|Anesthetics always pose some risk to the mare and foal. Most drugs given to broodmares can have potential adverse cardiopulmonary effects on the fetus. Therefore, administration of the anesthetic agent least likely to compromise the mare and foal is recommended. The goals of general anesthesia are: provide narcosis, relieve maternal pain, have minimal effect of anesthesia on maternal and fetal hemostasis, have minimal anesthetic time and provide for rapid, safe maternal and neonatal recovery.
Following are important considerations regarding anesthesia of the mare.
It is ideal to give sufficient fluids to stabilize the mare before anesthetic induction.
Administration of broad-spectrum systemic antibiotics prior to surgery is indicated since contamination is common when performing a C-section. Intravenous penicillin (20,000 IU/kg) and gentamicin (6.6 mg/kg) are recommended.
Flunixin meglumine (0.44 mg/kg body weight) can be administered intravenously if endotoxemia is a concern.
Pre-anesthetic agents given to the mare should cause minimal depression of the foal. Xylazine is preferred over a promazine derivative as blood pressure is less likely to be depressed. The recommended dosage of Xylazine is 0.25-0.5 mg/kg IV or 0.5-1.0 mg/kg IM. Xylazine does result in some bradycardia.
An IV infusion of guaifenesin (glycerol guaiacolate, GGE) at 5 percent to 10 percent via large-bore needle or a 12 or 14 gauge catheter followed by a bolus administration of 1.5 to 2.0 mg/kg ketamine is used for anesthetic induction. Alternatively guaifenesin and 1.5 to 2.0 grams of thiamylal sodium may be used.
A relatively insoluble inhalation and anesthetic gas such as isoflurane or sevoflurane should be used to maintain anesthesia. Advantages of gas anesthetics are that they are short-acting, they tend to increase cardiac output and they are less likely to promote uterine bleeding. Halothane and oxygen used to maintain anesthesia increase uterine incisional bleeding and are not recommended.
Once anesthetized, the mare should be monitored as she becomes recumbent. At this time, aseptic preparation should begin immediately.
Intra- and post-operative analgesia are important considerations as part of the C-section. Morphine can be administered intraoperatively to decrease surgical and postoperative pain. The recommended dose is 1 mg/kg in a constant rate infusion or in a bolus given over a 5- to 10-minute period. A constant rate infusion of lidocaine (0.05 mg/kg/min) may be used in conjunction with the morphine. While some morphine is transferred to the fetus, this is not typically of great concern. Subcutaneous injection of 15 to 20ml of bupivacaine in the incision line at the end of surgery may be done. This reportedly decreases post-surgical pain and may allow the foal to nurse without causing added discomfort to the surgical site of the dam.
Source: Ashlee Othick, Ted Stashak (2004): Handling C-section: indications and considerations. In: DVM Newsmagazine Mar 1, 2004; www.dvmnewsmagazine.com/dvm
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