Water and electrolyte fluxes in muscle, skin and tendon after thermal injury and ischaemia

Resuscitation of severe thermal injury with hypertonic saline dextran: effects on peripheral and visceral edema in sheep

BACKGROUND

Edema of tissue not directly injured by heat is a common complication after resuscitation of burn shock. Hypertonic 7.5% NaCl 6% dextran (HSD) infusion reduces early fluid requirements in burn shock, but the effects of HSD on peripheral and visceral tissue edema are not well-defined.

METHODS

We measured the microcirculatory absorptive pressures of burned and nonburned skin and tissue water content of skin and other tissues in anesthetized sheep after 70% to 85% total body surface area scald and resuscitation. Fluid infusion was initiated 30 minutes after injury using 10 mL/kg HSD (n = 11) or lactated Ringer's (LR) (n = 12), with infusion rates titrated to restore and maintain preburn oxygen delivery (DO2). Thereafter, both groups received LR infusions as needed to maintain DO2 until the study's end at 8 hours. Colloid osmotic pressure was measured in plasma, and combined interstitial colloid osmotic and hydrostatic pressures were measured in skin.

RESULTS

Both treatments successfully restored DO2, but fluid requirements were less with the HSD group than with the LR group (43+/-19 mL/kg vs. 194+/-38 mL/kg, respectively, p < 0.05). The peripheral and visceral tissue water contents at 8 hours postinjury until the end of the study in both burn groups were significantly higher than in nonburn controls. However, HSD-treated sheep had significantly less water content in the colon (less 28%), liver (less 9%), pancreas (less 55%), skeletal muscle (less 21%), and nonburned skin (less 12%) compared with LR-treated sheep (p < 0.05 for each). HSD-treated sheep maintained significantly higher (3 to 5 mm Hg) plasma colloid osmotic pressure than LR-treated sheep.

CONCLUSION

There were no observed differences in edema in burn skin between the two treatment groups. The early volume-sparing effect of HSD and reduction in tissue edema are likely attributed to an increased extracellular osmolarity and a better maintenance of the plasma oncotic pressure.

Burn resuscitation: crystalloid versus colloid versus hypertonic saline hyperoncotic colloid in sheep

OBJECTIVES

The present study was undertaken to assess the fluid balance and hemodynamic effects during the first 8 hrs of resuscitation in animals with a large body surface area burn, using lactated Ringer's solution, 6% hetastarch, and hypertonic saline dextran.

DESIGN

A prospective, blinded, controlled, terminal study, using anesthetized animals. The initial baseline period was followed by scald injury, and three different treatment regimens were administered from coded bags to achieve a physiologic end point.

SETTING

University laboratory.

SUBJECTS

Eighteen female sheep (35 to 45 kg) were anesthetized with isoflurane.

INTERVENTIONS

Test solutions (10 mL/kg of either lactated Ringer's solution, hetastarch, or hypertonic saline dextran) were infused 30 mins after the scald injury at a rate to restore and maintain the baseline oxygen delivery (DO2) value.

MEASUREMENTS AND MAIN RESULTS

Cardiovascular hemodynamics, plasma sodium concentration, plasma colloid osmotic pressure, and fluid balance were measured before and after scalding and resuscitation. After the initial 10-mL/kg test solution dose was given, lactated Ringer's solution was infused to achieve the same end point of baseline DO2 for the remainder of the 8 hrs. The scald caused an initial 30% reduction in cardiac output, a 20% reduction in mean arterial pressure, and 10% to 15% increase in hematocrit. All three test solutions restored and maintained baseline DO2 within 1 hr. However, hetastarch and hypertonic saline dextran reduced the net fluid volume over 8 hrs by 48% and 74%, respectively, compared with lactated Ringer's solution. Edema in the burn wound was not affected by treatment, while hypertonic saline dextran reduced edema in nonburned skin compared with both lactated Ringer's solution and hypertonic saline dextran. Plasma colloid osmotic pressure was significantly higher in the hetastarch and hypertonic saline dextran groups. A continuous decrease in plasma sodium concentrations from baseline values (140 to 145 mmol/L) was measured in the lactated Ringer's solution and hetastarch groups (130 to 133 mmol/L) over 8 hrs. Plasma sodium concentrations in the group receiving hypertonic saline dextran were increased (150 to 155 mmol/L) at 4 hrs, but returned toward baseline by 8 hrs.

CONCLUSIONS

Net volume loading can be reduced markedly by initial resuscitation of large body surface area burn injury using a colloid (hetastarch), and can be further reduced by use of hypertonic saline colloid. Hyponatremia was apparent in the isotonic crystalloid- and colloid-treated animals, but not in those animals treated with hypertonic saline colloid.

Effects of enriched lactate solution (ELS) for resuscitation after burn injury

Full skin thickness burns covering 35 per cent of the total body surface of rabbits were followed by measurements of Na-K ATPase and arterial blood gas analyses, before and after the burn injury. Studies of the effects of intravenous fluids with different compositions showed that the active transport of the cell membrane was depressed in vivo immediately after a burn injury, mainly due to acidosis. This phenomenon was not completely corrected by the Baxter formula which uses conventional lactated Ringer's solution. However, an improvement was observed in those groups given the 'Enriched Lactate Solution' (ELS) containing large quantities of lactate as the base source. These results suggest that ELS, which positively corrected acidosis in accordance with its concentration, is very effective and more appropriate than the conventional lactated Ringer's solution for early burn resuscitation.

Computer simulation of fluid resuscitation in thermal injury. A. B. Wallace memorial lecture 1987

Following thermal injury many subsystems of the human body interact closely. The effects both of the pathological event in one subsystem and the subsequent therapy are masked or compensated by changes in other homeostatic subsystems. Not until the capacity of the homeostatic subsystems and/or the therapy is inadequate will the effects become obvious. The very complex postburn situation explains why there are so many different shock-preventing fluid therapy programmes and such crude and insecure monitoring of the therapy. In these situations when there are too many factors to be grasped by the unaided human mind, a computer-based 'patient-simulator' could be of value in diagnosis, monitoring and therapy of the severely ill patient with trauma. An extensive pathophysiological model has been designed to describe fluid shifts and haemodynamics in connection with fluid therapy of traumatic patients. The model makes it possible to calculate and predict clinically important state variables on the basis of fluid input and fluid losses. Sample runs are presented for illustrations in haemorrhage and fluid and salt loading. The model is also used to simulate treatment of a burn patient and the results are compared with measured physiological and biochemical variables. Furthermore, four different formulae for resuscitation of patients with thermal injuries according to Evans, Brooke, Parkland and a hypertonic fluid programme are simulated. The results illustrate the potential use of the 'patient-simulator' for designing fluid resuscitation programmes and attempt to optimize them with respect to infusion rate of the fluid administered.