Effects of sustained post-traumatic shock and initial fluid resuscitation on extravascular lung water content and pulmonary vascular pressures in a porcine model of shock

Midterm effects of fluid resuscitation strategies in an experimental model of lung contusion and hemorrhagic shock

BACKGROUND

This study compared three different fluid resuscitation strategies in terms of respiratory tolerance and hemodynamic efficacy in a pig model of blunt chest trauma with lung contusion and controlled hemorrhagic shock. We hypothesized that the choice of fluid resuscitation strategy (type and amount of fluids) may impact differently contused lungs in terms of extravascular lung water (EVLW) 20 h after trauma.

METHODS

Anesthetized female pigs (n = 5/group) received five bolt shots to the right thoracic cage and allowed to hemorrhage for 30 min, with 25 to 30 mL/kg of blood loss. Pigs were randomly assigned to resuscitation groups that maintained a minimum mean arterial blood pressure of 70 mmHg with one of three methods: normal saline (NS), unrestricted normal saline; NOREPI, low-volume normal saline with norepinephrine; or HS-HES, hypertonic saline with hydroxyethyl starch. Control pigs were anesthetized, but received no injury or treatment. After 20 h, animals were killed to measure EVLW by gravimetry.

RESULTS

Fluid loading was significantly different in each group. All three treatment groups had higher EVLW than controls. Moderate, bilateral pulmonary edema was observed in the NS and HS-HES groups. The three treatment groups showed similar reductions in oxygenation. Static pulmonary compliance was diminished in the NS and HS-HES groups, but compliance was similar in NOREPI and control groups. The NOREPI group had pathological lactate levels.

CONCLUSIONS

This study demonstrated the impact of fluid resuscitation on contused lungs. Twenty hours after the trauma, all three resuscitation approaches showed modest clinical consequences, with moderate lung edema and reduced compliance in response to the infused volume.

The temporal evolution of acute respiratory distress syndrome following shock

BACKGROUND AND OBJECTIVE

The objective of this review is to provide an comprehensive overview of the evolution of acute respiratory distress syndrome (ARDS) in cellular, animal and human models with specific reference to sepsis and haemorrhage. Within this work we have attempted to describe the temporal evolution of the disease process.ARDS is a complication of pulmonary and systemic disease and it can follow sepsis or haemorrhage. The definition of this condition states an acute onset and this review seeks to clarify the time course of that onset following sepsis and haemorrhage. The underlying pathophysiological mechanisms include activation of the immune response, neutrophil activation and sequestration of these into the alveolus with subsequent tissue damage and hypoxia.

RESULTS

The biological evolution of these processes from sepsis or haemorrhage has been well described and the earliest measurable changes in the process occur within 15 min with the clinical manifestations of the syndrome occurring within 12 h. The rapid development of this condition should be considered during the treatment of haemorrhagic or septic shock.

Comparison of lactated Ringer's solution and a physiologically balanced 6% hetastarch plasma expander for the treatment of hypotension induced via blood withdrawal in isoflurane-anesthetized dogs

OBJECTIVE

To compare the effects of lactated Ringer's solution (LRS) with those of a physiologically balanced 6% hetastarch plasma expander administered to isoflurane-anesthetized dogs with hypotension induced by blood withdrawal.

ANIMALS

12 healthy Beagles.

PROCEDURE

Blood was withdrawn from isoflurane-anesthetized dogs (volume withdrawn measured) to a systolic arterial blood pressure (SAP) of 80 mm Hg. Six dogs each received either LRS or hetastarch solution (90 mL/kg/h, i.v.). Hemodynamic variables, pH, blood gas concentrations, PCV, serum electrolyte and total protein concentrations, and colloid osmotic pressure (COP) were determined at baseline, while SAP was 80 mm Hg, and after fluid treatment. The volume of fluid administered and rate of return of SAP to within 10% of baseline values were recorded.

RESULTS

Mean +/- SD volume of blood withdrawn to decrease SAP to 80 mm Hg was 173 +/- 38 mL. Hemodynamic variables decreased after blood withdrawal but returned to baseline values more rapidly after infusion of a smaller volume of hetastarch solution, compared with the response to LRS infusion. Whereas PCV and serum total protein concentration decreased after administration of either solution, COP decreased only after administration of LRS. The total volume of hetastarch solution and LRS required to restore and maintain SAP to within 10% of baseline values was 1.1 +/- 0.9 and 4.4 +/- 1.7 times greater than the volume of blood removed, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with LRS infusion, smaller volumes of hetastarch solution normalized and maintained SAP without lowering COP in isoflurane-anesthetized dogs after blood withdrawal.

Estimation of errors in determining intrathoracic blood volume using thermal dilution in pigs with acute lung injury and haemorrhage †

BACKGROUND

Global end diastolic volume (GEDV) has a constant and predictable relationship to intrathoracic blood volume (ITBV). The present study assesses the difference between ITBV derived from GEDV and ITBV measured directly in pigs with acute lung injury (ALI) and mild haemorrhage.

METHODS

We caused ALI in 12 anaesthetized pigs by i.v. injection of oleic acid and removed 10% of estimated blood volume. EVLW, GEDV, ITBV (COLD; Pulsion Medical Systems), Pa(o(2))/Fi(o(2)), lung compliance and haemodynamic variables were measured at baseline (time 0) and at 30 and 120 min. All animals were volume-resuscitated, followed by measurements at 180 min. A linear equation estimated from the 44 pairs of ITBV and GEDV values in 11 animals was applied iteratively to the four GEDV measurements in the 12th animal, enabling 48 comparisons between measured (ITBVm) and derived ITBV (ITBVd) to be made.

RESULTS

Increase in extravascular lung water index (EVLWi) was associated with significant pulmonary hypertension, worsening of oxygenation and compliance (repeated measures ANOVA; P<0.05). There was good within-subject correlation and agreement between ITBV(m) and ITBV(d) (r=0.72, mean bias 0.8 ml; sd 32 ml). Mean error in deriving ITBV from GEDV was 4.5%. (sd 4.2%; range 0.05-19%). There were no significant differences in errors in the presence of small (up to 10%) deficits in blood volume (F=1.0; P=0.41).

CONCLUSIONS

ITBV estimated by thermodilution alone is comparable to measurements made by the thermo-dye dilution technique in the presence of pulmonary hypertension and mild deficits in total blood volume.