Pulse Wave Transit Time (PWTT)

ECG and SpO2 readings are taken in to consideration,

PWTT is calculated for each beat from the ECG and peripheral pulse wave. The peripheral pulse wave is measured by an SpO₂ probe on the finger or toe.

PEP and a-PWTT

PWTT includes PEP (Pre-Ejection Period) and a-PWTT (Pulse Wave Transit Time in the Artery).

PEP ----------> Pre-ejection period

a-PWTT: -----> Pulse wave transit time at artery

PWTT:--------> PEP + a-PWTT

a-PWTT is the time it takes the pulse wave to travel from the aorta to a peripheral artery. a-PWTT is directly related to blood pressure. Unfortunately, a-PWTT cannot be measured directly. We can only measure PWTT, which also includes PEP.

PEP is the period just before the blood is pumped into the aorta. In general, PEP change over short periods of time is negligible in most cases so we can assume that PWTT corresponds to a-PWTT and therefore to blood pressure.
However, vasoactive and other drugs can cause significant changes in PEP and affect the correlation between PWTT and blood pressure.
Generally in most cases, we can say that PWTT corresponds to a-PWTT and blood pressure.

Relationship between blood pressure and pulse wave speed

When the heart pumps blood into the aorta, it also generates a pressure wave that travels along the arteries ahead of the pumped blood. This is the pulse wave.The speed of the pulse wave depends on the tension of the arterial walls. When the blood pressure is high, the arterial walls are tense and hard and the pulse wave travels faster. When the blood pressure is low, the arterial walls have less tension and the pulse wave travels slower.
This can also be understood by the following example. When a ping-pong ball is thrown against a hard table, the rebound is strong and fast. If the ping-pong ball is thrown against a soft blanket, the blanket absorbs the force and the rebound is weak and slow.

How PWTT detects change in blood pressure

 

Although the actual blood pressure itself cannot be determined from the speed of the pulse wave, a change in blood pressure is indicated by change in the speed of the pulse wave. Therefore, PWTT is used to detect change in pressure.
Change in PWTT indicates potential change in blood pressure. PWTT for each beat is compared to the PWTT of the last NIBP measurement. When PWTT change exceeds a threshold, it triggers NIBP measurement to measure the actual blood pressure.

You can increase or decrease the PWTT threshold to respond to larger or smaller blood pressure changes and trigger less frequent or more frequent NIBP measurements.



Source: http://www.nihonkohden.com

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.

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