European Journal of Cardiovascular Medicine

Spinal anesthesia constituted the established anesthetic protocol for elective cesarean deliveries.(1) (2) Spinal anesthesia has gained prominence as the preferred regional anesthetic modality for scheduled cesarean deliveries due to its rapid onset, dependable efficacy, and cost-effectiveness. However, one common adverse effect associated with spinal anesthesia is the reduction of systemic vascular resistance, leading to systemic hypotension. (3) Pregnant women exhibited heightened sensitivity to local anesthetics, diminished responsiveness to vasopressors, and lower mean arterial pressure (MAP) levels at full term.(4) Consequently, parturients may experience significant hypotension subsequent to central neuraxial blockade for lower segment cesarean section (LSCS). Maternal hypotension poses a considerable risk to both neonatal and maternal well-being.(5) Around 70% of parturients encounter hypotension subsequent to spinal anesthesia, a notably higher occurrence compared to approximately 33% observed in non-pregnant patients. Additionally, the hypotensive episodes experienced by pregnant individuals tend to be more severe and sudden in nature.(6) The clinical significance of this adverse effect has been underscored in numerous studies, demonstrating a correlation between hypotension and increased rates of morbidity and mortality.(7) Hypotension emerged as one of the most prevalent adverse events associated with spinal anesthesia, with reported incidences ranging from 15% to 33%, escalating to as high as 95% specifically for cesarean sections. (8) Hypotension induced by spinal anesthesia during Caesarean delivery stems from a combination of factors, including diminished vascular resistance attributable to sympathetic blockade,(9) and reduced cardiac output resulting from blood pooling in regions affected by the blockade. (4) (5) While it is recognized that aorto-caval compression by the gravid uterus and baseline volume status play roles in influencing the extent of hypotension, it's important to note that baseline peripheral vascular tone may also exert an influence. (10) Parturients at term, particularly those who are multiparous, typically exhibit decreased peripheral vascular tone.(8) (11) (12) The decreased peripheral vascular tone observed in parturients results in blood volume being sequestered in the extremities even prior to spinal anesthesia. The sympathetic blockade induced by spinal anesthesia exacerbates this blood pooling phenomenon. (13) Therefore, parturients with a lower baselinevascular tone may face an elevated risk of developing hypotension subsequent to spinal anesthesia. While heart rate and Non-invasive blood pressure (NIBP) remain the most common and conventional methods for intraoperative hemodynamic monitoring, they are limited in capturing beat-to-beat variations in perfusion dynamics. To address this limitation, perfusion index (PI) has been employed as a non-invasive measure to assess the likelihood of hypotension development following spinal anesthesia (14). Peripheral PI reflects changes in local blood volume pulsations and intravascular pulse pressure, influenced by vascular wall distensibility or tone. Low PI indicates vasoconstriction, while high PI suggests vessel dilation (15)(16)(17). Research indicates that measuring a finger PI >3.5 before spinal anesthesia for cesarean delivery can help identify women at risk for spinal hypotension. Additionally, low toe PI before spinal anesthesia indicates a higher risk due to aorto-caval compression by the gravid uterus, with the right toe PI commonly affected. Predictors of hypotension include baseline heart rate, heart rate variability, body mass index (BMI), advanced age, pre-operative anxiety, and perfusion index (15)(17)(18). This study seeks to explore the correlation between finger and right toe PI in predicting post-spinal hypotension

A prospective observational study was conducted at the Department of Anaesthesiology & Critical Care, Dr S. N. Medical College, Jodhpur over a period of 12 months to evaluate the correlation between perfusion index in the right toe and index finger as a predictor of post-spinal hypotension in parturients undergoing Lower Segment Cesarean Section (LSCS). Ethical clearance was obtained from the institutional Ethical Committee prior to commencement. The study enrolled 75 ASA-II classified patients scheduled for elective LSCS. Exclusion criteria comprised emergency cases, unavailability of monitoring sites, hypertensive patients or those on antihypertensive medication, individuals with diabetes mellitus or gestational diabetes, obesity (BMI ≥ 30), contraindications to spinal anesthesia, and specific obstetric conditions including placenta previa, pre-eclampsia, and gestational age beyond 36 to 40 weeks. Pre-anesthetic evaluations were conducted, and informed consent was obtained from patients and their relatives. Airway examinations were performed, and preoperative fasting adhered to the guidelines recommended by the Indian Society of Anaesthesiologists (ISA). Upon arrival in the operating theatre, parturients received preloading with Ringer lactate along with pre-anesthetic medication comprising Metoclopramide and Ranitidine. Spinal anesthesia was administered at the L3-L4 interspinous space using a 25G Quincke’s spinal needle with the patient in a sitting position, while monitoring heart rate, NIBP, respiratory rate, SpO2, and perfusion index. Bupivacaine was injected following confirmation of free cerebrospinal fluid flow. Vital parameters were monitored every 2 minutes until the 15th minute and thereafter every 5 minutes until the conclusion of the surgery. Hypotension was defined as a fall in systolic blood pressure of more than 20% of baseline value and was treated with volume expansion and if required, by incremental doses of mephentermine 3 to 6 mg. Bradycardia was defined as a fall in heart rate of more than 20% of baseline value or < 50 per minute and was treated with 0.6 mg intravenous atropine.
Statistical Analysis:
Data was entered into MS Excel and analysed with SPSS 20. Categorical data was compared with the chi-square test. Continuous variables were presented as Mean± SD and compared by t-test. Spearman’s rank correlation analysis was employed to assess the relationship between Index finger PI & Toe PI with the incidence of hypotension.

75 parturient were included in the study, with ages 18 to 34yrs were included. The mean age was 25.91yrs ±3.82, the mean weight was 61.01kg±6.86, and the mean height was 149.32cms±4.52. The higher percentage (42.8%) was in the age group of 25 to 30 years. And lower percentage (10.7%) was in the age group of <20 years. A higher percentage (45.3%) of study participants weighed 50 to 60kgs, and a lower percentage (13.4%) of study participants weighed>70kgs. a higher percentage (64%) of parturient with a height of 160 cm (36%). (Table 1)

The mean heart rate was 95.55bpm±14.9, the mean Finger PI was 5.64± 3.49, and the mean Toe PI was 3.38±3.36. The mean SBP was 127.47mmHg±9.95, mean DBP was 80.77mmHg±10.68, mean MAP was 98.28mmHg±8.70. The baseline Finger PI cut-off point determined by ROC analyses to predict hypotension was found to be 3.55. Participants were subsequently categorized based on age, weight, and height using this threshold value. (Table 2).

Comparison of Heart rate with baseline finger perfusion index showed that mean heart rate was found to be statistically significant in the 14min time interval in both the groups (>3.5 and <3.5) intra operatively after spinal anaesthesia. Similarly, the comparison between index finger perfusion index and baseline perfusion index among parturients revealed statistically significant mean finger PI values at 2 minutes, 4 minutes, and 12 minutes (P=0.003, 0.02, and 0.035 respectively) and statistically comparable values at other time intervals intraoperatively after spinal anaesthesia (P > 0.05) in both groups. (Table 3)
Comparison of toe perfusion index with baseline perfusion index among parturients revealed statistically significant mean toe PI values at 4 minutes, 6 minutes, 8 minutes, and 10 minutes (P=0.000, 0.018, 0.002, 0.056 respectively), and statistically comparable values at other time intervals intraoperatively after spinal anaesthesia (P > 0.05) in both groups. (Table 4)

Spearman’s rank correlation analysis revealed a highly significant correlation between baseline finger perfusion index (>3.5) and the number of hypotension episodes (rs = 0.400, P < 0.000). (Table 6)

In our current investigation, both groups categorized based on the cutoff value of baseline finger perfusion index (>3.5 and ≤3.5) displayed comparable demographic characteristics, including mean age (26.18±3.96 years in the >3.5 cutoff group and 26.18±3.96 years in the ≤3.5 cutoff group, P=0.873), mean weight (61.18±6.90 kg in the >3.5 cutoff group and 61.18±6.90 kg in the ≤3.5 cutoff group, P=0.873), and mean height (148.74±4.78 cm in the >3.5 cutoff group and 150.29±3.93 cm in the ≤3.5 cutoff group, P=0.155), with no statistically significant differences noted. These findings are consistent with previous studies by Toyama et al (19), Duggappa et al (20), Dr. Joseph George et al (21), and Mowafi et al (2), which similarly observed no significant associations between baseline perfusion index and demographic characteristics.
Moreover, our study's results align with existing literature regarding the utility of baseline perfusion index measurements in predicting hypotension following spinal anaesthesia. Toyama et al (19) established a baseline finger perfusion index cutoff of 3.5 with a sensitivity of 81% and specificity of 86%, whereas Duggappa et al (20) identified a cutoff of 3.85 with a sensitivity of 69.84% and specificity of 89.29%. In our investigation, we identified a similar baseline finger perfusion index cutoff of 3.55, albeit with a lower specificity of 51.1% and higher sensitivity of 83.3%. Additionally, we determined a baseline toe perfusion index cutoff value of 1.85 with a sensitivity of 80% and a specificity of 56%, consistent with the findings of Zu Z et al (25), who reported a sensitivity of 92% and specificity of 61.5% for the left toe area.
Notably, our study revealed a higher incidence of hypotension among patients with a baseline finger perfusion index >3.5 compared to those with a lower baseline index (53.2% vs. 17.9%, respectively). Similarly, previous studies have reported significant differences in hypotension incidence between groups categorized based on baseline perfusion index levels (19)(20), with all observed differences deemed clinically and statistically significant (P < 0.001).
Limitations: The perfusion index (PI) serves as a pivotal parameter in assessing a patient's vascular status, influenced by various environmental and biological factors such as patient movement, anxiety, and stress. To ensure precise baseline PI readings, our study employed stringent measures, including patient counseling and optimizing environmental conditions. To gain deeper insights into the patient's hemodynamic status, we correlated baseline Finger PI with non-invasive blood pressure measurements, despite the inherent time lag in the latter. However, it's essential to acknowledge that while this approach offers valuable information, it possesses limitations and cannot definitively confirm aortocaval compression without resorting to imaging techniques.
Furthermore, it's imperative to acknowledge the limitations inherent in our study, notably the relatively small sample size (n=75). Consequently, caution must be exercised in generalizing our findings to a broader population of parturients. Moreover, considering that PI is influenced by the vascular tone of digital vessels, it remains unclear how neuraxial block impacts this tone. Therefore, additional investigations are warranted to ascertain the universal applicability of PI as a non-invasive tool for predicting hypotension following spinal anesthesia (SAB).
Additionally, future research endeavors should focus on comparing PI with invasive hemodynamic monitoring to delineate its clinical utility more comprehensively. Until such studies are conducted and validated, it is prudent to approach the potential clinical application of PI with caution.

Parturients presenting with a perfusion index (PI) exceeding 3.5 are notably predisposed to experiencing hypotension subsequent to spinal anesthesia, possibly necessitating increased fluid administration and vasopressor support. Leveraging PI proves to be an effective strategy in anticipating hypotensive episodes among healthy parturients undergoing elective cesarean sections under subarachnoid block, with a baseline finger PI value of 3.55 and a baseline toe PI value of 1.85 identified as reliable predictors of hypotension. Incorporating continuous monitoring of toe PIs during the induction of spinal anesthesia may offer valuable insights into the likelihood of post-spinal hypotension and provide a practical reflection of aortocaval compression dynamics.
Acknowledgements

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