PV Loops and REBOA During Hemorrhage and Resuscitation

David P Stonko (  dstonko1@jhmi.edu ) Johns Hopkins https://orcid.org/0000-0002-2804-2857 Joseph Edwards R. Adams Cowley Shock Trauma Center, University of Maryland Medical System Hossam Abdou R. Adams Cowley Shock Trauma Center, University of Maryland Medical System Noha N Elansary R. Adams Cowley Shock Trauma Center, University of Maryland Medical System Eric Lang R. Adams Cowley Shock Trauma Center, University of Maryland Medical System Samuel G Savidge R. Adams Cowley Shock Trauma Center, University of Maryland Medical System Rebecca N Treffalls R. Adams Cowley Shock Trauma Center, University of Maryland Medical System Jonathan J Morrison (  jonathan.morrison@som.umaryland.edu ) R. Adams Cowley Shock Trauma Center, University of Maryland Medical System

Blood gas analyzer with rinse solution, or access to a lab with laboratory support Procedure The animal protocol begins with animal preparation and instrumentation. This is followed by the experimental portion of the protocol, see Figure 1. Here we commence hemorrhage, which is followed by a period of hemorrhagic shock, followed by full REBOA, then partial REBOA, then wean REBOA and continue resuscitation.
2. transport the animal to the procedure area.
3. place the animal under iso urane targeting 1.0 MAC by facemask. Transition to generally 10 ccs/kg TV, RR of 12-14 initially but to target a pCO2 of 30-45 and an FiO2 of 40% but adjusted appropriately as needed.
4. place the animal in sternal recumbency and intubate the animal with a 7.0 endotracheal tube. 5. make the animal supine and restrain.
6. Place all venous and arterial catheters using US guidance, and place all monitoring devices. Includes: -place an LV PV loop via a carotid or right brachial artery 7 fr sheath catheter.
-place a 7 fr sheath in either jugular down to the RA to be able to obtain central venous gases (and labs).
-place a 7 fr sheath in the other carotid or either brachial artery, and through this placean aortic pressure probe (which will remain proximal to the REBOA) -place a 7 fr sheath in the right or left jugular for central venous pressure probe -place an at least 7 fr sheath in either femoral vein through which we will hemorrhage and later resuscitate.
-place a 7 fr sheath in either femoral artery, though which place an aortic pressure probe (which will remain below the REBOA) -place an at least 8 fr (ideally 9 fr sheath) in either femoral artery to hold the REBOA catheter from below -also place EKG leads, oxygen saturation probe, rectal temperature probe and a bovie pad (after shaving). 7. Perform a lower abdominal laparotomy for cystostomy (place a foley catheter into the bladder) to facilitate bladder drainage.
8. Perform a left anterolateral thoracotomy. Place the 3 or 4mm ow probe around the coronary ow probe and add ultrasound jelly to the probe.
10. Perform a TIMEOUT. Con rm all line placements, con rm all sheaths work (drawback and ush), con rm uids are ready, that the timer is ready and reset, that data is being transduced through LabChart through appropriately labeled channels and saved. Con rm ventilatory settings. 11. Con rm uoroscopically that all catheters and devices are appropriately positioned.
3. Throughout baseline and resuscitation use the following guidelines: -Give one ampule of Calcium at start of resuscitation -Treat glucose < 65 with D50 -for pH < 7.2 give on ampule of bicarbonate -treat pCO2 as necessary with MV changes -during resuscitation, treat sustained MAP < 65 after starting uids with pressor, rst line is norepinephrine.
-get baseline blood resistivity, enter value into the PV catheter system control.
III. Bleed: 1. Bleed at a rate of 50ccs/min from venous CVC to goal of 45 mmHg systolic BP.
1. At end of shock obtain a VBG, and ABG if pO2 before was low or needed clinically 2. Obtain repeat blood resistivity and if needed then enter new value into PV catheter system. V. REBOA Period: has two subperiods: Full REBOA and Partial REBOA periods, ending with REBOA wean and .
2. Begin uid resuscitation. Start with return of all shed blood and one ampule of Calcium, then, as needed, in the remaining portion of the protocol we can give up to 3L of 0.9%NS total.
Vc: Full De ation, transition to post REBOA ICU period.
VI: ICU Period: 30 mins 1. Obtain a VBG and ABG at the start of this period.

Con rm ventilatory stability.
3. Ends with chem8, VBB, ABG, and troponin. Obtain full thickness heart tissue and place in formalin.
Obtain 5 tubes of blood, spin down and pipet off serum.
VII. Completion of trial.
1. Euthanize and dispose of animal.

Troubleshooting Time Taken
We approximate that laboratory/OR preparation time is approximately one hour and animal preparation as one hour. The formal protocol begins and takes a total of approximately three hours, see Figure 1, with an additional one hour for take down and clean up. Therefore, each animal takes about 6 hours to complete, for a total of an anticipated 5 animals a total of approximately 30 hours with the animals.

Anticipated Results
We anticipate 3 major portions of the results sections.
The rst section will be an overview of the include animals, including weights, volume of shed blood, and collect laboratory data from each study period. We would anticipate an increase in lactate and troponin during the study period due to the hemorrhage and likely further injury from aortic occlusion.
The second section of the results will examine the PV loops and the associated cardiac parameters from each period of study, and quantify their evolution across the pressure-volume plane in time. We will compute hemodynamic parameters such as ESPVR, EDPVR, stroke work, stroke volume, HR, cardiac output and compare these across study period. We would expect the known changes in the PV relationship from baseline to hemorrhagic shock: a movement of the PV loop down and to the left of the PV plane. Supplemental Figure 1 shows an example video of pressure-volume data over time throughout a one hour hemorrhage, obtained from a prior animal study in our lab. This data has been cleaned algorithmically, and plotted in Matlab. Here, the PV loop moves from the upper right corner of the plot to the lower left as the animal is hemorrhaged. REBOA should then move the PV loop to the left, but with unknown impact on CO and stroke work. Transitioning then from full to partially occlusive REBOA should drop the afterload and be more physiologic, thereby off-loading the heart and improving contractility while at least theoretically maintaining stroke work. Our hypothesis is that partial REBOA balances the afterload bene t in a hypovolemic model, against the reduced aortic compliance seen when a fully occlusive REBOA is placed. Our goal is then to resuscitate the animal with the REBOA down completely and normalize the PV relationship close to baseline. We would expect close but most likely imperfect normalization in the rst 30 minutes due to the stress and residual cardiac dysfunction.
The third portion of the results will examine coronary ow during each period of the study. We intend to examine the proportion of time spent in ow reversal from each study period, the average maximum ows during each cardiac cycle from each time period, and the total ow per second (absolute ow and ow relative to cardiac output).  Cartoon depiction of the swine heart with a pressure-volume catheter in the left ventricle, with theoretical segmentation delimitations, as well as pressure transducers in the aorta, SVC, and IVC, with depiction of in ated REBOA balloon in the descending aorta. Cartoon depiction of animal instrumentation. From superior to inferior and left to right: (1) right IJ with 7 fr. cannula in right atrium for central venous gases, (2) right carotid with 7 french (fr.) cannula with left ventricle PV catheter, (3) left IJ with right atrial pressure monitor and (4) left brachial artery with aortic (above the REBOA) pressure monitoring. Also, with an antero-lateral thoracotomy with a dissected LAD; (5) a ow probe around the LAD, and (6) EKG leads on left and right posterior chest. In the lower