BACKGROUND: Volume controlled ventilation (VCV) mode is the most commonly used conventional mode in anesthesia. VCV follows a constant flow pattern to deliver a preset tidal volume in the preset inspiratory time, thus ensuring constant minute ventilation. This flow pattern generates high inspiratory pressure that can lead to shear stress injury, barotrauma and volutrauma to the alveoli^[1] leading to microatelectasis and inflammatory mediator release characteristic of ventilator‑associated lung injury.

Pressure controlled ventilation (PCV) mode came as an alternative mode in laparoscopic surgeries. PCV delivers tidal volume at a preset pressure and inspiratory time. The flow, unlike VCV, is decelerating. This flow pattern has a high initial rise followed by a decrease and helps to attain the tidal volume at lower peak inspiratory pressures, and oxygenation is also better due to the initial high flow rates. However, with changing lung compliance, the tidal volume delivered varies, and there is always a risk of hypoventilation or hyperventilation.

Pressure regulated volume controlled mode (PRVC) is a new mode introduced recently in anesthesia workstations. PRVC features a user select tidal volume target that is autoregulated and pressure controlled.^[2] The ventilator calculates the compliance of the lung and establishes the lowest possible pressure to deliver the target tidal volume. It has the characteristic decelerating flow pattern, thus incorporating the benefits of both VCV and PCV.^[3]

Recently, few studies comparing the efficacy of PRVC over other modes on selected surgical cohorts have been published with varying results. Boules NS et al. has not observed any difference in respiratory and ventilatory parameters. Oxygenation index was comparable between both PCV and PRVC modes of ventilation when compared in patients undergoing abdominal cancer surgery under general anaesthesia.^[4]

Kothari A et al. had observed similar result when the compared patients’ undergoing laparoscopic cholecystectomy. In their study it was found that PCV and PRVC modes are superior to VCV mode in providing adequate oxygenation at lower peak inspiratory pressures but no significant difference has been observed between PCV and PRVC modes in context of oxygenation, airway pressure and compliance.^[5]Kocis KC et al. in infants undergoing surgery for congenital heart disease has found PRVC mode superior to VCV.^[6]

Due to varying results in different previous studies, in the present study we are going to compare conventional VCV mode with relatively newer PCV and PRVC modes of ventilation.

METHODOLOGY: 105 patients undergoing laparoscopic cholecystectomy under general anaesthesia will be randomly allocated to receive volume controlled (group V), pressure controlled (group P), or pressure regulated volume controlled (group PV) modes of ventilation. The randomization will be done after patients consented for the study. Randomization will be done by computer‑generated numbering system. A standard general anesthesia technique will be followed in all cases. Standard monitors including noninvasive blood pressure monitor, pulse oximeter, electrocardiogram, and capnogram will be done.

Ventilation will be carried out using Dameca Siesta i Whispa workstation in all patients. . In VCV mode, patients will be ventilated with a tidal volume of 8 mL/kg body weight In PCV mode, ventilation will be started with airway pressure which is needed to deliver tidal volume of 8 mL/kg body weight. In PRVC mode a target tidal volume of 8 mL/kg will be set with airway pressure limit of 20 cm of H2O. Inspiratory to expiratory ratio (0.5), inspired oxygen concentration (40%) and positive end‑expiratory pressure of 5 cm of H2O will be same in all modes. During insufflation of the abdomen, the intra-abdominal pressure will be maintained between 12 to 15 mmHg in all patients. Initial respiratory rate will be 12 breaths/ min in all patients, but after pneumoperitoneum is developed, the respiratory rate will be adjusted to achieve an end‑tidal carbondioxide (EtCO2) between 33 and 37 mm of Hg.

Arterial blood gas analysis (ABG) will be done in all patients 10 min after pneumoperitonium is developed and just before desufflation.

EXPECTED OUTCOME: In this study we will find out in which of these three ventilator modes volume controlled ventilation mode (VCV), pressure controlled ventilation mode (PCV) and pressure regulated volume controlled ventilation mode (PRVC), the airway pressures, gas exchange, oxygenation, and lung compliance are better maintained.

References:

1. Maeda Y, Fujino Y, Uchiyama A, Matsuura N, Mashimo T, Nishimura M. Effects of peak inspiratory flow on development of ventilator‑induced lung injury in rabbits. Anesthesiology 2004;101:722‑8.

2. Keszler M. Volume‑targeted ventilation. Early Hum Dev 2006;82:811‑8.

3. Keszler M, Abubakar K. Volume guarantee: Stability of tidal volume and incidence of hypocarbia. Pediatr Pulmonol 2004; 38:240‑5.

4. Boules NS, El Ramely MA. Does pressure-controlled ventilation–volume guaranteed differ from pressure-controlled ventilation in anesthetized patients. Ain-Shams Journal of Anesthesiology 2014; 07:96–100.

5. Kothari A, Baskaran D. Pressure‑controlled Volume Guaranteed Mode Improves Respiratory Dynamics during Laparoscopic Cholecystectomy: A Comparison with Conventional Modes. Anesthesia: Essays and Researches 2017;12(1): 206-11