To Study the Hemodynamic Changes from Supine to Prone Position in Asa II and III Patients Undergoing Major Spine Surgery in Prone Position using Flo Trac Sensor: An Observational Study

OBJECTIVES: This observational study assessed the hemodynamic changes that occurred in ASA II and III patients undergoing major elective spine surgery on changing position from supine to prone using the Flo Trac sensor. Additionally, it observed the effect of 10ml/kg of crystalloid fluid administered as a bolus before turning prone. METHODS: Twenty-nine patients were prospectively studied. Patients with valvular heart disease, chronic obstructive pulmonary disease, renal dysfunction and arrhythmia were excluded . After establishing venous access, radial arterial cannulation was undertaken and the Flotrac transducer was connected. Other routine monitors were connected. Induction was carried out with fentanyl, propofol and vecuronium; patients were intubated and mechanical ventilation established with tidal volumes of at least 8ml/kg. Anaesthesia was maintained with air /oxygen and Isoflurane titrated to a MAC of 0.8. Variables measured were heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), stroke volume variation (SVV), pulse pressure variation (PPV), cardiac output (CO) and cardiac index(CI). Variables were measured after induction in the supine position (T1) and every 5 minutes after turning prone up to 15 minutes (T2-T4). All patients received fluid bolus of 10ml/kg of crystalloids before change of position. A fall in cardiac index by more than 20% from baseline (T1) warranted treatment with crytalloids upto 10ml/kg and/or boluses of vasopressors. Failure to respond to these warranted starting inotropic agents. Statistical analysis was performed using SPSS software. A General Estimating Equations (GEE) analysis was performed to analyze the change in variables across the time points (T2-T4) along with the significance of change (p value), with T1 as the reference. A paired t-test analysis was additionally done between time points T1 and T4. Correlation between variables (PPV and CO, SVV and CO and PPV and SVV) were assessed in the prone position at two time points using Pearson correlation test. Levene's test for Equality of Variance was used to analyse the difference in variables among patients on differing prone supports and among diabetic versus non-diabetic patients. RESULTS: There was a significant change in SBP (p=0.025), SVV (p=0.002) and PPV(p=0.02) 5 minutes after change of position to prone. However, there was no significant fall (p>0.05) in CO or CI during this time. There was a significant change in all hemodynamic variables (HR: p<0.001, SBP p<0.001, MAP p=0.014, PPV:p=0.024, SVV p=0.002, CO p<0.001, CI: p=0.003) except DBP 15 minutes after turning prone. A strong positive correlation was found to exist between SVV and PPV at T2 (r=0.835; p=<0.001) and T4 (r=0.75; p<0.001) while CO correlated weakly with SVV and PPV. Type of support (Relton-Hall vs. bolsters) and presence of diabetes did not significantly affect PPV and SVV. In conclusion, there was a statistically significant change in all hemodynamic variables 15 minutes after turning prone. There was no significant fall in CO or CI 5 minutes after turning prone; whether this can be attributed to the fluid bolus administered before change in position cannot be established at present.