General Anaesthetics Flashcards
General anaesthetics
Cns depression (monitor for respiratory depression)
Loss of consciousness
Insensitivity to pain
Combine drugs to minimize adverse reactions
Mechanism of action
Increase threshold firing
Facilitate GABA
Decrease duration of nicotinic channels opening
Stages
Analgesia to sedation to anaesthesia
Stage I analgesia
Reduced pain sensation
Conscious
End of stage marked by loss of consciousness
Stage II: delirium or excitement
Loss of consciousness
Involuntary movement
Irregular respiration
Tachycardia, hypertension
Stage III surgical anaesthesia
4 planes (eye movement, depths of respiration, muscle relaxation)
Onset stage III (planes I and II)
Regular respiratory movement
Muscle relaxation
Normal heart and pulse rate
Beginning plan III into IV
Intercostal muscle paralysis (diaphragm breathing remains)
Absence of reflexes
Extreme muscle flaccidity
Plane IV
Cessation of respiration Pupils Max dilation Blood pressure falls rapidly If not reversed immediately patient will die Respiration artificially maintained
Minimal Alveolar Concentration
Compared potency
Minimum concentration required to prevent 50% of patients responding to stimulus
Lower MAC=more potent anaesthetic
Nitrous oxide
Colours less, odorless Low potency Light sedation and relaxation Anxiety relief Reduces concentration of other agents needed to obtain desired depth of anaesthesia
Nitrous oxide technique
100% oxygen for 2-3 minutes
Gradually add 5-10% nitrous oxide (number varies, average=35%)
100% oxygen for 5 minutes at end to avoid diffusion hypoxia
Diffusion hypoxia
Caused by rapid outflow of nitrous oxide, carbon dioxide, oxygen
Loss of carbon dioxide=decreases ventilation
Severe headache, nausea, vomiting
Nitrous oxide advantages
Rapid onset Easy administration Close control Rapid recovery Acceptable for children
Nitrous oxide pharmacological effects
Cns sedation (most commonly used in pediatric dentistry)
Adverse Effects
Misuse or faulty installation
Automatically limited concentration
Nausea and vomiting (light meal before, avoid large meal 3 hours after)
Reduces the activity of methionine synthetase (vitamin b12 functioning)
Nitrous oxide contraindications and dental issues
Respiratory obstruction COPD Emotional instability Pregnancy considerations Abuse
IV anaesthetics advantages
Rapid onset Titrate doses Gag reflex diminished Nausea/vomiting minimized Greater bioavailability Good for seizure prone patients
IV anaesthetics disadvantages
Venipuncture necessary Complications at venipuncture site Intensive patient monitoring Some IV drugs cannot be reversed by drunk antagonists Patients escorted home after treatment
IV Anaesthetics Contraindications
Pregnancy Hepatic dysfunction Thyroid dysfunction Adrenal insufficiency Maios or tcas within previous 14 days (opioids)
IV anaesthetics
Benzodiazepines Opioids Short acting barbiturates Ketamine Propofol
Benzodiazepines
Mostly commonly used
Include diazepam and midazolam (midazolam preferred-short action, better anxiety control, antegrade amnesia)
Avoid in elderly, children under 18 and pregnant patients
Iv opioids
Disadvantage=prolonged respiratory depression
Fentanyl is preferred
Morphine can be used for appts longer than 2 hours
Fentanyl
Rapid onset Action=30-60 minutes Cardiovascular stability No histamine release Contraindications (pregnancy, liver/kidney failure, COPD, Maois in last 14 days)
Iv short acting barbiturates
Thiopental
(Onset 20-30 seconds, action =15-30 minutes)
Contraindications (porphyria, previous allergy, asthmatics)
IV ketamine
Sedation without loss of consciousness Onset less than 1 minute Action=10 minutes caution with elderly and cv disease Contraindications (high blood pressure, epilepsy, heart disease, cv accident)
Iv propofol
Onset:30 seconds Less than 10 minutes action Rapid recovery Can cause hypotension Egg allergies contraindication Caution with elderly
Balanced general anaesthesia
Good control, relaxation, pain relief
Patient passes from stage I to III skipping signs of stage II
