HEART RATE RESPONSE TO AN I.V. TEST DOSE OF ADRENALINE AND LIGNOCAINE WITH AND WITHOUT ATROPINE PRETREATMENT

In order to evaluate the sensitivity of an adrenaline test dosefor detecting intravascular injection and the effect of atropinepretreatment, 90 ASA physical status I and II patients wereallocated randomly to two groups, to receive i.v. saline 1 ml(n = 46) or i.v. atropine 0.5 mg (n = 44). Five minutes later,all patients received an i.v. test does of 2% lignocaine 3 mlwith adrenaline 15 µg at a rate of 1 ml s^–1. Thegroups were similar with respect to basal heart rate (HR). HRremained unchanged after saline injection, but increased slightly5 min after atropine injection (mean 78 (SD 15) beat min^–1vs 87 (20) beat min^–1 (P <0.05). After the test doseof lignocaine with adrenaline, HR increased significantly inboth groups at 30 s, 1 and 2 min, and remained increased at3 min in the atropine group. The maximum increase in HR wasgreater in the atropine group than in the saline group (31 (4)beat min^–1 vs 26 (11) beat min^–1 (P < 0.05).However, when individual maximum HR changes are considered,five patients in the saline group and four in the atropine grouphad an increase 10 beat min^–1, and three patients in thesaline group had no change or a decrease in HR. Defining a positiveresult to a test dose as an increase in HR of > 10 beat min^–1,the sensitivity of the adrenaline test dose was 83 (5.5)% inthe saline group and 91 (3.5)% in the atropine group (ns). Thusa test dose containing 2% lignocaine 3 ml and adrenaline 15µg was not very sensitive for detecting intravascularinjection, as moderate or false negative responses occurredfrequently.