European Journal of Cardiovascular Medicine

Spinal anaesthesia (SA) is a widely used, safe, and cost-effective technique for lower abdominal and orthopaedic surgeries. Its advantages include rapid onset, minimal equipment requirements, and reduced systemic side effects. However, common complications include hypotension and bradycardia, primarily due to sympathetic blockade, leading to decreased systemic vascular resistance (SVR) and reduced cardiac preload. ^[1,2]

To prevent spinal anaesthesia-induced hypotension, fluid administration is a common strategy. However, indiscriminate preloading may lead to volume overload, especially in patients with comorbidities. Therefore, having a reliable, non-invasive predictor of fluid responsiveness is essential.

Point-of-care ultrasonography (POCUS) has gained popularity in recent years for hemodynamic monitoring. The measurement of the inferior vena cava (IVC) diameter and its variation with respiration—quantified as the IVC collapsibility index (IVCCI)—is a promising tool for assessing intravascular volume status. ^[3] While its use is well-established in critically ill, spontaneously breathing patients, patients undergoing general anaesthesia its role in preoperative settings, especially in healthy patients undergoing spinal anaesthesia, remains underexplored. ^[4,5,6]

This study aims to evaluate IVCCI as a predictor of fluid responsiveness and its potential role in guiding fluid therapy in elective surgical patients receiving spinal anaesthesia.

Study Design: Prospective, continuous, observational study

Duration: December 2020 to October 2022

Setting: MVJ Medical College and Research Hospital

Sample Size: 80 patients

Inclusion Criteria:

• Age between 20–60 years
• ASA Physical Status I and II
• Elective surgeries under spinal anaesthesia

Exclusion Criteria:

• Change in anaesthetic technique intraoperatively
• Obstetric surgeries
• Use of diuretics, ACE inhibitors, Angiotensin receptor blockers and SSRIs (Selective Serotonin Re-uptake Inhibitors).
• Intraoperative blood transfusion
• Preoperative IV fluids within 24 hours of surgery

After getting ethical clearance from the Ethical committee, 80 patients were enrolled under ASA I and II, aged between 20-60 years scheduled for elective surgeries.

Written informed consent was taken. A pre-anaesthetic evaluation was done comprising of history of previous medical or surgical illnesses, previous anaesthetic exposure, drug allergies and respiratory tract infections and any other cardiac, hepatic or renal disorders. General physical examination along with airway assessment and systemic examination was done.All patients were given anxiolytics the previous night and the next day morning before surgery.IV line with 18 G cannula was secured.

• IVC diameter at both inspiration and expiration was assessed by means of ultrasound.
• All measurements of IVC were performed in supine position using a curved array transducer with a frequency of 2-6 MHz (Acuson P500, Siemens Healthcare GmbH).
• The measurements of IVC diameter were taken in M-Mode, 1-2 cm below the level of the hepatic vein in the long axis subcostal view. IVCCI was calculated using the following equation:

IVCCI = [(IVCₑₓ – IVCᵢₙ) / IVCₑₓ] × 100

• Following which 500 ml RL was infused in 15 minutes and the IVC diameter at both inspiration and expiration was measured again. Later the patient was shifted to the operating room.

The Spinal Anaesthesia procedure is standardized here. Patient positioning was done in the lateral decubitus position and under sterile aseptic precautions, Spinal Anaesthesia was performed at the L3-L4 lumbar space using a 25G Quincke’s needle. A standard dose of Heavy Bupivacaine 0.5% (depending on the surgery and patient’s constitution) was injected slowly with the needle orifice oriented cranially. After injection patients were immediately positioned supine. And the NIBP (SBP, DBP, MAP) was measured every 10 minutes and other vital parameters like were recorded continuously till the end of surgery.

From December 2020 to October 2022, a total of 80 patients were enrolled in our study, comprising 41 females and 39 males. The mean age was 40.45 years, ranging from 20 to 60 years. There were no statistically significant differences in demographic characteristics between the study subgroups, ensuring comparability. The duration of surgery ranged from 15 minutes to 3 hours, which is consistent with the expected time frame for elective lower abdominal procedures under spinal anaesthesia. The uniformity in demographic and surgical characteristics strengthens the internal validity of our findings by minimising confounding factors.

Prior to fluid bolus administration, the mean IVCCI in our cohort was 40.51% (standard deviation [SD]: 3.06). Following the administration of a 500 ml fluid bolus, the mean IVCCI decreased to 36.37% (SD: 2.17) as shown in Table 1 and Figure 1. This reduction of approximately 4% suggests that the majority of patients demonstrated fluid responsiveness, as a decrease in IVCCI following volume expansion is indicative of improved right atrial filling and reduced respiratory variation in IVC diameter.

Table 1: Depicting (Mean ± SD) of IVCCI before and after RL infusion.

Figure 1: Depicting (Mean ± SD) of IVCCI before and after RL infusion.

In our study, the distribution of IVCCI change following a 500 ml Ringer’s Lactate infusion demonstrated varied fluid responsiveness among participants. A minimal change (<1%) in IVCCI was observed in 1% of patients, suggesting limited preload dependence in this subgroup. Mild changes of 1–3% were noted in 17% of patients, whereas the largest proportion—36%—exhibited a moderate change of 3–5%, indicating clinically relevant fluid responsiveness. Furthermore, 34% of patients demonstrated a change of 5–7%, and 12% showed a marked reduction of 7–10%, reflecting a higher baseline preload deficit as shown in Table 2 and Figure 2.

Table 2: Depicting % change in IVCCI after fluid administration

Figure 2: Depicting % change in IVCCI after fluid administration

This gradation highlights that while the mean group response indicated fluid responsiveness, there existed considerable inter-individual variability, emphasizing the importance of individualized assessment rather than reliance on a single cut-off value.

In the majority of cases, IVCCI decreased following administration of a 500 ml fluid bolus. Statistical analysis using a two-tailed t-test demonstrated a highly significant difference (p < 0.001) between pre- and post-bolus measurements. The mean baseline IVCCI was 40.51% (SD: 3.06), which decreased to 36.37% (SD: 2.17) after fluid administration, suggesting that most patients were fluid responsive.

Furthermore, a negative correlation was observed between IVCCI and hemodynamic parameters such as systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) (r = −0.20; p < 0.0001), indicating that higher collapsibility was associated with lower baseline blood pressures as shown in Figure 3.

Figure 3: Distribution of IVCCI and hemodynamic parameters like SBP, DBP, MAP and HR.

These findings support the role of IVCCI as a reliable, non-invasive predictor of volume status and hemodynamic response to fluid therapy in patients undergoing spinal anaesthesia.

Prolonged fasting before surgery often results in functional hypovolemia. Spinal anaesthesia exacerbates this due to sympathetic blockade, contributing to hypotension. ^[2] Traditional fluid preloading can prevent this but may be unnecessary in normovolemic patients and risky in comorbid individuals. ^[7] The Inferior Vena Cava Collapsibility Index (IVCCI) is a reliable, non-invasive tool widely used in critical care settings to assess fluid responsiveness.^[8]  However, limited studies have evaluated its application in healthy, spontaneously breathing ASA I and II patients.

Szabó et al. assessed 83 patients and found that an IVCCI ≥50% could predict postinduction hypotension in non-cardiac surgical patients under general anaesthesia with high specificity but low sensitivity. ^[9] Similarly, Ceruti et al. evaluated 160 patients undergoing SA and used IVCCI (>36%) to identify fluid responders, administering 500 ml boluses until patients became non-responders. ^[10] This approach effectively reduced hypotension.

Our findings are consistent with these reports. In our cohort of 80 ASA I and II patients undergoing elective lower abdominal surgery, overnight fasting without preoperative IV fluids resulted in elevated IVCCI values (mean 40.51% ± 3.06), suggesting hypovolemia. Administration of a 500 ml Ringer Lactate bolus reduced IVCCI (mean 36.37% ± 2.17), indicating improved intravascular volume. Perioperative haemodynamics remained stable, with minimal fluctuation in heart rate and blood pressure.

Previous literature presents mixed conclusions on IVCCI in spontaneously breathing patients. Mačiulienė et al. ^[4] found variable correlation between IVCCI and fluid responsiveness, whereas Mathieu Favre et al. ^[11] reported an 11% reduction in hypotension rates when a fluid protocol was guided by IVC ultrasound. Our results echo the latter, supporting its clinical utility in selected patients

Although SA is generally safe, hypotension can be more significant in elderly patients, those with cardiovascular risks, or those on medications like beta-blockers and ACE inhibitors. ^[12] Overzealous fluid loading can predispose to pulmonary oedema, especially in patients with impaired ventricular function. ^[13] Therefore, a targeted, ultrasound-guided approach such as IVCCI-based assessment balances the risks of under- and overhydration.

Our sensory block levels ranged from T6–T9, and intraoperative blood loss remained under 300 ml, minimising haemodynamic stress. These controlled conditions, along with preloading based on IVCCI, likely contributed to the stable parameters observed. Our findings support IVCCI as a useful bedside tool for guiding fluid therapy and preventing hypotension following spinal anaesthesia.

The IVC Collapsibility Index is a practical, non-invasive, and reproducible bedside tool for assessing fluid responsiveness. It can help tailor fluid therapy before spinal anaesthesia and potentially reduce the risk of hypotension. Our study demonstrates that IVCCI monitoring in elective surgical patients is both feasible and clinically valuable.

Limitations

• Single-centre study
• Limited to ASA I and II patients
• Not validated in patients with cardiopulmonary comorbidities
• Randomized control comparison could not be conducted due to ethical constraints regarding withholding fluids

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