European Journal of Cardiovascular Medicine

Post spinal hypotension is caused by decreased systemic vascular resistance due to the sympathetic blockade. Compression of Inferior vena cava by the gravid uterus further worsens this hypotension by decreasing the venous return. Venous stasis occurs in lower extermities. Nearly 70% of the patients experience hypotension following spinal anaesthesia during cesarean delivery ^[1]. Hemodynamic changes in the mother plays a crucial role due to the vulnerability of the fetus. In a multivariate analysis done by Ngan Kee and Lee et al. ^[3] maximum decrease in maternal systolic pressure was determined to be a significant factor which affects umbilical artery pH. Postspinal hypotension becomes a concern in pregnant women since it can affect maternal and fetal wellbeing resulting in maternal nausea, vomiting, fetal acidosis and depressed Apgar scores. According to the meta analysis done by Reynolds F et al. ^[2] cord blood pH was found to be significantly lower and the base deficit was higher in the parturients who underwent cesarean section under spinal anaesthesia compared with epidural and general anaesthesia. The femoral vein, a distal tributary of inferior vena cava is being close to the body surface and it can be easily detected by a high-frequency ultrasound probe. In the current era, ultrasonographic studies and techniques have gained popularity due to its wide availability, portability, less time consuming and non invasiveness. Therefore, in our study we hypothesized that the increased transverse diameter of the femoral vein will predict significant post spinal hypotension in women undergoing cesarean delivery.

The aim of the study is to determine the correlation between diameter of femoral vein before spinal anesthesia and Post spinal hypotension in patients posted for Cesarean Section and assess the use of Ephedrine in treating hypotension.

This Prospective observational cohort study was conducted for a period of 6 months at Government Rajaji Hospital, Madurai medical college. The study population involves 60 parturients between the age group 18– 40 years, full-term (> 37-week gestation) Primi gravida with singleton pregnancy of height 156 – 165 cm belonging to American Society of Anesthesiology Physical Status (ASA) score of II posted for Cesarean section under Spinal anesthesia who attained Upper sensory level of T4 – T5. Patient Refusal, ASA PS III–IV, Contraindications for spinal anaesthesia, Emergency cesarean delivery, Postdated pregnancy (> 42 weeks), Previous history of abdominopelvic surgery including LSCS, Chronic hypertension, Gestational hypertension or preeclampsia, Placenta previa, Abruptio placenta, Multiple gestation, Obese parturients with Body mass index [BMI] ≥ 35, Fetal anomalies and Peripheral vascular disease were included in the exclusion criteria.

Parturients were instructed to fast for at least 6 hours prior to the cesarean section. After explaining the procedure and getting informed written consent, Ultrasound measurements were recorded in the supine position 15 mins before spinal anesthesia. High-frequency linear array probe (5–12 MHz) was used for the measurement of the transverse diameter of right femoral vein. Transverse diameter was measured at end – expiration after visualizing in M-mode as shown in image 12.1. Parturient was then shifted to the operating room. 18 G intravenous cannula was secured and continuous monitoring done with standard monitors like pulse oximetry, non invasive blood pressure and electrocardiography. The first two measurements of resting blood pressure and heart rate with the parturient in the supine position were recorded and the average values were documented as baseline measurements. Spinal anaesthesia was given in right lateral position with inj. 0.5% Bupivacaine 2 cc and the patient was moved immediately to supine posture. A wedge is positioned beneath the right hip to cause left uterine displacement. Patients with upper sensory level below T6 and above T5 were excluded from the study. Intraoperatively, pulse rate, blood pressure and oxygen saturation were monitored continuously. Measurements recorded at 5 mins, 10 mins, 15 mins, 30 mins and 60 minutes were analyzed. Total intravenous fluids given before delivery, total dose of ephedrine and oxytocin used were recorded. In our study, we have defined hypotension as systolic blood pressure less than 20% from the baseline measurement. The following parameters were observed: Transverse diameter of femoral vein, Age, Weight, Height, Baseline BP, Baseline HR, Total intravenous fluid before delivery, Total dose of Ephedrine and Total dose of Oxytocin.

Figure 12.1: Photograph taken while measuring transverse diameter of femoral vein using M - Mode ultrasonography.

The collected data were analysed with IBM SPSS Statistics for Windows, Version 29.0. The central tendency of measured femoral vein diameter and mean arterial pressure is expressed in Mean and standard deviation. To find the efficacy of the transverse diameter of femoral vein to predict the Hypotension the Receiver Operating Characteristics curve (ROC) was used with Sensitivity, Specificity and Cut-off. In all the above statistical tools the probability value 0.05 is considered as significant level.

Sixty parturients were included in the study, of which hypotension was occurred in 20 parturients [33%] and 40 parturients [67%] does not experience hypotension as illustrated in the pie chart 12.2. The patients were thus categorized into hypotension group and No – hypotension group for comparing the observed parameters. There was no significant difference in age between both the groups with the mean of age 26.0 in hypotension group and 26.3 in the No – hypotension group. As enlisted in table 12.3 the mean body mass index was 26. 8 in hypotension group whereas it was 25.0 in the No hypotension group. Hence there is no significant difference in body mass index in both the groups.

Figure 12.2: illustrating incidence of hypotension in our study population

As featured in the bar chart 12.4, patients with various ranges of right femoral vein diameter observed in our study were as follows: 10% of parturients had less than 10 mm diameter, 28% between 10 – 10.9 mm, 23% between 11 – 11.9 mm, 27% between 12 – 12.9 mm and 12% above 13 mm respectively. By ROC analysis, the transverse diameter of the femoral vein measured in the supine position can predict paturients at risk of hypotension with AUC of 0.718 but with a p – value of 0.006 [Table 12.5]. The cut off value for femoral vein diameter was found to be 11.8 mm which exhibited a sensitivity of 75% and specificity of 67.5% as shown in table 12.6. The ROC curve for femoral vein diameter predicting post spinal hypotension is depicted in figure 12.7.

Table 12.3: enlisting the influence of various parameters on hypotension and no hypotension group

Bar graph 12.4: showing the proportion of parturients with different ranges of femoral vein diameter

Table 12.5: Table displaying Area under ROC curve with p – value and 95% confidence interval

Table 12.6: Table featuring cut off value of femoral vein diameter

Figure 12.7: Receiver operator curve for femoral vein diameter

Table 12.8: Comparison of parameters based on cut off value of femoral vein diameter

These patients were grouped into two based on the cut off value of femoral vein diameter [Table 12.8]. There was no significant difference in fluid administered before delivery in both groups [p – value = 0.889].  Meanwhile use of ephedrine was higher [Mean ephedrine use = 16.64] in patients with femoral vein diameter more than 11.8 mm which is statistically significant with a p – value of 0.004. There was no noticeable difference in oxytocin use in both the groups [p – value = 0.519].

Spinal anaesthesia is associated with decreased venous return which affects the preload and reduced systemic vascular resistance which causes decrease in afterload. Nearly 75% of the blood volume resides in the venous system. It is noteworthy that venodilation predominates after spinal anaesthesia. The reason why these parturients are more prone to hypotension is explained by the following factors: Normally in an uncomplicated pregnancy systemic vascular resistance decreases by about 20%. This occurs due to the vasodilatory effects of progesterone and prostaglandins [4]. Another factor which makes these patients more prone for hypotension is aortocaval compression. Almost complete obstruction of inferior vena cava occurs at term which patient is in supine posture [5, 6]. Blood returns from the lower extremities to the heart by the collaterals via intraosseous, vertebral, paravertebral and epidural veins which but it is less than venous return via inferior vena cava. Compression of inferior vena cava is evident by the fact that there is a 50% increase in femoral venous pressures in supine posture [7].

At term, nearly 15% of pregnant women experience bradycardia with a marked drop in blood pressure on attaining supine posture which termed as “Supine hypotension syndrome”. This bradycardia and hypotension develops over several hours. It results from substantial drop in venous return which is uncompensated by cardiovascular system [8].

Various research studies are being performed regarding post spinal hypotension and various methods were analyzed and observed for better prediction of postspinal hypotension. A study conducted between January 2010 and March 2011 by Toyama et al. [9] where they enrolled 39 patients, baseline perfusion index more than 3.5 was associated with profound hypotension following spinal anaesthesia. Also in the year 2014, Duggappa DR et al. [10] performed a study in 126 parturients where they assessed perfusion index and observed similar results.

Eighty five parturients who were scheduled for cesarean section under spinal anaesthesia were included in the research study of Sun et al [11] where they found that greater baseline pleth variability index was related to post spinal hypotension with area under ROC of 0.66, still it was not found to be a better predictor clinically. In a clinical trial conducted by Hanss et al. [12], Use of preoperative heart rate variability in predicting spinal hypotension was studied since heart rate variability changes can reflect sympatholysis occurring as a result of neuraxial blockade.

Between January 2019 and June 2019, Yao et al. [13] conducted a research study in 58 parturients who had undergone Cesarean section under Combined Spinal Epidural anesthesia. They included patients of age 18 to 40 years with singleton pregnancy and height of 156 – 170 cm. They also excluded patients of ASA class III and IV, morbidly obese and parturients posted for emergency cesarean delivery. They measured peak velocities, transverse diameter of femoral vein and anteroposterior diameters of inferior vena cava with the help of ultrasound 15 minutes prior to anaesthesia. They observed that the longer transverse diameter of the right femoral vein was associated with the occurrence of hypotension as a result of neuraxial anaesthesia [odds ratio = 2.022 and 95% confidence interval [CI] 1.261–3.243]. For the prediction of post-spinal hypotension, the area under the receiver operating characteristics curve was 0.759 with p – value of 0.001 [95% CI 0.628–0.890]. They concluded that the transverse diameter of right femoral vein more than 12.2 mm could predict hypotension after spinal anesthesia in cesarean delivery.

A prospective cross – sectional study performed by Cho RJ et al. [14] in about 97 patients at the medical intensive care unit where they found that femoral vein diameter less than or equal to 0.8 cm was able to predict CVP than 10 mmHg with area under the curve of 0.894. They concluded that femoral vein diameter measured using ultrasonography marks a reliable tool to predict central venous pressure.

NP, Sinha M et al. [15] carried out a prospective observational study in about ninety one parturients. Measurements were made in a supine posture with a 15-degree left lateral tilt. Maximum and minimum internal jugular vein [IJV] diameters [at the end of expiration and inspiration respectively] and IJV collapsibility index [IJVCI] were recorded using M-mode imaging during spontaneous and deep breathing. They included parturients aged 18 – 40 years with singleton pregnancy more than 37 weeks belonging to ASA physical status II. They excluded parturients with gestational hypertension, haemoglobin less than 7 g/dl, hemoglobinopathies, cardiovascular diseases or renal diseases and peripheral vascular disease. IJVCI had a sensitivity and specificity of 70% and 23% respectively during spontaneous breathing [using a cut-off point of 29.5%] for predicting post spinal Hypotension. While at deep breathing, IJVCI had a sensitivity and specificity of 77% and 27%, respectively [using a cut-off value of 37.5%] to predict post spinal hypotension. They concluded that preoperative assessment of USG guided IJV parameters cannot be used as a reliable predictor of post-spinal hypotension in parturients undergoing cesarean section. 

However, Panchal et al. [16] studied predictability of Inferior vena cava in assessing post spinal hypotension in parturients. Parturients of full term pregnancy scheduled for elective caesarean sections were recruited in the study. Inferior vena cava diameter was assessed preoperatively under ultrasound guidance in all the patients by subcostal approach. The mean inferior vena cava diameter was 17.4 ± 0.04 in expiration and collapsibility index was found to be less than 36 in 80% of patients. But only one patient experienced postspinal hypotension in their study. However they concluded that Inferior vena cava diameter assessed by ultrasonography can predict post spinal hypotension. Yet they required additional medical appliances for detection in most cases. Ultrasound being a part and parcel of Anaesthesiologists’ day to day practice, ultrasound guided techniques become a helpful tool to assess post spinal hypotension. Antero posterior diameter and velocities of IVC measured below xiphoid with the help of Cardiac probe were taken as indirect parameters to assess degree of IVC compression in the study conducted by Yao et al. [13]. But it was difficult to assess compressed IVC and its main branches under gravid uterus by ultrasonography. Being a superficial and an anatomically predictable structure, femoral vein is a better alternative to Inferior vena cava for assessing hypotension. Though internal jugular vein is also an easily accessible landmark, it was found to be a poor predictor of post spinal hypotension in research study carried out by NP, Sinha M et al. [15].

Sixty parturients who met our inclusion criteria were studied. Of which 20 patients developed hypotension which comprises 33% of the study population whereas 40 patients did not experience hypotension thus constituting 67% of the study group. In all these patients transverse diameter of femoral vein was assessed preoperatively with the help of ultrasonography 15 mins prior to the neuraxial blockade. It was observed that major proportion of patients in our study had femoral vein diameter between 10 – 10.9 mm followed by 12 – 12.9 mm.

There was no significant difference in the mean values of age between the Hypotension and No – hypotension group. This was similar to the study done by Yao et al. [13] where there was no difference with respect to age in the Hypotension and No – hypotension group with p – value of 0.986. The Body mass index was compared between both the groups and no significant difference was observed between both the groups. But in the study done by Yao et al. [13] maternal body mass index was observed to be higher in the hypotension group with a p – value of 0.040.

The ROC analysis of our study revealed the optimum cut off value to be 11.8 mm with a sensitivity and specificity of 75% and 67.5% respectively. While in the study performed by Yao et al. [13] the cut off value of femoral vein diameter was obtained as 12.2 mm with a sensitivity of 62.5% and specificity of 78.1%.

Based on the cut off value of femoral vein diameter, we categorized our study population into two groups. Even though no variation in intravenous fluid administered before delivery is noticed in both groups [p – value = 0.889], use of ephedrine was higher [Mean ephedrine use = 16.64] in patients with femoral vein diameter more than or equal to 11.8 mm. The ephedrine usage was lower in parturients with femoral vein diameter less than 11.8 mm [p – value of 0.004]. This correlation of ephedrine use with femoral vein diameter indirectly demonstrates association of hypotension with larger transverse diameter of femoral vein. The strength of our study is Ultrasound guided femoral vein parameter was measured by the same clinician. Hence inter – observer variability is avoided and influence of respiration over vessel dimension was avoided since all values were recorded at end – expiratory phase. However limitations include study being carried out in a single center, High risk patients were excluded from the study. Study was done only in selected group of patients: ASA II patients with specific range of anthropometric measure such as height.

Preoperative Ultrasonographic Assessment of Tranverse diameter of right common femoral vein can aid in Predicting the risk of hypotension in parturients undergoing cesarean delivery

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 parturients. Acta Anaesthesiol Scand. 2010; 54(8):909–21.
2. Reynolds F, Seed PT. Anaesthesia for Caesarean section and neonatal acid-base status: a meta-analysis. Anaesthesia. 2005 Jul; 60(7):636-53. doi: 10.1111/j.1365-2044.2005.04223.x. PMID: 15960713.
3. Ngan Kee WD, Lee A. Multivariate analysis of factors associated with umbilical artery pH and standard base excess after Caesarean section under spinal anaesthesia. Anaesthesia2003; 58: 125 – 30.
4. Poppas A, Shroff SG, Korcarz CE, et al. Serial assessment of the cardiovascular system in normal pregnancy. Role of arterial compliance and pulsatile arterial load. Circulation. 1997; 95(10):2407–2415.
5. Kerr MG, Scott DB, Samuel E. Studies of the inferior vena cava in late pregnancy. Br Med J 1964; 1:522-33.
6. Kerr MG. The mechanical effects of the gravid uterus in late pregnancy. J Obstet Gynaecol Br Commonw 1965; 72:513-29.
7. McLennan CE. Antecubital and femoral venous pressure in normal and toxemic pregnancy. Am J Obstet Gynecol 1943; 45:568-91.
8. Howard BK, Goodson JH, Mengert WF. Supine hypotensive syndrome in late pregnancy. Obstet Gynecol 1953; 1:371-7.
9. Toyama S, Kakumoto M, Morioka M, Matsuoka K, Omatsu H, Tagaito Y, Numai T, Shimoyama M. Perfusion index derived from a pulse oximeter can predict the incidence of hypotension during spinal anaesthesia for Caesarean delivery. Br J Anaesth. 2013 Aug;111(2):235-41. doi: 10.1093/bja/aet058. Epub 2013 Mar 21. PMID: 23518802.
10. Duggappa DR, Lokesh M, Dixit A, Paul R, Raghavendra Rao RS, Prabha P. Perfusion index as a predictor of hypotension following spinal anaesthesia in lower segment caesarean section. Indian J Anaesth. 2017 Aug;61(8):649-654. doi: 10.4103/ija.IJA_429_16. PMID: 28890560; PMCID: PMC5579855.
11. Sun S, Huang SQ. Role of pleth variability index for predicting hypotension after spinal anesthesia for cesarean section. Int J Obstet Anesth. 2014;23(4): 324–9.
12. Hanss R, Ohnesorge H, Kaufmann M, et al. Changes in heart rate variability may reflect sympatholysis during spinal anaesthesia. Acta Anaesthesiol Scand. 2007;51:1297–304.
13. Yao, SF., Zhao, YH., Zheng, J. et al.The transverse diameter of right common femoral vein by ultrasound in the supine position for predicting post-spinal hypotension during cesarean delivery. BMC Anesthesiol 21, 22 (2021).
14. Cho RJ, Williams DR, Leatherman JW. Measurement of Femoral Vein Diameter by Ultrasound to Estimate Central Venous Pressure. Ann Am Thorac Soc. 2016 Jan;13(1):81-5. 
15. N P, Sinha M, Kumar M, Ramchandani S, Khetrapal M, Karoo K, Mesa BK. Role of Internal Jugular Vein Collapsibility Index in Predicting Post-spinal Hypotension in Pregnant Women Undergoing Cesarean Section: A Prospective Observational Study. Cureus. 2023 May 23;15(5):e39389.
16. To Study The Correlation Between Preoperative Inferior Vena Cava Diameter And Intraoperative Hypotension During Spinal Anaesthesia In Caesarean Section . (2021). Indian Journal of Applied-Basic Medical Sciences, 23(36).