Comparison of lung injury after normal or small volume optimized resuscitation in a model of hemorrhagic shock

Early Identification of Acute Lung Injury in a Porcine Model of Hemorrhagic Shock

BACKGROUND

Acute lung injury (ALI) is a frequent complication after severe trauma. Lung-protective ventilation strategies and damage control resuscitation have been proposed for the prevention of ALI; however, there are no clinical or laboratory parameters to predict who is at risk of developing ALI after trauma. In the present study, we explored pulmonary inflammatory markers as a potential predictor of ALI using a porcine model of hemorrhagic shock.

MATERIALS AND METHODS

Female swine were randomized to mechanical ventilation with low tidal volume (V_T) (6 mL/kg) or high V_T (12 mL/kg). After equilibration, animals underwent pressure-controlled hemorrhage (mean arterial pressure [MAP] 35 ± 5 mmHg) for 1 h, followed by resuscitation with fresh whole blood or Hextend. They were maintained at MAP of 50 ± 5 mmHg for 3 h in the postresuscitation phase. Bronchoalveolar lavage fluids were collected hourly and analyzed for inflammatory markers. Lung samples were taken, and porcine neutrophil antibody staining was used to evaluate the presence of neutrophils. ELISA evaluated serum porcine surfactant protein D levels. Sham animals were used as negative controls.

RESULTS

Pigs that underwent hemorrhagic shock had higher heart rates, lower cardiac output, lower MAPs, and worse acidosis compared with sham at the early time points (P < 0.05 each). There were no significant differences in central venous pressure or pulmonary capillary wedge pressure between groups. Pulmonary neutrophil infiltration, as defined by neutrophil antibody staining on lung samples, was greater in the shock groups regardless of resuscitation fluid (P < 0.05 each). Bronchoalveolar lavage fluid neutrophil levels were not different between groups. There were no differences in levels of porcine surfactant protein D between groups at any time points, and the levels did not change over time in each respective group.

CONCLUSIONS

Our study demonstrates the reproducibility of a porcine model of hemorrhagic shock that is consistent with physiologic changes in humans in hemorrhagic shock. Pulmonary neutrophil infiltration may serve as an early marker for ALI; however, the practicality of this finding has yet to be determined.

Resuscitation with centhaquin and 6% hydroxyethyl starch 130/0.4 improves survival in a swine model of hemorrhagic shock: a randomized experimental study

PURPOSE

To investigate the effects of the combination of centhaquin and 6% hydroxyethyl starch 130/0.4 (HES 130/0.4) in a swine model of hemorrhagic shock.

METHODS

Twenty Landrace-Large White pigs were instrumented and subjected to hemorrhagic shock. The animals were randomly allocated in two experimental groups, the control (group CO, n = 10) and the centhaquin groups (0.015 mg/kg, n = 10, group CH). Acute hemorrhage was induced by stepwise blood withdrawal (18 mL/min) from the internal jugular vein until MAP decreased to 40-45 mmHg, whereas anesthesia remained constant. All animals received HES 130/0.4 solution in the resuscitation phase until their mean arterial pressure (MAP) reached 90% of the baseline. The animals were observed for 60 min, during which no further resuscitation was attempted.

RESULTS

The total amount of blood and the bleeding time did not differ significantly between group CO and group CH (120 ± 13 vs. 120 ± 14 mL, p = 0.6; 20 ± 2 vs. 20 ± 1 min, p = 0.62, respectively). During the hemorrhagic phase, only a difference in heart rate (97.6 ± 4.4 vs. 128.4 ± 3.6 beats/min, p = 0.038) was observed between the two groups. The time required to reach the target MAP was significantly shorter in the centhaquin group compared to controls (13.7 ± 0.4 vs. 19.6 ± 0.84 min, p = 0.012). During the resuscitation phase, a statistical significant difference was observed in MAP (75.2 ± 1.6 vs. 89.8 ± 2.1 mmHg, p = 0.02) between group CO and group CH. During the observation phase, a statistical significant difference was observed in SVR (1109 ± 32.65 vs. 774.6 ± 21.82 dyn s/cm⁵, p = 0.039) and cardiac output (5.82 ± 0.31 vs. 6.9 ± 0.78 L/min, p = 0.027) between the two groups. Two animals of group CO and seven animals of group CH survived for 24 h (p = 0.008). We observed a marked increase in microvascular capillary permeability in group CO compared to group CH, with the wet/dry weight ratio being significantly higher in group CO compared to group CH (4.8 ± 1.6 vs. 3.08 ± 0.6, p < 0.001).

CONCLUSIONS

The combination of centhaquin 0.015 mg/kg and HES 130/0.4 resulted in shorter time to target MAP, lower wet-to-dry ratio, and better survival rates after resuscitation from hemorrhagic shock.

Effect of hypertonic saline in the pretreatment of lung donors with hemorrhagic shock

BACKGROUND

Hemorrhagic shock-induced lung edema and inflammation are two of the main reasons for the rejection of lungs donated for transplantation. Hypertonic saline (HS) induces intravascular volume expansion and has considerable immunomodulating effects that might minimize edema. Our hypothesis is based on the use of a hypertonic solution for treatment of donors who are in shock in an attempt to increase the supply of lungs for transplantation.

METHODS

A total of 80 rats were allocated to four groups: one group was given an infusion of normal saline (NS; n = 20), one group received HS; n = 20, a sham group (n = 20), and a Shock group (n = 20). Half of the lungs from each group were evaluated in an ex vivo perfusion system, and the other half was used for measurements of cytokine levels and neutrophil counts.

RESULTS

In the ex vivo perfusion assessment, the pulmonary artery pressures of the animals in the NS and HS groups did not exhibit significant differences compared with those in the sham group (P > 0.05) but were lower than those in the Shock group (P < 0.01). Furthermore, the tumor necrosis factor-α levels and neutrophil counts were lower in the HS group than those in the Shock group (P < 0.01) and did not exhibit significant differences compared with those in either the NS and Sham groups (P > 0.05).

CONCLUSIONS

We showed that HS was equivalent to isotonic saline and contributed to the treatment of lungs subjected to hemorrhagic 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.

Pharmacological interventions in acute respiratory distress syndrome

Pharmacological interventions are commonly considered in acute respiratory distress syndrome (ARDS) patients. Inhaled nitric oxide (iNO) and neuromuscular blockers (NMBs) are used in patients with severe hypoxemia. No outcome benefit has been observed with the systematic use of iNO. However, a sometimes important improvement in oxygenation can occur shortly after starting administration. Therefore, its ease of use and its good tolerance justify iNO optionally combined with almitirne as a rescue therapy on a trial basis. Recent data from the literature support the use of a 48-h infusion of NMBs in patients with a PaO2 to FiO2 ratio <120 mmHg. No strong evidence exists on the increase of ICU-acquired paresis after a short course of NMBs. Fluid management with the goal to obtain zero fluid balance in ARDS patients without shock or renal failure significantly increases the number of days without mechanical ventilation. On the other hand, patients with hemodynamic failure must receive early and adapted fluid resuscitation. Liberal and conservative fluid strategies therefore are complementary and should ideally follow each other in time in the same patient whose hemodynamic state progressively stabilizes. At present, albumin treatment does not appear to be justified for limitation of pulmonary edema and respiratory morbidity. Aerosolized β2-agonists do not improve outcome in patients with ARDS and one study strongly suggests that intravenous salbutamol may worsen outcome in those patients. The early use of high doses of corticosteroids for the prevention of ARDS in septic shock patients or in patients with confirmed ARDS significantly reduced the duration of mechanical ventilation but had no effect or even increased mortality. In patients with persistent ARDS after 7 to 28 days, a randomized trial showed no reduction in mortality with moderate doses of corticosteroids but an increased PaO2 to FiO2 ratio and thoracopulmonary compliance were found, as well as shorter durations of mechanical ventilation and of ICU stay. Conflicting data exist on the interest of low doses of corticosteroids (200 mg/day of hydrocortisone) in ARDS patients. In the context of a persistent ARDS with histological proof of fibroproliferation, a corticosteroid treatment with a progressive decrease of doses can be proposed.

Mechanical ventilation is the determining factor in inducing an inflammatory response in a hemorrhagic shock model

BACKGROUND

Hemorrhagic shock (HS) is known to induce an inflammatory response by activating the immune system. This response is mainly caused by primed polymorphonuclear granulocytes (PMNs). Trauma patients often require mechanical ventilation (MV), which can cause additional pulmonary and systemic inflammation. The aim of this study was to evaluate the role of MV in the development of systemic and pulmonary inflammation in a HS model in rats.

MATERIALS AND METHODS

In male Sprague-Dawley rats, the effect of MV and HS on the systemic and pulmonary inflammatory responses was measured and compared. In five groups (control, sham, MV, HS, and MV + HS), the inflammation was measured at time point 300 min after the start of the experiment.

RESULTS

The systemic inflammatory response, expressed in absolute numbers of PMNs in blood and blood growth related oncogene (GRO-KC) levels, was significantly higher in MV rats compared with that in other groups. The pulmonary inflammatory response, expressed by PMNs in bronchoalveolar lavage fluid (BALF), BALF interleukin 6, BALF GRO-KC, and myeloperoxidase activity, was significantly higher in all ventilated rats compared with that in the controls or HS rats. There was, however, no additional effect of HS in MV as the inflammatory indices were similar in both groups.

CONCLUSIONS

Our data show that HS alone has minimal effect on the development of inflammation. MV (alone or in combination with HS) is the determining factor in inducing an inflammatory response. These results emphasize the importance of local (pulmonary) ventilation-induced damage in the development of systemic inflammation.

Effect of fluid loading during hypovolaemic shock on caspofungin pharmacokinetic parameters in pig

Introduction

Caspofungin treatment is frequently initiated in shock patients. In the present study, we investigated the influence of hypovolaemic shock requiring fluid loading on the plasma and pulmonary pharmacokinetic parameters of caspofungin in the pig.

Methods

After being anaesthetised and mechanically ventilated, 12 pigs were bled to induce a two-hour deep shock and resuscitated using normal saline based on haemodynamic goals. A one-hour infusion of 70 mg of caspofungin was started at the beginning of the resuscitation period. The lungs were removed four hours after caspofungin administration. Sixteen animals served as controls without haemorrhage. Caspofungin concentrations were measured by using high-performance liquid chromatography, and a two-compartment population pharmacokinetic analysis was performed.

Results

In the shock group, the volume of blood removed was 39 ± 7 mL/kg and a volume of 90 ± 17 mL/kg saline was infused throughout the resuscitation period. The extravascular lung water index was higher in the shock group (9.3 ± 1.6 mL/kg vs 5.7 ± 1 mL/kg in the control group; P < 0.01). In the shock group, the median (interquartile range) maximal plasma concentration was 37% lower than in the control group (21.6 μg/mL (20.7 to 22.3) vs 33.1 μg/mL (28.1 to 38.3); P < 0.01). The median area under curve (AUC) from zero to four hours was 25% lower in the shock group than in the control group (60.3 hours × μg/mL (58.4 to 66.4) vs 80.8 hours × μg/mL (78.3 to 96.9); P < 0.01), as was the median lung caspofungin concentration (1.22 μg/g (0.89 to 1.46) vs 1.64 μg/g (1.22 to 2.01); P < 0.01). However, the plasma-to-tissue ratios were not different between the groups, indicating that lung diffusion of caspofungin was not affected after shock followed by fluid loading. Pharmacokinetic analysis showed that the peripheral volume of distribution of caspofungin and intercompartmental clearance were significantly higher in the shock group, as was the total apparent volume of distribution.

Conclusions

Hypovolaemic shock followed by fluid loading in the pig results in a significant increase in the apparent volume of distribution of caspofungin and in a decrease in its plasma and pulmonary exposition. Although our model was associated with capillary leakage and pulmonary oedema, our results should be generalised to the septic shock with caution. Future investigations should focus on monitoring plasma caspofungin concentrations and optimal caspofungin dosing in shock patients.

Fluid management in acute lung injury and ards

ARDS is particularly characterized by pulmonary edema caused by an increase in pulmonary capillary permeability. It is considered that limiting pulmonary edema or accelerating its resorption through the modulation of fluid intake or oncotic pressure could be beneficial. This review discusses the principal clinical studies that have made it possible to progress in the optimization of the fluid state during ARDS. Notably, a randomized, multicenter study has suggested that fluid management with the goal to obtain zero fluid balance in ARDS patients without shock or renal failure significantly increases the number of days without mechanical ventilation. On the other hand, it is accepted that patients with hemodynamic failure must undergo early and adapted vascular filling. Liberal and conservative filling strategies are therefore complementary and should ideally follow each other in time in the same patient whose hemodynamic state progressively stabilizes. At present, although albumin treatment has been suggested to improve oxygenation transiently in ARDS patients, no sufficient evidence justifies its use to mitigate pulmonary edema and reduce respiratory morbidity. Finally, the resorption of alveolar edema occurs through an active mechanism, which can be pharmacologically upregluated. In this sense, the use of beta-2 agonists may be beneficial but further studies are needed to confirm preliminary promising results.

Pulmonary contusion: an update on recent advances in clinical management

Pulmonary contusion is a common finding after blunt chest trauma. The physiologic consequences of alveolar hemorrhage and pulmonary parenchymal destruction typically manifest themselves within hours of injury and usually resolve within approximately 7 days. Clinical symptoms, including respiratory distress with hypoxemia and hypercarbia, peak at about 72 h after injury. The timely diagnosis of pulmonary contusion requires a high degree of clinical suspicion when a patient presents with trauma caused by an appropriate mechanism of injury. The clinical diagnosis of acute parenchymal lung injury is usually confirmed by thoracic computed tomography, which is both highly sensitive in identifying pulmonary contusion and highly predictive of the need for subsequent mechanical ventilation. Management of pulmonary contusion is primarily supportive. Associated complications such as pneumonia, acute respiratory distress syndrome, and long-term pulmonary disability, however, are frequent sequelae of these injuries.

Paralytics in critical care: not always the bad guy

PURPOSE OF REVIEW

The use of neuromuscular blocking agents (NMBAs) in patients with acute respiratory distress syndrome (ARDS) and acute lung injury remains controversial, although frequent. This review analyzes the effects of NMBAs on thoracopulmonary mechanics, gas exchange, patient outcome and their potential adverse effects.

RECENT FINDINGS

NMBAs are used in 25-45% of acute lung injury/ARDS patients for a mean period of 12 days, especially in severe ARDS. Hypoxemia and facilitation of mechanical ventilation are the main indications of NMBAs. Two randomized controlled trials showed that the systematic early use of NMBAs is associated with a sustained improvement in oxygenation in ARDS patients. The most recent suggests a beneficial effect on proinflammatory response associated with ARDS and mechanical ventilation.

SUMMARY

The use of NMBAs in acute lung injury/ARDS patients is not marginal. Recent studies suggest a beneficial effect of early use of NMBAs on oxygenation and inflammation. The role of NMBAs in the occurrence of ICU-acquired neuromyopathies and lung atelectasis in ARDS patients remains largely questioned. The use of NMBAs in the early phase of ARDS could reinforce the beneficial effects of a lung-protective ventilation. In this context, the effect of NMBAs on the outcome of ARDS patients must be evaluated.

Effect of hypertonic saline pre-treatment on ischemia-reperfusion lung injury in pig

BACKGROUND

Hypertonic saline may be administered in the setting of lung transplantation but may affect the development of ischemia-reperfusion lung injury. This study investigated the effects of the pre-treatment by intravenous hypertonic saline in a pig model of single lung ischemia-reperfusion.

METHODS

Forty-three pigs (34 +/- 4 kg) under mechanical ventilation were randomly assigned to a left lung ischemia-reperfusion alone or preceded by 4-ml/kg 7.5% hypertonic saline, 33-ml/kg normal saline, or by the infusion of the vasodilator nicardipine. Animals without ischemia served as controls. After euthanasia, the left lung was sampled for histologic analysis and measurement of lung water and alveolar-capillary permeability.

RESULTS

Ischemia-reperfusion resulted in high-permeability pulmonary edema, hypoxemia, and increased interleukin-6 serum level. Hypertonic saline pre-treatment worsened pulmonary edema of the left lung (6.6 +/- 0.7 vs 4.8 +/- 0.8 ml/kg of body weight, p < 0.05) and resulted in a higher ratio of the protein level in the alveolar fluid to the serum protein level (0.41 +/- 0.04 vs 0.21 +/- 0.09, p < 0.05) and in a higher histologic damage score (11 [range, 9-11.75] vs 6.5 [range, 4.5-7.5], p < 0.05) without promoting pulmonary or systemic inflammation. Lung injury was affected neither by normal saline nor by nicardipine pre-treatment. Nicardipine did not influence the deleterious effect of hypertonic saline.

CONCLUSIONS

Pre-treatment by intravenous hypertonic saline worsened ischemia-reperfusion lung injury independently of its effects on the cardiac index or pulmonary circulation but probably through a direct effect of hyperosmolarity on endothelial permeability.