Fatty tissue must be handled gently during procedures, as if crushed it is prone to liquefactive necrosis. Since it has a poor blood supply, it heals slowly if damaged and is at risk of infection.
Fibrous connective tissue consists of a dense network of collagen and needs to be divided by sharp dissection. However, due to the proximity of nerves and blood vessels, this must be done with care and scissors may be preferable to use of a scalpel. Toothed forceps or tissue-holding forceps are needed to handle this tough tissue.
Muscle is very vascular and bleeds profusely when incised. If possible, use a surgical approach which avoids cutting muscles. If an approach has to be through a muscle, then it is better to split the muscle longitudinally between the fibres rather than cut it transversely, since this will not result in a significant loss of function once healing has occurred.
Good surgical technique aims to prevent excess bleeding from a surgical site, but if haemorrhage occurs, there are several ways to arrest it.
If in doubt, apply pressure. Digital pressure using a swab for a few minutes can be sufficient to arrest even quite severe haemorrhage. Always dab or press rather than wiping, as this will remove the clot and allow continued haemorrhage. For small vessels, a clot may form to seal the hole within a few minutes. If not, bleeding vessels can be picked up and crushed using suitable artery forceps, and then tied off with a ligature using a fine suture material, or sealed using diathermy or cautery, all of which apply heat to the vessels to coagulate them. Large vessels usually require ligatures for secure haemostasis. Metal clips can also be used, but they require special instruments for placement. Ligatures for haemostasis should be made of absorbable materials since non-absorbable materials can act as a focus for infection.
The amount of blood loss should be carefully monitored, as a very small volume is potentially very significant in a small animal. Mice for example typically have a total blood volume of less than 2 ml. In larger animals it is useful to weigh the swabs used to give an estimate of blood loss, so fluids can be infused at an appropriate rate. Whatever the size of the animal, good control of haemorrhage is always important to avoid post-operative swelling and to minimise surgical shock and risk to the animal.
Surgical instruments exist in vast numbers and varieties. The choice of instruments depends on the size of the animal, the organ system and tissues to be handled, availability, and the surgeon’s preference. Some of the more common instruments are described here. Although there are no instruments designed specifically for rodents, ophthalmic instruments and fine-surgery kits may be used for procedures on mice and rats. A selection of different instruments will be required for different procedures – one size does not fit all – and choosing the right instrument can improve the outcome of a surgical procedure.
Good-quality instruments are always worth the cost, and they must be looked after to ensure they remain in good condition. Surgical instruments must be used only for surgery. A veterinary surgeon can advise on choice of instruments. Instruments will be needed for the different parts of the surgical procedure: incision, dissection, haemostasis and closing the wound afterwards. Instruments are designed to be optimum for particular tasks, and therefore appropriate instruments should be selected for different parts of the procedure. It is not advisable to use instruments designed for one purpose for another; for example, artery forceps are not suitable for holding suture needles, and rat-toothed forceps are not appropriate for holding delicate tissues.
Scalpels are very sharp, and cause the minimal amount of trauma, resulting in faster healing with less tissue damage and scarring. However, because there is less tissue damage, they also cause significant bleeding. Scalpels should be used for cutting through skin and tough tissue. See Figure 10.2.
Scalpel blades are available in a variety of shapes and sizes, which are designed for different purposes. They may come individually wrapped and pre-sterilised, or non-sterile in packs. Before use, they should be attached to a suitable scalpel handle. Fixed-blade scalpels are also available.
- Size 10 blades are all-purpose blades with a rounded cutting edge, which can be used for most surgical procedures.
- Size 11 blades are pointed, with a straight blade, and are particularly useful for work involving fine cutting of connective tissue.
- Size 12 blades are curved with the cutting edge on the inside of the curve. They are useful for situations where the skin needs to be cut without damaging the structures beneath.
- Size 15 blades are a similar shape to size 10, but smaller and are useful all-purpose blades for fine work on small animals.
A scalpel should be held like a pen or a knife, and the tissue cut with a firm single stroke. The free hand should be used to tension the skin to ensure that the incision is straight and divides the full thickness of the skin in one stroke. When using size 10 or 15 blades, the wide round part of the blade should be used for cutting, rather than the tip.
Round-ended scissors should be used to cut through the body wall. Pointed scissors should not be used for this, to avoid damaging structures beneath. Scissors should not be used to cut skin as they cause more trauma and bruising than scalpels.
Diathermy and thermocautery units use an electric current to cut the skin and coagulate blood vessels at the same time. They can also be used just for haemostasis. These also cause more trauma and scarring than scalpels.
Scissors can be used for sharp or blunt dissection. Round-ended scissors are used for surgery, such as Mayo scissors. Fine-ended scissors are available for delicate work, for example Metzenbaum scissors. Scissors should be held with the ring or third finger through the loop and index finger close to the blades to allow fine control (Figure 10.3).
Forceps are used to hold tissue, organs or vessels while carrying out blunt dissection or suturing. Rat-toothed forceps have teeth to grip tissue firmly and are used in skin and tough tissue. Blunt forceps have serrated tips and are used in delicate tissue. Forceps should be held like a pencil or a pair of chopsticks (Figure 10.4).
Haemostatic or artery forceps are used to clamp and hold blood vessels. They can be curved or straight, and have crushing tips to trigger blood clotting by producing tissue damage. Artery forceps need to be in good condition with jaws that meet properly. Artery forceps need to be properly maintained and looked after to ensure that the jaws continue to close fully, and to that end they should not be used for any other purpose, to avoid damage to the instruments.
Spencer–Wells’ and Dunhill artery forceps are general-purpose haemostats. Halstead’s mosquito forceps are very fine, and are useful in small animals and for delicate work. Kocher’s artery forceps combine a rat-toothed tip with crushing jaws, and are useful for grasping bleeding vessels deep within tissues (Figure 10.5).
Following a surgical procedure, wounds may be closed with needles and suture material, skin clips, surgical staples or occasionally tissue glue.
Needle holders are hinged instruments used to hold curved needles while suturing tissue. Straight needles are usually held by hand. Needle holders come in many patterns (Figure 10.6 and Table 10.1), and may come with or without a ratchet which locks the jaws onto the needle, with or without integral scissors so separate scissors for cutting sutures are not necessary, and with or without rings. To a large extent personal preference dictates which type is used. For needle holders without a ratchet, considerable digital pressure may be required to hold the needle if the tissue is tough.
The jaws of needle holders are ridged such that rotation of the needle is minimised.
In addition, other instruments are available, designed for specific parts of the surgical procedure.
Towel clips are useful for securing paper or cotton drapes, so that surgical instruments and suture materials do not come into contact with non-sterile parts of the animal. They are available in a variety of patterns (Figure 10.7). Care must be taken in their use, however, since they have sharp teeth and can cause trauma if used incorrectly.
Allis tissue forceps are long forceps with small gripping jaws (Figure 10.8). They are useful for grasping pieces of tissue to hold them to one side temporarily, and cause relatively little trauma.
Retractors are used to improve surgical access and visibility, and to hold tissues to one side. They may or may not be self-retaining. Many different varieties of retractors are available. Gelpi retractors have small hooks on the end, which are inserted between the tissues to be separated. As the handles are pushed together, the hooks separate forcing the tissues apart and the ratchet holds the retractor open. Hohman retractors are designed for lifting bones in orthopaedic operations, and need to be held by an assistant (Figure 10.9).
Atraumatic clamps: when performing vascular or intestinal surgery, it may be necessary to occlude a vessel or organ temporarily without causing damage. It is essential to use the correct atraumatic bowel or vascular clamp in these circumstances, which will occlude the lumen without causing damage to the wall of the organ.
Suturing Techniques and Materials
The purpose of any material used for wound closure is to hold the wound together for long enough for healing to occur. It should then either disappear or be removed. Each layer should be closed separately, to maintain anatomical relationships, and there should be careful approximation of tissues and obliteration of dead spaces. This can be done with sutures, surgical staples or tissue glue.
Sutures are generally placed using needle holders and tissue forceps. Needle holders come in many patterns and sizes (see above), and the choice will depend largely on personal preference. Whichever one is chosen, it is essential to know how to hold it properly and manipulate it with dexterity. Practice is essential, using cadavers, skin simulators, freshly incised banana skins or foam rubber. Suture pads designed to mimic the texture of skin are available from numerous sources (e.g. www.vet-tech.co.uk/home/index.html).
There are several different suture materials and needles that provide an accurate and secure approximation of the wound edges. Ideally, the choice of the suture material should be based on the biological interaction of the materials employed, the tissue configuration and the biomechanical properties of the wound12.
All biomaterials placed within the tissue can damage the host defences and invite infection13, and surgical needles have a proven role in spreading blood-borne infection14. Therefore, the operator must take all reasonable steps to reduce the risk of contamination or injury during surgery.
Suture needles can be curved or straight, cutting or round bodied, and swaged on or threaded.
Curved needles are used where there is limited accessibility of the operative site. The greater the curvature of the needle, the less control there is of the tip. Generally, the straightest needle possible should be used. Curved needles are always placed using instruments, whereas straight needles can be held with instruments or fingers.
Suture needles may be round in cross section, or triangular, with three cutting edges. Round-bodied needles are atraumatic, and are designed to pass through tissues without leaving a hole, and as the needle passes through, the tissue closes tightly round the suture material forming a leak-proof suture line. They are used in soft tissues and in tissues where leakage must be avoided, such as bowel, blood vessels, internal organs and muscle.
Cutting needles are used in tough tissues, such as skin and fascia. Cutting needles leave triangular holes behind and should not be used in hollow organs as they encourage leakage of the contents.
Curved cutting needles may have the apex of the triangle on the inside of the curve, or the outside, in which case they are known as reverse cutting. With reverse cutting needles, the suture material is less likely to pull through the tissue, as the suture is not left sitting at an apex of the hole left in the tissues, and the needle has increased strength and resistance to bending (see Figure 10.10).