Hypotensive resuscitation of multiple hemorrhages using crystalloid and colloids.

Hypotensive resuscitation has been advocated as a better means to perform field resuscitation of penetrating trauma. Our hypothesis is that hypotensive resuscitation using either crystalloid or colloid provides equivalent or improved metabolic function while reducing the overall fluid requirement for resuscitation of hemorrhage. We compared hypotensive and normotensive resuscitation of hemorrhage using lactated Ringer's (LR) with hypotensive resuscitation using Hextend (Hex), 6% hetastarch in isotonic buffered saline. Instrumented conscious sheep were hemorrhaged in three separate bleeds, 25 mL/kg at T0 and 5 mL/kg at both T50 and T70. Resuscitation was started at T30 and continued until T180. Hypotensive resuscitation to a mean arterial pressure (MAP) of 65 mmHg was performed with LR or Hex using a closed-loop resuscitation (CLR) system for a LR-65 and Hex-65 treatment protocol. A control treatment protocol was resuscitation with LR to a MAP target of 90 mmHg, LR-90. All treatment protocols were successfully resuscitated to near target levels. Two animals in the hypotensive treatment protocols died during the second and third bleedings, one in the LR-65 and one in the Hex-65 treatment protocol. Mean infused volumes were 61.4 +/- 11.3, 18.0 +/- 5.9, and 11.6 +/- 1.9 mL/kg in the LR-90, LR-65, and Hex-65 treatments, respectively (*P < 0.05 versus LR-90). Mean minimum base excess (BE) values were +1.9 +/- 1.4, -5.8 +/- 4.3, and -5.9 +/- 4.0 mEq/L in the LR-90, LR-65, and Hex-65 treatments, respectively. Hypotensive resuscitation with LR greatly reduced volume requirements as compared with normotensive resuscitation, and Hex achieved additional volume sparing. However, trends toward lower BE values and the occurrence of deaths only in the hypotensive treatment protocols suggest that resuscitation to a target MAP of 65 mmHg may be too low for optimal outcomes.

Evaluation of hyperdynamic resuscitation in 60% TBSA burn-injured sheep.

It has been suggested that hyperdynamic (HD) resuscitation improves outcomes. We hypothesized that initial HD resuscitation of burn injury using fluid and inotropes would improve metabolic function as indicated by base excess. We used an anesthetized ovine model of 60% TBSA full-thickness flame burn with delayed resuscitation started at 90 min after burn and continued for 8 h. Three groups (n = 6 each) were included: 1) HD defined as cardiac index (CI) of 1.5x baseline achieved by using Ringer's lactate alone (HD-Fluid); 2) Ringer's lactate and dobutamine (HD-Drug); and 3) Parkland Formula (Parkland) as a control group. Statistical analysis performed using analysis of variance and Tukey's HSD test. Significance accepted at P < 0.05. Higher CI was achieved in both HD-Fluid and HD-Drug groups, e.g., at 8 h the CI was 4.6 +/- 0.4 and 4.7 +/- 0.6 L/min/m respectively, as compared with Parkland 3.6 +/- 0.5 L/min/m. The net fluid balance (fluid infused - urine output) was similar in both Parkland and HD-Drug groups, which were 2.5x more in HD-Fluid (P = 0.001). The mean postburn urinary outputs were similar in both Parkland and HD-Drug groups, e.g., Parkland (0.9 +/- 0.08 mL/kg/h), HD-Drug (1.0 +/- 0.2 mL/kg/h) and increased in HD-Fluid (3.7 +/- 1.0 mL/kg/h; P = 0.0005). Base excess remained positive in both HD-Drug (+2.5 +/- 1 mmol/L) and Parkland (+1.5 +/- 1.7 mmol/L), and declined to -4.0 +/- 3.6 mmol/L in HD-Fluid group (P = 0.036). We conclude that there may be no benefit to using hyperdynamic regimens for the initial resuscitation of burn injury.

Near-infrared spectroscopy-guided closed-loop resuscitation of hemorrhage.

BACKGROUND: Endpoint resuscitation has been suggested as a better means to resuscitate penetrating injury. We performed computer-controlled closed-loop resuscitation using invasive cardiac output (CO) or noninvasive skeletal muscle oxygen saturation (SkMusSO(2)) via near infrared spectroscopy (NIRS). METHODS: Conscious sheep received a 4.0-mm aortotomy and uncontrolled hemorrhage at t = 0 min (T0) while resuscitation started at T20 using lactated Ringer's solution. RESULTS: The aortotomy rapidly decreased the mean arterial pressure (MAP) to approximately 30 mm Hg and CO to 20% to 30% of baseline. The SkMusSO(2) endpoint group required only half as much fluid through 4 hours of resuscitation as the CO endpoint group (34.9 +/- 8.4 mL/kg vs. 63.1 +/- 9.4 mL/kg). CO and MAP were lower in the SkMusSO(2) group after T60. Mean infusion volumes were 180% and 100% of the bled volume collected at autopsy in the CO and SkMusSO(2) groups. Brain and muscle oxygenation and base excess were as high or higher in the CO endpoint group. CONCLUSION: Closed-loop resuscitation with either CO or SkMusSO(2) endpoints effectively performs fluid resuscitation of severe uncontrolled hemorrhagic shock. Limited resuscitation may achieve favorable clinical results with volumes less than recommended by Advanced Trauma Life Support guidelines.

Isoflurane but not mechanical ventilation promotes extravascular fluid accumulation during crystalloid volume loading.

BACKGROUND: The combination of isoflurane anesthesia and mechanical ventilation reduces urinary output and promotes redistribution of a crystalloid bolus into the extravascular space. The authors hypothesized that mechanical ventilation rather than isoflurane causes this alteration. METHODS: The fate of a 25-ml/kg, 20-min, 0.9% saline fluid bolus was studied in four different experiments per sheep: while conscious and spontaneously ventilating (CSV), while conscious and mechanically ventilated (CMV), while anesthetized with isoflurane and mechanical ventilated (ISOMV), and while anesthetized with isoflurane and spontaneously ventilating (ISOSV). RESULTS: By calculations based on the indicator dilution and mass balance principles, plasma expansion was similar between protocols. Isoflurane but not mechanical ventilation reduced urinary output and increased interstitial fluid volume (P < 0.001): At 180 min, mean total urinary outputs were 15.6 +/- 2.1 and 15.9 +/- 2.9 ml/kg in the CSV and CMV protocols and 2.7 +/- 0.6 and 3.1 +/- 1.1 ml/kg in the ISOSV and ISOMV protocols, respectively. The net changes in extravascular volume, assumed to be interstitial fluid volume, were 8.6 +/- 3.3 and 8.1 +/- 3.1 ml/kg, and 22.5 +/- 1.5 and 22.1 +/- 1.6 ml/kg in the corresponding protocols. Volume kinetic analysis demonstrated extravascular fluid accumulation associated with isoflurane anesthesia similar to the calculated interstitial accumulation of 20.2 +/- 0.5 and 26.5 +/- 0.3 ml/kg in the ISOSV and ISOMV protocols, respectively. CONCLUSION: Isoflurane, but not mechanical ventilation, decreased urinary excretion and increased interstitial fluid volume. Volume kinetic analysis indicated "third-space" losses due to isoflurane. Perioperative fluid retention may be associated not only with surgical tissue manipulation, but with anesthesia per se.