The Severity Of Hypotension Comparing Three Positions During Spinal Anesthesia For Cesarean Delivery

Spinal anesthesia is the most commonly used anesthetic for cesarean delivery. In part, this
is due to the ease of administration, reliability and low rates of adverse effects.
Additionally, the avoidance of general anesthesia allows the parturient to participate in
the birth experience, despite being in surgery.

Although hyperbaric local anesthetic solutions have a remarkable record of safety, their use
is not totally without risk. The side effects of spinal anesthesia are well described, but
most notably include hypotension (low blood pressure). Spinal hypotension is primarily due
to the vasodilatory effects of local anesthetics, and would occur in virtually all women if
not prevented or treated.

The incidence of hypotension in both the literature and in clinical practice ranges from 30%
to 50% of all patients. Recent literature using a continuous, non-invasive blood pressure
monitor suggests that hypotension occurs with greater frequency and may be associated with a
higher incidence of adverse effects to either mother or fetus. The incidence and degree of
hypotension have been associated with fetal acidosis, which is a sign of either poor
perfusion of the placental bed, or increased metabolism due to the blood pressure
medications.

The most effective treatment for spinal hypotension is uterine displacement using a hip
wedge; the use of a hip wedge after spinal anesthesia is a standard of care. Other
treatment, including fluid administration of either crystalloid or colloid, are either
partially effective, clinical impractical, or result in administering large doses of
medications that may have negative effects on the fetus.

Epidural anesthesia is associated with a reduction in the incidence and severity of
hypotension compared with spinal anesthesia. This is believed to be due to the slower onset
of sympathetic blockade with epidural anesthesia; this slow onset allows the physiologic
compensation to changes in blood pressure. Unfortunately, the slower onset and lower
reliability of epidural anesthesia prevents routine use in clinical practice for cesarean
delivery.

The investigators hypothesize that the position patients are in during spinal placement
might play a role in the severity of maternal hypotension. Interestingly, very few studies
have investigated this posibility. Gori, et al. (1) studied influence of seated versus
lateral positioning for spinal placement in Cesarean section. They found no significant
differences in onset times, Bromage score for motor block, recovery dynamics, and use of
ephedrine in two different positions; however, they did not compare the incidence and
severity of spinal hypotension. Yun, et al. (2) found that the severity and duration of
hypotension were greater when hyperbaric bupivacaine and fentanyl were induced in the
sitting position compared to lateral.

Of notice, in all these studies, the authors focused on the immediate positions when the
spinal mediation was injected; none has examined the effect of positioning after injection
during phase when spinal anesthesia is rising.

Density differences between intrathecal injectate and CSF may explain the observed postural
differences in extent of sensory block. Thus, the height of spinal anesthesia blockade could
be affected by patient positioning during and after spinal injection. A small incline in
positioning immediately after spinal injection may slow the rise of spinal blockade without
affecting the duration of spinal anesthesia. In the current protocol, the investigators
hypothesize that by slowing the rise of spinal anesthesia, the investigators might reduce
the severity of hypotension.

Inclusion Criteria:

- Singleton pregnancy

- Term gestation

- Scheduled cesarean delivery

- Spinal anesthesia for delivery

Exclusion Criteria:

- Significant fetal concerns

- Polyhydramnios

- Macrosomia

- Morbid obesity (BMI >40)

- Chronic hypertension

- Gestational hypertension

- Preeclampsia

- Type 1 diabetes

- Contraindications to spinal anesthesia