Ultrasonographic assessment of Intercostal muscle thickness for predicting weaning outcome in patients on Mechanical ventilation in the Intensive care unit.

Mechanical ventilation is a lifesaving tool for critically ill patients admitted to the ICU. Weaning from invasive mechanical ventilation is as important as putting the patient on a ventilator, and this process lasts for approximately 42% of the total time a patient spends on mechanical ventilation. While prolonged duration of mechanical ventilation can lead to diaphragm dysfunction, ventilator-associated pneumonia (VAP) and airway trauma, early unplanned extubation may lead to complications such as aspiration, respiratory distress and hypoxia. Therefore, determining the optimal time and mode of weaning is a very important factor for patient outcome. There has been a growing interest in parasternal intercostal muscle ultrasound as a predictor of weaning. The intercostal muscles are a two layered structure that span each of the intercostal spaces. The “parasternal intercostal muscles” lie ventrally between the sternum and the chondrocostal junctions, where the internal intercostal muscles are replaced by a fibrous aponeurosis. These muscles are active only during the inspiratory phase of the breathing cycle and interact together with the diaphragm and other extradiaphramatic inspiratory muscles. The parasternal intercostal muscles are crucial for respiration, whenever there is an increase in ventilatory demand due to hypoxemia, carbon dioxide retention, high fever or shock. Thickening of parasternal intercostal muscle occurs in the presence of diaphragm dysfunction, and measurement of this parameter may contribute to the assessment of patient respiratory reserve capacity. The activation intensity of the parasternal intercostal muscle indicates a balance between the patient’s ventilatory demand and respiratory reserve. In such cases, the parasternal intercostal muscle thickness fraction (PICTF %) will be increased, which in-turn provides information on low vs high respiratory effort and helps in estimating the success of weaning. PICTF % can be calculated as [peak inspiratory thickness-end expiratory thickness]÷end expiratory thickness) *100.The primary aim of our study is ultrasonographic assessment of parasternal intercostal muscle thickness fraction (PICTF%) for predicting weaning outcome in patients on mechanical ventilation in the ICU. The study also aims to compare the predictive values of diaphragmatic thickness fraction (DTF) and parasternal intercostal muscle thickness fraction (PICTF) for weaning success. The study will be conducted on 75 patients admitted to the ICU, above 18 years of age, after taking informed consent from patient/relatives.

1.Demographic parameters such as name, age, sex, MRD no, height, weight, BMI will be noted

2.Lab parameters including Complete blood count, Renal Function Test (KFT), Liver Function Test (LFT), serum electrolytes and serum glucose at inclusion.

3.Sequential Organ Failure Assessment (SOFA), Acute Physiology and Chronic Health Evaluation (APACHE II) score at the time of admission to ICU

4.Intake of any drugs affecting respiratory muscle function such as neuromuscular blockers (NMB), steroids, aminoglycosides (AG), organophosphates (OP).

5.Physiological parameters including Heart Rate (HR), Mean Arterial Pressure (MAP),Respiratory rate (RR), SpO2 at inclusion and during SBT will be charted.

6.ABG

• PH, PaCO2, PaO2, HCO3, Lactate before starting SBT and after 120 mins of  SBT to be assessed.

Patients’ readiness to wean from mechanical ventilation will be assessed by clinical judgement of ICU physician. Patient will be given SBT by putting the ventilator on PSV (Pressure Support Ventilation) mode of mechanical ventilation (MV) (0-PSV, PEEP-5cm H2O setting). Patient will be monitored for Heart rate, Noninvasive blood pressure (NIBP),Respiratory rate, Tidal volume, RSBI(Rapid shallow breathing index (RSBI) is calculated by dividing the respiratory rate (RR) by the tidal volume in litres), SpO2,Signs of respiratory distress- nasal flaring, sweating, agitation, Use of accessory muscle, ABG analysis- PaO2, PaCO2, PaO2/FiO2,Maximum Inspiratory Pressure, Maximum Expiratory Pressure, Parasternal intercostal muscle thickness fraction (PICTF%) – after 10 mins of SBT, Diaphragmatic parameters - Diaphragmatic thickness fraction - after 10 mins of SBT

*****Parasternal intercostal muscle thickness fraction (PICTF%)-

Second right parasternal intercostal muscle will be assessed with a10- to 15-MHz linear array transducer which will be placed at the level of the second right intercostal space, approximately 6 to 8 cm lateral to the edge of sternum, perpendicular to the anterior surface of the thorax in the longitudinal scan, with a window visualizing the second and third ribs. The second right parasternal inter-costal muscle will be identified as a three-layered biconcave structure, with a medial portion showing muscle echotexture and two linear hyperechoic membranes running respectively from the anterior and posterior aspects of the adjoining ribs. The ultrasound beam will be directed at the midsection of the muscle perpendicularly, where it is the thinnest at end-expiration using M mode. At the peak of inspiration and end of expiration, the thickness of the parasternal intercostal muscle will be measured between the inner and outermost hyperechoic layer of muscle fascial borders using frozen images. PICTF% will be measured as “[peak thickness at inspiration(a) − end-expiratory thickness(b)] divided by end expiratory thickness] × 100”.

All measurements will be repeated on at least three separate breaths and their average will be reported.

*****Diaphragm thickness fraction (DTF)-

DTF will be measured using M mode with a 7–10 MHz linear probe. The right hemidiaphragm will be visualized in the zone of apposition, on the midaxillary line between the 8th and 10th intercostal spaces. It will be recorded on M‐mode sonography in real time. During M‐mode imaging, the normally functioning diaphragm is represented as an echogenic line that moves freely during inspiration and expiration. Thickness will be measured by placing callipers on reflective lines at the end of inspiration and expiration.

DTF will calculated by formula: TI- TE ×100.

TE

When the SBT is successful after 120 mins, planned extubation will be performed on the basis of clinical assessment. All the patients will be followed up to 48 hrs for respiratory distress, and any requirement for non-invasive or invasive mode of mechanical ventilation. Incidence of VAP (Ventilator associated pneumonia) or any other complications, ICU mortality, need for tracheostomy and duration of ICU stay and duration of mechanical ventilation will be followed up.