Pre-Operative Measurement of Indices

 The patient will be wheeled into the pre operative area, and the procedures will be explained  to the patient and informed written consent will be obtained in a language that is understood  by the patient. Following this, the diameters of the Inferior Vena Cava, Abdominal Aorta,  Subclavian vein will be measured in supine position, as described below

 To  measure Caval Aorta index

 The IVC diameter will be measured using a curvilinear probe of 2 to 5MHz of the USG  machine. The probe will be placed in the subxiphoid region where the confluence of the  hepatic veins can be visualized that drain into the IVC in the B mode. 1cm caudal to the confluence of the  hepatic veins and IVC, the greatest internal anterior posterior diameter of the IVC in the  longitudinal plane will be measured, in the M mode. In the subxiphoid region, lying left  lateral to the IVC, will be the Aorta; the maximum internal AP diameter of the Abdominal  Aorta will be measured in the longitudinal plane, on the M mode 10 mm above the coeliac trunk.

                       Ultrasound guided Subclavian Vein Measurements

Ultrasonographic measurements will be performed before induction of general anesthesia . All patients will lie at supine position  and breathing spontaneously for at least 5 min before assessment. Right SCV diameters will be measured in the supine position using ultrasonography device and a high-frequency linear probe 6 to 14MHz. The short axis image of the SCV will be obtained by placing the probe just below the clavicle and scanning it from the midline laterally.

The patient in the supine position will be asked to do a normal inspiration and then a deep inspiration which is as deeply as possible and exhale naturally, and the minimum diameter and maximum diameter of the SCV will be measured in the M mode of ultrasound at a medium sweep speed during both normal and deep inspiration.

                       The mean of three measurements will be selected. 

                        Anesthetic Procedure

In the operation theatre, ASA standard monitors will be attached to the patient. The values of  Heart rate , systolic blood pressure , diastolic blood pressure  and mean  blood pressure, obtained in supine position before any intervention or drug  administration will be considered as Baseline Values. A 18G peripheral intravenous cannula  will be secured, and Ringer Lactate infusion will be started 10ml per kg per hr. Following drugs  will be administered for induction of general anesthesia.  Premedication with Inj. Midazolam  1mg i.v. stat, Inj. Fentanyl 2mcg per kg for analgesia Induction with Inj. Propofol 2mg per kg  for induction inhalational agent used will be Sevoflurane 2 to 4 percent to achieve a MAC of 1.0, &  Inj. Vecuronium 0.1mg per kg for muscle relaxation. For the next five minutes, the  hemodynamic parameters, i.e., HR, SBP, DBP, & MAP, will be measured every minute.  During these five minutes, the patient will be ventilated by volume-controlled mode with the  following ventilation setting: Tidal volume 6 to 8ml per kg, Frequency 12 per min, PEEP 0 cm of

 H  ₂ O, Inspiratory and expiratory ratio of 1 and 2. After the fifth minute, the        patient will be intubated to secure the airway.  Hypotension will be defined as a fall of SBP by more than 20 percent at any point of time, and it will be  treated by giving IV fluid, and or Inj. Mephentermine 3 to 6 mg i.v. bolus.