The use of a non-sedating antihistamine in a hyperbaric environment.

Abstract

Allergic symptoms and asthma have increased considerably over the past years. Pollen counts increase significantly in spring and early summer, causing symptoms involving the ear, nose and throat (ENT). Coincidentally, recreational scuba diving starts to peak at this time. Antihistamines may be taken by a diver to relieve ENT symptoms and prevent serious injury, especially where the diver has no particular wish to stop diving to allow for the infection or allergy to subside. However, antihistamines are associated with dry mouth and drowsiness. An additive effect or even potentiation of nitrogen narcosis, which causes cognitive or motor function decrements, is a reason not to recommend the use if antihistaminic drugs when diving. These recommendations are based on the theoretical pharmacological mechanisms of the drugs, which have not been verified with controlled clinical trails. One must also take into consideration the fact that in a hyperbaric environment, potentiation or attenuation of a drug may be an eventuality. Also, new effects may present themselves. Few studies (Sipinen et al., 1995; Taylor et aI., 2000) designed to test whether antihistamines aggravate nitrogen narcosis, cognitive or motor functions, or the appearance of cardiac arrhythmias have been carried out, and no such research has as yet been performed locally.

In fact, the taking of medication and diving is a very contentious issue. There are very few absolute guidelines in this regard. Generally, the use of medication, including over-the-counter (OTC) preparations such as antihistamines, while diving is not recommended. Minimal research has been carried out to determine alterations in pharmacodynamics and pharmacokinetics of medication in man under water or their effect in potentiating conditions like nitrogen narcosis, hyperventilation, hypothermia, and motion sickness. Thus, drawing from the above, and taking into account the increasing popularity of sport diving amongst the Maltese population, conducting a study to assess the effects of the administration of a non-sedating antihistamine (cetirizine) with pressure, provided some insight in this field of medicine which may prove useful to divers, medical practitioners and pharmacists alike. Such a study was aimed at: • evaluating the psychometric effects of antihistamines in a hyperbaric environment • evaluating whether these effects pose an added hazard to the risk of nitrogen narcosis Nitrogen narcosis affects mood, intellectual function, response to stimuli, balance and co-ordination, and the level of consciousness of the diver. It occurs as a diver is exposed to an increasing partial pressure of nitrogen and is of significant danger to the diver because it increase the risk of an accident and decreases the ability of the diver to cope with the emergency.

The project involved two separate studies. The first study focused on the evaluation of the effects of administration of antihistamines in 40 randomly selected fully qualified divers. A second study was conducted to elucidate information on drug-taking habits of divers using a questionnaire and involving 80 divers. The first study was a double-blind placebo-controlled type of study. Each subject was given a standard oral dose of an antihistamine or a placebo. After two hours had elapsed, blood was drawn from the subjects for subsequent analysis, and the subjects were subjected to four different psychometric tests under hyperbaria in a multi place hyperbaric chamber. The results thus obtained did not indicate any significant differences in performance between subjects under the effects of cetirizine and subjects that had been given the placebo. For some tests, however, differences were noted in the performance of the subjects with pressure. By means of the questionnaire, one could gain an insight to the drug-taking habits of a selection of local divers. It seems that preparations to relieve sinus congestion feature highly among the medications taken by divers. The interaction of such preparations and the underwater environment is also relatively common in these divers. No correlation was found between diving injuries and the drug-dive interaction. Physical and psychological fitness for diving has some basic requirements. Namely, divers must be able to equalise pressure readily in all body airspaces and divers must not be subject to impairment of consciousness, alertness, or judgement (Walsh, 1979). Thus, it is anticipated that the conclusions drawn from this study will go towards increasing the safety and pleasure of sport diving.