European Journal of Cardiovascular Medicine

Spinal anaesthesia (SA) or subarachnoid block (SAB)has several advantages over general anesthesia (GA) such as, single drug use, better post operative pain relief with SA, avoiding intubation, minimizing the risks of difficult intubation, use of multiple drugs.

However, SA has its own drawbacks with several side effects like bradycardia, hypotension, nausea, vomiting, dysarrhythmias and others which are a cause for concern during the perioperative period still this is the preferred mode of anesthesia for lower abdominal surgeries for its efficacy, rapidity of onset of action with minimal effect on physiological parameters and mental status when controlled techniques are used.2,3

The incidence of hypotension during SA varies between 7 to 42 % while incidence of   bradycardia is not well established. Varied incidence is due to the various risk factors such as age, gender, body mass index (BMI), the comorbidities, the pre - medications, reflex mechanism to cope with the pharmacological changes due to anesthetic agents and technique used. These underlying factors also has shown wide variation from available evidence.Hence, we propose to study prospectively to determine the intraoperative incidence of bradycardia and the associated risk factors during spinal anaesthesia.

We conducted this prospective clinical study at the department of anesthesiology in collaboration with the department of Surgery, M.S Ramaiah teaching hospital, undergoing surgical procedures under spinal anesthesia from Oct 2005 – March 2007.

We included the patients aged above 16 years, who belonged to ASA status 1 and 2, undergoing elective lower abdomen surgical procedures under spinal anesthesia. Patients with altered coagulation profile, spinal deformities and those who were not willing to be the part of study were excluded.

Procedure: Hospital Ethical committee approved the study protocol and ethical clearance certificate was obtained. Preanesthetic check- up was done one day prior to the surgery. A thorough general and systemic examination was carried out for baseline vital parameters, airway assessment, cardio-respiratory and CNS abnormalities. Patients’ laboratory investigations recorded.

The procedure of SAB explained to the patient and written informed consent was obtained. Preparation of patients included period of overnight fasting.  Premedication was done with oral Tablet Ondansetron 04 mg and Tablet Ranitidine150 mg at 4 hours before surgery with sips of water. Boyle anesthesia machine was checked. Appropriate size endotracheal tubes, two laryngoscopes with medium and large size blades, stylet and working suction apparatus were kept ready before the procedure. Emergency drug tray containing Atropine, Adrenaline, Ephedrine, Mephentermine, Hydrocortisone and Dopamine were kept ready. Patient was shifted to the OT table, IV access was obtained on the forearm with 18 Gauge IV cannula and IV infusion was started with either Ringer lactate, Normal saline or Dextrose normal saline.

The monitors connected to the patient included three lead ECG in Std. Lead II, non-invasive B.P, oxygen saturation using pulse Oximeter and baseline PR, BP and RR were recorded. Patients were positioned and under strict aseptic precautions. Lumbar puncture was performed with no: 23- or 25-gauge spinal needle Quincke type at L3-L4 or L2-L3 intervertebral space using midline approach. Following free flow of CSF, respective drug was administered according to the protocol. Patients were positioned supine immediately after the administration of intrathecal agents. Haemodynamic parameters - BP and HR –Baseline value 3, 5, 10, 30, 60, 90, 120 and 150 min depending on surgery. The obtained parameters were entered in the Microsoft excel and analysed using SPSS software version 21.0

Statistical Analysis

Distribution of age, gender and the incidence of comorbities were measured by percentage calculation, mean and standard deviation. The categorical variables were assessed using Pearson chi-square. Odds Ratio (OR) and 95% Confidence Interval (CI) were calculated. The variables were included if their respective Univariate analysis yielded P < 0.10. A backward stepwise elimination procedure based on the likelihood statistics (using removal probability of 0.10 and considering the change in classification accuracy) was also performed to identify the best subset of variables. In all the above test the “p” value of less than 0.05 was accepted as indicating statistical significance. Data analysis was carried out using Statistical Package for Social Science (SPSS, V 10.5) package.

Table 1: Basic demographic details

We can observe that the mean age of our study population was 52.83±15.88 years. Out of 300 patients we included, 78 (26%) of them were aged more than 50 years and the rest 222 (74%) were less than 50-year-old. The average weight was 56.05±8.26 kg. Distribution of age, gender did not have significant difference.

Figure 1: Distribution of Incidence of Bradycardia

Table 2: Distribution of Incidence of bradycardia against age

From the above table we can observe that the 64.6% of patients aged >50 years had developed bradycardia, which is significantly higher than those with <50 years. Whereas BMI did not have significant difference.

Figure 2: Distribution of incidence of bradycardia against gender of the study participants

There was almost equal distribution of the male and female patients among those who developed bradycardia, with p value of 0.61, which indicated no significant association between gender and incidence of bradycardia among our study population.

Table 3: Effect of Beta blockers on the incidence of bradycardia.

Patients who were on beta blockers had significant association with development of Beta blockers on administration of spinal anesthesia.

Table 4: Effect of CCB on the incidence of bradycardia.

The above table explains that the patients on CCBs had positive association with development of post spinal bradycardia.

Table 5: Significance of hypertension on the incidence of bradycardia.

Hypertension and diabetes did not have positive association but the CVS disorders had significant positive association with the incidence of bradycardia.

Table 6: Significance of Perioperative fluids on the incidence of bradycardia.

P > 0.05 (0.215) Perioperative fluids is not statistically significant

Table 7: Effects of drug dose on the incidence of bradycardia.

P > 0.05 (0.825) Drug dose is not statistically significant.

Table 8: Bradycardia in patients with history of anaemia and syncope respectively.

History of anaemia and syncope both had significant association with the incidence of Bradycardia after spinal anesthesia.All 48 patients developed bradycardia has been treated with Atropine. Also, all 48 patients who developed bradycardia had atleast one episode of either nausea or vomiting, indicating that the incidence of bradycardia is significantly associated with nausea and vomiting.

Spinal anesthesia is a technique, which has been used widely and frequently for many years. Efforts to improve the quality of anesthesia for patient have been the aim of all practicing   anesthesiologist. The incidence of hypotension is known but incidence of bradycardia not established and in various studies it ranges from 9 to 13 % and incidence of bradycardia increases with surgical events. In our study of the 300 patients were taken all patients received injection 0.5% hyperbaric Bupivacaine in varying doses. We found incidence of bradycardia 16% in our study.

Compare to earlier studies, in our study patients aged more than 50 years contribute to an statistically significant increase in the incidence of bradycardia. Gelaw M et al had reported similar outcome, even in their study the elderly patients were more prone for developing bradycardia, hence this clinical study had even suggested for prophylactic Atropine in their prospective cohort. This was consistent with the observation by Whiteside J et al. Whereas Carpenter RL et al and Lesser JB et al found younger age being increases the risk of bradycardia. We observed that the majority of the elder patients included in our study were known cases of Hypertension, they were on either beta blocker or CCBs, which in turn are the major factors behind bradycardia.

Unlike the earlier studies, in our study we did not find any significance of sex in increasing the incidence of bradycardia. p > 0.05 (0.613). Carpenter RL et al., Lesser JB et al, they found males are prone than females for bradycardia. This could be explained with the findings of Prabhavathi K et al, in which they have explained that Males as such will be having comparatively lower baseline for the heart rate than females. As the included cases here were suffering from pain due to the underlying surgical disease for which they have been posted for the surgery or the anxiety of surgery might have led to tachycardia among few patients. This would be the reason for no significant association between gender and the incidence of bradycardia in our patients.

Among our study population, we did not have significant association between the incidence of bradycardia and the BMI. Whereas Algarni RA et al had significant association with increased BMI. The study population in their trail were the pregnant women posted for the elective LSCS, which might have been the associated factor as well. Even in Chinachoti T and Tritrakarn T et al, BMI was a factor that increased the risk of hypotension as well as bradycardia.  

In our study we found ASA 1 patients have more incidence of bradycardia than other groups. P < 0.05 (0.001) as suggested in the following studies.Carpenter RL et al., Lesser JB et al., Liu S et al., also found ASA 1 patients have more incidence of bradycardia than other groups but Dohare S et al did not find such difference among their study population.

We found beta blocker and CCBs increases the risk of bradycardia as found in the earlier studies. p < 0.05 (0.000). Carpenter RL et al, Lesser JB et al, also found in their study beta blocker is a significant risk factor for bradycardia which is comparable to our study.

As these two drugs reduces the heart rate, they might aggravate the spinal block induced reduction in heart rate and thus the incidence of bradycardia.We found nausea increases the risk of bradycardia as found in the earlier studies. p < 0.05 (0.000). Carpenter RL et al, also found in their study nausea is a significant risk factor for bradycardia which is comparable to our study.

We found vomiting increases the risk of bradycardia as found in the earlier studies.            p < 0.05 ( 0.001). GratadourP et al, also found in their study vomiting is a significant risk factor for bradycardia which is comparable to our study.

In our study, CVS disorders increase the risk of bradycardia as found in the earlier studies. p < 0.05 (0.024). Liu S et al., found in their study that prolonged PR interval in the ECG is a significant risk factor for bradycardia.We found syncope increases the risk of bradycardia. p < 0.05 (0.022). Carpenter RL et al., found that syncope is a risk factor.We found hypertension increases the risk of bradycardia but diabetes has no significance. p < 0.05 (0.007) for hypertension and p value > 0.05 (0.099) for diabetes.Carpenter RL et al., found hypertension that is a risk factor.We found drug dose has no effect on the incidence of bradycardia. p < 0.05 (0.825). Carpenter RL et al., found that drug dose has no effect on the incidence of bradycardia. Also, there was no association between the incidence of bradycardia and the fluids administered, either the preload or the post load.

Majority of the clinical studies suggested that the increased dose of local anesthetic agent administered being strongly associated with the incidence of bradycardia, this could be due to the depth of blockade increasing with higher dose of the drug. Bupivacaine as such known to cause blockade of the inactivated cardiac sodium channels more potently than other LAs also been the cause of bradycardia. Hence, one of the limitation of study being not compared with other local anesthetic agents used for spinal block such as Ropivacaine.

In our study, the incidence of bradycardia was about 16% we found history of hypertension, syncope & anemia, ASA 1 patients, lower baseline heart rate, CCB, Betablockers, CVS disorders being the commonest risk factors for spinal anesthesia induced hypotension. Nausea and vomiting are significantly associated symptoms.

The awareness of these risk factors which significantly increases the incidence of bradycardia during SA helps in preventing the adverse crucial events of bradycardia and complications. It will also be a crucial step in preventing occurrence of such events by rational modification of the technique. Knowledge of such probable events in high-risk patients will allow early recognition & appropriate therapeutic intervention thus preventing further progress of complications.

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