intravenous fluid therapy in trauma and surgery, the implementation of such therapy to burn victims has improved survival. Edema generation aggravated by fluid therapy may, however, represent a source of increased morbidity. This paper presents a review of the literature on postburn edema generation, focusing mainly on fluid physiology. It is well documented that fluid is lost from the circulation into burned tissue because of a moderate increase in capillary permeability to fluid and macromolecules and a modest increase in hydrostatic pressure inside the perfusing microvessels. Recently it was discovered that a very negative interstitial pressure develops in thermally injured skin. This pressure constitutes a strong "suction" adding markedly to the edema generating effect of increased capillary permeability and pressure.

Peripheral vascular permeability following a thermal injury to the airway

Effects of thermal injury to the airway on the vascular permeability in the region of head and neck, were studied in the canine models. The thermal airway injury was produced by an inhalation of a gas burner's flame through the metallic tracheostomy cannula. The changes in vascular permeability were evaluated by calculating the reflection coefficient, which was obtained by the protein washdown technique into lymph. The reflection coefficient after the flame inhalation did not show any increases, while it increased significantly after a histamine infusion into the carotic artery. We concluded, that the vascular permeability in the unburned area does not increase at least in the first 3 hr after a thermal injury to the airway.

Increased negativity of interstitial fluid pressure contributes to development of oedema in rat skin following application of xylene

Intradermal interstitial fluid pressure (Pi) has been studied in rat skin during formation of inflammatory oedema caused by application of xylene. Pi was measured with sharpened micropipettes connected to a servocontrolled counter-pressure system. Control Pi averaged -1.3 +/- 0.6 (SD) mmHg. Following xylene application Pi decreased to -5.0 mmHg after 5 min and then increased to stabilize at about 0 mmHg at 45-60 min and later. When the transvascular fluid shifts accompanying the inflammatory reaction were prevented by inducing circulatory arrest prior to xylene application, Pi fell to -7.5 mmHg within 5 min and remained at this level throughout the observation period of 90 min. Aprotinin in large doses (80,000 KIE kg-1) before xylene application reduced the fall in Pi, whereas indomethacin had no effect. The increased negativity in Pi will add directly to a normal transcapillary net filtration pressure of about 0.5 mmHg, resulting in a 10- to 20-fold increase in this pressure. The present experiments therefore suggest that the interstitium plays an active role in oedema formation in the initial phase of xylene-induced inflammation in rat skin through the development of an increased negativity of Pi.

Transcapillary albumin extravasation in rat skin and skeletal muscle: effect of increased venous pressure

Plasma-to-tissue transport of radioactively labelled albumin has been used to study the effect of increased venous pressure on transcapillary albumin transport. Venous pressure was increased by inflating a balloon catheter in the inferior caval vein. Plasma-to-tissue transport of albumin was taken as the extravascular distribution space (EValb) for 125I-labelled human serum albumin (I-HSA) after 1 h. Venous pressure was increased from 2 to 20 mmHg in the experimental group. Interstitial fluid volume (IFV) was measured as the extravascular distribution space for 51Cr-EDTA. In control EValb was 9.24 X 10(-3) ml g-1 d. wt (SD = 1.28, n = 8) and 3.67 X 10(-3) ml g-1 d.wt (SD = 0.94, n = 8) in skin and skeletal muscle, respectively. Increasing venous pressure raised EValb and IFV in skin and skeletal muscle, but the increase in EValb was about 3 and 5% of the rise in IFV, resulting in capillary reflection coefficients for albumin of 0.94 in skin and 0.98 in skeletal muscle. The low transcapillary albumin transport relative to water transport is compatible with a two-pore model of transcapillary exchange where large pores (250 A) accounts for less than 5.5 and 2.5% of the total capillary filtrate of fluid in skin and skeletal muscle, respectively.

Analysis of altered capillary pressure and permeability after thermal injury

In order to investigate the effects of thermal injury on microvascular hemodynamics and permeability, hindpaw arterial (PA), venous (PV), and capillary (PC) pressures, blood (QB) and lymph (QL) flows, and lymph (CL) and plasma (CP) total protein concentrations were measured before and for 3 hr after a 10-sec 100 degrees C scald burn in 11 dogs. Prior to injury in eight experiments (Group I--permeability analysis) venous pressure was elevated by outflow restriction until the minimal CL/CP was obtained. In three experiments (Group II--hemodynamic analysis) outflow was not restricted. Lymph and plasma protein fractions ranging in size from 37 to 120 A were measured using gradient gel electrophoresis and capillary equivalent pore sizes were calculated. In the early postburn period, PC increased from 24 +/- 2 (mean +/- SE) to 47 +/- 5 mm Hg (P less than 0.05) and precapillary resistance (RA) decreased from 6.6 +/- 0.2 to 2.5 +/- 0.2 mm Hg/ml/min/100 g (P less than 0.05) while postcapillary resistance (RV) remained unchanged. Pre- to postcapillary resistance (RA/RV) fell by 74%. The reflection coefficient for total proteins (calculated as sigma = 1 - CL/CP) decreased from 0.87 +/- 0.01 to 0.45 +/- 0.02 (P less than 0.01). Permeability of the postburn capillary endothelium was described by using two populations of equivalent pores. Preburn pore radii were 50 and 300 A with 13% of the capillary filtrate passing through the large pores. Pore radii increased after injury to 70 and 400 A with 49% of the filtrate passing through the large pores. The postburn total tissue filtration coefficient (Kf) increased to 2.4 times the control. Over the first 3 hr postburn, 53% of the increase in capillary filtration was attributable to increased capillary pressure and 47% to increased permeability. We conclude that the early rapid edema formation following thermal injury is the result of marked increases in both capillary filtration pressure and filtration through large nonsieving pores.

Oedema measurements in a standard burn model

A highly standardized, reproducible burn model on rat hind paw as well as a method to measure oedema volume non-invasively is described. Along with a review of the literature on earlier methods to measure post-burn oedema we present a statistical evaluation of the present model with notes on its applicability in various experimental settings.

Early post-burn oedema in leucocyte-free rats

A highly standardized, reproducible burn model on rat hind paws with objective measurement of oedema volume was used to study the post-burn oedema formation in leucocyte-free rats as compared to a matched group of normal rats. No difference in oedema volume could be detected during the first 4 h post-burn. Thus the mechanical effect of sticking leucocytes in the injured area or leucocyte derived substances do not seem to play any significant role in the early local oedema formation which we postulate is entirely mediated by local events.