Journal of Obstetric Anaesthesia and Critical Care

ORIGINAL ARTICLE
Year
: 2018  |  Volume : 8  |  Issue : 1  |  Page : 20--23

Baseline heart rate as a predictor of post-spinal hypotension in patients undergoing a caesarean section: An observational study


MC Joshi1, K Raghu1, G Rajaram2, N Nikhil3, Shishir Kumar4, Anuj Singh1,  
1 Department of Anaesthesiology, Command Hospital (Air Force), Bangalore, Karnataka, India
2 Deartment of Anaesthesiology, 5 Air Force Hospital, Jorhat, Assam, India
3 Department of Anaesthesiology, Axon Specilaity Hospital, Bangalore, Karnataka, India
4 Department of Anaesthesiology, Military Hospital, Pithoragarh, Uttarakhand, India

Correspondence Address:
Dr. K Raghu
Senior Resident, Department of Anaesthesiology, Command Hospital (Air Force), Bangalore
India

Abstract

Background: Hypotension is a well-known side effect of spinal anaesthesia in obstetrics patients undergoing caesarean section. This is likely to affect both mother and fetal well-being. Systemic haemodynamics are modulated by autonomic nervous system (ANS). Evaluation of ANS may be helpful in predicting hypotension. The present study is designed to identify the subset of pregnant patients at higher risk of developing post-spinal hypotension based on baseline heart rate (HR) prior to administration of anaesthesia. Materials and Methods: This was a prospective study conducted on 100 patients aged 20–30 years, of American Society of Anaesthesiologists (ASA) grade I or II, scheduled for elective caesarean section under spinal anaesthesia. Patients were divided into two groups based on their baseline HR. Incidence of hypotension and ephedrine requirement following spinal anaesthesia were noted. Results: Thirty nine patients out of 100 developed hypotension (39%), of whom 27 were in the group with HR >91 beats per minute (bpm) (50.9%) and 12 patients were in the group with HR <90 bpm (25.5%). The incidence of hypotension was statistically significant between two groups (P = 0.0260). The use of ephedrine was greater in group with HR >91 bpm than group with HR <90 bpm (mean 3.9 ± 0.45 vs 4.34 ± 0.45, P = 0.0148) and it was statistically significant. Conclusion: Pre-operative baseline HR may be used to predict risk of post-spinal hypotension in obstetric patients undergoing caesarean section.



How to cite this article:
Joshi M C, Raghu K, Rajaram G, Nikhil N, Kumar S, Singh A. Baseline heart rate as a predictor of post-spinal hypotension in patients undergoing a caesarean section: An observational study.J Obstet Anaesth Crit Care 2018;8:20-23


How to cite this URL:
Joshi M C, Raghu K, Rajaram G, Nikhil N, Kumar S, Singh A. Baseline heart rate as a predictor of post-spinal hypotension in patients undergoing a caesarean section: An observational study. J Obstet Anaesth Crit Care [serial online] 2018 [cited 2020 Oct 26 ];8:20-23
Available from: https://www.joacc.com/text.asp?2018/8/1/20/230067


Full Text



 Introduction



Spinal anaesthesia is the most commonly used method of anaesthesia for caesarean section. The most common complication of spinal anaesthesia in pregnant patients is hypotension, with incidence of up to 71%.[1] Hypotension during spinal anaesthesia is mainly due to decreased systemic vascular resistance and blockade of preganglionic sympathetic fibres.[2]

Hypotension due to any cause may have serious deleterious effects on mother and neonate.[3] Specifically, hypotension as a result of anaesthesia can be prevented to some extent with prophylactic ephedrine,[4] pelvic tilt and intravascular volume expansion. However, none of the currently available strategies is entirely effective in preventing hypotension caused by spinal anaesthesia.[5] Therefore, prediction and prevention of maternal hypotension are potentially important.

Systemic haemodynamics are modulated by autonomic nervous system (ANS).[6] Pre-operative determination of the autonomic tone might provide an opportunity to detect patients at risk of developing severe haemodynamics impairment following spinal anaesthesia. There are several methods to determine autonomic tone. Of these, a convenient, handy and non-invasive method of measuring activity of ANS is analysis of heart rate (HR).[7]

With this backdrop of information, this study was conducted to determine the association of pre-operative HR with post-spinal hypotension in patients coming for caesarean section.

 Materials and Methods



This was a prospective study undertaken at a tertiary care centre between July 2017 and November 2017 after taking approval from Institution Ethical Committee. One hundred patients aged 20–30 years, of American Society of Anaesthesiologists (ASA) grade I or II, scheduled for elective caesarean section under spinal anaesthesia were included. Patients with significant cardiovascular, renal, hepatic diseases, thyroid disease and patients who refused to give consent were excluded from the study. All patients were explained in detail about the anaesthetic procedure and written informed consent was obtained.

Before spinal anaesthesia, all the patients were preloaded with 500 ml of lactated Ringer's solution 15 min prior to spinal anaesthesia. No anticholinergics were given as pre-medication. Basal HR was determined with pulse oximeter by taking average of five independent recordings, every minute in sequence. Baseline blood pressure was recorded by taking average of five independent recordings, every minute in sequence with the help of non-invasive blood pressure monitor. Patient's peripheral oxygen saturation, surface temperature, and electrocardiogram were monitored. Basal values were recorded.

We divided subjects into two groups based on their baseline HR. The patients having a HR of 90 beats per minute (bpm) or less were included in group 1, while those having HR of 91 bpm or more were included in group 2. The patients were placed in sitting position and dural puncture was performed at L3-L4 inter space. Hyperbaric bupivacaine (0.5%) 2.5 ml was injected intrathecally and patient made to lie down with wedge under right buttock. Blood pressure measurement was recorded immediately after subarachnoid block and repeated every 3 min in first 30 min and cycled to 5 min till end of surgery. Patients developing more than 20% drop in their mean arterial pressure (MAP) were noted and treated with parenteral ephedrine 3 mg bolus. Ephedrine treatment was repeated as indicated up to maximum of 30 mg throughout the surgery. The amount of ephedrine administered within 30 min after spinal anaesthesia was used to calculate ephedrine requirements.

Sample size estimation was based on previously published data evaluating maternal hypotension during caesarean section under spinal anaesthesia.[8],[9] We included 100 patients in the study to increase statistical power. Fisher's exact test was used to compare incidence of hypotension and Student's t-test was used to compare ephedrine requirements. P < 0.05 was considered statistically significant.

 Results



One hundred patients aged 20–30 years, of ASA grade I or II, scheduled for caesarean section under spinal anaesthesia were enrolled for this study [Table 1]. Patients were divided into two groups based on their baseline HR [Figure 1]. The patients having a HR <90 bpm in group 1, while those having HR >90 bpm were included in group 2; 47 patients were included in group 1 and 53 patients in group 2. There was no statistical difference between the two groups in age, weight, height, and duration of surgery. Incidence of hypotension and ephedrine requirement following spinal anaesthesia were noted. Thirty-nine patients out of 100 developed hypotension (39%), of whom 27 were in the group 2 (50.9%) and 12 patients were in the group 1 (25.5%). The incidence of hypotension was statistically significant between two groups (P = 0.0260) [Table 2]. The use of ephedrine was greater in group 2 than group 1 (mean 3.9 ± 0.45 vs 4.34 ± 0.45, P= 0.0148).{Table 1}{Figure 1}{Table 2}

 Discussion



Spinal anaesthesia is a commonly performed technique for obstetric patients coming for caesarean section.[10] The higher risk of maternal complications associated with general anaesthesia compared with central neuroaxial blockade has led to increased use of spinal anaesthesia for elective and emergency caesarean section.[11] Generally, spinal anaesthesia is well-tolerated, but the most common side effect of spinal anaesthesia is hypotension.[12] Hypotension following spinal anaesthesia may have serious adverse effects for both mother and foetus. There are many methods to prevent hypotension following spinal anaesthesia, which include pre-loading, pelvic tilt, prophylactic ephedrine, but no single method is entirely satisfactory and applicable to all patients.

Predictive factors of maternal hypotension during caesarean section under spinal anaesthesia that have been reported previously include HR >90 bpm, complaints of dysphoria following postural change from left lateral to supine position, high Pleth Variability Index (PVI) before anaesthesia.[13],[14],[15] Systemic haemodynamics are modulated by ANS.[6] Pre-operative determination of the autonomic tone might provide an opportunity to detect patients at risk of developing severe haemodynamics impairment following spinal anaesthesia. There are several methods to determine autonomic tone. Of these, a convenient, handy and non-invasive method of measuring activity of ANS is analysis of HR. Therefore, pre-operatively analysed HR may predict hypotension following spinal anaesthesia and identify at risk patients. This can prove beneficial in initiating measures to prevent hypotension in at risk patients.

Present study demonstrated that the higher the baseline HR, higher is the risk of developing hypotension during spinal anaesthesia. The cut-off value of HR >90 bpm was based on previous studies.[15]

Sakata et al.[8] conducted a study to predict hypotension during spinal anaesthesia for elective caesarean section by altered HR variability. They found out that hypotension occurred in 35/45 patients (77%), of whom 21 (60%) were in those who had LF/HF ratio >2, and 14 were in the LF/HF ratio <2 (40%) and it was statistically significant (P < 0.01). The normal variability of the HR is due to the actions of the two branches of the ANS. Because of continuous changes in the sympathetic and parasympathetic balance, the sinus rhythm exhibits fluctuations around mean HR. The rate of fluctuation (in terms of average duration of one cycle) can be discriminated into three ranges. There are (1) fast fluctuations (few seconds to ten seconds), (2) slow fluctuations (some ten seconds to a few minutes) and (3) very slow variation (few minutes to hours). Fast fluctuation (high frequency – 0.15–0.4 Hz) corresponds to respiratory sinus arrhythmia and is modulated solely by parasympathetic nervous system, which was proved in clinical and experimental observations of autonomic manoeuvres such as electrical vagal stimulation, muscarinic receptor blockade and vagotomy. Slow fluctuations (low frequency – 0.04–0.15 Hz) correspond to blood pressure oscillations (Mayer waves) and jointly modulated by the sympathetic and parasympathetic nervous system. The LF/HF is ratio of the power of low- and high-frequency components contributing to HR variability. The higher ratio indicates greater the pre-operative HR and also predicts severe maternal hypotension. Their results were comparable to our study in terms of predicting hypotension based on HR.

Shahram khan et al.[16] conducted a study to evaluate effect of pre-operative HR on post-spinal hypotension in obstetric patients. They found out that incidence of hypotension was more in group with HR >91 bpm (31.82%) than patients with HR <90 bpm (11.86%) with P value of <0.001. The results of our study are comparable to this study in correlating higher pre-operative HR and development of post-spinal hypotension.

Hanns et al.[17] conducted a study to evaluate effect of HR variability in predicting hypotension after spinal anaesthesia for elective caesarean delivery. They found out that LF/HF (the LF/HF is ratio of the power of low- and high-frequency components contributing to HR variability) ratio >2.5 may indicate a high risk of hypotension after spinal anaesthesia. An LF/HF ratio of <2.5 may indicate low risk of hypotension. The results of this study are comparable to ours in terms of correlating the higher pre-operative HR and post-spinal hypotension.

The main limitation of our study is the small sample size. However, we can use this evidence as basis for future research to better establish the relationship between pre-operative HR and post-spinal hypotension.

 Conclusion



There is significant association between pre-operative HR and post-spinal hypotension in obstetric patients undergoing caesarean section.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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