Pentafraction for superior resuscitation of the ovine thermal burn

The Influence of Obesity on Treatment and Outcome of Severely Burned Patients

Obesity and the related medical, social, and economic impacts are relevant multifactorial and chronic conditions that also have a meaningful impact on outcomes following a severe injury, including burns. In addition to burn-specific difficulties, such as adequate hypermetabolic response, fluid resuscitation, and early wound coverage, obese patients also present with common comorbidities, such as arterial hypertension, diabetes mellitus, or nonalcoholic fatty liver disease. In addition, the pathophysiologic response to severe burns can be enhanced. Besides the increased morbidity and mortality compared to burn patients with normal weight, obese patients present a challenge in fluid resuscitation, perioperative management, and difficulties in wound healing. The present work is an in-depth review of the current understanding of the influence of obesity on the management and outcome of severe burns.

Optimized fluid management improves outcomes of pediatric burn patients

BACKGROUND

One of the major determinants for survival of severely burned patients is appropriate fluid resuscitation. At present, fluid resuscitation is calculated based on body weight or body surface area, burn size, and urinary output. However, recent evidence suggests that fluid calculation is inadequate and that over- and under-resuscitations are associated with increased morbidity and mortality. We hypothesize that optimizing fluid administration during the critical initial phase using a transcardiopulmonary thermodilution monitoring device (pulse contour cardiac output [PiCCO]; Pulsion Medical Systems, Munich, Germany) would have beneficial effects on the outcome of burned patients.

METHODS

A cohort of 76 severely burned pediatric patients with burns over 30% of the total body surface area who received adjusted fluid resuscitation using the PiCCO system were compared with 76 conventionally monitored patients (C). Clinical hemodynamic measurements, organ function (DENVER2 score), and biomarkers were recorded prospectively for the first 20d after burn injury.

RESULTS

Both cohorts were similar in demographic and injury characteristics. Patients in the PiCCO group received significantly less fluids (P<0.05) with similar urinary output, resulting in a significantly lower positive fluid balance (P<0.05). The central venous pressure in the PiCCO group was maintained in a more controlled range (P<0.05), associated with a significantly lower heart rate and significantly lower incidence of cardiac and renal failure (P<0.05).

CONCLUSIONS

Fluid resuscitation guided by transcardiopulmonary thermodilution during hospitalization represents an effective adjunct and is associated with beneficial effects on postburn morbidity.

Combined burn and smoke inhalation injury impairs ovine hypoxic pulmonary vasoconstriction

OBJECTIVE

To examine the effects of combined burn and smoke inhalation injury on hypoxic pulmonary vasoconstriction, 3-nitrotyrosine formation, and respiratory function in adult sheep.

DESIGN

Prospective, placebo-controlled, randomized, single-blinded trial.

SETTING

University research laboratory.

SUBJECTS

Twelve chronically instrumented ewes.

INTERVENTIONS

Following a baseline measurement, sheep were randomly allocated to either healthy controls (sham) or the injury group, subjected to a 40%, third-degree body surface area burn and 48 breaths of cotton smoke according to an established protocol (n = 6 each). Hypoxic pulmonary vasoconstriction was assessed as changes in pulmonary arterial blood flow (corrected for changes in cardiac index) in response to left lung hypoxic challenges performed at baseline and at 24 and 48 hrs postinjury.

MEASUREMENTS AND MAIN RESULTS

Combined burn and smoke inhalation was associated with increased expression of inducible nitric oxide (NO) synthase, elevated NO2/NO3 (NOx) plasma levels (12 hrs, sham, 6.2 +/- 0.6; injury, 16 +/- 1.6 micromol.L; p < .01) and increased peroxynitrite formation, as indicated by augmented lung tissue 3-nitrotyrosine content (30 +/- 3 vs. 216 +/- 8 nM; p < .001). These biochemical changes occurred in parallel with pulmonary shunting, progressive decreases in Pao2/Fio2 ratio, and a loss of hypoxic pulmonary vasoconstriction (48 hrs, -90.5% vs. baseline; p < .001). Histopathology revealed pulmonary edema and airway obstruction as the morphologic correlates of the deterioration in gas exchange and the increases in airway pressures.

CONCLUSIONS

This study provides evidence for a severe impairment of hypoxic pulmonary vasoconstriction following combined burn and smoke inhalation injury. In addition to airway obstruction, the loss of hypoxic pulmonary vasoconstriction may help to explain why blood gases are within physiologic ranges for a certain time postinjury and then suddenly deteriorate.

DO PLASMA SUBSTITUTES HAVE ADDITIONAL PROPERTIES BEYOND CORRECTING VOLUME DEFICITS?

The best strategy for volume therapy has been the focus of debate and there are still no unique accepted guidelines. There is increasing evidence that some plasma substitutes possess additional effects on organ perfusion, microcirculation, tissue oxygenation, inflammation, endothelial activation, capillary leakage, and tissue edema that are beyond their volume replacing properties. Whether the different plasma substitutes differ with regard this additional effects was reviewed. The additional effects of plasma substitutes have mostly been studied experimentally or in animals, much less results are available in humans. The results are not uniform ranging from beneficial to even detrimental effects of a certain volume replacement strategy. Some important results from the literature are not reflected in the actual recommendations for treating volume deficits in the critically ill: although crystalloids have been shown to have considerable negative effects on microcirculation, organ perfusion, tissue oxygenation, and endothelial integrity, they are still often recommended as first choice volume replacement strategy. In several experimental studies hypertonic solutions have been shown to have various beneficial effects, they have not been, however, translated into humans. In future, the choice of the ideal volume replacement regimen should not only be focused on its volume restoring properties, but additional effects (e.g. on organ perfusion on, tissue oxygenation, inflammation, endothelial activation, capillary leakage) should also be taken into account when treating hypovolemia in the critically ill.

A prospective, randomized evaluation of intra-abdominal pressures with crystalloid and colloid resuscitation in burn patients

BACKGROUND

The volume of resuscitation in burn patients has been shown to correlate with intra-abdominal pressure (IAP). Limiting volume may reduce consequences of IAP and abdominal compartment syndrome. Colloid resuscitation has been previously shown to limit the volume required initially after burn.

METHODS

Thirty-one patients were prospectively followed. Inclusion criteria were a burn of 25% total body surface area with inhalation injury or 40% total body surface area without. Patients received crystalloid (Parkland formula) or plasma resuscitation. IAP was measured by means of urinary bladder transduction.

RESULTS

Mean age, area of burn, and baseline IAP were not different. Urine output was maintained. There was a greater increase in IAP with crystalloid (26.5 vs. 10.6 mmHg, p < 0.0001). Two patients in the plasma group developed IAP greater than 25 mmHg; only one patient in the crystalloid group maintained IAP less than 25 mmHg. More fluid volume was required with crystalloid resuscitation, 0.26 L/kg, versus 0.21 L/kg (p < 0.005). Correlation was seen in both groups between volume of fluid and IAP (crystalloid, r = 0.351; plasma, r = 0.657; all patients, r = 0.621).

CONCLUSION

Plasma-resuscitated patients maintained an IAP below the threshold of complications of intra-abdominal hypertension. This appears to be a direct result of the decrease in volume required. Lower fluid volume regimens should be given consideration as the incidence and consequences of intra-abdominal hypertension in burn patients continue to be defined.

Skin nitric oxide and its metabolites are increased in nonburned skin after thermal injuries

Local and systemic inflammation can lead to progression of burn wounds, converting second- to third-degree wounds or extending the burn to adjacent areas. Previous studies have suggested that the skin is an important site of production of nitric oxide (NO), synthesized by inducible nitric oxide synthase (iNOS) activation after injury. NO increases in burned wounds, but its formation in noninjured skin has not been investigated. We hypothesized that after severe burns, NO and cytotoxic peroxynitrite would increase in noninjured skin. We also tested the hypothesis that BBS-2, a specific inhibitor of iNOS, would impair NO formation after burn. Thirteen female sheep were randomized into burn injury and smoke inhalation (n = 5, group 1), burn and smoke treated with BBS-2 (n = 3, group 2), and sham (saline treatment, no injury) (n = 5, group 3). All the animals, including the sham-injury group, were mechanically ventilated for 48 h. Samples of nonburned skin and plasma were collected from each animal, and levels of NO and its metabolites were evaluated using a NO chemiluminescent detector. Nitrotyrosine and iNOS expression were determined in the skin by Immunoperoxidase staining, and scoring of masked slides (epidermis, hair follicles, vessels, glands, and stroma) was performed. Skin NO and metabolites significantly increased in the burn and smoke injury group, and this was inhibited by BBS-2. Nitrotyrosine expression also increased significantly in the skin of burned animals. BBS-2 prevented the increase of NOx but not the increase of nitrotyrosine expression in skin. Plasma levels of NO increased in burned animals when compared with sham, but this increase was not significant. The increase of NO and its metabolites after burn in noninjured skin is followed by a significant increase in peroxynitrite, a potent cytotoxic mediator.

The effects of hydroxyethyl starch on lung capillary permeability in endotoxic rats and possible mechanisms

In this study we examined the effects of hydroxyethyl starch (HES 200/0.5) on lung capillary permeability in endotoxic rats and explored the possible mechanisms. Male Wistar rats were randomly divided into seven groups treated with saline, lipopolysaccharide (LPS; 6 mg/kg), LPS plus HES (3.75, 7.5, 15, or 30 mL/kg), or HES (30 mL/kg) alone for 4 or 2 h. Lung capillary permeability, lung neutrophil accumulation, expression of CD11b on the blood neutrophil cell surface, lung cytokine-induced neutrophil chemoattractant protein level, and nuclear factor kappa B (NF-kappaB) activation in blood neutrophils and lungs were measured. HES at doses of 3.75 and 7.5 mL/kg significantly reduced LPS-induced increases of lung capillary permeability. HES was found to inhibit lung neutrophil accumulation, cytokine-induced neutrophil chemoattractant protein, and NF-kappaB activation in parallel and to inhibit CD11b expression in a dose-dependent manner. These findings demonstrate that HES has beneficial effects on capillary leak in acute lung injury and that the mechanisms underlying this action involve an antiinflammatory effect of HES, including inhibition of NF-kappaB activation.

IMPLICATIONS

A randomized, controlled laboratory experiment indicated that hydroxyethyl starch (HES) could reduce increased lung capillary permeability in endotoxemia. This effect may be due to an antiinflammatory effect of HES.

The inducible nitric oxide synthase inhibitor BBS-2 prevents acute lung injury in sheep after burn and smoke inhalation injury

In this study we examined the role of inducible nitric oxide synthase (iNOS) in acute respiratory distress syndrome (ARDS) in sheep with severe combined burn and smoke inhalation injury. BBS-2, a potent and highly selective iNOS dimerization inhibitor, was used to exclude effects on the endothelial and neuronal NOS isoforms. Seven days after surgical recovery, sheep were given a burn (40% of total body surface, 3rd degree) and insufflated with cotton smoke (48 breaths, < 40 degrees C) under anesthesia. BBS-2 was provided by constant infusion at 100 microg/kg/hour, beginning 1 hour after injury. During 48 hours, control sheep developed multiple signs of ARDS. These included decreased pulmonary gas exchange, increased pulmonary edema, abnormal lung compliance, and extensive airway obstruction. These pathologies were associated with a large increase in tracheal blood flow and elevated plasma NO2-/NO3- (NOx) levels. These variables were all stable in sham animals. Treatment of injured sheep with BBS-2 attenuated the increases in tracheal blood flow and plasma NOx levels, and significantly attenuated all the pulmonary pathologies that were noted. The results provide definitive evidence that iNOS is a key mediator of pulmonary pathology in sheep with ARDS resulting from combined burn and smoke inhalation injury.

Microvascular changes in large flame burn wound in sheep

Advances in local wound management with early excisional therapy have decreased morbidity and mortality of massive third-degree burn patients. Although blood redistribution within burned tissue is of clinical interest, few studies have longitudinally determined the regional blood flow of various layers of the burn wound. We used a conscious ovine model in which animals were subjected to 40% third degree burn. Burned tissue was divided into the four layers (i.e. skin, panniculus carnosus, adipose tissue, and skeletal muscle), and regional blood flow was determined separately, with fluorescent microspheres, while measuring systemic hemodynamics and total burned tissue microvascular fluid flux. The subburn adipose tissue exhibited a remarkable biphasic alteration in regional blood flow, whereas the skin layer showed only decreased blood flow during the whole experimental period. The increase in blood flow to the adipose tissue seems to be related to a sustained fluid filtrate in the postresuscitation period, resulting in edema formation mainly located in the adipose tissue at the endpoint.

Role of nitric oxide in vascular permeability after combined burns and smoke inhalation injury

Patients with severe burn and/or smoke inhalation injury suffer both systemic and pulmonary vascular hyperpermeability. We hypothesized that nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) plays a role in the changes in microvascular permeability seen with this injury. To test the hypothesis, we administered mercaptoethylguanidine (MEG), a selective iNOS inhibitor, to conscious sheep subjected to a combined smoke inhalation and third-degree burn injury to 40% of total body surface area. The sheep were surgically prepared for chronic study with lung and prefemoral lymph fistulas in order to estimate microvascular permeability. Both the groups and a control group of animals showed an increase in iNOS protein and message in their lungs. The control animals showed significant increases in either plasma or lymph NO2-/NO3- (NOx) concentration at 24 h after injury, with associated cardiac depression and hemoconcentration. The airway epithelium stained for nitrotyrosine. In the treatment group, NOx did not increase significantly in plasma or lymph throughout the experiment, there was no nitrotyrosine staining, hemodynamic depression was not observed, and the fluid requirement was significantly less than in the control group. Changes in pulmonary microvascular permeability were significantly suppressed by inhibition of iNOS. However, there was no significant difference between the two study groups in the microvascular permeability of burned tissue. These data suggest that NO produced by iNOS plays an important role in the changes in systemic and pulmonary microvascular permeability in combined smoke inhalation/third-degree burn injury, but does not affect the vascular permeability of third-degree-burned tissue in this type of injury.

Role of L-selectin in physiological manifestations after burn and smoke inhalation injury in sheep

The effects of a monoclonal antibody against L-selectin [leukocyte adhesion molecule (LAM)1-3] on microvascular fluid flux were determined in conscious sheep subjected to a combined injury of 40% third-degree burn and smoke inhalation. This combined injury induced a rapid increase in systemic prefemoral lymph flow (sQlymph) from the burned area and a delayed-onset increase in lung lymph flow. The initial increase in sQlymph was associated with an elevation of the lymph-to-plasma oncotic pressure ratio; consequently, it leads to a predominant increase in the systemic soft tissue permeability index (sPI). In an untreated control group, the increased sPI was sustained beyond 24 h after injury. Pretreatment with LAM1-3 resulted in earlier recovery from the increased sPI, although the initial responses in sQlymph and sPI were identical to those in the nontreatment group. The delayed-onset lung permeability changes were significantly attenuated by pretreatment with LAM1-3. These findings indicate that both leukocyte-dependent and -independent mechanisms are involved in the pathogenesis that occurs after combined injury with burn and smoke inhalation.

Anesthesia and pain management in pediatric burn patients

Patients with severe burn injury are a challenge for the pediatric anesthesiologist. Today with adequate care many children survive their trauma and have a good chance for complete functional and psychological rehabilitation. The anesthesiologist has to provide excellent care even for patients in suboptimal or unstable condition to enable wound debridement and grafting, because only rapid skin closure will stabilize the patient. Adequate pain treatment during all phases of burn treatment is mandatory.