Indian Journal of Anaesthesia 2008;52:Suppl (5):725-737
General Anaesthesia for Dentistry Naveen Malhotra
Summary The first general anaesthetics administered were for dental extractions. General anaesthesia for dentistry is not without risk and should not be undertaken as a first-line means of anxiety control. Considerations should always be given to the possibility of local anaesthetic techniques with or without conscious sedation. Patients requiring general anaesthesia for dental work are frequently children or individuals with learning difficulties. The standards of general anaesthesia for dentistry should be the same as those in any other setting. General anaesthesia in dentistry covers three main types of surgical procedures: Dental chair anaesthesia, Day care anaesthesia and In-patient anaesthesia. All standard equipments, gadgets, monitors and drugs for anaesthesia and resuscitation should be available and checked before administering anaesthesia. Each individual must have had appropriate experience of, and training in dental anaesthesia. Sevoflurane has largely replaced halothane as agent of choice for inhalation induction of anaesthesia and propofol is agent of choice for intravenous induction. The transparent neonatal mask for nasal ventilation offers significant advantages. Laryngeal mask airway is being used for all but the simplest extractions. The most commonly used operating position is semi-supine. In recovery, airway obstruction is common in patients undergoing dental procedures and they should be closely supervised by an experienced nurse. Routes of tracheal intubation in maxillo-facial surgical procedures are: oro-tracheal intubation, nasal intubation, retromolar intubation and submento-tracheal intubation. A team of vigilant and experienced anaesthesiologist and dental surgeon is able to prevent and manage the complications associated with dental procedures under general anaesthesia. Keywords
Surgery: Dental; Anaesthesia: General.
work routinely in operation theatres.4 Majority of the dental procedures can be performed under local anaesthesia which is inherently safe. Most dentists are skilled in techniques of local anaesthetics and nerve blocks.5 General anaesthesia should not be used as a method of anxiety control but for pain control, because more specific methods (local anaesthesia with or without conscious sedation and behaviour management techniques6) are available to manage anxiety. All general anaesthetics are associated with some risk and modern dentistry is based on the principle that all potentially painful treatment should be performed under local anaesthesia, if at all possible. General anaesthesia should be strictly limited to those patients and clinical situations in which local anaesthesia (with or without sedation) is not an option. 7-13
Introduction There is a long historical association between Anaesthesia and Dentistry. Some of the initial anaesthetics given were for dental extractions.1, 2 The first general anaesthetic administered for a dental extraction is credited to Horace Wells. Wells, on 11th December 1844, underwent extraction of one of his own wisdom teeth by a colleague whilst under the influence of nitrous oxide. In 1846, William Morton, a pupil of Wells, successfully demonstrated the properties of ether to facilitate dental extraction in Massachusetts.3 Dentistry, in its surgical and restorative aspect, is in majority based on office practice. Limited dentists
Associate Professor, Department of Anaesthesiology and Critical Care, Post Graduate Institute of Medical Sciences (PGIMS), Rohtak-124001 (Haryana) Correspondence to: Naveen Malhotra, 128/19, Naveen Niketan, Civil Hospital Road, Rohtak-124001 (Haryana), E-mail:
[email protected] 725
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In 1970s and 1980s there were numerous deaths, often in healthy children undergoing simple dental procedures under general anaesthesia. The reasons were multifactorial, including administration of anaesthesia in conditions with substandard monitoring, assistance and resuscitation equipments. Also, patients were poorly prepared for anaesthesia and surgery.3 However, currently there is a world wide trend that increasing number of children are receiving dental treatment under general anaesthesia.14-16.
who may not tolerate dental surgery under local anaesthesia or some may be failures of attempts using local anaesthesia. It is recommended that only specialist paediatric anaesthetists should administer general anaesthesia to very young children.
General anaesthesia in dentistry covers three main types of surgical procedures: 3
4. Dental phobia: Patients in whom long-term dental phobia will be induced or prolonged are administered general anaesthesia in first sitting. The long term aim in such patients should be the graduated introduction of treatment under local anaesthesia using, if necessary, conscious sedation and behaviour management techniques.
3. Mentally challenged patients: Such patients, because of problems related to physical/mental disability, are unlikely to allow safe completion of treatment under local anaesthesia.
1. Dental chair anaesthesia: It is outpatient anaesthesia, mainly for simple extraction of teeth especially in children. 2. Day care anaesthesia: It is for minor oral surgery.
5. Allergy to local anaesthetics: It is rare and is due to amide group of local anaesthetics. The preservative methylparaben can also cause allergic reactions. However, allergic reaction should be differentiated from vasovagal attacks, palpitation and flushing occurring as a result of absorption of adrenaline present in local anaesthetic solution.
3. In patient anaesthesia: It is for complicated extractions, oral surgical procedures and maxillofacial surgical procedures. Indications of general anaesthesia in dentistry 3, 7, 8, 12
6. Extensive dentistry & facio-maxillary surgery: Local anaesthesia is unsuitable in an awake patient when the dentistry is likely to be extensive.
Decisions about general anaesthesia can only be made on an individual patient basis, but its use in dentistry should be limited to: 1. Acute infection: In such clinical situations it would be impossible to achieve adequate local anaesthesia and so complete treatment without pain, e.g. management of acute dento-alveolar abscess and severe pulpitis. In these conditions, drug therapy or drainage procedures with other methods of pain relief are inappropriate or unsuccessful. The local anaesthetic may not be effective in such conditions because of local change in pH and there is a risk of spreading infection also.
General principles
2. Children: Majority of out-patient general anaesthesia in dentistry is administered to small children
The Clinical setting
Patient assessment The initial screening of patients for general anaesthesia should be performed as for any other anaesthetic. The anaesthesiologists should always be ready to discuss with dental colleagues policies for general anaesthesia, and their implications for an individual patient, to allow efficient patient management. 3, 12
Defining the setting in which a general anaesthetic 726
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is administered must take into account the ‘worst case scenario’ because the uneventful anaesthetic is not the problem. Complications of modern anaesthesia are rare, but skilled team work is required to prevent permanent harm to the patient. The further away from the support of other clinical services that an anaesthetic is administered, the greater is the risk of death should a complication occur. Ideally, all general anaesthetics for dentistry should be administered within the administrative aegis of the range of services typically provided by. The location of any such facility must allow easy access for emergency services.8
all the equipment before use and there should be immediate access to spare apparatus in the event of failure. Maintenance must be in accordance with the manufacturer’s instructions. Facilities for the supply and storage of medical gases must meet the relevant regulations.8
Staffing standards Each individual must have had appropriate experience of, and training in, dental anaesthesia. The anaesthesiologist must have a dedicated assistant (operating department assistant or practitioner, nurse or dental nurse) with recognised training in this role and no other contemporaneous responsibilities. Because the dentist also requires assistance, a minimum of four people are required for any procedure under general anaesthesia. Until consciousness returns, a patient recovering from general anaesthesia must be appropriately protected and monitored continuously in adequate recovery facilities. Such monitoring should be undertaken by the anaesthesiologist or a dedicated individual who is appropriately trained, and directly responsible to the anaesthesiologist. 8
Equipments, monitors and drugs All standard equipments, gadgets, monitors and drugs for anaesthesia and resuscitation should be available and checked before administering anaesthesia. This includes (not exclusive) anaesthesia machine, vaporizers, oxygen, nitrous oxide, breathing circuits (adult and paediatric), nasal and facial masks, oral and nasal airways, different laryngoscopes with all sizes of blades, all range of nasal and oral tracheal tubes, independent suction apparatus, etc. SAFE agents (Short acting fast emergence) have particular place in day care anaesthesia.3, 7
Aftercare
Minimum monitoring standards during anaesthesia should be followed. Peripheral arterial oxygen saturation, ECG, non-invasive blood pressure and capnography (when tracheal intubation is performed) should always be done. A precordial stethoscope can be very helpful. The anaesthesiologist should be clinically vigilant and continuously monitor colour of lips and mucosa, and movements of chest and reservoir bag. The alarms of monitors should never be switched off.10, 11
The brief nature of most dental procedures means that the majority of patients may be managed on an ‘ambulatory’ basis. Modern anaesthetic drugs permit rapid recovery of consciousness and early discharge, but it should be recognised that it may take more than 24 hours for all traces of the agents to be eliminated. Thus when, in the opinion of the anaesthesiologist, patients are ready for discharge they must be accompanied by a responsible, legally competent adult who has been given clear instructions regarding the implications of anaesthetic ‘hangover’ effects. All patients must be assessed specifically for fitness for discharge by the anaesthesiologist. The administration of general anaesthetics for longer periods of time demands a level of recovery facility that can only be provided in a modern day-surgery unit, and standard criteria for the du-
All resuscitation drugs and equipments, including defibrillator should be immediately available. Moreover, the whole staff should be adequately trained in resuscitation (adult and paediatric). The dental chair should be capable of head-down tilt and should be movable in the event of power failure. The anaesthetist must check 727
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ration of day-stay procedures apply. 7-9
Pre-anaesthetic preparation
Types of dental surgery
The patient is explained about the anaesthetic and dental procedure and clear fluids are allowed up to 4 hours preoperatively. A proper consent should always be taken. The patient must be accompanied before and after the surgery and supervised by an adult for 24 hours.
Dental surgery comprises exodontia, which is removal of teeth, and conservation, which is filling them, crowning them and other restorative measures. Exodontia : Removal of teeth, it is usually a short procedure.
Premedication
Conservation: Conservation operations take longer and often involve using a drill, which squirts water, so a pharyngeal pack is necessary to prevent aspiration even with a cuffed endotracheal tube.11
This is not usual, but may be used in children with especially challenging behaviour. Chloral hydrate (50100mg.kg-1), trimeprazine (2mg.kg-1) or midazolam (0.5–0.75 mg.kg-1) may be given orally mixed with a small quantity of juice to disguise the taste, or intranasally (midazolam 0.2–0.3 mg.kg-1). The patients are instructed to empty their bladder and bowels before surgery.10, 11
Consent Written and informed consent by the patient or parent/ guardian if the patient is minor or mentally challenged.
Induction of anaesthesia
Dental chair anaesthesia
In small children, gaseous induction using sevoflurane (with parental presence) is often easiest. Since its introduction, sevoflurane has largely replaced halothane as agent of choice because inhalation is quick and smooth and there are limited cardiovascular and respiratory effects.19 Sevoflurane supplementation of 66% nitrous oxide in oxygen is used. Sevoflurane may either be introduced in 2% increments every 2 to 3 breaths to a maximum of 8%, with maintenance of anaesthesia at or around 4%, or it may be introduced at the maximum concentration of 8%, with maintenance at 4%. Induction using 8% sevoflurane does not appear to cause any adverse effects.20 However, if sevoflurane is not available halothane is preferred over isoflurane that is irritant and can lead on to coughing and laryngospasm.21 Desflurane offers the advantage of reduction in recovery time.22 A pulse oximeter and ECG should be placed before the child goes to sleep. A cannula must be inserted once the child is asleep for all but the briefest general anaesthetic, for example extraction of one tooth that takes a couple of seconds.
The common indications are: 1. Children: Majority of patients are children between ages 4 and 10 years requiring extraction of tooth/ teeth. Such patients frequently have upper respiratory tract infection. 2. Adult patients with acute infection. 3. Mentally challenged patients. Only ASA physical status class I & II patients should be administered Dental Chair Anaesthesia or Office-Based anaesthesia care. Patients with compromised airway requiring advanced airway management devices, haemodynamic instability requiring invasive monitoring and those who require prolonged post-operative care should be operated in an in-patient setting. Congenital cardiac anomalies and syndromes (predisposing to difficult airway, unstable spine, etc) should be specifically looked for in paediatric patients. 3, 7, 11, 17, 18
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mask may indicate breathing. Still, constant vigilance is needed as the bag on the breathing circuit may not move even with adequate ventilation, and no CO2 trace will be obtained.3, 11 Adenotonsillar hypertrophy can compromise the nasal airway and nasopharyngeal airways have been shown to significantly improve airway patency and reduce episodes of airway obstruction.23
Older children may be offered a choice of gaseous or intravenous induction, and letting them decide is a good way of enlisting cooperation because the child feels less threatened. Propofol is agent of choice for intravenous induction and it ensures clear headed recovery and good anti-emesis, however thiopentone can also be used. Ketamine has delayed recovery characteristics and induces dysphoria. Application of local anaesthetic cream (EMLA) to the skin will ensure that insertion of the cannula is painless. However, it has to be applied one hour prior to procedure which can be difficult in out-patient setting.3, 11
Laryngeal mask airway (LMA) is being used for all but the simplest extractions. It provides some barrier to aspiration when compared to mask. The armoured variety is more suitable as its tube is narrower and takes up less room in the mouth and its flexibility makes it easier to keep out of the dentist’s way. It is important to hold the LMA firmly in place during the surgery because it has a tendency to move. Downward pressure on the jaw during extractions may obstruct it.24-25
Airway for exodontia The type of airway chosen depends on the surgery, and it is vital to liaise with the surgeon. Extraction of a few easy baby teeth is done using a transparent neonatal mask over the nares. The surgeon inserts a gauze pack from one buccal sulcus to the other in order to prevent too much mouth breathing and aspiration of tooth fragments. A gag or bite-block is positioned on the side opposite the extractions to open the mouth. However, the nasal mask is still used by some dental anaesthetists (Fig. 1). The transparent neonatal mask has significant advantages: the external nares can be seen with a transparent mask so that it is possible to check that they are not obstructed, and misting of the
The airway is shared by the anaesthesiologist and dentist. Too large mouth gag should not be used because it can make airway maintenance difficult. The oral pack should not be placed too far posteriorly in the mouth, otherwise it can compromise nasal airway. The anaesthetist must hold the patient’s head both to prevent excessive movement of the neck, which can cause pain postoperatively, and to provide support to the jaw and counter pressure to the dentist’s pushing and pulling.
Operating position
Fig.1
The operating position is controversial. Traditionally, patients sat upright in the dental chair but it can cause postural hypotension. The sitting position has gradually become less common for dental surgery under general anaesthetic. In the supine position, the incidence of airway obstruction is high due to falling back of tongue and there is greater risk of pharyngeal soiling due to blood. Overall, maintaining airway with nasal mask is difficult in supine position. The most commonly used position is semi-supine. In this position, erect head and neck helps in maintenance of airway, besides cardiovascular and respiratory advantages of semi-reclin-
Mask for nasal ventilation 729
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ing position and elevated legs.3, 7, 11
supervised by an experienced nurse. Oxygen supplementation ameliorates the severity of desaturation but does not prevent it. 28 The patients are monitored in the recovery area for at least 30 minutes before returning to dental clinic. No oral fluids are given for 2-3 hours to avoid vomiting and aspiration.
Airway for conservation Operations for dental conservation and periodontal procedures tend to take longer and to involve quantities of water being squirted into the mouth. They should therefore be performed with an endotracheal tube and pharyngeal pack in place to prevent aspiration, which can otherwise occur even with a cuffed tube. It is usual to intubate nasally. An LMA makes the surgery difficult because it leaves little space for the dental drill and suction.11
Postoperative analgesia Extraction of baby teeth is not especially painful. The main problem is the psychological trauma of waking up uncomfortable in a strange place. It is important that the parents are present, and the administration of paracetamol 10-15 mg.kg-1 is usually all that is needed. Analgesia may be given rectally (paracetamol or diclofenac suppositories) during the operation, but for short operations this is of no major advantage. Ibuprofen or paracetamol may be given orally in liquid form in recovery.
Maintenance For short operations it is often easier to use a technique involving spontaneous respiration of inhalational agent, nitrous oxide and oxygen, which gives flexibility and rapid recovery. Using 50% inspired oxygen concentration is beneficial and has been shown to decrease the incidence and severity of hypoxaemic episodes. Incremental doses/continuous/ target controlled infusion of propofol can be used for maintenance of anaesthesia. For extensive and complicated restorations, it is better to paralyse and ventilate the patient.
The extraction of adult teeth is undoubtedly painful. Non-steroidal analgesics are effective, and it has been shown that oral diclofenac given on admission is as effective as rectal diclofenac given peroperatively.11
Fitness for discharge Patients should be clinically observed to be alert, oriented, able to stand and walk unassisted, and haemodynamically stable. There should be no obvious surgical complications. Simple scoring systems, like Aldrete post anaesthetic recovery score (uses colour, respiration, circulation, consciousness and activity as criteria) can be applied.7
Recovery The tooth sockets continue to bleed after dental extraction, especially in the presence of infection. Initially, patients are best nursed in left lateral position with a degree of head-down tilt to encourage drainage of any blood and secretions away from the larynx and administered 100% oxygen. Thorough but gentle oropharyngeal suctioning is done. The LMA or endotracheal tube should not be removed until the cough reflex has returned. Removal of the LMA while the child is still deeply anaesthetized has been associated with lower oxygen saturations in dental patients.26 A study of deaths related to dental anaesthesia found that more than half occurred in recovery.27 Significant desaturation is common after brief dental anaesthesia and the principal cause is airway obstruction, these patients should be
Day care anaesthesia In day care facility, patient undergoes formal admission to the hospital but is discharged home later in the day. The procedures which are usually done are minor oral surgical procedures including laser treatment and limited extractions. The surgical procedure usually lasts not longer than one hour and there are no anticipated post operative complications. The patients are 730
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usually adults belonging to ASA physical status class I or II. They are accompanied by a responsible adult and home circumstances should be suitable for continuing post-operative care.
ever, it is pertinent to note that these patients can have swelling of face, missing or loose teeth, pain and trismus limiting the mouth opening or a maxillo-mandibular fixation may be in situ. Thorough airway evaluation should be done and necessary radiographs evaluated, especially the antero-posterior and lateral views of neck. The nasal patency should be done to facilitate nasal intubation. Such patients may have polytrauma and complete evaluation is necessary, including complete haemogram. Neurological evaluation is necessary in patients with co-existing head injury. The electrolyte status must be assessed because such patients have a limited oral intake (usually liquids). 3, 7
Patients are assessed formally by the anaesthesiologist and investigated. Usually for patients below 40 years complete blood examination and urine complete examination is done. For patients aged 40 years or more an ECG is done. Adequate preoperative fasting is necessary, usually six hours for adults and four hours for children. If patient is anxious, premedication is advised in form of oral alprazolam or midazolam, but it can delay recovery. A proper consent is taken. Intravenous induction with propofol is done in adults and older children. Neuromuscular blockade is achieved with atracurium or vecuronium. The use of depolarizing neuromuscular blocking agent succinylcholine is best avoided in such predominantly ambulatory patients because of muscle pains. Naso-tracheal intubation is commonly done but oro-tracheal intubation can be done if only one side of the mouth is to be operated. Pharynx is properly packed. Anaesthesia is maintained with administration of halothane / sevoflurane and nitrous oxide in oxygen. Diclofenac and dexamethasone are administered to reduce pain and swelling. Local anaesthetic may be infiltrated into the sockets by the surgeon, or a block is performed if surgery is limited to one or two quadrants. For more extensive procedures, short acting opioid like fentanyl is administered. Long acting opioid, like morphine is avoided in day care surgery.3, 11
Principles of airway management7, 29 1. Patients with complex maxillo-facial injuries are potential difficult airway patients. Difficult airway trolley should be checked and immediately available. 2. Do not administer neuromuscular blocking agent until it is possible to do mask ventilation. 3. Maxillo-Mandibular Fixation: It is important to understand that in patients with panfacial trauma, surgical reconstruction often involves intraoperative maxillo-mandibular fixation to restore dental occlusion and it is the important aspect of surgical procedure. The fixation is done with high tensile strength elastic bands (common) or classical wires. Discuss with the surgeon, the possibility of removing maxillo-mandibular fixation just before induction of anaesthesia. Removal of bands/wires can make airway management quite easier. It can be redone intra-operatively after securing the airway. If possible, subsequent removal at the end of surgery makes tracheal extubation and recovery simple. The maxillo-mandibular fixation can be finally put in situ in the ward once patient is fully conscious and airway oedema subsided.
In- patient anaesthesia It is for complicated extractions, oral surgical procedures and maxillofacial surgical procedures (fixation of maxillary, mandibular and nasal fractures, mandibular set back, maxillary advancement, osteotomies and removal of tumours.
4. Throat pack is put to prevent ingestion of blood into the stomach or it’s settling above the cuff of tracheal tube.
Pre-anaesthetic evaluation It is same as for any other major operation. How731
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nasotracheal tube. Further, the presence of nasotracheal tube can interfere with the surgical reconstruction of naso-orbital - ethmoid (NOE) complex.31-33
5. A reinforced or flexo-metallic tube is most commonly used for tracheal intubation. 6. Such patients commonly receive steroids perioperatively to reduce airway oedema.
C) Retromolar intubation 34, 35
7. A tongue suture is applied if there is gross airway oedema and mouth is open.
When orotracheal intubation is not feasible and nasotracheal intubation contraindicated, retromolar intubation is indicated to secure the airway perioperatively. In this technique, oral endotracheal intubation is done with a flexometallic tracheal tube which is then placed in the retromolar region. The retromolar space is the space behind the last erupted upper and lower molar teeth. The retromolar tube is stabilized in position by fixation to first or second molar tooth in ‘figure of eight’ fashion. (Fig. 2) It allows intraoperative maxillo-mandibular fixation, thus restoring dental occlusion, which is the important step for successful facio-maxillary surgery.
8. Displacement of tracheal tube can occur because the tracheal tube is quite close to the surgical field. Proper fixation of tracheal tube should be done and anaesthesiologist should be vigilant to promptly detect it. 9. Routes of tracheal intubation
A) Oral tracheal intubation: It can be done under direct laryngoscopic view, fiberoptic bronchoscope guided, by using lighted stylet, through LMA (guided by fiberoptic bronchoscope) or intubating LMA. Oro-tracheal intubation is not feasible if intraoperative maxillo-mandibular fixation is to be done.30
B)Nasal intubation: It is the most common route of tracheal intubation. It can be laryngoscope guided, fiberoptic bronchoscope guided or blind. Depending upon the clinical circumstances the patient may be anaesthetized and breathing spontaneously or paralyzed, or may be awake. Nasal passage is well prepared with a vasoconstrictor and a topical anaesthetic.
Fig 2 Retromolar Intubation
The adequacy of retromolar space can be determined by introducing the index finger in the patient’s mouth and asking him or her to close the mouth. If there is no compression on finger, the retromolar space is adequate. Success of retromolar intubation can also be increased by selecting one size smaller tracheal tube which has a corresponding smaller outer diameter.
However, nasotracheal intubation is not possible in some patients (10-15%) due to associated skull base fractures, cerebrospinal fluid rhinorrhoea (any attempt towards nasotracheal intubation may lead to passage of tracheal tube into cranium, meningitis, sepsis and epistaxis), fractures of nasal skeleton and anatomical obstruction of nasal airway (deviated nasal septum, nasal spur, and hypertrophied nasal turbinates). These conditions cause physical obstruction to the passage of
Advantage: This technique avoids the need of any surgical technique i.e. tracheostomy and submentotracheal intubation for securing airway perioperatively. Disadvantages: These are minor and avoidable732
Naveen Malhotra. General anaesthesia for dentistry
endotracheal tube at the submental skin exit point is noted. It is usually 2 cm more than the oral fixation. This helps in checking the tube position intraoperatively. The tube is fixed in position with suture (as chest tube drain). (Fig. 3)
1. The tracheal tube can interfere with the main surgical field and positioning and application of dental fixation devices. 2. Too jealous fixation of flexometallic tracheal tube with wire ligature should not be done because it can deform the tube.
D) Submento-tracheal intubation 29, 36-39 Submento- tracheal intubation is an alternate technique of airway management in patients with cranio - faciomaxillary trauma when retromolar intubation is not possible. It is an alternative to short-term tracheostomy. Fig 3 Submento-Tracheal Intubation
Technique
Intraorally, the tracheal tube lies in the sublingual sulcus between the tongue and mandible. It is away from the surgical field and allows intraoperative maxillomandibular fixation. The total procedure is usually completed within 5-10 minutes and the blood loss is minimal (
