Hypotension is the most common complication of regional blockade. A systolic blood pressure of less than 100 mmHg, or a fall of greater than 30% should be considered significant (1). Hypotension usually results from the physiologic effects of sympathetic blockade on the cardiovascular system and will be exacerbated by aortocaval compression (Figure 28.1) (Chapter 28) or reverse Trendelenberg positioning. It is important to bear in mind the other possible causes of a low blood pressure in the parturient who has a functioning epidural block (Table 6.2).

The incidence of hypotension can be markedly reduced by the employment of preventative measures. A reduction from 79%-100% to 0-10% has been demonstrated as a result of the use of the left lateral position, intravenous preloading, and vasopressor therapy (2, 3).

The management of hypotension should be approached in three stages:

1. Commence supportive measures to stabilise maternal blood pressure: (Table 6.1)
Untreated hypotension will be poorly tolerated by the mother. Secondary complications of organ hypoperfusion may result. These include loss of consciousness with associated hypoventilation, regurgitation and cardiac dysrhythmias. Acidosis may be severe. In shocked patients, hypotension may become self-perpetuating. The fetus suffers the same risks. Supportive measures should be instituted early regardless of the cause.

2. Consider possible causes of hypotension in the mother: (Table 6.2)
Sympathetic blockade is the most predictable cause of hypotension in a patient who has recently had a form of neuraxial blockade established. Other causes are possible and must be considered. After the delivery, the important causes of post-partum haemorrhage should be borne in mind (Table 74.1).

3. Maintenance of the welfare of the fetus: (Table 6.3)
Uterine blood flow is poorly autoregulated and as such is strongly dependent upon maternal mean arterial blood pressure. If hypotension occurs in the mother, her cardiovascular reflexes will act to shunt blood away from non-vital organs (including the uterus). This has the effect of restoring central blood pressure as a means of preserving flow to the vital organs of brain and heart. Vasoconstriction will occur in non-vital organs because their vasculature is richly endowed with alpha adrenoreceptors. Uterine blood flow falls in direct proportion to the decrease in maternal blood pressure. Hypotension that appears to be well tolerated by the mother may be causing hypoxaemia and asphyxia in the fetus. It has been demonstrated that infants of hypotensive mothers ( Mean Arterial Pressure < 70 mmHg) whilst achieving normal Apgar scores (Table 35.1) had weak rooting and sucking reflexes for a period of two days after birth (4).

References:
1. Norris M: Obstetric Anesthesia. Lippincott, 1993, p616

2. Kang YG, Abouleish E, Caritis S: Prophylactic intravenous ephedrine infusion during spinal anesthesia for cesarean section. Anesth Analg 1982;61:839

3. Clark RB, Thompson CH: Prevention of spinal hypotension associated with cesarean section . Anesthesiology, 1976;45:670

4. Hollmen AI, Joupilla R, Koivisto M: Neurologic activity of infants following anesthesia for cesarean section. Anesthesiology 1978 248:350