Tıbbi Şırınga Pompaları İçin Tıkanıklık Basıncı Ölçme Cihazı

Abstract

Perfüzyon pompaları, hastaların damariçi tedavilerinde kullanılan ilaçların kontrollü bir biçimde nakledilmesini sağlayan yüksek hassasiyetli cihazlardır.Birçok mekanik ve elektronik birimden oluşmakla birlikte önemli kısımlarından biri tıkanıklık algılama sistemidir. Tıkanıklık basıncı genellikle iletim hattında sıkışma, ezilme ve bükülme yaşandığında yada vanaların çalışma durumunda değiştirilmesi ile yükselmekte, zaman zaman akışın durmasına yol açmaktadır. Bu durum hastanın yaralanmasına yol açabilmektedir. Cihaz tıkanıklık sebebiyle istenen değerlerde çalışmadığında hatalar oluşmakta ve tedavi ihtiyaçları karşılanamamaktadır. Tedavinin uygulanacağı hastaların özelliklerine göre farklı basınç değerlerinde çalışılmalıdır. Yeni doğan bebek ile birkaç aylık bir bebeğin tedavilerinde dahi farklı basınç değerleri tehlike durumu oluşturmaktadır. Tıkanıklık algılamada hastanın özellikleri önem taşımaktadır. Yeni nesil cihazların tasarımında tıkanıklık algılama sistemine gösterilen önem artmaktadır. Eski cihazlarda tıkanıklık algılama sisteminin daha çok mekanik yapı kullanılarak tasarlandığı görülmektedir. Geleneksel bir biçimde birçok perfüzyon pompa sisteminde aynı mekanizmaya rastlamak mümkündür. Bu sistemin avantajları olduğu kadar güvenlik bakımından dezavantajları da bulunmaktadır. Tezin amacı, geleneksel yöntemlerle imal edilmiş ve kullanımda olan cihazlarda kullanılabilecek taşınabilir tıkanıklık algılama sistemi geliştirmektir. Sistem şırınganın takıldığı yere yerleştirilmektedir. Sistemin önünde yer alan bir sensör mekanizmaya şırınganın arkası yerleştirilmektedir. Başka bir ifade ile şırınga ile pompanın itici mekanizması arasına ölçüm sistemi yerleştirilmektedir. Sistem genel bir biçimde şırınganın arkasındaki kuvveti ölçmektedir. Elde edilen kuvvet değerinden şırınga bilgileri de göz önünde bulundurularak basınç değeri hesap edilir. Basınç değeri hasta özelliklerine göre alarm seviyesine geldiğinde cihaz sesli uyarı vermektedir. Ölçüm mekanizmasında kuvvet değerini ölçen piezorezistif özellikte sensör, direnç değerini gerilime dönüştüren bir ara devre, mikro denetleyici, gösterge birimi ve sesli uyarı birimi bulunmaktadır. Ayrıca devrenin AC şebeke gerililmi ile çalışabilmesi için güç katı ve 9V DC ile çalışabilmesi için güç girişi bulunmaktadır. Piezorezistif kuvvet sensörünün ürettiği cevap test edilerek analiz edilmiştir. Maksimum 30 libre, 25 libre ve 1 libre kuvvet değerleri için üç adet farklı yapıda sensör incelenmiştir. İstanbul Teknik Üniversitesi, Yapı Mühendisliği Bölümü Laboratuvarlarında sensörlerin ölçüm karakteristikleri incelenmiştir. Tıkanıklık algılama sistemi 100gr ile 3kg arasında uygulanan kuvvetler ile test edilmiş, cihaz tarafından üretilen cevabın uygulanan kuvvetle eşdeğer olduğu görülmüştür. Cihaz perfüzyon pompası üzerinde denenmiş ve yüksek doğrulukta çalıştığı gözlenmiştir.

A perfusion pump is a sensitive device that is used to control delivering process of medications applied to intravenous system of patients. Although it is composed of many mechanical and electrical units, the most critical feedback information is obtained from occlusion detection system. Syringe pumps generally comprise a barrel, or syringe, a pusher with a plunger, a step motor to generate a force, control circuits, power circuits, user interfaces and occlusion detection system. The syringe is typically filled with chemical, nutritional or biological substances, which are mixed to obtain a uniform solution. The pusher mounted to the motor forces a plunger through the syringe. As the plunger moves through the syringe, the composed medication is forced out into catheters and pumped through the patient. During the delivering of medication, it is possible for an occlusion to emerge in the delivery path. For example, a stopcock, slider valve or a pinched linemay be closed, as a result delivery path occluded. Such a condition may cause injuriesto the patient if the occlusionis not detected. Theincreased occlusion pressure by a closed stopcock, slider valve or pinched line, rarely stop the operation of the pump. The device cannot operate with the accurate rates, some errors emerges on the system. As a result, it cannot get the desired medical procedure for patient. In other words, when an occlusion occurs in the delivery path, medication delivery problems to the patient emerge even though the pump continues to function. Thus, the occlusion prevents the infusion pump from injecting the medicationto the patient in the desired dosage until the occlusion iseliminated. Therefore, a rapid detection of occlusions along the delivery path is a keyfeature of a reliable pump system. Besides occlusion detection, measurement of the occlusion pressure is also a critical security requirement. Acceptable pressure rate depends on the patientcondition. When a newborn child and a mature person are compared, different pressure values are considered as dangerous. We see a trend in the importance of the perfusion pump occlusion detection system design on the new generation devices. The older pumps use mechanical occlusion detection methods mounted on their system. Traditionally, the same mechanism may be seen in many models. There are certain advantages and disadvantages of this mechanism regarding patient security. The aim of the thesis is to design and build a mobile occlusion detection device that can be utilized on the traditionally manufactured perfusion pumps. By the use of sensor mechanism placed in front side of device we measure the force applied to the back of the syringe. In other words, we place the device between syringe and syringe pusher. In general, an occlusion in the infusion line will cause the force, or pressure, in the syringe to increase. Therefore, force between the pusher of the syringe pump and the syringe plunger will increase. Occlusion detection systems that use transducers are used in the modern pumps. In the study of thesis, theresponse of piezoresistive force sensors has been analyzed. The sensors that have three different measurement characteristics with maximum 25 lb, 10 lb and 1 lb force rates, have been investigated. The response characteristics of three sensorshave been recorded and investigated in the Istanbul Technical University, Structurel Engineering Laboratories. After the response observation of sensors under the different force values, about fifty samples are obtained from the sensor, and average filter is applied to the values to eleminate variation of the measurement because of the hysteresis structure of it. As a second method, median filter is applied to the fifty values which ordered by using bubble sort algorithm. Although variation in the second method is calculated as %4.38, it is obtained %1.76 by applying average filter to the measured values. In order to evaluate the filter efficiency, repeatability tests are implemented on the sensor. In the first test procedure, a couple of 300 gr masses are applied to sensor, in the second, masses are picked up over the sensor. The test is repeated approximately 60 times and repeatability is found as 0,38. Such as to observe the repeatability under bigger force values, 2,100gr masses are applied on the sensor. It is found that the repeatability is about 0.79. In the next step, by applying different masses to sensor, the overall system response is analyzed and the characteristic curve of the system is obtained. In order to fit a curve and generate a function to the characteristic response of measurement system, linear, quadratic, cubic and ninth degree function is fitted, the best result is held by ninth degree polinom. It is calculated the regression 0.9994, RMSE 0.2985 and SSE is 2.317. The hardware mechanism of the measurement system is consisted from three seperatedcircuits. In the first circuit, generated resistance is converted to voltage with single power supply by using non-inverting opamp, namely, MCP 6001. In the second circuit, seven segment, three digit user screen is designed to give information about the measurement. It is also used to enter the type of syringe to calculate force regarding diameter of the syringe. With the aim of getting information from user such as diameter of the syringe and threshold value for patient, four push buttons are added on the user interface board. Three buttons are used for numbers and one is only used to save and enter data. The third circuit is main board on which the microcontroller 16F785 is mounted. The main board is composed from a 220AC to 9VDC transformer, microcontroller, 7805 voltage regulator, MOC3051 AC switch integrate, a triac, and led driver transistors. The software of the measurement system is developed on Mikroelektronika MicroC IDE and the designsof the circuits areperformed on Proteus software (version 7.7). In such infusion pumps, an alarm is generated when the force between the pusher and the plunger or the pressure in the syringe increases above a predetermined threshold. As such, the alarm is either “on” or “off” depending on whether the threshold has been passed. As a consequence, the user has no way to know whether the pressure in the syringe is building up to an unacceptable level that precedes the threshold.The user only knows when the alarm is reached. Thus, remedial action can be taken to open the infusion path. As a result, the system works on measurement of the force at the back of syringe. Obtained data is used on the estimation of pressure value by considering the syringe dimensions. The dimension values or the type of the syringe is entered by user using user interface circuit. User also gives the critical threshold value by examining the condition of patient and application. When the pressure value excess the limit based threshold valuean audible alarm is set, and emergency switch is turned to off. Emergency switch can control any alarm system or infusion pump to prevent patients from injuries.