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Pediatric and neonate incubators
Chapter 78
Pediatric and neonate incubators Almir Badnjevića,b, Lejla Gurbeta Pokvića,b, Lemana Spahića a
Department of Genetics and Bioengineering, Faculty of Engineering and Natural Sciences, International Burch University, Sarajevo, Bosnia and Herzegovina, bMedical Device Inspection Laboratory Verlab Ltd., Sarajevo, Bosnia and Herzegovina
Pediatric and neonate incubators today are more sophisticated than the first prototypes but basic functions remained the same. They provide controlled environmental conditions needed to treat prematurely born infants who are not able to endure all the conditions outside the womb or infants born with certain diseases or health conditions. Patients in incubator have difficulties in thermal regulation because of the poor thermal insulation, relatively large surface area, a small amount of mass to act as a heat sink, and they have no ability to conserve heat by changing body position. There are four different mechanism of heat lost for patients in incubator that must be taken into account when designing these medical devices. These include radiation, conduction, convection, and evaporation. Heat loss through radiation is related to the temperature of the surfaces surrounding the infant but not in direct contact with the infant. Conduction occurs through direct contact with a surface with a different temperature. Heat in incubator is transferred by convection when air currents carry heat away from the body surface and evaporation occurs when water is lost from the skin. Incubators, today, differ in design and accessories depending on manufacturer, but main parts of these electrical medical devices, based on various manufacturer specification, are (Fig. 1): ● ● ● ● ● ●
● ● ●
transparent chamber, power supply, AC-powered heater, electric fan motor to circulate the heated air, water tank for controlling the humidity of air, sensors for measuring temperature, relative humidity, sensor of skin temperature, and air flow sensor, microprocessor-based temperature controller, sir filters, oxygen supply,
514
● ●
alarms and safety features, and access ports for nursing care.
Controlled environmental conditions in incubator are achieved by regulation of temperature, humidity, oxygen lever, air flow, and sound level. There are two main control modes used in these devices: (1) air temperature control mode and (2) skin temperature control mode. Incubators can be divided into two groups: (1) stationary and (2) transport incubators. Difference between transport and stationary incubators are mainly concerned about power supply. Requirements for battery for transport incubators are more complex than for the stationary incubators. When designing transport incubators back up power sources need to be ensured, so if external AC is not available that incubator can switch to external DC source and if that is not available that incubator can use external batteries as power supply to provide stable conditions for transport of patient. Also, most of transport incubators only have air temperature control mode and are supported with lifesaving equipment. The incubator consists of rigid transparent box called chamber, which has side openings. Transparent material is used for chamber which needs to be designed to resist the strains of transportation and to absorb impacts and ensure thermal insulation properties. Most usually chamber is placed on mount which has ability adjust the angle position of the box. The side openings on the box provide accessibility to patient for resuscitation or procedures without jeopardizing thermal stability. Most usually in incubator design, openings on the incubator chamber are provided along one of the longer sides of the incubator and provision is made for convenient displacement of the mattress or other infant support laterally out of and back into the enclosed space of the incubator through the door. At the same time, armholes or similar access ports can also be provided, to enable attendants to give attention to the infant within the incubator, Clinical Engineering Handbook. https://doi.org/10.1016/B978-0-12-813467-2.00079-1 Copyright © 2020 Elsevier Inc. All rights reserved.
Pediatric and neonate incubators Chapter | 78 515
Access port doors (iris type)
Exhaust air vent holes
Exhaust air vent holes
Perspex canopy Baby tray Oxygen added Sensor of thermostat Fresh air Bacterial filter
Oxygen gauge tube
Heating element Motor
Dispensing apparatus
Fan
Humidification control
FIG. 1 Schematics of an infant incubator.
without withdrawing the infant support. Longer sides of incubators are intended to be accessible and the one with control panel unit is considered to be front of incubator. Controlled environmental conditions in incubator mean that the air inside the chamber is held on certain temperature with certain percentage of humidity present in the air. Air intake is usually found at the bottom of the device. The fan with motor drive, placed underneath the chamber, takes the room air and blows it over or through the heating element and the humidifier. A heating element made from coiled resistance wire known as the tube-type (flat or coiled) heater is used in most incubators. To prevent system from overheating, the power rating of heater used in incubator is much less than in the other devices. Typical power rating of heater in incubators is between 100 and 300 W. The heater is controlled by an electronic temperature control unit. The incubator reading, that is, reading from temperature sensors and reading of relative humidity of air inside of chamber can displayed digitally on control panel of incubator, or using analog indicators. Humidifier is most usually a water tank. To ensure moisturizing, the heated air flows over the water in the water container and gets moistened. The humidity is often regulated by closing and opening of valve over the water container closing and opening a deflector plate over the container. Air inlets allow heated and humidified air to enter the chamber, while air outlets take the air from the chamber allowing the air circulation inside the chamber. The humidifier should be filled up only with distilled water
only in order to avoid corrosive damage to the incubator. The general requirements for incubators in order maintain the body temperature of the baby between 36 °C and 37.2 °C are to be able to create an ambient air between 34 °C and 38 °C with a humidity of 40%–90%. For oxygenation therapy, incubators can be equipped with modules for dosing oxygen into the heated and moistened air. The oxygen concentration is also electronically controlled using microprocessor. If incubator does not pose these modules for dosing the oxygen into the air inside the chamber, oxygen can be applied in chamber through a hose connection from an external cylinder, oxygen concentrator, or from the central gas supply. Most oxygenation equipment is compatible with most incubators. Alternatively, the baby gets the additional oxygen directly through a nasal cannula which pipes oxygen directly into the nostrils. Maintaining maximum purity of the air circulated in the incubator is enabled by usage of different filters. Also, the purity of air in the incubator can be achieved by introduction of oxygen into the circulation system in a manner to pass through the filter so that not only the replacement air but also the oxygen, when used, is subject to the filtering action. In this way, bacteriological impurities originating even in the oxygen supply are substantially eliminated. Inside the chamber, above the heater and humidifier, cradle for patient is installed. This cradle is most usually equipped with additional scale for measuring the weight of a newborn and can move right, left, up, and down. Monitoring and observation equipment is often built
516 SECTION | 8 Medical devices: Utilization and service
into the infant incubator unit which include cardiac monitors, brain-scan equipment, blood-monitoring equipment, thermometers, and other instruments for observing vital signs. For treatment of certain medical conditions, medical professionals use ultraviolet (UV) lamps. These lamps can be put over the incubator chamber since the chamber is transparent. When undergoing treatment with UV light, precautions should always be taken to prevent the unnecessary exposure of UV light to healthy skin. In order to ensure safety of the infants, all electronically controlled incubators are equipped with alarming system which tracks the state of the environment within the incubator and alarm the medical staff in case of odd settings. To ensure proper functioning of infant incubators, stable and high-quality delivery of energy is needed to ensure the security of the modern clinical settings. When it comes to an electric failure in the health institution, the incubator’s internal energy source needs to be able to keep the unit in active mode for few hours in case of power loss. Battery capacity depends on manufacture. In the case of sudden voltage jumps, operation may be interrupted or may result in incorrect operation. For these reasons, units of uninterruptable power supply (UPS) are placed with incubators. Besides, infant incubators with closed chamber and controlled environmental conditions that can be stationary or transport, one additional type can be recognized. It is called infant warmer. This medical device consists of a biocompatible bed on which medical professionals place infant and transparent side panels. The bed of infant warmer is placed on the rail mounting system. Heater is placed above the bed and delivers radiant heat to the patient inside providing unified heat. Heaters in infant warmers are typically made from quartz or ceramic. When designing this medical device, type of heater is very important because it has direct impact on time needed for warmer to meet the desired temperature. Each additional minute of cold stress can lead to increased morbidity for an infant. They are characterized by lower power consumption and long life of the heating element lead to considerable cost savings in healthcare institutions. These devices also have air temperature control mode and skin temperature control mode. Skin temperature probe monitors infant temperature. The control unit contains the electronic circuits and controls radiant heater and the observation light. The manual mode of operation (air temperature control mode) allows selecting the level of radiant heat output which is indicated by the percentage power displayed on the control panel. The control circuit maintains the selected level of radiant heat. The manual mode has a preheat setting which allows the warmer to be preheated. In the automatic mode (skin temperature control mode) of operation, the patient’s control temperature is chosen. A skin temperature probe is used to monitor the patient skin temperature. The control system modulates the radiant heat to maintain the patient at the selected control temperature. In most cases, the patient
temperature, control temperature, and elapsed time displays are digital for ease of viewing. Visual and audio alarms are present for safety.
Preventive maintenance qualitative tests 1. Chassis/housing: examine the exterior of the unit for cleanliness and general physical condition. Be sure that plastic housings are intact, that all hardware is present and tight, and that there are no signs of spilled liquids or serious abuse. 2. Infant incubators: remove any tape adhered to the unit. Check all rubber and plastic gaskets in the unit for signs of deterioration. The condition of the hood is important for power control of the environment. Ensure the hood is free of cracks, warping, or other deterioration signs. Verify all parts are assembled correctly. Remove the hood, bed, baffle, main deck, and other parts and thoroughly inspect the interior for foreign objects, deterioration, or misassembly of internal components that could interfere with performance. 3. Mount/fasteners: if the device is mounted on a stand or cart, examine the condition of the mount. If it attached to the wall, or rests on a shelf, check the security of the attachment of every screw on the hood. Operate the iris-type port closures to ensure proper function. Examine the iris diaphragms and port sleeves for tears. Verify that disposable irises are being replaced after each incubator use. Check that all nuts and bolts are tightened fully. Use a screwdriver and systematically try to tightening replaced after each incubator use, these items are not reusable. 4. Casters/brakes: if the device moves on casters, check their condition. Look for accumulations of lint and thread around the casters, and be sure that they turn and swivel, as appropriate. Check the operation of brakes and swivel locks, if the unit is so equipped. 5. AC plug/receptacles: examine the AC power plug for damage. Attempt to wiggle the blades to check that they are secure. Shake the plug and listen for rattles that could indicate loose screws. If any damage is suspected, open the plug and inspect it. Should the equipment be placed on a cart that has extra electrical receptacles for other equipment, insert AC plugs into each and verify they are firmly held. Verify that no damage is present in the cart receptacles. 6. Line cord: inspect the cord for signs of damage. If damaged, replace the entire cord or if the damage is near one end, cut out the defective portion. Wire a new power cord or plug on the same polarity. Check the line cords of battery chargers. 7. Strain reliefs: examine the strain reliefs at both ends of the line cord. Be sure that they hold the cord securely.
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If the line cord is detachable, it is recommended that the cord be affixed to the unit so that it cannot be removed by the operator. 8. Circuit breaker/fuse: if the device has a switch-type circuit breaker, check that it moves freely. If the device is protected by an external fuse, check its value and type against that marked on the chassis and ensure that a spare is provided. 9. Tubes/hoses/bulbs: check the condition of all tubing, cuff, hoses, and bulbs (if present). Be sure that are not cracked, kinked, or dirty. Inspect all oxygen orifices to make sure that they are clear and free of foreign matter. Preventive maintenance protocols. 10. Cables: inspect the cables of sensors, electrodes, remote control and their strain reliefs, and general conditions. Carefully examine cables to detect breaks in the insulation and to ensure that they are gripped securely in the connectors at each end to prevent rotation or other strain. 11. Fittings/connectors: examine all fittings and electrical cable connectors for general condition. Electrical contact pins or surfaces should be straight and clean. Fittings should be tight and should not leak. If keyed connectors are used, make sure that the keying is correct. 12. Electrodes/probes: confirm that special paddles and electrodes are available if appropriate for the area of use. Examine all paddles and probes for physical conditions and cleanliness. Should the equipment have fluids, dried electrode gel, or debris on it, inform the clinical staff. Clean paddles and electrode surfaces if needed and ensure they are completely dry before testing. Ensure that probe labels clearly identify the associated units. Improperly interchanged probes of different types or from different manufacturers may adversely affect temperature control. Confirm that any necessary transducers (if applicable) are on hand and check their physical condition. 13. Filters: if the device has a switch-type circuit breaker, check that it moves freely. If the device is protected by an external fuse, check its value and type against that marked on the chassis and ensure that a spare is provided. Clean filter. 14. Controls/switches: before changing any controls or alarm limits, check their position any settings appear inordinate (e.g., alarm limits at the ends of their range), consider the possibility of inappropriate clinical use or of incipient device failure. Record the settings of those controls that should be returned to their original positions following the inspection. Examine all controls and switches for physical condition, secure mounting, and correct motion. Check that control knobs have not slipped on their shafts. Where a control should operate against fixed-limit stops, check for proper alignment, as well as positive stopping. Check membrane switches for
15.
16.
17. 18.
19.
20. 21.
membrane damage (e.g., from fingernails, pens). During the course of the inspection, be sure to check that each control and switch performs its proper function. Heater: disassemble the heating unit enough to expose the heating element. Examine the element for severe discoloration or foreign deposits. Heating elements normally change color with use, but dark, distinct surface spotting may indicate that material has come into contact with the element, possibly after falling through the air duct. Foreign matter touching the hot surface could cause a fire or the generation of noxious fumes. If you find such discoloration, examine the control unit compartment for signs of overheating. If screw terminals connect the heating element to the control circuitry, check that they are tight. Motor/fan/pump: inspect fan blades for deterioration and damage. Ensure fan is securely attached to drive shaft and that the coupling is present and intact. Check that clearance between the fans and housing are adequate by looking for signs of rubbing. In some cases, an improperly inserted control module and heater assembly in the incubator base has bent and disabled fan. Verify whether if fan requires lubrication or not. Observe the fan in operation to determine if there are excessive vibrations or wobbling. Fluid levels: check all fluid levels, including lead-acid battery levels. Battery/charger: inspect the physical condition of batteries and battery connectors, if readily accessible. Check operation of battery-operated power-loss alarms, if so equipped. Operate the unit on battery power for several minutes to check that the battery is charged and can hold a charge. (The inspection can be carried out on battery power to help confirm adequate battery capacity.) Check battery condition by activating the battery test function or measuring the output voltage. Check the condition of the battery charger and, to the extent possible, confirm that it does, in fact, charge the battery. Be sure that the battery is recharged or charging when the inspection is complete. Some batteries require periodic deep discharges and recharging to maintain a maximum battery capacity. If this is recommended by the manufacturer, verify that it is being performed on schedule. Indicators/displays: during the course of the inspection, confirm the operation of all lights, indicators, and visual displays on the unit and charger, if so equipped. Be sure that all segments of a digital display function properly. User calibration/self-test: verify operation of these features, if applicable. Alarms: operate the device in a way that activates all the alarms. Check that any associated interlocks function. Check action of disconnected-probe alarm, if unit
518 SECTION | 8 Medical devices: Utilization and service
so equipped. If the device has an alarm-silence feature, check the reset method. 22. Audible signals: operate the device to activate any audible signals. Confirm appropriate volume, as well as the operation of a volume control, if so equipped. If audible alarms have been silenced or the volume set too low, alert clinical staff to the importance of keeping alarms at the appropriate level. 3. Labeling: check that all necessary labels, conversion 2 charts, and instruction cards are present and legible. Incubators: since incubators carry oxygen, a fire hazard sign must be visible. Also, a sign warning of the effects of high oxygen concentrations should be present (high oxygen concentration can cause fibroplasias and blindness in infants). 24. Accessories: check the hood thermometer for cracked glasses or separations in the liquid column. If the liquid column has separated, it might be possible to consolidate it by removing the thermometer and carefully dipping it into hot water. If the thermometer has an expanded space at the top, the liquid will pool in the small reserve chamber. When the gap in the column disappears into the pool, cool the thermometer and recheck it. Repeat the process if necessary. Be careful not to overheat the thermometer, for the liquids in it will expand and crack the glass. If the position of the mattress is adjustable, check the ease of motion and security of lock mechanism. Examine mattress for cleanliness. If the unit is used in the presence of flammable anesthetics, check that a conductive mattress cover is used.
Preventive maintenance electrical safety test a. Grounding resistance: using an ohmmeter, electrical safety analyzer, or multimeter with good resolution of fractional ohms, measure and record the resistance between the grounding pin of the power cord and exposed (unpainted and not anodized) metal on the chassis. A maximum of 0.5 Ω is recommended. b. Leakage current: measure chassis leakage current to ground with the grounding conductor of plug-connected equipment temporarily opened. Operate the device in all normal modes, including on, standby, and off, and record the maximum leakage current. Chassis leakage current to ground should not exceed 300 μA.
Preventive maintenance quantitative tests a. Temperature control: check the action of the primary and safety thermostats with the incubator fully assembled. Set the temperature to 36 °C. Test the thermostats
according to the manufacturer’s instructions, and record on the form the temperature at which safety or backup thermostats turns off heater. b. Skin temperature alarms: if the incubator is equipped with high and low skin temperature alarms, verify alarm function. Adjust skin temperature set point to 36 °C. Place sensor in incubator and allow temperature to stabilize. Remove the sensor from the incubator and verify that alarm activates. To verify the high skin temperature alarm, place sensor near the heaters exit where the temperature is higher than the stabilize temperature throughout the incubator. Note point at which high alarm responds. c. Safety thermostat: to test the operation of safety thermostat and high-temperature alarm, disable primary thermostat or disconnect from control circuit so heater remains on continuously. In some cases, this can be achieved by turning temperature control to max setting. It is possible to speed up the rise in temperature by supplementing the incubator heater output with a heat gun. Record hood thermometer and the true mid-hood temperature at which the alarm activates. It is important the air not be heated too quickly, for the mid-hood temperature may increase faster than the hood thermostat temperature and have the alarm go off before expected time. d. Air temperature alarms: if the incubator is equipped with high and low air temperature alarms other than those that are controlled by a secondary temperature controller, verify that the alarms are functional. Adjust the air temperature set point to 36 °C and allow the air temperature to stabilize. Verify that low air temperature alarms activates when the incubator hood opens. To test the high air temperature, set the point to 36 °C and increase temperature inside with outside source (hair blower or heat gun). Set (°C)
Delivered (°C)
36 Hi alarm Low alarm Alarm activated Verify other quantitative tests that may apply for transport incubators.
Preventive maintenance a. Clean the exterior and interior b. Lubricate and clean fan assembly if required c. Calibrate if needed d. Replace filter and battery if needed based on scheduled parts replacement policies
Pediatric and neonate incubators Chapter | 78 519
Further reading Badnjevic, A., Gurbeta, L., Boskovic, D., Dzemic, Z., 2015. Medical devices in legal metrology. In: IEEE 4th Mediterranean Conference on Embedded Computing (MECO). Budva, Montenegro, pp. 365–367. 14–18 June, 2015. Badnjevic, A., Gurbeta, L., Jimenez, E.R., Iadanza, E., 2017. Testing of mechanical ventilators and infant incubators in healthcare institutions. Technol. Health Care 25 (2), 237–250.
Badnjević, A., Cifrek, M., Magjarević, R., Džemić, Z., 2018. Inspection of Medical Devices for Regulatory Purposes. Series in Biomedical Engineering. Springer, ISBN: 978-981-10-6649-8. Gurbeta, L., Izetbegović, S., Badnjević-Čengić, A., 2018. Inspection and testing of infant incubators. In: Badnjević, A., Cifrek, M., Magjarević, R., Džemić, Z. (Eds.), Inspection of Medical Devices. Series in Biomedical Engineering, Springer, Singapore.
Pediatric and neonate incubators Almir Badnjevića,b, Lejla Gurbeta Pokvića,b, Lemana Spahića a
Department of Genetics and Bioengineering, Faculty of Engineering and Natural Sciences, International Burch University, Sarajevo, Bosnia and Herzegovina, bMedical Device Inspection Laboratory Verlab Ltd., Sarajevo, Bosnia and Herzegovina
Pediatric and neonate incubators today are more sophisticated than the first prototypes but basic functions remained the same. They provide controlled environmental conditions needed to treat prematurely born infants who are not able to endure all the conditions outside the womb or infants born with certain diseases or health conditions. Patients in incubator have difficulties in thermal regulation because of the poor thermal insulation, relatively large surface area, a small amount of mass to act as a heat sink, and they have no ability to conserve heat by changing body position. There are four different mechanism of heat lost for patients in incubator that must be taken into account when designing these medical devices. These include radiation, conduction, convection, and evaporation. Heat loss through radiation is related to the temperature of the surfaces surrounding the infant but not in direct contact with the infant. Conduction occurs through direct contact with a surface with a different temperature. Heat in incubator is transferred by convection when air currents carry heat away from the body surface and evaporation occurs when water is lost from the skin. Incubators, today, differ in design and accessories depending on manufacturer, but main parts of these electrical medical devices, based on various manufacturer specification, are (Fig. 1): ● ● ● ● ● ●
● ● ●
transparent chamber, power supply, AC-powered heater, electric fan motor to circulate the heated air, water tank for controlling the humidity of air, sensors for measuring temperature, relative humidity, sensor of skin temperature, and air flow sensor, microprocessor-based temperature controller, sir filters, oxygen supply,
514
● ●
alarms and safety features, and access ports for nursing care.
Controlled environmental conditions in incubator are achieved by regulation of temperature, humidity, oxygen lever, air flow, and sound level. There are two main control modes used in these devices: (1) air temperature control mode and (2) skin temperature control mode. Incubators can be divided into two groups: (1) stationary and (2) transport incubators. Difference between transport and stationary incubators are mainly concerned about power supply. Requirements for battery for transport incubators are more complex than for the stationary incubators. When designing transport incubators back up power sources need to be ensured, so if external AC is not available that incubator can switch to external DC source and if that is not available that incubator can use external batteries as power supply to provide stable conditions for transport of patient. Also, most of transport incubators only have air temperature control mode and are supported with lifesaving equipment. The incubator consists of rigid transparent box called chamber, which has side openings. Transparent material is used for chamber which needs to be designed to resist the strains of transportation and to absorb impacts and ensure thermal insulation properties. Most usually chamber is placed on mount which has ability adjust the angle position of the box. The side openings on the box provide accessibility to patient for resuscitation or procedures without jeopardizing thermal stability. Most usually in incubator design, openings on the incubator chamber are provided along one of the longer sides of the incubator and provision is made for convenient displacement of the mattress or other infant support laterally out of and back into the enclosed space of the incubator through the door. At the same time, armholes or similar access ports can also be provided, to enable attendants to give attention to the infant within the incubator, Clinical Engineering Handbook. https://doi.org/10.1016/B978-0-12-813467-2.00079-1 Copyright © 2020 Elsevier Inc. All rights reserved.
Pediatric and neonate incubators Chapter | 78 515
Access port doors (iris type)
Exhaust air vent holes
Exhaust air vent holes
Perspex canopy Baby tray Oxygen added Sensor of thermostat Fresh air Bacterial filter
Oxygen gauge tube
Heating element Motor
Dispensing apparatus
Fan
Humidification control
FIG. 1 Schematics of an infant incubator.
without withdrawing the infant support. Longer sides of incubators are intended to be accessible and the one with control panel unit is considered to be front of incubator. Controlled environmental conditions in incubator mean that the air inside the chamber is held on certain temperature with certain percentage of humidity present in the air. Air intake is usually found at the bottom of the device. The fan with motor drive, placed underneath the chamber, takes the room air and blows it over or through the heating element and the humidifier. A heating element made from coiled resistance wire known as the tube-type (flat or coiled) heater is used in most incubators. To prevent system from overheating, the power rating of heater used in incubator is much less than in the other devices. Typical power rating of heater in incubators is between 100 and 300 W. The heater is controlled by an electronic temperature control unit. The incubator reading, that is, reading from temperature sensors and reading of relative humidity of air inside of chamber can displayed digitally on control panel of incubator, or using analog indicators. Humidifier is most usually a water tank. To ensure moisturizing, the heated air flows over the water in the water container and gets moistened. The humidity is often regulated by closing and opening of valve over the water container closing and opening a deflector plate over the container. Air inlets allow heated and humidified air to enter the chamber, while air outlets take the air from the chamber allowing the air circulation inside the chamber. The humidifier should be filled up only with distilled water
only in order to avoid corrosive damage to the incubator. The general requirements for incubators in order maintain the body temperature of the baby between 36 °C and 37.2 °C are to be able to create an ambient air between 34 °C and 38 °C with a humidity of 40%–90%. For oxygenation therapy, incubators can be equipped with modules for dosing oxygen into the heated and moistened air. The oxygen concentration is also electronically controlled using microprocessor. If incubator does not pose these modules for dosing the oxygen into the air inside the chamber, oxygen can be applied in chamber through a hose connection from an external cylinder, oxygen concentrator, or from the central gas supply. Most oxygenation equipment is compatible with most incubators. Alternatively, the baby gets the additional oxygen directly through a nasal cannula which pipes oxygen directly into the nostrils. Maintaining maximum purity of the air circulated in the incubator is enabled by usage of different filters. Also, the purity of air in the incubator can be achieved by introduction of oxygen into the circulation system in a manner to pass through the filter so that not only the replacement air but also the oxygen, when used, is subject to the filtering action. In this way, bacteriological impurities originating even in the oxygen supply are substantially eliminated. Inside the chamber, above the heater and humidifier, cradle for patient is installed. This cradle is most usually equipped with additional scale for measuring the weight of a newborn and can move right, left, up, and down. Monitoring and observation equipment is often built
516 SECTION | 8 Medical devices: Utilization and service
into the infant incubator unit which include cardiac monitors, brain-scan equipment, blood-monitoring equipment, thermometers, and other instruments for observing vital signs. For treatment of certain medical conditions, medical professionals use ultraviolet (UV) lamps. These lamps can be put over the incubator chamber since the chamber is transparent. When undergoing treatment with UV light, precautions should always be taken to prevent the unnecessary exposure of UV light to healthy skin. In order to ensure safety of the infants, all electronically controlled incubators are equipped with alarming system which tracks the state of the environment within the incubator and alarm the medical staff in case of odd settings. To ensure proper functioning of infant incubators, stable and high-quality delivery of energy is needed to ensure the security of the modern clinical settings. When it comes to an electric failure in the health institution, the incubator’s internal energy source needs to be able to keep the unit in active mode for few hours in case of power loss. Battery capacity depends on manufacture. In the case of sudden voltage jumps, operation may be interrupted or may result in incorrect operation. For these reasons, units of uninterruptable power supply (UPS) are placed with incubators. Besides, infant incubators with closed chamber and controlled environmental conditions that can be stationary or transport, one additional type can be recognized. It is called infant warmer. This medical device consists of a biocompatible bed on which medical professionals place infant and transparent side panels. The bed of infant warmer is placed on the rail mounting system. Heater is placed above the bed and delivers radiant heat to the patient inside providing unified heat. Heaters in infant warmers are typically made from quartz or ceramic. When designing this medical device, type of heater is very important because it has direct impact on time needed for warmer to meet the desired temperature. Each additional minute of cold stress can lead to increased morbidity for an infant. They are characterized by lower power consumption and long life of the heating element lead to considerable cost savings in healthcare institutions. These devices also have air temperature control mode and skin temperature control mode. Skin temperature probe monitors infant temperature. The control unit contains the electronic circuits and controls radiant heater and the observation light. The manual mode of operation (air temperature control mode) allows selecting the level of radiant heat output which is indicated by the percentage power displayed on the control panel. The control circuit maintains the selected level of radiant heat. The manual mode has a preheat setting which allows the warmer to be preheated. In the automatic mode (skin temperature control mode) of operation, the patient’s control temperature is chosen. A skin temperature probe is used to monitor the patient skin temperature. The control system modulates the radiant heat to maintain the patient at the selected control temperature. In most cases, the patient
temperature, control temperature, and elapsed time displays are digital for ease of viewing. Visual and audio alarms are present for safety.
Preventive maintenance qualitative tests 1. Chassis/housing: examine the exterior of the unit for cleanliness and general physical condition. Be sure that plastic housings are intact, that all hardware is present and tight, and that there are no signs of spilled liquids or serious abuse. 2. Infant incubators: remove any tape adhered to the unit. Check all rubber and plastic gaskets in the unit for signs of deterioration. The condition of the hood is important for power control of the environment. Ensure the hood is free of cracks, warping, or other deterioration signs. Verify all parts are assembled correctly. Remove the hood, bed, baffle, main deck, and other parts and thoroughly inspect the interior for foreign objects, deterioration, or misassembly of internal components that could interfere with performance. 3. Mount/fasteners: if the device is mounted on a stand or cart, examine the condition of the mount. If it attached to the wall, or rests on a shelf, check the security of the attachment of every screw on the hood. Operate the iris-type port closures to ensure proper function. Examine the iris diaphragms and port sleeves for tears. Verify that disposable irises are being replaced after each incubator use. Check that all nuts and bolts are tightened fully. Use a screwdriver and systematically try to tightening replaced after each incubator use, these items are not reusable. 4. Casters/brakes: if the device moves on casters, check their condition. Look for accumulations of lint and thread around the casters, and be sure that they turn and swivel, as appropriate. Check the operation of brakes and swivel locks, if the unit is so equipped. 5. AC plug/receptacles: examine the AC power plug for damage. Attempt to wiggle the blades to check that they are secure. Shake the plug and listen for rattles that could indicate loose screws. If any damage is suspected, open the plug and inspect it. Should the equipment be placed on a cart that has extra electrical receptacles for other equipment, insert AC plugs into each and verify they are firmly held. Verify that no damage is present in the cart receptacles. 6. Line cord: inspect the cord for signs of damage. If damaged, replace the entire cord or if the damage is near one end, cut out the defective portion. Wire a new power cord or plug on the same polarity. Check the line cords of battery chargers. 7. Strain reliefs: examine the strain reliefs at both ends of the line cord. Be sure that they hold the cord securely.
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If the line cord is detachable, it is recommended that the cord be affixed to the unit so that it cannot be removed by the operator. 8. Circuit breaker/fuse: if the device has a switch-type circuit breaker, check that it moves freely. If the device is protected by an external fuse, check its value and type against that marked on the chassis and ensure that a spare is provided. 9. Tubes/hoses/bulbs: check the condition of all tubing, cuff, hoses, and bulbs (if present). Be sure that are not cracked, kinked, or dirty. Inspect all oxygen orifices to make sure that they are clear and free of foreign matter. Preventive maintenance protocols. 10. Cables: inspect the cables of sensors, electrodes, remote control and their strain reliefs, and general conditions. Carefully examine cables to detect breaks in the insulation and to ensure that they are gripped securely in the connectors at each end to prevent rotation or other strain. 11. Fittings/connectors: examine all fittings and electrical cable connectors for general condition. Electrical contact pins or surfaces should be straight and clean. Fittings should be tight and should not leak. If keyed connectors are used, make sure that the keying is correct. 12. Electrodes/probes: confirm that special paddles and electrodes are available if appropriate for the area of use. Examine all paddles and probes for physical conditions and cleanliness. Should the equipment have fluids, dried electrode gel, or debris on it, inform the clinical staff. Clean paddles and electrode surfaces if needed and ensure they are completely dry before testing. Ensure that probe labels clearly identify the associated units. Improperly interchanged probes of different types or from different manufacturers may adversely affect temperature control. Confirm that any necessary transducers (if applicable) are on hand and check their physical condition. 13. Filters: if the device has a switch-type circuit breaker, check that it moves freely. If the device is protected by an external fuse, check its value and type against that marked on the chassis and ensure that a spare is provided. Clean filter. 14. Controls/switches: before changing any controls or alarm limits, check their position any settings appear inordinate (e.g., alarm limits at the ends of their range), consider the possibility of inappropriate clinical use or of incipient device failure. Record the settings of those controls that should be returned to their original positions following the inspection. Examine all controls and switches for physical condition, secure mounting, and correct motion. Check that control knobs have not slipped on their shafts. Where a control should operate against fixed-limit stops, check for proper alignment, as well as positive stopping. Check membrane switches for
15.
16.
17. 18.
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20. 21.
membrane damage (e.g., from fingernails, pens). During the course of the inspection, be sure to check that each control and switch performs its proper function. Heater: disassemble the heating unit enough to expose the heating element. Examine the element for severe discoloration or foreign deposits. Heating elements normally change color with use, but dark, distinct surface spotting may indicate that material has come into contact with the element, possibly after falling through the air duct. Foreign matter touching the hot surface could cause a fire or the generation of noxious fumes. If you find such discoloration, examine the control unit compartment for signs of overheating. If screw terminals connect the heating element to the control circuitry, check that they are tight. Motor/fan/pump: inspect fan blades for deterioration and damage. Ensure fan is securely attached to drive shaft and that the coupling is present and intact. Check that clearance between the fans and housing are adequate by looking for signs of rubbing. In some cases, an improperly inserted control module and heater assembly in the incubator base has bent and disabled fan. Verify whether if fan requires lubrication or not. Observe the fan in operation to determine if there are excessive vibrations or wobbling. Fluid levels: check all fluid levels, including lead-acid battery levels. Battery/charger: inspect the physical condition of batteries and battery connectors, if readily accessible. Check operation of battery-operated power-loss alarms, if so equipped. Operate the unit on battery power for several minutes to check that the battery is charged and can hold a charge. (The inspection can be carried out on battery power to help confirm adequate battery capacity.) Check battery condition by activating the battery test function or measuring the output voltage. Check the condition of the battery charger and, to the extent possible, confirm that it does, in fact, charge the battery. Be sure that the battery is recharged or charging when the inspection is complete. Some batteries require periodic deep discharges and recharging to maintain a maximum battery capacity. If this is recommended by the manufacturer, verify that it is being performed on schedule. Indicators/displays: during the course of the inspection, confirm the operation of all lights, indicators, and visual displays on the unit and charger, if so equipped. Be sure that all segments of a digital display function properly. User calibration/self-test: verify operation of these features, if applicable. Alarms: operate the device in a way that activates all the alarms. Check that any associated interlocks function. Check action of disconnected-probe alarm, if unit
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so equipped. If the device has an alarm-silence feature, check the reset method. 22. Audible signals: operate the device to activate any audible signals. Confirm appropriate volume, as well as the operation of a volume control, if so equipped. If audible alarms have been silenced or the volume set too low, alert clinical staff to the importance of keeping alarms at the appropriate level. 3. Labeling: check that all necessary labels, conversion 2 charts, and instruction cards are present and legible. Incubators: since incubators carry oxygen, a fire hazard sign must be visible. Also, a sign warning of the effects of high oxygen concentrations should be present (high oxygen concentration can cause fibroplasias and blindness in infants). 24. Accessories: check the hood thermometer for cracked glasses or separations in the liquid column. If the liquid column has separated, it might be possible to consolidate it by removing the thermometer and carefully dipping it into hot water. If the thermometer has an expanded space at the top, the liquid will pool in the small reserve chamber. When the gap in the column disappears into the pool, cool the thermometer and recheck it. Repeat the process if necessary. Be careful not to overheat the thermometer, for the liquids in it will expand and crack the glass. If the position of the mattress is adjustable, check the ease of motion and security of lock mechanism. Examine mattress for cleanliness. If the unit is used in the presence of flammable anesthetics, check that a conductive mattress cover is used.
Preventive maintenance electrical safety test a. Grounding resistance: using an ohmmeter, electrical safety analyzer, or multimeter with good resolution of fractional ohms, measure and record the resistance between the grounding pin of the power cord and exposed (unpainted and not anodized) metal on the chassis. A maximum of 0.5 Ω is recommended. b. Leakage current: measure chassis leakage current to ground with the grounding conductor of plug-connected equipment temporarily opened. Operate the device in all normal modes, including on, standby, and off, and record the maximum leakage current. Chassis leakage current to ground should not exceed 300 μA.
Preventive maintenance quantitative tests a. Temperature control: check the action of the primary and safety thermostats with the incubator fully assembled. Set the temperature to 36 °C. Test the thermostats
according to the manufacturer’s instructions, and record on the form the temperature at which safety or backup thermostats turns off heater. b. Skin temperature alarms: if the incubator is equipped with high and low skin temperature alarms, verify alarm function. Adjust skin temperature set point to 36 °C. Place sensor in incubator and allow temperature to stabilize. Remove the sensor from the incubator and verify that alarm activates. To verify the high skin temperature alarm, place sensor near the heaters exit where the temperature is higher than the stabilize temperature throughout the incubator. Note point at which high alarm responds. c. Safety thermostat: to test the operation of safety thermostat and high-temperature alarm, disable primary thermostat or disconnect from control circuit so heater remains on continuously. In some cases, this can be achieved by turning temperature control to max setting. It is possible to speed up the rise in temperature by supplementing the incubator heater output with a heat gun. Record hood thermometer and the true mid-hood temperature at which the alarm activates. It is important the air not be heated too quickly, for the mid-hood temperature may increase faster than the hood thermostat temperature and have the alarm go off before expected time. d. Air temperature alarms: if the incubator is equipped with high and low air temperature alarms other than those that are controlled by a secondary temperature controller, verify that the alarms are functional. Adjust the air temperature set point to 36 °C and allow the air temperature to stabilize. Verify that low air temperature alarms activates when the incubator hood opens. To test the high air temperature, set the point to 36 °C and increase temperature inside with outside source (hair blower or heat gun). Set (°C)
Delivered (°C)
36 Hi alarm Low alarm Alarm activated Verify other quantitative tests that may apply for transport incubators.
Preventive maintenance a. Clean the exterior and interior b. Lubricate and clean fan assembly if required c. Calibrate if needed d. Replace filter and battery if needed based on scheduled parts replacement policies
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Further reading Badnjevic, A., Gurbeta, L., Boskovic, D., Dzemic, Z., 2015. Medical devices in legal metrology. In: IEEE 4th Mediterranean Conference on Embedded Computing (MECO). Budva, Montenegro, pp. 365–367. 14–18 June, 2015. Badnjevic, A., Gurbeta, L., Jimenez, E.R., Iadanza, E., 2017. Testing of mechanical ventilators and infant incubators in healthcare institutions. Technol. Health Care 25 (2), 237–250.
Badnjević, A., Cifrek, M., Magjarević, R., Džemić, Z., 2018. Inspection of Medical Devices for Regulatory Purposes. Series in Biomedical Engineering. Springer, ISBN: 978-981-10-6649-8. Gurbeta, L., Izetbegović, S., Badnjević-Čengić, A., 2018. Inspection and testing of infant incubators. In: Badnjević, A., Cifrek, M., Magjarević, R., Džemić, Z. (Eds.), Inspection of Medical Devices. Series in Biomedical Engineering, Springer, Singapore.