To the Editor:—
In our routine practice, we have observed an apparent association between choice of vasopressor used during spinal anesthesia for cesarean section and rostral spread of spinal blockade to cold sensation. We are not aware of such an association having been reported previously.
For cesarean section, we routinely use a needle through needle combined spinal epidural technique at L3/4. Two ml of plain spinal bupivacaine 0.5%, combined with 20 μg of fentanyl, is given in the sitting position, and 10 ml of epidural saline is given via the Tuohy needle, before the epidural catheter is passed. The patient is then placed in the supine position with left lateral tilt. This produces effective spinal anesthesia for most patients without the need to top up the epidural, but approximately 25% of patients develop cervical level neural blockade to cold sensation. However, we have observed that when we use an infusion of phenylephrine to prevent hypotension, the incidence of cervical level neural blockade to cold sensation seems to be lower than when we use a combination of phenylephrine and ephedrine (in a ratio of 100 μg:3 mg, respectively).
This unexpected observation has led us to retrospectively analyze the results from a recently published, randomized, double-blind study from our hospital. 1In that study we compared phenylephrine (100 μg/ml) (phenylephrine group), ephedrine (3 mg/ml) (ephedrine group), and a combination of phenylephrine (50 μg/ml) with ephedrine (1.5 mg/ml) (combination group), given by infusion during spinal anesthesia for elective cesarean section in low-risk, term pregnancies. Four spinal anesthetic techniques were used in the study, and randomization to group was stratified for each anesthetic technique. Technique 1: 2.5 ml of spinal hyperbaric 0.5% bupivacaine with 20 μg of fentanyl, given in the sitting position. Technique 2: 2 ml of spinal levobupivacaine 0.5% with 20 μg of fentanyl, and 10 ml of epidural saline, given in the sitting position. Technique 3: 2 ml of spinal levobupivacaine 0.5% with 20 μg of fentanyl, given in the left lateral position. Technique 4: 2.5 ml of spinal levobupivacaine 0.5% with 10 μg of fentanyl, given in the left lateral position. Spinal anesthetics were performed at L3/4 and patients were then placed supine with left lateral tilt. Table 1shows the number of patients with cervical level neural blockade to cold sensation for each vasopressor group. Neural blockade to cold sensation was assessed using ethyl chloride spray and was recorded at the time of skin incision. There was no difference in the spinal-skin incision interval for the vasopressor groups. All patients with cervical level neural blockade to cold sensation had good hand grasp strength, and none had respiratory difficulty.
The incidence of cervical level neural blockade to cold sensation was lowest in the phenylephrine group and highest in the ephedrine group. For 6 of the 14-ephedrine group patients with cervical level neural blockade to cold sensation the level was above C4. These observations suggest that choice of vasopressor may affect rostral spread of spinal anesthetic. Increased epidural volume can enhance spread of spinal anesthetic. 2Perhaps phenylephrine causes greater epidural vein constriction than ephedrine. This may decrease enhancement of spread of spinal anesthetic by engorged epidural veins of pregnancy. However, our observations are based on retrospective data analysis. The hypothesis that choice of vasopressor therapy can affect the spread of spinal anesthetic and, if so, the mechanism and its clinical significance, needs to be examined in well-designed prospective studies.