202407280000
Status:
Orthognathic surgery
shared airway
need to check occlusion of teeth intra-op
Bleeding
Minimizing blood loss intra-operatively can be difficult, especially during maxillary surgery
The bony mid-face receives an extensive blood supply and the posterior maxilla is also in close proximity to a rich venous plexus. Bleeding can therefore be heavy from both soft tissue and bone.
Surgical haemostasis is hampered by limited access and the ease with which the surgical field is rapidly obscured by blood. Identification of vessels traversing bone can be difficult both before and after osteotomy.
Bleeding can occur from branches of the third part of the maxillary artery and on occasions from the pterygoid venous plexus which can lead to major blood loss.
Techniques used to minimize bleeding and improve the surgical field include
- positioning the patient head up,
- ensuring there is no impediment to venous drainage,
- induced-hypotension
- infiltration of large doses of epinephrine-containing local anaesthetic solutions
‘Dental’ anaesthetic solutions contain higher concentrations of epinephrine (1:80 000) than used in other types of surgery, and patients who are typically young, fit and healthy may show a marked increase in heart rate and sometimes arterial pressure after their use. Unless expected, these may easily be mistaken for signs of light anaesthesia.
Usage should be limited to a maximum of 300 µg/h of epinephrine
Airway
In the event of nasal intubation proving impossible, there are three alternatives. In retromolar intubation, an attempt is made to pass a reinforced oral TT (inserted conventionally) behind the most posterior molars, thus still allowing the teeth to be brought into occlusion. With submental intubation, the end of the conventionally inserted oral TT is passed (minus its connector) through the floor of the mouth and out percutaneously. Neither of these is ideal from the surgical perspective and the risk of accidental TT dislodgement is high. Tracheotomy is theoretically another option.
In the event of damage to the TT between the pilot-balloon and cuff, oropharyngeal packing may sometimes be enough to compensate for a small leak of air from the deflated cuff where tube exchange would otherwise be very difficult
Throat packs are used routinely in many (but not all) centres. They reduce the amount of blood entering the stomach, offer some degree of protection from bony debris, and aid the stability and security of the TT
Analgesia
Mandibular and maxillary nerve blocks performed by the surgeons can be utilized to aid postoperative pain relief. Furthermore, they also have the potential to reduce the stress response to surgery, reduce fluctuations in heart rate and arterial pressure and reduce the dose requirements of hypotensive agents
PONV
Intra-operative steroids, usually dexamethasone, are administered primarily to minimize postoperative swelling but are also efficacious anti-emetics and contribute to analgesia.
Induced hypotension
There is some level-one evidence that induced-hypotension can reduce blood loss, transfusion rate, and operating time associated with orthognathic surgery9 but this is all controversial
The making of osteotomy cuts in the maxilla is usually associated with the most bleeding directly whereas other stages of surgery such as ‘down-fracture’ of the maxilla (Fig. 1) may be more stimulating and indirectly make haemostasis challenging. Unfortunately, the ‘down-fracture’ usually has to be completed before blood loss can be fully controlled.
During induced-hypotension, mean arterial pressure should be reduced by no more than 30% of the patient’s normal with an absolute lower limit of 55mmHg (in ASA I patients).
contraindications to induced hypotension
- ischaemic heart disease,
- uncontrolled hypertension,
- diabetes,
- severe anaemia,
- haemoglobinopathies (such as Sickle cell anaemia),
- cerebrovascular disease,
- hepatic and renal impairment
| Drug | Administration and dose | Advantages | Disadvantages |
|---|---|---|---|
| Volatile agents | As required | Convenience and familiarity if already being used for anaesthesia | Prolonged recovery PONV |
| Remifentanil | As required | Convenience and familiarity if already being used for anaesthesia | Need for additional opioids after operation Acute postoperative opioid tolerance |
| SNP | Infusion Up to 1.5 µg/kg/min |
Venous and arteriolar dilatation Potent and reliable hypotension Rapidly titratable (half-life ∼2 min) |
Reflex tachycardia and tachyphylaxis may limit its effects Rebound hypertension Cyanide toxicity |
| GTN | Infusion 10–400 µg/min |
No dangerous breakdown products | Venodilator only Less efficacious than SNP Tachyphylaxis |
| Clonidine | Infusion or bolus 1 µg/kg |
Vasodilatation with heart rate control Analgesic properties Ease of administration Not negatively inotropic |
Postoperative sedation Rebound hypertension after stopping infusion |
| β-blockers | Depends on drug | Vasodilatation with heart rate control Ease of administration |
Bronchospasm Negatively inotropic Metabolic effects |
| Magnesium | Bolus 20–60 mg/kg |
Vasodilatation with heart rate control Analgesic properties Ease of administration No rebound hypertension |
Modest decrease in blood pressure Prolonged neuromuscular block |
Emergence / extubation
remove throat pack
airway cleared w/ suction
ensure haemostasis adequate
smooth emergence
rigid inter-maxillary fixation now uncommon
Post-op problems
airway (cf bleeding tonsils)
PONV
References
Anaesthesia for Cosmetic and Functional Maxillofacial Surgery BJA Ed