Review: perspectives on renal and visceral protection during thoracoabdominal aortic aneurysm repair

Abstract

Open repair of a thoracoabdominal aortic aneurysm (TAAA) is an extensive operation and associated with significant perioperative morbidities and mortality, in large part due to distal aortic ischemia secondary to aortic cross-clamping that is necessitated during repair. Distal aortic ischemia may manifest as complications of the kidneys and viscera. Postoperative renal complications range from temporarily elevated levels of creatinine resulting from impaired kidney function to acute renal failure necessitating dialysis that may persist after hospital discharge. Continued advances in the management and adjuncts associated with TAAA repair since the groundbreaking era of E.S. Crawford have led to improved postoperative outcomes following surgery, but the dramatic improvements seen in reducing rates of spinal cord deficits, mesenteric ischemia and other serious postoperative complications have not been seen in contemporary rates of postoperative renal failure. We provide an overview of the various surgical techniques and adjuncts as they relate to the management of visceral and renal ischemia.

Introduction

Open repair of a TAAA is an extensive operation and associated with significant perioperative morbidities and mortality, in large part due to distal aortic ischemia secondary to aortic cross-clamping that is necessitated during repair. Distal aortic ischemia may manifest as complications of the kidneys and viscera. Postoperative renal complications range from temporarily elevated levels of creatinine resulting from impaired kidney function to acute renal failure necessitating dialysis that may persist after hospital discharge. The incidence of postoperative acute renal dysfunction after TAAA ranges from 12 to 50% [1–4], although this can be difficult to assess across aortic centers because there is great variability in how acute renal dysfunction is defined (Table 1). Although postoperative dialysis is necessitated in far fewer patients, approximately 2–17% patients will need such treatment [1–3, 5, 7, 8], and it may additionally decrease long-term survival [9, 10]. Despite a relatively low incidence of mesenteric ischemia—reported incidences range from 1 to 3% of patients [1, 4, 11] undergoing open distal aortic repair—such complications are associated with increased rates of mortality, up to 62% [11].

Table 1.

Varying definitions of postoperative renal dysfunction after TAAA repair

Author (first)	Year publ.	Definition of acute renal dysfunction
Coselli [1]	2016	SCr increased to double its baseline value or the need for new-onset postoperative dialysis
Estrera [5]	2015	Increase of 1 mg/dL of SCr per day for 2 consecutive days, clinical diagnosis of acute renal failure, or the need for new-onset postoperative dialysis
Tshomba [3]	2014	SCr increased to 1.5 times
Kulik [6]	2011	Need for new-onset postoperative dialysis
Cina [2]	2002	SCr increased to double its baseline value at least once during the hospital stay

TAAA thoracoabdominal aortic aneurysm, SCr serum creatinine level

Continued advances in the management and adjuncts associated with TAAA repair since the groundbreaking era of E.S. Crawford [12] have led to improved postoperative outcomes following surgery, but the dramatic improvements seen in reducing rates of spinal cord deficits, mesenteric ischemia and other serious postoperative complications have not been seen in contemporary rates of postoperative renal failure. For example, in the Crawford era (1960 to 1991), the rate of renal failure after TAAA repair was 5.5% overall, and in the Coselli era (1986 to present), the overall rate of postoperative renal failure remains similar at 5.7% [1, 12]. However, this lack of improvement may be related to elevated rates of preoperative kidney disease and other co-morbidities in contemporary TAAA patients. In our analysis of 3309 TAAA repairs [1], we identified elevated rates of preoperative serum creatinine levels, increased age, and the presence of aortic rupture as independently predictive of postoperative renal failure; additionally predictive were factors related to operative complexity such as the need for extensive (extent II) repair, the need to manage any of the four renal or visceral arteries (namely, endarterectomy, stenting, or the use of bypass grafts), as well as increased aortic clamp times, and increased operative ischemic times of the renal arteries.

Additionally, clinicians should be aware of the nephrotoxic effects of vascular contrast agents that are commonly used as part of preoperative imaging studies to evaluate the aneurysm and cannulation sites as well as to determine kidney size and ascertain whether or not its perfusion is compromised. The risk of radiocontrast-induced nephropathy is greatly enhanced in patients with preexisting renal impairment and especially so in patients with diabetic nephropathy [13]. Several agents, as well as various hydration techniques, have been administered during imaging studies to protect the kidneys. Of these, acetylcysteine is the most commonly used; however, its effectiveness is unclear, and it remains under investigation [14]. Whenever possible, surgery should be delayed at least 24 h after such imaging to reduce the risk of contrast-induced nephropathy. Below, we provide an overview of the various surgical techniques and adjuncts as they relate to the management of visceral and renal ischemia.

Passive shunting

In 1955, Etheredge and colleagues used a polyethylene shunt to transport blood from the descending thoracic aorta to the infrarenal aorta during one of the earliest open TAAA repairs [15]. For the next decade or two, a variety of shunts and bypass grafts were used to passively direct pulsatile arterial flow to the kidneys and viscera [16, 17]. However, the pulsatile nature of the flow meant that end-organ oxygen delivery was dependent upon having both adequate proximal arterial pressure and blood oxygenation. Due to these setbacks, passive shunts have fallen out of the majority favor and have been replaced at many centers with mechanical circulatory support systems, which allow for ease of control of flow rates and distal aortic pressure.

Although we do not use shunts in our practice, contemporary proponents of passive shunts continue to use modified techniques to provide visceral and renal perfusion during TAAA surgery [18–21]. Most recently, Monnot and colleagues [18] reported the use of temporary passive shunts in ten patients with extensive occlusive atherosclerotic iliac disease, which would otherwise make the use of retrograde mechanical perfusion problematic. In these patients, a single side graft anastomosed to the left axillary artery led to a bifurcated graft in which two catheters were placed. Upon opening of the aneurysm, the catheters were inserted into the superior mesenteric and right renal arteries and passively perfused, with satisfactory results.

Mechanical perfusion systems

Left heart bypass

During open TAAA repair, left heart bypass (LHB) is a commonly used technique to provide isothermic self-oxygenated blood to the distal aorta while the proximal anastomosis is being completed [22, 23]. A mainstay in our practice, we use LHB as a standard adjunct during repair of Crawford extent I and II TAAA repairs [24, 25]; it is occasionally used in less extensive TAAA repairs (extent III and IV) to effectively unload the heart during repair.

Left heart bypass uses closed-circuit, in-line centrifugal pump technology to establish a temporary bypass from the left atrium to either the distal descending thoracic aorta or the femoral artery to provide blood to the distal aorta and its branching arteries, including those of the kidneys and viscera. In our practice after the intravenous administration of heparin (1.5 mg/kg), cannulation of the outflow line is typically accomplished with a 24-Fr angled-tip venous cannula which is connected to the venous drainage line of the LHB circuit and inserted into an opening in the inferior left pulmonary vein to the left atrium; cannulation of the inflow line is done through a 20- or 22-Fr angled-tip arterial cannula which is connected to the arterial line of the LHB circuit and inserted into the distal descending thoracic aorta (commonly just a few centimeters proximal to the celiac axis) (Fig. 1). When we first began using LHB, the left femoral artery was the primary site for arterial inflow and the descending thoracic aorta was only used in patients with femoral or iliac artery occlusive disease; however, using the distal descending thoracic aorta is generally easier to accomplish because there is no need to expose (or repair) the femoral artery, and it has become our preferred approach. When selecting cannulation sites, care should be taken to avoid sites with intraluminal thrombus to avoid distal embolization. Bypass flows are generally set between 1500 and 3500 mL/min [23, 24]. In our most recent review of our 3309 TAAA experience, LHB was used in 60.9% of extent I repairs and 82.0% of extent II repairs; in contrast, only 6.5% of extent III and 0.9% of extent IV repairs [1].

Fig. 1.

Illustration of left heart bypass during the proximal portion of an extent II thoracoabdominal aortic aneurysm repair. Placement of the aortic clamp and opening of the proximal descending thoracic aorta (a). Left heart bypass is used as the proximal anastomosis is performed (b). Used with the permission of Baylor College of Medicine

Our group has used LHB since its introduction in the late Crawford era, and through retrospective studies we have primarily established its benefit in reducing rates of postoperative spinal cord deficit but also indicated a trend towards reduced rates of renal failure [26]. Schepens et al. described their results with left heart bypass and found the use of LHB significantly reduced the risk of postoperative dialysis [27].

Cardiopulmonary bypass with hypothermic circulatory arrest

Cardiopulmonary bypass permits the use of mechanically oxygenated blood; combined with hypothermic circulatory arrest (HCA), it is routinely employed by some centers during open TAAA repair. Notably, such use of HCA is commonly limited to extents I–III—a clamp-and-sew approach is reserved for extent IV repairs. Advantages include obtaining a bloodless field, avoiding proximal clamping of the distal aorta, improved access to the distal aspect of the aortic arch, and generally reduced rates of postoperative renal failure and spinal cord deficit [6, 8, 28–31].

The primary drawbacks of using HCA during TAAA repair include hypothermic induced coagulopathy, bleeding complications related to an increased use of heparin, cold lung injury, and an increased risk of stroke. Overall, the risk of stroke in contemporary TAAA repair is low (1–2%) [1], but in series of descending thoracic and thoracoabdominal aortic aneurysm repairs using HCA as a standard approach, the risk of stroke appears to be roughly doubled (3–4%) [8, 28].

We do not routinely use HCA during TAAA repair, and instead employ this technique only when circumstances preclude safe application of a proximal aortic clamp, such as in very large aneurysms (i.e., those over 10 cm) or in some cases of rupture; our report on 3309 TAAA repairs indicates we used HCA in only 1.5% of repairs [1]. Briefly, following the administration of heparin (4 mg/kg), cardiopulmonary bypass is initiated when a long femoral multiholed venous cannula is advanced into the right atrium with its placement verified using transesophageal echocardiography. Drainage is assisted through cannulation of the left atrium through the left inferior pulmonary vein. Arterial cannulation is typically performed using a 20- or 22-Fr straight cannula in the femoral artery. Circulatory arrest is initiated after the patient has been cooled to deep hypothermia. A clamp is sometimes placed on the mid-descending thoracic aorta to permit distal aortic perfusion via the femoral cannula while the proximal anastomosis is being completed. Rewarming is achieved using the proximal circulation, and in the more complex extent I and II repairs, rewarming is delayed until visceral arterial reattachment is completed [32].

Cold renal perfusion

The use of crystalloid and other solutions for providing cold renal perfusion during open TAAA repair has emerged as widely-used strategy, and several methods of perfusion have been reported. However, most centers that use HCA as a routine adjunct during TAAA repair typically do not additionally perfuse the renal arteries. Cold renal perfusion is performed after the aneurysm is opened, exposing the ostia of the renal arteries, and is typically accomplished via an independent roller-head pump circuit. A set of small-diameter, balloon-tipped catheters are then inserted into the origins of the renal arteries [24]. Contemporary practice guidelines endorse the consideration of cold crystalloid or cold blood renal perfusion during TAAA repair (class IIb, level of evidence B) but do not address other substrates [33]. Cold renal perfusion may be especially beneficial in patients with preoperative renal failure undergoing open distal aortic repair [34].

Our current approach to cold renal perfusion has evolved based on the results of our two randomized trials evaluating different methodologies for renal perfusion during open TAAA repair. During the first of these studies [35], we examined the rates of postoperative renal dysfunction in patients who underwent open TAAA repair who were randomly assigned to receive renal perfusion with either isothermic blood (n = 16) or cold crystalloid (lactated Ringer’s solution; n = 14) [35]. We found that patients that received renal perfusion with isothermic blood had significantly greater rates of postoperative renal dysfunction and that the use of cold crystalloid was independently protective against acute kidney dysfunction. Our second randomized clinical trial [36] compared the use of different cold perfusates: blood versus crystalloid. We hypothesized that the use of cold blood would be more renal protective. Interestingly, the results of our second randomized clinical trial indicated no statistical difference in the rates of renal failure or mortality between patients who received cold crystalloid versus cold blood, and showed that changes in urinary biomarkers were similar between the two study groups. Because a secondary finding showed a higher incidence of spinal cord deficit in the cold blood group, we favor the use of cold crystalloid as our current perfusate.

There is considerable variety in the perfusates used to provide cold renal perfusion during TAAA repair—blood, saline, lactated Ringer’s, Ringer’s acetate, plasmalyte, and histidine-tryptophan-ketoglutarate (Custodiol) have all been reported (Table 2) [1, 3, 5, 7, 8, 34, 37, 38]. Additives commonly added to perfusates include mannitol, methylprednisolone, and heparin. Tshomba and colleagues compared the use of cold Custodiol against the use of cold crystalloid in 42 matched pairs of patients undergoing TAAA repair. They reported that acute kidney injury was significantly decreased in the Custodiol group despite an overall longer renal ischemic time [3].

Table 2.

Comparison of techniques for renal protection during TAAA repair

Author (first)	Year publ.	TAAA repairs n	Extent II repairs n	Use of LHB (all extents) %	Use of HCA (all extents) %	Use of CRP (all extents) %	CRP method	CRP perfusate	Renal failure (dialysis)* %
Girardi [34]	2017	482	96	26.6	9.0	20.5	Intermittent	Plasmalyte	5.3
Coselli [1]	2016	3309	1066	44.7	1.5	58.4	Intermittent	Lactated Ringer’s	7.6
Wynn [37]	2015	455	86	0	0	100	Single bolus	Lactated Ringer’s	2.6
Estrera [5]	2015	1250	310	85.9	NR	NR	NR	NR	16.6
Tshomba [3]	2014	84	25	70.2	0	100	Continuous	Custodiol Lactated Ringer’s	2.4
Kouchoukos [8]	2013	243	97	0	100	0	–	–	3.7
Schepens [7]	2009	571	272	72.3	6.0	NR	Intermittent	Ringer’s acetate	6.5

TAAA thoracoabdominal aortic aneurysm, LHB left heart bypass, HCA hypothermic circulatory arrest, CRP cold renal perfusion, NR not reported

*Renal failure necessitating temporary or permanent dialysis

We provide cold renal perfusion during TAAA repair whenever the ostia of the renal arteries are sufficiently exposed; in our experience, this included 17.3% of extent I TAAA repairs, 65.8% of extent II, 77.4% of extent III, and 84.3% of extent IV [1]. After the renal ostia are isolated, we place 9-Fr Pruitt balloon-tipped catheters connected to a standalone roller-head pump circuit directly into the left and right renal artery ostia (Fig. 2). For our renal perfusate, we use cold (4 °C) standard Ringer’s lactate with added mannitol (12.5 g/L) and methylprednisolone (125 mg/L). We deliver our cold crystalloid perfusate as an initial 200–300 mL bolus to each kidney, and follow this with further 100–150 mL mini-boluses every 10 to 15 min until arterial flow is reestablished [24]. While other centers employ the use of continuous renal perfusion during TAAA repair, in our practice, we have opted for an intermittent renal perfusion technique in order to maintain systemic temperature greater than 32 °C as well as to avoid the complications of fluid overload.

Fig. 2.

Illustration of cold renal perfusion and selective visceral perfusion during an extent II thoracoabdominal aortic aneurysm repair. Upon the completion of the proximal anastomosis, left heart bypass is discontinued (a). Selective visceral perfusion is accomplished with a rerouted line off of the left heart bypass circuit to perfuse the celiac axis and superior mesenteric artery with isothermic blood. Cold renal perfusion is accomplished via a separate roller-head pump completely autonomous from the LHB circuit to deliver cold crystalloid solution via catheters directly into the ostia of the renal arteries. Perfusion continues as a 3-vessel patch anastomosis is prepared (b). Used with the permission of Baylor College of Medicine

Selective visceral perfusion

Selective visceral perfusion (SVP) is a technique that involves mechanically perfusing the celiac axis and the superior mesenteric artery to minimize the total mesenteric and hepatic ischemic time during TAAA repair. A handful of experienced aortic centers use this technique to typically provide either isothermic or cold blood to the visceral arteries [30, 38–41]. At our institution, we selectively perfuse the celiac axis and superior mesenteric artery using isothermic self-oxygenated blood most commonly during extent II TAAA repairs and occasionally in other extents. Following completion of the proximal aortic anastomosis and the discontinuation of LHB, 9-Fr Pruitt balloon catheters are inserted into the origins of the celiac axis and superior mesenteric artery from a Y-branch off of the rerouted LHB circuit (Fig. 2). Isothermic blood is provided at a rate of 400 to 500 mL/min [24]. In our comprehensive experience regarding 3309 TAAA repairs, SVP was used in 6.6% of extent I repairs, 63.3% of extent II repairs, 5.5% of extent III repairs, and 0.7% of extent IV repairs [1].

Although definitive evidence supporting the use of SVP is lacking [33], we continue to use it because of a potential reduction in the risk of postoperative coagulopathy and bacterial translocation from the bowels as well as being relatively easy to perform without an apparent increase in operative risk. Although it can be difficult to identify nuanced subclinical visceral complications, we have established elevated hepatopancreaticobiliary values after extent II TAAA repair that appear correlated with ischemic times [42]. Additionally, Safi et al. found that providing SVP during extent II TAAA repair prevented a harmful postoperative elevation of markers for hepatic dysfunction [38].

Management of renal and visceral arteries

In the earliest TAAA repairs performed by DeBakey and others [16], the renal and visceral arteries were routinely reattached by using individual branch grafts. In the Crawford era, reattachment shifted towards the use of island or patch anastomosis containing all four arteries [12]. Today, we commonly employ a modified Crawford approach to reattach an island containing the celiac axis, SMA, and the right renal arteries with a separate button reattachment of the left renal artery, which tends to become somewhat displaced from the other arteries (Fig. 3) [24]. Frequently, the renal and visceral arteries are additionally managed during repair with the use of endarterectomy, bypass grafts, or balloon expandable stents to improve the blood-carrying capacity of these arteries. In our recent experience regarding 3309 TAAA repairs, the renal and visceral arteries were managed by endarterectomy, bypass, or stenting in 9.6% of extent I repairs, 47.8% of extent II repairs, 54.1% of extent III repairs, and 60.5% of extent IV repairs [1].

Fig. 3.

Illustration of cold renal perfusion of the left renal artery (a) during construction of the distal anastomosis. The displaced left renal artery is reattached as a separate button after the distal anastomosis is completed (b). Used with the permission of Baylor College of Medicine

Endarterectomy has been used since the 1950s to remove occlusive atherosclerotic material near the ostia of the renal and visceral arteries. Crawford established that renal endarterectomy in patients with preoperative renal dysfunction had significantly improved renal outcomes [43]. However, endarterectomy is not without risk, because it thins the aortic wall, which could make these arteries susceptible to dissection, thrombosis, or perforation from balloon catheters. If significant stenosis is present at the renal arteries, we often place a balloon-expanded stent [44]. Small diameter stents may be used in any of the four renal or visceral arteries but are most commonly placed in the renal arteries. Stents are useful in obliterating the false lumen in cases of dissection, aiding patency of ostia near the patch anastomosis, tacking the intimal edges after endarterectomy, and facilitating the use of balloon catheters.

Summary

The prevention of renal and visceral ischemia during open repair of thoracoabdominal aneurysms remains a central component in improving patient outcomes. Multiple strategies have evolved as methods to combat the dire morbidity and mortality that renal and visceral ischemic complications can incur. Notably, in experienced aortic centers, the preferred use of adjuncts is variable (Table 2). Further study is necessary to better understand trends in why renal and visceral ischemia develop as well as to work towards reducing rates of related postoperative complications.

Compliance with ethical standards

Informed consent and ethical statement

This is a review article; a statement on informed consent and ethics does not apply.

Conflict of interest

The authors declare that they have no conflict of interest.