Left ventricular outflow tract velocity time integral versus inferior vena cava collapsibility index for prediction of spinal anaesthesia induced hypotension during abdominal hysterectomy an observational study

Spinal anaesthesia is a safe and reliable method frequently used in various lower abdominal, orthopaedic, obstetric and gynaecological surgeries. It has advantages such as the rapid onset of action, cost-effectiveness and ease of administration. However, hypotension and bradycardia are common side effects of spinal anaesthesia that may lead to several adverse outcomes including coronary ischaemia and delirium. Hypotension following spinal anaesthesia results from the sympathetic blockade and decreased cardiac output (1). Patients with inadequate volume reserve before induction of anaesthesia, older age, known hypertensives, patients with diabetes mellitus are highly susceptible for post- spinal hypotension. Many methods such as preventive empirical volume loading or prophylactic vasopressors, have been used to lower the incidence of hypotension following spinal anaesthesia (2). However, intravenous volume preload carries the potential for volume overload, particularly in patients with cardiac disease (3). Furthermore, due to different definitions of hypotension and diverse patient populations, the effect of volume preload on prevention of hypotension is still controversial. (2)

While recognition and correction of latent hypovolemia are crucial for safe spinal anesthesia practice, assessment of the intravascular volume status is challenging for clinicians. Traditionally anaesthetists have assessed static hemodynamic modalities such as blood pressure, heart rate (HR) variability, central venous pressure for assessing volume status.

Point of care ultrasound (POCUS) and focused cardiac ultrasound are now considered the 21st century stethoscopes with the unparalleled diagnostic modality as they provide real time, dynamic assessment of patient’s hemodynamic status.

Sonographic determination of inferior vena cava (IVC) diameter collapsibility index (IVCCI) has been extensively used for assessing volume status. But. IVCCI was found to have poor diagnostic accuracy for prediction of post-spinal anaesthesia hypotension (PSH) in spontaneously breathing patients predicting post-spinal hypotension in adult patients undergoing elective surgery. (4)

The change in dimensions of the IVC depends entirely on fluctuations in intrathoracic pressure therefore, in spontaneously breathing patients, the degree and the rate of the respiratory effort is an important and difficult-to-quantify variable. Thus, respiratory variations in the IVC diameter provide only weak to moderate diagnostic accuracy in predicting fluid responsiveness (5,6)

The left ventricular outflow tract (LVOT) is the origin of cardiac output. Velocity time integral (VTI) is the length of the hypothetical column of blood which passes through Doppler ultrasound. The left ventricular outflow tract velocity time integral (LVOT VTI) as assessed by transthoracic echocardiography (TTE), is being used in intensive care as a measure of stroke volume (SV) and to guide fluid therapy. (7) LVOT -VTI has been reported to have good diagnostic accuracy (77.4%) for prediction of hypotension after general anaesthesia. (8,9)

Women undergoing abdominal hysterectomy are likely to develop post spinal hypotension (PSH) often due to advanced age, starvation , bowel preparation before surgery and sometimes large uterus size due to large fibroids. Accurate prediction of spinal anesthesia-induced hypotension could enhance clinical decision-making, alter therapeutic management, and lead to appropriate early interventions. Hence this prospective observational study is designed to assess the diagnostic accuracy of LVOT -VTI for prediction PSH in patients undergoing elective abdominal hysterectomy and to compare it with IVC-CI.