Substance and pharmacokinetic mechanism of action
Primary pharmacodynamic mechanism of action
Half-life
Dosage repetitive i.v. bolus
Dosage of continuous i.v. infusion
Esmolol-specific antagonist at adrenergic β1-receptor
Decrease of cardiac chrono- and inotropy
9 min
100 μg/kg up to cumulative 500 μg/kg/min
Up to 125 μg/kg/min
Glyceryl trinitrate increase of intracellular cGMP by nitric oxide
Vasodilation (venous > arterial) with resulting reduction in cardiac preload
2–3 min
25 μg up to cumulative 75–100 μg/min
Up to 300 μg/min
Norepinephrine agonist at adrenergic α1/2- and β1-receptors
1. Vasoconstriction (α1/2)
2–3 min
0.1–0.15 μg/kg
0.01–0.3 μg/kg/min
Epinephrine agonist at adrenergic α1/2-and β1/2-receptors
1. Increase of cardiac ino- and chronotropy (β1)
2. Vasoconstriction (α1/2)
2–3 min
0.1–0.15 μg/kg
0.01–0.1 μg/kg/min: increase of heart rate and contractility
0.1–0.3 mcg/kg/min: vasoconstriction
Intra-aortic Balloon
Endoclamping of the aorta with a large-size compliant balloon such as Reliant® (Medtronic) or the Coda (Cook) has been shown to be useful in patients with unstable hemodynamics and/or those patients unresponsive to fluids and catecholamines (Fig. 11.1). Endoclamping can be used for both the endovascular and the surgical approach. In stable low-pressure patients, especially when a large retroperitoneal hematoma has been identified preoperatively, it can also be used during the EVAR procedure to avoid further volume increase of the hematoma. The balloon can be placed under local anesthesia, utilizing a long (preferably ≥40 cm) sheath for prevention of caudal migration during and after inflation. To avoid balloon-related complications, the inflation site should be free of major atherosclerotic aortic disease or aneurysm. Moreover, as the balloon is placed superior to the major branches of the abdominal aorta, the duration of the balloon inflation should be kept as short as possible, since inflation brings about temporary renovisceral ischemia.
Fig. 11.1
Intraoperative angiogram. After placing a guide wire, an aortic balloon is delivered and inflated suprarenal (here supraceliac) to achieve proximal hemorrhage control
Discussion
Based on the early positive experience and subsequent systematic follow-up of the patients at our center, we have routinely applied the principles of hypotensive hemostasis for nearly 20 years. The feasibility of EVAR in rAAA using hypotensive hemostasis, including permissive hypovolemia, controlled hypotension, and local anesthesia, was reported by our group in 2001 [19]. In this series of 21 patients, restricted volumes of fluids and erythrocyte transfusions were enough to maintain hemodynamic stability prior to the completion of EVAR (Fig. 11.2).
Fig. 11.2
Total amount of fluids and transfusions given preoperatively, intraoperatively, and postoperatively. Fluids crystalloids and/or colloids, Ec erythrocytes, FFP fresh frozen plasma, Tc thrombocytes, (Modified from Lachet et al. [19])
Generally, most patients remain stable with preserved mental function at a systolic blood pressure of 70–90 mmHg. To achieve stable hemodynamics at this blood pressure level, very limited amounts of fluids and vasoactive pressors are necessary during EVAR under local anesthesia. As a first step, analgesia is optimized to decrease the sympathomimetic activity. Low dosages of opioids are used and titrated to the desired effect. In patients undergoing interventions under local anesthesia, special care must be taken not to abolish consciousness and risk compromising spontaneous breathing and the protective airway reflexes. Advantages of local anesthesia include the preservation of sympathetic tone, yielding improved hemodynamic stability, preservation of muscle tone, and thereby the possibility to better contain the bleeding, and, in addition, any procedure under local anesthesia offers the best neurological monitoring. The main disadvantages are related to eventual acute loss of consciousness and an uncontrolled airway, suboptimal pain control, and the patient not lying still. Conversely, general anesthesia has the advantages of a controlled airway and optimal pain control. However, by using general anesthesia, most of the advantages of local anesthesia are lost, and it is more time-consuming when compared to local. If general anesthesia is required for an open operation, the patient should be fully prepped and draped prior to induction, and, ideally, an aortic occlusion balloon should first be placed under local anesthesia so that it can be inflated in cases of severe hypotension at any point prior to or during the procedure.
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