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ORIGINAL ARTICLE
Year : 2023 | Volume
: 13
| Issue : 1 | Page : 58-64
Effect of intra-abdominal pressure on maximum level of intrathecal sensory block: A preliminary randomized controlled trial
Jubin Jakhar, Michell Gulabani, Asha Tyagi, Ashok K Sethi
Department of Anesthesiology and Critical Care, University College of Medical Sciences and GTB Hospital, Delhi, India
Correspondence Address:
Dr. Asha Tyagi
Department of Anesthesiology and Critical Care, University College of Medical Sciences and GTB Hospital, Delhi - 110 095
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/JOACC.JOACC_41_22
Objectives: Increase in Intra-Abdominal Pressure (IAP) is commonly accepted as a cause for intrathecal dose sparing and consequently higher level of sensory block during pregnancy. There is however very little actual data evaluating the relationship. Thus, we aimed to evaluate association between IAP and maximum level of sensory block following intrathecal injection of hyperbaric bupivacaine as well as plain levobupivacaine for cesarean section. Methods: Preliminary randomized controlled blinded trial included females aged 18-40 years, scheduled for elective cesarean section under single-shot subarachnoid block. After randomization, they received either intrathecal hyperbaric bupivacaine (group H) or plain (isobaric) levobupivacaine (group P) in a dose of 12.5 mg (n = 40 each). IAP was measured before and after the spinal block, using the recommended intravesical technique. The maximum level of sensory block and the IAPs were measured in each patient. Results: There was no significant correlation of IAPprespinal with maximum level of sensory block for group H (P = 0.334; rs = -0.157) or group P (P = 0.637; rs = -0.078). Similarly, there was no significant correlation of the IAPpostspinal: group H (P = 0.370; rs = -0.145); and group P (P = 0.714; rs = -0.061). Both group H and group P had similar IAPprespinal (15.9 [14.3-18.2] and 15.3 [14.3-17.4] mmHg, respectively) (P = 0.474); as well as IAPpostspinal (15.2 [13.8-17.2] and 14.6 [13.4-16.0] mmH, g respectively) (P = 0.239). Among ancillary observations, duration of sensory block was significantly longer for group P versus group H (133.6 ± 24.2 and 103 ± 23.4 mins; P < 0.000). However, the maximum levels of sensory and motor block, respective times required to achieve them, as well as incidences of intraoperative hypotension and bradycardia were statistically similar between group H and group P (P > 0.05). Conclusions: The IAP was raised to the level of conventionally defined intra-abdominal hypertension (>12 mmHg) in patients scheduled for elective cesarean section. However, despite being increased, the IAPprespinal or IAPpostspinal did not show any significant association with the maximum level of sensory block (P > 0.05).
Keywords: Cesarean section, intra-abdominal pressure, pregnancy, sensory block
During pregnancy, a higher level of sensory block and consequently an intrathecal dose sparing effect is known to occur. One of the hypothesized reasons for this is the increased intra-abdominal pressure (IAP) due to a gravid uterus.[1],[2],[3],[4] Raised IAP acts by one of two probable mechanisms in raising the block level.[2],[3] Most likely it affects the retroperitoneal area causing an inward movement of soft tissue into the inter-vertebral foramina. A less likely cause is compression of inferior vena cava resulting in cerebrospinal fluid shift cranially, culminating in the altered intrathecal drug spread and higher level of sensory block.
Raised IAP is well documented in pregnant patients scheduled for cesarean section.[4],[5],[6],[7] It is conventionally stated that raised IAP is one of the causes of the higher sensory block level during cesarean delivery.[8] On literature review however, we could find very little actual data evaluating the relationship.
Indeed, we could locate only three studies evaluating for possible association between IAP and spinal block characteristics during pregnancy.[1],[9],[10] Herein, while Seyhan et al.[1] found lack of any relationship between the two variables, Sitkin and colleagues[9] noted a positive association of IAP greater than 16 mmHg and higher sensory block levels; Ni et al.[10] also found a significant positive association between the two variables.
These previous studies vary with regards to baricity of the intrathecal drug used, and the time of measuring IAP. Intrathecal drug baricity is an independent predictor of sensory block level, and could hence affect its relationship with IAP as well.[11],[12],[13] While the authors of two of previous studies used hyperbaric anesthetic,[1],[9] plain local anesthetic was used in one,[10] probably contributing to the inconclusive results. Additionally, the IAP before and after a spinal block may vary due to motor blockade of abdominal wall. The IAP was measured prior to the spinal block in one study,[9] and after establishing a sensory blockade in the other two.[1],[10]
Against this background, the present study aimed to objectively evaluate the association between IAP and maximum level of sensory block following intrathecal injection of hyperbaric versus isobaric local anesthetic, in patients scheduled for elective cesarean section.
Materials and MethodsThis preliminary randomized controlled double-blinded trial was initiated after Institutional Ethical Committee's approval and obtaining informed written consent from all participants. It is registered with the Clinical Trial Registry of India with reference number CTRI/2017/11/010465 and was conducted from October 2017 to April 2019.
Pregnant patients with ASA physical status II or III, aged 18-40 years, scheduled for elective cesarean section under single-shot subarachnoid block were included. Those with factors known to affect level of sensory block including extremes of height (<5 feet and >6 feet), body mass index (BMI) >30 kg m-2, or scoliotic/kyphotic deformity on inspection and with any contraindication to IAP measurement such as neurogenic bladder, hematuria, coincidental abdominal masses, etc., were excluded.
Patients were randomized to receive either hyperbaric (group H) or plain (group P) intrathecal local anesthetic by using a computer generated random number table which was concealed by sealed opaque envelopes.
The patient as well as person measuring the IAP and the maximum sensory block level were not aware of the nature of the intrathecal injection, hence blinded to the group allocation.
IAP measurement and related observations:
Foley bladder catheter was inserted in the operating room if not already in situ and IAP was measured using intravesical technique.[14] An 18G intravenous cannula was inserted aseptically into the drain tube of the Foley catheter. This was in communication with two three-way stop-cocks and a transducer. A 500 ml saline vac and a syringe were connected to the two stop cocks, respectively. The transducer was zeroed at the level of mid-axillary line, at the iliac crest for all IAP measurements. The pressure was measured after injecting 25 ml of saline into bladder and ensuring closed communication of transducer. The IAP was measured during end-expiration. For checking that the pressure signal was correctly transduced, gentle compressions of the abdomen were seen to cause changes in IAP tracing. At both times of measurement, the IAP was observed twice to confirm variation of less than 5%. The second reading then represented the final IAP value. All measurements of IAP were made by a single observer.
The IAPprespinal was measured just prior to the spinal block with patient in supine with 10° left lateral tilt position; and IAPpostspinal once the sensory block level reached at least T6 while patient was in supine with 10° left lateral tilt position. The IAPpostspinal was measured once level of T6 sensory block was achieved, to eliminate variations in IAP arising from different extent of abdominal wall relaxation.
The anesthetic management of these patients was standardized as per routine practice. Single-shot subarachnoid block was performed at L3-L4 intervertebral space using 25 G Quincke's needle via midline approach with patient in sitting position. The intrathecal local anesthetic injected was as per group allocated (i.e., 12.5 mg of 0.5% hyperbaric bupivacaine or plain levobupivacaine; and administered at the rate of 0.3-0.5 ml sec-1 with opening pointing cephalad). Immediately after completion of block patient was positioned in 10° left lateral tilt position. The degree of tilt was measured using an angle measurement device (Vitachem; India).
The sensory block level was assessed by complete absence to pin prick sensation in midline. It was taken as the last dermatome with absence of sensation to pin prick. Sensory block assessment continued every 2 min from the completion of intrathecal injection after placing the patient in supine position with 10° left tilt, until 3 consecutive identical levels were achieved. This level was defined as the maximum level of sensory block, and the time to its first recording as the time to attain maximum sensory block. Thereafter, the sensory block level was assessed every 5 min till delivery of baby, followed by every 15 min till it receded to a dermatomal level of T10. The time taken for regression of the sensory block level by 2 dermatomes and to T10 was also calculated. To calculate time related characteristics for spinal block, the completion of intrathecal injection was marked as time "zero".
The motor block was also assessed every 2 min after placing the patient in supine position with 10° left tilt, until the maximum sensory block level was achieved; thereafter, it was assessed every 5 min till delivery of baby. The modified Bromage score was used to assess the motor blockade (0 = no motor block; 1 = hip flexion blocked; 2 = hip and knee flexion blocked; 3 = hip, knee and ankle flexion blocked).[15]
Time from completion of intrathecal injection to positioning the patient supine with 10° left tilt was also noted.
Systolic and diastolic pressures, as well as the heart rate were observed at 2-min intervals after positioning the patient in supine with left tilt till maximum sensory block level was achieved; and at 5-min intervals throughout remaining surgery till delivery of baby. Hypotension was defined as fall of >20% in systolic blood pressure from the baseline or value <100 mmHg whichever was higher; and was treated by boluses of intravenous ephedrine 6 mg.
Bradycardia was defined as heart rate less than 60 bpm accompanied with hypotension, or <50 beats min-1; and treated by intravenous bolus of atropine 0.3 mg. The demographic and obstetric details were also recorded.
Sample size
At the time of conceptualization of this study, there was no evidence evaluating effect of IAP on spinal block characteristics when using plain local anesthetic intrathecally. This was thus designed as a preliminary study with 80 patients randomized to two groups.
Statistical analysis
Normal distribution of quantitative data was tested using Kolmogorov-Smirnov test. Data was represented as mean ± SD for normally distributed variables and median [IQR] for non-normally distributed variables. Categorical data was presented as percentages or numbers. Comparison between the two groups of normally distributed quantitative data was done using t-test; Mann-Whitney U test for non-normally distributed; and Wilcoxon test for non-normal paired data (IAP prespinal and postspinal measurements). To evaluate the correlation of IAPprespinal and IAPpostspinal with maximum level of sensory block Spearman correlation test was used. Repeated measures were compared between two groups using general linear model of Analysis of Variance (ANOVA). Categorical variables were compared using Chi-square or Fischer's exact test as appropriate. The dermatomes assessed for level of sensory block were numbered as 1 for T1 and 17 for L5 for purpose of intergroup comparison. The statistical comparison of repeated variables (sensory and motor block, as well as hemodynamic parameters) was done for initial 10 min only. This was done since beyond this time, majority of patients had achieved the maximum sensory block level (n = 38 in each group) and hence there would be significant attrition of data after this time. Statistical analysis was done using SPSS software version 23.0 (IBM corp). A P value <0.05 was considered as statistically significant.
ResultsThe CONSORT flow chart is depicted in [Figure 1].There was no significant correlation of IAPprespinal or IAPpostspinal with the maximum level of sensory block for group H (P = 0.334; rs = -0.157; and P = 0.370; rs = -0.145, respectively); or group P (P = 0.637; rs = -0.078; and P = 0.714; rs = -0.061, respectively).
The individual IAPprespinal and maximum level of sensory block for each patient of both groups is depicted in [Figure 2]; while for IAPpostspinal and maximum level of sensory block is depicted in [Figure 3].
Figure 2: Scatter plot for IAPprespinal and maximum level of sensory block
Figure 3: Scatter plot for IAPpostspinal and maximum level of sensory blockThe IAPprespinal was noted to be 15.9 [14.3-18.2] mmHg for group H and 15.3 [14.3-17.4] mmHg for group P, with no significant difference between the two groups (P = 0.474). The IAPpostspinal was also similar between group H and group P (15.2 [13.8-17.2] and 14.6 [13.4-16.0] mmHg, respectively) (P = 0.239).
The maximum level of sensory block was statistically similar between group H and group P (T5.0 ± 0.9 and T4.8 ± 0.8, respectively) (P = 0.231). It ranged from T4 to T6 for group H; and from T3 to T6 for group P.
The level of sensory block at the time of measurement of IAPpostspinal was also similar between both groups (group H: T6 ± 0.4 and group P: T6 ± 0.5, respectively) (P = 0.411).
IAPprespinal was significantly higher than IAPpostspinal for group H: 15.9 [14.3-18.2] versus 15.2 [13.8-17.2] mmHg, respectively, P < 0.001; as well as for group P: 15.3 [14.3-17.4] versus 14.6 [13.4-16.0] mmHg, respectively, P < 0.001.
Most of the intrathecal block characteristics including time taken to position patient supine with 10° left tilt after completion of intrathecal injection, maximum levels of sensory and motor block and respective times required to achieve them; as well as intraoperative adverse effects, that is, incidence of high sensory level (cephalad to T4), hypotension, and bradycardia were statistically similar between group H and group P [[Table 1]; P > 0.05].
However, the duration of sensory block was significantly longer for group P versus group H, as evident by the greater time for two segment regression (P < 0.001) as well as regression to T10 dermatome level (P < 0.001) [Table 1].
The demographic, obstetric, and baseline hemodynamic parameters except for heart rate, were similar between group H and group P [[Table 2]; P > 0.05].
Duration of surgery was similar between group H and group P (56.4 ± 20.4 min and 49.0 ± 16.2 min, respectively; P = 0.080).
DiscussionThe various reasons for the greater intrathecal spread or consequent reduction in dose during pregnancy include change in lumbar lordosis, decreased volume and density of cerebrospinal fluid volume, increased IAP, and progesterone mediated increase in neuronal sensitivity.[16],[17],[18],[19],[20] Amongst these causes, increase in IAP leading to higher block levels has been cited since a long time.[8] On scrutiny of published literature we could however locate very little data actually evaluating the relationship.[1],[9],[10]
The present results included a lack of influence of IAP on maximum level of sensory block, irrespective of baricity of intrathecal drug. This finding did not change for IAP measured before or after a spinal block.
Among the three previous studies that are available, a positive association between IAP and cephalad spread of spinal anesthesia in parturients was seen following the use of plain bupivacaine in one of them.[10] The IAP was however, not measured before administration of spinal anesthesia which could possibly be the reason for the contrasting results as compared to ours. Also, the intrathecal dose used by the authors was lesser than in our study (10 vs. 12.5 mg). It is possible that the effect of IAP on block level is amplified at lower doses, while greater doses may mitigate the association. The other two studies[1],[9] used intrathecal hyperbaric bupivacaine, and showed contrasting results.[9] Seyhan et al.,[1] noted lack of any correlation between IAP and maximum level of sensory block, as also its onset time and recovery in parturients receiving single-shot spinal anesthesia in a dose of hyperbaric bupivacaine similar to ours. Thus, their observations, are in concordance with the present study results.
The average BMI of patients in the earlier studies[10] noting a positive relationship between IAP and sensory block was 28 kg m-2 while in our study it was approximately only 25 kg m-2. It is known that obesity is an independent factor associated with rise in IAP, as well as increase in level of sensory block.[8],[11],[21],[22] An increased BMI causes higher IAP by a direct mechanical effect of the increased adipose tissue on abdominal cavity,[22],[23] thus lowering cerebrospinal fluid volumes and a consequent rise in sensory block.[9] Thus, this could be a contributing factor for the lack of association between the IAP and highest level of sensory block achieved in the present study.
We evaluated prespinal as well as postspinal IAP due to the concern of altered abdominal compliance after the block, with consequently altered IAP. Previous evidence offers no standardization regarding the optimal time of IAP measurement in pregnant patients, that is, before or after the spinal block. We observed significantly lower postspinal IAP as compared to prespinal IAP in both groups.
This however did not alter the lack of association witnessed between IAP and sensory block level. However, this does indicate a need to standardize time of IAP measurement (i.e., before or after the spinal block) for further research.
Another reason for which we noted the postspinal IAP measurement was in relation to the likely timing of intrathecal drug spread. It is known that intrathecal bupivacaine may not be completely fixed up to 20 to 25 min following the injection.[24],[25],[26] During this time, it is the postspinal rather than prespinal IAP that would be affecting the intrathecal drug spread and hence sensory block level. All of the previous studies evaluating correlation of IAP with sensory block level[1],[9],[10] had evaluated the postspinal IAP.
Certain pertinent conclusions regarding IAP itself in pregnant patients can also be made based on our observations. The median [IQR] of prespinal as well as the postspinal IAP was ≥12 mmHg in both groups. The baseline values, that is, IAPprespinal was 15.9 mmHg and 15.3 mmHg for the two groups which qualify as conventionally defined IAH. There are earlier studies that have evaluated IAP during pregnancy in women scheduled for cesarean section.[4],[5],[6],[7],[27],[28] These have also noted increased IAP in the range of conventionally defined IAH: 14 ± 2.6 mmHg.[4],[6],[27] The only study wherein the mean IAP was not in the range of IAH, also showed 25% patients to have an IAP ≥12 mmHg.[5] It is noted that while up to 9.2% pregnant patients had a normal IAP at time of cesarean section, it was increased to range from 16 to 20 mmHg in 40.3%, and 21-25 mmHg in 1.5%.[28] Thus, our observation of increased IAP, whether at prespinal or after the spinal block, in both groups in the range of conventionally defined IAH is a consistent finding in the scanty previous evidence.
Abdominal compartment syndrome (ACS) is defined as IAH, associated with new organ dysfunction or failure.[14] Hence, clinical and laboratory parameters defining organ dysfunction are of critical importance for early diagnosis of this life-threatening condition with high morbidity and mortality. International guidelines on IAH and ACS do not differentiate between pregnant and non-pregnant patients when evaluating and managing IAP. Measurement of IAP has been regarded as essential in establishing a diagnosis of IAH and ACS since imaging findings and signs/symptoms are not considered sufficient to make a diagnosis.[15]
However, previous data and our own findings of raised IAP during pregnancy need to be addressed and normal IAP during pregnancy needs to be defined separately. It is recommended that the IAP be measured in clinical practice as the intravesical pressure through indwelling Foley catheter, with patient in supine position.[23] We used the intravesical technique but the patient was in a 10° left lateral position rather than supine. In pregnant patients, it has been previously noted that the IAP may be falsely elevated in supine position due to the pressure effects of gravid uterus on urinary bladder.[5] For the same reason, it may be preferable to measure the IAP in left lateral tilt position during pregnancy.
As an ancillary observation, we also compared the intrathecal block characteristics following hyperbaric bupivacaine or plain levobupivacaine. The time of onset to maximum level of sensory block was insignificantly shorter with hyperbaric bupivacaine as compared to plain levobupivacaine. This is in sync with earlier evidence comparing hyperbaric versus plain solution[29] and more pertinently comparison between intrathecal hyperbaric bupivacaine and plain levobupivacaine as well.[30],[31] The significantly shorter duration of block with hyperbaric bupivacaine, is also a result consistent with earlier studies comparing it with plain levobupivacaine.[30],[31] We observed lack of any significant differences in the motor block characteristics and hemodynamic parameters between the two groups. This is in contradiction to earlier studies comparing intrathecal hyperbaric bupivacaine and plain levobupivacaine.[30],[31],[32] However, since our study was not powered to detect differences in intrathecal block characteristics between the two groups, these should not be used for conclusive evidence.
The present findings should be viewed in perspective of the limited sample size.
Based on our findings, we conclude that there is no significant correlation between the IAP, whether measured before or after subarachnoid block, and the maximum level of sensory block was observed. This finding is seen for both hyperbaric as well as plain intrathecal local anesthetic despite the IAP being raised in pregnant patients. Also, a spinal block results in significant fall of IAP probably due to a decrease in abdominal wall compliance consequent to the motor blockade of abdominal muscles.
Thus, we recommend that an increased IAP during pregnancy should not be used to alter the intrathecal drug dose requirement in non-obese patients.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflicts of interest
There are no conflicts of interest.
References
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