USG in ICU - Overview of Ultrasound in Critical Care Dr....

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Overview of Ultrasound in Critical Care r. yanendra grawal Dr. Gyanendra Agrawal Senior Resident Deptt. of Pulmonary Medicine
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eed for USG Need for USG • In critically ill patients physical examination is quite limited and inaccurate • USG has potential to reinvigorate physical exam n , proving accuracy improving accuracy •I m p attributes: portability, lack of radiation, repeatability, p a bu es po ab y, ac o ad a o , epea ab y, absence of consumables, being battery powered • Information can be stored for documentation, transmission, consultation Can J Surg 2000;43:207–211 Am J Med Sci 1990; 299:175–178 Crit Care Med 2006; 34:2153–2157
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hether we should be doing it ??? Whether we should be doing it ??? Basic ultrasound skills should be part of the armamentarium of critical care • Far from being competitive or conflicting, it is complementary • Brief (10 hrs) formal training in handheld ECHO system, intensivists able to perform limited TTE in 94% and interpreted correctly in 84%- changed management in 7% of patients 37% of patients ACEP/ SCCM guidelines include USG by intensivists Intensive Care Med (2008) 34:243–249 J Cardiothorac Vasc Anesth 1998; 12:10–15 ACEP Emergency Ultrasound Guidelines, 2001
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hat is Ultrasound? What is Ultrasound? • Human sensitivity: 20 - 20,000 Hz • Ultrasound: >20,000 Hz • Diagnostic Ultrasound: 2.5 - 14 MHz • Frequency is determined by the sound source only nd not by the medium in which the sound is and not by the medium in which the sound is traveling
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ltrasound roduction Ultrasound Production Piezoelectric effect: – Crystals vibrate at given frequency when an alternating current is applied – Crystal acts as speaker and microphone Electrical oscillation Returning signal Crystal ib ti Crystal istortion vibration distortion Transmitted ultrasound Reflected ultrasound
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asic physics Basic physics Most of the reflection occurs at interfaces between tissues having different echo density Crit Care Med 2007 Vol. 35, No. 8 (Suppl.)
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SG image USG image • Reflected signal gives information about depth and nature of tissue • On the grey scale, high reflectivity (e.g. bone) is white low reflectivity (e.g. muscle) is grey no reflectivity (e.g. air) is black • Deeper structures on lower portions of display screen and superficial on upper portion
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asic physics Basic physics • Velocity= frequency x wavelength Frequency Penetration Resolution Study depth 2.5 3.5 good less deep 5.0 7.5 less good superficial
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ransducer Transducer Crit Care Med 2007 Vol. 35, No. 8 (Suppl.)
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ransducers Transducers ormats Formats linear- rectangular field of view – sector- pie-shaped field of view • Linear array transducers iezoelectric lements linearly rranged - piezoelectric elements linearly arranged • Phased array transducers - smaller scanning surface - good for echocardiography -more xpensive oeepes e - elements are activated with phase differences to allow steering of the ultrasound signal
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canning kills Scanning Skills Try different windows • A lot of gel Transducer movements: otate Rotate – Angle (Tip-toe) – Pivot (fan-shaped movement) Transducer placement basics: – longitudinal view – transverse view – coronal view
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This note was uploaded on 12/03/2011 for the course MEDICINE 350 taught by Professor Dr.aslam during the Winter '07 term at Medical College.

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USG in ICU - Overview of Ultrasound in Critical Care Dr....

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