Phenylephrine with anesthesia

Dyer RA, Reed AR, van Dyk D, Arcache MJ, Hodges O, Lombard CJ, Greenwood J, James MF. Hemodynamic effects of ephedrine, phenylephrine, and the coadministration of phenylephrine with oxytocin during spinal anesthesia for elective cesarean dehvery. Anesthesiology 2009 111(4) 753-65. 

The answer is d. (Hardman, p T36J The addition of a vasoconstrictor, such as epinephrine or phenylephrine, to certain short-acting, local anesthetics is a common practice in order to prevent the rapid systemic absorption of the local anesthetics, to prolong the local action, and to decrease the potential systemic reactions. Some local anesthetics cause vasodilation, which allows more compound to escape the tissue and enter the blood. Procaine is an ester-type local anesthetic with a short duration of action due to rather rapid biotransformation in the plasma by cholinesterases. The duration of action of the drug during infiltration anesthesia is greatly increased by the addition of epinephrine, which reduces the vasodilation caused by procaine. 

In brain slices, even though no anesthesia is present, there is a reduction in both noradrenergic and other inputs to these cells (e.g., from sensory systems) thus most of these neurons become silent. Consistent with this interpretation is the fact that all presumed serotonergic neurons we have tested in the brain slice are uniformly activated by norepinephrine or the < ragonist phenylephrine, applied either iontophoretically or in the perfusion medium (51). Similarly, in... 

The clinical uses of these drugs are associated with their potent vasoconstrictor action. They are used to restore or maintain blood pressure during spinal anesthesia and certain other hypotensive states. The reflex bradycardia induced by their rapid intravenous injection has been used to terminate attacks of paroxysmal atrial tachycardia. Phenylephrine is commonly used as a nasal decongestant, although occasional nasal mucosal... 

Procaine hydrochloride Novocain) is readily hydrolyzed by plasma cholinesterase, although hepatic metabolism also occurs. It is not effective topically but is employed for infiltration, nerve block, and spinal anesthesia. It has a relatively slow onset and short (1 hour) duration of action. All concentrations can be combined with epinephrine. It is available in dental cartridges with phenylephrine as the vasoconstrictor. 

When phenylephrine was used together with tetracaine in spinal anesthesia, 10 of 80 patients developed transient dysesthesia (SEDA-22, 155). Provocation of myocardial ischemia (17), acute edema of the lung (18), and ischemic colitis (SEDA-22, 155) were not so clear-cut. 

Phenylephrine is indicated in the treatment of vascular failure in shock, shock-like states, drug-induced hypotension, or hypersensitivity to overcome paroxysmal supraventricular tachycardia to prolong spinal anesthesia as a vasoconstrictor in regional analgesia and to maintain an adequate level of BP during spinal and inhalation anesthesia. Phenylephrine is a powerful postsynaptic alpha-receptor stimulant with little effect on the beta receptors of the heart (see also Figure 39). 

The shrinking of mucous membranes decreases operative bleeding while improving surgical visualization. Comparable vasoconstriction can be achieved with other local anesthetics by the addition of a low concentration of a vasoconstrictor such as phenylephrine (0.005%). Epinephrine, topically applied, does not prolong the duration of action of local anesthetics applied to mucous membranes because of poor penetration. Maximal safe total dosages for topical anesthesia in a healthy 70-kg adult are 300 mg for lidocaine, 150 mg for cocaine, and 50 mg for tetracaine. 

There have been many studies of the efficacy of phenylephrine in the marmgement of anesthesia-induced hypotension and comparisons with other pressor agents, mostly ephedrine and in many cases in women undergoing cesarean section. 

In 43 term parturients who were randomized to a bolus dose of ephedrine 10 mg with or without phenylephrine 40 micrograms during spinal anesthesia, the incidences of hypotension, defined as a systolic blood pressure below lOOmmHg or a fall of 20% from baseline, were 80% versus 95%, but the difference was not significant [3CF]. The authors concluded that adding phenylephrine to ephedrine did not improve the effect of ephedrine alone in preventing or treating hypotension in these cases. 

In 125 parturients who underwent cesarean delivery with spinal anesthesia, who were randomized to an intravenous infusion of phenylephrineephedrine in one of five different concentration ratios, the authors concluded that adding ephedrine to phenylephrine appeared to confer no advantage compared with phenylephrine alone [31 J. 

In 80 women who underwent cesarean section and were randomized to prophylactic phenylephrine (1.5 micrograms/kg plus a continuous infusion at 1.5 micrograms/kg/ minute) or ephedrine (0.1 mg/kg plus continuous infusion at a rate of 0.5 mg/kg/hour) immediately after spinal anesthesia, the overall incidence of hypotension was 11%, and there was no significant difference between the groups [39/f. However, phenylephrine was associated with more episodes of hypertension (28% versus 25%) and bradycardia (2.3% versus 0%). Umbilical cord blood parameters and Apgar scores were similar. After the end of the infusion there were episodes of hypotension in 72% of those who had received phenylephrine and 28% of those who had received ephedrine. 

In 132 women who underwent cesarean section, intravenous phenylephrine, ephedrine, or phenylephrine + ephedrine were given immediately after spinal anesthesia and adjusted according to the systolic blood pressure [41 ]. There were more episodes of hypotension and tachycardia with ephedrine... 

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