Effects of caudal block with mepivacaine on resting ventilation and ventilatory response to carbon dioxide in sedated children

Benefit and risks of local anesthetics in infants and children

Regional anesthesia has become a routine part of the practice of anesthesiology in infants and children. Local anesthetic toxicity is extremely rare in infants and children; however, seizures, dysrhythmias, cardiovascular collapse, and transient neuropathic symptoms have been reported. Infants and children may be at increased risk from local anesthetics compared with adults. Larger volumes of local anesthetics are used for epidural anesthesia in infants and children than in adults. Metabolism and elimination of local anesthetics can be delayed in neonates, who also have decreased plasma concentrations of alpha(1)-acid glycoprotein, leading to increased concentrations of unbound bupivacaine. Most regional anesthetic procedures in infants and children are performed with the patient heavily sedated or anesthetized; because of this, and because a test dose is not a particularly sensitive marker of intravenous injection in the anesthetized patient, detection of intravascular local anesthetic injection is extremely difficult. The same local anesthetics used in adult anesthetic practice are also used in infants and children. Because of its extremely short duration of action, chloroprocaine has been used primarily for continuous epidural techniques in infants and children. The use of tetracaine has generally been limited to spinal and topical anesthesia. Lidocaine (lignocaine) has been used extensively in infants and children for topical, regional, plexus, epidural and spinal anesthesia. The association between prilocaine and methemoglobinemia has generally restricted prilocaine use in infants and children to the eutectic mixture of local anesthetics (EMLA). Because of its greater degree of motor block compared with other long-acting local anesthetics, etidocaine has generally been limited to plexus blocks in infants and children. Mepivacaine has been used for both plexus and epidural anesthesia in infants and children. Because postoperative analgesia is often the primary justification for regional anesthesia in infants and children, bupivacaine, a long-acting local anesthetic, is the most commonly reported local anesthetic for pediatric regional anesthesia. Given the lower toxic threshold of bupivacaine compared with other local anesthetics, the risk-benefit ratio of bupivacaine may be greater than that of other local anesthetics. Two new enantiomerically pure local anesthetics, ropivacaine and levobupivacaine, offer clinical profiles comparable to that of bupivacaine but without its lower toxic threshold. The extreme rarity of major toxicity from local anesthetics suggests that widespread replacement of bupivacaine with ropivacaine or levobupivacaine is probably not necessary. However, there are clinical situations, including prolonged local anesthetic infusions, use in neonates, impaired hepatic metabolic function, and anesthetic techniques requiring a large mass of local anesthetic, where replacement of bupivacaine with ropivacaine, levobupivacaine or (for continuous techniques) chloroprocaine appears prudent.

The effects of epidural anesthesia on ventilatory response to hypoxia

STUDY OBJECTIVE

To evaluate the effects of epidural morphine on the ventilatory response to hypoxia in patients having abdominal surgery and to compare the effects of epidural lidocaine.

DESIGN

Open-label, randomized study.

SETTING

Shimane Medical University Hospital, Shimane, Japan.

PATIENTS

Sixteen consenting, unpremedicated ASA physical status I and II patients undergoing abdominal surgery.

INTERVENTIONS

Patients were administered 2 mg of morphine diluted in 10 ml of saline or 10 ml of 2% lidocaine from an epidural catheter that was inserted the day before surgery.

MEASUREMENTS AND MAIN RESULTS

On the day before surgery, ventilatory parameters consisting of minute expiratory volume (VE), tidal volume (VT), respiratory frequency (f), and oxygen saturation by pulse oximeter (SpO2) were measured during resting state and hypoxic challenge. The same measurements were repeated 30 minutes after the epidural injection before surgery. The slope of VE/SpO2 decreased significantly from 1.6 +/- 0.3 to 1.2 +/- 0.2 after epidural morphine, although ventilatory values such as f, VT, VE, and PaCO2 were unchanged. Epidural lidocaine produced no significant changes in ventilatory response.

CONCLUSION

Epidural anesthesia with morphine, but not lidocaine, reduced the ventilatory response to hypoxia indicated by VE/SpO2.