Background : Hypotension is most common complication of spinal anesthesia for patient undergoing LSCS. Hypotension can cause adverse outcome for both maternal and fetal .Early detection and treatment for hypotension to improve maternal and fetal outcome .Perfusion index (P.I) during spinal anesthesia for predicting hypotension in a patient undergoing LSCS. Methodology: In this study, 40 parturient belonging to ASA2 posted for elective LSCS. Under spinal anesthesia with adjusted dose of hyperbaric bupivacaine 0.5% at the L2-L3 or L3-L4 interspace .MAP ,HR, Spo2 and P.I. were recorded at 1 minute interval after the SAB up to 10 minute and then 5 minute interval till end of surgery and compared with baseline hemodynamics parameter and perfusion index . Results :Mean age of the case is 26.925 with 4.95 sd. Mean SBP for 640 entries is 107.39 with 12.11 sd. Mean P.I. for 640 entries is 3.56 with 2.04 sd. There is a significant negative correlation (p<0.0001) between SBP and P.I. suggesting that P.I. increased in patient with hypotension .There is a statistically significant mean difference between before and after oxytocin bolus with hemodynamic variable of SBP ,DBP ,MAP SPO2 and P.I. |
Conclusion: The P.I. is useful tool for predicting hypotension in parturient undergoing LSCS under spinal anesthesia .
One of the most popular surgical procedures worldwide is the caesarean section[1]. Subarachnoid block is the preferred form of anaesthesia employed for this procedure as it is quick to administer, provides a good surgical field and ensures good post operative pain relief[7]. The incidence of hypotension following spinal anaesthesia in the normal population is 15-33%, whereas in parturients it increases to 60-80% which can have detrimental effects on both mother and foetus [2,7]. There are a multitude of reasons why hypotension is so common in the obstetric population. The physiological changes in a full term gravid female result in a decrease in the sympathetic tone and peripheral pooling of blood, aortocaval compression in the supine position[3], lumbar lordosis and reduced CSF volume, increased sensitivity to local anaesthetics and decreased sensitivity to vasoconstrictors[4,5,6]. Spinal anaesthesia induced sympathectomy further exacerbates the condition and can result in severe hypotension in some patients.
Routinely hypotension is detected by the Non-Invasive blood pressure readings, set at fixed intervals, followed by treatment of hypotension using fluid and vasopressor administration. This method's effectiveness is, however, constrained by the inability to measure beat-to-beat fluctuation in perfusion dynamics. Perfusion index (PI) is defined as the ratio of pulsatile blood flow to non‑pulsatile blood flow in the peripheral vascular tissue, measured using a pulse oximeter based on the amount of Infrared light absorbed[9]. It is a cheap, dynamic and non-invasive method which can help predict hypotension and enable early intervention. In our study we investigate the serial correlation between perfusion index and hemodynamic variables in parturients following subarachnoid block and also the effect of oxytocin administration on the same.
A prospective observational study was conducted from October 2021 to November 2021 in a tertiary care hospital in south India after attaining institutional ethics committee clearance. Each participant provided their written, informed permission in the study. A prospective observational study was used for the research.
Inclusion criteria
Pregnant women posted for elective caesarean section under spinal anaesthesia belonging to American society of Anaesthesiologists Physical Status (ASA-PS) Class II.
Exclusion Criteria
-Contraindications to Neuraxial Anaesthesia
-POG <36w or >41w
-Cardiovascular comorbidities
-Obstetric Complications
-Peripheral Vascular disease
-Disorders of autonomic nervous system
Anaesthetic technique
In this study, 40 parturients belonging to ASA II posted for elective LSCS under spinal anaesthesia were included. Standard monitoring with 3-lead electrocardiography, automated non-invasive blood pressure (NIBP), pulse oximetry (SpO2) and perfusion index (PI) was performed for baseline values and intraoperative monitoring done with Nikon Kohden LifeScope VS. Baseline haemodynamic parameters and continuous perfusion index were measured with patient in supine position using a pulse oximeter probe attached to the left index finger. Systolic blood pressure (SBP), Diastolic blood pressure (DBP), Mean arterial pressure(MAP), Heart rate (HR), SpO2 and PI were recorded at 1 min intervals after the SAB up to 10 min and then at 5 min intervals till the end of surgery. Intravenous (IV) access was secured in the left hand using a 18G IV cannula. Each parturient was coloaded with 500 ml of Ringer lactate. Spinal anaesthesia was performed by an anaesthesiologist blinded to the baseline PI values, using Quincke’s 26-G spinal needle in left lateral decubitus position with height adjusted dose of injection hyperbaric bupivacaine 0.5% at the L2-L3 or L3–L4 interspace. Sensory block level was checked after 1 and 5 mins of spinal anaesthesia administration. Hypotension was defined as a decrease in SBP > 20% or MAP <65mmHg and treated with IV bolus of 6 mg of ephedrine and 100 ml of Ringer lactate. Bradycardia was defined as HR <60 beats/min and treated with injection atropine 0.6 mg IV bolus. Following extraction of the baby, Injection oxytocin 2.5 units IV bolus was given followed by an infusion of Oxytocin 7.5 units over the next 1 hour. Patients who required additional oxytocics and/or additional surgical interventions and patients with intraoperative blood loss greater than 1000ml were excluded from our study.
Statistical analysis:
Data was entered in Microsoft excel 2019 and was analyzed using MedCalc version 20.0.14. The quantitative variables were expressed as mean, standard deviation and range. The strength and direction of correlation between Systolic Blood Pressure (SBP) and Perfusion Index was assessed using Pearson’s correlation coefficient (r). The difference in the SBP, DBP, MAP and perfusion index before and after administration of IV oxytocin was assessed using paired t-test and p value of <0.05 was considered as significant. Correlation between before and after values was done using Pearson’s correlation coefficient (r). The positive “r” value indicates positive correlation between two variables and a negative “r” value indicates negative correlation. The significance of correlation was considered if p value is < 0.05.
Total number of cases = 40
Mean age of the cases ± SD = 26.925 ± 4.95 years
Mean Height ± SD = 5’6” ± 0.19
Mean weight ± SD = 64.92 ± 6.33 Kgs
Table 1: Tailed correlation of SBP and PI
Parameters |
No. of entries |
Mean |
Std. Deviation |
Range |
SBP (in mmHg) |
640 |
107.39 |
12.11 |
62-148 |
Perfusion Index |
640 |
3.56 |
2.04 |
0.6-11 |
Number of entries(N) = 640
Correlation coefficient (r) = -0.1805
95% confidence interval for r = -0.2544 to -0.1045
Significance = p <0.0001
The negative Pearson’s correlation coefficient indicated that there is inverse relation between Systolic Blood Pressure (SBP) and Perfusion Index (PI) suggesting that PI increased in patients with hypotension. This is clinically significant (p<0.0001)
Figure 1: Correlation between SBP and PI.
Table 2: Correlation between hemodynamic variables and perfusion index before and after oxytocin bolus
CORRELATION |
NO. OF CASES |
NO. OF PAIRED ENTRIES |
CORRELATION CO-EFFICIENT |
95% CI FOR “r” VALUE |
SIGNIFICANCE (P VALUE) |
BEFORE HR AND AFTER HR |
40 |
258 |
0.398 |
0.2903 TO 0.4963 |
<0.0001 |
BEFORE SBP AND AFTER SBP |
40 |
258 |
0.090 |
-0.03 TO 0.21 |
0.1455 |
BEFORE DBP AND AFTER DBP |
40 |
258 |
0.221 |
0.1025 TO 0.3349 |
0.0003 |
BEFORE MAP AND AFTER MAP |
40 |
258 |
0.011 |
-0.1106 TO 0.1336 |
0.8522 |
BEFORE PI AND AFTER PI |
40 |
258 |
0.5699 |
0.4812 TO 0.6470 |
<0.0001 |
BEFORE SPO2 AND AFTER SPO2 |
40 |
258 |
0.1868 |
0.06618 TO 0.302 |
0.0026 |
Among all the parameters, there is significant difference in Heart Rate (HR), DBP, PI and SPO2 before and after oxytocin bolus as shown in Table 3 .
The mean DBP, mean SBP, mean MAP showed decreasing trend after oxytocin bolus. Whereas, the mean Perfusion Index is greater after oxytocin bolus when compared to before oxytocin. The comparison's p value is statistically consequential. However, for Heart rate, the difference between before and after oxytocin bolus was not statistically significant.
Table 3: Correlation between P.I and haemodynamic parameters before and after Oxytocin bolus
PARAMETERS |
MEAN VALUES (BEFORE OXYTOCIN BOLUS) |
MEAN VALUES (AFTER OXYTOCIN BOLUS) |
P VALUE |
HEART RATE |
90.74 |
88.77 |
0.2468 |
SPO2 |
99.32 |
96.37 |
0.0066 |
SBP |
107.70 |
104.33 |
0.036 |
DBP |
65.79 |
60.29 |
< 0.0001 |
MAP |
78.96 |
74.89 |
0.0008 |
PI |
2.78 |
3.83 |
<0.0001 |
Hypotension following subarachnoid block is a common finding in the obstetric population undergoing LSCS. This is because of the physiological changes observed in term gravida patients which are exaggerated with spinal induced sympathectomy. Traditional methods to predict which patients are more susceptible to developing severe hypotension are not as effective. Early detection of patients susceptible to hypotension can lead to additional interventions to prevent the complications to the mother and fetus.
Perfusion index is a non-invasive method of assessing peripheral perfusion using a pulse oximetry probe. The fingertip pulse oximeter estimates the SpO2 from differential absorption of red and infrared light by the tissues. Red light (660nm) is preferentially absorbed by deoxygenated blood and infrared light (940nm) is absorbed by oxygenated hemoglobin. The pulse oximeter computes the ratio between these two signals and relates this ratio to the arterial oxygen saturation, using an inbuilt algorithm. Pulse oximeters discriminate between arterial blood and other components by determining the change in transmitted light caused by the flow of arterial blood. The absorbance of both wavelengths has a pulsatile component, which represents changes in the volume of arterial blood between the source and the detector. The non pulsatile component is from connective tissue, bone and venous compartment. The perfusion index (PI) is the ratio of the pulsatile component (arterial) and non‑pulsatile component of light reaching the detector. The PI’s values range from 0.02% for a very weak pulse to 20% for an extremely strong pulse[8]. Increase in PI indicates a vasodilated state with increased blood flow whereas a decrease more likely reflects a vasoconstricted state. Parturients with a high baseline perfusion index are expected to have lower peripheral vascular tone and hence are at higher risk of developing hypotension following spinal anaesthesia.
Ginosar et al. demonstrated that increase in PI following epidural anaesthesia is a clear and reliable indicator of sympathectomy[9]. Our study shows that there is a statistically significant correlation between increase in PI values and decrease in Systolic blood pressure observed after subarachnoid block[9]. This could be due to sympathectomy of the upper limb causing vasodilatation in the hand. The same was observed by Roshana Prasad Mallawaarachchi et al in her study of serial PI after SAB[1].
In a study conducted by Dugappa et al a baseline PI value of greater than 3.5 was taken to indicate an increased likelihood of developing hypotension post SAB[5]. Toyama et al.35 who did regression analysis and ROC curve analysis, concluded that a baseline perfusion index cut‑off point of 3.5 could be used to identify parturients at risk for such hypotension[4].
In our study we have compared PI values throughout the intraoperative period against the Systolic BP, Diastolic BP and HR along with the changes with administration of oxytocin.
In our study, the negative Pearson’s correlation coefficient indicated that there is inverse relation between Systolic Blood Pressure (SBP) and Perfusion Index (PI) suggesting that PI increased in patients with hypotension and as hypotension was corrected, PI values decreased accordingly. This is clinically significant finding as we can use PI values to monitor the effectiveness of our interventions.
Similar findings were published in a study by Roshana Prasad Mallawaarachchi et al. where a highly significant correlation was found between increase in perfusion index and the hypotension.
We also studied the correlation between PI and hemodynamic variables before and after oxytocin bolus. The mean PI is greater after oxytocin bolus when compared to before oxytocin which also coincides with a decrease in SBP, DBP and MAP after oxytocin administrations- statistically significant. Thus, PI can also be used to predict patients at risk for hypotension post larger oxytocin boluses.
P.I can be used to predict hypotension in parturients undergoing caesarean section under sub arachnoid block. Serial PI values rather than baseline PI measurements are useful in predicting hypotension in patients and in assessing the response to vasoconstrictors and fluid boluses in these patients, enabling early and effective interventions in this population. PI can also be used to predict hypotension following Oxytocin administration in these patients.
Acknowledgement: Nil
Conflict Of Interest: None
Financial Support: None
Ethics Statement: The ethical clearance for the study was obtained from the Institutional ethics committee of SS institute of Medical Sciences And Research Centre , Davangere, Karnataka ( IERB 521 – 09/03/2022) .