It appears that Russian special forces used aerosolised fentanyl and gaseous halothane during a siege to end last month's terrorist occupation of a Moscow theatre. The combination seems to have been designed to stun the terrorists with the fentanyl, a potent synthetic opiate, and then to push them to unconsciousness with the halothane, a volatile halogen derivative.

Many questions arise, but we focus on four particular ones. The answers are based on information from commonly known sources as well from classified ones, explaining the lack of literature citations in this article.

Did the Russian authorities try to cover up? For several days after the siege, Russian authorities declined to identify the gas, earning criticism from doctors who had to guess what sort of treatment to give to innocent victims caught up in it.

Previous contacts with Russian medical practitioners have shown that, in the past, their approach to medicine has been more pragmatic than in most Western countries. One could see a link with the former Soviet importation system of "Western" drugs, without proper clinical, pharmacological or toxicological knowledge. It is therefore likely that the term "ignorance" is more appropriate than "cover-up" in the handling of the victims.

Emergency specialists claim that lack of information and antidotes does not prevent physicians from treating patients symptomatically. Besides, the effects of fentanyl should have been obvious since surgeons use it daily. Medical support seemed to be underestimated and not well co-ordinated. This could be deduced from the way people were carried out of the theatre, the apparent lack of sufficient ambulances, and the rather unprepared admittance at various hospitals.

It can be concluded that the complexity of the medical support required was underestimated in the preparation of the action to end the occupation. This endorses the evidence that medical tactics should be fully integrated in the planning of such operations.

Hostages reported witnessing assault troops administering antidotes — most probably naloxone — but they hesitated about the number of syringes used and the way the antidote was administered. The presence of some anaesthetists or paramedics at the scene with mayo cannulae and respiration bag devices could have saved the lives of many of the victims.

Was the choice of fentanyl and halothane appropriate? An "incapacitant" is a chemical agent which produces a persisting disabling condition for hours or days. It should:

• Be highly potent at low doses

• Be able to alter the higher regulatory activity of the central nervous system (CNS) during several hours or days.

• Not be life threatening or produce permanent injury in effective reasonable doses

These criteria should eliminate opiates since they show a low margin of safety. In high doses, fentanyl can cause severe respiration depression and lead to coma — a condition seen in many of the hostages carried out of the theatre.

Furthermore, it loses its incapacitating potency quickly, explaining the need for halothane for the final knock-out. Odourless and non-combustible, halothane works through the nervous system. In regular anaesthesia its use has been limited because of its hepatotoxicity. In larger concentrations, it can provoke respiratory failure and cardiac problems. According to the World Health Organization it should only be applied with artificial respiration equipment at hand. The use of a massive amount in such a closed space seems a deadly gamble. In our opinion, a better choice would have been sevoflurane.

Since fentanyl and halothane enforce each other's respiratory depression, the high-dosed combination of both compounds might be considered a serious misjudgement.

Is there evidence that certain gases could be used in a safe way in similar circumstances, incapacitating terrorists but without serious long-term effects for the weakened, dehydrated and hungry hostages? First, for clarification, the fentanyl was aerosolised, ie, not a gas. In order to make a proper choice of incapacitant, it is important to look to its safety margin (ie, the ratio of lethal to incapacitating dose). But if a quick effect is desired, high doses tend to be used. In a building such as the Moscow theatre, there are several factors that influence efficiency:

• As the nebula disperses, the concentration of the incapacitant reduces and this means that several sources of incapacitant are needed

• The relative weight of the gas towards air might provoke different concentrations of incapacitant in corners and angles

• The recipients differ with respect to age, sex, state of general health, fatigue, dehydration and panic or fatalism (which influence respiration)

• If the aerosol takes up a large volume it can push away the air, resulting in asphyxia

• There needs to be quick evacuation of the stunning compounds after the assault

There are some compounds that could be appropriate for use in similar circumstances. CNS depressants, such as 3-quino-clinidinyl benzilate (BZ), block the peripheral and central muscarinic action of acetylcholine, resulting in a disruption of the cognitive functions. Hence, forces using them have to wear protective clothing. Less than 1mg of BZ produces delirium for days. The safety margin (ratio of lethal to incapacitating dose) in people is estimated to be at least 30. BZ-intoxication could however lead to random unpredictable behaviour.

CNS stimulants, such as D-lysergic acid diethylamide (LSD) cause excessive neuronal activity by facilitating neurotransmission, overloading the higher regulatory centres, inhibiting concentration and appropriate action and causing indecisiveness.

As little as 50µg of LSD produce dramatic psychological changes. Doses of 2–5mg have been taken without harm (apart from, sometimes, convulsions) and animal studies suggest that much higher doses may be tolerated. Initial effects appear within a few minutes of inhalation. The question of long-term effects is unresolved, but single exposures to doses in the clinical range appear unlikely to cause permanent biological damage.

But even for those products, too many factors can influence the activity and assessment of the variable sensitivities in individuals is impossible.

Can individuals carry antidotes to protect themselves against such attacks? This is really not realistic. Many agents might be used, some with specific antidotes, some without.

Even if one had a battery of antidotes, how could one know which agent has been used, let alone the probable lack of time one would have just to unwrap it.

In general, there are no detector systems for these agents, only limited field laboratory methods for their identification in environmental samples. Therefore, initial diagnosis rests almost entirely upon clinical acumen. Entry of aerosols through the respiratory tract makes respirators essential, but some agents may as well be absorbed percutaneously.

To conclude ...

if the Moscow rescue operation had been performed with better medical involvement, the number of victims might have been much lower. However, had nothing been done, the outcome may have been worse. The Russian special forces were surely facing a dilemma.

ACKNOWLEDGEMENTS Thanks are due to Dr Col Bellanger of the Belgian Medical Service HQ, and Dr Jean Pirson, chief of the burns unit at the Belgian Military Hospital.

  * PDF files on PJ Online require Acrobat Reader 4 or later.