Malcolm J Boyle

A dramatic drop in blood pressure following prehospital GTN administration
Emerg Med J 2007; 24: 225-226 [Abstract] [Full text] [PDF]

ksanyal01{at}doctors.org.uk Kaushik Sanyal K Sabanathan

Lowering of blood pressure is a reflex phenomenon after GTN ingestion.GTN is a nitric oxide donor The response is due to increase in cGMP level. The metabolic consequence of this bio activation depends on the chemical structure. This is a systemic arterial response, with some effect on the platelet aggregation but no expression of the adhesion molecule. The other hypothesis is that it activates ATP sensitive K+ channel. Low blood pressure is due to decrease venous return .In case of coronary circulation it targets large vessel and prevents coronary steal. The presence or absence of level of GTN in blood after sublingual administration is via a large volume of distribution and rapid rate of total body clearance which depends not only on liver, but also other organs for elimination.Bezold Zarisch reflex states that cardio-pulmonary and carotid –aortic reflex in an intact vagii serves as a defence mechanism .In this circumstances of hypotension and bradycardia needs restore of blood volume deficit and venous return. This choice could be atropine, ephedrine.

mark.mallet{at}ruh-bath.nhs.uk Mark L Mallet

In our practice this vagally-mediated response to sublingual GTN is not uncommon, and perhaps occurs more frequently in nitrate-naive patients. Indeed this is the basis for its use in head-up tilt testing, where it increases the sensitivity of the procedure to induce vaso-vagal syncope. The traditional attribution of this response to the 'Bezold- Jarish' reflex is now considered unlikely, although credible alternative explanations are few! The apparent use of aspirin to treat this patient's hypertension is also worthy of comment.