Local anaesthetics Continued »


are equal for lignospan and articaine. The FDA have approved articaine 4 per cent with adrenaline ı:ı00,000 to age four years in paediatric patients. The popularity of articaine cannot be


disputed within the dental profession. In the USA in 2009, 4ı per cent of all dental local anaesthetic used was articaine. In 20ı2, the market share for articaine in Germany was 97 per cent and in the same year it was shown that 70 per cent of dentists use articaine in Austrailia.


ADRENALINE-CONTAINING ANAESTHETICS Adrenaline causes constriction of blood vessels by activating alpha-ı adrenergic receptors. It aids hemostasis in the operative field and delays absorption of the anaesthetic. This delayed absorption decreases the risk of systemic toxicity and lengthens it’s duration of action. Adrenaline can cause considerable cardiac stimulation due to its affect as a beta-ı adrenergic agonist30


.


CARDIOVASCULAR INFLUENCES Adrenaline is an agonist on alpha, beta-ı and beta-2 receptors. It is a vasoconstrictor as the tiny vessels in the submucosal


tissues contain only alpha receptors 3ı


. There is much debate regarding the influence of adrenaline on patients with cardiovascular disease. Dionne et al studied the influence of three cartridges of the American formulation Lidocaine with adrenaline ı:ı00,000. Submucosal injection of this dosage increased cardiac output, heart rate and stroke volume. Systemic arterial resistance was reduced and mean arterial pressure remained unchanged32 Likewise, Hersh et al observed similar


.


results following the administration of articaine containing ı:ı00,000 and ı:200,000 adrenaline. Although the influence of adrenaline reported by Hersh et al was minor, it is noteworthy that all ı4 participants were healthy and taking no medication, yet two of these patients experienced palpitations33


. A dose of approximately two cartridges of


lignospan containing adrenaline ı:80,000, is the most conservative and frequently cited dose limitation for patients with significant cardiovascular disease. Ultimately, the decision requires the dentist to practice sound clinical judgement and to discuss any concerns with that patient’s doctor if necessary. Peak influences of adrenaline occur within five to ı0 minutes following injection and they decline rapidly33


.


Another practical suggestion is to determine the dosage based on patient


assessment. If the medical status of a patient is questionable, a sensible protocol is to record baseline heart rate and blood pressure preoperatively and again following administration of two cartridges of lignospan containing ı:80,000 adrenaline. If the patient remains stable, additional doses may be administered, followed by a reassessment of vital signs 30


.


HYPERTENSION After administering one to two cartridges of adrenaline-containing local anaesthetic with careful aspiration and slow injection and the patient exhibits no signs or symptoms of cardiac alteration, additional adrenaline containing local anaesthetic may be used. A safe option preferred by some dentists is to firstly use a minimal amount of adrenaline-containing local anaesthetic and then supplement as necessary with an adrenaline-free anaesthetic34


. The risk of the anaesthesia wearing off


too soon, resulting in the patient producing elevated levels of endogenous adrenaline because of pain, would be much more detrimental than the small amount of adrenaline in the dental anaesthetic35


.


DRUG INTERACTIONS Beta-adrenergic blocking drugs increase the toxicity of adrenaline-containing local anaesthetics. It inhibits enzymes in the liver and decreases hepatic blood flow. Therefore, it is advisable not to give large doses of local anaesthetic to patients on beta blockers. There have been multiple reports of stroke and cardiac arrest within the literature36


and aspiration can also help prevent undesirable reactions37


pressure advisable39 .


Verapamil, which is a popular calcium channel blocker, increases the toxicity of 2 per cent lignospan. As for patients taking beta-adrenergic blocking drugs, two cartridges should be the limit40


. With


regards to bupivacaine, calcium channel blockers enhance the cardiotoxicity of this longer acting anaesthetic4ı


. Antihypertensives are the main


cardiovascular drugs that interact with anaesthetics containing adrenaline. Theoretically, beta-blockers, diuretics and calcium-channel blockers may all result in adverse reactions when used with adrenaline-containing local anaesthetics 42 Adrenaline causes alpha and beta-


.


adrenergic agonism. Alpha-adrenoreceptor stimulation results in vasoconstriction of peripheral blood vessels. Whereas beta- adrenoreceptor stimulation decreases vascular resistance due to vasodilation of vessels in the liver and muscles, therefore reducing diastolic blood pressure. If beta- effects are blocked, the alpha-adrenergic stimulation leads to an unopposed increase in systolic blood pressure triggering a cerebrovascular accident. Therefore, if more than one to two


cartridges are needed in such patients adrenaline-free solutions should be administered. An advantage however of beta-adrenoreceptor blockers in dental patients is that the heart is protected from the elevation in rate produced by beta- adrenergic stimulation from exogenous adrenaline 43


. Diuretics can affect the metabolic


. Slow administration .


Judicious use of adrenaline is


recommended for patients medicated with nonselective beta blockers. Unlike selective agents that only block beta-ı receptors on the heart, nonselective agents also block vascular beta-2 receptors. In this case the alpha agonist action of adrenaline becomes more pronounced and both diastolic and mean arterial pressures can become dangerously increased. This is often accompanied by a sudden decrease in heart rate. Significant consequences of this interaction are well documented38


.


The interaction with beta blockers follows a time course similar to that observed for normal cardiovascular responses to adrenaline. It commences after absorption from the injection site and peaks within five minutes and declines over the following ı0-ı5 minutes. Adrenaline is not contraindicated in patients taking nonselective beta blockers but doses must be kept minimal and monitoring of blood


actions of adrenaline. Increased levels of adrenaline reduces the plasma concentration of potassium44


. These


reductions have been documented in patients receiving dental local anaesthetics containing adrenaline45


. In patients


undertaking oral surgery procedures who are taking non-potassium-sparing diuretics, there have been incidences of adrenaline-induced hypokalaemia44


.


It should remembered that calcium channel blocking drugs may also increase adrenaline-induced hypokalaemia46


.


ANGINA PECTORIS AND POST- MYOCARDIAL INFARCTION The use of adrenaline containing local anaesthetics is advisable as part of a stress reduction protocol. The dosage of the adrenaline should be limited to that contained in two cartridges of lignospan 2 per cent ı:80,000 adrenaline. For patients with unstable angina, a recent myocardial infarction less than six months previously or a recent coronary artery


Continued » Ireland’s Dental magazine 27


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