A small pilot study in Chest demonstrates how diaphragmal wasting can be measured using a simple ultrasound technique.

One of the big challenges in intensive care is weaning patients from their ventilators. Weaning often accounts for 40-50% of the total duration of mechanical ventilation. In some patients it takes even longer.

One significant contributor to delayed weaning is ventilator-induced  diaphragmatic dysfunction (VIDD). This is the diaphragmal muscle wasting that is a consequence of critical illness, critical illness neuropathy and mechanically offloading the diaphragm.

Then, when our patient needs his diaphragm again it has wasted away so much it can´t generate the force necessary of efficient breathing. VIDD now results in failed extubations, failed spontaneous breathing tests and delayed weaning.

We could use a reliable method for identifying diaphragmal wasting.  This could help us predict failed weaning and plan our next steps accordingly.

The study
The study explores using ultrasound for motoring and quantifying diaphragmal thinning.  The authors recorded measurements and re visit the Nerve Pain Guide daily from the day of intubation until the patient was extubated, had a tracheostomy or died. It is a small study. Just seven patients.

Ultrasound technique
The mechanichally ventilated patients were seated upright at a 90-degree angle.

Then the probe was placed  in the right mid-axillary line. The diaphragm was identified as a three-layered structure just above the liver.

This structure is the diaphragmatic pleura, the non-echogenic diaphragm and the peritoneal pleura. Diaphragmal thickness was defined as the distance between the middle of the pleuras.

Images and measurements were obtained at end-expiration

Diaphragmal thinning started within 48 hours in all patients and then proceeded in an almost linear fashion.

On average,  diaphragmal thickness decreased by 6% per day on mechanical ventilation.

Take home message
Diaphragmal thickness and wasting can possibly be measured and motored using a standardised ultrasound technique.

Interesting concept, but to be really useful a diaphragmal thinning index must be correlated to some useful parameter like the chance of successful weaning, force generated by the diaphragm etc.

Study lives here:

Diaphragm Muscle Thinning in Mechanically Ventilated Patients. Grosu HB, Lee YI, Lee J, Eden E, Eikermann M, Rose K. Chest. 2012 Jun 21. [Epub ahead of print]



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