Introduction and Need for study

Spinal Anaesthesia is a frequently employed anaesthesia technique in clinical practice. It is usually preferred for infra umbilical surgeries. However, most commonly noted complication following spinal anaesthesia is Post spinal anaesthesia hypotension (PSAH). PSAH occurs as a result of sympathetic blockade causing vasodilation of the arterioles, eventually leading to hypo perfusion and ischemia of vital organs. Pre-operative volume may differ depending upon the physical status, comorbidities, fasting, that make the patients susceptible to intra operative hypotension. Timely intervention is needed to prevent hypotension following spinal anaesthesia thereby reducing morbidity and mortality among the patients.  

 Several measures such as intra vascular volume preload or prophylactic vasopressors has been used to prevent intra operative hypotension. But, these measures pose a danger of volume overload, especially in patients with a pre-existing cardiac or renal pathology.

Several assessments have been tried to predict hypotension such as heart rate variability, perfusion index and passive leg raise test with equivocal results.^[1]

 Ultrasonography is emerging as an useful tool in daily clinical practice. Ultrasonography of Inferior vena cava (IVC) during spontaneous respiration helps to assess the volume status in a patient^[2]. Measuring the collapsibility index of IVC is found to be definitive, easy, low cost and non- invasive,  yet it has its own limitations in patients with upper abdominal tenderness, guarding of the abdomen, abdominal distension or in bronchial asthma or any respiratory illness.

Axillary vein/Subclavian vein is found to be an appropriate alternative for IVC to assess the volume status.^[3]

 Axillary/Subclavian vein is located near the surface of the skin but is subject to less external compression by the probe compared with the internal jugular or femoral veins and is easily assessed in most patients by using a linear probe.

 The goal of this study is to predict hypotension in patients receiving spinal anaesthesia by assessing the collapsibility index of infraclavicular axillary vein during spontaneous respiration and deep inspiration.

  REVIEW OF LITERATURE

 Choi et al. studied the preoperative diameter and collapsibility index of the subclavian vein (SCV) or infraclavicular axillary vein to predict the occurrence of hypotension after induction of general anaesthesia in patients scheduled for laparoscopic cholecystectomy. A total of 77 patients were recruited in this study and 19 patients among them developed hypotension of 34.1± 6.6 mm Hg. They were noted to have a higher collapsibility index of SCV during spontaneous breathing (P=0.009) and a higher collapsibility index of SCV during deep inspiration (P=0.002). This study concluded that the collapsibility index of the SCV during deep inspiration was a significant predictor of occurrence of intraoperative hypotension and percentage fall in MAP after general anaesthesia induction.^[4]

 Salama et al. evaluated the efficacy of IVC collapsibility index (IVCCI) and IVC to aorta diameter (IVC: Ao) index, measured pre-operatively for predicting post spinal anaesthesia hypotension. A total of 100 patients were enrolled in the study of which 45 patients developed PSAH and it was inferred that pre-operative IVCCI and IVC: Ao  index are good predictors of occurrence of PSAH, with IVC: Ao being a better predictor of PSAH.^[5]

Ceruti et al. evaluated the need for ultrasonography of IVC (IVCUS) guided volume optimization to prevent post-spinal hypotension. A prospective, randomised, cohort study, 160 patients scheduled for surgery under spinal anaesthesia were categorised into IVCUS group and Control group (group C) where there was no ultrasonography assessment made. The relative risk reduction of hypotension between the groups was 35% and the need for vasoactive drugs in the IVCUS group was relatively lower compared to the control group and the total amount of fluid administered was significantly higher in the IVCUS group compared to the control group. Here, IVC collapsibility was correlated with the amount of fluid administered. They also concluded that IVCUS is an effective method to prevent post spinal anaesthesia hypotension by administration of fluid through IVC via ultrasonography guidance before spinal anaesthesia.^[2]

 Zhang et al. studied the need for inferior vena caval ultrasonography before induction of General anaesthesia to predict hypotension. A total of 104 patients were recruited, but only 90 patients were analysed as the IVC scanning was unsuccessful in those 14 patients and mean blood pressure, maximum IVC diameter and collapsibility index were noted preoperatively obtained from the 90 patients included in the study. This study inferred that pre-operative ultrasonography was indeed a reliable predictor of hypotension after induction of general anaesthesia where the collapsibility index more than 43% was considered as threshold.^[6]

 Kent et al. conducted a prospective study regarding the interchangeability of IVC collapsibility index and SVC collapsibility index to assess intravascular volume status in surgical intensive care patients where 34 patients participated in the study. They underwent serial, paired assessment of IVC-CI and SVC-CI using portable ultrasound devices. It was concluded that SCV collapsibility index was a reasonable adjunct to IVCCI in surgical intensive care unit patients and the correlation between the two techniques is acceptable and overall measurement bias is noted to be low.^[3]

 OBJECTIVE OF THE STUDY:

 Determination of collapsibility index of the infraclavicular axillary vein during spontaneous respiration and deep inspiration to predict hypotension post spinal anaesthesia.

  MATERIAL AND METHODS:

 Source of data:

In this study, patients of either gender aged between 18 and 65 years, undergoing elective surgeries requiring spinal anaesthesia at M S Ramaiah Medical College and Hospital will be enrolled after taking a written informed consent.

 DURATION OF STUDY:

 March 2021-October 2022.

20 months.

 METHOD OF COLLECTION OF DATA:

 Sample size: 286 patients

 The study by Kent et al. (184:561 -566) has shown that IVC CI and SCV/AV CI has acceptable correlation. In the study by Salama et al. (36:297- 302) the incidence of PSAH was 45%. Based on  this findings with a absolute power of 5 and desired confidence level of 95%, it is estimated that 286 patients need to be recruited for this study.

 TYPE OF STUDY: Prospective observational study

Inclusion criteria:

 Patients undergoing elective surgery under spinal anaesthesia.

  Aged above 18 -65 years of either sex.

ASA Physical Status I and II.

 Exclusion criteria:

 Any contraindications for spinal anaesthesia.

BMI>30kg/m².

Pregnant women

  Emergency surgeries

 Autonomic neuropathy

 Methodology:

 Patients fulfilling the inclusion criteria will be taken up for the study after written informed consent.

 In the pre operative room, all patients will be lying supine, breathing spontaneously for at least 5 minutes before examination, followed by ultrasonography of the infraclavicular axillary vein using the Venue 40 (GE electronics) instrument and a linear high frequency ultrasound probe by an experienced anaesthesiologist. The axillary vein, beginning at the lower margin of the teres major as a continuation of Brachial vein and continues its course proximally until it terminates at the lateral margin of the first rib to become the subclavian vein. The infraclavicular axillary vein lies in the deltopectoral groove, deep to the pectoralis minor muscle. The probe is placed in the sagittal plane over the middle third of the clavicle and traced laterally to visualise the vein.

 The patients will be instructed to breathe normally at rest (spontaneous respiration) and then to inspire as deeply as possible and expire naturally (deep inspiration).The diameter of the infraclavicular axillary vein during spontaneous respiration (dAVmin) and deep respiration (dAVmax) will be recorded in M mode. The collapsibility index of the infraclavicular axillary vein will be given by (dAVmax - dAVmin)/dAVmax *100.

 No prior fluid loading will be done. Baseline vitals such as heart rate, blood pressure, and oxygen saturation will be noted during ultrasound study.

 The patient will then be transported to the operating theatre and vitals will be noted just prior to administration of spinal anaesthesia with the patient lying supine. Spinal anaesthesia will be performed with the subject in sitting position at L3-L4 intervertebral space with 25G Quincke needle and 3 ml of Inj. Bupivacaine 0.5% heavy will be administered. Patient will be immediately put in supine position and heart rate, blood pressure and oxygen saturation will be monitored every minute for the first ten minutes following which the vitals will be measured every five minutes till the end of the surgery. There will be neither any change in the position of the patient nor any surgical intervention in the first ten minutes. The Anaesthetist who will be performing the subarachnoid block and monitoring the intraoperative vitals will be blinded to the ultrasonographic measurement of subclavian diameter and collapsibility index. The level of spinal blockade, intra operative blood loss and volume of fluid administered will be noted and assessed.

 Crystalloids fluids will be infused at a rate of 10ml/kg body weight/hour after spinal anaesthesia.

 In this study, intraoperative hypotension is defined as an absolute value of SBP less than 90mm Hg or decrease in systolic blood pressure of more than 20% of the baseline or an absolute value of MAP less than 60mm Hg. Patients will then be divided into two groups depending on whether they develop PSAH or not.

  Any episodes of hypotension will be treated with fluid bolus of 200ml and if hypotension persists, bolus doses of IV of Inj. Ephedrine 6mg will be given. Inj. Atropine 0.6mg IV will be given for bradycardia (HR<50bpm).

 The correlation between preoperative collapsibility index of infraclavicular vein and developing hypotension will be assessed in this study.

 Statistical Analysis:

 Descriptive statistics will be employed to describe the continuous variables such as age, height, weight, Body mass index (BMI), etc. Percentages will be employed to describe categorical variables such as gender, ASA physical status, development of hypotension, presence of comorbidities, etc. Differences in the quantitative variables between the two groups such as those who developed hypotension and who did not develop hypotension will be tested for statistical significance by ‘Student t test’. In case the data does not follow normal distribution, non-parametric tests of significance will be employed. To test for differences in percentages between those who developed hypotension versus those not developing hypotension will be tested for statistical significance by Chi-square test of significance will be employed. To find out the independent predictors for development of hypotension, multivariate logistic regression analysis will be employed.

Sensitivity, specificity, positive and negative likelihood values will be estimated at different level of percentage deep inspiration. To predict the patients who are likely to develop hypotension versus not developing, receiver operating curve (ROC) drawn to estimate the cut off levels of deep inspiration.

References

 1. Duggappa DR, Lokesh M, Dixit A, Rinita Paul, RS Raghavendra Rao, P Prabha. Perfusion index as a predictor of hypotension following spinal anaesthesia in lower segment caesarean section. Indian J Anaesth 2017; 61:649 -654.

2.  Ceruti S, Anselmi L, Minotti B, D Franceschini, J Aguirre, A Borgeat, et al. Prevention of arterial hypotension after spinal anaesthesia using vena cava ultrasound to guide fluid management. Br J Anaesth 2018; 120:101 -108.

3.   Kent A, Bahner DP, Boulger CT, Daniel SE, Eric JA, David CE, et al. Sonographic evaluation of intravascular volume status in the surgical intensive care unit: a prospective comparison of subclavian vein and inferior vena cava collapsibility index. J Surg Res 2013; 184:561 -566.

4.Choi MH, Chae JS, Lee HJ, Woo JH. Pre-anaesthesia ultrasonography of the subclavian vein/infraclavicular axillary vein for predicting hypotension after inducing general anaesthesia: a prospective observational study. Eur J Anaesthesiol.2020; 37:474 -48.

5.Salama ER, Elkashlan M. Pre-operative ultrasonographic evaluation of inferior vena cava collapsibility index and caval aorta index as new predictors for hypotension, after spinal anaesthesia: a prospective observational study. Eur J Anaesthesiol 2019; 36:297 -302.

6.Zhang J, Critchley LA. Inferior vena cava ultrasonography before general anaesthesia can predict hypotension after induction. Anaesthesiology 2016; 124:580 -589.