The Potential of the Nasal Mucosa Route: DISCUSSION

In: Health

17 Sep 2009


The number of times that CPR has been performed in the dental setting is unknown, because there have been no exact statistical data. However, considering the high prevalence rate for dental diseases, the possibility cannot be ignored that CPR could be necessary during dental treatment. Intravenous drug administration is a highly reliable and certain method to use during CPR; however, because peripheral blood vessels may not be palpable in patients with circulatory collapse, easy and expeditious establishment of an IV route cannot always be expected. According to one report of prehospital cardiopulmonary collapse in children, the success rate of establishing a peripheral venous access route was only 18%, even by physicians in the emergency department.

Cut down is basically a time-consuming method. The success rate of central venous access is not always high without sufficient continuous training, and severe complications often occur. During CPR, time is extremely precious, and it is undesirable to use several minutes merely to establish an IV route. Therefore, in cases where establishment of an IV access route is difficult, several alternative routes, such as subcutaneous, intra-lingual, intracardiac, intraosseous, intramuscular, and intratracheal routes, have been reported. However, subcutaneous and intralingual administrations are ineffective. Intracardiac administration easily causes fatal complications, such as cardiac tamponade and coronary artery and myocardial laceration, and is a difficult route of administration to perform. Although good results with intraosseous administration in pediatric cases were reported, there have been no reports of adult cases, and training to learn the puncture process is necessary. Considering the high density of adult bones, this could be a time-consuming procedure. viagra plus

Intramuscular administration is an effective administration route of epinephrine for anaphylaxis, but it requires 5 minutes to reach a peak plasma level, and its maximum plasma level is not thought to be enough for CPR. Intratracheal administration is thought to be the most effective alternative administration route; however, most dentists have not been trained to perform expeditious endotracheal intubation in emergency situations. Therefore, an administration route that is appropriate to the education and training that most dentists receive is obviously necessary.

Because the nasal mucosa has the advantage of drug absorption from a rich blood flow and no first-pass effect, it has been used as an administration route for hypotensive drugs and premedication before anesthesia. However, because epinephrine has a strong va soconstriction effect on local blood vessels, a sufficient increase in its concentration in blood is not obtainable by topical administration. Because dental needleless injectors like the SyriJet can administer drugs in tissue by applying them under pressure, the possibility exists that they can transfer a sufficient amount of epinephrine into the blood before its vasoconstrictive effects occur. Actually, as described in the “Results” section, epinephrine concentration in the blood reached a peak 15 seconds after administration. This showed that pressure administration from the nasal mucosa could expeditiously transfer an amount of epinephrine sufficient to cause a rise in blood pressure.

The primary advantages of using the nasal mucosa as an alternative emergency administration route are the minimal training required and the use of emptied local anesthetic cartridges filled with epinephrine. This method can be immediately performed in dental clinic rooms where preparation for an emergency is not always the same as in operating rooms or intensive care units. Moreover, because dentists use this method when performing treatment in the facial region, they can perform this method with less hesitation in this region compared with other regions (eg, intracardiac administration). Also, severe complications did not occur. (Possible complications caused by injection pressure and the high concentration of epinephrine can occur; however, only a small amount of bleeding was observed in the study group.) The application of this method to patients with asthma or allergic reaction may also be considered, except for severe cases that require endotracheal intubation for airway maintenance.

Before this method is clinically applied, it may be useful to look more closely at some of its features. Although the baroreceptor reflex control of heart rate is generally suppressed by inhalation anesthetics, the suppression by isoflurane is weaker than that of halothane or enflur-ane. The heart rate regulation mechanism of the dogs’ baroreceptor reflex is suppressed by the inhalation of 2.6% isoflurane but not 1.3%.Only 1.0% isoflurane was used in this experiment.

Therefore, it may be considered that the unchanged heart rate was due to the heart rate regulation of the baroceptor reflex, as was observed in the clinical situation.
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The relatively short duration of epinephrine effects may make additional injection necessary. When additional administration is necessary, another site should be chosen because absorption via nasal mucosa cannot be expected due to the peripheral blood vessel contractile effect of the epinephrine administered already. Therefore, the opposite nostril should be chosen instead for injection. Another candidate for injection is the hard palate mucosa where the blood vessels are located between the injection site and bone and the pressure at injection does not escape.Finally, evaluation of the amount of epinephrine administered for a given condition is necessary. The absorption of epinephrine administered in the nasal mucosa greatly depends on local blood flow, and an approximately 60% increase in blood flow was observed under inhalation anesthesia compared with that during an unanesthetized state. During external cardiac massage, the amount of blood flow was approximately one third of that during normal circumstances.
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This experiment was performed under conditions in which blood flow was approximately 5 times greater (1/ [1.6 x 1/3]) than what was expected in external cardiac massage. Whichever administration route is selected during cardiac arrest, if effective cardiac massage must be performed to maintain at least a necessary minimal amount of blood flow for absorption and systemic distribution, resuscitation does not succeed. This method, in which drug absorption depends on blood flow in the nasal mucosa, is greatly influenced by decrease in local blood flow. Therefore, although 400 |xg was an effective amount in this experiment, it might be of questionable efficacy during cardiac arrest and CPR. Therefore, it is necessary to evaluate the effective dose of intranasal administration of epinephrine using experimental models with decreased blood flow in the nasal mucosa or cardiac arrest models.

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