Inhalation sedation I Flashcards
What is conscious sedation? (3)
A technique in which the use of a drug or drugs produces a state of depression of the CNS enabling treatment to be carried out.
Both verbal contact and protective reflexes are maintained in the patient throughout the period of sedation.
The drugs & techniques used to provide conscious sedation for dental treatment should carry a margin of safety wide enough to render loss of consciousness unlikely.
Demand for sedation (4)
Visiting dentist is second most common fear after public speaking (USA 1987)
Child Dental Health Survey 2013
-50% moderately anxious
-10% extremely anxious
‘The control of anxiety and pain is fundamental to the practice of dentistry’ (GDC, 2002)
Deaths at dentist from GA in practice
Sedation techniques (6)
Inhalation – nitrous oxide/oxygen, sevoflurane
Intravenous – midazolam, propofol
Transmucosal – midazolam (intranasal, buccal)
Oral – temazepam, diazepam, midazolam, ketamine
Intramuscular - ketamine
Combination of above
Nitrous oxide today (3)
Recreational use
‘Hippie crack’ - legal high
Deaths due to hypoxia
Properties of of nitrous oxide (5)
Volatile
Denser than air – 1.0:1.5
Least potent - MAC50 is 104
Often used in anaesthesia as carrier/induction gas
Poorly soluble – rapid onset/rapid recovery
Pharmacokinetics of nitrous oxide/ oxygen sedation (6)
Inhaled into lungs with oxygen through nasal mask Travels down partial pressure gradient Alveolus to capillaries Hardly metabolised – 0.004% Excreted through lungs Elimination half-life ~ 5 minutes
Pharmacodynamics of nitrous oxide/ oxygen sedation (4)
Analgesic
Anaesthetic
Hypnotic
Anxiolytic - GABA
Stages of anaesthesia (4)
1) Analgesia
2) Excitement
3) Surgical analgesia
4) Respiratory paralysis
Stage 1 of anaesthesia - analgesia (3)
Plane 1
Moderate sedation & analgesia (5-25% N20)
Plane 2
Dissociation sedation and analgesia (20-55% N20)
Plane 3 Total analgesia (50-70% N20)
Adequate sedation (8)
Awake Feels relaxed Suggestive state Giggling Verbal responses Maintaining mouth open Reduced blink rate Spontaneous respiration
Over-sedation symptoms (9)
Patient no longer enjoying the effects Hysterical laughter, tears Decreased cooperation Nausea/vomiting Mouth closing – repeatedly Snoring Incoherent speech Irrational and sluggish responses Loss of consciousness
Indications for sedation (7)
Social -mild anxiety / needle phobias / gagging / fainting -to enable cannulation Medical -conditions aggravated by stress -conditions where continuous oxygen delivery is beneficial -conditions which affect co-operation Dental -unpleasant procedures -avoid GA in medically compromised
Contraindications for sedation (8)
Social
-severe anxiety / claustrophobia / no consent / no escort
-lack of understanding
Medical
-blocked nose / URTI / unable to nose-breathe
-recent eye / middle ear / sinus / intracranial surgery
-bleomycin therapy / Myaesthenia Gravis
pregnancy – 1st and 3rd trimesters
Dental
-traumatic procedures / unsuitable for LA alone
-treatment on upper anterior teeth – lip trapped
Safety features/ checks for sedation (4)
1) Pin index
2) Scavenging at 40L/minute
3) Nasal mask and tubing
4) Oxygen failsafe
5) Max 70% N20
6) Oxygen flush
7) Air entertainment valve
8) Reservoir bag
N2O / O2 pre-op instructions (5)
Light meal
Take routine medicines as usual
Children must be accompanied to and from their appointment by a competent adult
Do not bring other children
Can cause dizziness/ nausea/ headaches at higher doses
Technique
Safety checks, consent, check escort
Introduce to child (giggle gas etc.)
Start O2 and turn up flow rate (5-6L/min)
Fit mask and encourage nose breathing
Titrate N2O - 10% per min to 30% and then 5% per min until sedated
Hypnotic suggestion, clinical monitoring
100% O2 minimum of 3 minutes to recover
Record keeping for sedation (8)
Consent and escort Safety checks completed Second appropriate person (dental nurse) Mask size Flow rate Max dose Response/ level of co-operation Recovery time
Reducing exposure in sedation - COSHH exposure limits (4)
COSHH exposure limits – 100ppm TWA over 8 hours
Active scavenging at 45L/min
-statutory requirement in UK
-at level of nasal hood
Passive scavenging
-floor level extractor fan, opening window
Supplementary high volume aspiration
Reducing exposure (4)
Rubber dam -inconclusive but seems logical Well fitting mask Good technique -reduce mouth breathing / conversation/titrate carefully Good initial patient assessment
Occupational hazards in sedation (7)
Reproductive Haematological Neurological Also reports -hepatic disease -renal disease -cytotoxicity -malignancy
Reproductive occupational hazards from sedation (3)
Miscarriage
-maternal and paternal influences
-twice as likely to miscarry if scavenging not provided
Reduced fertility in dental assistants working unscavenged offices for over 5 hours per week
Possible risk of teratogenesis
Haematological hazards from sedation (4)
N2O oxidises vitamin B12
Inactivates methionine synthase
Impairs DNA synthesis, affecting haematopoesis
Pernicious anaemia
Neurological occupational hazards from sedation (3)
Methionine essential for myelin synthesis
Peripheral neuropathy
Spinal cord degeneration/ myelopathy
Cumulative effect of occupational hazards from sedation depends upon (4)
Pattern of exposure
Tissue sensitivity
Vitamin B12 intake and stores
Extent to which methionine synthase is deactivated
Evidence for N2O/ O2 sedation (3)
Success (Shaw et al, 1996)
–90% of children aged 4-17 years manage extractions successfully with LA and N2O/O2 sedation
-97% of parents and children satisfied
Time (Wilson et al, 2007) -
-takes an average of 7 mins to reach adequate sedation
Cost (Jameson et al, 2007)
-245.47 per patient for dental care under advanced conscious sedation
-359.91 per patient under GA
Advantages of inhalation sedation (6)
- Non-invasive technique
- Drug level easily altered or discontinued
- Minimal impairment of reflexes
- Drug administered and excreted through the lungs so no metabolism and thus rapid recovery
- No fasting required
- Some analgesia
Disadvantages of inhalation sedation (9)
- Lack of potency of nitrous oxide
- Expense of equipment
- Requirement for a clear nasal airway
- Intrusion of nasal mask into operating field
- Patient perception of equipment
- Space occupying equipment
- Chronic exposure of staff
- Potential for staff addiction
- Lack of operator control
Suitable patients for inhalation sedation (6)
- Unpleasant treatment
- Anxious children/Anxious adults
- Needle phobia
- Patients who retch easily
- People with special needs
- Medically compromised patients
Contraindications to inhalation sedation (a lot)
- Respiratory tract obstruction
- Nasal obstruction
- Cyanosis at rest due to chronic cardiac or respiratory disease
- Inability to communicate or co-operate (age, severe learning difficulty)
- First trimester of pregnancy
- Acute fear of the GA mask
- Multiple sclerosis
- Myasthenia gravis
- Claustrophobia
- Severe personality disorders
- Recent ophthalmic surgery using inter-ocular gases
- Any condition where there is air entrapment in the body eg myringoplasty, head injury, pneumothorax, maxillofacial injury etc
- Procedures where the mask may interfere with operative work
- Current medication check BNF eg methotrexate
Problems associated with ASA III patients (4)
- Consultation with medical colleagues advised
- Stable but may deteriorate rapidly
- Deterioration aggravated by anxiety and stress
- Diagnosis of deterioration difficult particularly under sedation
Properties of an ideal inhalation sedation agent (9)
- Alleviate fear and anxiety
- Produce a degree of amnesia and analgesia
- Suppress vomiting reflex, but not protective reflexes
- Prolong potential operating time
- Be rapidly effective
- Be easily eliminated
- Have no side effects
- Be safely and easily administered by the operator
- Require no special precautions or procedures
Nitrous oxide systemic effects (10)
- CNS Depression of all senses
- CVS Slight depression at high concentrations
- RS Non-irritant, slight increase in minute volume
- Non allergenic
- No significant effect on GIT, liver, kidney
- Increases incidence of spontaneous abortion?
- Decreases fertility if long exposure?
- Inhibits action of methionine synthetase for Vitamin B12 production, can cause impaired bone marrow function.
- Thus can affect DNA production and produce pernicious anaemia like effects
- Long term exposure leads to peripheral sensory neuropathy
Minimum alveolar concentration (5)
- MAC is defined as the minimum alveolar concentration of anaesthetic at 1 atmosphere that produces immobility in 50% of those patients or animals exposed to a noxious stimulus
- It is a measure of anaesthetic potency
- MAC is reduced in the elderly and by other sedative agents
- Nitrous oxide 105% Isoflurane 1.15% Sevoflurane 0.65%
Diffusion hypoxia (5)
- Described by Fick 1955
- Seen in the 10 minutes following cessation of inhalation sedation
- After administration is terminated, the rapid elimination of nitrous oxide into the lungs dilutes the oxygen within the alveoli and lowers the alveolar oxygen concentration
- Responsible for most reports of headache, nausea and lethargy post-operatively
- Prevented by routine administration of 100% oxygen for 3-5 minutes post-operatively
Reducing occupational exposure (lots)
- Regular servicing of machine and checking by staff
- Vent dental suction out of the surgery
- Minimise leaks from poorly fitting facemasks
- Check flowmeters are not inadvertently left on,
- Limit length of appointment
- Use low concentrations where possible
- Take regular breaks
- Use a large room if possible
- Adequate room ventilation, open windows, fans at floor level
- Active or passive scavenging to remove pollution at source
- Encourage the patient not to talk or mouthbreathe
- Use rubber dam
- N2O monitors
- Secure equipment at the end of the day
Possible effect of chronic exposure to high levels of nitrous oxide (7)
- Teratogenic effects
- Increased rate of spontaneous abortion
- Decreased fertility
- Increased incidence of hepatic disease/Impairment of renal function
- Non specific neurological disease
- Bone marrow dysfunction
- Anaemia like symptoms
Abuse of nitrous oxide (6)
- Used for pleasurable and recreational purposes since 1772
- Main abusers are professionals with easy access to the drug
- Always keep a cylinder stock record. 1 nitrous oxide cylinder will be used up for about 2.5 oxygen cylinders
- Prolonged exposure toxic to rapidly dividing cells
- Peripheral neuropathy, numbness, pain tingling in extremities, that may be irreversible
- Although nitrous oxide has been legal in the past, since the Psychoactive Substances Act came into effect on 26 May 2016, it is now illegal to supply or import nitrous oxide for human consumption
Safety features - nitrous oxide (lots)
- Used for pleasurable and recreational purposes since 1772
- Main abusers are professionals with easy access to the drug
- Always keep a cylinder stock record. 1 nitrous oxide cylinder will be used up for about 2.5 oxygen cylinders
- Prolonged exposure toxic to rapidly dividing cells
- Peripheral neuropathy, numbness, pain tingling in extremities, that may be irreversible
- Although nitrous oxide has been legal in the past, since the Psychoactive Substances Act came into effect on 26 May 2016, it is now illegal to supply or import nitrous oxide for human consumption
