Chest wall and lung mechanics during acute hemorrhage in anesthetized dogs

Short-term effects of low-volume resuscitation with hypertonic saline and hydroxyethylstarch in an experimental model of lung contusion and haemorrhagic shock

OBJECTIVES

This study aimed to assess the short-term respiratory tolerance and haemodynamic efficiency of low-volume resuscitation with hypertonic saline and hydroxyethylstarch (HS/HES) in a pig model of lung contusion and controlled haemorrhagic shock. We hypothesised that a low-volume of HS/HES after haemorrhagic shock did not impact contused lungs in terms of extravascular lung water 3hours after trauma.

METHODS

A lung contusion resulting from blunt chest trauma was induced in 28 anaesthetised female pigs with five bolt-shots to the right thoracic cage, followed by haemorrhagic shock and fluid resuscitation. Pigs were randomly allocated into two groups: fluid resuscitation by 4ml/kg of HS/HES, or fluid resuscitation by 10ml/kg of normal saline (NS). Monitoring was based on transpulmonary thermodilution and a pulmonary artery catheter. After 3h, animals were euthanized to measure extravascular lung water (EVLW) by gravimetry.

RESULTS

Blunt chest trauma was followed by a transient collapse and hypoxaemia in both groups. Post-mortem gravimetric assessment demonstrated a significant difference between EVLW in the NS-group (8.1±0.7ml/kg) and in the HS/HES-group (6.2±0.6ml/kg, P=0.038). Based on a pathological EVLW threshold of > 7ml/kg, results indicated that only the NS-group experienced moderate pulmonary oedema, contrary to the HS/HES-group. After haemorrhagic shock, HS/HES infusion enabled the restoration of effective mean arterial pressure and cardiac index. Intrapulmonary shunting increased transiently after fluid resuscitation but there was no significant impairment of oxygenation.

CONCLUSION

In this pig model of lung contusion, the short-term assessment of fluid resuscitation after haemorrhagic shock with 4ml/kg of HS/HES showed that pulmonary oedema was avoided compared to fluid resuscitation with 10ml/kg of NS.

Effects of acute hemorrhage on intrapulmonary shunt in a pig model of acute respiratory distress-like syndrome

BACKGROUND

In acute respiratory distress syndrome (ARDS), gas exchange and respiratory system mechanics (compliance) are severely impaired. Besides ventilatory parameters, the degree of respiratory abnormality can be influenced by the circulatory state. This study investigated the influence of acute hypovolemia on the respiratory system.

METHODS

We performed a secondary analysis of a previous study including 8 pigs with ARDS-like syndrome induced by lung lavage and surfactant depletion method (ARDS group) and 10 mechanically ventilated pigs with no intervention (CTRL group). Animals of both groups were subjected to hemorrhage and retransfusion successively. We reanalyzed the effect of acute blood volume variations on intrapulmonary shunt (shunt), arterial oxygenation (PaO2:FiO2), global oxygen delivery (DO2) and respiratory system compliance (Crs).

RESULTS

In the ARDS group, after hemorrhage, shunt decreased (-28 +/- 3.5 % (p < 0.001)), respiratory system compliance (Crs) increased (+5.1 +/- 1.0 ml/cm H2O (p < 0.001)) moreover, there was a concurrent increase in PaO2:FiO2 (+113 +/- 19.1 mmHg; p < 0.001) but this did not prevent a reduction in DO2 (-317 +/- 49.8 ml/min; p < 0.001). Following retransfusion, shunt and Crs return towards pre-hemorrhage values. Similar changes, but of smaller magnitude were observed in the CTRL group, except that no significant changes in oxygenation occurred.

CONCLUSIONS

The present analysis suggests that an acute decrease in blood volume results in a decrease in shunt with a parallel improvement in arterial oxygenation and an increase in Crs during ARDS-like syndrome. Our results strengthen the importance to integrate the circulatory condition in the analysis of the state of the respiratory system. However, the translation of this physiological model in a clinical perspective is not straightforward because our model of acute and severe hemorrhage is not strictly equivalent to a progressive hypovolemia, as could be obtained in ICU by diuretic. Furthermore, the present model does not consider the impact of blood loss induced decrease of DO2 on other vital organs function.

TRIAL REGISTRATION

'Not applicable'.

Acute hemorrhagic shock decreases airway resistance in anesthetized rat

We studied the relation between changes in pulmonary and systemic hemodynamics to those in the airway resistance, respiratory tissue mechanics, and thoracic gas volume (TGV) following acute hemorrhage and blood reinfusion in rats. Forced oscillation technique was used to measure airway resistance (Raw), respiratory tissue damping, and elastance at baseline and after stepwise 1-ml blood withdrawals up to 5 ml total, followed by stepwise reinfusion up to full restoration. Mean systemic (Pam) and pulmonary arterial pressures and suprarenal aortic blood flow were measured at each step. In supplemental animals, plethysmographic TGV, Pam, and respiratory mechanics measurements were performed. Blood volume loss (BVL) led to proportional decreases in Raw (66.5 ± 8.8 vs. 44.8 ± 9.0 cmH2O·s·l−1 with 5 ml, P < 0.001), Pam, and aortic blood flow. In contrast, tissue damping increased significantly (1,070 ± 91 vs. 1,235 ± 105 cmH2O/l, P = 0.009 with 5 ml BVL), whereas tissue elastance did not change significantly. TGV significantly increased with acute BVL (3.7 ± 0.2 vs. 4.2 ± 0.2 ml, P = 0.01). Stepwise reinfusions produced opposite changes in the above parameters, with Raw reaching a higher value than baseline ( P = 0.001) upon full volume restoration. Both adrenalin ( P = 0.015) and noradrenalin levels were elevated ( P = 0.010) after 5-ml blood withdrawal. Our data suggest that the decreases in Raw following BVL may be attributed to the following: 1) an increased TGV enhancing airway parenchymal tethering forces; and 2) an increase in circulating catecholamines. The apparent beneficial effect of a reduction in Raw in acute hemorrhagic shock is counteracted by an increase in dead space and the appearance of peripheral mechanical heterogeneities due to de-recruitment of the pulmonary vasculature.

Adverse effect of complete thoracic evacuation during chronic pneumothorax in a dog

OBJECTIVE

To describe an unusual response to evacuation of a chronic pneumothorax in a dog.

CASE

Resolution of a pneumothorax is usually associated with lung expansion and a marked improvement in pulmonary function. In the case presented here, evacuation of a chronic pneumothorax improved oxygenation, but markedly impaired ventilation.

CLINICAL RELEVANCE

This is a previously unreported complication associated with the treatment of pneumothorax in dogs. It suggests that in some cases of chronic pneumothorax, total evacuation of the pleural air pocket may improve oxygenation but ventilation deteriorates and increases PCO2, causing further complications.

Detection of alveolar epithelial injury by99mTc-DTPA radioaerosol inhalation lung scan following blunt chest trauma

DTPA clearance rate is a reliable index of alveolar epithelial permeability, and is a highly sensitive marker of pulmonary epithelial damage, even of mild degree. In this study, 99mTc-DTPA aerosol inhalation scintigraphy was used to assesss the pulmonary epithelial membrane permeability and to investigate the possible application of this permeability value as an indicator of early alveolar or interstitial changes in patients with blunt chest trauma. A total of 26 patients was chest trauma (4 female, 22 male, 31-80 yrs, mean age; 53+/-13 yrs) who were referred to the emergency department in our hospital participated in this tsudy. Technetium-99m diethylene triamine pentaacetic acid (DTPA) aerosol inhalation scintigraphy was performed on the first and thirtieth days after trauma. Clearance half times (T1/2) were calculated by placing a mono-exponential fit on the curves. Penetration index (PI) was calculated on the first-minute image. On the first day, mean T1/2 value of the whole lung was 63+/-19 minutes (min), and thirtieth day mean T1/2 value was 67+/-21 min. On the first day, mean PI values of the lung and 30th day mean PI value were 0.60+/-0.05, and 0.63+/-0.05, respectively. Significant changes were observed in radioaerosol clearance and penetration indices. Following chest trauma, clearance of 99mTc-DTPA increased owing to breakdown of the alveolar-capillary barrier. This increase in the epithelial permeability of the lung appears to be an early manifestation of lung disease that may lead to efficient therapy in the early phase.

Hemorrhage and resuscitation induce delayed inflammation and pulmonary dysfunction in mice

BACKGROUND

It is well known that hemorrhagic shock induces inflammatory changes. Our objective was to study the histologic and biochemical changes in the lung and evaluate alterations in respiratory function after hemorrhage and resuscitation (H/R) in mice.

METHODS

After 30 min of hemorrhagic shock, mice were resuscitated with shed blood to restore mean arterial blood pressure to baseline. A sham group was anesthetized and instrumented for 30 min, but did not undergo hemorrhage. Myeloperoxidase (MPO) levels were measured and histologic analysis was performed on lung tissue. Pulmonary function was evaluated using whole-body plethysmography (WBP) 1, 3, and 5 days postprocedure. Alveolar function was evaluated by measuring carbon monoxide uptake via gas chromatography 5 days after H/R.

RESULTS

Five days after H/R, mice exposed to shock had significantly higher lung MPO levels and showed greater histologic evidence of lung injury. Airway resistance (Penh) in the sham mice was 0.91 +/- 0.06 versus 1.21 +/- 0.09 in the hemorrhage group (P < 0.01). Alveolar function was significantly decreased in the H/R group (70.8 +/- 3.6%) compared with shams (81.6 +/- 1.8%) (P < 0.05).

CONCLUSIONS

Hemorrhage and resuscitation cause delayed biochemical, histologic, and physiologic changes in the lung. These were marked by increased lung MPO, increased neutrophils, and decreased alveolar function. The alterations of pulmonary function and structure were most severe 5 days after H/R.