Correlation between Weight of the Baby and the Level of Sensory Blockade in Spinal Anaesthesia for Caesarean Section: An Observational Study.

BACKGROUND: The spread of local anaesthetics during spinal anaesthesia is affected by various factors and can be unpredictable especially in parturients undergoing caesarean section. Factors like abdominal girth, symphysis fundal height etc have to studied to know their impact on level of sensory blockade. We hypothesized a study to find any correlation between weight of the baby and the level of sensory blockade.
METHODS: 46 parturients posted for elective caesarean section belonging to American Society of Anaesthesiologists (ASA) physical status 1 and 2 were included in the study. Maternal height and weight were noted down before entering operation theatre. All patients were instituted subarachnoid block with 2 cc of 0.5% of hyperbaric bupivacaine in sitting position. Level of sensory blockade was assessed with pin prick along midline of the patient every min till 5th minute and 5 minutes till 15th minute. The birth weight of baby was recorded soon after delivery.
RESULTS: The weight of the baby and height of the mother were correlated with the sensory blockade of T4. The number of babies weighing more than 3.5 kgs were 3 in our study out of which 2 babies were associated with maximum sensory blockade at 15th minute. It amounts to 66.7% when compared with 14.7% in babies weighing 2.5 to 3.5 kgs which is suggestive of significance ('P' value of 0.093).
CONCLUSION: There is no statistically significant correlation between weight of the baby and the level of sensory blockade.

INTRODUCTION

Spinal anesthesia for cesarean delivery is now widely preferred because of ease, effectiveness, and minimal side effects on fetus.[1] However, spread of spinal anesthesia can be unpredictable, especially in parturients due to increased abdominal pressure and decreased lumbosacral subarachnoid space volume.[23] Increased height of block can lead to high spinal anesthesia and hypotension whereas low level of blockade can lead to inadequate anesthesia and patient discomfort. Hence, various parturient factors such as height, weight, body mass index, body surface area, truncal length, symphysis-fundal height, abdominal circumference, and weight gain during pregnancy have been studied to know their effects on the level of sensory blockade after spinal anesthesia which have led to inconclusive or negative results.[456]

Among the studied factors, only “height” of parturient was found to be correlating with the level of sensory blockade.[6] Instead of indirect parameters such as symphysis-fundal height or abdominal circumference, we framed a study to know the correlation between birth weight of baby and level of sensory blockade.

MATERIALS AND METHODS

Fifty parturients posted for elective cesarean section belonging to American Society of Anesthesiologists physical status 1 and 2 were included in the study after obtaining their consent. The study was approved by the Institutional Ethical Committee.

Parturients with preeclampsia and eclampsia, twin pregnancies, poly- or oligo-hydromnios, those having systemic diseases involving cardiac, renal, or hepatic dysfunction, and patients with contraindications to spinal anesthesia were excluded from the study.

Height (in cm) and weight (in kg) of parturients were measured before shifting into operation theater. On operating table, intravenous access was secured and a crystalloid (Ringer's lactate) infusion was started. Routine hemodynamic monitoring such as electrocardiogram, noninvasive blood pressure monitoring, and oxygen saturation were instituted. Under strict aseptic precautions, patient was given subarachnoid block in the sitting position with 2 cc of 0.5% of hyperbaric bupivacaine with 25-gauge Quincke spinal needle. After injecting the drug, patients were placed in the supine position with the table tilt of 15° to the left to avoid supine hypotension. Supplemental oxygen was provided at 5 L/min through Hudson's mask. Following block, level of sensory blockade was evaluated from umbilicus to epigastric region to the center of neck along the midline of patient every minute till 5th min and every 5 min till 15th min. Blood pressure was measured every 2 min and decrease in >20% of resting blood pressure was treated with boluses of intravenous ephedrine and any bradycardia was treated with intravenous atropine 0.5 mg. The weight of newborn baby was recorded soon after delivery. Further, hemodynamics was managed as per the preference of attending anesthesiologist.

RESULTS

Keeping the power of 80% and confidence interval of 95%, a sample size of thirty would be required based to correlation coefficient of 0.69 between level of sensory blockade and fetal birth weight. We included fifty patients considering the dropouts. A total of fifty parturients were enrolled in the study and four dropped out as three patients had inadequate blockade and one patient had twin pregnancy.

The statistical software SPSS software version 18.0 and R environment version 3.2.2 (PASW Statistics for Windows, Version 18.0. Chicago: SPSS Inc) were used for the analysis of the data. Chi-square/Fisher's exact test has been used to find the significance of study parameters on categorical scale between two groups. Microsoft Word and Excel have been used to generate graphs and tables. The demographic data are shown in Table 1. The subjects for this study were 46 women within the age range of 24.76 ± 1.95 in years, weight in the range of 61 ± 11.36 (kg), and the height of 154 ± 6.8 cm. The weight of fetuses was 2.81 ± 0.45.

Table 1

Demographic data

The maximum sensory blockade level of spinal anesthesia was T4 which was achieved at 5th min in one patient and seven patients in 15th min. Out of seven parturients, babies of five parturients weighed between 2.3 and 3.5 kg and two babies weighed >3.5 kg.

The number of babies weighing >3.5 kg were three in our study, of which two babies are associated with maximum sensory blockade at 15th min. It amounts to 66.7% when compared to 14.7% in babies weighing 2.5–3.5 kg. This is of suggestive significance with P = 0.093 [Figure 1].

Figure 1

Weight of the baby and the level of sensory blockade

The maximum sensory blockade level of T4 was achieved in one patient with height of 150–160 at 5th min and in 10th min each patient achieved T4 level from 150 to 160 cm and <150 cm group. At 15th min, two patients achieved sensory blockade from both <150 cm and in 160–170 cm group and three patients [Figure 2].

Figure 2

Height of the mother to max level of sensory blockade

The maximum sensory blockade level of T4 was achieved in one patient at 5th min in patient with height of 145–155 cm. It was achieved in two patients each of <145 cm and >165 cm tall patients at 15th min and in three patients of height between 145 and 155 cm and this was statistically insignificant.

DISCUSSION

Spinal anesthesia is the most common technique used for cesarean delivery. Excessive block increases hemodynamic instability and patient risk, whereas inadequate spread of local anesthetics cannot provide a satisfactory surgical condition.[2] Therefore, factors affecting the spread of spinal anesthesia in obstetric patients have been investigated in many studies.[47] Characteristics of the local anesthetic solution, technique, and patient's general condition have been found to be contributory. Parturient's parameters such as symphysis fundal height, and abdominal circumference have been studied to know their correlation with the sensory blockade.[489] These parameters are roughly depictive of the fetal weight. Apart from cases of poly- or oligohydromnios, it is usually fetal weight that determines the abdominal girth and indirectly abdominal pressure in parturients.

The increased abdominal pressure decreases the lumbosacral spinal fluid volume and results in increased level of blockade following spinal anesthesia.[10] Increased abdominal pressure leads to inward movement of soft tissue in intervertebral foramen resulting in displacement of cerebrospinal fluid and engorgement of epidural venous plexus leading to shrinking of dura.[6] Jawan et al. showed increased cephalad spread with spinal anesthesia in parturients with twin pregnancies compared to singleton pregnancies.[11] Even though this study was conducted in early nineties, no other study has investigated the possibility of fetal weight affecting the sensory blockade. We analyzed the correlation between level of blockade and baby's birth weight soon after delivery.

The spread of spinal anesthesia is determined by factors such as baricity of local anesthetic and position of patient. We induced all our patients in sitting position and with same volume (2 cc/10 mg) of 0.5% hyperbaric bupivacaine. Optimum dosage of 0.5% hyperbaric bupivacaine for cesarean section has been studied by Danelli et al., who reported that dose of 9.5–10.5 mg of bupivacaine provided adequate anesthesia in 95% of parturients.[12] Hence, we kept our dose of 10 mg of 0.5% bupivacaine constant for all the patients.

The amount of crystalloid preload has also been studied as a factor affecting sensory blockade, reporting that rapidly injected crystalloids just before spinal anesthesia augment the blockade.[13] Hence, we kept our crystalloid infusion rate constant in all our parturients. Speed of injection of local anesthetic into the subarachnoid space was also kept constant (0.1 ml per sec) to avoid augmentation of blockade by rapid injection.

None of the studies have evaluated the correlation between sensory blockade and the weight of the baby. Although not as a primary outcome, Chung et al. did find some correlation between the weight of the neonate and the amount of ephedrine used in treating hypotension.[9]

Wei et al. have found significant correlation between abdominal circumference and cephalad spread of spinal anesthesia in both normal population as well as parturients.[2] Similar finding was reported by Kuok et al., who found that at 5th min, increased abdominal circumference lead to higher level of sensory blockade.[5] This finding was also corroborated by Baysal et al., who found large abdominal circumference shortened the time taken for sensory block to reach T4.[14] Effect of intra-abdominal pressure on sensory blockade has been studied with negative results.[8] The cerebrospinal fluid volume is important patient factor for block height,[1516] but ultrasound determined diameter of lumbar dural sac also did not correlate with sensory blockade in parturients undergoing caesarean delivery.[17]

Even though height of the patient is important determinant in level of blockade, studies in parturients have given inconclusive results with Harten et al., Baysal et al., Siddiqui et al., finding positive correlation,[151819] whereas Norris et al. did not find significant correlation.[20]

Limitations of the study

We did not study the effect of fetal birth weight on the incidence of hypotension and vasopressor requirement. In our study, we correlated the birth weight of baby with the sensory blockade, knowing that exact birth weight of baby is impossible to know before administering the spinal anesthesia. Further studies can be conducted to know how ultrasonically measured weight of the baby correlates with the level of sensory blockade after spinal anesthesia.

As of now, there is not a single parameter which can predict the sensory blockade in parturients. Some combination of parameters has to be studied to know the predictability of spinal anesthesia spread.

CONCLUSION

We did not find any statistically significant correlation between birth weight of the baby with level of sensory blockade in parturients undergoing cesarean section.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.