Medicine
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Standardized Hemorrhagic Shock Induction Guided by Cerebral Oximetry and Extended Hemodynamic Monitoring in Pigs
Chapters
Summary May 21st, 2019
Hemorrhagic shock is a severe complication in seriously injured patients, which leads to life-threatening oxygen undersupply. We present a standardized method to induce hemorrhagic shock via blood withdrawal in pigs that is guided by hemodynamics and microcirculatory cerebral oxygenation.
Transcript
This standardized model of hemorrhagic shock induction guided by cerebral oxymetry and external hemodynamic monitoring can be used to simulate a realistic clinical scenario. The main advantage of this model is its simple and highly flexible design, which allow various levels of cardio cellulatory impairment to be easily selected. This techniques allows the evaluation of different therapy concepts of hemorrhagic shock such as fluid resuscitation, coagulation, and catecholamine therapy.
This technique provides insight into the different pathophysiological aspects of hemorrhagic shock and hemodynamic effects on cerebral regional oxygenation, as assessed by near infrared spectroscopy. Visualization of hemorrhagic shock can be critical because the compensation mechanisms of the animals can disguise hemodynamic instability for long period of time. Before beginning covering the inguinal area, apply ultrasound gel to the ultrasound probe and cover the inguinal of an anesthetized approximately 28 kilogram two to three month old pig with a sterile fenestrated drape.
Scan the right femoral vessels with ultrasound using the doppler technique to distinguish between the artery and the vein. Visualize the longitudinal axis of the right femoral artery and puncture the right femoral artery under ultrasound visualization with a Seldinger needle under permanent aspiration with a five milliliter syringe. Bright red, pulsating blood confirms correct positioning of the aspired needle position.
After disconnecting the syring, insert the guide wire and retract the Seldinger needle. Visualize the right femoral vein before rotating the probe 90 degrees to switch to a longitudinal view of the vein. Next, puncture the right femoral vein under ultrasound visualization with the Seldinger needle under permanent aspiration with the five milliliter syringe.
A high oxygen level is indicative of arterial blood and a low oxygen level is a sign of venous blood. After disconnecting the syringe, insert the guide wire and retract the Seldinger needle. Visualize both right vessels under ultrasound to control the correct wire position and push a two millimeter arterial introducer sheath over the guide wire into the right artery and the central venous line into the right femoral vein.
Then aspirate all of the ports and flush the ports with saline solution. For a pulse contour cardiac output, or PiCCO measurement, insert the PiCCO catheter into the right arterial introducer sheath and connect the catheter with the arterial wire of the PiCCO system and the arterial transducer directly to the PiCCO port. Next connect the venous measuring unit of the PiCCO system with the right venous introducer sheath.
Switch the three way stopcocks of both transducers open to the atmosphere to calibrate the systems to zero, according to the manufacturer's instructions. Turn on the PiCCO system and confirm that a new patient is being measured. To calibrate the continuous cardiac output measurement, click TD for thermo dilution and load four degree Celsius physiological saline solution into a 10 milliliter syringe.
Click start and quickly and steadily inject 10 milliliters of the cold saline solution into the venous measuring unit. Then wait until the measurement is complete and the system requests a repetition before repeating the procedure two more times. For cerebral regional oxygenation monitoring, first stick two self adherent near infrared spectroscopy sensors to the forehead of the pig and connect the pre-amplifier to the monitor and the color coded sensor cable connectors to the pre-amplifier.
Close the pre-amp locking mechanism and attach the sensors to the sensor cables. After switching on the monitor, click new patient, enter the study name, and click done. Check the incoming signal.
When the signal is stable, click baseline menu and set baselines. If the baseline has already been entered, click yes and event mark to confirm the new baseline. Then use the arrow buttons on the keyboard under next event to select the three induction event followed by select event.
For hemorrhagic shock induction, connect the left arterial introducer sheath with a three way stopcock and equip one port of the three way stopcock with a 50 milliliter syring and one with an empty infusion bottle. Measure and document the exact hemodynamic parameters and calculate 40%of the cardiac index and mean arterial pressure as hemodynamic targets. Select the 93 blood loss event in the near infrared spectroscopy system and aspirate 50 milliliters of blood into the syringe.
Switch the tree way stopcock and push the blood into the empty bottle. Note the removed blood volume and monitor the arterial blood pressure, cardiac index, and the cerebral regional oxygenation saturation closely. Then, select the 97 hypotension event.
Using hemorrhagic shock has challenging critical aspects and should performed with caution, as hemodynamic instability can lead to sudden death. With ongoing blood removal, cardio circulatory decompensation as monitored by a significant decrease in the cerebral regional oxygen saturation, cardiac index, intrathoracic blood volume index and global end diastolic volume index occur. Furthermore, significant tachycardia and a decrease in arterial blood pressure are common manifestations of hemorrhagic shock.
The stoke volume variation increases significantly while extravascular lung water content and systemic vascular resistance are usually unaffected. After ending the blood withdrawal, the hemodynamic values and cerebral regional oxygenation saturation typically remain at a critically low level. The hemoglobin content and hematocrit do not directly decrease during hemorrhagic shock induction, but lactate levels rise and the central venous oxygen saturation decreases.
Hemorrhagic shock is a serious complication in severely injured patients that can lead to life threatening oxygen under supply. A fast and effective therapy is required to avoid serious organ damage. This procedure can be expanded hemodynamic therapy concept like fluid resuscitation or catecholamine administration.
To investigate different methods for optimizing treatment. This new model paves the way for the evaluation of new therapy concepts of hemorrhagic shock because it simulates a realistic scenario similar to clinical emergency situations. Working with human and animal blood can be hazardous.
Always wear gloves, a face mask, and safety glasses to avoid infectious disease contamination.
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