Study of changes in inferior vena cava diameter using ultrasonography guided technique preoperatively and intraoperatively in patients undergoing spinal anesthesia for lower limb and perianal surgeries

Introduction Neuraxial blockade (Spinal, Epidural and Caudal neuraxial blocks) has various routine clinical applications for surgery, obstetrics, acute postoperative pain management, and chronic pain relief.1 Single-injection subarachnoid block or epidural anaesthesia by using local anaesthetic drug is most commonly used for the lower abdomen, pelvic organs (e.g., prostate, uterus and urinary bladder), and lower limbs surgeries, and for caesarean deliveries. Neuraxial blocks result in one or a combination of sympathetic blockade, sensory blockade, or motor blockade depending on the dose, concentration, and volume of injected local anaesthetics. Despite these similarities, there are significant technical, physiologic, and pharmacologic differences, spinal anaesthesia, requires a small mass (i.e., volume) of drug to produce rapid (<5 minutes), profound, reversible sensory analgesia in comparison with epidural and caudal anaesthesia. Therefor spinal anaesthesia almost devoid systemic pharmacologic side effects of local anaesthetic drug when compared to other neuraxial blocks like caudal and epidural analgesia. Unfortunately, these neuraxial blocks leads to blockade of the peripheral (T1-L2) and cardiac (T1-T4) sympathetic fibres in addition to sensory and motor fibres, which is responsible for reduced arterial blood pressure by decreasing cardiac output and systemic vascular resistance1,2,3 Spinal anaesthesia is commonly used in routine clinical practice. Hypotension, bradycardia, nausea, vomiting and shivering are common side effects observed following spinal anaesthesia. Hypotension followed by spinal anaesthesia is mainly attributed to both the factors including reduced systemic vascular resistance (SVR) and reduced cardiac output. There are so many factors which can affect intraoperative blood pressure after spinal anaesthesia including preoperative volume status, comorbidities, physical status, pre-operative medications, duration of fasting and fluid resuscitation. Spinal Induced Hypotension (SIH) is a very common side effect with an incidence of 15.3–33% which may lead to organ hypo-perfusion and ischemic events if not managed timely.4,14 Preoperative assessment of inferior vena cava (IVC) diameters by ultrasonography and calculation of IVC collapsibility index (IVC-CI) might identify patients with intravascular volume depletion. Therefore, to give clinically relevant conclusions, it has become very important for us to be more precise about the definition of hypotension under anaesthesia, best method of IVC diameter assessment by ultrasound, and also to provide the cut-offs for IVC diameter and the collapsibility index for prediction of hypotension after anaesthesia.5 To minimize hemodynamic impairment, preventive empiric volume loading is commonly performed in anaesthesia before giving spinal anaesthesia. However, fluid preload has been proved to lower the incidence of SIH and significantly decrease vasopressor requirements. Various parameters have been studied in past few years to estimate intravascular volume status of patients before inducing spinal or general anaesthesia. Ultrasonographic determination of inferior vena cava (IVC) diameter was used in spontaneously breathing patients for assessment of intravascular volume and was reported to be reliable, noninvasive, and easy.6 If we can find strong correlation between blood pressure variation and IVCCI, we can calculate and decide cutoff value for hypotension or low volume status of patient and thus we can manage patients prior to any end organ damage. We can also avoid unnecessary fluid preload, sometimes which may lead to fluid overload. We can also perform a bedside ultrasound to know volume status in ICU patients before and after starting fluid therapy where fluid management plays a crucial role in prognosis of patient. Now days ultrasound is not only limited to radiologist, Point of care ultrasound is being popular in the field of emergency physicians, and anaesthesiologists. It can also be used for patients in ICU setups to guide goal directed fluid therapy especially in patients with renal failure, cardiac failure and sepsis. Recently, few studies were conducted for measurement of Inferior Vena Cava Compressibility Index (IVCCI) and they have also concluded IVCCI as a reliable or good predictor of arterial hypotension after induction of general anaesthesia.7,8,9 The aim of this study was to evaluate the ultrasound guided IVC diameter changes preoperatively and intraoperatively in patients undergoing spinal anaesthesia for lower limb and perianal surgeries.