A comparative study of pulse pressure variability and inferior vena cava dispensability index for evaluation of fluid responsiveness at 2 different tidal volumes during mechanical ventilation

Hypovolemia leading to hypotension after induction of anaesthesia is common occurrence due to action of anaesthetic drugs and pre-op starvation. Intra operative hypotension has been implicated as major contributing factor for post-operative morbidity; it may prolong hospital stay and is associated with major postoperative complications including acute kidney injury, myocardial injury and death. Thus, intra-operative fluid resuscitation plays a major role in maintaining the hemodynamic stability in surgical patients This study is a comparative study of pulse pressure variability and inferior vena cava dispensability index for evaluation of fluid responsiveness at 2 different tidal volumes during mechanical ventilation. Approval for conducting the study will be taken from Institutional Ethics Committee. Patients for the study will be selected by simple random sampling method from those who fulfil the inclusion criteria. A multipara monitors with facility to measure PPV from arterial pressure waveforms and record vital signs of the patients will be used. Routine anaesthesia induction with 1.5–2.5 mg/kg Propofol, 0.5 mg/kg Atracurium (0.6– 1.0 mg/kg Rocuronium) .TV adjustment will be carried out after about 10 min when the hemodynamics of the patient become stable. If hypotension occurs during the surgery before giving bolus, it will be treated as per standard protocol by fluid infusion or drug therapy. The TV will be adjusted to 8 mL/kg and the respiratory rate will be maintained at 9 cycles/min. Heart rate (HR), diastolic blood pressure, systolic blood pressure, mean arterial pressure (MAP), PPV, peak pressure (Ppeak), plateau pressure, the VTI of the left ventricular outflow tract, and IVC-DI will be recorded. The velocity-time integral (VTI) of the left ventricular outflow tract will be measured by transthoracic echocardiography. Blood flow of the left ventricular outflow tract will be recorded by pulsed Doppler echocardiography on an apical five-chamber view. Sample volume lines will be placed in the aortic annulus and VTI will be measured. The IVC diameter (IVC inspiration/IVC expiration) will be measured at the subxiphoid transabdominal long axis, the position of the section will be 2–3 cm from the distal end of the right atrial opening of the IVC. The diameter of the IVC at the end of inspiration (IVC inspiration) and the diameter of the IVC at the end of expiration (IVC expiration) will also be measured. The IVC-DI is calculated as (IVCinspiratory - IVCexpiratory)/ IVCexpiratory X 100%. The TV will be adjusted to 10 mL/kg and the respiratory rate will be maintained at 9 cycles/min. The indices will be recorded after maintenance for 2 min and the airflow will be maintained at 1L/min. So, Measurements will be taken for total of 4 times -2 times before fluid infusion and 2 times after fluid infusion. Before and after fluid infusion, tidal volume will be adjusted to 8 and 10 ml/kg. After each adjustment measurements will be taken. Fluid challenge: Ringer’s lactate solution (RL) will be infused intravenously over a 10-min period with a total infusion volume of 6 mL/kg that served to observe fluid responsiveness. The tidal volumes of 8 and 10 mL/kg will be adjusted immediately after the fluid challenge and maintained for 2 min, and then the above indices will be recorded again.  There is no grouping done before the study. Patients with an increased VTI of the left ventricular outflow tract (â–² VTI) ⩾15% after the fluid challenge will be classified as fluid responsive (R group) and patients with a â–² VTI of < 15% will be analysed and classified as fluid non-responsive (NR group).