4. Circulation drugs for pre-hospital emergencies – May 2015
What is an emergency responder without tools of the trade with which to render assistance? And when it comes to tools of the modern trade, what better than emergency drugs. And when it comes to pre-hospital emergency drugs, what better than those that work on the cardiovascular system. ‘Medicine for nurses’ by W. Gordon Sears written back in 1935 had just this covered.
Drugs acting on the circulatory system
- Drugs acting on the heart. The most important of these are the digitalis group. Their action has been discussed in connection with atrial fibrillation and it has been seen that they depress the conducting tissues of the heart (i.e. the bundle of His), slow the pulse and increase the force of ventricular contraction. A tincture of digitalis 5-15 minims is required.
- Drugs which raise the blood pressure. These may act either by increasing the force of the cardiac contraction or by constricting the blood vessels and are circulatory stimulants, given by injection, e.g. strychnine, adrenalin, pituitrin, camphor. Proprietary preparations include cardiazol, coramine and icoral.
- Drugs which lower the blood pressure. These act by dilating the blood vessels and are used especially in angina pectoris and hypertension, e.g. amyl nitrate 2-5 minims by inhalation, liquor tinitratis ½-1 minims.
- Drugs which arrest haemorrhage. Those which are applied locally are called styptics and include the astringents, e.g. tannic acid, alum, iron perchloride, silver nitrate and also adrenalin. Recently, snake venom obtained from the viper has been found valuable when used in a diluted form. When applied to a mucous membrane or cut surface they cause contraction of the blood vessels.
- Those given internally include opium and morphia which check restlessness. To check bleeding from the pregnant uterus, ergot or pituitrin are given because they have a special action on this organ causing its muscle to contract.
The ambitions haven’t changed much over the eight decades. Act on the heart, modify heart rate, increase contractility, raise the blood pressure, lower the blood pressure all find places in current guidelines. But do any of the drugs? Adrenalin is still a mainstay. Digitalis is fading fast but not gone. Nitrates are still a big player.
Arresting haemorrhage is still looking for a great saviour and snake venom hasn’t really taken off in this role. Viper venom is good at causing coagulation. So good in fact that without antivenom it will lead to disseminated intravascular coagulation. Tranexamic acid interferes with breaking down fibrin which forms a strong part of a clot along with platelets. It may have a bright future in pre-hospital bleeding management.
Tannic acid may be better known as a wood stain but unbelievably still hasn’t lost its anti-bleeding and wound dressing roles entirely. Silver nitrate long held an antiseptic role in wound management as well even given its propensity to turn skin black. Its use was widespread before antibiotics. It was used to treat eye infections though dosing was important. The side effect of excess chemical was blindness! As for strychnine, it is difficult to get over the lengthy discussions of its toxicity to consider that it once had any medicinal purpose.
What does retain its anti-bleeding role is adrenalin though having widespread uses in this regard. Pituitrin may have been overtaken by purer forms of oxytocin but it also remains an essential part of reducing post partum bleeding.
Jeff Kenneally www.prehemt.com