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Frontiers in Anesthesiology ·

Volume 5 - 2026 | https://doi.org/10.3389/fanes.2026.1873909

Set-point shifts in peri-anesthetic fluid homeostasis: a conceptual framework informed by α 2-agonist diuresis

  • Shotaro Nagahama1,2*corresponding author
  1. 1JAVA Incorporated Association, Tokyo, Japan
  2. 2Department of Veterinary Anesthesia, Veterinary Teaching Hospital, Faculty of Applied Biological Sciences, Gifu University, Gifu, Japan
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Abstract

Peri-anesthetic fluid handling is marked by an apparent contrast: general anesthesia often suppresses urinary excretion of administered fluid, whereas α 2-agonists such as dexmedetomidine can produce sustained, often dilute polyuria with a risk of hypernatremia. This article proposes a working set-point-shift model in which these opposing phenotypes are interpreted as state-dependent changes in the operating point of fluid regulation. Here, set-point is used operationally to describe a testable shift in the relation between filling state and urine-output phenotype, not to imply that a new defended reference value has already been experimentally demonstrated. Within this framework, general anesthesia is viewed as establishing a wet-biased, retention-biased state through convergent hemodynamic, neuroendocrine, and autonomic influences, whereas α 2-agonists may oppose this bias and shift the system toward a dry-biased, excretion-permissive state through AVP-linked, sympatholytic, and potentially peripheral α 2-dependent pathways. Human peri-anesthetic reports and comparative veterinary physiology provide convergent support for altered regulatory behavior, although the evidence remains insufficient to prove a single governing mechanism. The model generates measurable predictions: greater α 2-agonist exposure should increase the probability, earlier emergence, and persistence of dilute polyuria; α 2-associated polyuria should show serial urine and serum osmotic trajectories consistent with free-water loss when replacement is inadequate; and, during general anesthesia without α 2 exposure, breakthrough diuresis should emerge nonlinearly only after cumulative filling and related venous, atrial, or neuroendocrine permissive signals cross a threshold under relatively stable global hemodynamics. Thus, anesthetic oliguria and α 2-associated polyuria are framed as opposing phenotypes that generate testable predictions about peri-anesthetic fluid regulation, rather than as unrelated bedside anomalies.

Keywords

1 Introduction

In awake individuals, fluid balance is typically maintained by close coupling between intake and excretion: water loading is rapidly countered by increased free-water clearance, limiting sustained deviation from a regulated internal state (1). Under general anesthesia, this coupling often appears to weaken. Despite fluid administration, urine output frequently decreases, and perioperative oliguria is commonly interpreted through a narrow lens of renal perfusion and acute kidney injury risk (2–4). Experimental and volume-kinetic work further supports that anesthetized surgical states can markedly depress urinary excretion of infused fluid, although this effect should be understood as part of the broader anesthetic-surgical state rather than as a volatile-agent-specific phenomenon alone (5, 6).

At the same time, perioperative and ICU reports describe striking polyuria during dexmedetomidine infusion—often characterized by dilute urine and a tendency toward hypernatremia that resolves when the infusion is reduced or stopped (7–11). These episodes are often approached as isolated adverse events rather than as potentially physiology-informing perturbations.

This article proposes a working physiological model: general anesthesia and α2-agonists can be interpreted as shifting the apparent set-point of fluid homeostasis along a wet–neutral–dry axis. Here, “set-point” is used in a practical and operational sense to denote a state-dependent operating point maintained by compensatory regulation, rather than a fixed reference value or an experimentally demonstrated new defended reference. “Wet-biased” and “dry-biased” refer to the direction of regulatory bias—toward conservation (retention-biased) vs. excretion permissiveness—not to the patient's absolute total body water or extracellular fluid volume at a given moment. Accordingly, the same absolute fluid status may be experienced by the control system as relatively “underfilled” or “overfilled” when the operating point shifts, producing marked changes in urine output without requiring an immediate change in body water content.

Within this framework, anesthesia tends to establish a wet-biased (retention-biased) state that favors conservation, whereas α2-agonists can oppose this bias—via neuroendocrine and autonomic pathways—toward a dry-biased (excretion-permissive) state in which sustained diuresis becomes a plausible phenotype (12–15). Framed this way, peri-anesthetic urine output becomes less a binary readout of “kidney function on/off” and more a reflection of a drug-modifiable regulatory architecture.

By integrating mechanistic physiology with human and veterinary observations, we introduce a unified set-point model of peri-anesthetic fluid homeostasis and outline testable predictions and clinical implications, particularly when α2-agonists are incorporated into anesthetic practice.

2 General anesthesia as a wet-biased set-point

General anesthesia commonly shifts the organism toward water and sodium conservation. Many anesthetic techniques reduce arterial pressure and cardiac output, thereby placing renal perfusion closer to the limits of autoregulation and reducing glomerular filtration—conditions that favor conservation responses (3, 4). However, peri-anesthetic oliguria is not readily explained by perfusion mechanics alone. In a randomized clinical study, sevoflurane anesthesia reduced urine output and sodium excretion and increased plasma renin compared with propofol anesthesia, consistent with a wet-biased (retention-biased) regulatory state (16). Moreover, population volume kinetic analyses indicate that general anesthesia can strongly suppress the urinary excretion of infused crystalloid fluid, consistent with a wet-biased set-point rather than a simple input–output coupling (5, 6).

Crucially, the neuroendocrine milieu during surgery often amplifies conservation. Surgical stress and nociceptive input engage stereotyped endocrine responses (17), and perioperative arginine vasopressin (AVP) secretion can rise through non-osmotic stimuli such as stress and relative underfilling (1). During abdominal procedures, peritoneal opening and intraperitoneal or visceral manipulation may further augment AVP release (18), reducing free-water clearance through collecting duct mechanisms. In parallel, renal sympathetic nerve activity (RSNA) and renin–angiotensin–aldosterone signaling can promote tubular sodium and water reabsorption, defending effective circulating volume even when absolute fluid balance is being manipulated clinically (12).

Mechanistic studies strengthen the plausibility of this retention-biased phenotype by linking volatile anesthesia to renal sympathetic activation. In a translational series spanning pediatric anesthesia and large-animal models, sevoflurane was associated with renal sodium and water retention, reduced renal blood flow, and increased RSNA; renal denervation normalized renal excretory function and improved renal blood flow during sevoflurane anesthesia, implicating renal sympathetic pathways as a key mediator (19). A review further summarizes how anesthetic agents may influence RSNA in ways relevant to perioperative kidney physiology and fluid handling (20).

From a set-point perspective, intraoperative oliguria can be a physiologically plausible output of a wet-biased regulated state shaped by converging hemodynamic, neuroendocrine, and autonomic influences. This interpretation is not clinically reassuring by itself: the same low-output phenotype may coexist with impaired perfusion, insufficient effective circulating volume, or evolving kidney injury. Because these influences are difficult to partition cleanly in vivo—and vary with agent choice, surgical stress, ventilation, temperature, and vasoactive co-medications—the magnitude of the wet-shift is likely context-dependent rather than fixed. Nonetheless, this framing clarifies why forcing urine output to a preconceived numeric target by escalating crystalloid may be ineffective—or harmful—until the regulatory state shifts (2, 3).

3 α2-Agonists: mechanistic pathways for a dry-biased set-point shift

This section outlines plausible mechanistic pathways by which α2-agonists may shift the fluid-homeostasis set-point toward an excretion-permissive (dry-biased) operating state. Evidence for the resulting urine-output phenotype is summarized in the subsequent human and veterinary sections.

α2-Adrenergic agonists can counter the wet-biased set-point of general anesthesia by reshaping central autonomic outflow and neuroendocrine signaling. Dexmedetomidine's clinical pharmacology is dominated by central sympatholysis with context-dependent hemodynamic effects (13). Dexmedetomidine inhibits hypothalamic paraventricular nucleus neurons involved in autonomic regulation and AVP-related pathways, providing a plausible central substrate for AVP-linked suppression rather than direct proof that this mechanism alone explains clinical polyuria (21).

In addition, by reducing sympathetic outflow—including to the kidney—α2-agonists may diminish RSNA-driven tubular reabsorptive tone (12, 13). The hemodynamic profile of dexmedetomidine, often including an early pressor phase followed by sympatholytic hypotension, can contribute transiently to pressure natriuresis or diuresis (13). However, in many settings the clinically salient pattern appears to be a relatively dilute, high-output diuresis that is difficult to attribute to a one-off pressure effect alone and is consistent with a dry-biased regulated state.

Clinically, bolus dosing may produce abrupt bursts of diuresis, whereas continuous infusion may stabilize a high-output pattern. Within the set-point lens, these observations motivate the hypothesis that α2-agonists can shift the operating point toward an excretion-permissive equilibrium, rather than merely producing an idiosyncratic or purely hemodynamic diuretic response. The following sections summarize the clinical pattern in humans and the controlled comparative physiology that most directly supports receptor-mediated pathways.

4 Clinical evidence: dexmedetomidine-induced polyuria in humans

Human evidence is dominated by case reports and small series, but the pattern is remarkably stereotyped: urine output rises abruptly to high volumes, urine becomes dilute, serum sodium may rise if replacement lags, and the phenotype resolves with dose reduction or discontinuation (7–11). These reports often exclude obvious osmotic diuresis drivers, such as glucose or mannitol, and do not suggest structural renal injury as the primary mechanism.

Within conventional teaching—where anesthesia is expected to favor oliguria—such episodes appear paradoxical. Under a working set-point model, they become coherent: dexmedetomidine may shift the operating state toward a dry-biased equilibrium, making sustained free-water loss possible despite the surrounding anesthetic milieu. The human literature supports a recognizable α2-associated urinary phenotype more strongly than it establishes its mechanism. In most reports, AVP or copeptin, urine osmolality, sodium excretion, and standardized hemodynamic-volume data are incomplete or unavailable; mechanistic inference therefore depends on integrating these human phenotypes with comparative and experimental physiology.

5 Comparative physiology: insights from veterinary anesthesia

Veterinary physiology provides unusually direct support because controlled studies can measure urine indices and hormones systematically. In dogs, medetomidine administration produces dose-dependent increases in urine output with decreased urine osmolality and specific gravity, alongside decreases in plasma AVP at higher doses and increases in atrial natriuretic peptide (ANP) (14).

Additional experiments show that α2-antagonists can attenuate medetomidine-induced diuresis and reverse accompanying changes in AVP-related indices, supporting receptor-mediated mechanisms rather than nonspecific nephrotoxicity (15).

In cats, medetomidine also induces diuresis, while xylazine-related feline studies show that α-adrenergic antagonism can modify related α2-mediated diuretic phenotypes (22, 23).

Rat studies using the peripherally restricted α2-adrenoceptor antagonist vatinoxan further suggest that peripheral α2-dependent mechanisms may contribute to this urinary phenotype. Vatinoxan attenuated urinary output or spontaneous urinary voiding during medetomidine-based sedation, although these findings do not by themselves distinguish renal urine production from lower urinary tract voiding or directly define AVP-linked water handling (24, 25).

Across species, these findings strengthen two points: (i) α2-agonists can reproducibly generate a dilute, high-output state, and (ii) the phenotype is receptor-mediated and may involve convergent central neuroendocrine, autonomic, and peripheral α2-dependent processes rather than a single pathway—consistent with a shift toward a dry-biased regulatory equilibrium.

6 A unified set-point shift model of peri-anesthetic fluid homeostasis

The working set-point model integrates three lines of evidence into a single framework (Figure 1). Here, “general anesthesia” is used as a practical umbrella for a convergent peri-anesthetic retention-biased state shaped by anesthetic drugs, neuroendocrine stress responses, and related modifiers, rather than to imply a single uniform mechanism. Importantly, the wet–neutral–dry axis denotes regulatory bias (retention-biased vs. excretion-permissive set-point), not an absolute measure of total body water or extracellular volume. Because the reference relationship can shift, the same absolute fluid content may be reinterpreted as relatively “underfilled” or “overfilled,” producing marked changes in urine output without requiring an immediate change in body water content.

  • (I) Awake state (neutral set-point): Intake and excretion are tightly coupled; free-water clearance adjusts rapidly to stabilize osmolality and volume around a neutral set-point (1).
  • (II) General anesthesia (wet-biased set-point): Hemodynamic changes together with stress-related neuroendocrine shifts move the operating state toward conservation. In this wet-biased state, oliguria is physiologically plausible as an output of neuroendocrine conservation, but it should not be interpreted as inherently benign or reassuring. The same phenotype may coexist with impaired perfusion, insufficient effective circulating volume, or evolving kidney injury; contextual assessment remains necessary (2–4). Evidence from randomized renal-function studies, volume-kinetic analyses, and translational renal-neurophysiology work supports the plausibility of retention-biased regulatory behavior within this broader peri-anesthetic state (5, 16, 19).
  • (III) α2-agonists (dry-biased set-point): Through central/autonomic effects, AVP-linked mechanisms, and potentially peripheral α2-mediated processes, α2-agonists can oppose the anesthesia-induced retention bias and shift the set-point toward an excretion-permissive state (13–15, 21, 24, 25). Clinically, this can manifest as sustained, often relatively dilute diuresis consistent with an altered regulatory equilibrium rather than a transient pressure-only effect (7, 8, 11).
A set-point shift model of peri-anesthetic fluid homeostasis. Conceptual prediction of threshold-like diuresis during graded volume expansion (schematic), with major arterial-pressure changes set aside: urine output increases nonlinearly as relative filling crosses from a wet-biased (retention-biased) into a dry-biased (excretion-permissive) regime. General anesthesia shifts this threshold-like transition rightward, whereas α2-agonists shift it leftward. The vertical dashed lines indicate state-specific threshold-like transition regions; their leftward and rightward displacement illustrates a shift of the response curve itself, rather than movement along a single fixed curve. By contrast, transient changes in blood pressure, filling, or fluid loading would be expected mainly to move the patient along a given curve. The curves are conceptual and are not derived from quantitative experimental data.
Figure 1. A set-point shift model of peri-anesthetic fluid homeostasis. Conceptual prediction of threshold-like diuresis during graded volume expansion (schematic), with major arterial-pressure changes set aside: urine output increases nonlinearly as relative filling crosses from a wet-biased (retention-biased) into a dry-biased (excretion-permissive) regime. General anesthesia shifts this threshold-like transition rightward, whereas α2-agonists shift it leftward. The vertical dashed lines indicate state-specific threshold-like transition regions; their leftward and rightward displacement illustrates a shift of the response curve itself, rather than movement along a single fixed curve. By contrast, transient changes in blood pressure, filling, or fluid loading would be expected mainly to move the patient along a given curve. The curves are conceptual and are not derived from quantitative experimental data.

This new-equilibrium behavior is not alien to renal physiology. Strong perturbations commonly provoke counter-regulation and settle into regulated steady states rather than driving linear, unbounded loss or retention. Classic examples include loop-diuretic braking/diuretic resistance (26) and mineralocorticoid escape, in which sodium excretion returns toward intake despite persistently elevated mineralocorticoid drive (27).

A useful contrast with the conventional intuition is that this model does not assume a fixed urine-output curve on which patients merely move as volume changes. Instead, anesthesia and α2-agonists are proposed to shift the curve itself, so that the same observed filling condition can map to different relative positions—and thus different urine-output phenotypes. Operationally, movement along a curve would be inferred when transient changes in filling, arterial pressure, or fluid loading alter urine output without changing the underlying volume–diuresis relationship. A curve shift would be supported when the threshold or slope of that relationship differs between anesthetic or drug states under otherwise comparable hemodynamic, osmotic, and drug-exposure conditions.

Why a threshold-like breakthrough diuresis is physiologically plausible even under anesthesia: even in anesthetized preparations, diuresis and urine dilution can be gated by central volume or atrial-pressure signals linked to AVP suppression. Increasing left atrial pressure in anesthetized dogs provokes a reversible water diuresis with a fall in circulating AVP, and this response is abolished when AVP is clamped exogenously (28). Conversely, in anesthetized rats, acute volume expansion fails to elicit volume diuresis or natriuresis when right atrial pressure is prevented from rising—despite similar cardiac output and mean arterial pressure—supporting the idea that volume permissiveness depends on central pressure/stretch signals beyond arterial pressure alone (29). These findings provide a mechanistic backbone for a key prediction of the model: under a wet-biased anesthetic set-point, escalating fluid may remain clinically silent until the system crosses a permissive transition, such as atrial/venous pressure or related neuroendocrine thresholds, after which urine output can rise nonlinearly. The shape, location, and reproducibility of such thresholds in human perioperative patients are currently unknown; the animal experiments support physiological plausibility rather than defining a quantitative human threshold.

A related clinical corollary is that some patients without overt hypovolemia may become oliguric or nearly anuric soon after induction of general anesthesia, yet later begin to produce urine as time under anesthesia and cumulative fluid administration increase, even when arterial pressure and other global hemodynamic variables appear relatively stable. In the proposed model, this pattern does not necessarily indicate delayed correction of a simple volume deficit. Rather, once anesthesia has shifted the curve rightward into a wet-biased state, subsequent fluid accumulation can move the patient along that shifted curve: urine output remains suppressed until cumulative filling and related venous, atrial, or neuroendocrine permissive signals cross a threshold, after which diuresis emerges nonlinearly.

7 Discussion

7.1 Testable predictions

The model yields several testable predictions. Direct evidence for a true curve shift would require showing that the volume–urine-output relationship itself is displaced under controlled anesthetic, hemodynamic, osmotic, and drug-exposure conditions, rather than only a change in urine output at a single filling state. Experiments should therefore compare graded volume–diuresis curves across awake, anesthetized, and α2-exposed states while measuring arterial pressure, cardiac output or stroke-volume surrogates, venous or atrial filling indices, AVP or copeptin, urine osmolality, sodium excretion, and serum sodium/osmolality.

  • (I) α2 exposure–urine phenotype relation: Under otherwise comparable anesthetic and fluid conditions, greater α2-agonist exposure—through a higher loading dose, higher infusion rate, longer infusion duration, or greater cumulative exposure—should increase the probability, earlier emergence, and persistence of dilute polyuria. Dose reduction, discontinuation, or pharmacologic antagonism should shift the phenotype back toward lower urine output and greater urine concentration, provided that osmotic diuresis, diuretic therapy, uncontrolled hemodynamic change, and structural renal injury are excluded. Veterinary studies of medetomidine dose effects and α2 antagonism provide templates for this exposure-response design (14, 15, 22–25).
  • (II) Serial osmotic and electrolyte trajectory: If α2-agonist-associated polyuria reflects a dry-biased excretion-permissive state, urine osmolality or specific gravity should fall before or during the rise in urine output. Serum sodium and serum osmolality should remain stable only if free-water losses are replaced adequately; otherwise, they should increase progressively. Direct AVP or copeptin measurement would test whether the trajectory is accompanied by inappropriately low or falling antidiuretic signaling relative to plasma tonicity (7–11, 14, 15).
  • (III) Autonomic/RSNA signature: If renal sympathetic tone contributes to the wet-to-dry shift, indices consistent with reduced RSNA influence—such as altered sodium handling, reduced renal reabsorptive tone, or changes in renin–angiotensin–aldosterone activity—should accompany the urinary phenotype. Established renal neurophysiology and anesthesia-specific RSNA data identify candidate markers and experimental conditions for testing this pathway (12, 19, 20).
  • (IV) Breakthrough diuresis during wet-biased anesthesia: During general anesthesia without α2-agonist exposure, graded cumulative fluid administration should not necessarily produce a linear urine-output response. When arterial pressure and other global hemodynamic variables are relatively stable, urine output should remain low until central filling, venous/atrial pressure, or related neuroendocrine permissive signals cross a threshold, after which urine output and free-water clearance should rise nonlinearly. The feasibility of a pressure-independent volume-permissiveness mechanism is supported by anesthetized preparations where atrial pressure drives AVP-linked water diuresis (28) and where preventing right atrial pressure rise abolishes volume diuresis/natriuresis despite similar MAP and cardiac output (29). In human perioperative patients, the quantitative threshold, curve shape, and reproducibility of this transition remain empirical questions.
  • (V) Reversibility signature: Withdrawal or dose reduction of α2 infusion should drive a reversible return toward the wet-biased state, with urine concentration increasing and urine output falling. This response should occur without evidence of structural renal injury and should be temporally closer to α2 exposure than to unrelated fluid boluses or surgical events (7, 8, 10, 11).
  • (VI) Central–peripheral dissociation: If peripheral α2-dependent processes contribute materially to the dry-biased phenotype, peripherally restricted α2 antagonism should attenuate the urinary phenotype without requiring complete reversal of central sedation. Rat vatinoxan studies support this possibility, but definitive experiments should distinguish renal urine production from lower urinary tract voiding and should measure urine osmolality, sodium excretion, glucose, AVP/copeptin, hemodynamics, and drug exposure (24, 25).

7.2 Implications for peri-anesthetic fluid therapy

This interpretation should be placed alongside, rather than in opposition to, individualized goal-directed fluid or hemodynamic therapy. Goal-directed strategies primarily use dynamic cardiovascular variables, stroke volume, cardiac output, arterial pressure, or related perfusion endpoints to guide fluid and vasoactive therapy (30, 31). The present framework addresses a different question: why urine output may decouple from those hemodynamic targets when renal excretion is governed by a shifted peri-anesthetic regulatory state. Thus, the model does not replace goal-directed therapy; it clarifies why urine output alone should not be treated as an isolated fluid target within such strategies.

A low urine output is neither automatically benign nor automatically a marker of renal injury. In a wet-biased state, it may reflect neuroendocrine conservation; in other contexts, it may signal hypoperfusion or evolving kidney injury. Escalating crystalloid purely to normalize urine output can contribute to fluid overload (2–4, 30). The key clinical task is not simply to normalize urine output, but to classify the urinary phenotype in context: retention-biased oliguria under anesthetic-surgical stress, breakthrough diuresis after cumulative filling, α2-associated dilute polyuria, osmotic or diuretic-driven polyuria, lower urinary tract-related output changes, or oliguria associated with evolving renal injury.

This classification matters because peri-anesthetic urine output is an imprecise surrogate for renal blood flow, renal oxygen delivery, or structural kidney injury. It is shaped by neuroendocrine and autonomic regulation, including AVP and renal sympathetic tone, by drug-dependent operating states, and by the time course of fluid administration (3, 12, 19).

Under a dry-biased set-point during α2-agonist infusion, the key hazard is progressive intravascular depletion if urinary losses are not matched—particularly when clinicians interpret high urine output as reassuring renal competence. If replacement lags, hypernatremia becomes a predictable risk in high-output states (7, 8, 32). The same framework may also help interpret abrupt increases in urine output when α2-agonists are introduced during recovery or in the post-anesthetic period, where a drug-induced dry shift may become unmasked against a changing background state.

7.3 Limitations and scope of the model

This framework is intentionally simplified and should be understood as an explanatory construct and working physiological hypothesis, not as evidence that a new defended reference value has been demonstrated or as a claim of a single governing mechanism. In humans, the supporting evidence remains limited: most perioperative dexmedetomidine-associated polyuria data are case-based, and direct AVP or copeptin measurements are uncommon (7, 8, 10, 11). Anesthesia and critical illness also introduce multiple overlapping influences—such as surgical stress, inflammation, ventilation, temperature, and co-medications—that can shift fluid regulation along the wet–dry axis in parallel. The framework is least informative when urine output is dominated by established acute kidney injury, uncontrolled hypotension or low cardiac output, osmotic diuresis including hyperglycemia or mannitol, diuretic therapy, obstructive or lower urinary tract factors, or measurement artifacts. Species differences further affect the quantitative expression of urine dilution and concentrating capacity, although the overall directionality appears conserved (14, 22–25).

Yet this simplification is also a practical strength. By compressing multiple interacting mechanisms into a coherent set-point framework, the model helps classify urine output as a state-dependent regulatory readout rather than a direct report of renal perfusion, oxygen delivery, or structural kidney injury. In doing so, it reduces the risk of reflexive urine-output chasing, provides a compact way to interpret apparently discordant oliguria and diuresis, and generates falsifiable predictions about when these phenotypes should persist, reverse, or emerge abruptly under changing peri-anesthetic conditions.

7.4 Broader relevance for anesthesia physiology

Homeostatic set-point shifts are a familiar theme in anesthesia: anesthetic drugs do not merely perturb measured variables; they shift thresholds and operating points that govern compensatory responses. In thermoregulation, the vasoconstriction and shivering thresholds are displaced, producing redistribution hypothermia and altered temperature-regulatory ranges (33). Ventilatory control is likewise shifted: opioids and anesthetics depress the hypercapnic ventilatory response, effectively moving the CO2 operating point at which compensatory ventilation is robustly recruited (34). Volatile anesthesia attenuates arterial baroreflex function, and this attenuation may persist into recovery (35, 36). The fluid set-point axis proposed here fits naturally into this broader idea—anesthesia as the management of drug-modifiable regulated states, rather than isolated numeric abnormalities to be corrected reflexively.

8 Conclusion

This article proposes a working set-point-shift model for peri-anesthetic fluid homeostasis. In this view, general anesthesia biases the operating state toward conservation (wet-biased), whereas α2-agonists can oppose this bias and promote an excretion-permissive (dry-biased) phenotype with sustained, often dilute diuresis. Its value lies not in asserting a demonstrated single mechanism, but in providing a compact interpretive framework that organizes complex physiology into clinically meaningful patterns and testable predictions, including α2 exposure-response relationships, serial urine and serum osmotic trajectories, and threshold-like breakthrough diuresis under relatively stable global hemodynamics. By reframing anesthetic oliguria and α2-associated polyuria as opposing phenotypes within a shared regulatory framework, the model generates testable predictions and clarifies why urine-output phenotypes should be classified physiologically rather than treated as isolated numeric targets.

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Footnotes

Edited by: Anne-Françoise Rousseau, University of Liège, Belgium

Reviewed by: Eman Teema, Suez Canal University, Egypt

Massimo Meco, San Carlo Clinic of Paderno Dugnano, Italy

Statements

Conflict of interest

The author SN is the representative director of JAVA Incorporated Association, an organization engaged in veterinary anesthesia education, research, and consulting. The author declares that there are no other commercial or financial relationships that could be construed as a potential conflict of interest.

Funding

The author(s) declared that financial support was not received for this work and/or its publication.

Data availability

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Author contributions

SN: Conceptualization, Visualization, Writing – original draft, Writing – review & editing.

Acknowledgements

The author thanks Sanae Shibata, DVM, PhD (Joint Department of Veterinary Medicine, Faculty of Applied Biological Sciences, Gifu University, Gifu, Japan) for helpful discussions and comments.

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Citation

Nagahama, S. (2026). Set-point shifts in peri-anesthetic fluid homeostasis: a conceptual framework informed by α 2-agonist diuresis. Frontiers in Anesthesiology, Volume 5. https://doi.org/
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5 - 2026

Copyright

© 2026 Nagahama.

License: https://creativecommons.org/licenses/by/4.0/

*Correspondence: Shotaro Nagahama

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