الفهرس 
Physics and PrinciplesOnly 14 pages are availabe for public view
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Abstract
Ultrasound is becoming increasingly useful to the anesthesiologist for patient monitoring, intraoperative diagnosis and research. Advances in ultrasound technology will bring increases in the number of indications for its usage.
Modern ultrasound transducers employ piezoelectric crystals to transmit ultrasound and receive echoes. Ultrasound techniques include the A-mode, B-mode, M-mode, two-dimensional (2-D) scan and recently 3-D scan.
Transesophageal echo, ultrasound transducer mounted on the tip of a gastroscope. It can visualize the heart from behind through the esophagus. These transducers are single plane, multiplane, or pediatric transducers. A main application of TEE as a sensitive cardiac monitor is the detection of myocardial ischemia. Based on the idea that within seconds after interruption of myocardial blood flow, normal inward movement and thickening of the affected myocardium ceases. TEE can now detect the various degrees of segmental wall motion abnormalities (SWMA).
Another application of TEE is the assessment of left ventricular function regarding preload, afterload, wall stress and contractility. The cardiac function could be well quantified, both global and regional quantification. Using the principle of acoustic impedance difference between air and blood, contrast echocardiography is now in common use.
Since the development of Doppler echocardiographic technology, ultrasound can evaluate the anatomy and function of the heart valves; mitral valve is the best. It can also diagnose dynamic subvalvular stenosis. It can also judge efficacy of repair and can change the plan of surgery.
With introduction of the pediatric TEE transducer, a new diagnostic channel and a safe approach to congenital heart surgery was created.
TEE has proved itself to be the most sensitive method for detection of air embolism that might occur during neurosurgical procedures done with the patient in a sitting position and could be lethal if recognition is delayed.
Other uses as its ability to diagnose aortic dissection presence and extent of pericardial effusion, intracardiac masses, vegetations, calcification and thrombi.
So TEE is especially valuable in the ICU setting, in cardiac surgery, cardiac patients undergoing non-cardiac surgery, and non-cardiac patients undergoing major surgery where marked fluid shift, altered ventricular compliance, acute ischemia, mechanical ventilation, changes in the heart rate, and use of variety of drugs and anesthetics that affect the cardiovascular system are all expected.
Transcranial Doppler (TCD) is another application for the ultrasound in anesthesiology. It provides a new method for investigating the human cerebral circulation. It gains access to the intracranial vasculature through natural foramina;
(a) transtemporal window, (b) transorbital window, (c) transforaminal window.
Increasing interest in using TCD as a monitor mandates an appreciation of the effects of the intraoperative anesthetic drugs on cerebral blood flow velocity.
Although cerebral embolism is clearly one of the major causes of stroke, there are no methods at present that can be routinely used to detect emboli. In the clinical situation, this can result in uncertainty in the diagnosis and delays the initiation of appropriate treatment to prevent further emboli from entering the cerebral circulation, Doppler ultrasound may be used to detect arterial emboli.
TCD permits continuous non-invasive monitoring of the flow velocity in basal cerebral arteries. This makes it possible to monitor the influence of the flow velocity in an arteriovenous malformation or angiomas on the surrounding brain lesions.
The development of TCD spurred the use of pulse wave Doppler ultrasound for assessing hemodynamic changes and monitoring for emboli during cardiopulmonary bypass.
Concern about cerebral perfusion has made intraoperative monitoring more common with carotid surgery than with any other neurosurgical or vascular procedure.
TCD has become one of the most fruitful and innovative non-invasive techniques for the investigation of the cerebral circulation in the ICU. Analysis of the TCD waveform and flow velocity can indirectly provide information about cerebral blood flow, vascular resistance, intracranial pressure and cerebral perfusion pressure. Although much of the data collected to date are descriptive, TCD offers potential applications to guide therapeutic decisions and outcome prediction.
Detection of subarachnoid hemorrhage, vasospasm and cerebral circulatory abnormalities of CBF are known to occur after traumatic head injury. As information about these abnormalities can help in neurosurgical management.
In the last years, since TCD is introduced, it quickly won a place among the established tests of cerebral circulation not merely because the tests are painless, non-invasive and easily repeatable but because it provides additional information regarding cerebrovascular function, which is very important in stroked patients and assessment of response to thrombolytic therapy.
When TCD is applied carefully to study the entire intracranial circulation in patients who have met the clinical criteria for brain death, it can be useful confirmatory test. Inexpensive, the examination can be performed rapidly at the bedside and may be repeated as often as needed.
Ultrasound has been used to provide a safe,esay and reliable method for cannulation as sometimes Obtaining peripheral i.v. access can be a challenge even to experienced physicians, especially in infants, obese adults, i.v. drug abusers, oedematous patients, or patients who are frequently hospitalized. Providing ultrasound guided cannulation of peripheral veins and central venous access has solved a lot of problems associated with traditional methods also using axillary vein for cannullation has proven to be a remarkable alternative with less side effects
Utrasound has proven useful in regional anesthesia with its different types e.g. epidural anesthesia,upper and lower extremities block
Other uses of ultrasound may include ultrasound-guided supraclavicular and infraclavicular approach for regional anesthesia of the brachial plexus, a valuable method for providing anesthesia of the forearm and hand for surgery in these areas. It could be used as an alternative to the landmark-guided techniques.