What is a defibrillator

2.0: What is a defibrillator.

The goal here is to try to understand what the machine is trying to do. Let’s say your patient pops into a nasty rhythm – not handling it very well, not making much of a blood pressure; and you want to deliver electricity – what do you need?

2.1: The monitor.

you need to be able to see what’s going on. This is of course one of the 

reasons why our patients are monitored at the bedside: so you can see 

what rhythm your patient is in. Defibrillators are built to travel– so they 

have a built in monitor screen.

2.3: The capacitor.

  

Generally you need a battery to run any transportable medical device.

Due to rechargeable batteries these devices are so heavy. The battery

stores electricity,when machine is plugged in to AC. The capacitor fills

up with electricity when you push the button that selects charge .

2.4: The paddles and the pads:

Paddles

Self Adhesive Pads

Internal Paddles

paddles are considered “old-tech” – nowadays the thing to do is to slap on 

sticky defibrillation pads that hook up to the machine – the same ones as 

external pacing pads – then stand back, charge and discharge the machine 

from a few feet away. The shock can be delivered to the heart by means of 

electrode placed on chest of the patient(External defibrillation) or the electrode

may be held directly against the heart when the chest is open

(internal defibrillation). Higher voltage are required for external defibrillation 

than for internal defibrillation.

2.5: Theory of operation.

Schematic diagram of a defibrillator

Above schematic show basic circuit diagram of DC Defibrillator. A Variable auto transformer forms the primary of a high voltage transformer. The output voltage transformer is rectified by a diode rectifier and is connected to vacuum type high voltage change over switch. In position 1, the switch is connected to one end of an oil filled micro farad capacitor. In this position, the capacitor charge to a voltage set by the positioning of the auto transformer. When the shock is delivered to the patient, a foot switch or a push button mounted on the handle of the electrode is operated. The high voltage switch change over to position 2 and the capacitor is discharged across the heart through the electrode. The inductor in the circuit slow down the discharge from capacitor by induced counter voltage. This give the output pulse a physiologically favorable shape. The dis advantage of using inductor is that any practical inductor will have its own resistance and dissipates part of the energy during the discharge process. The shape of waveform that appears across electrodes will depend upon the value of the capacitor and inductor used in the circuit. The discharge resistance which the patient represent for defibrillating pulse may be regarded as purely ohmic resistance of 50-100 Ω approximately for typical electrode size of 80 cm2. The typical discharge pulse of defibrillator is shown in fig.3 b. Using this design, external defibrillation uses: –50 to 100 Joules of energy when electrodes are applied directly to the heart –Up to 400 Joules when applied externally ,Capacitors used range from 10 to 50F .Voltage using these capacitors and max energy (400J) ranges from 1 to 3 kV . Energy loss result in the delivery of less than theoretical energy to the heart

Defibrillator: Rectangular-Wave

 •Capacitor is discharged through the subject by turning on a series silicon- controlled rectifier.

 •When sufficient energy has been delivered to the subject, a shunt silicon- controlled rectifier short-circuits the capacitor and terminates the pulse, eliminating a long discharge tail of the waveform

•Output control can be obtained by varying:

          –Voltage on the capacitor

          –Duration of discharge

•Advantages of this design:

          –Requires less peak current

          –Requires no inductor

          –Makes it possible to use physically smaller electrolytic capacitors

          –Does not require relays ·

Monophasic pulse width is typically programmable from 3.0 to 12.0 msec

Biphasic positive pulse width is typically programmable from 3.0 to 10.0 msec, while the negative pulse is from 1.0 to 10.0 msec ·

Studies suggest that biphasic pulses yield increased defibrillation efficacy with respect to Monophasic pulses.

Reference : http://coep.vlab.co.in

Ventricular Fibrillation  

PHOTO-THERAPY

PHOTO-THERAPY

Phototherapy lights emit light in the blue-green spectrum (wavelengths 430-490nm).  It is NOT ultraviolet light.

 "CONVENTIONAL" AND "INTENSIVE" Phototherapy?

"Intensive phototherapy" means the irradiance of the light is at least 30µW/cm2 per nm as measured at the baby's skin below the center of the phototherapy lamp.  A hand-held

Radiometer

radiometer can be used to measure the spectral irradiance emitted by the light.  Because measurements taken directly under the lights will be higher, measurements should ideally be made at several locations and averaged.  The appropriate radiometer will vary based on the phototherapy system used, so manufacturer recommendations should be followed.

With "Conventional phototherapy" the irradiance of the light is less, but actual numbers vary significantly between different manufacturers.  In general, it is not necessary to rountinely measure irradiance when administering phototherapy, but units should be checked periodically to ensure that the lamps are providing adequate irradiance, according to the manufacturer's guidelines.

In adults, prolonged exposure to blue light can cause retinal damage.  Although retinal damage from phototherapy has not been reported, eye covers for newborns are standard prophylaxis.

some people who are around blue lights for prolonged periods will feel nauseated.  Yellow plastic placed on the outside of the isolate may mitigate this effect.  

 There are no specific guidelines for when to discontinue phototherapy.  Evidence of hemolysis and age of the infant will impact the duration.  In some cases, phototherapy will only be needed for 24 hours or less, in some cases, it may be required for 5 - 7 days.  The AAP Guidelines suggest that an infant readmitted for hyperbilirubinemia, with a level of 18 mg/dL or more, should have a level of 13 - 14 mg/dL in order to discontinue phototherapy.  In general, serum bilirubin levels should show a significant decrease before the lights are turned off. 

HOW CAN PHOTOTHERAPY BE MAXIMIZED?

 

The effectiveness of phototherapy is determined largely by the distance between the lamps and the infant, so phototherapy can easily be intensified by bringing the lamps closer to the infant.  Because a closed isolette does not allow the lamps to be moved in close, if there is a concern about the effectiveness of phototherapy, an isolette should not be used.  With the infant in an open bassinet, it is possible to bring the lamps to within 10 cm of the infant.  An undressed term infant with not be overheated with this arrangement, however is is important that halogen spotlights NOT be used.  Halogen lights can get hot, and burns may result if used this way.  Special blue, regular blue, and cool white lights are all acceptable alternatives.

Increasing the skin surface area exposed to phototherapy will also maximize treatment.  Commonly, an overhead phototherapy unit is combined with a bili blanket that can be place under the infant.  Some of these blankets or pads are rather small, so 2 or 3 of these units may be needed to supply more complete coverage from below.  Lining the sides of the bassinet with white blankets or aluminum foil can also increase the effectiveness of phototherapy.

Sourse Links:

http://www.d-rev.org/about.html

How "Air in-line' alarm work

Ultrasonic sensors provide key safety feature for infusion pumps

Infusion pump is that accurately dispenses medication and fluids, such as morphine and nutrition, into a patient’s circulatory system. A key safety feature of the pump is an ‘air-in-line’ detection system, which monitors for the presence of air bubbles in the fluid.

“Accurate detection of air bubbles is vital in maintaining the health and recovery of patients, Air embolisms can lead to serious complications in blood flow and the heart’s operation.”

There are other technologies that are used to detect air bubbles such as infrared. However, ultrasonic technology provides the most accurate and reliable detection. .

How Ultrasonic Sensors Work

Ultrasonic sensors depend on two separate devices: an ultrasonic transducer and a detector. An ultrasonic transducer is any device that converts energy into an ultrasonic frequency. Though dog whistles and several other devices can convert mechanical energy into an ultrasonic frequency, ultrasonic transducers are usually made from piezoelectric crystals that can change size when a voltage is applied to them. When an alternating current is applied to a piezoelectric crystal, it vibrates extremely fast and produces an ultrasonic sound wave. The detector is also made of a piezoelectric crystal, but produces a voltage when an ultrasonic frequency comes in contact with it, effectively producing the opposite results. A sensor calculates the time that it takes in between broadcasting the ultrasonic frequency and receiving the incoming waves.

How to detect air in line 

 If there is fluid in the infusion line between the sensors then a signal is received, but when air passes through a reduced signal is received. This change in signal generates an alarm, alerting the user that an air gap is present, and the pump automatically stops infusion.