Surgical Access to the Ovine Fetus the Left Flank Approach

Research Article

Austin J Obstet Gynecol. 2017; 4(2): 1076.

Surgical Access to the Ovine Fetus the Left Flank Approach

Pringle KC¹*, Seki Y² and Kitagawa H²

¹Department of Obstetrics and Gynaecology, University of Otago, Wellington, New Zealand

²Division of Pediatric Surgery, St Marianna University School of Medicine, Japan

*Corresponding author: Pringle KC, Professor of Paediatric Surgery, Department of Obstetrics and Gynaecology, University of Otago, Wellington, New Zealand

Received: September 06, 2017; Accepted: November 07, 2017; Published: November 15, 2017

Abstract

Introduction: Most researchers using ovine fetal models use an infraumbilical midline incision. This approach is simple, but has a significant incidence of maternal complications, most of which are not reported. This paper presents a left flank approach, which is less painful and causes few complications.

Materials and Methods: The senior author developed this approach, with a Veterinary colleague, during the development of a fetal lamb model for the creation and repair of a diaphragmatic hernia. The evolution of this approach and the changing anaesthetic techniques are presented.

Results and Discussion: This approach has minimal complications. Wound infections are rare, although sterile seromata are common. Blood loss is minimal. The ewes are usually up and eating normally within an hour of completing the procedure.

Conclusion: This approach is slightly more technically demanding. However, the low morbidity makes it an excellent approach to the fetal lamb.

Keywords: Fetal lambs; Fetal surgery; Ovine models

Abbreviations

L: Left; R: Right; lab: laboratory; DH: Diaphragmatic Hernia; OU: Obstructive Uropathy; BOO: Bladder Outlet Obstruction; U/S: Ultrasound; ETT: Endotracheal Tube; OG: Orogastric; IV: Intravenous

Introduction

From the very early fetal lamb models [1-5] researchers have utilised a midline infra-umbilical or paramedian incision. A rare exception was Burrington, who explored fetal wound healing [6] and used a Right (R) muscle-splitting incision. Ventral incisions in ewes have a significant morbidity, almost none of which is reported. A rare exception to this statement is the report by Schinckel and Ferguson [1], who reported that 6 of 9 ewes operated on through a paramedian incision had incisional herniae at term. Wound infections are common and the senior author has personal experience of repairing a massive incisional hernia in a ewe who had previously been used for fetal lamb cannulation experiments by another researcher in an era when it was acceptable to use experimental animals for more than 1 experiment. The hernia was, in fact, repaired through the left flank incision described below.

Materials and Methods

Breeding

Ewes bred specifically for research are purchased from the AgResearch farm at Kaitoke, about 1 hour’s drive north of Wellington. If necessary the ewes are synchronised by insertion of Controlled Internal Drug Release sponges containing progesterone 12 days before mating. Rams wearing a harness carrying a coloured crayon are left with the ewes overnight 140 days before the planned delivery. Ewes not marked are regarded as not being pregnant. 14-17 days later, the rams are again exposed to the ewes, carrying a different coloured crayon. Ewes marked a 2nd time are regarded as not having been mated during the first encounter, and are excluded from the flock. At between 40 and 50 days gestation, the ewes undergo a veterinary assessment to ensure that they are healthy and an Ultrasound (U/S) to confirm the pregnancy and identify singletons, twins and other multiples. In general, triplets and quadruplets are not utilised for research procedures, although such lambs may sometimes be used as normal controls. Prior to surgery, they are acclimatised to a limited supply of sheep nuts. Each ewe is weighed on the farm shortly before transport.

Transport

In general, we attempt to keep the ewes in the Laboratory environment for as short a time as possible. They are, therefore, transported to the Laboratory (lab) in a covered utility vehicle 24-72 hours prior to the planned day of surgery. They are housed in open pens with ewes being fasted being segregated by open mesh fencing. No ewe is ever left on her own. The concrete floors are covered with a layer of shavings derived from untreated pine. They are allowed free access to Lucerne hay and limited amounts of sheep nuts.

Pre-op fasting

Twenty-four hours preoperatively, the food is removed, although they are allowed free access to water. This differs from the approach most commonly described by most researchers using ovine models, with fasting of up to 48 hours being common [4,5]. However, we have found that sheep starved for prolonged periods tend to attempt to eat their bedding, and even if they are denied water for up to 48 hours, their rumen still is full of fluid. Sheep scheduled for surgery are kept in a separate cage, but are always able to see other sheep.

Induction

Approximately 30 minutes prior to the planned procedure, meloxicam 20mg/ml (1mg/kg) is administered by subcutaneous injection as a post-operative analgesic. The ewe is transported from the pen to the operating theatre in a mobile tilting cage (Figure 1). The sheep is encouraged up a ramp and held fast in a grip. She is wheeled into the operating theatre, positioned next to the operating table and tilted on to her left side. The flap holding her head is released and the neck over the jugular vein is clipped (Figure 2). The jugular vein is easily demonstrated by obstructing it just above the clavicle, immediately medial to the sternomastoid. The jugular vein is cannulated with an 18Gauge needle and the ewe is injected with a ketamine (10mg/kg)/diazepam (0.5mg/kg) mixture. Within 2 minutes, the grip can be released and the ewe rolled over on to the operating table. The tongue is grasped with a gauze swab and pulled out over the lower jaw, taking care to avoid lacerating it on the teeth. Intubation is performed using a long straight-blade laryngoscope. In most cases a 7mm Endotracheal Tube (ETT) with a low-pressure balloon is used. A plastic bite-block is passed over the end of ETT and the tube is tied to the upper jaw with string, with the ties passing around the both the upper and lower jaw, so the ewe cannot open or close her mouth. The ETT is connected to an anaesthetic machine and anaesthesia is maintained using a nitrous oxide/oxygen mixture (both 2 l/min) and 1-2% isoflurane (Figure 3). Mechanical ventilation is only used if the ewe is breath-holding or if the plane of anaesthesia needs to be deepened. Amoxycillin (15mg/kg) is administered by intramuscular injection into the supraspinatus muscle. The scapula deep to the muscle ensures that no vital organs are injured. An Oro- Gastric (OG) tube is passed to drain the stomach of fluid and gas. We use a 2cm polyethylene tube with 1cm side-holes cut in the gastric end. The tube is kept frozen between uses. Care must be taken when passing the tube, as excessive force can result in an oesophageal tear, which is usually lethal. If the tube thaws before it is reaches an adequate position, it is removed, washed and re-frozen.