IHS key points

Question 1

indications

Answer 1

mild/mod anxiety
needle phobia
hyper gag reflex
multiple quadrant tx in young kids
traumatic procedures
medical conditions aggravated by stress - asthma
unaccompanied adults requiring sedation
age (can understand)
ASA1
preventively for traumatic procedures or ortho ext - esp if no tx experience

Question 2

contraindications

Answer 2

may not match their coping style (monitor)
common cold
mouthbreather
extreme anxiety
tonsillar/adenoidal enlargement
severe COPD
1st trimester pregnancy?
fear of "mask"/claustrophobia
pts with limited ability to understand
unsuccessuful prev attempt
NM disease e.g. myesthenia gravis, MS

Question 3

age cut off

Answer 3

no absolute, generally 7yrs and over
prev experience
maturity
understanding
pt prep by parent

Question 4

equipment

Answer 4

gas cylinders
 - blue N2O
 - black with white top O2
 - may be piped gases in hospital
pressure reducing valves
flow control meter
reservoir bag
gas delivery hoses
nasal hood
waste gas scavenging system

Question 5

quantiflex O2 flow meter

Answer 5

measures flow rates of up to 10l/min
readings taken from equator of ball
accuracy +/- 5%
white meter

Question 6

air entrainment valve

Answer 6

if gases fail valve opens - allows room air into circuit

they can continue to breathe if machine switches off

Question 7

mixture control dial

Answer 7

tells you % O2 - can’t turn it lower than 30% (safety)

Question 8

flow control knob

Answer 8

how many l/min

Question 9

nitrous oxide flow meter

Answer 9

blue
measure flow rates of up to 10l/min
read centre of ball
accuracy +/- 5%

Question 10

O2 flush button

Answer 10

flushes O2 35l/min
v fast O2 delivery
emergency use only

Question 11

reservoir bag

Answer 11

2/3l bag, rubber or silicone
- smaller available for children
full of air and O2
bag should move visibly with each inspiration and expiration
helps to monitor respiration - emulates pts lungs
- helps you know what flow rate to give them
- must not collapse - need to increase flow rate
- if stuffed - reduce flow rate
want 12-16 breaths/min

Question 12

gas delivery hoses

Answer 12

2.5cm diameter, corrugated
universal joints
one hose delivers fresh gases from machine
one hose delivers waste gas to scavenging system
non-return valve in expiratory limb prevents rebreathing expired gases
single use breathing circuits - tubing and mask

Question 13

nasal mask/hood

Answer 13

various sizes
should form a seal around nose (gases shouldn’t escape)
2 connections to breathing circuit

Question 14

pin index system

Answer 14

prevents wrong cylinder being attached

can’t attach wrong gas

Question 15

diameter index system

Answer 15

prevents cross-contamination of piping

Question 16

minimum O2 delivery

Answer 16

30%

Question 17

O2 fail safe

Answer 17

operates when O2 pressure <40psi

if O2 runs out machine switches off

Question 18

scavenging system

Answer 18

external to the quantiflex machine or piped gas system
active scavenging of waste gases - small negative pressure (so they get sucked away)
changing surgery air reduces N2O levels - 15 changes of room air per hour
watch for pt mouth breathing
- expelling waste gas into atmosphere not system
check mask seal to reduce contmination
use dam - reduce mouth breathing, reduce some of waste gas expelling

Question 19

safety features of quantiflex

Answer 19

air entrainment valve
O2 flush button
O2 monitor - see what they are receiving
reservoir bag - emulate pt lungs
colour coding - pin index system
scavenging system
O2 and N2O pressure dials
pressure reducing valves
one way expiratory valve
quick fit connection for positive pressure O2 delivery
2 tanks esp for O2 - back tank is a reserve
 - so you always have enough O2
minimum O2 delivery 30%
O2 fail safe - if runs out machine switches off

Question 20

advantages

Answer 20

rapid onset 2-3mins
rapid peak action 3-5mins
depth altered either way - can turn sedation up and down
flexible duration
rapid recovery when N2O turned off
no injection (but may need LA)
few SEs, safe
drug not metabolised
some analgesia (better for ischaemic than inflammatory)
- fingers and toes a bit tingly/numb
no amnesia - in future may be happy to do without sedation

Question 21

disadvantages

Answer 21

£ equipment
£ gases
space occupying equipment
not potent, need cooperation
 - just helps them cope a bit
 - won't disarm a pt who isn't wanting tx
requires ability to breathe through nose
chronic exposure risk?
staff addiction
difficult to accurately determine actual dose
 - accuracy not great +/- 5%
 - if pt speaks to you they are breathing through mouth
 - leakage if nasal hood not fitting
less muscle relaxation

Question 22

signs of adequate sedation

Answer 22

pt relaxed/comfortable
 - feeling like just before you fall asleep
pt awake
low blink rate
laryngeal reflexes unaffected
vital signs unaffected
gag reflex reduced
mouth open on request
decreased reaction to painful stimuli (LA easier)
decrease in spontaneous movements
verbal contact maintained

Question 23

symptoms of adequate sedation

Answer 23

mental and physical relaxation
lessened awareness of pain
paraesthesia - lips, fingers, toes, legs, tongue - tingly
lethargy
euphoria
detachment 'floating feeling'
warmth (take jackets off first)
altered awareness of passage of time
dreaming (daydream)
small controllable "fit of the giggles"

Question 24

if have anxious parent what can you get them to do?

Answer 24

watch the bag

Question 25

pre-op instructions to parent and child

Answer 25

have a light meal before appt
take routine meds as normal
children accompanied by competent adult
 - be aware pregnant women can't be in surgery while 
   IHS
 - only child having IHS allowed in surgery
adults accompanied at their first appt
 - after can attend alone
no alcohol on day
wear sensible clothing
arrange childcare during and after appt
if have cold blocking nose cancel appt
plan to remain in clinic for up to 30mins after tx

Question 26

monitoring during tx

Answer 26

clinical - don’t need electronic
keep talking to pt - agree with nurse in advance
- nodding/thumbs up response

Question 27

if pt oversedated:

Answer 27

increase O2 in 5-10 % increments until adequate

Question 28

if pt undersedated

Answer 28

reduce O2 in 5% increments until satisfactory

Question 29

technique

Answer 29

set up machine
select nasal hood (size in notes)
connect to hoses
set mixture dial to 100% O2
settle pt in chair, reinforce explanations of procedure
set flow to 5-6l/min
position hood and encourage nasal breathing
check reservoir bag movements
pt to be comfortable with hood for 1min
reduce O2 by 10%
ask pt to signal when begin to feel different
wait 1min and repeat
after O2 reaches 80% reduce by 5% per min
stop titration when pt ready for tx
- keep asking pt
constant reassurance and hypnotic suggestion
- visualisation
- behavioural management
- suggest to them that they feel comfortable, dreamy
- quiet calm voice
monitor for S+S of adequate sedation
adjust level of O2 as required

Question 30

too small reservoir bag movements

Answer 30

check seal and look for mouth breathing

+/- reduce flow

Question 31

too large reservoir bag movements

Answer 31

increase flow rate

Question 32

diffusion hypoxia

Answer 32

can occur with administration of inadequate O2 during/immediately after N2O anaesthesia
influences PO2 within alveolus
theoretical risk - doesn’t happen as equipment always delivers enough O2

Question 33

success

Answer 33

50-90%?
difference
 - pt pop
 - greater success for ortho ext (motivated)
 - poorer in pts with pain
 - appropriate pt assessment/selection

Question 34

at end of tx

Answer 34

recovery - gradually increase O2 by 10-20% per min or turn straight to 100% - doesn’t make a lot of difference
administer 100% O2 2-3mins to prevent diffusion hypoxia
remove hood and turn gas flow off
return pt to upright slowly, give praise and reassurance

Question 35

after tx

Answer 35

adult pts may leave unaccompanied at dentist’s discretion
<16yrs need competent adult
before discharge
- ensure they feel normal before they stand up/leave
- ask how pt felt procedure went
pt may feel shivery after IHS
- reassure pt common/normal and passes quickly
- put jumper back on
- “like after you finish a race”

Question 36

physical properties of N2O

Answer 36

sweet odour, pleasant to inhale, non-irritant
- nasal hoods - strawberry, orange
liquid in cylinders, pressure constant until all liquid evaporates
low tissue solubility so rapid onset and fast recovery
MAC value in excess of 1atm so GA without hypoxia impossible
mild analgesic hence term relative analgesia (RA), still need LA

Question 37

N2O adverse reactions

Answer 37

hypoxia
malignant hyperpyrexia (controversial)
 - AR trait
 - muscle contracture
 - acidosis
 - hyperkalaemia
 - hyperpyrexia
loss of protective reflexes
diffusion hypoxia
pressure/vol effects - ear - tinnitus
psychological 
 - euphoria
 - hallucinations
 - claustrophobia
fire
headache, paraesthesia, tingling

Question 38

concenctrations of N2O

Answer 38

10-30%

don’t go beyond 30% N2O

Question 39

complications - pt

Answer 39

nausea/vomiting
unintentional LOC
- rare as titrated so slowly, usually related to: extreme young age of child, polypharmacy, use of multiple drugs

Question 40

complications - staff

Answer 40

toxicity: esp B12 suppression

staff addiction

Question 41

anaesthetic agents - controlling exposure under COSHH legislation

Answer 41

no evidence N2O exposure causes developmental defects in foetus or any other reproductive health effects

animal and lab studies - “exposures of ≥1000ppm for ≥8hrs per day suggest inhibition of new cell production”

occupational exposure standard - 100ppm over 8hr TWA period
- 1/5 of the exposure level at which effects were seen in animals

studies show it reduces fertility if have excessive levels

Question 42

control of occupational exposure to N2O in dental surgery

Answer 42

a properly maintained gas delivery system
a scavenging nosepiece - fits well “tiger marks”
vented suction (scavenging) machine
fans to sweep air away from the operator
rubber dam to minimise pt speech
minimise pt speech

= without these the air in the surgery can contain 500-6700ppm

Question 43

toxicity of NO to dentists

Answer 43

liver disease
miscarriage
bone marrow suppression
addiction
carcinoma
birth defects

Question 44

advanced IV sedation - propofol

Answer 44

12+ years
target controlled infusion sedation - titrate
anaesthetist administered
useful for v long or v short procedures
can be increased or decreased for particular bits
mean rapid onset and recovery

Question 45

POIs - verbal and written

Answer 45

due to effects of sedation may have amnesia
adult knows how to care for you
will be slightly drowsy, go home and rest
DON’T
- ride bike/active sports/training
- pour boiling water into a cup
- do a job involving unguarded machinery
- take alcohol
- take sedative drugs without medical advice
- make important decisions
be careful on social media as you may be a bit muddled and lack judgement