LASER

Question 1

what are the main features of a laser?

Answer 1

monochromatic = all light is of same wavelength (same energy and frequency)

coherent = all in same phase (dont cancel one another out)

collimated = all parallel (non divergent)

Question 2

what does LASER stand for?

Answer 2

light amplification by stimulated emission of radiation

Question 3

how do LASERs work?

Answer 3

consists of a laser medium exposed to flash light and bound either end by reflective material where one end has a small opening for light to escape for use.

1. flash lamp provides energy for the electrons of atoms within the lasing medium to be excited to a higher energy level
2. when they drop back down in energy level they release the energy as a photon of energy. (spontaneous emission)
3. if a photon of energy hits another electron in excited level it causes 2 photons to be released both with equal wavelength, parallel and in phase with one another (stimulated emisiion)
4. this results in amplification of light energy as more and more photons of light are released and go on to further stimulate others
5. these photons will be reflected back and forth via the reflective material at either end
6. creating intense light which is monochromatic, coherant and collimated from a low energy source
7. at one end there is a small window allowing a focused beam of light to escape and be used.

Question 4

why is light in a LASER of one wavelength?

Answer 4

the wavelength is determined by the laser medium / lasting medium

these are various substances depending on purpose of laser e.g. CO2 lasers produce wavelength of 10.6um

depends on the electrons and atoms within that medium and the difference between low and high energy states that determines the energy within photon they release and hence its wavelength.

Question 5

what is meant by the term ‘lase’

Answer 5

when more electrons are in a higher energy state than ground state , the medium is said to lase.

Question 6

what are the differences between continuous and pulsed wave lasers?

Answer 6

continous - the source of light is continous, creates very high energy continous output. can be too damaging in surgery

pulsed = output is split into short pulses of varying duration. more controlled confined source of heat and more useful in surgery.

Question 7

how is the energy of a wave related to its frequency?

Answer 7

E = frequency x planks constant (h)

Question 8

do you know any specific types of lasers and the wavelength they produce and their uses?

Answer 8

CO2 gas medium = 10.6um = infrared. superficial cutting and precise good for airway surgery

Nd -YAG (solid) = 1060nm = infrared - used for coagulation and cutting in surgery, endoscopic and airway. good for GI bleeds.

Argon Laser - 500nm - blue/green visible light. used for dermatology

ruby - for tattoe removal.

Question 9

what does the application of a laser depend on?

Answer 9

its wavelength
depth of penetration
what substances absorb it

Question 10

most lasers are in infrared spectrum, why is a red light seen?

Answer 10

safety feature added so user knows where it is pointing for guidance

Question 11

how are lasers classified?

Answer 11

based on their power output.
7 classes in total

class 1 is low power. cannot emit radiation of any known hazard for skin or eye
class 1m - same as above as long as not via a lens
class 2 - lower power - not damage unless maintained stare into beam
class 2m - same as above as long as not via a lens

class 3a
class 3b - need eye protection , low risk to skin

class 4 ->0.5Watts power. hazard to skin and eyes. most surgical lasers. eye protection is essential

Question 12

tell me some uses of surgical laser?

Answer 12

cutting e.g. in airway surgery

removal of moles

breaking down renal stones - laser lithotripsy

retinal eye laser surgery

Question 13

what is meant by population inversion?

Answer 13

when more than 50% of the atoms are in their excited state.

Question 14

what are the safety concerns regarding lasers ?

Answer 14

environment
* fires and explosions- provides energy for ignition

staff
* damage to eyes, burns
* e.g. if they hit optic nerve could cause complete blindness, if they hit retina blind spot

patient
* burns, damage to eyes
* unconscious so cant react to pain
* airway fire risk

Question 15

what precautions are taken to minimise risks of laser?

Answer 15

Staff and general:
protection - goggles
trained staff - laser safety officer present
signs on doors
non reflective material in the room - black matt finish
fire extinguisher available

patient:
if used in the airway, minimum amount of O2 less than 30%
ET tube cuff filled with saline
eye protection
wet swabs to protect tube.
laser resistant tube.

Question 16

what are the features of a laser safe ET tube?

Answer 16

stainless steel flexible spiral
double cuff
non combustible
fill cuff with saline

Question 17

how is an airway fire managed?

Answer 17

1. declare incident
2. stop laser
3. call for help
4. flood site with saline
5. switch off oxygen source
6. remove tube
7. ventilate with bag/mask
8. maintain anaesthesia with TIVA
9. once fire is out, examine airway with fibreoptic, likely to need intubating again and follow up for swelling / injury
10. ITU admission - associated with ARDS, ABG CXR. give dexamethasone

Question 18

what can an airway fire result in?

Answer 18

swelling of the airway - hence need intubating to protect airway from obstruction

ARDS like picture - gradually worsening hypoxaemia over next 48hrs