Raymond Kozody MD FRCP(C),

Key words
ANAESTHETIC TECHNIQUES: subarachnoid block; ANAESTHETICS, LOCAL: tetracaine; SYMPATHETIC NERVOUS SYSTEM, CATECHOLAMINES: epinephrine; SPINAL CORD: blood flow.
135 ± 2 138 ± 9 146 ± 7
7± 1 6± 1 6± 1
164 ± 26 167 ± 28 150 ± 27
178 ± 3 195 ± 13 175 ± 12
143 ± 7 108 ± 9* 113 ± 6 *
7± 1 10 ± 2 9± 1
5± 1 13 ± 2 11 ± 2
233 ± 19 229 ± 25 211+28
167 ± 12 161 ± 8 167 ± 14
n = 6 in each group. Results are Mean ± S.E.M. *p < 0.05 when compared to pre-injection measurements.
in the femoral artery and vein. A left inguinal incision was used for the retrograde insertion of a catheter through the femoral artery into the left ventricle, using continuous pressure monitoring. The position of the left ventricular catheter was subsequently validated by post-mortem examination. A Swan-Ganz thermodilution catheter was inserted into the pulmonary arterial circulation using the left jugular vein. Following the surgical preparation each animal was allowed to stabilize for 40 minutes. Statham transducers were used for measuring mean arterial blood pressure (MABP) and pulmonary capillary wedge pressure (PCWP). The transducers were calibrated to zero at the mid-thoracic level. Heart rate (HR) and MABP were continuously recorded, while PCWP was determined prior to and between flow determinations. Data was recorded using a Hewlett-Packard monitor (Model 7758C) and a recorder (Model 7758A). Cardiac output was determined in duplicate prior to flow determinations. The cardiac output was measured by the thermodilution of 5 ml of room temperature physiological saline using an Edwards CO Computer (Model 9520A). A variation of five per cent or less between cardiac output measurements was accepted. Core temperature was continuously measured using the thermistor on the thermodilution catheter.
Spinal cord and spinal dural blood flow in the cervical, thoracic and lumbosacral regions were measured in dogs using the radioactive microsphere technique. Measurements were taken before and 20 and 40 minutes after lumbar subarachnoid injection of one of the following: (1) physiologic saline; (2) tetracaine 20 mg or (3) tetracaine 20 mg with epinephrine 200 ixg. No significant change in spinal cord or spinal dural blood flow occurred following subarachnoid physiologic saline or tetracaine with epinephrine. Dogs receiving subarachnoid tetracaine demonstrated a significant increase in lumbosacral spinal cord, and thoracic and lumbosacral dural blood flow at 20 and 40 minutes following injection. Cervical dural blood flow was significantly increased at 40 minutes after subarachnoid tetracaine. Lumbar subarachnoid tetracaine (20 mg) produces a regional spinal cord and generalized dural hyperemia which is prevented by the addition of epinephrine (200 (xg).
From the Department of Anaesthesia, University of Manitoba, Winnipeg, Manitoba. Address correspondence to: Dr. Raymond Kozody, Department of Anaesthesia, Health Sciences Centre, 700 William Avenue, Winnipeg, Manitoba, Canada R3E0Z3. Supported by the Health Sciences Centre Research Foundation and the University of Manitoba Faculty Fund. CAN ANAESTH SOC J 1985 / 32: 1 / pp 23-9
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TABLE I injection
CANADIAN ANAESTHETISTS' SOCIETY JOURNAL Haemodynamic parameters in dogs prior to and following intrathecal
Groups Saline
MABP (mmHg)
PCWP (mmHg)
C.I. (ml-kg- •min~')
H.R. (beatstmin)
Pre-injection 20 min post-injection 40 min post-injection Tetracaine Pre-injection 20 min post-injection 40 min post-injection
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Raymond Kozody MD FRCP(C), Richard J. Palahniuk MD FRCP(C),
Maureen O. Cumming RN BSC
Spinal cord blood flow following subarachnoid tetracaine
Prolongation of tetracaine spinal anaesthesia through the use of epinephrine as an adjunct has been well documented.1"4 The mechanism of epinephrine induced prolongation of tetracaine spinal anaesthesia is however controversial. Classical theory has lead to the concept that prolongation of spinal anaesthesia by the use of epinephrine is through vasoconstriction of the regional circulation. Studies using intrathecal lidocaine and bupivacaine with epinephrine have shown that the duration of clinically useful spinal anaesthesia is not prolonged by the addition of epinephrine.4"6 These studies suggest that regional vasoconstriction may not be an important factor. Other studies suggest that epinephrine may augment spinal analgesia by a direct spinal neuronal antinociceptive mechanism.7'8 We recently demonstrated that lumbar subarachnoid epinephrine (200 jxg) did not affect the spinal cord circulation but did produce regional dural vasoconstriction.9 In view of the present uncertainty this study was undertaken to determine the effects of subarachnoid tetracaine with and without epinephrine on the spinal cord and spinal dural circulations. Methods Eighteen mongrel dogs of either sex weighing 15-32 kg (19.8 ± 4.4, mean ± S.D.) were studied. The animals were anaesthetized with pentobarbitone, 30 mg-kg"1 induction dose followed by a maintenance dose of 2-5 ing-kg^-hr" 1 . After tracheal intubation, the animals were ventilated using an Ohio Model 300 ventilator with 100 per cent oxygen at a tidal volume of 15 ml-kg" 1 . The respiratory rate was adjusted to maintain a PaCO2 of 35-43 torr. The University of Manitoba guidelines for the humane use of animals were followed. The surgical preparation consisted of a right inguinal incision for insertion of poly vinyl catheters