Inhalation Sedation II Flashcards
Advantages of inhalation sedation?
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?
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?
Unpleasant tx Anxious pt Needle phobia Pts who retch easily People with special needs Medically compromised patients
Contraindications to inhalation sedation?
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 GA mask
Multiple sclerosis
Myasthenia gravis
Claustrophobia
Severe personality disorders
Opthalmic surgery using inter-ocular gases
Procedures where mask may interfere with operative work
Current medication - methotrexate
Problems associated with ASA III patients?
Consultation with medical colleagues advised
Stable but may deteriorate rapidly
Deterioration aggravated by anxiety and stress
Diagnosis of deterioration difficult particularly under sedation
Treat pt when they are in their best health
Properties of an deal inhalation sedation agent?
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 and easily eliminated
Have no side effects
Be safely and easily administered by the operator
Require no special precautions or procedures
Nitrous oxide features?
Non-irritating, sweet smelling gas
44 bar pressure in blue cylinder
Cylinder contains liquid under pressure and cools in use
Carried in blood in physical solution only
Strong analgesic
Oxygen features?
Odourless gas
137 bar full cylinder pressure
Black cylinder with white shoulder
Relieves hypoxia
Nitrous oxide systemic effects?
CNS depression of all senses
CVS slight depression at high concentrations
Non-allergenic
No signif effect on GIT, liver, kidney
Inhibits action of methionine synthetase for vitamin B12 production, can cause impaired bone marrow function = can affect DNA production and produce pernicious anaemia like effects
Long term exposure leads to peripheral sensory neuropathy
What is MAC?
Minimum alveolar concentration
= Minimum alveolar concentration of anaesthetic at 1 atmosphere that produces immobility in 50% of those patients or animals exposed to a noxious stimulus
Measures anaesthetic potency
MAC is reduced in elderly and by other sedative agents
MAC of nitrous oxide, isoflurane, sevoflurane?
NO 105%
Isoflurane 1.15%
Sevoflurane 0.65%
What is diffusion hypoxia?
How to prevent diffusion hypoxia?
Seen in the 10 mins following cessation of inhalation sedation
After administration is terminated, the rapid elimination of NA 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 3-5mins post operatively
How to reduce occupational exposure?
Regular servicing of machine and checking by staff
Vent dental suction out of surgery
Minimise leaks from poorly fitting facemasks
Check flowmeters are not inadvertently left on
Limit length of appt
Use low concs if possible
Take regular breaks
Use large room
Room ventilation, open windows, fans at floor level
Encourage pt not to talk or mouthbreathe
Use rubber dam
N20 monitors
Secure equipment at end of day
Possible effects of chronic exposure to high levels of nitrous oxide?
Teratogenic effects Increased rate of spontaneous abortion Decreased fertility Increased incidence of hepatic diseases/impairment of renal function Non specific neurological disease Bone marrow dysfunction Anaemia like symptoms
