Cross-Clamping During Elective Abdominal Aortic Aneurysm Surgery

DEMOGRAPHICS Scenario Name: Abdominal Aortic Aneurysm (AAA) Repair Simulation Developer(s): Jennifer J. Smith, MD; Johann Cutkomp, RA; Avinash B. Kumar, MD, FCCP Date(s) of Development: August to September 2009 Target Audiences: (circle all that apply) CURRICULAR INFORMATION Educational Rationale Abdominal aortic aneurysm (AAA) repair continues to be a common but complex surgical procedure with significant implications for the anesthesiologist. These patients can have multiple comorbidities, and anesthesia care warrants knowledge and clear understanding of the pathophysiologic changes with cross-clamping of the aorta and the subsequent hemodynamic. Inexperience or lack of clear understanding of the tenets of anesthesia management in this scenario can have disastrous consequences. The purpose of this case is sixfold: Identify the risk factors that increase a patient's morbidity and mortality during AAA repair. Discuss the value of various hemodynamic monitors that may be used in this scenario. (It is likely that there are limited data supporting the choice of one kind of monitor over the other.) Discuss the physiological changes associated with cross-clamping and unclamping of the abdominal aorta. Discuss the anticipated hemodynamic changes associated with cross-clamping/unclamping and methods to manage these changes. Discuss the appropriate use of hemodynamic agents (vasopressors, inotropes, and vasodilators), intravenous (IV) fluids, and blood products in an unstable patient. Develop communication skills necessary for leading a team through a medical crisis. Learning Objectives At the conclusion of this scenario, learners will be able to understand and discuss the different physiological changes that occur during abdominal cross-clamping and unclamping and be able to anticipate these changes (1–3). At the conclusion of this scenario, learners will have demonstrated appropriate use of vasopressors and safe blood product administration at appropriate times during the scenario (1,3,4). At the conclusion of this scenario, learners will be able to identify which hemodynamic monitors or lines are appropriate (2,4). At the conclusion of this scenario, learners will be able to identify patients who have comorbidities that may increase morbidity and mortality (1,4,5). At the conclusion of this scenario, learners will have demonstrated skill in running an advanced cardiac life support (ACLS) code situation and communicating effectively with other members of the operating room team during a medical crisis (6). At the conclusion of this scenario, learners will have demonstrated communication to the surgical team regarding the stability of the patient (5,7). Guided Study Questions What are the physiological changes associated with aortic clamping and cross-clamping? What are the appropriate steps to take before aortic cross- clamping and unclamping? What are the comorbidities of a patient that can influence the morbidity and mortality? What are the vasoactive agents that should be readily available for an AAA repair, and what is the basis for your choice of vasoactive agent? What are the appropriate transfusion triggers, and how do you determine the choice of blood products (platelets, fresh-frozen plasma, cryoprecipitate, etc.) to be used in the case? What are the appropriate steps in the ACLS algorithm for an unstable patient with ventricular tachycardia? References Used 1. Chaikof EL, Brewster DC, Dalman RL, et al. The care of patients with an abdominal aortic aneurysm: the Society for Vascular Surgery practice guidelines. J Vasc Surg 2009;50(suppl 4):S2–S49. 2. Thomson DA. Anesthesia for patients with an abdominal aortic aneurysm. Best Pract Res Clin Anesthesiol 2000,14;1:187–197. 3. Miller R, ed. Anesthesia for Vascular Surgery. Miller's Anesthesia. 6th ed. Philadelphia, PA: Churchill Livingstone; 2005:2070–2080. 4. Wozniak MF, LaMuraglia GM, Musch G. Anesthesia for open abdominal aortic surgery. Int Anesthesiol Clin 2005;43:61–78. 5. Toomtong P, Suksompong S. Intravenous fluids for abdominal aortic surgery. Cochrane Database Syst Rev 2010;(1):CD000991. 6. Dager WE, Sanoski CA, Wiggins BS, Tisdale JE. Pharmacotherapy considerations in advanced cardiac life support. Pharmacotherapy 2006;26:1703–1729. 7. Martin KA, Giles FB, Pomposelli AD. National outcomes after open repair of abdominal aortic aneurysms. Ann Vascular Surg 2010;24:106–112. PREPARATION The department of Anesthesiology Simulation Center at the University of Iowa is equipped with a Medical Education Technologies Inc. (Sarasota, FL)-Standard Man human patient simulator. The simulation is interfaced with a Datex-Ohmeda AS/3 (GE Healthcare, NJ) anesthesia machine. The machine is case ready to reflect a standard setup in the operating rooms at the University of Iowa. This includes having the American Society of Anesthesia recommended monitors, a retractable ceiling column for gas delivery/suction/evacuation system (Covidien-Nellcor, Boulder, CO), and Alaris Infusion pump-8100 (CareFusion, San Diego, CA)—all connected to the simulation; a Phillips HeartStart Xl defibrillator (Phillips Healthcare, Andover, MA) is available at the bedside. The drugs ready for use on the anesthesia cart include induction drugs, muscle relaxants, opioids, and common vasoactive drugs (phenylephrine and ephedrine). All other drugs are available in the drug cart and can be prepared, labeled, and administered by the learner in an efficient manner. The simulation center has the capability to record each simulator session, and the recorded material can be made available for the debriefing sessions as needed. The simulation subjects are usually tested in groups of three with at least one senior (late CA2 or CA3) resident. The goal is to have each resident complete at least two scenarios every 6 months. A brief set of instructions for the operator and expected learner actions for each of the scenarios is outlined in Table 1.Table 1: Operator Instructions and Expected Learner Actions for Each ScenarioTable 1: (Continued)Scenario 1: Background and Briefing Information for Facilitator/Coordinator's Eyes Only The first scenario depicts the physiological changes in a routine AAA repair. The patient is relatively stable without any significant cardiorespiratory comorbidities. The facilitator will act as the staff anesthesiologist and will remain in the room until the patient is asleep with pertinent lines and low thoracic epidural in place. A member of the simulator staff will read the lines of the surgeon. The learner will be left alone with the surgeon and will have to communicate effectively when the cross-clamping and unclamping occur. When the surgeon states that cross- clamping of the aorta will occur in 5 minutes, the resident will start to decrease the blood pressure in anticipation of clamping—either by increasing the anesthetic agent or by using nitroglycerin. The resident will have to communicate with the surgeon about blood loss and giving blood products just before unclamping. When the surgeon states that unclamping of the aorta will take place, the resident should prepare by increasing minute ventilation on the ventilator, administering sodium bicarbonate and fluids, and turning on correct vasoactive medications at appropriate doses. This scenario is very stable without any significant morbidity. Scripts After staff anesthesiologist leaves the room:Surgeon: “We are 5 minutes out from aortic cross-clamping.”After cross-clamping and associated hemodynamic changes:Surgeon: “What is the estimated blood loss and most recent hematocrit? Do you think he needs blood?”Learner: “Approximately 600 mL of estimated blood loss. The hematocrit is down to 28.” (Learner will make decision on giving blood at this time.)Before unclamping:Surgeon: “We are 5 minutes away from unclamping, please prepare the patient.” Patient History for Scenario 1: Can be Discussed With the Participant The patient is a 73-year-old man who presents to the emergency room with several days of abdominal pain and vomiting. He states that the pain is 4 of 10 currently in his abdomen. He has never experienced pain like this before. The pain came on abruptly and is constant in nature. Nothing he has done has made the pain better. He has been nauseated and has not been able to keep anything down for 3 days. He has had decreased urine output over the last few days as well. He denies any other complaints, including chest pain or dyspnea. Scenario 2: Background and Briefing Information for Facilitator/Coordinator's Eyes Only The second scenario is a more advanced scenario that depicts morbidity and mortality in an AAA repair. The patient is relatively unstable, with a number of underlying comorbidities and currently showing signs of end organ involvement, including unrelenting abdominal pain and development of oliguria. The facilitator will act as the staff anesthesiologist and will remain in the room until the patient is asleep with pertinent lines and epidural in place. A member of the simulator staff will play the surgeon. The learner will be left alone with the surgeon and will have to communicate effectively when the aortic cross-clamping and unclamping occur. The learner will notice that the patient's blood pressure is running low (systolic blood pressure, 80–90 mm Hg) after induction and will have to: Turn down the epidural infusion rate or stop completely. Start the patient on phenylephrine (either boluses or an infusion early in the case). Make a decision based on cardiac output and cardiac index data (either using the pulmonary artery [PA] catheter data or placing a transesophageal echocardiography [TEE]) to guide therapy with fluids, vasoactive medications, or inotropes. Because of the early need for modulating therapy using cardiac output and cardiac index data, the learner should consider placing the TEE probe well before cross- clamping is set to occur. The focus of the TEE examination should be on left ventricular contractility and left ventricular filling. The findings of the TEE should supplement the PA catheter data to guide therapy. Once the decision is made to place the TEE probe, the anesthesia faculty member states the preaortic cross- clamping findings of the TEE examination. (The results maybe stated simply and/or TEE clips from archival collections can be displayed for the learner to interpret.) The staff anesthesiologist will also be available to state the changes in the TEE examination after the cross- clamp has been applied. Confirm that blood products are available in the operating room at the start of the procedure. Confirm that a rapid fluid infuser is primed and ready at the start of the case in anticipation of increased IV fluid, blood product requirements. The surgeon will announce that cross-clamping will commence in 5 minutes. The learner will have to decide whether to turn off the phenylephrine for cross-clamping. There will be no hemodynamic changes during application of the cross- clamp. The learner will have to communicate with the surgeon regarding increased blood loss during the case and his/her decision to transfuse blood products. They will also have to communicate the ongoing need for pressor support while the aorta is cross-clamped. When the surgeon states that unclamping the aorta will take place, the learner should prepare by increasing minute ventilation, administering sodium bicarbonate and fluids/blood, and turning on correct vasopressors. On unclamping the aorta, the patient will deteriorate with low blood pressure and arrhythmia. The learner should also talk to the surgeon about reclamping the aorta as the patient begins to deteriorate rapidly. The learner will have to identify the severity of the issue, call for help, and start the ACLS algorithm. Scripts Proceed with the case and after the staff anesthesiologist leaves the room:Surgeon: “We are 5 minutes out from aortic cross- clamping.”After cross-clamping and associated hemodynamic changes:Surgeon: “What is the estimated blood loss and most recent hematocrit? Do you think he needs blood?”Learner: “Approximately 1000 mL of estimated blood loss. The hematocrit is down to 24. The patient has required vasopressor support with phenylephrine throughout the cross-clamping.”Before unclamping:Surgeon: “We are 5 minutes away from unclamping, please prepare the patient.”After unclamping and during hypotension and arrhythmia:Learner: “The patient's blood pressure has dropped and he is in ventricular tachycardia. Nurse, please get the crash cart and call overhead for help.” Scenario 2: Elements That Can be Discussed With the Participant Patient History The patient is a 73-year-old man who presents to the emergency room with abdominal pain and vomiting that started 24 hours ago. He states that the pain now is 6 of 10 (pain score was 3/10 on admission) currently in his abdomen. He has experienced this same pain 3 years ago when it was found that he had a ruptured AAA, which was repaired at that time. The pain came on abruptly and is constant in nature. Nothing he has done has made the pain better. He has been nauseated and has not been able to keep anything down for 3 days. He has had decreased urine output over the last 24 hours as well. He also complains that his heart is racing but denies any chest pain or SOB. On reviewing the computed tomography scans, the vascular surgeon thinks that the aneurysm may be leaking and is concerned about a possible contained rupture of the AAA. The surgeon books the case as urgent and says that the patient needs to go for surgery within the next 2 hours, as he is already demonstrating a progression in his presenting symptoms. After discussing with the surgeon, the staff anesthesiologist places an epidural for postoperative pain control. The patient presents to the operating room after successful epidural placement without any medications in the catheter. In the operating room, the patient has an awake arterial line and PA catheter placed before induction. The patient underwent a modified rapid sequence induction with Etomidate and Rocuronium. There were no significant changes in the vital signs on induction. A TEE probe was available but not placed in the patient at this time. NOTES TO INSTRUCTORS AT THE CONCLUSION OF THE SESSION An unbiased debriefing is essential at the end of the session. The anesthesia management of a patient undergoing an open AAA repair is complex and has a significant impact on outcomes. The instructors should highlight the role of adequate preoperative preparation for the anticipated events during the case. The role of choosing the appropriate hemodynamic monitors and the systematic approach of choosing the appropriate vasoactive agent should be emphasized. The common pitfalls encountered during these cases including more than anticipated blood loss or inadequate fluid resuscitation should be emphasized. The importance of guiding hemodynamic therapy using data from the PA catheter and TEE should be emphasized. The information from the TEE examination is to help guide therapy, and the learner should not get entangled in the intricacies of the TEE examination itself. The option of reclamping the aorta should be discussed with the surgeon if the patient deteriorates rapidly. Emphasis on familiarity with the ACLS protocols and clear communication with the surgeons especially when the patient is hemodynamically unstable is key to ensure a good outcome. Adequate reference materials and, if needed, handouts are to be provided. It is imperative to have an active teaching module with involvement of both the learner and instructor in a nonintimidating fashion. The option of recording the sessions for debriefing can be used for more advanced learners, and this may be especially useful for instructors for self-evaluation as well. DEBRIEFING AND UNIVERSITY OF IOWA SIMULATOR CENTER EXPERIENCE We have implemented this scenario in about 12 simulations with CA1 and CA3 residents. This is probably one of the more complex scenarios that we have had the residents work on in the past year. We have at least two CA1 residents work together through scenario 1. At the start of the scenario, the discussion usually gets centered on the choice of epidural versus doing a general anesthetic. Once redirected into the scenario, the limitations of the CA1 residents are in the interpretation and application of the PA catheter data to modulate therapy. The delay in the anticipation and readiness of the team to start antihypertensives (eg, nitroglycerine and sodium nitroprusside) in response to cross-clamping was consistent across several learners. Scenario 2 is truly more complex with a number of possible discussion points and almost always runs longer and has branched off into a number of different subroutines. The anesthesia staff states that the TEE information and actual clips were not made available during this particular scenario. The TEE discussions are dependent on the individual resident's experience and can become a central discussion point if the coordinator does not recenter the discussion to the case. The choice of vasoactive drugs is a key discussion point that always yields valuable information to the instructor about the learner's decision-making process. We were consistently impressed by the systematic approach to a deteriorating situation by the CA3 residents. The ACLS and code scenario tend to be a low point, and, usually, we have already gone beyond the allocated time for the scenario at this time. Having a positive outcome (the patient lives) at the end of the case can be emotionally reassuring for the residents, and we modified the simulation to include that in the scenario after the first test run. ACKNOWLEDGMENTS The authors acknowledge the excellent faculty members of the Department of Anesthesia Simulation Laboratory, Ann Willemsen-Dunlap, PhD, CRNA and Paul Leonard, MD, PhD, for their help in testing the scenario and Christina Spofford, PhD, MD, for her constructive review.FigureFigureTableTableTableTableTable