Role of Inferior Vena Cava Dispensability Index in Predicting Hypotension of Cement Syndrome in Hip Replacement Surgery Under General Anaesthesia

Preoperative Settings:

Patients scheduled for elective hip replacement surgeries involving cementation at Ain Shams University Surgery Hospital will be identified and those meeting the inclusion criteria will be approached and enrolled after providing informed consent.

Patients will be confirmed to have fasted for 8 hours before surgery. Medical history will be taken, examinations performed, and laboratory results will be reviewed. A wide bore intravenous line (18-gauge) will be secured, and standard monitoring (ECG, blood pressure measurement, and pulse oximetry) will be applied.

Baseline blood pressure, heart rate, and mean arterial pressure will be recorded.

Intraoperative procedure:

To induce general anaesthesia, we will be using fentanyl (1-2 μg/kg), propofol (1.5-2 mg/kg) and non-depolarizing muscle relaxants (rocuronium or cis-atracurium) according to age, weight, chronic organ function and the needs of the surgery.

All patients are monitored continuously using ECG, pulse oximetry and capnography starting from the beginning of manual ventilation. Ventilatory parameters adjusted to PCO2 <40 mmHg (respiratory rate 12 breaths per minute,), with a tidal volume of 6 to 8 ml/kg, positive end-expiratory pressure (PEEP) of 6 cmH2O and inspired oxygen fraction (FiO2) of 50.

Noninvasive blood pressure measurements (mean arterial pressure (MAP) are obtained at 10 min intervals although the operation, an additional measurement is obligatory 2 min after induction, drug administration and during measurement of IVC-DI and 5 min pre- and post-cementing for 15 min, all measurements will be performed in the semi-recumbent position (head elevated 30°).

The inferior vena cava will be visualized in B-mode using ultrasound machine with Low-frequency curvilinear probe (2-5 MHz) or phased-array probe while patient in supine position the probe will be placed in subxiphoid (subcoastal) area, just below the sternum (from a longitudinal paramedian subxiphoid view). IVC can be differentiated from the aorta utilizing pulse wave Doppler. With M-mode imaging, done 2 to 3 cm distant to the right atrium, The last section of the vein, which is proximal to the hepatic vein inflow and 0.5-3 cm from the right atrium, will be selected, with Use of the callipers to measure the maximum IVC diameter (Dmax) during inspiration and the minimum IVC diameter (Dmin) during expiration. Then the IVC distensibility index is calculated and recorded using the formula: IVC distensibility index = [(maximum diameter on inspiration-minimum

diameter on expiration)/minimum diameter on expiration (Lujan Varas et al, 2015). All IVC measurements are taken post intubation 3 times and the mean value recorded. Patients will be divided into two groups.

Group A: those who develop hypotension post cementation. Group B: those who do not develop hypotension post cementation. In the study Hypotension will be defined as MAP < 60 mmHg or a decrease in SBP by > 20% from baseline. In case of persistent mean arterial pressure less than 55 mmHg, a 6 mg dose of ephedrine will be titrated. After two doses of ephedrine, another fluid bolus of 5 ml/kg will be given, followed by another dose of ephedrine until hypotension is corrected.

The primary outcome:

Cut off value of IVC-DI at which we can predict the incidence of hypotension following cementing in orthopedic surgery.

Secondary outcomes Intra-operative hemodynamic, the need of vasoactive drug administration, and the amount of fluid administered.