Patient Monitor Systems PDF

BM552 Medical Instrumentation II Patient monitoring systems IntelliVue Mobile Caregiver Philips IntelliVue...

BM552 Medical Instrumentation II Patient monitoring systems IntelliVue Mobile Caregiver Philips IntelliVue MX850 Philips CARESCAPE B850 monitor GE Healthcare Patient Information Center iX (PIC iX) Philips CARESCAPE Central Station Smartsigns Compact 1200 GE Healthcare Huntleigh  Patient monitor The monitor typically comprises of a set of modules for real‐time measurement of various physiological parameters. The most monitored and displayed parameter modules are:  Electrocardiogram (ECG)  Heart rate  Pulse oxygen saturation (SpO2)  Pulse rate  Respiration rate  Body temperature  Noninvasive and invasive blood pressure (BP) Some monitors are also designed to include: Cardiac output, ETCO2, EEG, intracranial pressure, and airway respiratory/anesthetic gas concentrations  Patient monitor They consist of several sensors, display devices, signal processing electronic circuits, and communication links for displaying or recording the results elsewhere through a monitoring network. They include computing capabilities and display trend information on measured parameters. The monitors have been designed for patients of all ages, adults, pediatric, and neonatal.  These monitors have minimum 19in. Touch screen color thin film transistor (TFT) display with minimum six waveforms of standard parameters. They have continuous 12 lead ECG facilities including 12 lead ST segment analysis capabilities. They also include at least 24 hours graphical and tabular trends of all parameters, with alert alarms. The monitors have uninterrupted power supply (UPS) backup at least for 1hour.  Central station The central station receives, consolidates, and displays the information about the physiological parameters, usually received from several bedside patient monitors. Some central stations especially designed for ambulatory patients often include portable radio transmitters, receivers, and antennas (telemetry systems) to allow monitoring of mobile ambulatory patients. Such systems are useful for evaluating and observing trends in physiological parameters of patients in intensive care settings. Central stations usually come with large size displays, say, minimum 32 in., with capability of monitoring 10 beds with at least two waveforms from each bedside. Other facilities include parameters to be displayed in numeric form, audio and visual alarm indicators, storage facility of minimum of 20 events, automatic arrhythmia detection, and facility for 24‐hour full record for at least three waveforms Block diagram of a typical patient monitor MCU, microcontroller unit; MPU, micro processing unit  Temperature Measurement Temperature monitor is intended for continuous monitoring of body temperature. The measurement is done by converting the temperature to the electrical signal by a sensor, which is usually a thermistor. A thermistor is a type of resistor whose resistance varies depending upon the temperature. If the resistance of the thermistor decreases with increasing temperature, the device is called a negative temperature coefficient (NTC) thermistor. The signal from the thermistor is amplified and given to the ADC, whereas the processing and control functions are performed by a microcontroller. The probe accuracy is ±0.1 °C. Oral and rectal probes utilize single‐use disposable probe covers, which limit cross‐contamination. Generally, the thermistor measures temperature at discrete intervals and then calculates the rate of change according to a known algorithm. This allows the thermometer to predict the end point that the thermistor would reach if it were left in the mouth until it reached mouth temperature. This predictive feature allows the thermometer to arrive at an accurate oral temperature reading in approximately 4 seconds and in about 15 seconds for rectal temperatures. The probe must be in contact with tissue for at least three minutes for accurate temperature measurement. Temperature readings may be displayed in Fahrenheit or Celsius scales.  Pulse Oximetry (SpO2) and Pulse Rate Measurement Pulse oximetry takes advantage of the fact the blood absorbs certain wavelengths of light differently when it is oxygenated than when it is deprived of oxygen. The SpO2 monitor performs most conveniently and accurately with the finger clip sensor, which may be used on all fingers except the thumb.  Pulse oximetry system determines arterial oxyhemoglobin saturation (% SpO2) by measuring the absorption of red (660nm) and infrared (IR) (940) light passed through the tissues. The SpO2 probe has two light emitter diodes (LEDs) and a photodetector.  The red diode and an IR diode emit light alternately according to certain program. Absorption of light at these wavelengths differs significantly between blood loaded with oxygen and blood lacking oxygen.  Oxygenated hemoglobin absorbs more IR light and allows more red light to pass through. Deoxygenated hemoglobin allows more IR light to pass through and absorbs more red light.  The LEDs sequence through their cycle of one on, then the other, then both off about 30 times/s, which allows the photodiode to respond to the red and IR light separately and adjust for the ambient light baseline The ratio of the red‐light measurement to the IR light measurement is calculated  Pulse Oximetry (SpO2) and Pulse Rate Measurement  The amount of light that is transmitted and not absorbed is measured. These signals are in the form of pulses, which fluctuate in time because the amount of arterial blood that is present varies in each heartbeat.  By subtracting the minimum transmitted light from the peak transmitted light in each wavelength, the effects of other tissues are corrected for the effects of other tissues, such as skin pigmentation, tissue thickness, and motion artifacts. The ratio of the red‐light measurement to the IR light measurement is then calculated by the processor, and this ratio is then converted to SpO2 by the processor via a lookup table based on the Beer–Lambert law.  The signal processing circuit comprises of low noise amplifier, high pass filter, and an ADC followed by a microcontroller for calculations of SpO2 and pulse rate and interfacing with the LCD digital display.  The pulse signal bar graph is an indicator of the strength and quality of the detected pulses. In case of an alarm condition, the monitor will indicate an alarm condition by flashing of light and audio beeping while continuing to monitor and display the patient’s current SpO2% and pulse rate. The alarm will automatically reset when the patient’s condition returns to within the preset alarm parameters. Masimo pulse oximeter  Electrocardiograph ECG monitoring is the basic requirement in vital signs monitors. The measurement could be based on single lead, 3 lead, 5 lead, or 12 lead configuration. For continuous monitoring, the ECG signals are usually picked up by using pre‐gelled electrodes. For ECG, each electrode requires a precision instrumentation amplifier to extract a very small signal that rides on a large common mode signal. A buffer amplifier circuit is included for impedance transformation to ensure that the circuit has a high input impedance and a low output resistance.  Electrocardiograph The common mode rejection ratio is improved by using ‘right leg drive’ circuit? This is followed by precision amplifiers and filter circuits with high pass filter (usually 0.5 Hz) and low pass filter (around 150 Hz). Active filter amplifiers are required to set a very specific band (0.5–150 Hz) to capture the ECG QRS wave signal. In multi‐channel systems, such as a 12 lead ECG monitor, it is common to multiplex signals and given into a common analog‐to‐digital converter (ADC). It is also common for multi‐channel ECGs to have automated lead detection to enable multi‐configuration operations. For continuous monitoring, single or three lead ECG is monitored using pre‐gelled adhesive type electrodes are used. However, for acquiring a 12 lead ECG, limb lead electrodes are typically placed on the wrists and ankles. The six precordial (chest) leads are placed on specific locations. Most monitors acquire 12 lead ECG data and perform the interpretive analysis based on the full frequency of 0.05–150Hz. However, the ECG print‐ out usually has 0.05–40Hz bandwidth. Computerized ECG analysis results are automatically printed on 12 lead ECG reports. ECG based heart rate is derived from the QRS complex of the ECG, by measuring the time interval between two complexes  Respiratory Rate Measurement Impedance pneumography is a commonly used technique to monitor a person’s respiration rate. It is implemented by either using two electrodes or four electrodes method. The basis of this technique is the changes in the electrical impedance of the person’s thorax caused by respiration or breathing. For measurement of respiration rate by impedance pneumography, it is required to inject high frequency current into the body. The current that is injected is up to 100μA of current at 10 kHz. The high frequency AC signal injected into the body acts as a carrier that is amplitude modulated by the low frequency signal generated as a result of the breathing action. On the receiver side, this modulated signal is demodulated in order to extract the low frequency breathing signal. After demodulation, the signal is low pass filtered to the 2–4 Hz bandwidth level to remove unwanted noise. The demodulated and filtered output is then digitized by a high‐precision ADC and given to the processor.  Blood Pressure (Non‐invasive) Measurement Noninvasive blood pressure (NIBP) monitor measures BP using the oscillometric measurement technique to determine systolic, diastolic, and mean arterial pressures and pulse rate. The measurement can be initiated manually or set to recur automatically at predetermined intervals. The oscillometric technique does not use Korotkoff sounds to determine BP; rather, it monitors the changes in pressure pulses that are caused by the flow of blood through the artery. The process involves automatically inflating the cuff around the upper arm of the patient to the operator selected pressure level. The pressure is selected at which the pressure generated by the cuff stops the flow of blood in the brachial artery. The cuff then immediately begins to deflate in a stepped fashion according to a certain algorithm requirements and will determine systolic pressure and diastolic pressure from the pulses sensed by the cuff at various pressure levels. Bui N. et at,. 2019. EBP: A Wearable System For Frequent and Comfortable Blood Pressure Monitoring From User's Ear. In The 25th Annual International Conference on Mobile Computing and Networking (MobiCom '19). Association for Computing Machinery, New York, NY, USA, Article 53, 1–17. https://doi.org/10.1145/3300061.3345454  Blood Pressure (Non‐invasive) Measurement As the pressure is reduced, the arterial blood will generate a pulse signal. The pulse signal is filtered and amplified in a high pass filter (about 1 Hz), and the output is converted into digital signal by the ADC. The systolic, diastolic, and mean BPs are derived through software using a microcomputer. Different sized cuffs are used for neonate, pediatric, and adult patients to avoid the measurement error. Excessive pressure in the cuff is prevented by using a protection electric circuit. At the completion of a measurement cycle, the systolic and diastolic pressures are displayed. BP measurements when programmed for automatic operation are made once in the selected time intervals. The period can be selected from 3 to 90 minutes. The measured values are kept on display until the next BP measurement is initiated. The pressure sensor most used is piezoresistive silicon sensor in the Wheatstone bridge configuration. The pressure sensing element combines resistors and an etched diaphragm structure to provide an electrical signal that changes with pressure. As the diaphragm moves under pressure, a small voltage is generated that changes proportional to the pressure applied to the diaphragm. This bridge signal is then amplified in a precision amplifier. This is typically followed by an active filter to limited unwanted noise at higher frequencies. Amplifiers with low noise, low drift, and high gain are necessary to minimize measurement errors and ensure accurate readings. The amplified and filtered signal is then given to the ADC for processing. The NIBP monitor measures the pulse rate by tracking the number of pulses over time. Sharman, J.E., Tan, I., Stergiou, G.S. et al. Automated ‘oscillometric’ blood pressure measuring devices: how they work and what they measure. J Hum Hypertens (2022). https://doi.org/10.1038/s41371‐022‐00693‐x Automated BP measuring devices (BPMDs) For the oscillometric method, systolic and diastolic BPs are estimated typically by characteristic ratios of an envelope fitted to the ‘oscillations’ with systolic BP at about 50% (range 45–73%) of maximal amplitude on the rising phase of the waveform envelope and with diastolic BP at about 70% (range 69–83%) of maximal amplitude on the falling phase of the waveform envelope: Mean arterial pressure is estimated on the oscillometric waveform envelope at the point of maximal amplitude Digital readouts are provided for systolic and diastolic BPs and occasionally for mean arterial pressure Non‐invasive BP System Block Diagram  Blood Pressure (Invasive) Measurement Invasive pressure monitor is intended for measuring arterial, venous, intracranial, and other physiological pressures using an invasive catheter system with a compatible transducer. The monitoring method usually involves the conversion of fluid pressure into an electrical signal, which is achieved with a pressure transducer. The transducer is connected to a patient’s indwelling pressure catheter using an assembly of tubing, stopcocks, adapters, flush valves, and fluids, commonly known as a flush system.  EtCO2 Monitoring The end‐tidal CO2 (EtCO2) monitor is based on the capnometric principle that depends upon non‐dispersive IR spectroscopy. The device continuously measures the amount of CO2 during each breath and displays the amount present at the end of exhalation (EtCO2). The sample is obtained by the side stream method and can be used with intubated or non intubated patients. Respiration rate is also derived from the capnography waveform and displayed in breaths per minute. An EtCO2 sensor continuously monitors carbon dioxide (CO2) that is inspired and exhaled by the patient. The sensor employs non‐dispersive IR spectroscopy to measure the concentration of CO2 molecules that absorb IR light. The IR source illuminates the sample cell and the reference cell. This IR light source generates only the specific wavelengths characteristic of the CO2 absorption spectrum.