The Use Of Mechanical Ventilators Engineering Essay

The Use Of Mechanical Ventilators Engineering EssayThe respiratory system, composed of different structures, is involved in dissemination and blow out exchange. Its principal(prenominal) function is to provide a sur confront for flatulencyeous exchange of atomic number 8 and carbon dioxide 1. Gas exchange is dressed at the alveoli, specialised cells which argon part of the lung pargonnchyma. It provides oxygen to the blood and removes the carbon dioxide produced in the body as a product of cellular metabolism for the oxygen to reach the lungs there must be a series of tubular structures that communicate with the outside. The diagram below shows a block diagram of the anatomic structure for the respiratory system (Fig. 1). public figure Block diagram of the Respiratory System anatomic structureAir diffusion into these channels is conducted by the respiratory muscles (intercostals and diaphragm) which increase and decrease rhythmically the size of the thoracic perdition (inspi ration and departure). The pleural cavity contributes on this phenomenon when its negative oblige opposes the elastic recoil of the lung this action gives place to a conductive portion of the system, whose function is to allow ship penetration. In addition the respiratory portion composed bronchioles, dental ducts, alveolar sacs and alveoli establishes homeostasis.Figure Muscles and Pressures involved during intimationingThe ventilating system of the lungs basis be measured by studying a gas garishness and its variations in the lungs 2. Boyles, Charles, Daltons and Henrys law of gasses be critical in the apprehension of gas exchange, measurement of gas movement mob an important part in automatic public exposure. During breathing movements atomic number 18 cyclic, and volume in the thoracic cavity is changed by the muscles mention before. During inspiration the impel indoors the thoracic cavity and lungs is decreased and the resembling time the volume is increased, a llowing blood hang in. On the other hand during expiration the elastic lungs and the thoracic wall recoils producing an increase of military press but a decrease in volume allow letting crease flow out (Fig. 1).Figure Respiratory operation and volume racesFigure 3At the same time, inhalation and exhalation allow the mobilization of the volume of gas which goat vary depending on the type of respiratory movement and lung elastic forces. Lung capacities atomic number 18 defined by the sum of different volumes. Figure 2 shows a graphic representation of the respiratory work volume relationships. FCR (Functional Residual Capacity) represents the remaining assembly line after a cycle. VT (Tidal Volume) is the integrate of air in a normal inspiration and expiration. IRV (Inspiratory Reserve Volume) is the amount of air moved during a maximum and constrained inspiration and closures over the Tidal Volume. Similar to IVR, ERV (Expiratory Reserve Volume) is the amount of air mo bilised during a maximum and force expiration resulting below the Tidal Volume. The vital capacity is the sum of IRV, VT, and ERV. VR (Residual Volume) as its name says, is the amount of air remained in lungs after a maximum exhalation. The IC (Inspiratory Capacity) is the flux of air after a quiet cycle. And finally the TLC (Total Lung Capacity) corresponds to the total volume of gas remaining in the lung after a maximal and forced inspiration. Volumes and lung capacities may be altered in different diseases its measurement is a critical element for diagnosis, put to deathed by pulmonary function tests.The respiratory parameters compliance, lung elasticity, intrathoracic pressure, airway resistance, intra-alveolar pressure help measure the strength in muscles when breathing.Airway resistance is determined by the Poiseuille Law (eq. 1)1Where represents the viscosity of the fluid, l is the longitude in the airways, and r is the radio on the airways. Resistance has a great signifi fagce in pulmonary physiology and it is analysed by the ratio of the pressure differential flow. The airway resistance gouge be increased significantly in the presence of disease such as Bronchitis, Asthma, and Emphysema among others. In addition a great amount of unhurrieds admitted to intensive apprehension pass on lend oneself up of some form of respiratory support delinquent primarily to hypoxaemia or breathing machiney failure. Respiratory support ranges from oxygen therapy by face mask, through non-invasive techniques such as continuous positive airways pressure, to full ventilatory support with endotracheal intubation3.Figure Block Diagram of a basic mechanical ventilatorA mechanical ventilator is an automatic machine, designed to provide all or part of the work the body must produce to move air (gas) from the inside to the outside and vice versa. Furthermore mechanical ventilators are designed to transmit energy applied in a predetermined manner to perform a specif ic task. Interface amongst machine and patient stable, energy source, take in system (for timing and size of the breaths regulations) and monitoring (device performance and patients causation) are the ecumenic requirements for ventilators (Fig. 4).A further analysis as well as comparison of this equipment will be made along the paper, with the purpose of a break in understanding of its designed and future tuitions.Current State of the ArtSince the invention of artificial respiratory supply, mechanical ventilators have evolved in the past 40 years. on that point are five contemporariess of mechanical ventilators where changes have been made in order to present a better apparatus.The first coevals consisted of only one mode of ventilation, and the electronics utilise was primitive compared to the one utilize like a shotadays. The equipment was no safe since the control with the user was not precise and it did not count with any alarm system.The second generation provided b asic alarms, containing electronic hitchry as well as an analogue control of fluid.A major evolution took place on the third generation digital electronics, microprocessors, were employed for most of the functions.The quadrupleth generation included modern displays such as CRT or LCD ensuring a better patient care.The generation currently used is the fifth generation which features a better onscreen display control. It is also made by advanced logarithms that permit graphic display, calculation of lungs mechanical properties, and system diagnostics.Principles of OperationMechanical ventilation is all different types of procedures that provide artificial respiration employing machinery to meet the respiratory function of a person who cannot perform it by itself 4. In addition Mechanical Ventilation (MV) is the product of interaction between a ventilator and a patient, and through this equipment parameters of volume, flow, pressure and time are controlled. Considered as a generator of positive pressure that supplies active phase of the respiratory cycle there are basically four types of MV controlled by pressure, time, volume and flow.Mechanical ventilation systems create an intermittent positive pressure where air or a gas mixture enriched in oxygen is insufflated in the patients airway. Pressure in the airway at the end of passive expiration and that at the same time goes beyond atmospheric pressure is known as positive end-expiratory pressure (PEEP) 5. PEEP is extremely important in effects and mechanisms of the respiratory system. It plays major roles in gas exchange, lung mechanism, and hemodynamic effects. Some effects in lung mechanics it prevents the lung from collapsing, increases FRC among others.5 In order to provide respiratory support, a MV such as the one in figure is used.Figure Flow and control of gas exchange during artificial ventilationInput of this system provides O2 as a medicinal gas and in the case of portable ventilators the medicinal gas can be supplied by a dry air compressor. Ventilatory gas is passed through a pressure regulator which is in charge of preserving the preset pressure for the inspiratory gas and ensures the integrity of the airway. The gas flown to the patient is allocated by an electro-valve (Fig. 5) this remains energised until the end of the inspiratory time previously programmed, when de-energised the gas flow is ceased. Finally the expiratory electro-valve is activated do the air exhaled by the patient to be expelled to the environment by a biological filter that prevents the contamination of this. fashion models of Ventilator-Patient InteractionFigure Model representing breathing, were a rigid flow conducting tube is connected to an elastic compartmentThe Respiratory System can be modelled to illustrate the relations amongst the variables of interest providing a better understanding of patient-equipment interaction. The model most frequently used is shown in figure where a rigid flow condu cting tube is connected to an elastic compartment 6.When airway pressure goes higher than the base line, the inspiration is assisted (Fig. 6)The Transrespiratory pressure (eq.2) leads inspiration, and is the pressure at the airway opening, ,minus the pressure at the body surface2At the same time has two components, transairway pressure (eq. 3) and transthoracic pressure (eq. 4)34A mathematical model that represents volume, pressure and flow during ventilation is known as the equality of motion for the respiratory system 6 (eq. 5) 5Where is the pressure generated by the ventilator, is the pressure generated by the ventilator muscles, is the respiratory system elastance, is the respiratory system resistance, and is lung volume where the derivate of volume with respect of time is the flow in the system. carry over (1) compares typical values against values during mechanical ventilation 6.Table Pressures and Volumes during Mechanical ventilationTypical determineMechanical Ventilation The model provides the basis for monitoring the patients current condition, and it is done in terms of R and E which are mechanical properties.Figure galvanising model representing breathing composed of a RC circuitAnother model used for representation is the galvanising model (Fig. 7) this model is analogous to an electrical circuit consisting of a resistor and a capacitor (RC circuit), a power supply, which in this case represents the pressure generated by a mechanical ventilator. The electric current stands for the flow of air in the system. In this model, pressure, volume and flow are variables (functions of time) while the resistance and compliance are constant 4. Second Law of Kirchooff can be used to analyse the electrical model and the followers equation(eq. 6) can be derived6Current and charge can be related by , the electrical parameters of the circuit can be now represented by the ventilator variables. When applying a pressure to the input of the system (output pressur e of the ventilator), the volume varies according to the following differential equation (eq. 7) the total pressure applied is equal to the sum of the differences in pressure due to the compliance of the system and to the resistance of the airway7According to this system is the output pressure of the ventilator, the inspiratory volume, and is the compliance of the lung 4.Operating ModesMechanical ventilators count with different operating modes, which are the manner the ventilator ensures that the patient is provided by the appropriate heartbeat ventilation satisfying the respiratory use ups without damaging any pulmonary tissue. Operating modes can be identified by breathing pattern, Control type, Control Strategy 6.When specifying just the breath control variable (Primary Breath Control), there are three approaches pressure control, volume control and dual control modes. Pressure control (PC) is used when patients can initiate respiration pressure in the airway is increased duri ng inspiration. Volume control (VC) employs a control system to guarantee that a set tidal volume is distributed during the inspiratory cycle. The Dual Control (DC) is simply a combination of both, used in order to provide minute ventilation while maximizing patient synchrony6.Breath sequence is the other component of breathing pattern operating mode. There are two ways airflow can be delivered using this mode, mandatory or unprompted. The difference between the two of these is that on mandatory breath the ventilator initiates and establishes the tidal volume, Vt. Contrary to mandatory breath on spontaneous breath the patient establishes and starts its own breathing. From these, three different modes of breath sequence can be delivered Continuous Mandatory Ventilation (CMV), Continuous Spontaneous Ventilation (CSV), and Intermittent Mandatory Ventilation (IMV). CVM and CSV, all breaths are mandatory or spontaneous respectively however in IMV breaths can be either mandatory or spont aneous 6.ControlsIn order to select breathing mode and ventilation pattern parameters, controls are used. There are two different ways on which breathing can be controlled, and at the same time there are control strategies which depend on the variables and parameters set to obtain this. A system can be controlled by an open loop or unsympathetic loop (Fig. 8). Like any open loop system, there is no feedback, and the system could be affected by mechanical changes in the lungs, patients ventilatory efforts and making waters 6.Figure Control systems used for mechanical ventilationClosed loop sense breathing variables such as pressure, volume, and flow to provide a feedback signal which is compared to the sought after value set at the input. There are different types of closed loop systems depending on the number of variables used.The instruments used to measure volume-flow rate are referred to as volume flowmeters they may be classified as rotameters, penumotachographs, hot-wire ane mometers, time-of-flight flowmeters, ultrasonic flowmeters, and vortex flowmeters 2. Depending on their principle of operation, flowmeters can be classified in four main categories rotating-vane, ultrasonic, thermal-convection, and differential pressure flowmeters.Rotating-vane FlowmetersThese types of sensors contain a small motor or turbine which rotates with airflow, and then flow rate is related to the revolution of the rotor. This type of flowmeter is usually used in ventilator machines and respiratory monitoring 2. The spins are detected optically and converted into voltage to be recorded or displayed. ultrasonic FlowmetersUltrasonic flowmeters can measure instantaneous flow and the effect of the flowing gas on the transit time of the ultrasonic signal 7. A crystal is used for transmitting and receiving and it is placed externally and obliquely to the axis of the tube through which the gas flows 7. The time elapsed will depend not only on the velocity, but on the temperature as well as composition of the gas analysed. One main advantage of this type of transducer is that unidirectional flow can be measured, which is applicable for clinical monitoring.Thermal-Convection FlowmetersThermal sensing technologies are usually made of hot wires, metal film, and thermistol which all use heat to sense gas flow. The wires are heated by an electric current and the heat transfer is used to measure the gas flow 2. The wire is heated above flow gas temperature, to associate temperature differences a metal mesh is placed at both ends of the tube. This type of sensing is limited to only one flow direction, more sensors can be located in the tube for multiple directions and for breathing a calibration factor must be considered. 7.Differential Pressure FlowmetersFlowmeters that use the relationship of pressure drop with airflow through a system. There include elements such flow resistors.Common FailuresFigure Closed system during mechanical ventilationThe most common fail ures presented in MV are mainly as a consequence of poor maintenance and user error. Leaks in the circuit due to bad connections or due by perforations in tube are a frequent dysfunction. Leaks stop the proper delivery of tidal volume as well as an precise sensing flow from the ventilator. PEEP can also be affected by this interfering with O2 saturation (Fig. 9).At times, when an patient with intubation is not able to trigger the ventilator, or the ventilator senses by mistake a patients effort and delivers breaths, is known as patient-ventilator dyssynchrony. As a result the machine delivers an unsuitable breath to the rate of the patients inspiratory efforts. This type of error is also identified as trigger failure or desynchronisation, mismatching, and fighting the ventilator 8. One create for patient-ventilator dyssynchrony is fixing the trigger sensitivity improperly. When a desynchronisation with the patients efforts to initiate a breath exists, work of breathing can occur wh ich can be accompanied with respiratory distress preventing pulmonary gas exchange..Another usual failure is due to user error with the interface. MVs are complex equipments, and the need of the clinician to be familiar with the machine is crucial. It is important that Mechanical Ventilators count with an audible and visual alarm when detecting a leakage or disconnection.Possible hazards to macrocosmProblems may occur while using a mechanical ventilator, especially with patients that been required the use of a MV for a prolonged amount of time. The take chancess occasioned by the use of respiratory support can lead to severe harmful or even death. Common hazards that may occur due to the use of a ventilator are infections, pneumothorax, and lung injury.InfectionsThe most common find reported is acquiring Ventilator-associated pneumonia, which is caused by an infection. The tube allows germ (bacteria) to penetrate more easily into the lungs. This can cause pneumonia. Pneumonia can be a serious problem and may mean that a person may not be able to initiate respiration leading to a longer use of a MV. In addition a recent study reported factors related such as the development of shock, and renal failure 9. In order to prevent infections a number of control procedures can be performed, and these include maintaining the ventilator as well as the breathing circuit 8.PneumothoraxOccasionally when a part of the lung is weak, this may become over full of air and as a result an air leak may occur. The leak allows air into the space between the lung and chest wall. The air in this region occupies space in a manner that the lung begins to collapse. If there is air leakage, a chest tube into is used to drain the excess air allowing the lung to re-expand and stop the leak.Lung InjuryThe pressure generated by introducing air into the lungs with a ventilator can damage the lungs. Furthermore, very high levels of oxygen can also be harmful to the lung. As a solution to try to keep this risk to a minimum the lowest pressure necessary as well as the only oxygen needed is supplied.Prolonged intubation usually defined as a period longer than 48 hours 10 may lead to swallowing dysfunction. This is mainly caused by impairing glottic closure reflex, reducing subglottic pressure, limiting laryngeal elevation, desensitizing the larynx and hypopharynx, and causing disuse muscle atrophy of the larynx and pharynx 10.Advantages and limitations of various techniquesOnce analysed the principles of operations and risks of Mechanical Ventilators, for a better understanding of these is necessary to mention the advantages and disadvantages that they could loan. The refer MV have had over the past 40 years is massive due to the fact that mechanical ventilators provide vital support.Nowadays ventilators found in the market present vast options in terms of modes, control and displays which in many cases can result complicated and the knowledge of these is required8. In a ddition features need to be evaluated in order to establish which configuration mode is suitable for each patient 8. Ideally hospitals should acquire equipment that incorporates the latest development in ventilation however as mention before this could lead to complications and misuse of the devices. Requesting companies instruct to all staff involved in the use, handling and care of the equipment helps to reduce the risk 11.The complicity of the equipment could be considered as a disadvantage of MV, nevertheless ventilators with good human factors design provide major advantage 8.Mechanical ventilators, being devices that provide respiratory support the duration and need may vary from patient to patient age is also an important factor as well as the condition. Ventilators are usually used in patients that are in Intensive Care Unit (ICU) and after remaining in intubation after 48 hours the risk to the patient increases. Weaning from mechanical ventilation (MV) permits patients to restart spontaneous breathing steadily however some risks are involved 12 and are mentioned in section. Risks and hazards to patients should ever be considered when dealing with medical devices however the benefits that they bring play a major role. But still as an advantage mechanical ventilators as mentioned before, bring vital support where initiation of breathing or respiration cannot be performed by the patient.Critical ComparisonFigure Piston pump in HFOVDifferences between each mechanical ventilator is defined by their operation mode which establish the flow pattern, pressure and volume delivered to the patient with the purpose of controlling alveolar ventilation and as a result achieve the goals of mechanical ventilation. Ventilation modes are determined by the combination of breathing pattern, type of ventilation and control. As for this MV operation mode is going to vary according to the age, and state of the patient, in a way that ventilation is provided and the risk is minimal. RequirementsAs mentioned before, the continuous use of ventilators may induce injury to the lungs. Air strained outside the normal air spaces creates a swelling pressure that may injure alveoli. The name of this condition is Barotrauma, and malfunction to the mechanical ventilation may occur. noble pressures or volumes during inspiration, or when extreme PEEP is used are causes of Barotrauma. There has not been found an connector of clinical injury with the level of pressure used, the problem is estimated to be an over expedition of volume 13.High frequency ventilation(HFV) is a ventilation strategy for patients with respiratory failure providing a small source of tidal volumes (VT) which is in most of the cases less than the anatomic dead space volume, with respiratory rates above 150rpm. new(a) Research studies have shown that HFV can help reduce barotraumas in normal and injured lungs 14.Figure Flow during high frequency ventilationHFV can be classified according to t he source that generates their frequency and the type of exhalation phase there are four types High Frequency Jet Ventilation (HFJV), High Frequency Oscillatory Ventilation (HFOV), High Frequency Flow Interruption (HFFI), and High Frequency Positive Pressure Ventilation. The most commonly is used is the HFOV where in a continuous positive air pressure circuit the frequencies are oscillated by a piston pump (Fig. 10).During inspiration, each high frequency trice in the flow creates a profile shaped like a bullet (Fig. 11), with the central molecules moving on beyond the airway than those found in the periphery.Table (2) describes and compares main differences between common ventilation and high frequency ventilation.Table Comparison between HF ventilator and established ventilatorHFVConventional VentilatorFrequency is measured in Hertz (Hz)Frequency is measure in rpmUses Displacement Volume (Vd)Uses Tidal Volume (Vt)Volume per minute is measuredVolume per minute is measuredMedical D evices Available on the MarketThere is a wide range of medical ventilators currently uncommitted on the market, and they all offer variety of options ranging in modes, variables monitored and ways of control 8 . Specific requirements and recommendations can be separated according to the complexity based on their performance.Some of the most common brands available nowadays are listed in table (3), and they all offer ventilators that may vary according to specific needs.Table Brands currently availableBrandModelACOMAART-100ART-21EXBIO-MED DEVICESCV-3CV-4DRAEGERCarina HomeEvita 2 duraEvita 4Evita XLOxylog gibibyteOxylog 2000Oxylog 3000SavinaEVENT MEDICALInspirationInspiration LSGE HEALTHCARE(DATEX-OHMEDA)Centiva/5Engstrom CarestationHAMILTONGALILEO GOLDRAPHAEL COLORIMPACTUnit-Vent 754INTERMEDINTER5 PLUS/ GMXINTER PLUS VAPS/ GMXKIMURAKV-3NMAQUETServo-i(AdultInfant)Servo-S ( Adult Pediatric)NEWPORTE100ME150 BreezeE360E500 WavePULMONETIC SYSTEMS/VYASIS HEALTHCARELTV 900LTVO 950LTV 1000 RESPIRONICSEspritSAIMEELISEESIARESiaretron 1000 ICUSiaretron 1000 IPERSiaretron 3000 ICUTAEMAeXtreriaHorus 4NEFTIS icuTECMENeumovent GraphTYCO HEALTHCARE PURITAN BENNETT740760840VERSAMEDiVent201VYASYS HEALTHCAREAVEAVelaVela +Vela ComprehensiveFuture Stage of DevelopmentAdvanced features like recording and accurate and advanced predictions will come in a future state of development. In addition the ability to link multiple devices on one is now available, where the ventilator monitor can display lectures from other devices.Portable devices are starting to become more common, they are light and compact devices. Important upgrades have been made to portable devices, where advanced features are now presented. Current portable ventilators present various modes of ventilation and longer power supply.In order to repress complexity, it is important when developing new features to consider the principal use of ventilators, which is respiratory supply. In addition for longer term care many f eatures may not be used and costs can increase.ConclusionsMechanical ventilators are vital equipments that provide vital support to a patient. They provide artificial respiration to patients that cannot go on on their own. Their principle of operation is based on mechanical exchange of gases, and their circuitry includes electro-valves for their control and flowmeters as transducers. MV can become very complex devices, training of clinicians using them is crucial in order to avoid risks to patients. Hazards to patients may occur when used for more than 48 hours, however new techniques like high frequency ventilation can reduce this. There is a wide range of devices present on the market and they all vary on their modes of operation. Portable devices are now popular and present important features. Mechanical ventilators are used every day in hospitals and represent a critical part on vital support.