European Journal of Cardiovascular Medicine

Spinal anaesthesia remains one of the most frequently employed regional anaesthesia techniques for infraumbilical surgical procedures, offering advantages including rapid onset, profound blockade, and avoidance of airway manipulation¹. Since its introduction into clinical practice over a century ago, the fundamental challenge of predicting the final dermatomal level of sensory blockade has persisted as a central clinical concern for anaesthesiologists worldwide².

The clinical importance of achieving an appropriate level of spinal blockade cannot be overstated. An excessively high block may result in extensive sympathectomy-induced hypotension, bradycardia, and respiratory embarrassment due to intercostal muscle weakness³. Conversely, an inadequate block height may fail to provide surgical anaesthesia, necessitating supplemental analgesia or conversion to general anaesthesia during an ongoing procedure, exposing the patient to additional risks and discomfort⁴.

The cephalad spread of local anaesthetic agents within the cerebrospinal fluid (CSF) is influenced by three categories of factors: drug-related factors (baricity, dose, volume, concentration), technique-related factors (patient positioning, injection site, needle type, speed of injection), and patient-related factors⁵. Among these, drug and technique variables are largely controllable by the anaesthesiologist and can be standardised. However, patient-related characteristics introduce substantial inter-individual variability that cannot be eliminated through standardisation of technique⁶.

Hyperbaric bupivacaine 0.5% with 8.25% dextrose represents the most widely used local anaesthetic solution for spinal anaesthesia globally⁷. Its hyperbaric nature provides greater predictability compared to isobaric solutions, as spread is more consistently influenced by gravity and patient positioning⁸. Nevertheless, even with hyperbaric solutions, significant variability in block height persists among patients receiving identical doses under seemingly identical conditions⁹.

Contemporary understanding suggests that lumbosacral CSF volume is the primary determinant of the extent of spread for a given dose of local anaesthetic¹⁰. Patients with smaller CSF volumes exhibit more extensive cephalad spread. While direct measurement of CSF volume using magnetic resonance imaging is impractical in routine clinical practice, various anthropometric measurements have been investigated as surrogate markers. Vertebral column length (VCL), defined as the distance from the C7 vertebra to the sacral hiatus, demonstrates an inverse relationship with CSF volume¹¹. Abdominal circumference (AC) and intra-abdominal pressure show positive correlations with cephalad spread, likely mediated through compression of the inferior vena cava and engagement of the epidural venous plexus, which reduces lumbosacral CSF volume¹².

The published literature reveals inconsistent findings regarding the relative importance of various patient characteristics. A large retrospective study by Kim and colleagues identified five independent predictors of peak block height: bupivacaine dose, height, weight, gender, and age, with their predictive model accounting for approximately 72% of the observed variability¹³. However, this study did not include VCL or AC measurements. Conversely, a study by Bala and colleagues examining hyperbaric ropivacaine found that abdominal circumference significantly correlated with maximal sensory level (correlation coefficient 0.680, p<0.05), while vertebral column length did not reach statistical significance (p=0.06)¹⁴. Studies in obstetric populations have demonstrated that both intra-abdominal pressure and VCL are significant predictors, but pregnancy-induced physiological changes limit applicability to non-pregnant surgical patients¹⁵.

Given these inconsistencies and gaps in the literature, a comprehensive evaluation of multiple patient characteristics within a single study using a standardised anaesthesia protocol is warranted. The present study aims to address these gaps by prospectively evaluating the relationship between patient characteristics—including demographic variables (age, gender, height, weight, BMI) and anthropometric measurements (VCL, AC)—and the cephalad spread of 3 mL of 0.5% hyperbaric bupivacaine in patients undergoing elective infraumbilical surgeries.

Study Design, setting & population A prospective observational study was conducted to examine the relationship between patient characteristics and the cephalad spread of spinal anaesthesia. The study was conducted in the Department of Anaesthesiology at a tertiary care teaching hospital over a period of 12 months. The target population comprised adult patients aged 18-60 years, with ASA physical status I or II, scheduled for elective infraumbilical surgical procedures under spinal anaesthesia. Inclusion Criteria: • Patients aged 18-60 years of either gender • ASA physical status I or II • Scheduled for elective infraumbilical surgeries under spinal anaesthesia • Willing to provide written informed consent Exclusion Criteria: • Contraindications to spinal anaesthesia • Known allergy to amide local anaesthetics • Significant spinal deformity or previous spinal surgery • Inability to sit upright for the procedure • Pregnancy • Morbid obesity (BMI > 40 kg/m²) • Extremes of weight (<40 kg or >100 kg) • Previous hip or pelvic surgery • Intra-abdominal tumours or masses • Failed dural puncture or need for intraoperative positioning changes Sample Size Calculation Sample size was calculated based on an expected correlation coefficient of 0.4 between patient characteristics and cephalad spread. With a two-tailed α error of 0.05 and power of 80%, the minimum required sample size was 47 patients. To account for potential dropouts, 54 patients were enrolled. Procedure for Data Collection Pre-anaesthetic Evaluation: One day prior to surgery, demographic data were recorded. Vertebral column length (C7 to sacral hiatus) and abdominal circumference (at iliac crest level) were measured with the patient sitting. Spinal Anaesthesia Administration: On the day of surgery, standard monitoring was applied and intravenous preload given. Under aseptic conditions, using a midline approach at L3-L4, 3 mL of 0.5% hyperbaric bupivacaine was injected intrathecally at 0.2 mL/sec with the needle orifice directed cephalad. Patients were immediately placed in the supine horizontal position. Assessment: A blinded observer assessed sensory block level by loss of pinprick sensation at 2, 5, 10, 15, 20, 25, and 30 minutes post-injection. Heart rate and blood pressure were recorded at 2-minute intervals for the first 10 minutes, then at 5-minute intervals. Motor block was assessed using the Modified Bromage Scale.

Data Management

Prior to analysis, the dataset was cleaned and exported to SPSS version 26.0 for statistical analysis.

Table 1: Demographic and Anthropometric Characteristics of Study Participants (N=54)

A total of 54 patients completed the study, comprising 29 males and 25 females. The mean age of participants was 42.6 ± 11.8 years (range: 19-60 years), with a median age of 44.0 years. The study population had a mean height of 163.4 ± 8.7 cm (range: 148-182 cm) and mean weight of 67.2 ± 11.4 kg (range: 45-95 kg). The calculated body mass index (BMI) averaged 25.1 ± 3.6 kg/m², ranging from 18.4 to 34.2 kg/m². Regarding anthropometric measurements, the mean vertebral column length (measured from C7 to sacral hiatus) was 59.8 ± 4.2 cm (range: 51-69 cm), while the mean abdominal circumference (measured at the level of the iliac crest) was 82.4 ± 9.6 cm (range: 65-108 cm).

Table 2: Sensory Block Characteristics (N=54)

The median maximal sensory block level achieved following intrathecal administration of 3 mL of 0.5% hyperbaric bupivacaine was T8, with an interquartile range of T6 to T10. The range of maximal sensory block extended from T4 (the highest block observed) to L1 (the lowest block observed), demonstrating substantial inter-patient variability despite administration of a fixed dose under standardised conditions. The mean time required to achieve the maximal sensory block level was 17.4 ± 4.2 minutes following intrathecal injection.

Table 3: Correlation Between Patient Characteristics and Maximal Sensory Block Level

Univariate correlation analysis revealed several significant associations between patient characteristics and the cephalad spread of spinal anaesthesia. Abdominal circumference demonstrated the strongest positive correlation with block height (r = 0.612, p < 0.001), indicating that larger abdominal girth is associated with higher sensory block levels. Vertebral column length showed a strong negative correlation (r = -0.523, p < 0.001), confirming that shorter vertebral columns result in more extensive cephalad spread. Height exhibited a significant negative correlation (r = -0.486, p < 0.001), with taller patients achieving lower block levels. Age demonstrated a modest but significant positive correlation (r = 0.312, p = 0.021), indicating that older patients tend to achieve higher blocks. BMI also showed a significant positive correlation (r = 0.294, p = 0.031). However, weight alone did not correlate significantly with block height (r = 0.158, p = 0.253).

Table 4: Comparison of Block Levels and Key Characteristics Between Male and Female Patients

Significant gender-based differences were observed in both anthropometric measurements and block characteristics. Male patients (n=29) were significantly taller than female patients (n=25) (168.7 ± 6.4 cm vs. 157.3 ± 5.8 cm, p < 0.001) and had significantly longer vertebral column lengths (62.4 ± 3.1 cm vs. 56.8 ± 3.5 cm, p < 0.001). However, no significant difference was observed in abdominal circumference between males and females (81.9 ± 9.1 cm vs. 83.0 ± 10.2 cm, p = 0.674). Female patients achieved significantly higher maximal sensory block levels compared to males, with median block levels of T7 (IQR: T6-T8) versus T9 (IQR: T7-T10), respectively (p = 0.008).

Table 5: Multiple Linear Regression Model for Predictors of Maximal Sensory Block Level

Multivariate regression identified four independent predictors of maximal sensory block level: abdominal circumference (β = 0.458, p < 0.001), vertebral column length (β = -0.398, p < 0.001), height (β = -0.237, p = 0.032), and age (β = 0.178, p = 0.044). Gender and BMI were not significant in the adjusted model. The model explained 70.9% of the variance in block height (R² = 0.709), yielding the predictive equation: Peak Block Level = 15.324 + 0.118(AC) - 0.156(VCL) - 0.042(Height) + 0.031(Age).

Table 6: Complications and Stratification by Block Height

Complications occurred in 22.2% (hypotension), 7.4% (bradycardia), 14.8% (nausea/vomiting), and 3.7% (inadequate block). Stratification by block height revealed a significant dose-response relationship: patients with blocks ≥T6 had a 53.3% incidence of hypotension versus 4.8% in those with blocks ≤T9 (p < 0.001). Bradycardia and nausea/vomiting were also significantly more frequent in the high-block group (p = 0.042 and p = 0.028, respectively). In contrast, inadequate block occurred only in the low-block group (9.5%), though this was not statistically significant (p = 0.186). These findings highlight the clinical trade-off between inadequate anaesthesia and haemodynamic complications based on block height.

This prospective observational study investigated the relationship between patient characteristics and the cephalad spread of spinal anaesthesia following administration of 3 mL of 0.5% hyperbaric bupivacaine in 54 patients undergoing infraumbilical surgeries. The key findings demonstrate that abdominal circumference, vertebral column length, height, and age are independent predictors of maximal sensory block level, collectively explaining 70.9% of the observed variability.

The strongest independent predictor was abdominal circumference, which demonstrated a significant positive correlation with block height (r = 0.612, p < 0.001) and emerged as the most influential variable in the regression model (β = 0.458, p < 0.001). This finding aligns with the physiological understanding that increased abdominal girth elevates intra-abdominal pressure, leading to compression of the inferior vena cava and engagement of the epidural venous plexus¹⁶. The engorged venous plexus displaces cerebrospinal fluid from the lumbosacral region cephalad, reducing the effective volume available for dilution of the injected local anaesthetic and resulting in a higher block¹⁷. Our results are consistent with those reported by Bala and colleagues, who studied 70 patients receiving hyperbaric ropivacaine and found a significant correlation between abdominal circumference and maximal sensory level (r = 0.680, p < 0.05)⁽¹⁴⁾. The clinical significance of this relationship is substantial. Patients in the highest abdominal circumference tertile (>88 cm) achieved median blocks at T6 compared to T10 in the lowest tertile (<76 cm), with correspondingly higher rates of hypotension (44.4% vs. 5.6%).

Vertebral column length demonstrated a strong negative correlation with block height (r = -0.523, p < 0.001) and emerged as the second most important predictor (β = -0.398, p < 0.001). This inverse relationship is intuitively logical: a fixed dose of local anaesthetic distributes over a shorter spinal column in patients with reduced vertebral length, resulting in higher concentrations reaching more cephalad dermatomes¹⁸. Height also remained an independent predictor (β = -0.237, p = 0.032) even after accounting for vertebral column length, suggesting that overall stature contributes additional predictive information. Our findings differ somewhat from those of Bala and colleagues, who reported that vertebral column length did not reach statistical significance (p = 0.06) in their study¹⁴. Kim and colleagues, in their large retrospective study of 1,297 patients, identified height as an independent predictor, consistent with our findings, though they did not measure vertebral column length¹³.

Age demonstrated a significant positive correlation with block height (r = 0.312, p = 0.021) and remained an independent predictor (β = 0.178, p = 0.044). Each decade of age was associated with an increase in block height of approximately 0.3 dermatomes. This finding is consistent with the existing literature and may be explained by age-related reduction in cerebrospinal fluid volume, increased neuronal sensitivity to local anaesthetics, and degenerative spinal changes⁽¹⁹⁾. Kim and colleagues similarly identified age as an independent predictor, though the effect became most pronounced over 75 years¹³.

Female patients achieved significantly higher blocks (median T7) compared to males (median T9) (p = 0.008). However, gender did not remain significant in multivariate analysis after accounting for anthropometric differences. Female patients had significantly shorter stature and vertebral column lengths than males, both of which predict higher blocks. This clarifies that the clinically observed tendency for women to achieve higher blocks is explained by their smaller anthropometric dimensions rather than gender itself ²⁰.

Although BMI showed a significant univariate correlation with block height (r = 0.294, p = 0.031), it did not remain significant in the multivariate model (p = 0.391). This suggests that BMI fails to capture the specific aspect of body habitus most relevant to spinal block characteristics—namely, central adiposity reflected in abdominal circumference. Reliance on BMI alone for dose adjustment may be misleading; direct measurement of abdominal circumference provides more relevant information²¹.

The multivariate regression model explains 70.9% of the variance in maximal sensory block level, which compares favourably with Kim and colleagues' model (R² = 0.72)¹³. Our model achieved similar explanatory power using four easily measurable patient characteristics. The predictive equation—Peak Block Level = 15.324 + 0.118(AC) - 0.156(VCL) - 0.042(Height) + 0.031(Age)—allows estimation of expected block height. For example, a patient with large abdominal circumference (95 cm), short vertebral column (55 cm), short stature (155 cm), and advanced age (55 years) would be predicted to achieve a block at T3-T4 with the standard 3 mL dose and would benefit from dose reduction.

Our findings confirm the relationship between block height and haemodynamic complications. Patients with blocks at or above T6 had a 53.3% incidence of hypotension, compared to only 4.8% in patients with blocks at or below T9 (p < 0.001). This underscores the clinical importance of avoiding excessively high blocks²². Conversely, patients with low blocks (≤T9) had a 9.5% incidence of inadequate anaesthesia, highlighting the rationale for individualised dosing.

This study has several strengths: prospective design, single operator eliminating inter-operator variability, blinded outcome assessment, inclusion of multiple anthropometric measurements, and adequate sample size. Limitations include single-centre design, exclusion of morbidly obese and elderly patients, fixed dose design, and lack of direct CSF volume measurement.

Abdominal circumference, vertebral column length, height, and age are independent predictors of cephalad spread following spinal anaesthesia with 0.5% hyperbaric bupivacaine for infraumbilical surgeries, collectively explaining 70.9% of the variability in block height. Incorporation of these simple anthropometric measurements into routine pre-anaesthetic evaluation may enhance the ability to predict block height and select appropriate doses, optimising block adequacy while minimising haemodynamic complications.

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