Spinal anesthesia (SA) is a locoregional anesthetic technique in which a local anesthetic (LA) is injected into the cerebrospinal fluid (CSF), in direct contact with the nerve roots. It is an anesthetic technique frequently used for infra-umbilical surgeries [1]. Its advantages include technical simplicity, rapid onset, and low cost [1]. Despite these benefits, hypotension and bradycardia are the most common and predominant adverse effects. Thus, post-spinal anesthesia hypotension (PSAH) is the most frequent complication, with a prevalence ranging from 15% to 33% [2]-[4] in the general population and up to 65% in the specific context of cesarean section [5]. Hypotension may lead to adverse postoperative events such as myocardial infarction, postoperative delirium, and acute kidney injury, as well as an increased 30-day postoperative mortality after non-cardiac surgery [6]-[8].

Fluid resuscitation, in the prevention and management of PSAH, aims to increase stroke volume and improve vital organ perfusion and oxygen delivery [9]. Predicting fluid responsiveness, or determining whether fluid administration will result in the expected significant increase in cardiac output, remains a major concern for clinicians [10]. Various invasive techniques, such as invasive arterial pressure monitoring, pulmonary artery catheterization, PiCCO®, and Vigileo®, have been described to assess preload and other components of hemodynamic status. However, their widespread use remains controversial because of their high cost and relatively high complication rates [11]. Other non-invasive methods include non-invasive blood pressure monitoring, the passive leg-raising test, and ultrasound.

Ultrasound is a useful non-invasive tool that is increasingly used by anesthesiologists in the operating room, with a short learning curve. Its advantages include reliability, portability, ease of use, and the absence of complications. It allows the measurement of several parameters, including the inferior vena cava (IVC), which has been used in intensive care and the perioperative period as a hemodynamic assessment tool [12][13]. Ultrasonographic assessment of the inferior vena cava collapsibility index (IVC-CI) and the subclavian vein collapsibility index (SCV-CI) represents a simple, non-invasive technique for evaluating intravascular volume status [13][14].

In low-resource countries, more than half of anesthesia-related maternal deaths are caused by post-spinal anesthesia hypotension. Hemodynamic management during spinal anesthesia relies mainly on strategies such as empirical prophylactic fluid loading and/or the prophylactic use of vasopressors to reduce the incidence of PSAH. This approach is not always patient-tailored and is primarily based on monitoring heart rate (HR), mean arterial pressure (MAP), and systolic arterial pressure (SAP) [15][16]. The incidence of deaths related to PSAH is highest in these settings due to limited resources for optimizing perioperative management [15]. Therefore, implementing point-of-care ultrasound in perioperative management could improve patient care. Goal-directed fluid therapy may allow the appropriate use of fluids, vasopressors, and inotropes, leading to better outcomes [17].

The objective of our study was to evaluate the contribution of IVC and SCV monitoring to hemodynamic management during spinal anesthesia. We hypothesized that IVC and SCV monitoring would be beneficial for optimizing hemodynamic management in patients undergoing spinal anesthesia.

After obtaining ethical approval from the Ethics Committee of the Faculty of Medicine of the University of Yaoundé I (FMSB) and administrative authorization from the Military Hospital of Region No. 1 (HMR No. 1), we conducted a single-blind randomized clinical trial over a period of eight (8) months in the Department of Anesthesiology of the Military Hospital of Region No. 1 in Yaoundé (HMR1).

All patients aged over 18 years undergoing surgery under spinal anesthesia, classified as ASA physical status I or II, were eligible for inclusion. Exclusion criteria were: body mass index (BMI) > 30 kg/m²; pregnancy; cardiovascular diseases such as systemic arterial hypertension, heart failure, or unstable angina; presence of a pacemaker; pulmonary arterial hypertension; mean arterial pressure (MAP) < 65 mmHg; cardiac arrhythmias; diabetes mellitus; acute kidney injury; poor ultrasonographic visualization of the inferior vena cava and/or subclavian vein; and potentially hemorrhagic surgical procedures.

Data entry was performed using CSPro software version 8.0. Data analysis was conducted using SPSS software version 22.0. Graphs were generated using SPSS version 22.0 and Microsoft Excel 2016. Consecutive sampling with 1:1 random allocation was used. Each patient was randomly assigned to one of the two study groups corresponding to the protocols under investigation. Both groups included an equal number of patients.

Sample size:

Sample size was calculated using OpenEpi software based on the Kelsey et al. formula. Parameters included a two-sided significance level (1 − α) of 95%, statistical power (1 − β) of 80%, a non-exposed/exposed ratio of 1, an expected outcome proportion among exposed participants of 34% (the percentage of patients who developed hypotension after spinal anesthesia in the first study by Ni et al., 2022, to evaluate the power of preoperative IVCCI for predicting hypotension after induction of spinal anesthesia), and an odds ratio of 10. The total sample size with continuity correction was 68 participants, comprising 34 exposed and 34 non-exposed subjects.

A p-value < 0.05 was considered statistically significant for all analyses.

Figure 1. CONSORT flow diagram.

During the study period, 100 patients were enrolled, of whom 20 were excluded. Forty patients were allocated to the ultrasound-guided group and forty to the standard group (see Figure 1).

Table 1. Demographic and clinical characteristics according to the intervention group.

Table 2. Preoperative fasting characteristics and preoperative parameters according to the intervention group.

Table 3. Spinal anesthesia procedural characteristics according to the intervention group.

Table 4. Pre-induction inferior vena cava ultrasound characteristics - Ultrasound-guided group.

Table 5. Pre-induction ultrasound characteristics of the subclavian vein during deep breathing.

Table 6. Pre-induction ultrasound characteristics of the subclavian vein during quiet breathing.

Table 7. Intraoperative complications according to the intervention group.

The most frequently encountered complications in both groups were arterial hypotension in 15 patients (18.8%), bradycardia in 5 patients (6.25%), and nausea in 6 patients (7.50%). The incidence of hypotension in the ultrasound-guided group was 9 cases (22.5%) compared with 6 cases (15.0%) in the standard group, with no statistically significant difference between the groups.

The mean dose of ephedrine was 9.0 ± 3.4 mg in both groups, 8.9 ± 3.3 mg in the ultrasound-guided group, and 9.2 ± 3.8 mg in the standard group. The median dose of atropine was similar in the standard group and the ultrasound-guided group, at 0.5 [0.5 - 0.6] mg.

Table 8. Total atropine and ephedrine doses.

The distribution of fluids throughout the procedure is illustrated in Figure 2.

Figure 2. Distribution of fluid volume according to the intervention group and induction time (mL).

The mean age was 35.51 ± 14.02 years, with extremes ranging from 19 to 80 years. The most represented age group was 39 - 59 years, with no significant association between the two groups. These findings are similar to those reported by Yang et al., who reported a mean age of 36.36 ± 7.15 years [19]. In contrast, other studies reported a higher mean age, around 49 - 59 years [12][13][20], which may be explained by the inclusion of patients with cardiovascular comorbidities in those studies.

Regarding the type of surgery, orthopedic procedures were the most frequent (42.5%), a finding comparable to that of Roy et al., who reported a rate of 39% [21]. In our study, this may be explained by the high prevalence of traumatic conditions in younger populations and by the fact that the study was conducted in a military hospital.

In our study, the mean IVC collapsibility index (IVC-CI) was 15.3 ± 11.5%. This value was similar to that reported by Sumit et al., with a mean IVC-CI of 16.14 (9.79 - 23.18) [22]. In contrast, Ni et al. reported a mean IVC-CI of 40.7 ± 6.9%, and Eeshwar et al. reported a mean value of 33.64 ± 14.9% in ASA I and II patients[12][20]. This discrepancy may be explained by the fact that, in our study as well as in that of Sumit et al., patients with cardiovascular diseases were excluded, suggesting an influence of cardiovascular conditions—particularly hypertension—and their treatments on vascular morphology. Moreover, in spontaneously breathing patients, voluntary respiratory effort varies among individuals and affects the ability of respiratory variations in IVC diameter to predict fluid responsiveness. It has been shown that breathing patterns can influence IVC diameter and venous return.

The overall incidence of hypotension was 15 cases (18.8%). In the ultrasound-guided group, hypotension occurred in 9 patients (22.5%) compared with 6 patients (15.0%) in the standard group, with no statistically significant difference. These results differ from those reported in other studies, which showed higher incidences ranging from 23% to 45% [12][20][22]. This difference may be related to larger sample sizes in those studies and to the inclusion—except in the study by Sumit et al.—of hypertensive patients, who may be at higher risk of hypotension due to baroreceptor dysregulation.

The total volume of crystalloid administered throughout the procedure was 100 ± 99 mL (minimum 0, maximum 500 mL) in the ultrasound-guided group versus 1174.3 ± 565.7 mL (minimum 240, maximum 3000 mL) in the standard group, with a statistically significant difference between the two groups. In the study by Ni et al., the mean total volume in the standard and ultrasound-guided groups was 345 (285 - 670) mL and 330 (0 - 560) mL, respectively. The mean post-induction volume in the ultrasound-guided group was 0 (0 - 0) mL versus 0 - 335 mL in the standard group, with a significant difference between groups [12]. The similarity of findings in the ultrasound-guided groups may be explained by ultrasound-guided fluid management; however, in our study, the fluid protocol in the standard group differed, as we applied the 4-2-1 rule and accounted for insensible losses.

The total ephedrine dose was 9.0 ± 3.4 mg in both groups, with mean doses of 8.9 ± 3.3 mg in the ultrasound-guided group and 9.2 ± 3.8 mg in the standard group, with no significant difference. In the study by Ni et al., the frequency of vasoactive drug use was compared and was higher in the standard group (17 cases, 27%) than in the ultrasound-guided group (7 cases, 11.9%), with a significant difference between the two groups [12].

Study limitations

Only patients classified as ASA physical status I - II, without comorbidities, were included in the study. The single-blind randomization design may constitute a potential source of bias. All measurements were performed by a single operator to improve measurement precision; however, the presence of intra-observer variability cannot be excluded.

In our study population, ultrasound-derived indices of the subclavian vein (SCV) and inferior vena cava (IVC) were lower than those reported in the literature. Although the incidence of hypotension was higher in the ultrasound-guided group, this difference was not statistically significant. In contrast, the volume of fluids administered and the dose of ephedrine used were higher in the standard group compared with the ultrasound-guided group.