Comparative analysis of diaphragmatic thickness fraction with parasternal muscle thickness fraction by the use of ultrasonography for predicting weaning in adults receiving mechanical ventilation.

Mechanical ventilation has emerged as commonly used tool in saving lives of patients experiencing heightened work of breathing with altered pulmonary gas exchange for effective ventilation and oxygenation.

Weaning is the process of gradually reducing ventilator assistance so that spontaneous respiration can be restored.

Traditionally ventilator derived factors like the

RSBI (rapid shallow breathing index),

Tracheal occlusion airway pressure,

NIF (negative inspiratory force) index and

other indices, along with clinical criteria that monitor the respiratory rate and oxygenation, have been studied and often utilized to guide successful weaning.

Recently ultrasound guided parameters are being used. USG guided measurement of diaphragmatic and parasternal muscle thickness being the most widely used index.

Conduct Of Study

Once the weaning criteria has been attained, patients will be subjected to recording of conventional ventilator derived parameters which are rapid shallow breathing index (RSBI), Negative inspiratory Force (NIF) and Occlusion Pressure (P0.1), RSBI values less than 105, NIF values less than or equal to 25, occlusion pressure value less than 4.2cm H2O as well as ultrasound derived diaphragmatic and parasternal parameters to predict the successful weaning.

All the parameters will be recorded from the day a particular patient is initiated on CPAP/ASB mode of ventilation. All the ultrasonography parameters will be noted twice a day and ventilator derived parameter will be noted once a day starting from day of weaning to complete discontinuation of mechanical ventilation for at least 24 hours which will be considered as successful weaning.

In the ultrasound guided intervention diaphragm thickness and parasternal thickness derived parameters will be recorded twice a day. Each time mean of three readings of diaphragm and parasternal derived parameters will be taken in the observations.

The number of patients requiring reintubation will also be noted. At the end of study, the data will be decoded and analyzed accordingly.

Technique of diaphragm ultrasound:

All the Diaphragmatic ultrasounds in ICU will be performed by an experienced anesthesiologist using high frequency linear array probe of 6 to 12 MHz.

The probe will be placed in the right subcostal margin between the mid clavicular and anterior axillary line, parallel to the excursion of the diaphragm.

2D B mode will be used to search the line of right hemidiaphragm.

The diaphragmatic excursions will be measured in M mode from baseline to point of maximum height of inspiration at the zone of apposition of diaphragm and rib cage.

Diaphragm thickness will be measured in the zone of apposition of the diaphragm and rib cage in the mid axillary line between the eighth and tenth intercostal space by placing the curvilinear probe allowing placement of M mode line parallel to the excursion of the diaphragm.

MEASUREMENTS:

Following observations will be drawn from the diaphragm ultrasound:

1 Diaphragm thickness at end of inspiration and expiration

2 Amplitude AMP in centimeters will be measured.

3 The diaphragm thickness fraction in percentage will be calculated as the difference between diaphragm thickness at inspiration and diaphragm thickness expiration divided by diaphragm thickness at expiration multiply by 100.

Technique of parasternal ultrasound

An ultrasound of the second intercostal muscle ultrasound will be performed.

The thickness of parasternal intercostals will be calculated with a high frequency of 6to 12 MHz USG probe at the level of the second intercostal space, 6 to 8 cm away from the sternal edge to visualize the second and third ribs.

Then, M-mode will be used to measure the thickness at the end of inspiration and expiration. The average of three consecutive readings will be used for analysis.

The maximum and minimum thickness of the parasternal intercostals during three consecutive tidal breaths will be taken and averaged.

Then, the PICTF in percentage will be calculated using the following formula: Maximum–minimum thickness/minimum thickness, expressed as a percentage. All the respiratory muscle analysis will be done after a 120 minute SBT. PICTF percentage will be measured as peak thickness at inspiration minus end-expiratory thickness divided by end-expiratory thickness multiply by 100.

All the observations will be noted in the prescribed performa. Utrasound derived diaphragmatic and parasternal factors used for weaning will be noted and comapritive analysis between the two will be done.