ANAESTHESIA IN DENTAL CHAIR

General anaesthesia in dentistry is seldom required and is reserved for patients who are intolerant to local anaesthesia, for example small children or for patients who are mentally disabled or agitated. Rarely for difficult dental extractions or  for dental releasing surgeries, General anaesthesia is administered to adults also. Still most of these cases can be managed under conscious sedation, supplemented with local anaesthesia or nerve blocks.

As a rule patients should be premedicated with atropine to reduce oral secretions and to reduce the occurrence of vasovagal syncope.(In children this may be administered at the dose of 0.02mg/kg IV following  induction and iv line placement) In a co operative child the IV cannula may be secured  after topical application of EMLA cream also. Intravenous induction with Propofol and lidocaine  may be condsidered for children above 3 yrs. A nasal mask or LMA may be used to protect the airway with additional pre op oral packing, particularly when nasal mask is used for delivering inhalational anaesthesia. Maintenance of anaesthesia is continued with oxygen, nitrous oxide with isoflurane allowing spontaneous ventilation. Alternatively inhalation induction with sevoflurane or halothane is preferred for children less than 3 yrs.The eyes should be protected. For maintenance, propofol or sevoflurane may be continued. Additional analgesia may be obtained by local nerve blocks by surgeon. If possible the child my be placed in the lateral position keeping the  head low with proper stabilisation of head and neck.Use of nitrous oxide may be reduced or stopped with concurrent administration of short acting analgesics like fentanyl, to prevent hypoxia,provide analgesia and to make available 100% oxygen. Post op analgesia can be achieved with paracetamol or diclofenac suppositories or with intramuscular opioids.

Another technique called inhalational sedation is used for adults who are unwilling for local anaesthesia. Here conscious sedation is given using iv anaesthetic agents followed by analgesia  supplemented with local anaesthetics once the sedative effect is established.Patients are given slow incremental doses of midazolam with oxygen and less than 50% nitrous oxide.A soft but weighted mask is put over the nostrils. It is essential that patient is conscious throughout the procedure and can control his airway. The patient should be able to communicate with the surgeon during the procedure. Mouth props are discouraged as they mask the patients inability to keep the mouth open, - an ominous sign of oversedation. Standard monitoring include  NIBP, ECG, Temperature probe  and Pulse Oximetry. Patient should be given 100 % oxygen following the procedure to avoid diffusion hypoxia and flumazenil should be available to reverse the residual effect of benzodiazepines effect,  if required.

When to think of  intubation?

• Difficult access as in impacted tooth, macroglossia, short neck
• Excessive uncontrolled bleeding
• maxillofacial or major dental surgery
• Mentally handicapped
• Obstruction of nasal passages, large adenoids where nasal mask is not effective

If adenoid hypertrophy is not suspected, nasal intubation following suxamethonium can be considered.

Problems in dental chair

• Reduced venous return, so more severe reaction to a vasovagal attack due to pain
• Increased chance of air embolism in sitting position
• Unprotected airway ie shared airway between surgeon and anaesthetist
• Aspiration of blood or mucus can cause  laryngospasm,
• Adrenaline in local anaesthetic can cause arrhythmias in presence of halothane
• Higher incidence of  arrhythmias due to stimulation of 5 th cranial nerve
• Nasal bleeding if nasal airway is used to deliver the anaesthetic
• Fainting due to cerebral hypoxia or cardiac arrest may be unrecognised
• Difficulty in initiating CPCR once cardiac arrest occurs
• Foreign body obstruction of the airway by needles or dentures,necessitating removal by bronchoscopy
• Uncontrolled and profuse bleeding into the airway in patients not screened for coagulopathies especially in out patients
• Higher incidence of infective endocarditis
• Anaphylaxis, to local anaesthetics or other drugs
• Malignant hyperpyrexia if halothane is used
• Difficulty in administering post op analgesia

Reconstructive surgery; General anaesthesia with endotracheal intubation advised.There is a possibility of surgical emphysema or mediastinal emphysema following use of air turbine dental drills.Stop nitrous oxide. Diagnose a rare pneumothorax, as positive pressure ventilations are harmful.

What to do in case of a cardiac arrest ?

Cardiac arrest is rare  and can occur in the middle aged or above, who are in high risk for myocardial infarction, mostly precipitated by pain or vasovagal hypotension.It is essential to differentiate cardiac arrest from vasovagal syncope or anaphylaxis where patients can be unrensponsive with  bradycardia or feeble and absent peripheral pulses Controversial opinion exists on whether to keep the patient in dental chair or to be placed supine in floor for cardiac compressions during  cardiac arrest.According to Australian Dental Journal Volume 48 Issue 4, Pages 244 - 247, it is possible for those trained in basic life support to perform CPR effectively in the dental chair.If the cause for cardiac arrest is VF immediate  defibrillation should be attempted in dental chair. Following are the guidelines from Dental Council of New Zealand Code of Practice Medical Emergencies in Dental Practice.  

ADULT COLLAPSE
1. Ensure your own safety and then ensure the victim is out of further danger.
2. Check responsiveness. Gently stimulate the victim and shout, “Are you all right?”
3. Send or shout for help.
4. Open the airway with chin lift, head tilt or jaw thrust. Remove obvious causes of airway obstruction.
5. Within 20 seconds check for breathing and assess for signs of circulation.Feel the carotid pulse while looking for other signs of life, movement or breathing.
6. If circulation is absent, the onset of arrest occurred within two minutes, a defibrillator is not immediately available and chest compressions have not already been started, give a single precordial thump.
7. Go for help if no help is available.
8. Give two effective breaths, sufficient to make the chest rise and fall. Make up to five attempts to deliver these breaths.
9. Position hands over the junction of the lower and middle third of the sternum. Compress the chest at a rate of 100 per minute. Depth of compression is 4-5cm. Both single and double rescuers should deliver cycles of 30 compressions, followed by two attempted breaths.
10. Ratio of compressions to breaths 30:2.
 
 CHILDHOOD COLLAPSE

Whereas in adults the focus is on early defibrillation, in children the focus is on early ventilation.
1. Ensure your own safety and ensure the victim is not in further danger.
2. Assess responsiveness by speaking loudly or pinching gently. Do not shake a baby. If unresponsive, shout or send for help.
3. Open the airway with head tilt (but avoid excessive extension) and chin lift.Use the jaw thrust manoeuvre if you suspect cervical trauma. Keep the mouth slightly open and remove any obvious cause of airway obstruction.
4. If the chest or abdomen moves but there is no breathing at the mouth,reattempt airway opening and consider foreign body obstruction.
5. If the breathing is absent or inadequate, give five breaths each lasting 1-1.5 seconds (for an infant, give a mouthful of air at a time).
6. Taking no more than 10 seconds, check for the presence of circulation.
7. If no circulation is present, or if you are unsure, or if in an infant the pulse rate is less than 60 per minute, start external chest compressions at the rate of 100 compressions per minute.
8. For a child aged 1-8 years, press down on the breastbone with the heel of one hand only. For an infant, press down on the breastbone using 2-3 fingers of one hand only.
9. Ratio of compressions to breaths for CPR in child, 30:2.
10. After one minute of CPR, if you are alone and have not already done so,shout or go briefly for help.
11. Resume CPR as soon as possible.
12. After every three minutes of CPR, reassess the circulation.

ANAPHYLAXIS
A potentially life threatening immune reaction to drugs.The usual Presentation is by Urticaria, angioedema, hypotension, tachycardia, bronchospasm.

Management
Dependens on severity of presentation.
Assess the degree of cardiovascular collapse (pulse and blood pressure).
Assess the degree of airway obstruction (upper - angioedema, lower –bronchospasm).
ABC of resuscitation,including supporting airway, airway devices, iv cannulation, iv adrenaline 0.001mg/kg/mt, IV fluids and steroids.

Ref: A Practice of Anaesthesia, wylie and churchill davidson's 7 th edition, Oxford hand book of anaesthesia, 2002, New zealand dental council, code of practice