Effect of dopamine on hypotension induced by spinal anesthesia T. CABALUM. M.D. M. ZUGAIB, M.D. S. LIEB. M.D.

B. NUWAYHID. M.D.*

C. R. BRINKMAN III. M.D. N. S. ASSALI. M.D.

Lo., Angeles, Calijinnia Chronically instrumented, near-term pregnant sheep were subjected to autonomic blockade with spinal anesthesia. Systemic arterial pressure, heart rate, and uterine blood flow decreased and uterine vascular resistance increased during the spinal blockade. Infusion of dopamine during the spinal hypotension corrected the disturbed circulatory parameters. These data provide evidence that: (1) the peripheral circulation of the near-term pregnant sheep is as sensitive as that of pregnant women to autonomic blockade, (2) the sensitivity is probably related to factors other than the changes in venous pressure in areas below the pelvis, and (3) dopamine represents a useful agent in the management of spinal hypotension. (AM. J. OeSTET. GYNECOL. 133:630, 1979.)

PREVIOUS STUDIES have shown that the circulation of near-term pregnant women and sheep is extremely sensitive to various modes of autonomic blockade. 1· 7 Intrathecal anesthesia or intravenous administration of ganglionic blocking agents such as trimethaphene (Arf(mad) or tetraethylammonium chloride (TEAC) results in a fall in the arterial blood pressure, heart rate, cardiac output, and regional blood flows. The mechanisms for this reponse are thought to be related to loss of venomotor tone, leading to venous pooling, decreased venous return to the heart, decreased cardiac output, and hypotension.'- 7 We have recently demonstrated in normotensive pregnant and nonpregnant sheep that dopamine infusion produces a rise in the arterial and venous pressures. accompanied by an increase in the cardiac output and uterine blood flow. 8 Since the basic patho-

From the Department of Obstetrics and GynmJlogy, University of California, Los Angeles, School of Medicine. Presented at the Twenty~fitih Annual Meeting of the Soci,ety for Gynecologic lnvestigatwn. Atlanta, Georgia, March 15·18, /978. Reprint requests: Dr. N. S. Assali, Department uf Obstetrics and Gynecology, University of Calzjornw, Lu.1 Angeles, School of Medicim, Los Angeles. Califomin 90024. *Recipient of Career Development Award HIJ 110253-0 I.

630

genetic factor of circulatory shock that follows autonomic blockade in pregnant subjects is the loss of venomotor tone. the action of dopamine on the venous circulation and cardiac output appears to render it a suitable agent in the management of spinal hypotension. The present studies were designed to test this hypothesis by observing the hemodynamic response to dopamine infusion in pregnant sheep subjected to spinal anesthesia.

Material and methods Studies were carried out and completed on nine pregnant ewes (gestations of I 08 to 120 days) chronically instrumented for measurement of arterial pressure, heart rate, uterine blood flow, and blood respiratory gases and pH by techniques previously reported. H," Essentially, a catheter was inserted into the carotid artery and served for monitoring the arterial pressure and heart rate and for collecting blood samples anaerobically. Another catheter was inserted into the internal jugular vein and served for drug administration. An electromagnetic flow transducer was implanted around the common internal iliac artery to monitor the blood flow to both uterine horns. A postoperative recovery period of at least one week was allowed before any study was performed. 0002-9378/79/060630+05$00.50/0

©

1979 The (

V. Mosby Co.

Volume 133 Number 6

Effect of dopamine on spinal anesthesia-induced hypotension

At the time of the experiment, the ewe was brought to the operating room and was placed on a special table on her side. A small catheter was inserted into the subarachnoid space for intrathecal anesthesia. The experimental protocol comprised the follo\ving four periods: ( l) The control period lasted 30 to 40 minutes, during which the circulatory parameters were recorded every 2 to 3 minutes, while blood respiratory gases and pH were analyzed once. (2) The spinal hypotensive period then followed, during which doses of Pontocaine were injected intermittently through the spinal catheter with the goal to achieve a 30% to 40% fall in the blood pressure: the ewe was allowed to remain in this hypotensive state for 15 minutes. During this period, the circulatory parameters were recorded continuously while blood respiratory gases and pH were determined once. (3) The dopamine period followed, during which this agent was infused intravenously, starting with a rate of 2.5 J..tg/kg/minute and increased in a stepwise manner until a rate of 25 J..tg/ kg/minute was reached. Arterial pressure, heart rate, and blood flow were recorded continuously whereas blood respiratory gases and pH were analyzed once or twice. (4) The experiment ended with a recovery period during which dopamine was discontinued and each animal was observed for an additional 30 to 60 minutes. Pressure, Ho,v. hearl rate, and blood respiratory gases and pH were computed by techniques previously described. H. " Results

Conditions of the animals. All ewes had recovered from surgery and had resumed their normal activities and feeding habits prior to the initiation of the experiments. The control values for the various circulatory parameters and blood respiratory gases were within the ranges of data previously published. 8 • 9 Effects of spinal anesthesia. In Fig. 1 values are presented which were obtained from eight animals for arterial pressure, uterine blood flow, and heart rate in the control, spinal hypotension, and dopamine infusion periods; the average of several readings recorded during the recovery period is also depicted. These eight animals were grouped together because their arterial pressure fall in response to spinal anesthesia ranged from 25~~ to 457r. All circulatory parameters were relatively stable during the control period. Foilowing spinal anesthesia, the mean arterial pressure fell significantly and remained at a level \vhich \Vas about 30o/c, belov~' control values for the 15 minutes of the spinal hypotensive period (Fig. 1 and 2).

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Effect of dopamine on hypotension induced by spinal anesthesia.

Effect of dopamine on hypotension induced by spinal anesthesia T. CABALUM. M.D. M. ZUGAIB, M.D. S. LIEB. M.D. B. NUWAYHID. M.D.* C. R. BRINKMAN III...
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