Regional anaesthesia is the preferred technique for caesarean sections, offering superior maternal and neonatal safety profiles compared to general anaesthesia [1]. Among regional techniques—epidural, spinal, and combined spinal-epidural—spinal anaesthesia (subarachnoid block) is most commonly used due to its rapid onset, effective analgesia, technical simplicity, and reduced maternal and fetal exposure to systemic anaesthetic agents [2,3].

However, spinal anaesthesia is frequently associated with maternal hypotension, primarily caused by sudden sympathetic blockade, which leads to peripheral vasodilation and venous pooling, subsequently reducing venous return and cardiac output [4,5]. Hypotension after spinal anaesthesia can compromise uteroplacental perfusion, potentially resulting in neonatal acidosis, low Apgar scores, and maternal symptoms such as nausea, vomiting, and dizziness [6].

Therefore, preventing or mitigating hypotension is a key goal in the anaesthetic management of parturients. One widely adopted approach is intravenous fluid administration, either as a preload (administered before spinal injection) or as a coload (administered concurrently with the block). Preloading, typically performed 15–20 minutes prior to the block with crystalloids, may have limited efficacy due to rapid redistribution of the fluid and hormonal influences such as atrial natriuretic peptide-induced diuresis [7].

In contrast, coloading, where fluid is administered at the onset of the spinal block, has been shown to better support intravascular volume during the critical period of sympathetic vasodilation, thus maintaining cardiac output and blood pressure more effectively [8,9]. While vasopressors remain the cornerstone of treatment for established hypotension, effective fluid strategies such as coloading can reduce the frequency and dose requirements of vasopressors, improving maternal haemodynamic stability and fetal outcomes [10,11].

Recent evidence, including meta-analyses and randomized controlled trials, suggests that crystalloid coloading may be more effective than preloading in reducing the incidence of spinal-induced hypotension in elective caesarean sections [9,12]. This study was therefore conducted to compare the incidence of hypotension in parturients receiving preloading versus coloading with crystalloids during elective caesarean section under spinal anaesthesia.

OBJECTIVE

Primary Objective:

To compare the proportion of spinal anaesthesia-induced maternal hypotension in parturients undergoing elective caesarean section who receive preloading versus coloading with crystalloids.

Study Design and Setting

This was a hospital-based prospective observational study conducted in the Department of Anaesthesiology at Government Medical College, Thiruvananthapuram. The study was carried out over a period of 1.5 years following approval from the Institutional Human Ethics Committee.

Study Population

The study included parturients aged between 20 and 35 years with term singleton pregnancies who were scheduled to undergo elective lower segment caesarean section (LSCS) under spinal anaesthesia. Written informed consent was obtained from all participants prior to enrolment.

Inclusion and Exclusion Criteria

Inclusion criteria were term singleton pregnancies in parturients aged 20–35 years undergoing elective LSCS under spinal anaesthesia. Exclusion criteria included patient refusal, uncontrolled pre-existing or pregnancy-induced hypertension, known cardiovascular disease, uncontrolled diabetes mellitus, history of antenatal haemorrhage, and fetal anomalies identified during antenatal evaluation.

Sample Size and Sampling Technique

Based on a reference study, the sample size was calculated using the formula for comparing two proportions. The estimated proportion of hypotension was 60% in the preload group and 36% in the coload group. With a power of 80% and a significance level of 5%, the required sample size was 64 per group, resulting in a total of 128 participants. Consecutive sampling was used to recruit eligible parturients until the desired sample size was achieved.

Grouping and Intervention

Participants were grouped based on the fluid administration technique practiced by the attending consultant. The preload group received 20 ml/kg of crystalloids within 20 minutes before administering spinal anaesthesia. The coload group received the same volume of crystalloids at the time of initiating spinal anaesthesia.

Anaesthetic Technique

Upon arrival in the operating theatre, standard monitoring was established including non-invasive blood pressure (NIBP), electrocardiography (ECG), and pulse oximetry. Baseline parameters such as heart rate, systolic and diastolic blood pressure, mean arterial pressure, respiratory rate, and oxygen saturation were recorded. Two 18-gauge intravenous cannulas were inserted, and urinary catheterisation was performed for intraoperative urine output monitoring.

Spinal anaesthesia was administered in the left lateral position using a 23-gauge Quincke needle at the L3–L4 interspace, through which 10 mg of 0.5% hyperbaric bupivacaine was injected intrathecally. The patient was then placed in the supine position with a 15-degree left lateral tilt to reduce aortocaval compression.

Intraoperative Monitoring and Management

Blood pressure was monitored every 2 minutes for the first 20 minutes after spinal injection, every 10 minutes for the next 40 minutes, and every 15 minutes for the subsequent 30 minutes. Hypotension was defined as a decrease in systolic blood pressure of 20% or more from baseline and was treated with 6 mg boluses of intravenous ephedrine. The number and total dosage of ephedrine required were documented.

Patients were instructed to report any symptoms of hypotension, such as nausea, vomiting, palpitations, or blurred vision, which were recorded during the procedure. Sensory block level was assessed using a pinprick test every 3 minutes starting from 3 minutes post-injection. After delivery, 20 IU of oxytocin was added to normal saline and infused at a rate of 4 ml/kg/hour throughout the surgery.

Neonatal Assessment and Postoperative Monitoring

Neonatal Apgar scores at 1 and 5 minutes were assessed and recorded by the attending paediatrician. Following the procedure, all parturients were transferred to the recovery room for continued monitoring of vital signs. Supplemental oxygen was provided as required.

Data Collection and Statistical Analysis

Data were recorded using a structured proforma. The collected data were entered into Microsoft Excel and analyzed using SPSS version 27. Categorical variables such as incidence of hypotension and maternal symptoms were summarized as proportions and analyzed using the Chi-square test. Continuous variables such as age and blood pressure were expressed as means with standard deviations and compared using the Student’s t-test. A p-value of less than 0.05 was considered statistically significant.

Ethical Considerations

Institutional Ethics Committee approval was obtained before the initiation of the study. Written informed consent was taken from all participants. Confidentiality and anonymity were maintained throughout the study, and no additional financial burden was imposed on the patients.

A total of 128 parturients were included in the study, equally distributed into two groups: Preload (n = 64) and Coload (n = 64).

1. Patient Characteristics

Table 1: Patient Characteristics

The mean age of participants in the preload group was 28 years with a standard deviation (SD) of 4.43, while the coload group had a mean age of 27 years (SD = 4.41). The calculated t-value was 0.20, and the p-value was 0.98, indicating that the difference in age between the two groups was not statistically significant.

Similarly, the mean BMI in both the preload and coload groups was 26.6 kg/m², with SDs of 6.06 and 6.07 respectively. The t-value was –0.03 and the p-value was also 0.98, confirming no statistically significant difference in BMI between the two groups. (Table 1)

2. Baseline Haemodynamic Parameters

Table 2: Baseline Parameters

The mean heart rate in the preload group was 79.7 beats per minute (± 7.68), while in the coload group it was 79.2 beats per minute (± 7.31). The t-value was 0.37 and the p-value was 0.72, indicating that the difference in heart rate between the two groups was not statistically significant.

The mean systolic blood pressure (SBP) was 117.9 mmHg (± 10.36) in the preload group and 118.6 mmHg (± 10.06) in the coload group. The t-value for this comparison was –0.36 with a p-value of 0.72, again showing no statistically significant difference between the groups.

The mean diastolic blood pressure (DBP) in the preload group was 67.7 mmHg (± 8.12), compared to 67.1 mmHg (± 7.04) in the coload group. The t-value was 0.44, and the p-value was 0.66, which is also not statistically significant. (Table 2)

3. Incidence of Spinal Anaesthesia-Induced Hypotension

Table 3: Hypotension Incidence

In the preload group, 38 out of 64 participants (59.4%) experienced spinal anaesthesia-induced hypotension, while 26 participants (40.6%) did not.

In contrast, in the coload group, only 22 out of 64 participants (34.4%) developed hypotension, and the remaining 42 participants (65.6%) maintained stable blood pressure.

The Chi-square value was 8.01, with a corresponding p-value of 0.005, indicating that the difference in the incidence of hypotension between the two groups is statistically significant. (Table 3)

4. Incidence of Bradycardia

Table 4: Bradycardia Incidence

In the preload group, 53 out of 64 participants (82.8%) developed bradycardia following spinal anaesthesia, while only 11 participants (17.2%) did not.

In the coload group, 41 participants (64.1%) experienced bradycardia, whereas 23 participants (35.9%) maintained

normal heart rates.

The Chi-square value was 5.77, and the p-value was 0.02, indicating a statistically significant difference between the two groups. (Table 4)

5. Requirement of Ephedrine (E6)

Table 5: Ephedrine Requirement

In the preload group, 16 out of 64 participants (25.0%) required ephedrine (E6) to manage hypotension following spinal anaesthesia, while 48 participants (75.0%) did not.

In the coload group, only 8 out of 64 participants (12.5%) required ephedrine, with the remaining 56 participants (87.5%) maintaining adequate blood pressure without vasopressor support.

The Chi-square value was 3.28, and the p-value was 0.07, indicating that the difference between the groups was not statistically significant. (Table 5)

6. Trend in Systolic Blood Pressure Over 90 Minutes

Figure 1: Mean Systolic BP Trend (0–90 min)

The preload group showed a more pronounced drop in systolic blood pressure in the initial 20 minutes following spinal anaesthesia. The coload group maintained relatively stable systolic pressures throughout the 90-minute observation, demonstrating better short-term haemodynamic control. (Figure 1)

7. Trend in Diastolic Blood Pressure Over 90 Minutes

Figure 2: Mean Diastolic BP Trend (0–90 min)

Both groups showed a decline in diastolic pressure post spinal anaesthesia, with a more significant early drop in the preload group. The coload group showed quicker recovery to baseline by the 60-minute mark, suggesting better preservation of vascular tone. (Figure 2)

Spinal anaesthesia, commonly referred to as a subarachnoid block, is widely used for caesarean section due to its rapid onset, reliability, and safety when compared to general anaesthesia. It facilitates delivery without significant neonatal exposure to anaesthetic agents and avoids the maternal risks associated with airway manipulation and aspiration [1,2]. Only a small dose of local anaesthetic is required to achieve effective anaesthesia, minimizing the risk of systemic toxicity and fetal drug transfer [3].

Despite these advantages, spinal-induced hypotension (SIH) remains the most common and concerning complication, occurring in up to 70–85% of parturients without preventive measures [4,5]. It results from sympathetic blockade that leads to vasodilation, venous pooling, and reduced venous return, thereby compromising cardiac output and uteroplacental perfusion. Maternal manifestations include nausea, vomiting, dizziness, and in severe cases, loss of consciousness. For the fetus, sustained hypotension can lead to hypoxia, acidosis, and low Apgar scores [6,7].

To counteract this, fluid loading strategies, either as preloading (before spinal block) or coloading (during block onset), are used. Crystalloids are commonly chosen due to their availability and safety, although they have a short intravascular half-life of 15–20 minutes due to rapid redistribution [8]. Preloading may be less effective due to this timing mismatch. Coloading, on the other hand, better matches the onset of vasodilation and helps maintain effective circulating volume at the most critical time [9].

Our study compared these two approaches in 128 parturients undergoing elective caesarean sections under spinal anaesthesia. The groups were comparable in terms of age, BMI, and baseline haemodynamics, reducing the risk of confounding. The primary objective was to compare the incidence of spinal-induced maternal hypotension, while the secondary objectives included assessing symptomatic hypotension (nausea, vomiting), ephedrine (E6) requirement, and neonatal Apgar scores.

The incidence of SIH was significantly higher in the preload group (59.4%) compared to the coload group (34.4%) (p = 0.005). These findings are consistent with previous research. A study by Borse et al. reported hypotension rates of 60% in the preload group and 36% in the coload group [1]. Dyer et al. also noted a significant reduction in hypotension with coloading during the pre-delivery period [3], while other studies have reported similar trends with hypotension rates of 70–84% in preload groups [11]. Chandel et al. [12], Rao et al. [13], and Khan et al. [14] also demonstrated lower rates of hypotension in coload groups. A meta-analysis by Banerjee et al. strongly supported the superiority of coloading over preloading [9].

Regarding symptomatic hypotension, nausea occurred in 7.8% of the preload group and 4.7% of the coload group. Vomiting was reported in 4.7% and 1.6%, respectively. No participant experienced blurred vision. Similar symptom patterns were observed in studies by Rao et al. [13] and Ni et al. [2], reinforcing the clinical benefit of coloading in improving maternal comfort.

The requirement of vasopressor (E6) was also higher in the preload group, with 25% needing ephedrine compared to 12.5% in the coload group. Though this difference was not statistically significant (p = 0.07), it suggests a clinically meaningful reduction in pharmacological intervention, supporting findings from Dyer et al. [3] and Bajwa et al. [17].

Importantly, there was no significant difference in neonatal Apgar scores between the two groups, indicating that both fluid loading strategies were equally safe for fetal outcomes. This is consistent with prior studies by Zainab Farid et al. [18], Khan et al. [14], and Jacob et al. [19], which concluded that coloading does not compromise neonatal well-being.

To minimize bias, participants were blinded to their group allocation, and objective measurements (automatic monitoring of BP) were used. The paediatrician assigning Apgar scores was also unaware of group assignments, reducing the potential for assessor bias.

In conclusion, our findings demonstrate that coloading with crystalloids significantly reduces the incidence of spinal-induced hypotension and decreases the need for vasopressors and symptomatic intervention, without affecting neonatal outcomes. These results strongly support the routine use of coloading as a standard practice in spinal anaesthesia for caesarean section.

This study compared the effectiveness of preloading versus coloading with crystalloids in preventing spinal anaesthesia-induced hypotension in parturients undergoing elective caesarean section. The results clearly demonstrated that coloading significantly reduced the incidence of hypotension, bradycardia, and the need for vasopressor support compared to preloading. Although differences in the incidence of nausea, vomiting, and E6 (ephedrine) requirement were not statistically significant, they favored the coload group clinically.

Importantly, both fluid loading techniques were associated with similar neonatal outcomes, as reflected by comparable Apgar scores, confirming the safety of both strategies for the newborn.

In conclusion, coloading with crystalloids at the time of spinal anaesthesia administration is a more effective strategy than preloading for minimizing maternal hypotension without compromising neonatal well-being. Based on these findings, coloading should be preferred as a standard practice during spinal anaesthesia for caesarean delivery.

Conflict of interest: Nil

1. Borse YM, Patil AP, Rajesh S. Comparative study of preloading and co-loading with Ringer lactate for prevention of spinal hypotension in elective caesarean section. Int J Med Anaesthesiol. 2020;3(1):30–2.
2. Ni HF, Liu HY, Zhang J, et al. Crystalloid coload reduced the incidence of hypotension in spinal anaesthesia for caesarean delivery, when compared to crystalloid preload: a meta-analysis. Biomed Res Int. 2017;2017:3462529.
3. Dyer RA, Farina Z, Joubert IA, et al. Crystalloid preload versus rapid crystalloid administration after induction of spinal anaesthesia (coload) for elective caesarean section. Anaesth Intensive Care. 2004;32(3):351–7.
4. Carpenter RL, Caplan RA, Brown DL, et al. Incidence and risk factors for side effects of spinal anesthesia. Anesthesiology. 1992;76(6):906–16.
5. Ngan Kee WD. Prevention of maternal hypotension after regional anesthesia for cesarean section. Curr Opin Anaesthesiol. 2010;23(3):304–9.
6. Reynolds F. Regional analgesia and anaesthesia for childbirth. BMJ. 1995;311(6996):355–8.
7. Hawkins JL, Koonin LM, Palmer SK, et al. Anesthesia-related deaths during obstetric delivery in the United States, 1979–1990. Anesthesiology. 1997;86(2):277–84.
8. Mercier FJ. Fluid loading for caesarean delivery under spinal anaesthesia: have we studied all the options? Anesth Analg. 2011;113:677–80.
9. Banerjee A, Stocche RM, Angle P, Halpern SH. Preload or coload for spinal anaesthesia for elective caesarean delivery: a meta-analysis. Can J Anaesth. 2010;57(1):24–31.
10. Gunusen I, Karaman S, et al. Effects of fluid preload compared with crystalloid co-load plus ephedrine infusion on hypotension and neonatal outcome during spinal anaesthesia for caesarean delivery. Anaesth Intensive Care. 2010;38:647–53.
11. Dyer RA, Piercy JL, Reed AR, et al. Hemodynamic changes associated with spinal anaesthesia for caesarean delivery in severe preeclampsia. Anaesthesiology. 2008;108:802–11.
12. Chandel A, et al. Crystalloid preloading vs coloading in preventing spinal-induced hypotension during caesarean section. JMSCR. 2020;8(1):58–63.
13. Rao AR, et al. Comparison of effects of preloading and coloading with Ringer lactate in elective caesarean section cases under spinal anaesthesia. IOSR J Dent Med Sci. 2015;14(10):57–64.
14. Khan M, et al. Preload versus coload and vasopressor requirement for the prevention of spinal anaesthesia induced hypotension in non-obstetric patients. J Coll Physicians Surg Pak. 2015;25(12):851–5.
15. Oh AY, et al. Influence of the timing of administration of crystalloid on maternal hypotension during spinal anaesthesia for cesarean delivery: preload versus coload. BMC Anesthesiol. 2014;14:36.
16. Hanss R, Bein B, Francksen H, et al. Heart rate variability-guided prophylactic treatment of severe hypotension after subarachnoid block for elective cesarean delivery. Anaesthesiology. 2006;104:635–43.
17. Bajwa SJ, Kulshrestha A, Jindal R. Co-loading or pre-loading for prevention of hypotension after spinal anaesthesia: a therapeutic dilemma. Anesth Essays Res. 2013;7(2):155–9.
18. Farid Z, Mushtaq R, Ashraf S, Zaeem K. Comparative efficacy of crystalloid preloading and co-loading to prevent spinal anaesthesia-induced hypotension in elective caesarean section. Pak J Med Health Sci. 2016;10(1):42–6.
19. Jacob R, et al. Crystalloid preload versus crystalloid coload for parturients undergoing caesarean section under spinal anaesthesia. J Obstet Anaesth Crit Care. 2012;2(1):15–19.