A Rat Model of Ventricular Fibrillation and Resuscitation by Conventional Closed-chest Technique

The overall goal of this procedure is to gain insight into the pathophysiology of cardiac arrest and to explore new resuscitation strategies. This is accomplished by first surgically instrumenting the animal to measure various physiological parameters that are collected in a data acquisition system for subsequent offline analysis, cardiac arrest is produced by electrically inducing ventricular fibrillation or vf. For this step, a pre curved G wire is inserted into the right external jugular vein and advanced into the right ventricle, enabling the delivery of an electrical current for the induction of vf.

After eight minutes of untreated VF chest compression is initiated by using a piston device, gradually increasing the compression depth while moving the animal into a piston position that yields the highest aortic diastolic pressure. After eight minutes of chest compression, defibrillation is attempted by delivering electrical shocks to the animal. Animals that are successfully resuscitated are monitored to assess the effects of resuscitation interventions on post resuscitation, hemodynamic and metabolic function, and on survival.

Though this method can provide insight into new resuscitation strategies, it may also be useful for exploring the underlying mechanisms by which therapies work at the cellular level through tissue analysis and assessment of circulating marker. The red model of cardiac arrest and resuscitation that you're going to see today was developed back in 1988 by Irene Bonta and my mentor Professor Max Harry Wilde. The model has been used extensively throughout the world, and we believe that the visual representation of the model is going to be helpful for scientists.

Students interested in the field of cardiopulmonary resuscitation, This rat model of cardiac arrest enclosed chest resuscitation can be useful in furthering our understanding of the pathophysiology of cardiac arrest and the development of novel resuscitation approaches To facilitate advancement of the PE 25 catheter into the descending thoracic aorta begin by making a two centimeter incision on the right inguinal area of an anesthetized adult rat at a 90 degree angle relative to its groove. Next, use a pair of hemostats to blunt, dissect the surrounding connective tissue, exposing the femoral vessels and nerve use curved microdissection forceps to expose the vascular sheath around the vessels. Then travel with microdissection forceps underneath the femoral artery vein and nerve, and support them at a 90 degree angle relative to the vessels when both vessels and nerve are supported.

Use another pair of curved microdissection forceps to separate the artery from the nerve and vein to a length of about one centimeter. Once separated, insert one distal and one proximal ligature beneath the vessels. Use a surgeon's knot to firmly tighten the distal ligature, followed by two single knots.

Tighten the proximal ligature with a loose surgeon's knot. Next, make a small incision on the vessel near the distal ligature at a 60 degree angle relative to the vessel with a pair of microdissection scissors cutting approximately one quarter of the cross-sectional area. Then insert a 22 gauge needle with a tip blunted and bent at a 70 degree angle into the vessel opening while gently pulling the distal ligature with the hemostats to stabilize the vessel.

Now lift the introducer needle gently to expose the lumen and guide the PE 25 catheter under the introducer, removing the needle. Once the catheter tip has been inserted, advance the catheter to the eight centimeter mark to position its tip into the descending thoracic aorta, and then tighten the proximal ligature by adding two additional single knots securing the catheter to the vessel. This shot of the neck displays a previously cannulated right external jugular vein to expose the trachea.

Next, use hemostats to expand the incision toward the midline and then use the hemostats to further blunt, dissect the sternal hyoid, sternal thyroid, and mastoid sections of the CTO cephalic muscles. Use a tissue spreader to maintain exposure of the trachea. Then pull out the tongue to stretch the airway with a firm grip advance.

A five F tracheal cannula mounted on a stylet with a tip pointing upward, seeking to enter the upper airway, vocal cords and trachea. Successful tracheal intubation can then be confirmed by the recognition of the characteristic capnographic waveform. Before starting the cardiac arrest and resuscitation protocol, measure the cardiac output and various pressures to verify hemodynamic stability.

Once the baseline values have been recorded, remove the three-way stop cock from the three F polyurethane catheter inserted into the right external jugular vein of the animal and advance the softer tip of the G wire, approximately seven centimeters. Seeking to enter the right ventricle while monitoring the ECG and the aortic pressure. Next, turn on the 60 hertz AC generator and gradually increase the current while monitoring the aortic pressure.

Maintain the current for three minutes and the intensity after two minutes. Turn off the current after three minutes, then remove the guide wire. Recap the jugular catheter with a three-way stop cock and remove the ground needle.

After allowing VF to continue spontaneously for the desired duration, turn on the ventilator and gradually increase the compression depth from zero to 10 millimeters. During the first minute of chest compression, move the animal slightly sideways and sroc. Seeking to find a position that yields the highest aortic diastolic pressure for a given compression depth.

Then continue increasing the compression depth during the second minute until a target aortic diastolic pressure is achieved. Maintain chest compressions for the desired duration before attempting defibrillation. Immediately before completing the chest compressions, apply conductive gel to a rat customized defibrillation paddle of a commercially available biphasic waveform defibrillator, and charge the defibrillator.

Then interrupt the chest compression and after verifying that the heart remains in VF by the ECG readout, deliver an electrical shock of five joules across the chest wall. Observe for the return of an electrically organized ECG with aortic pulses and a mean aortic pressure of greater than or equal to 25 millimeters.Mercury. If the mean aortic pressure is less than 25 millimeters, mercury resume chest compressions for another 30 to 60 seconds regardless of the electrical rhythm.

Determine the resuscitation outcome at the completion of the defibrillation compression cycles according to the flow chart. Then increase the ventilation rate from 25 to 60 per minute after the return of spontaneous circulation, lowering the fraction of inspired oxygen from 1.0 to 0.5 After 15 minutes of spontaneous circulation, finally monitor the animal until it is completely recovered. Using this protocol, it was demonstrated that the sodium hydrogen exchanger isoform one inhibitors IDE and a V 4 4 5 4 B enabled the development of a predefined aortic diastolic pressure with less depth of chest compression, yielding a higher coronary perfusion pressure to depth ratio post resuscitation.

Both compounds ameliorated myocardial dysfunction, but survival was greater with Carri ride as illustrated in the figure suggesting that IDE is a more effective sodium hydrogen exchanger isoform one inhibitor than a VE for resuscitation from cardiac arrest. In this rat model, Once mastered, the surgical instrumentation can be completed in 90 minutes. Following this procedure, blood can be collected for measurements of markers of organ and organal Injury on the heart can be harvested for molecular analysis.

After watching this video, you will have a good understanding of how to induce when trigger fibrillation in the red, how to effectively perform close chest resuscitation, how to reestablish cardiac activity, and identify variables to monitor in order to assure the success of the experiment.