European Journal of Cardiovascular Medicine

Spinal anaesthesia was the standard anaesthetic procedure for elective caesarean delivery. (1) (2) Spinal anaesthesia has now emerged as the technique of choice among regional anaesthetic techniques for routine scheduled caesarean delivery. This was because it was fast, reliable and cost-effective. One of the common side effects consists of a reduction of systemic vascular resistance, with systemic hypotension. (3) Pregnant women were more sensitive to local anaesthetics, less  responsive to vasopressors and had lower mean arterial pressure (MAP) at the term. (4) Hence, the parturient can develop profound hypotension following central neuraxial blockade for the lower segment caesarean section (LSCS). Maternal hypotension can have serious adverse effects on neonatal and maternal outcomes. (5) Approximately 70% of parturients develop hypotension following spinal anaesthesia as compared to only about 33% of non-pregnant patients and the degree of hypotension was more severe and abrupt. (6) The clinical importance of this adverse effect had been shown in several studies which proved that hypotension correlated with morbidity and mortality. (7) Hypotension was one of the most frequent adverse events of spinal anaesthesia with an incidence of 15-33% up to 95% for caesarean section. (8) Spinal anaesthesia-induced hypotension during Caesarean delivery was the result of decreased vascular resistance due to sympathetic blockade,(9) & decreased cardiac output due to blood pooling in blocked areas of the body. (4) (5) Although Aorto-caval compression by the gravid uterus and baseline volume status are known to affect the degree of hypotension, baseline peripheral vascular tone may also have an influence. (10) Peripheral vascular tone is decreased in parturients at term, especially in multiparous patients. (8) (11) (12) Decreased peripheral vascular tone results in blood volume being trapped in the extremities even before spinal anaesthesia, and the sympathetic blockade with spinal anaesthesia would further increase the blood pooling. (13) Therefore, parturients with low baseline vascular tone may be at an increased risk of developing hypotension after spinal anaesthesia. Heart rate and Non-invasive blood pressure (NIBP) were the commonest and standard methods of hemodynamic monitoring intra-operatively, but beat-to-beat variation in perfusion dynamics cannot be measured by this method and limits its efficacy. (14) Therefore perfusion index was used to assess the perfusion dynamics and was considered a non-invasive method to detect the likelihood of the development of hypotension following SAB. Peripheral perfusion index (PI) changes with local blood volume pulsations and intravascular pulse pressure, which are influenced by vascular wall distensibility or tone. Low PI means vasoconstriction, while high PI means vessel dilation..(15)(16) (17) Measuring finger PI >3.5 before spinal anaesthesia for caesarean delivery can identify women at risk for spinal hypotension. Low toe PI before spinal anaesthesia shows a higher risk due to auto-cavel compression by a gravid uterus. Right to PI is more often affected. Some of the study's predictors were baseline heart rate, heart rate variability, body mass index (15), advanced age, pre-operative anxiety(17), and perfusion index (18). This study aimed to evaluate whether baseline perfusion index can predict post-spinal hypotension in LSCS and to find the correlation between the finger and right toe in the prediction of post-spinal hypotension.

A prospective observational, single-blind study to determine the sensitivity and specificity of perfusion index in the right toe and index finger as a predictor of post-spinal hypotension in parturients undergoing LSCS, was conducted in the Department of Anaesthesiology & Critical Care, Dr S. N. Medical College, Jodhpur for 12 months. Ethical clearance from the institutional Ethical committee was obtained before the study. We included 75 patients of who were undergoing elective Lower Segment caesarean procedures, of ASA-II. Our Exclusion criteria were, Emergency cases, Unavailability of monitoring sites (minimum two-one in upper limb and one in lower limb) due to any reason, Hypertensive patient or patient on medication for Hypertension, Diabetes Mellitus patient and gestational diabetes mellitus, Obese (BMI =30 or above), Patient unfit for spinal anaesthesia due to any reason like coagulopathy, local infection at site, Raised Intra Cranial Tension, Indeterminate neurological disease, Vertebral Column disorder etc., Parturient with Placenta-previa, Pre-eclampsia, Cardiovascular Cerebrovascular disease, Gestational DM, Gestational age <36 or >40 weeks. Pre-anaesthetic check-up was done. After obtaining Informed consent from the patients and relatives, an airway examination was also done and preoperative fasting was kept as per Indian Society of Anaesthesiologists (ISA) fasting guidelines i.e. 8 hours for fatty meals, 6 hours for solids and, 4 hours for milk and 2 hours for clear liquid was ensured. (19) Upon arrival at the operation theatre, Parturients were preloaded with Ringer lactate and given Metoclopramide and Ranitidine as pre-anaesthetic medication. Spinal anaesthesia was then given in the L3-L4 interspinous space with a 25G Quincke’s spinal needle in a sitting position while heart rate, NIBP, respiratory rate, Sp02, and perfusion index were monitored. Bupivacaine was injected after confirming the free flow of cerebrospinal fluid. Vital parameters were monitored every 2 minutes till the 15th minute and then every 5 minutes till the end of 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. ROC curve compared baseline PI with hypotension of 75 patients.

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 (Table 1). 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 parturients 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 ROC analysis revealed that baseline Finger PI was suitable for detecting parturients at risk for hypotension (AUC=0.73, P=0.001; Figure 1). The baseline Finger PI cut-off point that predicted hypotension as determined by the ROC analyses was 3.55 with a sensitivity of 83.3% [95% confidence intervals (CI)] and a specificity of 51.1% (95% CI). The baseline Toe PI cut-off point that predicted hypotension as determined by the ROC analysis was 1.85 with a sensitivity of 80% [95% confidence intervals (CI)] and a specificity of 56% (95% CI). (Table 2)

In the present study, all the two groups (based on cut off value of baseline Finger PI >3.5 and 3.5 cut off and 26.18±3.96 years in group 3.5cut off and 61.18±6.90 kg in group II, P=0.873), mean height (148.74±4.78cm in group >3.5 cut off and 150.29±3.93 cm in group <3.5 cut off, P=0.155), it was not found to be statistically significant. Similar findings were found in the previous studies conducted by other authors like Toyama et al.(19), Duggappa et al.(20), Dr Joseph George et al.(21) Mowafi et al(2) found that decreased PI indicates vasoconstriction after epidural test doses. Ginosar et al(22) showed that increased PI indicates sympathectomy after epidural anaesthesia. Lima et al(23) found PI useful in identifying inadequate perfusion in critically ill patients. However, Yokose et al(24) found PI had no predictive value for hypotension in pregnant women undergoing LSCS after neuraxial block. Differences in methodology may explain this variation. Baseline PI values from a pulse oximeter could assess hypotension following SAB in pregnant women undergoing LSCS. In a study of parturients undergoing LSCS, Toyama et al.(19) found a baseline PI cut-off of 3.5 for predicting hypotension, with a sensitivity of 81% and specificity of 86%. Duggappa DR et al.(20) found a cut-off of 3.85, with a sensitivity of 69.84% and specificity of 89.29%. In another study, Dr Joseph George et al.(21) found a cut-off of 3.6, with a sensitivity of 80% and specificity of 60%. In our study with 75 parturients found a similar baseline Finger PI cut-off of 3.55 but with a lower specificity of 51.1% and higher sensitivity of 83.3%. The present study determined a baseline Toe PI cut-off value of 1.85 with a sensitivity of 80% and a specificity of 56%. Zu Z et al(25) found a higher sensitivity of 92% and specificity of 61.5% with an optimal cut-off point of 2.2 for the left toe area under the ROC curve. The optimal cut-off point for the right toe was 1.3 with a sensitivity of 61.9% and specificity of 84.6%, comparable to the present study's cut-off value. Both studies found that toe PIs did not change in parturients with hypotension after spinal anaesthesia, but increased among those who did not develop hypotension, indicating aortocaval compression clinically. Our study found that patients with a preoperative pulse index (PI) value greater than 3.5 had a 53.2% incidence of low blood pressure compared to 17.9% in those with a PI value less than 3.5. Another study reported that parturients with high baseline PI had an 82% incidence of hypotension, compared to 25% in those with low baseline PI(19). Similarly, another study revealed the incidence of hypotension was 71.42% in Group II compared to 10.5% in Group I.(20) All differences were clinically and statistically significant with a P-value of less than 0.001.
Limitations: The perfusion index (PI) is a critical parameter in assessing a patient's vascular status and is known to be susceptible to a variety of environmental and biological factors, including patient movement, anxiety, and stress. To address this, we implemented rigorous measures to ensure accurate baseline readings of PI, including counselling the patient and creating optimal environmental conditions. To better understand the patient's hemodynamic status, we correlated the baseline Finger PI with non-invasive blood pressure, which measures with a time lag. It's worth noting that while this approach provides valuable insight, it has limitations and cannot confirm aortocaval compression without imaging techniques. It's important to recognize that our study was limited by a small sample size (n=75). Therefore, our results cannot be generalized to a larger population of parturients. Additionally, as PI is dependent on the vascular tone of digital vessels, the question remains whether neuraxial block affects this tone. Further studies are required to determine the utility of PI as a universal non-invasive tool to predict hypotension following SAB. Furthermore, additional studies should be conducted to compare PI with invasive hemodynamic monitoring to better understand its usefulness. It's imperative to emphasize that the potential utility of PI in clinical practice should be approached with caution until further studies are completed.

Parturients with PI >3.5 are at a higher risk of developing hypotension after spinal anaesthesia and may require more fluids and vasopressors. PI is an effective tool for predicting hypotension in healthy parturients undergoing elective caesarean section under subarachnoid block, with a baseline Finger PI value of 3.55 and a baseline Toe PI value of 1.85 for predicting hypotension. Continuous monitoring of toe PIs during induction of spinal anaesthesia may help predict post-spinal hypotension and reflect aorto-cavel compression.
Acknowledgements

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