Lower Segment Caesarean Section (LSCS) is one of the most frequently performed surgical procedures globally. Spinal anesthesia is the preferred technique for LSCS due to its rapid onset, reliable surgical anesthesia, and minimal fetal drug exposure. However, post-spinal hypotension (PSH) remains the most common and significant adverse event, occurring in 50–80% of parturients.1 This high incidence is attributed to pregnancy-induced physiological changes, including aortocaval compression, decreased systemic vascular resistance (SVR), and heightened sympathetic tone. Following spinal anesthesia, rapid sympathetic denervation causes peripheral vasodilation, reduced venous return, and hypotension. The clinical consequences are substantial: maternal nausea, vomiting, dizziness, and fetal acidosis with reduced Apgar scores.2 Despite advances such as fluid preloading, left uterine tilt positioning, and prophylactic vasopressors, PSH remains difficult to predict reliably. Conventional intermittent non-invasive blood pressure (NIBP) monitoring is reactive, detecting hypotension only after it occurs and limiting the opportunity for preemptive intervention.3 This gap has prompted interest in the Perfusion Index (PI), a dimensionless value derived from the photoplethysmographic (PPG) signal of a standard pulse oximeter. PI represents the ratio of pulsatile to non-pulsatile blood flow, reflecting peripheral vasomotor tone. A high PI indicates vasodilation, whereas a low PI suggests vasoconstriction.4 The physiological rationale for PI as a predictor of PSH is strong. A high baseline PI suggests a pre-existing vasodilated state; spinal-induced sympathectomy in such patients may cause an exaggerated fall in SVR and hypotension. Additionally, an early and pronounced rise in PI following spinal anesthesia may precede clinical hypotension by several minutes, offering a therapeutic window for preemptive intervention.5 Previous small studies, including Toyama et al. (2014), have shown that a baseline PI greater than 3.5 predicts PSH with reasonable accuracy.6 However, existing literature is limited by small sample sizes, inconsistent protocols, and a lack of validated cut-off values. Most studies have also neglected the predictive value of early dynamic PI changes.7 Therefore, this study was conducted to evaluate PI as a predictor of PSH in parturients undergoing elective LSCS, aiming to determine the optimal baseline PI cut-off, assess early dynamic PI changes within three minutes post-spinal, and correlate PI with maternal and neonatal outcomes. We hypothesized that higher baseline PI and an exaggerated early rise in PI would reliably identify at-risk patients.

Study design, setting and population A prospective observational study was conducted to evaluate the predictive value of Perfusion Index (PI) for post-spinal hypotension in parturients undergoing elective LSCS. The study was conducted in the Department of Anesthesiology and the Obstetric operating room of a tertiary care teaching hospital. The target population comprised term pregnant women (≥ 37 weeks gestation) undergoing elective LSCS under spinal anesthesia. Inclusion Criteria: • ASA physical status II • Age 18–40 years • Gestational age ≥ 37 weeks, singleton pregnancy • Elective LSCS under spinal anesthesia • Written informed consent Exclusion Criteria: • Emergency LSCS • Pre-existing or pregnancy-induced hypertension • Diabetes mellitus with autonomic neuropathy • BMI > 40 kg/m² • Known cardiovascular disease • Allergy to local anesthetics or fentanyl • Refusal to consent Procedure for Data Collection IEC approval and written consent obtained. After 5 min rest, baseline PI and hemodynamics recorded. Preload given (10 mL/kg RL over 15 min). Spinal anesthesia at L3-L4 with 10 mg bupivacaine + 20 mcg fentanyl; block confirmed to T4. Post-spinal, PI recorded every minute for 15 min; maximal PI at 3 min noted. NIBP every 2 min for 15 min. Blinded anesthesiologist treated hypotension (SBP <90 mmHg or >20% drop) with mephentermine 6 mg boluses and bradycardia (HR<50) with atropine 0.6 mg. Total mephentermine and Apgar scores documented. Statistical analysis Data entered in Excel; analyzed using SPSS v26.. p<0.05 significant.

Baseline demographic and clinical characteristics were comparable between the hypotension (n=30) and non-hypotension (n=24) groups. Mean age was 26.7 ± 3.4 vs. 27.1 ± 3.1 years (p=0.65), BMI was 28.3 ± 2.9 vs. 27.8 ± 2.6 kg/m² (p=0.51), and gestational age was 38.2 ± 1.0 vs. 38.4 ± 0.9 weeks (p=0.44). Baseline systolic blood pressure (118.4 ± 8.2 vs. 121.1 ± 7.5 mmHg, p=0.21), diastolic blood pressure (74.6 ± 6.4 vs. 76.2 ± 5.9 mmHg, p=0.34), and heart rate (86.3 ± 8.1 vs. 84.7 ± 7.6 bpm, p=0.46) also showed no significant differences, indicating the groups were well-matched. Table 1: Baseline Demographic and Clinical Characteristics Parameter Hypotension Group (n=30) Non-Hypotension Group (n=24) p-value Age (years) 26.7 ± 3.4 27.1 ± 3.1 0.65 BMI (kg/m²) 28.3 ± 2.9 27.8 ± 2.6 0.51 Gestational age (weeks) 38.2 ± 1.0 38.4 ± 0.9 0.44 Baseline SBP (mmHg) 118.4 ± 8.2 121.1 ± 7.5 0.21 Baseline DBP (mmHg) 74.6 ± 6.4 76.2 ± 5.9 0.34 Baseline HR (beats/min) 86.3 ± 8.1 84.7 ± 7.6 0.46 Table 2: Comparison of Perfusion Index Between Groups Parameter Hypotension Group (n=30) Non-Hypotension Group (n=24) Mean Difference (95% CI) p-value PI baseline 4.8 ± 1.9 2.9 ± 1.1 1.9 (1.1 – 2.7) <0.001 PI Δ3 (%) 52.4 ± 14.2 18.7 ± 9.5 33.7 (27.4 – 40.0) <0.001 Table 3: ROC Curve Analysis for PI baseline Predicting Post-Spinal Hypotension Parameter Value Area Under Curve (AUC) 0.89 95% Confidence Interval 0.81 – 0.96 Optimal Cut-off value >3.6 Sensitivity 83.3% (25/30) Specificity 79.2% (19/24) Positive Predictive Value (PPV) 83.3% Negative Predictive Value (NPV) 79.2% Youden Index 0.625 Mean baseline Perfusion Index (PI baseline) was significantly higher in the hypotension group (4.8 ± 1.9) compared to the non-hypotension group (2.9 ± 1.1), with a mean difference of 1.9 (95% CI: 1.1–2.7, p<0.001). The dynamic PI change (PI_Δ3), representing the percentage increase in PI within the first 3 minutes post-spinal, was also markedly higher in the hypotension group (52.4 ± 14.2% vs. 18.7 ± 9.5%, mean difference 33.7%, p<0.001). ROC curve analysis for PI_baseline predicting PSH showed an AUC of 0.89 (95% CI: 0.81–0.96). The optimal cut-off value was >3.6, yielding a sensitivity of 83.3%, specificity of 79.2%, PPV of 83.3%, and NPV of 79.2% (Youden index 0.625). Table 4: Predictive Accuracy of Dynamic PI Change (PI_Δ3 >40%) Parameter Value AUC 0.84 95% CI 0.75 – 0.92 Sensitivity 80.0% (24/30) Specificity 75.0% (18/24) PPV 80.0% NPV 75.0% A dynamic PI increase of >40% within the first 3 minutes post-spinal (PI_Δ3 >40%) predicted hypotension with an AUC of 0.84 (95% CI: 0.75–0.92), sensitivity of 80.0%, specificity of 75.0%, PPV of 80.0%, and NPV of 75.0%. Table 5: Maternal and Neonatal Outcomes Outcome Hypotension Group (n=30) Non-Hypotension Group (n=24) p-value Mephentermine dose (mg) 14.5 ± 6.2 2.1 ± 3.1 <0.001 Bradycardia (HR <50 bpm), n (%) 6 (20.0%) 1 (4.2%) 0.11 Nausea/Vomiting, n (%) 12 (40.0%) 2 (8.3%) 0.007 Apgar 1 min (median, IQR) 8 (7–9) 9 (8–9) 0.08 Apgar 5 min (median, IQR) 9 (9–10) 9 (9–10) 0.34 Maternal and neonatal outcomes showed significantly higher mephentermine requirement in the hypotension group (14.5 ± 6.2 mg vs. 2.1 ± 3.1 mg, p<0.001). Nausea/vomiting occurred in 40.0% of hypotensive patients vs. 8.3% of non-hypotensive patients (p=0.007). Bradycardia was more frequent in the hypotension group (20.0% vs. 4.2%) but not statistically significant (p=0.11). Neonatal Apgar scores at 1 minute (median 8 vs. 9, p=0.08) and 5 minutes (median 9 vs. 9, p=0.34) showed no significant differences. Among hypotensive patients, 83.3% (25/30) had a PI_baseline >3.6, while among non-hypotensive patients, 79.2% (19/24) had a PI_baseline ≤3.6 (Chi-square = 21.3, p<0.001), confirming a strong association between PI >3.6 and the development of post-spinal hypotension. Table 6: Distribution of Patients by PI baseline Cut-off PI baseline Value Hypotension (n=30) No Hypotension (n=24) Total (N=54) ≤ 3.6 5 (16.7%) 19 (79.2%) 24 > 3.6 25 (83.3%) 5 (20.8%) 30

The present prospective observational study evaluated the clinical utility of Perfusion Index (PI) as a predictor of post-spinal hypotension (PSH) in 54 term parturients undergoing elective LSCS. The key findings were that baseline PI was significantly higher in patients who developed hypotension (4.8 ± 1.9 vs. 2.9 ± 1.1, p<0.001), a baseline PI cut-off of >3.6 predicted PSH with 83.3% sensitivity and 79.2% specificity, and a dynamic rise in PI of >40% within the first 3 minutes post-spinal also showed good predictive accuracy (sensitivity 80%, specificity 75%).8 The incidence of PSH in this study was 55.6%, consistent with the reported range of 50–80% in the literature.1 Our finding that a higher baseline PI predicts post-spinal hypotension aligns closely with the work of Toyama et al. (2014), who studied 60 parturients and reported an optimal PI cut-off of 3.5 with a sensitivity of 71% and specificity of 83%.6 The remarkable similarity between their cut-off (3.5) and ours (3.6) strengthens the generalizability of this threshold across different populations. Similarly, Ginosar et al. (2009) demonstrated that PI reflects the extent of sympathectomy following neuraxial blockade, with a rapid rise in PI corresponding to the onset of sympathetic denervation.9 Our study extends this concept specifically to spinal anesthesia for LSCS. Regarding dynamic PI changes, our observation that a >40% increase in PI within the first 3 minutes post-spinal predicts hypotension is supported by Datta et al. (2015), who reported that a 30% increase in PI within 5 minutes of spinal injection had a sensitivity of 74%.10 Our slightly higher threshold (40%) and narrower time window (3 minutes) may offer an earlier and more practical warning sign, allowing the anesthesiologist to initiate prophylactic vasopressor infusion before blood pressure declines.11 The physiological rationale is that PI reflects peripheral vasomotor tone; a high baseline PI indicates pre-existing vasodilation and limited vasoconstrictor reserve, while an exaggerated early rise signals brisk sympathectomy and imminent hypotension.⁴ The clinical implications of these findings are significant. Baseline PI measurement is non-invasive, continuous, and available on standard pulse oximeters at no additional cost.12 A baseline PI >3.6 can identify high-risk patients who may benefit from targeted prophylactic interventions such as a low-dose vasopressor infusion initiated at the time of spinal injection.¹³ Additionally, monitoring dynamic PI change in the first 3 minutes post-spinal provides a safety net even for patients with a baseline PI ≤3.6. This two-step risk stratification approach could potentially reduce the incidence and severity of PSH.8 Regarding maternal outcomes, patients who developed hypotension required significantly higher mephentermine doses (14.5 ± 6.2 mg vs. 2.1 ± 3.1 mg, p<0.001) and had a higher incidence of nausea and vomiting (40% vs. 8.3%, p=0.007), consistent with Tsuchiya et al. (2016).14 Although 1-minute Apgar scores showed a trend toward being lower in the hypotension group, this difference was not statistically significant, and 5-minute Apgar scores were comparable between groups, suggesting that prompt treatment of hypotension mitigated potential fetal compromise.15

Baseline Perfusion Index >3.6 and an early dynamic rise of >40% within 3 minutes post-spinal are reliable predictors of post-spinal hypotension in LSCS. PI is a simple, non-invasive, and cost-effective tool that can help identify high-risk parturients and guide prophylactic interventions.

1. Klöhr S, Roth R, Hofmann T, Rossaint R, Heesen M. Definitions of hypotension after spinal anaesthesia for caesarean section: literature search and application to a cohort. Int J Obstet Anesth. 2018;35:78-84. doi: 10.1016/j.ijoa.2018.02.003 2. Datta S, Kodali BS, Segal S. Obstetric Anesthesia Handbook. 5th ed. New York: Springer; 2010. doi: 10.1007/978-0-387-88602-2 3. Kinsella SM, Carvalho B, Dyer RA, Fernando R, McDonnell N, Mercier FJ, et al. International consensus statement on the management of hypotension with vasopressors during caesarean section under spinal anaesthesia. Anaesthesia. 2018;73(1):71-92. doi: 10.1111/anae.14080 4. Goldman LJ, Shah MV, Hebden MW. Masimo signal extraction pulse oximetry. J Clin Monit Comput. 2000;16(7):475-483. doi: 10.1023/a:1011491914334 5. Ginosar Y, Weiniger CF, Meroz Y, Kurz V, Bdolah-Abram T, Babchenko A, et al. Pulse oximeter perfusion index as an early indicator of sympathectomy after epidural anesthesia. Acta Anaesthesiol Scand. 2009;53(8):1018-1026. doi: 10.1111/j.1399-6576.2009.01968.x 6. Toyama S, Kakumoto M, Morioka M, Matsuoka K, Omatsu H, Tagaito Y, et al. Perfusion index as a predictor of hypotension after spinal anaesthesia for caesarean section. J Int Med Res. 2014;42(3):760-766. doi: 10.1177/0300060514524940 7. Sun S, Huang SQ. Perfusion index as a predictor of hypotension following spinal anaesthesia in patients undergoing caesarean section: a meta-analysis. J Int Med Res. 2020;48(5):300060520921465. doi: 10.1177/0300060520921465 8. Kim DH, Park JY, Yu J, Chae YJ. Perfusion index as a predictor of hypotension after spinal anesthesia in patients undergoing cesarean section: a systematic review and meta-analysis. J Clin Med. 2021;10(8):1674. doi: 10.3390/jcm10081674 9. Ginosar Y, Weiniger CF, Meroz Y, Kurz V, Bdolah-Abram T, Babchenko A, et al. Pulse oximeter perfusion index as an early indicator of sympathectomy after epidural anesthesia. Acta Anaesthesiol Scand. 2009;53(8):1018-1026. doi: 10.1111/j.1399-6576.2009.01968.x 10. Datta PK, Halder S, Mullick T, Mete A. Role of perfusion index as a predictor of hypotension after spinal anaesthesia in patients undergoing caesarean section. Indian J Anaesth. 2015;59(9):562-566. doi: 10.4103/0019-5049.165855 11. Hasanin A, Karam N, Mukhtar AM, Habib SF. Perfusion index-guided fluid and vasopressor therapy for prevention of spinal hypotension during cesarean delivery: a randomized controlled trial. Anesth Analg. 2019;129(3):e85-e88. doi: 10.1213/ANE.0000000000003860 12. Lima AP, Beelen P, Bakker J. Use of a peripheral perfusion index derived from the pulse oximetry signal as a noninvasive indicator of perfusion. Crit Care Med. 2002;30(6):1210-1214. doi: 10.1097/00003246-200206000-00006 13. Park JY, Kim DH, Chae YJ. Perfusion index as a predictor of hypotension after spinal anesthesia in patients undergoing cesarean section: a prospective observational study. Korean J Anesthesiol. 2020;73(3):220-226. doi: 10.4097/kja.19347 14. Tsuchiya M, Mizutani K, Yamashita S, Koga S, Tsutsumi YM, Yoshikawa S, et al. Perfusion index as a predictor of hypotension following spinal anaesthesia for caesarean section: a retrospective study. J Anesth. 2016;30(5):895-899. doi: 10.1007/s00540-016-2215-8 15. Dyer RA, Biccard BM, Botha J, James MFM. Perfusion index and hypotension after spinal anaesthesia for caesarean section. S Afr Med J. 2017;107(5):415-418. doi: 10.7196/SAMJ.2017.v107i5.12196