Background

• Postoperative pulmonary complications (PPCs) are common and increase patient mortality. PPC includes respiratory infection, respiratory failure, pleural effusion, atelectasis, pneumothorax, bronchospasm, and aspiration pneumonitis.General anaesthesia and mechanical ventilation are important causative factors for PPC’s. One of the most common complications of spine surgeries are PPC as the surgery is done in prone position and can be a long duration surgery.

• The newest concept of driving pressure (DP) ventilation and mechanical power has shown to reduce PPCs in surgical patients. DP ventilation is (Pplat- PEEP) and is the pressure required for alveolar opening.Mechanical power refers to the quantity of energy per unit of time, measured in joules per minute (J/min). It is calculated as 0.098 x VT x respiratory rate x [(Ppeak -(0.5 x DP)]

Purpose and need of the study

• The effect of driving pressure guided ventilation on different types of surgeries is practiced although its effect on lumbar spine surgeries has not been explored. Our aim is to assess the association of driving pressure and mechanical power on the occurrence on postoperative pulmonary complications in lumbar spine surgeries.

Methodology - Patients are randomised into two groups: Conventional ventilation group and Driving pressure guided ventilation group. A sample size of 50 with 25 in each group will be recruited. R programming version 4.1.2(R core team 2023,Vienna,Austria) will be the software used for statistical analysis. Descriptive statistics will be summarized with Mean ± SD for continuous variables and Number (%) for categorical values. Inferential statistics will be done using Student t test for continuous variables and Chi square test to test the association of outcome between the groups.

• Standard anesthesia will be given to these patients  along with a postinduction Arterial blood gas(ABG) .Patient will be positioned prone and ventilated with the following settings based on the group:

• Conventional ventilation (CV) group: Volume controlled mode(VCV), Fractional inspired oxygen (FiO2)-0.5, Positive end expiratory pressure(PEEP) 5 cm H2O, Respiratory rate(RR)-12-14/min to maintain EtCO2 32-36 mm Hg, Inspiratory: Expiratory ratio(I:E)=1:2,Tidal volume(VT)-6ml/kg predicted body weight(pbw).

• Driving pressure ventilation group (DV):Along with conventional settings , recruitment which involves gradual increase of PEEP from 5 to 10 and then to 15cm H2O for every 5 breaths will be done. After 10 breaths, a decrease of PEEP to 10 will be then done. Driving pressure will be measured at the 10th respiratory cycle. A slow decrease of PEEP every 2cm H2O (from 10 to 8 and then to 6) after every 10 breaths will be done.  At the end of 10th respiratory cycle in each PEEP, the DP will be calculated. Thereafter, the patient will be ventilated with the PEEP corresponding to the lowest DP for the next hour. Repeat cycle of recruitment and lowest DP based ventilation will be done every hour until the end of surgery.

• Every 15 min, hemodynamic parameters and ventilatory parameters will be noted. Pre extubation ABG will be done and postoperatively patients will be followed up for PPCs at 12 hours, postopday(POD)1, POD3 and POD7 or at the time of discharge whichever is earliest. A lung ultrasound will be done on POD3 in the ward to identify any signs of PPCs.