Introduction

Cesarean section (C-section) is the most common abdominal surgery performed in small ruminants.¹ Incidence can vary with indication and by geographic location, with some reports stating 482 of 15,584 (3%) of small ruminant pregnancies.^2–4 Several methods for C-section have been described, including ventral midline, paramedian, and ventrolateral approaches under general anesthesia; but more often, the procedure is performed in standing or sedated ruminants via a left paralumbar fossa laparotomy or left oblique laparotomy.⁴ The most common reason for C-section in goats is failure of cervical dilation (“ringwomb”), but fetal malpositioning, fetopelvic size disproportion, fetal abnormalities, and pregnancy toxemia are also reported.⁴

Goats are poor candidates for general anesthesia, as C-sections are often performed on an emergent basis without holding the animal off feed, which predisposes them to regurgitation and aspiration pneumonia⁵; these, in turn, can prolong hospitalization, increase cost to the owner, and potentiate loss of life in severe instances. Furthermore, administration of anesthetic agents such as propofol or propofol-sevoflurane have been shown to induce substantial hypotension in the fetus and reduce uterine activity in the dam.⁶

Common methods for flank desensitization in small ruminants include local incisional blocks, inverted-L blocks, and proximal and distal paravertebral blocks.⁷ Additionally, epidural analgesia can be used; however, these can have a prolonged duration of sensory and motor blockade, resulting in goats being unable to stand for up to 3 hours for lidocaine⁸ and 11 hours for bupivacaine.⁹ In small ruminants, the subarachnoid space is easily accessed at the lumbosacral intervertebral space, and drugs administered at this site exert local action in the substantia gelatinosa layer of the dorsal horn of the spinal cord.¹⁰ The spinal cord of the goat extends beyond the lumbosacral junction,¹¹ which can result in inadvertent subarachnoid injection of a higher dose of anesthetic when epidural injection is being attempted.¹² It is then more practical to intentionally perform a subarachnoid injection with an appropriate dose of anesthetic, and use the presence of the cerebrospinal fluid as a definite indicator of successful injection. Subarachnoid injections exert a local effect in the dorsal horn of the spinal cord, requiring less drug to be administered to achieve the same analgesic effect as systemic administration. As such, they are also associated with fewer systemic effects and a longer duration of action and are less affected by peridural fat and blood vessels, compared to epidural administration.¹⁰ However, there is a paucity of veterinary literature evaluating the use of intrathecal analgesics in goats undergoing C-sections.

The objective of this case series was to evaluate the analgesic efficacy of lumbosacral intrathecal lidocaine for analgesia in goats undergoing C-sections via left paralumbar fossa celiotomy. We hypothesized that intrathecal lidocaine would provide adequate analgesia of sufficient duration for C-section in goats, with a rapid return of hind limb motor function.

Materials and Methods

Medical records of goats undergoing C-sections performed at the University of Florida Large Animal Hospital from January 2020 to November 2021 were identified and reviewed. Patients were excluded if intrathecal lidocaine was not the primary method of analgesia, the surgery was performed under general anesthesia, or if anesthetic, surgical, or discharge records were incomplete or missing. Patients were categorized based on the previously described American Society of Anesthesiologists’ system on a scale from 1 (clinically normal) to 5 (moribund, not expected to survive).¹³ Goats were sedated with midazolam (0.2 mg/kg) and either butorphanol (0.05 mg/kg) or methadone (0.2 mg/kg) IV, administered flow-by oxygen via face mask (7 L/min), and restrained in sternal recumbency with the hind legs pulled slightly cranially. Subjects were administered preservative-free 2% lidocaine (1 mg/kg) intrathecally at the lumbosacral space using a 20-gauge 3.5-inch (0.9 X 90-mm) spinal needle under aseptic technique (Figure 1). Patients were maintained in sternal recumbency for 5 minutes during preparation for surgery to achieve full blockade, then restrained in right lateral recumbency with the hindlimbs tied to the table with disposable pet leads for C-section via left paralumbar fossa celiotomy in all patients. Intra-operative monitoring included heart rate via ECG, and indirect, noninvasive blood pressure in 3 patients. Data collected included age, body weight, efficacy of analgesia, quality of surgery, mean surgical time, time to stand (in minutes following intrathecal injection of lidocaine), duration of hospitalization, and anesthetic complications. Adequacy of analgesia was assessed by the attending surgeon after the patient had been aseptically prepared and draped (5 minutes after intrathecal injection) using a scale¹⁴ previously described. Briefly, noxious stimuli were applied with a 21-gauge needle in the superficial and deep muscles of the hindlimbs, flanks, and caudal to the last rib. Antinociceptive response was scored by the surgeon after aseptic preparation of the abdomen using the following classification scheme: 1, normal strong reaction; 2, depressed reaction; 3, moderate analgesia (no response to needle-prick); 4, complete analgesia (no response to needle insertion into muscle). Quality of surgery (surgical plane) was subjectively graded in each instance as acceptable or unacceptable by the same surgeon (GLE) and was determined based on lack of patient movement when performing the skin incision, manipulating the uterus, performing the hysterotomy, and extracting the fetuses.

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Representative images of sedated goats restrained in sternal recumbency with the hind limbs pulled slightly cranially for lumbosacral intrathecal administration of preservative-free 2% lidocaine (1 mg/kg) before cesarean section between January 2020 and November 2021. A and B—With aseptic technique, a 20-gauge 3.5-inch (0.9 X 90-mm) spinal needle is inserted on dorsal midline at the lumbosacral space, 1 to 2 cm caudal to the level of the tuber coxae. C—The presence of CSF in the hub of the spinal needle confirms correct placement within the subarachnoid space.

Citation: Journal of the American Veterinary Medical Association 260, 15; 10.2460/javma.22.05.0191

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Results

Age at presentation was 5 ± 2 years and weight on admission was 52 ± 21 kg. Breeds consisted of 3 Nigerian dwarfs, 2 Alpine, and 1 each mixed breed and Oberhasli. Two goats received methadone, and 5 received butorphanol; no difference in sedation effect was described by any of the attending anesthetists. Efficacy of analgesia was graded as 4 (complete analgesia) in 6 goats and 3 (moderate analgesia) in 1 goat. Quality of surgery was deemed acceptable in all surgeries. Recorded surgical time was 95 ± 20 minutes, with time to stand postoperatively at 182 ± 61 minutes. Duration of hospitalization was 4.7 ± 2.6 days. Complications encountered included ruminal tympany in 1 goat (relieved with intra-operative orogastric intubation) and mild hypothermia (rectal temperature, 37.2 °C; corrected with a forced-air warming system [Bair Hugger; 3M]) and partial block in 1 goat. In the instance of the partial block, administration of propofol (0.3 mg/kg, IV) during kid extraction allowed for successful completion of the procedure.

Discussion

To the authors’ knowledge, this was the first study to describe the efficacy of lumbosacral intrathecal lidocaine analgesia in sedated goats undergoing cesarean sections (C-sections). Our results supported our hypothesis that C-sections can be performed in sedated goats in right lateral recumbency using intrathecal lidocaine as the primary mode of analgesia.

The complications (ruminal tympany and hypothermia) encountered in this case series were consistent with sedated surgeries in small ruminants.⁵ In the instance of the partial block, live kids were suspected and the goat was restrained in right lateral recumbency before waiting the full 5 minutes for total blockade, resulting in incomplete analgesia of the flank. Upon reflection, this may have caused the lidocaine to “sink” to the right side within the vertebral canal when the goat was laid in right lateral recumbency, causing a right unilateral blockade, thus reducing the chances of the anesthetic exerting its effect in the substantia gelatinosa of the dorsal horn of the spinal cord on the area of interest (left paralumbar fossa).¹⁰ Indeed, this phenomenon of unilateral spinal analgesia has been used in calves that underwent repair of unilateral femoral fractures.¹⁵ Considering the measured specific gravities were 1.005 for caprine CSF and 1.014 for preservative-free lidocaine during this study, it is possible that these 2 components may undergo a stratification phenomenon within the vertebral canal; however, further study is warranted. Given that the remaining 6 goats all had sufficient analgesia at the time of skin incision, with 8 live kids born during C-section, it is reasonable to say that 5 minutes in sternal recumbency provided sufficient time for the blockade to reach full efficacy in the substantia gelatinosa and should be observed in all patients when administering intrathecal lidocaine.

Various methods for analgesia of the left flank have been described in ruminants, including paravertebral and inverted-L blocks. One of the most common is local or peri-incisional administration of lidocaine (“line block”). Potential disadvantages of this technique include increased bleeding due to local vasodilatory effects of lidocaine, delayed healing, incomplete analgesia of deeper tissue layers, potential for toxicosis due to the high volume required, and inability to extend the incision without first administering more lidocaine.⁶ Administration of intrathecal lidocaine avoids these potential incisional complications, and at the time of writing, no incisional complications or infections were observed.

The major advantages of intrathecal lidocaine are its duration of action (shorter compared to other local anesthetics such as mepivacaine and bupivacaine) and fast return of hindlimb motor function (182 minutes in our study) compared to 11 hours for bupivicaine.⁹ These factors allowed for the completion of the C-section procedures with a mean ± SD surgery duration of time of 96 ± 20 minutes for the goats of the present study. In our experience, other methods of analgesia, such as epidural administration of bupivacaine, can lead to extraordinarily prolonged periods (> 36 hours) of recumbency in goats. This leads to decreased movement, which can result in transient vagal indigestion or ruminal atony of the patient, causing a longer duration of hospitalization and increased financial cost to the owner. In this case series, intrathecal lidocaine was shown to have a short duration of action and quick return of hindlimb motor function, which allows the patients to stand and eat more rapidly, thereby promoting ruminal health and reducing risks associated with postanesthetic recumbency.

The main limitations of this case series are the small sample size, lack of a control group, and the limitations inherent in all retrospective studies (selection bias). Additionally, because flank analgesia was assessed only once prior to skin incision (due to the need to aseptically prepare the patient for surgery), conclusions about onset of flank analgesia cannot be made from this study; only that it reached effect after 5 minutes, allowing completion of the procedure. Finally, only short-term follow-up to discharge was collected, reducing the chance of identifying long-term complications.

In conclusion, intrathecal lidocaine administration provided flank analgesia of sufficient duration for goats undergoing C-sections and resulted in quicker return to hindlimb motor function postoperatively than historically reported for epidurals. When using this method of analgesia, patient restraint in sternal recumbency for 5 minutes is recommended to achieve full blockade.