Patients referred for oral and maxillofacial surgical procedures may be suffering from systemic disorders or undergoing treatment with drugs. Either of these situations may complicate the operation, including the choice and administration of an anaesthetic, sedation or local anaesthesia. A full medical history is therefore essential and should be rechecked periodically if the patient attends for a prolonged period. With certain systemic disorders, liaison with the surgeon or physician treating these disorders is important. Advances in drug therapy occur rapidly and where a patient is taking medication with which the oral surgeon is not familiar, reference should be made to the current British National Formulary or a similar publication.

A medical history must cover certain areas to be complete. The overall scheme may vary between clinicians, but most follow a pattern similar to that described in Chapter 1. After taking the medical history a patient may be assigned to a category derived from the American Society of Anesthesiologists (ASA) Physical Status Classification System. The purpose of this system is to assess the degree of a patient’s ‘sickness’ prior to sedation, an anaesthetic or before performing surgery. Describing a patient’s preoperative physical status in this way is used for record keeping, for communicating between colleagues and to create a system that facilitates statistical analysis. It is not intended as a measure to predict operative risk. The classification system consists of six categories as shown in Table 3.1.

Table 3.1 ASA Physical Status (PS) Classification System

Physiological Conditions

Pregnancy

It is best to try to avoid prescribing drugs during pregnancy. This is not always practical but in certain groups, particularly those with a history of spontaneous abortion, treatment should be delayed until after parturition, if possible.

Use of local anaesthetic with adrenaline is acceptable in pregnant patients. With general anaesthesia, one danger to the foetus is hypoxia, which must be prevented by adequate oxygenation. Patients should be treated in the left lateral position to avoid pressure from the gravid uterus on the inferior vena cava, which if not done could lead to the supine hypotension syndrome. Ideally general anaesthesia during pregnancy should be avoided, but if this is not possible, specialist anaesthetic services must be available.

The optimum time for operation is the second trimester, i.e. fourth, fifth and sixth months of pregnancy, as danger to the foetus is least at this time. In the second and third trimesters the foetus is growing but is still susceptible to the effects of infections and drugs.

A hypersensitive gag reflex may be present in some pregnant patients. Apart from the avoidance of drug prescriptions wherever possible during pregnancy, this is another reason why extensive oral surgery under local anaesthesia may best be postponed until after parturition.

Intravenous sedation must be avoided in the first trimester and the last month of the third trimester; ideally it is best avoided altogether during pregnancy. Nitrous oxide can interfere with vitamin B₁₂ and folate metabolism and should not be used in the first trimester, although it does not appear to be teratogenic. The duration of exposure if used should be less than 30 minutes and 50% oxygen should be administered with avoidance of repeated exposures.

In general anaesthesia, there is an increased likelihood of vomiting during induction of anaesthesia in the third trimester. Another concern is the risk late in pregnancy of general anaesthesia inducing respiratory depression in the foetus. There is little evidence of teratogenic effects in humans of general anaesthetic agents.

All drugs should be considered as potentially being teratogenic and should therefore be avoided wherever possible, but particularly in the first trimester. It is important to check in the British National Formulary before any prescriptions are written in this group of patients.

Breast-Feeding

Drugs taken by the mother while breast-feeding can be transferred to the breast milk in some cases and therefore the infant could be affected. The British National Formulary includes an appendix highlighting which drugs are implicated.

Endocrine Disorders

Diabetes Mellitus

Diabetes mellitus is a disease characterised by a rise in blood glucose levels and urinary excretion of glucose. Osmotically, increased amounts of water are also excreted (polyuria). Such patients have an increased susceptibility to infection. It is the most common endocrine disorder likely to be encountered by the oral surgeon. The main subdivisions of diabetes mellitus are into type I and type II. Type I diabetes mellitus has an autoimmune origin whereas type II has a genetic background and these patients are usually overweight. Due to the so-called ‘obesity epidemic’, type II diabetes is becoming more common in younger people. Emotional stress or infection may increase the severity of the disease.

Type I diabetes mellitus is usually treated with insulin, type II diabetes mellitus is usually treated with dietary control with or without oral hypoglycaemic agents. In uncontrolled diabetes mellitus hyperglycaemia may occur, but this is of slow onset and the patient is so obviously ill that it is unlikely to present as an emergency in the dental surgery.

Hypoglycaemia

Hypoglycaemia on the other hand, can occur with alarming suddenness. Weakness, hunger, pallor, a rapid pulse, confusion/aggression and loss of consciousness are all signs. Treatment is to give sugar by mouth if conscious or 1 mg glucagon intramuscularly if not. Preparations such as GlucoGel® (formerly Hypostop Gel) have been developed for use as an oral preparation. It is important to observe the patient after treatment for hypoglycaemia to ensure that no relapse occurs.

Local Anaesthesia

Where a diabetic patient is to have an operation under local anaesthesia, normal diet and insulin should be taken at the usual time and the patient treated first on the list. It is not necessary to use adrenaline-free local anaesthetic solutions, but the operation should not be unduly prolonged, nor must the patient miss meals or snacks.

General Anaesthesia

Patients taking insulin who have a severe acute infection or need a general anaesthetic should be admitted to hospital. It is wise to obtain the advice of a diabetologist in such cases. When a general anaesthetic is to be given, the physician will advise according to the following broad principles. Patients taking long-acting insulin are changed to the soluble form and rebalanced. All but the most severe diabetic patients will then receive their normal insulin and carbohydrate till midnight on the day before operation. Next morning they should be first on the operating list. Blood glucose estimations are carried out and an infusion of glucose, potassium and insulin (GKI) is usually administered to keep blood glucose at optimal levels.

Postoperative Care

The surgeon must take measures to minimise/control infection at the operative site by careful oral prophylaxis, and antibiotics may be prescribed. Blood glucose estimates are continued until the patient resumes normal diet and controlling medication.

Adrenal Corticosteroids

The adrenal cortex produces hormones that are of importance to the surgeon since among their functions they affect the balance of electrolytes, depress the immune response and play a significant part in the body’s reaction to stress. Their secretion is stimulated by the adrenocorticotrophic hormone (ACTH) produced by the anterior lobe of the pituitary gland via a feedback loop (the hypothalamo-pituitary-adrenal (HPA) axis). When the amount of ACTH in the circulation reaches the necessary level, its production is inhibited.

Corticosteroids, or their synthetic equivalents, are used in medicine for replacement therapy of insufficiency, which may be chronic and primary as in Addison’s disease, or chronic and secondary as in hypopituitarism. They are also used in the treatment of a wide variety of medical conditions such as asthma and the collagen disorders.

Adrenal Crisis and Supplemental Steroids

Adrenal crisis may result from adrenocortical hypofunction, leading to hypotension, shock and death. The use of supplemental steroids prior to dental surgery in patients at risk of adrenal crisis is a contentious issue. The rationale for steroid supplementation is as follows: a normal physiological response to the stress of trauma is to increase corticosteroid production. If, due to hypoadrenalism, this response is absent, hypotension, collapse and death will occur if no treatment is provided (see Chapter 4). The HPA axis will fail to function if either the pituitary or the adrenal cortex ceases to function. This happens in secondary hypoadrenocorticism since administration of corticosteroids leads to negative feedback to the hypothalamus causing decreased ACTH production and adrenocortical atrophy. The atrophy means that an adequate endogenous steroid boost cannot be produced in response to stress.

Recent studies suggest that dental surgery may not require supplementation. Certain procedures, however, such as third molar surgery or the treatment of very apprehensive patients, may still require ‘steroid cover’ (see Chapter 4). If supplementary steroids are not used in patients at possible risk from an adrenal crisis, it is wise to monitor the blood pressure. If the diastolic pressure falls by more than 25%, an intravenous steroid injection (100 mg of hydrocortisone) is indicated.

Patients with Addison’s disease should receive steroid cover. If a patient is under the care of an endocrinologist and taking steroids, it is wise to consult with them prior to carrying out surgery.

Thyroid Disorders

Disorders of the thyroid gland should be considered by the surgeon if a history of thyroid problems is elicited. Improved pharmacological control of thyroid disorders has considerably reduced risk in this group of patients undergoing surgery/anaesthesia but the considerations below are still potentially important.

Hyperthyroidism

If hyperthyroidism is poorly controlled, this group of patients may have sympathetic overactivity which makes them more prone to fainting. There is no particular risk associated from adrenaline in local anaesthetics exacerbat­ing sympathetic overactivity when normal doses are used. Use of intrave­nous sedation may heighten the effects of antithyroid drugs, and this should be remembered.

Hypothyroidism

Intravenous sedatives should be avoided or low doses used as “myxoedema coma” may be induced in these patients if the replacement therapy (usually thyroxine) is inadequate. Local anaesthesia is safe in this group. Similar comments apply to general anaesthesia and the possibility of associated ischaemic heart disease should be borne in mind in these patients.

Allergy

Anaphylaxis

See Chapter 4.

Angioedema

Angioedema is a disorder in which there is widespread oedema due to increased vascular permeability as a result of an allergic reaction. Two forms exist; one is hereditary and is an apparently exaggerated response to minor trauma. It is characteristically shared by other genetically related members of the family. The disorder is due to a lack of C1 esterase inhibitor and a consequent initiation of the complement cascade. Administration of fresh frozen plasma (FFP) prior to surgery provides sufficient inhibitor to prevent the problem. In the event of a spontaneous oedematous episode, the patient should be treated with systemic steroids.

The non-hereditary type is a kind of urticaria in which there is an allergic response to food and certain drugs. Trauma seldom produces serious complications but the use of allergenic substances may do so. Should an acute reaction occur it should be treated as for anaphylactic shock as described in Chapter 4.