|Ahead of print publication
Correlation of symphysiofundal height and abdominal girth with the incidence of hypotension in cesarean section under spinal anesthesia using bupivacaine with fentanyl as adjuvant: A clinical study
Prabha Parthasarathy, Rashmi R Aithal, RS Raghavendra Rao, Shreyavathi Raghuram, R Ramesh, Anis Nazneen
Department of Anesthesiology, Bangalore Medical College and Research Institute, Bengaluru, Karnataka, India
Rashmi R Aithal,
“Vasantha Vihar”, H. No: 3w-5-490/4, Bejai Post, Near Kadri Temple, Mangaluru - 575 004, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background and Aims: A decreased lumbosacral subarachnoid space volume is a major factor in cephalad intrathecal spread of local anesthetic in term parturients due to compressive effect of the gravid uterus. The aim of this study was to assess the relationship of symphysiofundal height (SFH) and abdominal girth (AG) with the incidence of hypotension and the highest level of sensory blockade. Settings and Design: This study was a prospective observational study. Materials and Methods: Ninety parturients under the American Society of Anesthesiologists physical status class II within the age range of 20–30 years, weighing between 60 and 65 kg, and height between 150 and 155 cm were studied, and the SFH and AG of all parturients had been measured just before spinal anesthesia. Hyperbaric bupivacaine 9 mg with 12.5 μg intrathecal fentanyl was administered for subarachnoid block. The incidence of hypotension and the highest level of sensory block were assessed. Statistical Analysis: Correlation analysis (Spearman's rank test) was applied to analyze the data, and P < 0.05 was considered to be statistically significant. Results: The incidence of hypotension was higher with increasing SFH (16.9% with SFH of 30–35 cm, 78.37% with SFH of 36–40 cm; correlation coefficient Ρ =0.338) and with increasing AG (5.3% with AG between 85 and 89 cm, 35.7% with AG 90–94 cm, 62.8% with AG 95–99 cm; Ρ =0.341), and both were statistically significant (P < 0.001). There was a statistically significant correlation between increasing SFH and maximum sensory block achieved (Ρ =0.157, P < 0.001). There was increased level of sensory blockade with increased AG but was not statistically significant (Ρ =0.011, P = 0.32). Conclusion: In term parturients undergoing cesarean section under spinal anesthesia, the SFH has a significant positive correlation with the incidence of hypotension and ascent of spinal anesthesia. AG also has a positive correlation with the incidence of hypotension but is not significant with the ascent of spinal anesthesia.
Keywords: Abdominal girth, cesarean section, hypotension, spinal anesthesia, symphysiofundal height
|How to cite this URL:|
Parthasarathy P, Aithal RR, Raghavendra Rao R S, Raghuram S, Ramesh R, Nazneen A. Correlation of symphysiofundal height and abdominal girth with the incidence of hypotension in cesarean section under spinal anesthesia using bupivacaine with fentanyl as adjuvant: A clinical study. Anesth Essays Res [Epub ahead of print] [cited 2019 May 25]. Available from: http://www.aeronline.org/preprintarticle.asp?id=257932
| Introduction|| |
Spinal anesthesia is the most preferred anesthetic method for cesarean section since it provides easy and rapid induction and effective sensory and motor blockade with no significant effects on the fetus. However, in a pregnant woman, many of the physiological changes that occur during pregnancy increase the effect of a local anesthetic (LA) injection. The incidence of hypotension following spinal anesthesia can vary between 55% and 90%. Contrary to the traditional belief, the change in venous capacitance due to sympathetic blockade rather than a decrease in cardiac output has been postulated as a major cause for hypotension in these patients., The extent of sympathetic block is determined by the spread of LAs in the subarachnoid space.
Many variables have been suggested as influencing the ultimate spread of sensory blockade such as height, weight, body mass index of the patient, and fetal weight, but the roles of these factors are controversial. The use of adjuvants to LA such as intrathecal fentanyl with bupivacaine also influences the spread of the LA and the incidence of hypotension., Intrathecal fentanyl up to 25 μg can be used with not much side effects or effects on the fetus.
The size of the enlarged uterus may influence the LA spread by affecting the pressure in the subarachnoid space, thereby influencing sympathetic blockade. Symphysiofundal height (SFH) and abdominal girth (AG) measure the size of the gravid uterus and have classically been used to assess the fetal growth during pregnancy. SFH is measured in cm from the pubic symphysis to the highest point in the midline at the fundus of the uterus, in a supine position, and AG is measured in cm at the lower border of umbilicus.
Chung et al. conducted a study to determine the relationship between SFH and the intravenous (IV) ephedrine dose in parturients undergoing cesarean section under spinal anesthesia and found a statistically significant positive correlation between SFH and the amount of ephedrine administered.
Hypotension is a physiological effect of subarachnoid block, with level of autonomic block bearing direct influence on the severity of hypotension. Lumbosacral cerebrospinal fluid (CSF) volume is a very important determinant of the spread of drug injected in subarachnoid space., Onuki et al. at the Department of Anesthesiology, Tokyo, conducted a study to examine pregnancy-induced changes in the lumbosacral volume and dural sac surface area. The main finding of this study was that compression of the dural sac surface area was associated with engorged veins in the epidural space resulting in a gestation-related reduction in the CSF volume and dural sac surface area.
In the case of parturient women, pressure on the inferior vena cava (IVC) by the gravid uterus causes expansion of the lumbar vein and vertebral artery around the spinal cavity and shrinkage of the subarachnoid space with the reduction of CSF. This may augment the cephalad spread of intrathecally administered drug. SFH and AG measurements give an indirect measure of the extent of IVC compression, which may influence the lumbosacral CSF volume.
Hence, this clinical study was designed to see the effect of SFH and AG on the incidence of hypotension and the spread of LA under spinal anesthesia with bupivacaine and fentanyl as an adjuvant.
| Materials and Methods|| |
Institutional ethical committee approval was obtained. A prospective observational study was conducted involving 90 parturients posted for cesarean section under spinal anesthesia at our institute, from October 2018 to December 2018. Parturients aged between 20 and 30 years, belonging to the American Society of Anesthesiologists class II physical status, weighing between 60 kg and 65 kg, and height between 150 and 155 cm were included in the study. Informed consent was obtained from all parturients.
Those parturients in active labor, with placenta previa, twin pregnancies, oligohydramnios or polyhydramnios, pregnancy-induced hypertension, intrauterine growth retardation, ruptured membranes, significant medical or obstetric morbidity, obstructed labor, abnormal lie and presentation, more than three previous cesarean deliveries, patients with spine deformities, and those who did not give valid informed consent were excluded from the study.
We hypothesized that there would be a positive correlation between SFH and AG with the incidence of hypotension. A sample size of 84 was obtained with an alpha error of 0.05, power of 90%, and using a correlation coefficient of SFH and AG with the incidence of hypotension, based on previous studies. We included 90 parturients in this study to compensate for dropouts and better validation of results.
All parturients were subjected to preanesthetic checkup that included medical history, physical examination, and review of clinical laboratory tests such as hemoglobin, platelet count, white cell count, bleeding time, clotting time, blood sugar levels, blood urea, serum creatinine, and ECG, as required.
All parturients were kept nil by mouth 8 h before surgery. SFH was measured from the upper margin of the uterine fundus to the superior margin of the pubic symphysis in the supine position on a horizontal table, and AG was measured using a tape at the lower border of the umbilicus in the preoperative preparation room by the same obstetrician for all cases and was not revealed to the anesthesiologist. A total of three readings were taken, and the maximum of three values was considered. In the operation theater, noninvasive blood pressure (BP), pulse oximetry, and electrocardiogram monitors were connected, and 10 ml/kg of Ringer lactate was infused through peripheral venous access using 18-gauge IV cannula 15 min before administration of subarachnoid block (SAB). Baseline resting heart rate (HR) and systolic, diastolic, and mean arterial BPs were recorded.
Dural puncture was performed in the left lateral recumbent position with 27-gauge Quincke needle by a midline approach under aseptic precautions. After checking the CSF outflow, 0.5% hyperbaric bupivacaine – 1.8 ml (9 mg) with 12.5 μg intrathecal fentanyl was given at the rate of 0.1 ml/s without changing the direction of the bevel. Immediately after injection, the patient was put in the supine position with 15° left lateral tilt of the table. Sensory level was checked along the midline every minute until the level did not change during three consecutive assessments, thus determining the maximum level of sensory blockade. IV fluids were administered at a rate of 100 ml in 10 min. After completing the drug injection, the patients' arterial BP, HR, respiratory rate, and arterial oxygen saturation(SpO2) were measured at regular intervals. Injection oxytocin 10 units was administered by separate infusion at a rate of 20 mu/min to all parturients following extraction of the baby.
Hypotension was defined as more than 20% fall in systolic BP from the baseline value and was treated with injection ephedrine 6 mg IV, and the same dose was repeated if there was persistent fall after 2 min. Bradycardia was defined as HR <60 beats/min and treated with injection atropine 0.6 mg IV. Oxygen supplementation was given at the rate of 5 L/min throughout the surgery. Parturients in whom the level of the sensory block did not reach T8 level, those requiring additional oxytocics, and those with excessive intraoperative bleed were excluded from the study. Patients with inadequate block were administered general anesthesia. The side effects such as hypotension, nausea, and vomiting were also observed and recorded. Primary outcome measures were the incidence of hypotension and the maximum level of sensory block. The degree of hypotension measured by vasopressor (ephedrine) usage and the incidence of nausea and vomiting were secondary measures.
All measurements were presented as mean ± standard deviation. Correlation analysis (Spearman's rank test) was performed to find the correlations of the SFH and AG with the incidence of hypotension and level of maximum sensory blockade. For analytical purposes, SFH and AG were presented as ordinal data with defined class intervals. The incidence of hypotension, level of sensory block, and vasopressor use were categorized accordingly. Chi-square test was applied for categorical data, and one-way ANOVA test was applied for discrete data. P < 0.05 was considered statistically significant for all the tests. The data were analyzed using SPSS 22 version software (IBM Corp. Released 2013. IBM SPSS Statistics for Windows, Version 22.0. Armonk, NY: IBM Corp.).
| Results|| |
All the enrolled parturients completed the study, and none of them were excluded. The mean age, weight, and height of parturients enrolled for the study were 24.37 ± 3.05 years, 61.59 ± 1.37 kg, and 152.06 ± 1.58 cm, respectively. The incidence of hypotension in the cesarean section under spinal anesthesia using bupivacaine with fentanyl as an adjuvant is 42% (38 out of 90 parturients). [Figure 1] depicts the BP trends among the groups. The mean SFH was higher in parturients with hypotension (35.81 ± 1.74 cm) compared to those without hypotension (33.62 ± 1.48 cm). The mean AG was higher in parturients with hypotension (96.39 ± 2.48 cm) compared to those without hypotension (92.23 ± 3.5 cm).
The incidence of hypotension was higher with increasing SFH (16.9% with SFH of 30–35 cm, 78.37% with SFH of 36–40 cm; correlation coefficient Ρ = 0.338) and with increasing AG (5.3% with AG between 85 and 89 cm, 35.7% with AG 90–94 cm, 62.8% with AG 95–99 cm; correlation coefficient Ρ =0.341), and both were statistically significant (P < 0.001) [Table 1] and [Table 2].
The use of rescue vasopressor (ephedrine) paralleled the incidence of hypotension. The mean requirement of ephedrine was higher in parturients whose SFH was above 36 cm, compared to those women whose SFH was <36 cm (P < 0.001). The mean requirement of ephedrine was higher in women whose AG was 95–99 cm compared to those of 85–94 cm (P < 0.001) [Table 1] and [Table 2].
The mean SFH corresponding to maximum sensory levels of T4, T6, and T8 was 37.2 ± 2.68 cm, 34.68 ± 1.71 cm, and 33.41 ± 1.84 cm, respectively. The mean AG corresponding to maximum sensory levels of T4, T6, and T8 was 96 ± 0.01 cm, 93.93 ± 3.97 cm, and 93.65 ± 1.46 cm, respectively [Figure 2] and [Figure 3].
|Figure 2: Correlation of symphysiofundal height with maximum sensory level|
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There was a statistically significant correlation between increasing SFH and maximum sensory block achieved (Ρ = 0.157, P < 0.001). There was increased level of sensory blockade with increased AG but was not statistically significant (Ρ = 0.011, P = 0.32) [Table 3] and [Table 4].
|Table 3: Correlation of symphysiofundal height with the incidence of hypotension and maximum sensory level|
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|Table 4: Correlation of abdominal girth with the incidence of hypotension and maximum sensory level|
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| Discussion|| |
The present study showed a positive correlation of SFH and AG with the incidence of hypotension and the maximum level of sensory block.
Hypotension is a physiological effect of subarachnoid block, with level of autonomic block bearing direct influence on the severity of hypotension. Lumbosacral CSF volume is a very important determinant of the spread of drug injected in subarachnoid space., In the case of parturient women, pressure on the IVC by the gravid uterus causes expansion of the lumbar vein and vertebral artery around the spinal cavity and shrinkage of the subarachnoid space with the reduction of CSF. This may augment the cephalad spread of intrathecally administered drug. SFH and AG measurements are used in obstetric practice to clinically assess the intrauterine growth of the fetus. They may give an indirect measure of the extent of IVC compression, which may influence the lumbosacral CSF volume.
In a study conducted by Chung et al. to determine the relationship between SFH and the dose of IV ephedrine administered for hypotension in spinal anesthesia for cesarean sections, there was a statistically significant correlation between the SFH and ephedrine dose required, which is in agreement with the observations of our study.
Lee et al., in their study, explored the effects of abdominal circumference, trunk length, and their combination on the level of spinal anesthesia in the term parturient and concluded that parturients with greater AG values tended to have higher dermatomal levels during spinal anesthesia. In our study, there was a positive correlation between increasing AG and higher dermatomal levels but was not statistically significant. However, there was a statistically significant positive correlation between the incidence of hypotension and increasing AG.
In a dose-finding study, ED50 and ED95 of intrathecal bupivacaine did not show a varied response in obese and nonobese patients undergoing cesarean delivery, and there was no difference with regard to secondary outcomes such as hypotension, vasopressor use, nausea, and vomiting. However, recent studies have highlighted the benefit of height and weight adjusted intrathecal drug regimen for parturients undergoing cesarean section under spinal anesthesia., The changes in the anatomical configuration of the spinal canal during pregnancy may influence the cephalad spread of LA. The speed of injection, specific gravity of a LA, and the body position can significantly affect the occurrence of hypotension during spinal anesthesia in parturient women. A recent magnetic resonance imaging-based study has demonstrated a significant reduction in the volume of IVC in a pregnant woman in the supine posture.
In the present study, an attempt was made to avoid most of these confounding variables by keeping the subject enrollment based on a narrow range of height and weight and by adopting standard and uniform measures such as use of a single dose of hyperbaric drug, speed of injection, and use of left lateral tilt.
To avoid interobserver variability, SFH and AG were measured by the same obstetrician throughout the study period.
The amount of fluid administered before SAB can affect the maximum sensory blockade level due to its effect on dynamics of CSF flow in lumbosacral region. In the present study, all parturients were preloaded, and the BPs measured after the fluid infusion were considered as the reference value. The amount of intraoperative fluid administration and use of oxytocin were kept uniform to avoid its influence on hypotension and ephedrine requirement.
Contrary to the observations of earlier studies,, there was a significant positive correlation of the SFH and AG with the maximum level of sensory block achieved and the incidence of hypotension, which may be attributed to the use of fixed dose of intrathecal drug rather than height-adjusted dose in the present study.
There are limitations in the present study. We could not measure the actual pressures in IVC or subarachnoid space, which may provide objective evidence of influence of uterine size on the extent of IVC compression and in turn the lumbosacral subarachnoid space volume. Future studies using ultrasound and other imaging modalities are required to establish a correlation between SFH and AG and pressure changes in IVC and subarachnoid space and also to prognosticate the incidence and severity of hypotension.
| Conclusion|| |
In term parturients undergoing cesarean section under spinal anesthesia, the SFH has a significant positive correlation with the incidence of hypotension and ascent of spinal anesthesia (highest level of the sensory blockade). AG also has a positive correlation with the incidence of hypotension but is not significant with the ascent of spinal anesthesia.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]