Determination of the cut-off value for estimated stroke volume variation as a predictor of fluid responsiveness

Abstract

Background

Estimated stroke volume variation (esSVV) serves as a noninvasive indicator of fluid responsiveness measured using the estimated continuous cardiac output (esCCO) system. However, the cutoff value for esSVV has not yet been established. The aim of this study was to determine the cutoff value for esSVV.

Methods

In this prospective observational study, patients scheduled for general anesthesia were included. Following anesthesia induction, the esCCO system was calibrated, and the blood pressure at that time was recorded as the baseline value. A fluid challenge was initiated when the blood pressure decreased by > 10% from the baseline systolic pressure, at least 5 min after calibration. A colloidal solution (300 ml) was administered over a 15-min period. The esSV measured 5 min before infusion was compared to the maximal esSV recorded 5 min after completing the infusion. Moreover, patients with an esSV increase of > 10% were categorized into the responder group, whereas those with a < 10% increase were classified into the non-responder group. A receiver operating characteristic curve was generated, and the area under the curve (AUC) was calculated.

Results

We identified 43 and 40 cases of esSVV and SVV, respectively. The AUC for esSVV was 0.73, with a threshold value of 7.3%, whereas that for SVV was 0.65, with a threshold value of 12%.

Conclusion

The established cutoff value for esSVV was 7.3%. Hence, it may be a useful tool for managing circulation, particularly given that its cutoff value has now been determined.

Trial registration

University Hospital Medical Information Network (UMIN) Clinical Trials Registry (UMIN register no. UMIN000049595 on November 24, 2022).

Background

The aim of circulatory management during general anesthesia is to maintain adequate blood pressure and organ perfusion. Blood pressure is influenced by preload, afterload, and cardiac contractility, necessitating the appropriate management of each of these components. Managing preload requires monitoring changes in circulating blood volume and implementing suitable infusion strategies.

Pulse pressure variation (PPV) and stroke volume variation (SVV) have been used as indicators of fluid responsiveness during general anesthesia [1, 2]. However, these methods are invasive, requiring the use of an intravenous arterial pressure line or the FloTrac system (Nippon Becton Dickinson Company, Ltd., Tokyo, Japan). Conversely, the estimated stroke volume variation (esSVV) is a noninvasive metric for assessing SVV and was derived using an estimated continuous cardiac output (esCCO) system (Nihon Kohden, Tokyo, Japan). The esCCO system continuously calculates cardiac output (CO) derived from noninvasive monitoring parameters during anesthesia. It is believed to correlate with CO measured using arterial pressure, as well as with intermittent bolus thermodilution [3, 4]. Pulse wave transit time (PWTT) is defined as the interval from the peak of the R wave in an electrocardiogram (ECG) to 30% of the peak amplitude of the waveform derived from the first derivative of the pulse wave. This parameter can be quantified using its inverse relationship with stroke volume (SV) (Fig. 1; adapted with permission from Nihon Kohden Corporation). The SV calculated using the esCCO system is known as the estimated stroke volume (esSV), derived using the following equation:

Fig. 1.

Method for measuring the pulse wave transit time (adapted with permission from Nihon Kohden Corporation) The pulse wave transit time (PWTT) is defined as the interval between the R wave of the electrocardiogram (ECG) to the onset of the pulse wave of peripheral oxygen saturation (SpO₂) PEP, pre-ejection period

1

The esSVV value was calculated by averaging 16 consecutive esSVV measurements taken over two-breath cycles.

Measuring esSVV requires the use of a compatible monitor, ECG, blood pressure monitor, and dedicated peripheral capillary oxygen saturation (SpO₂) adhesion probe (TL-281T-1B); nonetheless, it can be conducted noninvasively.

The cutoff value for fluid responsiveness of esSVV has been previously reported to be 6.1% [5] or 6.4% [6]. However, research on this cutoff is limited and insufficient, leaving the appropriate value as an index unclear. Thus, the aim of this study was to contribute to determining the cutoff value of esSVV based on fluid loading during general anesthesia.

Methods

In this prospective observational study, a multi-institutional collaboration was held with the Nihon Kohden Corporation. The study was approved by the Research Ethics Committee of the University of Fukui on October 18, 2023 (approval no. 20230071) and registered with the University Hospital Medical Information Network (UMIN) Clinical Trials Registry on November 24, 2022 (UMIN register no. UMIN000049595). Informed consent was obtained from all participants.

The study included adult patients who underwent general anesthesia and had an intra-arterial pressure line inserted between February and November 2024. The sample size was calculated, and a target of 50 participants was established. Individuals with arrhythmias, including supraventricular rhythm irregularities such as atrial fibrillation, two- and three-stage pulse, second- and third-degree atrioventricular block, and ventricular extrasystole, as well as those requiring pacing, intra-aortic balloon pumps, or artificial cardiopulmonary support, were excluded. Furthermore, patients whose CO was not commensurate with their body size due to extreme obesity or cardiac decompensation and those deemed unsuitable by the investigator were also excluded.

Measurement

Upon entering the operating room, the patient was equipped with an ECG monitor, a dedicated SpO₂ probe on the left finger, and a noninvasive blood pressure monitor on the upper arm. Venous access was established, and crystalloid fluid administration was initiated using an infusion pump at a rate of 6 ml/kg. General anesthesia was induced, and following intubation, the infusion rate was reduced to 2 ml/kg. Total intravenous anesthesia or inhalation was used to maintain general anesthesia, with the drug dosage adjusted at the discretion of the attending anesthesiologist. Ventilator settings were established using either pressure-controlled ventilation alone or with an added volume guarantee. Tidal volume, respiratory rate, and positive end-expiratory pressure (PEEP) were determined at the discretion of the attending physician, and an intra-arterial pressure line was inserted into the radial artery and connected to the FloTrac system (Nippon Becton Dickinson Company Ltd., Tokyo, Japan). After determining the surgical position, the esCCO system was calibrated by ensuring that the difference between the systolic and mean blood pressures (sBP and mBP, respectively) measured using the noninvasive blood pressure monitor and those obtained from the objective arterial line was within 5%. The blood pressure at this time was recorded as the baseline (Fig. 2).

Fig. 2.

Research flow After the surgical position was determined, the estimated continuous cardiac output was calibrated, and the blood pressure at this time was recorded as the baseline. A fluid challenge was initiated when the systolic blood pressure (sBP) decreased by more than 10% from baseline at least 5 min after calibration. During this procedure, 300 ml of colloidal solution was administered over a 15-min period. The estimated stroke volume (esSV) 5 min before the start of the fluid challenge and its maximum value during the 5 min after the fluid challenge were recorded

A fluid challenge was initiated when the sBP decreased by > 10% from the baseline, at least 5 min after calibration. During this procedure, 300 ml of a colloidal solution (Voluven 6%, Otsuka Pharmaceutical Factory, Tokushima, Japan) was administered over 15 min. Subsequently, the infusion rate was adjusted to 2 ml/kg, and administration continued for an additional 5 min. For data analysis, a 25-min segment of data was used, spanning from 5 min before the initiation of the fluid challenge to 5 min following its conclusion. Performance-enhancing agents were prohibited during this period.

The esSV value 5 min before (pre-esSV value) and the maximum esSV value 5 min after (post-esSV value) the fluid challenge were recorded. The values of the estimated stroke volume index (esSVI), esSVV, SVI, SV, SVV, sBP, and mBP were recorded concurrently with the pre-esSV and post-esSV values. Additionally, the values of esSVV, sBP, and mBP were determined. Patients with esSV increases exceeding 10% were classified in the responder group, whereas those with < 10% increases were classified in the non-responder group. The maximum SV and SVV values recorded 5 min after the fluid challenge were compared with those recorded 5 min before the challenge.

Statistical analysis

A case range of approximately 30–50 was previously reported for esSVV [6, 7]. In a previous study [6], the receiver operating characteristic (ROC) curve analysis yielded an area under the curve (AUC) of 0.904, with 27 patients classified as responders and 19 as non-responders, resulting in a kappa value of 0.704 (ratio of the non-responder group to the responder group). With an AUC of 0.90, an estimated precision of 0.1 (half value of the 95% confidence interval), and a kappa of 0.704, the sample size was determined to be 51 cases. Consequently, the target number of cases was set at 50. Furthermore, based on an SVV meta-analysis [8–10], the majority of cases involved a single transfusion; hence, transfusions were limited to one per patient.

The ROC curves for esSVV and SVV were generated, and the corresponding AUC was calculated. A paired t-test was used to compare the esSV, esSVI, esSVV, SV, SVI, SVV, sBP, and mBP values before and after the fluid challenge. Statistical analyses were conducted using EZR (Jichi Medical University, Tochigi, Japan) [11] and JMP Pro18.1.0 software (SAS Institute Inc., Cary, NC, USA). Results are presented as mean ± standard deviation, and statistical significance was set at p < 0.05.

Results

Among the 50 patients included, three withdrew from the study prematurely because they experienced significant hypotension and subsequently received treatment with boosting agents. Hence, only 47 adult participants (14 male and 33 female) were included. Notably, four and seven patients were excluded from the esSV and SV analyses, respectively, owing to incomplete data, leaving 43 patients in the esSV and 40 in the SV group for the final statistical analysis (Fig. 3). Thirty-three patients had open abdominal surgery, while 12 had laparoscopic surgery. The surgical positions comprised 31 patients who used the supine position and 16 who used the lithotomy position. The ventilator settings were as follows: tidal volume, 4–9 ml/kg; respiratory rate, 10–15 breaths per min; and PEEP, 4–8 mmHg. Throughout the study, the respiratory settings remained unchanged, and the ventilator settings did not significantly differ between the responder and non-responder groups.

Fig. 3.

Study flow Three patients withdrew from the study prematurely because they experienced significant hypotension and subsequently received treatment with boosting agents. Consequently, this study included 47 adult participants. Notably, four and seven patients were excluded from the estimated stroke volume (esSV) and stroke volume (SV) analyses, respectively, owing to incomplete data, leaving 43 patients in the esSV group and 40 in the SV group for the final statistical analysis. An additional analysis involving 33 patients, excluding 10 who experienced insufflation or positional changes during the fluid loading protocol, as well as those exhibiting significant decreases in lung compliance

The esSV-responder group included 21 patients, whereas the non-responder group included 22 patients. Similarly, the SV-responder group comprised 27 patients, whereas the non-responder group included 13 patients. Significant differences in height were identified between the SV-responder and non-responder groups. However, other patient background characteristics did not significantly differ between the SVV and esSVV groups (Table 1).

Table 1.

Characteristics of the study participants

	Estimated stroke volume group (n = 43)		Stroke volume group (n = 40)
	Responder group (n = 21)	Non-responder group (n = 22)		Responder group (n = 27)	Non-responder group (n = 13)
Sex (male/female)	6/15	8/14		11/16	1/12
Age	60.29 ± 9.20	61.00 ± 9.86		61.63 ± 10.02	56.92 ± 7.43
Height (cm)	162.04 ± 7.54	160.65 ± 7.46		162.54 ± 7.26	157.76 ± 6.15*
Weight (kg)	62.84 ± 11.88	61.82 ± 13.20		62.54 ± 14.09	60.25 ± 9.12

Data are presented as mean ± standard deviation values

Significant differences in height were observed in the stroke volume group (*p < 0.05). No significant differences were observed in other patient characteristics

*p-value < 0.05 was considered statistically significant

The pre-infusion esSVV values were 9.03 ± 2.35% and 6.82 ± 2.67% in the responder and non-responder groups, respectively, with the responder group exhibiting significantly higher values than the non-responder group did. In contrast, the SVV values were 13.6 ± 5.28% and 10.88 ± 3.78% in the responder and non-responder groups, respectively, with no significant difference between the two groups. Fluid challenge administration resulted in a significant increase in esSVI, from 35.50 ± 5.30 to 42.03 ± 5.60 ml/m² in the responder group (p < 0.001) and from 39.37 ± 7.35 to 41.28 ± 7.14 ml/m² in the non-responder group (p < 0.001). Additionally, sBP in the responder group increased significantly from 85.48 ± 10.54 to 110.29 ± 25.01 mmHg (p < 0.001), while in the esSV-non-responder group, it increased from 90.19 ± 12.37 to 96.81 ± 17.38 mmHg (p = 0.03) (Table 2). The infusion resulted in a significant increase in the SVI from 34.58 ± 7.34 to 43.45 ± 8.67 ml/m² in the SV-responder group (p < 0.001). However, this increase was not statistically significant in the SV-non-responder group, in which the SVI changed from 41.93 ± 5.46 to 42.72 ± 5.64 ml/m² (p = 0.31) (Table 3). The esSVV changed from 9.03 ± 2.35% to 9.37 ± 4.78% (p = 0.67) in the esSV-responder group and from 6.82 ± 2.67% to 6.95 ± 3.69% (p = 0.82) in the esSV-non-responder group. In the responder group, the SVV decreased from 13.60 ± 5.28% to 8.83 ± 3.79% (p < 0.001), whereas in the non-responder group, it was no significantly decreased from 10.88 ± 3.78% to 7.94 ± 3.12% (p = 0.08). The AUC for esSVV was 0.73, with a cutoff value of 7.3%, a sensitivity of 0.91, and a specificity of 0.64 (Fig. 4). Conversely, the AUC for SVV was 0.65, with a cutoff value of 12%, a sensitivity of 0.63, and a specificity of 0.62 (Fig. 5). The AUC did not significantly differ between esSVV and SVV.

Table 2.

Changes in estimated stroke volume variation before and after fluid challenge

	Responder group (n = 21)
	Estimated stroke volume (esSV) (ml)		Estimated stroke volume index (esSVI) (ml/m2)		Estimated stroke volume variation (esSVV) (%)		Systolic blood pressure (sBP) (mmHg)		Mean blood pressure (mBP) (mmHg)
	Before	After	Before	After	Before	After	Before	After	Before	After
Mean ± standard deviation (SD)	59.24 ± 11.60	70.24 ± 13.39	35.50 ± 5.30	42.03 ± 5.60	9.03 ± 2.35	9.37 ± 4.78	85.48 ± 10.54	110.29 ± 25.01	59.81 ± 8.52	76.5 ± 17.74
p-value	0.00*		0.00*		0.67		0.00*		0.00*

	Non-responder group (n = 22)
	esSV (ml)		esSVI (ml/m2)		esSVV (%)		sBP (mmHg)		mBP (mmHg)
	Before	After	Before	After	Before	After	Before	After	Before	After
Mean ± SD	65.0 ± 16.62	68.27 ± 16.80	39.37 ± 7.35	41.28 ± 7.14	6.82 ± 2.67	6.95 ± 3.69	90.19 ± 12.37	96.81 ± 17.38	63.43 ± 9.63	67.90 ± 11.69
p-value	0.00*		0.00*		0.81		0.03*		0.04*

Data are presented as mean ± standard deviation values

In both groups, esSVV showed no significant changes (p = 0.67 and 0.81 in the responder and non-responder groups, respectively)

esSV Estimated stroke volume, esSVI Estimated stroke volume index, esSVV Estimated stroke volume variation, sBP Systolic blood pressure, mBP mean blood pressure

*p-value < 0.05 was considered statistically significant

Table 3.

Changes in stroke volume variation before and after fluid challenge

	Responder group (n = 27)
	Stroke volume (SV) (ml)		Stroke volume index (SVI) (ml/m2)		Stroke volume variation (SVV) (%)
	Before	After	Before	After	Before	After
Mean ± standard deviation (SD)	56.93 ± 11.56	71.93 ± 15.58	34.58 ± 7.34	43.45 ± 8.67	13.60 ± 5.28	8.83 ± 3.79
p-value	0.00*		0.00*		0.00*

	Non-responder group (n = 13)
	SV (ml)		SVI (ml/m2)		SVV (%)
	Before	After	Before	After	Before	After
Mean ± SD	67.08 ± 8.36	68.31 ± 8.18	41.93 ± 5.46	42.72 ± 5.64	10.88 ± 3.78	7.94 ± 3.12
p-value	0.33		0.31		0.08

Data are presented as mean ± standard deviation values. *p-value <0.05 was considered statistically significant

Fig. 4.

Receiver operating characteristic curve for estimated stroke volume variation The receiver operating characteristic curve for estimated stroke volume variation showed an area under the curve of 0.73, with a cut-off value of 7.3%. Sensitivity and specificity were 0.91 and 0.64, respectively

Fig. 5.

Receiver operating characteristic curve for stroke volume variation The receiver operating characteristic curve for stroke volume variation (SVV) showed an area under the curve of 0.65. The determined cutoff value for SVV was 12%, with sensitivity and specificity values of 0.63 and 0.62, respectively

Indicators of fluid responsiveness can be influenced by insufflation maneuvers, alterations in patient positioning, and reduced lung compliance. Consequently, we conducted an additional analysis involving 33 patients, excluding 10 who experienced insufflation or positional changes that occurred during the fluid loading protocol, as well as those exhibiting significant decreases in lung compliance.

There were 14 and 19 patients in the esSVV responder and non-responder groups, respectively. The esSVV decreased from 8.54 ± 2.22% to 7.69 ± 2.87% in the responder group and from 6.63 ± 2.74% to 6.39 ± 2.82% in the non-responder group (Table 4). This change was not statistically significant (p = 0.11); however, esSVV reduced in the responder group following the fluid challenge. The AUC was 0.72, and the cut-off value of 7.3% (Fig. 6) was consistent with the overall analysis results. Following the exclusion process, the study comprised 18 patients in the SVV responder group and 13 patients in the SVV non-responder group. Within the responder group, SVV significantly decreased from 12.19 ± 4.81% to 8.26 ± 3.37% (p < 0.01). Conversely, in the non-responder group, it decreased from 10.88 ± 3.78% to 7.94 ± 3.12%; however, this change was not statistically significant (p = 0.08) (Table 5). (Figure 7).

Table 4.

Changes in EsSVV excluding cases of pneumoperitoneum, positional changes, and marked reduction in pulmonary compliance

	Responder group (n = 14)
	Estimated stroke volume (esSV) (ml)		Estimated stroke volume index (esSVI) (ml/m2)		Estimated stroke volume variation (esSVV) (%)		Systolic blood pressure (sBP) (mmHg)		Mean blood pressure (mBP) (mmHg)
	Before	After	Before	After	Before	After	Before	After	Before	After
Mean ± standard deviation (SD)	59.00 ± 13.12	68.64 ± 13.98	36.42 ± 5.71	42.40 ± 5.79	8.54 ± 2.22	7.69 ± 2.87	88.64 ± 10.64	105.79 ± 18.04	61.07 ± 9.78	72.07 ± 12.19
p-value	0.00*		0.00*		0.11		0.00*		0.00*

	Non-responder group (n = 19)
	esSV (ml)		esSVI (ml/m2)		esSVV (%)		sBP (mmHg)		mBP (mmHg)
	Before	After	Before	After	Before	After	Before	After	Before	After
Mean ± SD	67.84 ± 16.21	71.21 ± 16.20	40.48 ± 7.11	42.50 ± 6.86	6.63 ± 2.74	6.39 ± 2.82	91.11 ± 12.67	96.89 ± 18.17	64.11 ± 9.75	68.32 ± 12.24
p-value	0.00*		0.00*		0.62		0.08		0.08

Data are presented as mean ± standard deviation. Statistical significance was set at p < 0.05

The esSVV was reduced in both groups; however, this reduction was not statistically significant (p = 0.11 and 0.62 in the responder and non-responder groups, respectively)

esSV Estimated stroke volume, esSVI Etimated stroke volume index, esSVV Estimated stroke volume variation, sBP Systolic blood pressure, mBP Mean blood pressure

Fig. 6.

Receiver operating characteristic curve for estimated stroke volume variation excluding specific cases The receiver operating characteristic curve for estimated stroke volume variation, of pneumoperitoneum, positional changes, and marked reduction in pulmonary compliance showed an area under the curve of 0.72, with a cut-off value of 7.3%. The sensitivity and specificity were 0.86 and 0.68, respectively

Table 5.

Changes in SVV excluding cases of pneumoperitoneum, positional changes, and marked reduction in pulmonary compliance

	responder (n = 18)
	SV (ml)		SVI (ml/m2)		SVV (%)		sBP (mmHg)		mBP (mmHg)
	before	after	before	after	before	after	before	after	before	after
Mean ± SD	61.67± 10.25	77.72± 15.85	37.50± 6.22	47.07± 8.19	12.19± 4.81	8.26± 3.37	91.61± 11.27	102.89± 20.74	64.28± 9.16	71.17± 13.76
p value	0.00*		0.00*		0.01*		0.01*		0.01*

	non- responder (n = 13)
	SV (ml)		SVI (ml/m2)		SVV (%)		sBP (mmHg)		mBP (mmHg)
	before	after	before	after	before	after	before	after	before	after
Mean ± SD	67.08± 8.36	68.31± 8.18	41.93± 5.46	42.72± 5.64	10.88± 3.78	7.94± 3.12	88.31± 12.80	97.15± 15.74	61.15± 10.80	67.62± 10.29
P value	0.33		0.31		0.08		0.09		0.09

In the responder group, SV, SVI, and SVV showed significant changes

(*p < 0.05) There were no significant changes in the non-responder group. Data are presented as the mean ± standard deviation

SV Stroke volume, SVI Stroke volume index, SVV Stroke volume variation, sBP Systolic blood pressure, mBP Mean blood pressure

 *P-value, when less than 0.05 is considered statistically significant

Fig. 7.

Receiver operating characteristic curve for stroke volume variation excluding specific cases The receiver operating characteristic curve for estimated stroke volume variation, of pneumoperitoneum, positional changes, and marked reduction in pulmonary compliance, showed an area under the curve of 0.57, with a cut-off value of 13%. The sensitivity and specificity were 0.50 and 0.69, respectively

Discussion

In this study, we sought to determine the cutoff value for esSVV based on infusion loading during general anesthesia. This cutoff was determined to be 7.3%, which appears to be higher than that reported in previous studies [5, 6].

Laparotomy has been the focus in previous studies; however, we included laparoscopic surgery, as well as cases involving the lithotomy position. The differences in outcomes may have been influenced by the surgical procedure and patient positioning.

In contrast, the established cutoff value for SVV has been reported to be 10–15% [12, 13]. The SVV results obtained in this study were also consistent with these established values. Notably, the cutoff value of esSVV was lower than that of SVV. If the same target values as those for SVV had been applied, fluid responsiveness could have been underestimated, potentially leading to insufficient circulating blood volume. We anticipated a decrease in esSVV in the responder group following fluid challenge; however, the esSVV values did not decrease in either group. However, the variation in esSVV before and after infusion included instances in which the infusion resulted in a significant increase in esSVV. One patient in whom esSVV increased during infusion showed decreased pulmonary compliance. The patient underwent laparotomy, during which the diaphragm was compressed using a laparotomy apparatus and intraoperative maneuvers. This compression likely resulted in reduced lung compliance, which may have subsequently decreased the preload and influenced the esSVV value. SVV, an indicator of infusion responsiveness, also significantly increases with the manipulation of pneumoperitoneum [14]. Furthermore, transitioning from the supine position to the Trendelenburg position enhances venous return. No vasopressor was used, and the infusion volume was standardized; nevertheless, insufflation and positional alterations during the fluid challenge may have influenced esSVV. Inadequate ventilation and low lung compliance can limit the measurement of PPV [15] and may similarly affect esSVV values. In further analyses that excluded variables such as pneumoperitoneum, alterations in body position, and significant reductions in lung compliance, which can influence indices of fluid responsiveness, no changes were observed in the results of the SVV group. Conversely, in the esSVV group, although the difference was not statistically significant, esSVV was reduced following fluid administration. Consequently, similar to other fluid responsiveness indices, esSVV may also be susceptible to such influences, necessitating caution in interpreting the results. The esSVV is a noninvasive indicator of fluid responsiveness. Its advantages include applicability in circulatory management for patients who do not require an arterial pressure line and its utility during abrupt alterations in circulatory dynamics in patients lacking an arterial pressure line. For instance, esSVV may prove beneficial in scenarios such as emergency cesarean sections conducted under general anesthesia, circumstances in which the placement of an arterial pressure line is unfeasible, or during instances of sudden massive hemorrhage.

This study has some limitations. As mentioned previously, patients with significant arrhythmias or those requiring pacing were excluded from the study, as measuring esSVV in these patients was challenging because of the inability to correctly measure the PWTT.

In this study, the attending physicians were responsible for the ventilator settings, which were not standardized across the study period. No alterations were observed in the ventilator settings during the study, nor were there statistically significant differences between groups. This lack of standardization may have influenced the results.

Additionally, similar to SVV and PPV, esSVV requires patients to be on ventilation for accurate measurements [16]. Furthermore, intraoperative positional adjustments, pneumoperitoneum maneuvers, and variations in the respiratory status may influence esSVV measurements. Therefore, caution should be exercised while evaluating esSVV under these conditions.

Finally, although esSVV was reduced following fluid loading in the esSVV responder group, the difference was not statistically significant. To assess the efficacy of the cutoff value established in this study, future research should involve a prospective analysis using the identified esSVV cutoff value as a reference indicator to determine whether fluid administration can enhance SV and blood pressure.

In conclusion, the cutoff value for esSVV was 7.3% in this study. As a noninvasive indicator of fluid responsiveness, esSVV may be a useful tool for managing circulation, particularly given that its cutoff value has now been determined. Nevertheless, the utility of esSVV may be affected by variables such as body position, intraoperative maneuvers, and respiratory status. Therefore, caution is advised when interpreting the fluid responsiveness.

Abbreviations

PPV

Pulse Pressure Variation

SVV

Stroke Volume Variation

esSVV

Estimated Stroke Volume Variation

esCCO

Estimated continuous cardiac output

CO

Cardiac Output

PWTT

Pulse Wave Transit Time

ECG

Electrocardiogram

sBP

Systolic blood pressure

mBP

Mean blood pressure

SpO₂

Peripheral capillary oxygen saturation

SVI

Stroke Volume Index

SV

Stroke Volume

ROC

Receiver Operating Characteristic

AUC

Area Under the Curve

PEEP

Positive End-expiratory Pressure

Authors’ contributions

Y.Y.: conception and design, acquisition, statistical analysis, and drafting of the manuscript; S.M.: acquisition, analysis, and interpretation of data; Y.M.: conception and design, and critical revision of the manuscript for important intellectual content. All authors participated in manuscript preparation and approved the final version.

Funding

This research was supported by the Japan Agency for Medical Research and Development (AMED) (Grant Number: JP22hk0102081).

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Declarations

Ethics approval and consent to participate

The study protocol was approved by the Research Ethics Committee of the University of Fukui on October 18, 2023 (approval no. 20230071), and was conducted in accordance with the Declaration of Helsinki. Informed consent was obtained from all patients for participation in this study.

Consent for publication

Not applicable.

Competing interests

This study involved a multi-institutional collaboration with the Nihon Kohden Corporation. The authors disclose that Nihon Kohden Corporation provided services and control software in accordance with the Clinical Trials Act of Japan.