Comparison of diaphragmatic atrophy in patients on ventilator support with SIMV+PS mode and PRVC mode: A Prospective Randomized Controlled Trial

Mechanical ventilation which is assisting or replacing spontaneous breathing, is used in patients who are unable to maintain life with spontaneous ventilation. It is one of the most commonly used life supportive therapies in Intensive Care Unit. The main objectives of mechanical ventilation are supporting or manipulating pulmonary gas exchange, preventing and treating atelectasis, restoring and maintaining adequate functional residual capacity and reducing work of breathing. It causes respiratory muscle atrophy, particularly of the diaphragm, which is the main respiratory muscle accounting for 60-80% of the inspiratory work. This diaphragm muscle atrophy is due to its under usage during mechanical ventilation and it starts as early s 12-18 hours after initiation of mechanical ventilation and the maximal decrease happens by 72 hours after which there is  no further significant damage. Studies have found that diaphragmatic atrophy is associated with duration and mode of ventilation. Ventilator modes can be classified as controlled, assist, pressure support and dual modes. The patient’s respiration is fully supported by the controlled modes of ventilation. There is an increase in protease activity in the respiratory muscles, particularly the diaphragm which in turn will cause atrophy. Assist modes in which the ventilator provides partial support to the patient’s respiratory efforts, may lead to decreased diaphragmatic atrophy. Newer modes of ventilation are designed to allow spontaneous respiration during any part of the ventilatory cycle with assistance to each spontaneous breath. Thus the respiratory muscles including diaphragm are not completely unloaded. Here we are going to compare SIMV PS mode and PRVC mode of ventilation to find out which mode causes less diaphragmatic atrophy. In SIMV PS mode ( Synchronized Intermittent Mandatory Ventilation with Pressure Support ), the ventilator’s assistance is in the form of a fast high flow assistance to a set pressure limit with the time of the end of the support is determined by the patient’s lung characteristics. PRVC ( Pressure Regulated Volume Control ) mode is volume targeted, pressure control mode where patient or time triggered time cycled breaths are delivered by the ventilator. It combines the advantages of both volume controlled and pressure controlled modes of ventilation. There are direct and indirect methods of assessing diaphragm muscle thickness. Ultrasonography is being used as the main entity for the diaphragmatic assessment as it is portable and non invasive method. Here the patients will be randomly allocated into two groups by computer generated random number chart. the concealment of allocation is achieved by telephonic allocation. Once randomized, intensivist taking USG measurements will not be blinded. The statistician will be blinded to the two groups. Before starting the study baseline parameters like demographic data, anthropometric data and history of any comorbid illness is noted down. The diaphragm thickness will be measured using ultrasonography. First reading will be taken within 6 hours of initiation of mechanical ventilation as baseline recordings. Second reading will be taken at 72 hours after initiation of mechanical ventilation. Both these recordings will be taken by same physician. Thickness of the diaphragm will be measured with straight probe at zone of transition on the mid axillary line at the liver window on the right and the spleen window on the left side. Three measurements will be taken and the average of them will be taken as a reading. Nutritional status may act as a confounding factor, which can be reduced by starting the enteral feeds within 24 hours of ICU admission. The quadriceps muscle thickness measurements are taken which acts as control. The other possible confounding factor is the swelling of the diaphragm due to inflammation which can be assessed by serum procalcitonin levels at 72 hours in both groups. Here, we hypothesize that PRVC mode of ventilation causes less diaphragmatic atrophy than SIMV PS mode. In this study we plan to compare the extent of diaphragmatic atrophy in mechanically ventilated patients caused by these two modes.