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368 G. Castellani et al.
The BaSICS trial showed that among critically ill patients requiring uid chal­lenges, the use of a balanced solution (Plasma-Lyte 178) compared with 0.9% saline solution did not signicantly reduce 90-day mortality (primary outcome) nor the development of AKI and use of RRT [40].
The Plus study compared BMES (Plasma-Lyte 148) or saline as uid therapy in the intensive care unit (ICU) for 90 days. The primary outcome was death from any cause within 90 days after randomization. Secondary outcomes were receipt of new RRT and the maximum increase in the creatinine level during ICU stay. The authors found no evidence that the risk of death or acute kidney injury among critically ill adults in the ICU was lower with the use of BMES than with saline [41].
The criteria used to determine AKI in these trials are different. The PLUS study evaluated mean, peak, and rise in serum creatinine levels and the initiation of RRT as prespecied outcomes of kidney function. In contrast, the BaSICS investigators determined stages of AKI according to the current consensus denition, and the SMART investigators compared major adverse kidney events at 30 days, a compos­ite outcome, between treatment groups. A systematic review and meta-analysis on this topic indicate that the estimated effect of using balanced crystalloids rather than saline for intravenous uid therapy in a heterogeneous population of critically ill adults ranges from a 9% relative reduction to a 1% relative increase in death by 90 days [42]. Overall, there is a high probability that the average treatment effect of using balanced crystalloids is to reduce mortality.
Colloids
Colloids contain oncotic macromolecules that largely remain in the intravascular compartment. The rationale behind the usage of these solutions is that they maintain intravascular oncotic pressure and expand the intravascular volume more effectively and for a longer duration than crystalloids.
Album
in
The SAFE resuscitation uid and found no difference in outcomes (organ failures, days in ICU, days of ventilation, days of RRT) [43]. A post hoc analysis of traumatic brain injury patients from the same cohort found albumin to be harmful [44]. The ALBIOS study had as primary outcome mortality at 28 days with no difference between albumin and crystalloids; the secondary outcomes were death at 90 days (not different) and the number and degree of organ dysfunction (not different) [
study, in 2004, randomized patients to 4% albumin or saline as a
45].
31 Management of AKI: Fluids 369
Starches
The relation between hydroxyethyl starch (HES) use and outcome was investigated in two trials:
The 6s trial compared HES with Ringers lactate in critically ill patients and found an increased risk of death and usage of RRT in the HES group [46].
Another study, in 2012, found no signicant difference in 90-day mortality between patients resuscitated with 6% HES (130/0.4) or saline [47]. However, more patients who received resuscitation with HES were treated with RRT.
Gelatins
Regarding gelatins, a systematic review with meta-analyses found an increased risk of AKI and RRT with the usage of gelatins compared with crystalloids [48]. Table 31.2 displays the main studies which assessed uid administration strategies in AKI. In conclusion, there is only a limited role for colloids as a therapy to prevent AKI. To date, no published clinical trials have specically compared different crystalloid uids in patients with established AKI. Existing data support the preferential use of buffered solutions for uid resuscitation of patients at risk of AKI who do not have hypochloremia. Saline 0.9% is the preferred solution for patients with hypovolemia and hypochloremia (e.g., following prolonged vomiting). When used, chloride concentrations should be monitored.

Conclusion

The uid manag ement of critical patients with AKI should include the following:
Thorough assessment and reassessment of both volume and hemodynamic status.
Hemodynamic
Avoidance o
In cases choice, while chloride-rich solutions may be considered for hypochloremia.
f u
of hypovolemia, balanced crystalloid solutions should be the primary
should be systematically explored.
status
id overload is essential.
370 G. Castellani et al.
Table 31.2 Main trials on administration of colloids in ICU patient
ALBIOS
Study SAFE [43]
Setting 16 ICUs in
Australia and New Zealand
[45 CHEST [47]
]6’s[ ]46
100 ICUs in Italy
26 ICUs in Denmark, Norway,
32 hospitals in Australia and
New Zealand Finland, and Iceland
Design Multicenter,
randomized, double-blind
Multicenter open-label trial
Multicenter, parallel­group, blinded trial
Multicenter, pro-
spective, blinded,
parallel-group,
randomized, con-
trolled trial
Number of patients 6997 1818 804 7000
Population ICU adults ICU adults ICU adults ICU adults
Intervention 4% albumin 20% albu-
min +
6% HES 130/0.42
6% HES 130/0.4
crystalloid
Control Normal saline Crystalloid
alone
Primary outcome (intervention
vs. control)
Death at 28 days (726 vs. 729,
0.87)
Death from any cause at 28 days
p
(285 vs. 288,
p 0.94)
Ringers acetate
Death (201 vs. 172, p 0.03) or end stage kidney fail-
at
ure
Normal saline
Death within
90 days (597 vs.
566, p 0.26)
90 days (1 vs.
1)
Secondary outcome (intervention vs. control)
Days in ICU (6.5 vs. 6.6, p
0.44) days in hospital (15.3 vs. 15.6, p0.30) days of mechanical ventilation (4.5 vs. 4.3, P
Death at 90 days (365 vs. 389, p 0.29)
RRT in 90 days period (87 vs. 65, p
0.04) Severe bleeding (38 vs. 25, p
0.09)
Acute kidney
injury
(34.6% vs. 38%,
p0.005) and fail-
ure
(10.4% vs. 9.2%,
p 0.12).
RRT (235 vs.
196, p 0.04)
0.74) days of RRT (0.5 vs. 0.4, p0.41)
ICU intensive care unit, AKI acute kidney injury,
RRT renal
replace therapy, 6% HES 6%
hydroxyethyl starch
31 Management of AKI: Fluids 371

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26. RENAL Replacement Therapy Study Investigators, Bellomo R, Cass A, et al. An observational study uid balance and patient outcomes in the Randomized Evaluation of Normal vs. Augmented Level of Replacement Therapy trial. Crit Care Med. 2012;40(6): 1753–60. https://doi.org/10.1097/CCM.0b013e318246b9c6.
27. Liu KD, Thompson BT, Ancukiewicz M, et al. Acute kidney injury in patients with acute lung injury: impact of uid accumulation on classication of acute kidney injury and associated outcomes. Crit Care Med. 2011;39(12):2665– 71. https://doi.org/10.1097/CCM.
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29. Raimundo M, Crichton S, Martin JR, et al. Increased uid administration after early acute kidney injury is associated with less renal recovery. Shock. 2015;44(5):431–7. https://doi.org/
10.1097/SHK.0000000000000453.
30. Skytte Larsson J, Bragadottir G, Krumbholz V, Redfors B, Sellgren J, Ricksten SE. Effects of acute plasma volume expansion on renal perfusion, ltration, and oxygenation after cardiac surgery: a randomized study on crystalloid vs colloid. Br J Anaesth. 2015;115(5):736–42.
https://doi.org/10.1093/bja/aev346.
31. Gambardella I, Gaudino M, Ronco C, Lau C, Ivascu N, Girardi LN. Congestive kidney failure in cardiac surgery: the relationship between central venous pressure and acute kidney injury. Interact Cardiovasc Thorac Surg. 2016;23(5):800–5. https://doi.org/10.1093/icvts/ivw229.
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33. National Heart L and BIARDS (ARDS) CTN, Wiedemann HP, Wheeler AP, et al. Comparison of two uid-management strategies in acute lung injury. N Engl J Med. 2006;354(24):2564–75.
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34. Myles PS, Bellomo R, Corcoran T, et al. Restrictive versus liberal abdomin
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Chapter 32
Management of AKI: Vasopressors
Paolo Persona and Tommaso Pettenuzzo

Introduction

Acute kidney injury (AKI) represents a critical complication in various clinical settings, with hypotension emerging as a signicant determinant, particularly fol­lowing surgical procedures. The maintenance of normal renal function hinges on adequate renal perfusion pressure (RPP), a delicate balance determined by the interplay between mean arterial pressure (MAP) and central venous pressure (CVP). When hypotension compromises renal perfusion, interventions such as uid resuscitation and vasopressor therapy become imperative to optimize the function of kidney microcir culation. The choice of vasopressor agents and inotropic agents in the management of AKI demands careful consideration, reecting the underlying etiology of shock and AKI, whether sepsis, hepatorenal syndrome, cardiac failure, anaphylaxis, or others. Each vasopressor exerts unique effects on adrenergic receptors, inuencing vascular tone, cardiac output, and renal perfusion. Additionally, natural hormones like vasopressin and angiotensin II, along with terlipressin, offer alternative mechanisms of vasopressor support, expandi ng the therapeutic options for vasodilatory states. Despite the evolving landscape of vaso­pressor therapy, clinical evidence remains inconclusive regarding the superiority of one vasoactive agent over others in preventing or treating AKI. This underscores the complexity of renal perfusion dynamics and the multifaceted pathophysiology underlying AKI development. Understanding the indications and contraindications of vasopressor use within the context of AKI is paramount for optimizing patient outcomes and mitigating the risks associated with renal hypoperfusion. This chapter
Supplementary Information The online version contains supplementary material available at
https://doi.org/10.1007/978-3-031-66541-7_32.
P. Persona ( Department of Surgery, Institute of Anesthesiology and Intensive Care, Padua University Hospital, Padua, Italy
© The A. Cotoia et al. (eds.), Nutrition, Metabolism and Kidney Support,
https://doi.org/10.1007/978-3-031-66541-7_32
) · T. Pettenuzzo
Author(s), under exclusive license to Springer Nature Switzerland AG 2024
375
376 P. Persona and T. Pettenuzzo
aims to elucidate the pathophysiology of renal perfusion disorders, offering insights into the mechanisms of action and clinical considerations surrounding vasopressor therapy in the management of AKI.

Pathophysiology of Renal Perfusion

Renal function relies on maintaining adequate RPP, which is the difference between MAP and CVP [1]. RPP determines renal blood ow (RBF), representing approx­imately 20% of cardiac output or about 1.2 L/min [1]. Acute changes in either MAP and/or CVP can alter RPP. In healthy subjects, RBF is maintained relatively stable over a wide range of RPP, typically 60–100 mmHg, thanks to the autoregulation provided by the sympathetic nervous system, the pre-glomerular myogenic reex, the tubulo-glomerular feedback, and the neurohormonal activation [ 2 ].
The symp athetic nervous system innervates the entire renal vascular tree through the action of norepinephrine on adrenergic receptors, primarily distributed on the renal artery. The myogenic reex is driven by the increase in RPP, leading to the stretching of afferent arterioles and consequent vasoconstriction. The tubulo­glomerular feedback involves vasoconstriction triggered by the detection of an increase in chloride ions in the macula densa. When RPP drops below the autoregulation range, RBF is maintained by alpha-adrenergic receptor activation. In situations where autoregulation is lost, such as during shock, renal ow becomes dependent on the relationship between MAP and CVP. The inow pressure to the nephrons is renal artery pressure, whi ch depends on MAP. All vasopressors act on the renal artery. Afferent arteriole tone is regulated by the myogenic reex and tubulo-glomerular feedback, while efferent arteriole tone is controlled by vasopres­sin and angiotensin II. Microcirculation is inuenced by all vasopressors. However, vasopressin and angiotensin II mainly alter the ow in vasa recta through manipu­lation of salt and water content [ renal function more than MAP [4]. Indeed, lowering CVP can improve renal function in patients with heart failure [5].
Renal microcirculation is a complex network of shunts between microvessels (arteries and veins) in the renal cortex, maintaining medullary blood ow at almost 20% of RBF and a partial pressure of oxygen close to 20 mmHg. Consequently, the renal medulla is more sensitive to hypoxia than the cortex.
3]. The outow pressure, CVP, seems to inuence

Acute Kidney Injury

Hypotension stands as one of the main determinants of acute kidney injury (AKI), particularly in the postoperative period [6], where the prevalence of AKI varies from
2.9% to 57.4% [7]. The optimal MAP target in critically ill patients to mitigate the risk of AKI remains a topic of debate. The Surviving Sepsis Campaign guidelines
32 Management of AKI: Vasopressors 377
suggest a MAP target of 65 mmHg [8]. However, some authors propose that intensive care unit (ICU) patients with sepsis may face the risk of AKI even with a MAP of 85 mmHg [9]. Furthermore, in chronically hypertensive patients, a higher MAP target may prove benecial [10]. Adequate intravascular volume resuscitation, vasopressors, and inotropic agents constitute the cornerstone of optimizing renal hemodynamics [3]. Crystalloids represent the rst-line therapy in hypotensive patients, with balanced solutions preferred over 0.9% saline due to the risk of AKI progression and the need for renal replacement therapy [ overload exacerbates renal oxygenation [14] and may compromise renal function and patient survival [ systemic vascular resistance, such as severe pancreatitis, anaphylaxis, burns, and liver failure, renal autoregulation is disrupted. Persistent hypotension, despite intra­vascular volume optimization, places patients at risk for AKI development [17]. In sepsis, renal damage develops because of endothelial cell injury, impaired intercellular communication, glycocalyx shedding, coagulation dysfunction, leuko­cyte and platelet adhesion, and microthrombosis [ despite adequate RPP. When MAP targe ts cannot be achieved solely with uid therapy, vasopressors and inotropic agents are employed to enhance kidney micro­circulation. The sympathomimetic effects on alpha- and beta-adrenergic receptors of exogenous dopamine, norepinephrine, and epinephrine result in increased vascular tone and cardiac output (CO) [17]. Vasopressin and angiotensin II, two naturally occurring hormones, along with terlipressin, a vasopressin analog, have been suggested as adjunctive treatments for vasodilatory states, owing to their non­catecholaminergic vasopressor effect [ excessive renal arterial vasoconstriction remains narrow and subject to debate [20]. Notably, some studies propose that exposure to catecholamines may be detri­mental to renal function [
15, 16]. During conditions of high cardiac output and low
18]. These alterations may occur
19]. The threshold between benecial and
21].
11–13]. However, uid

Norepinephrine

Norepinephrine exerts a potent effect on alpha-1 adrener gic receptors and a moderate effect on beta-1 adrenergic receptors, leading to robust vasoconstriction and a modest increase in cardiac output [17]. The heart rate typically remains unchanged or may even decrease due to reex bradycardia resulting from the elevated MAP. Norepinephrine is the preferred rst-line vasopressor for treating septic shock [17].
It has
been theorized that norepinephrine induces renal vasoconstriction and decreases renal blood ow (RBF), potentially causing hypoperfusion and renal ischemia. Additionally, norepinephrine infusion-mediated elevation in glomerular ltration rate (GFR) may enhance sodium delivery into the medullary tubules, inducing relative medullary hypoxia [ essential hypertension, and hypovolemic hypotension, norepinephrine infusion has been observed to decrease splanchnic [ retrospective observational study involving 5053 adult patients undergoing cardiac
22]. Under normal circulatory conditions,
23, 24]
and renal blood ow [2527]. A
378 P. Persona and T. Pettenuzzo
surgery with cardiopulmonary bypass indicated that exposure to norepinephrine was signicantly associated with a 1.95-fold increase in AKI occurrence [28]. Similarly, a retrospective analysis of 32,250 patients undergoing major abdominal surgeries in the United States identied increased vasopressor use as correlated with a higher incidence of AKI [29].
However, sepsis or other of alpha-adrenergic receptor responsiveness in vascular smooth muscle [30], vaso­dilatation secondary to nitric oxide release [31], and microvascular obstruction related to coagulation dysfunction [32]. Under these conditions, restoring vascular tone and ensuri ng adequate RPP may improve RBF and GFR [33].
Several animal studies support the notion that norepinephrine-mediated adrener­gic stimulation during vasodilated hypotension may enhance RBF. In dogs infused with incremental doses of norepinephrine, renal vascular resistance appeared to increase from baseline, yet total RBF progressively increased with escalating doses up to 1.6 mcg/kg/min [34]. Another study in conscious dogs receiving clinically relevant norepinephrine dosages (0.2–0.4 mcg/kg/min) demonstrated increased RBF and decreased renal vascular resistance, independent of prostaglandin-mediated vasodilation, beta-receptor stimulation, or angiotensin­induced changes in vascular tone [35]. In endotoxemic dogs, norepinephrine infu­sion did not induce any decrease in RBF [36]. Similarly, norepinephrine infusion increased both RBF and RPP in a comparable population of animals [37]. Clinical studies have corroborated these ndings. In ten patients studied after liver transplant surgery, norepinephrine infusion increased GFR, RBF, and oxygen delivery and consumption, while not affecting renal vascular resistance, urine ow, or renal oxygen extraction [38]. In a prospective study involving 56 patients with extremely low resistance states due to abdominal sepsis, norepinephrine infusion (dosage ranging between 0.1 and 2 mcg/kg/min) was associated with a signicant increase in creatinine clearance after 48 h [39]. Overall, these investigations support the notion that clinically relevant doses of norepinephrine infusion do not exert signif­icant renal vasoconstriction. Instead, most of the renal vasodilatory effect of intra­venous norepinephrine can be attributed to baroreceptor-mediated decreased renal sympathetic tone secondary to the increased systemic blood pressure [33].
vasodilated states are characterized by downregulation

Epinephrine

Epinephrine exhibits potent beta-1 adrenergic receptor activity and moderate beta-2 and alpha-1 adrenergic receptor effects [ output, while decreasing systemic vascular resistance, with variable effects on MAP. This is due to the beta-1 adrenergic receptor-mediated inotropic and chronotropic effects, while the vasoconstriction induced by alpha-1 adrenergic receptor activity is often counteracted by beta-2 adrenergic receptor-related vasodi-
17].
lation [ increased systemic vascular resistance. Epinephrine use is also associated with
However, at higher doses, alpha-1 adrenergic stimulation may lead to
17]. At low doses, it increases cardiac