Influence of negative expiratory pressure ventilation on hemodynamic variables during severe hemorrhagic shock

Permissive hypoventilation equally effective to maintain oxygenation as positive pressure ventilation after porcine class III hemorrhage and whole blood resuscitation

BACKGROUND

Prehospital anesthesia may lead to circulatory collapse after severe hemorrhage. It is possible that permissive hypoventilation, refraining from tracheal intubation and accepting spontaneous ventilation, decreases this risk, but it is not known if oxygen delivery can be maintained. We investigated the feasibility of permissive hypoventilation after class III hemorrhage and whole blood resuscitation in three prehospital phases: 15 min on-scene, 30 min whole blood resuscitation, and 45 min after.

STUDY DESIGN AND METHODS

19 crossbred swine, mean weight 58.5 kg, were anesthetized with ketamine/midazolam and hemorrhaged to a mean (SD) 1298 (220) mL (33%) and randomized to permissive hypoventilation (n = 9) or positive pressure ventilation with FiO2 21% (n = 10).

RESULTS

In permissive hypoventilation versus positive pressure ventilation, indexed oxygen delivery (DO2 I) decreased to mean (SD) 4.73 (1.06) versus 3.70 (1.13) mL min-1  kg-1 after hemorrhage and increased to 8.62 (2.09) versus 6.70 (1.56) mL min-1  kg-1 at completion of resuscitation. DO2 I, indexed oxygen consumption (VO2 I), and arterial saturation (SaO2 ) did not differ. Permissive hypoventilation increased the respiratory rate and increased pCO2 . Positive pressure ventilation did not deteriorate circulation. Cardiac index (CI), systolic arterial pressure (SAP), hemoglobin (Hb), and heart rate did not differ.

DISCUSSION

Permissive hypoventilation and positive pressure ventilation were equally effective to maintain oxygen delivery in all phases. A respiratory rate of 40 was feasible, showing no signs of respiratory fatigue for 90 min, indicating that whole blood resuscitation may be prioritized in select patients with severe hemorrhage and spontaneous breathing.

Intrathoracic Pressure Regulator Performance in the Setting of Hemorrhage and Acute Lung Injury

INTRODUCTION

Intrathoracic pressure regulation (ITPR) can be utilized to enhance venous return and cardiac preload by inducing negative end expiratory pressure in mechanically ventilated patients. Previous preclinical studies have shown increased mean arterial pressure (MAP) and decreased intracranial pressure (ICP) with use of an ITPR device. The aim of this study was to evaluate the hemodynamic and respiratory effects of ITPR in a porcine polytrauma model of hemorrhagic shock and acute lung injury (ALI).

METHODS

Swine were anesthetized and underwent a combination of sham, hemorrhage, and/or lung injury. The experimental groups included: no injury with and without ITPR (ITPR, Sham), hemorrhage with and without ITPR (ITPR/Hem, Hem), and hemorrhage and ALI with and without ITPR (ITPR/Hem/ALI, Hem/ALI). The ITPR device was initiated at a setting of -3 cmH2O and incrementally decreased by 3 cmH2O after 30 minutes on each setting, with 15 minutes allowed for recovery between settings, to a nadir of -12 cmH2O. Histopathological analysis of the lungs was scored by blinded, independent reviewers. Of note, all animals were chemically paralyzed for the experiments to suppress gasping at ITPR pressures below -6 cmH2O.

RESULTS

Adequate shock was induced in the hemorrhage model, with the MAP being decreased in the Hem and ITPR/Hem group compared with Sham and ITPR/Sham, respectively, at all time points (Hem 54.2 ± 6.5 mmHg vs. 88.0 ± 13.9 mmHg, p < 0.01, -12 cmH2O; ITPR/Hem 59.5 ± 14.4 mmHg vs. 86.7 ± 12.1 mmHg, p < 0.01, -12 cmH2O). In addition, the PaO2/FIO2 ratio was appropriately decreased in Hem/ALI compared with Sham and Hem groups (231.6 ± 152.5 vs. 502.0 ± 24.6 (Sham) p < 0.05 vs. 463.6 ± 10.2, (Hem) p < 0.01, -12 cmH2O). Heart rate was consistently higher in the ITPR/Hem/ALI group compared with the Hem/ALI group (255 ± 26 bpm vs. 150.6 ± 62.3 bpm, -12 cmH2O) and higher in the ITPR/Hem group compared with Hem. Respiratory rate (adjusted to maintain pH) was also higher in the ITPR/Hem/ALI group compared with Hem/ALI at -9 and - 12 cmH2O (32.8 ± 3.0 breaths per minute (bpm) vs. 26.8 ± 3.6 bpm, -12 cmH2O) and higher in the ITPR/Hem group compared with Hem at -6, -9, and - 12 cmH2O. Lung compliance and end expiratory lung volume (EELV) were both consistently decreased in all three ITPR groups compared with their controls. Histopathologic severity of lung injury was worse in the ITPR and ALI groups compared with their respective injured controls or Sham.

CONCLUSION

In this swine polytrauma model, we demonstrated successful establishment of hemorrhage and combined hemorrhage/ALI models. While ITPR did not demonstrate a benefit for MAP or ICP, our data demonstrate that the ITPR device induced tachycardia with associated increase in cardiac output, as well as tachypnea with decreased lung compliance, EELV, PaO2/FIO2 ratio, and worse histopathologic lung injury. Therefore, implementation of the ITPR device in the setting of polytrauma may compromise pulmonary function without significant hemodynamic improvement.

Automated expiratory ventilation assistance through a small endotracheal tube can improve venous return and cardiac output

BACKGROUND

Positive pressure ventilation can decrease venous return and cardiac output. It is not known if expiratory ventilation assistance (EVA) through a small endotracheal tube can improve venous return and cardiac output.

RESULTS

In a porcine model, switching from conventional positive pressure ventilation to (EVA) with - 8 cmH₂0 expiratory pressure increased the venous return and cardiac output. The stroke volume increased by 27% when the subjects were switched from conventional ventilation to EVA [53.8 ± 7.7 (SD) vs. 68.1 ± 7.7 ml, p = 0.003]. After hemorrhage, subjects treated with EVA had higher median cardiac output, higher mean systemic arterial pressure, and lower central venous pressure at 40 and 60 min when compared with subjects treated with conventional ventilation with PEEP 0 cmH₂0. The median cardiac output was 41% higher in the EVA group than the control group at 60 min [2.70 vs. 1.59 L/min, p = 0.029].

CONCLUSION

EVA through a small endotracheal tube increased venous return, cardiac output, and mean arterial pressure compared with conventional positive pressure ventilation. The effects were most significant during hypovolemia from hemorrhage. EVA provided less effective ventilation than conventional positive pressure ventilation.

Tidal volume in animal models of hemorrhagic and endotoxic shock

The aim of this study was to examine the characteristics of lung, kidney and small intestine injury caused by early resuscitation from hemorrhagic shock (HS) and endotoxic shock (ES) when ventilating with different tidal volumes (Vts). The study also considered the determination of the appropriate Vt for use in mechanical ventilation (MV) during treatment for shock. Resuscitated rabbits were ventilated with varying Vts for 120 min following 60 min of HS or ES. The histopathology, ultrastructure and apoptotic index (AI) of the lung, kidney and small intestine were then measured. Organs from the high-Vt groups (VT=12-15 ml/kg) showed the highest pathological scores (PSs; P<0.05). For HS, the renal PS and AI of the HS-M group (Vt=8-10 ml/kg)were lower than those of the HS-L group (Vt=4-6 ml/kg) and the lung PS and AI of the HS-C (control) group were lower compared with those of the HS-M group. For ES, the lung PS of the ES-L group was lower compared with that of the ES-M group (Vt=8-10 ml/kg) and the lung AI of the ES-C (control) group was lower compared with that of the ES-L group (Vt=4-6 ml/kg). When ventilated with the same Vt, ES resulted in higher PSs in the lung and intestine and a lower renal PS (P<0.05) than HS. MV was not recommended for either shock type. When it was necessary for MV to be applied, low Vt (4-6 ml/kg) protected the lung in ES. Moderate Vt (8-10 ml/kg) may be relatively safe to use for HS.

Arginine vasopressin: a promising rescue drug in the treatment of uncontrolled haemorrhagic shock

Haemorrhagic shock is one of the most frequent types of shock. If haemorrhage cannot be controlled and fluid resuscitation as well as catecholamines are insufficient to stabilize cardiovascular function, uncontrolled haemorrhagic shock occurs. Several approaches have been suggested as promising alternatives to volume resuscitation. The rationale for the use of arginine vasopressin (AVP) is the pharmacologic amplification of the neuroendocrine stress response. AVP-mediated vasoconstriction is the first physiologic step to haemostasis and shifts blood away from the bleeding site towards the heart, lungs and brain. Particularly, when uncontrolled haemorrhage is accompanied by traumatic brain injury this may help to reduce secondary neurological damage. Since AVP can prevent acute death only transiently, it must comprehensively be combined with rapid hospital admission, immediate control of haemorrhage followed by aggressive fluid resuscitation and blood transfusion. This review article summarizes current experimental and clinical evidence on the use of AVP in uncontrolled haemorrhagic shock.

Influence of ventilation strategies on survival in severe controlled hemorrhagic shock

OBJECTIVE

To investigate the effect of different ventilation settings on hemodynamic stability in severe controlled hemorrhagic shock.

DESIGN

Prospective, randomized, controlled animal study.

SETTING

Research laboratory in a university hospital.

SUBJECTS

Approximately 35-45 kg domestic pigs.

INTERVENTIONS

Twenty-four domestic pigs were bled 45 mL/kg (estimated 65% of their calculated blood volume) and then ventilated with either 0 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 0 respiratory rate 14), or with 5 cm H2O positive end-expiratory pressure, a respiratory rate of 28 ventilations/min, and a tidal volume reduced by half (positive end-expiratory pressure 5 respiratory rate 28), or with 5 cm H2O positive end-expiratory pressure and a respiratory rate of 14 ventilations/min (positive end-expiratory pressure 5 respiratory rate 14). After 1 hr study phase surviving animals, received fluid resuscitation and were monitored for further 1 hr.

MEASUREMENTS AND MAIN RESULTS

Pulmonary variables, hemodynamic variables, and short-term survival. There were no significant differences in mean arterial blood pressure and cardiac index after hemorrhage. After 20 mins of different ventilation strategies mean arterial blood pressure was 40 +/- 3 mm Hg in the positive end-expiratory pressure 0 respiratory rate 14 group, vs. 24 +/- 6 mm Hg the positive end-expiratory pressure 5 respiratory rate 28 group (p < 0.05) vs. 19 +/- 3 mm Hg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Cardiac index was 65 +/- 5 mL/min/kg in the positive end-expiratory pressure 0 respiratory rate 14 group vs. 37 +/- 5 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 28 group(p < 0.01) and 20 +/- 3 mL/min/kg in the positive end-expiratory pressure 5 respiratory rate 14 group (p < 0.01). Mean airway pressure and positive end-expiratory pressure correlated strongly with mean arterial blood pressure and cardiac index. None of the positive end-expiratory pressure 0 respiratory rate 14 animals died in the study phase, whereas six of seven positive end-expiratory pressure 5 respiratory rate 28 animals, and all seven positive end-expiratory pressure 5 respiratory rate 14 animals died.

CONCLUSIONS

In this porcine model of severe hemorrhagic shock, reduction of positive end-expiratory pressure was the most important ventilation strategy component influencing hemodynamic stability. Reducing mean airway pressure by decreasing tidal volumes and increasing respiratory rates seemed to have less influence on cardiopulmonary function and survival than 0 cm H2O positive end-expiratory pressure.

Management of bleeding following major trauma: a European guideline

INTRODUCTION

Evidence-based recommendations can be made with respect to many aspects of the acute management of the bleeding trauma patient, which when implemented may lead to improved patient outcomes.

METHODS

The multidisciplinary Task Force for Advanced Bleeding Care in Trauma was formed in 2005 with the aim of developing guidelines for the management of bleeding following severe injury. Recommendations were formulated using a nominal group process and the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) hierarchy of evidence and were based on a systematic review of published literature.

RESULTS

Key recommendations include the following: The time elapsed between injury and operation should be minimised for patients in need of urgent surgical bleeding control, and patients presenting with haemorrhagic shock and an identified source of bleeding should undergo immediate surgical bleeding control unless initial resuscitation measures are successful. A damage control surgical approach is essential in the severely injured patient. Pelvic ring disruptions should be closed and stabilised, followed by appropriate angiographic embolisation or surgical bleeding control, including packing. Patients presenting with haemorrhagic shock and an unidentified source of bleeding should undergo immediate further assessment as appropriate using focused sonography, computed tomography, serum lactate, and/or base deficit measurements. This guideline also reviews appropriate physiological targets and suggested use and dosing of blood products, pharmacological agents, and coagulation factor replacement in the bleeding trauma patient.

CONCLUSION

A multidisciplinary approach to the management of the bleeding trauma patient will help create circumstances in which optimal care can be provided. By their very nature, these guidelines reflect the current state-of-the-art and will need to be updated and revised as important new evidence becomes available.