ANZCVS 2018 Flashcards
a) Referring to the diagram, identify the different gross anatomical parts of the stomach and the major arterial vessels that supply the stomach and spleen, as indicated by the letters A to L.
A: Fundus B: Body C: Pyloric antrum D: Pylorus E: Celiac F: Splenic G: Right Gastric H: Left Gastric I: Hepatic J: Left Gastroepiploic K: Right Gastroepiploic L: Short Gastrics
b) A splenectomy can be performed by ligation of the individual hilar arteries. Alternatively, the main vessels can be ligated for rapid removal of the spleen. What are the names of these vessels and which organ is affected if they are ligated in the incorrect location?
Three-ligature splenectomy: Splenic A/V; Left Gastroepiploic A/V; Short gastric A/V
* Ligation of the splenic A. must be performed distal to the pancreatic branch to the left limb of the pancreas.
- Name the structure that needs to be opened to visualise the left limb of the pancreas.
Ventral leaf (pars profundus) of the greater omentum
- State the anatomic components that make up the boundaries of the epiploic foramen.
The Epiploic Foramen connects the greater and lesser peritoneal cavities. It is bounded ventrally by the peritoneal lining of the portal vein within the hepatogastric ligament, dorsally by the peritoneal covering of the caudal vena cava, caudally by the hepatic artery covered by mesoduodenum and cranially by the liver. The foramen faces the right side. Digital pressure applied to the ventral aspect of the foramen during surgery can be used to temporarily deprive the liver of blood supply by compression of the portal vein and hepatic artery (Pringle Maneuver).
d) List the three (3) openings within the diaphragm and the structures that pass through each one.
- Foramen of the Caudal Vena Cava: Caudal Vena Cava and Right Phrenic Nerve
- Esophageal Hiatus: Esophagus, Dorsal and ventral Vagus Nerve Trunks
- Aortic Hiatus: Aorta, Azygous Vein, Hemiazygous Vein and Thoracic Duct
e) Name the two (2) main arteries that supply the colon and explain the importance of blood supply when performing surgery on the descending colon.
- Cranial Mesenteric Artery (produces the Right, Middle and Left Colic arteries)
- Caudal Mesenteric Artery (produces the Cranial Rectal artery)
One must be careful to avoid ligating the Cranial Rectal artery when performing a subtotal colectomy. Ligate the left colic and the vasa recta of the Cranial Rectal artery supplying the section of descending colon to be resected.
f) Provide the anatomic name of the adipose tissue structure identified at the cranial aspect of a ventral midline coeliotomy and discuss the embryological origin of this structure.
Falciform Ligament: Remnant of the primitive fetal mesentery which contains the umbilical vein. Extends between the liver, the diaphragm and ventral body wall.
g) List the three (3) main ligaments associated with the support of the ovary. Name the vessel(s) that supply the ovarian artery and the vessel(s) that the ovarian vein(s) enter.
Ligaments supporting the ovaries: Suspensory Ligament, Mesovarium, Proper ligament.
a) Following hemostasis, name and describe the stages of open skin wound healing. Include in your answer the processes occurring within the wound, the main cells/tissues involved and the approximate time an uncomplicated wound will spend in each stage.
1) Hemostasis (not discussed here)
2) Inflammation (2-3 days): Activated platelets release cytoplasmic granular contents including PDGF, VEGF and TGF-Beta. Platelet also convert cell membrane phospholipids into prostaglandins and thromboxane through Cyclooxygenase activation, which convert the initial sympathetically mediated vasoconstriction into vasodilation. Thrombin-activated fibrinogen is converted into fibrin, which polymerizes under the influence of factor XIII to form a fibrin/platelet scaffold (provisional extracellular matrix). This stabilizes the wound edges and provide limited wound strength. It also provides an initial barrier to infection. Blood products dry and form a crust, preventing further hemorrhage and allowing healing to progress underneath the surface.
• Debridement Subphase (3-5 days) PDGF and other chemoattractants stimulate the migration of neutrophils (6 hours), monocytes (12 hours) and lymphocytes (24 hours). Neutrophils phagocyte microorganisms and devitalized tissues, as well as produce proteolytic substances. Monocytes leave blood vessels through diapedesis and differentiate into macrophages at 24-48 hours post-wounding. (monocytes are essential for wound healing, neutrophils are not). Macrophages phagocytize microorganisms, secrete collagenase and produce chemotactic and growth factors that stimulate the differentiation of local mesenchymal stem cells into fibroblasts. Lymphocytes contribute to the immunologic response to foreign debris and improve the rate and quality of the tissue repair.
3) Proliferation (3 to 5 days): Fibroblasts stimulated by TGF-beta, tissue O2 concentration (20mm Hg) and slightly acidic environment produce Type III collagen which gradually replaces the fibrin meshwork and becomes vascularized under the influence of VEGF, forming granulation tissue within 3 to 5 days (vascular buds follow fibroblasts). Collagen fiber direction remains random for the first 5 days, but subsequently follows the direction of tension lines. Granulation tissue provides a barrier to infection, surface for epithelial migration and protection for myofibroblasts. Myofibroblasts within the granulation tissue promote wound contraction. Epithelial cells multiply under the influence of TGF and migrate over granulation tissue towards the center of the wound. These cells can migrate under eschar and produce collagenase which dissolves the base of the scabs for shedding. Epithelial cell proliferation ceases once desmosomal contact is reestablished (contact inhibition). The initial epithelium is thin and fragile, but the basement membrane is quickly reestablished allowing cell proliferation and redevelopment of a robust, stratified, squamous epithelial structure. Epithelialization occurs more quickly in moist and O2-rich environment.
4) Remodeling (14+ days): Collagen type III is gradually replaced by Type I as wound strength increases, but the wound only regains about 20% of original strength in the first 21 days. Only about 80% of original strength is ever regained, typically several months after injury. Granulation tissue is gradually removed by fibrinolytic enzymes and blood vessels recede. Collagen is reorganized according to skin tension lines, and non-functional collagen is degraded by MMP’s produced by macrophages, epithelial, endothelial cells and fibroblasts.
b) Discuss the treatments or interventions that could be utilised to reduce infection risk and optimise wound healing in an open wound, including reference to what stage of healing is at the highest risk of infection and why.
The Inflammatory Phase of healing (including the debridement subphase) is the period when infection is most likely to occur. This is the result of poor blood supply caused by tissue trauma, presence of devitalized tissue that serves as substrate for bacteria, increased levels of MMP’s which degrade ECM and limited leukocyte function. This is where wounds can get ”stuck” , usually due to hypoxia, ischemia or the formation of bacterial biofilms.
- Wound lavage: Typically performed after initial wound hair clipping, utilizing isotonic electrolyte solution, sterile saline or tap water (not ideal since hypotonic). Antibacterials like chlorhexidine or povidone-iodine may be added to decrease contamination but could contribute to further tissue damage. Topical antibiotics have little effect of bacteria once infection is already established. Tris-EDTA can be added to lyse gram-negative bacteria (i.e. E. coli, Pseudomonas, Proteus vulgaris). Lavaging the wound (rather than scrubbing) at 7 to 8 psi is recommended. This is accomplished by adding a pressure bag to a 1L bad of fluid, pressurizing to 300psi, and delivering through a 18G needle.
- Debridement: Accomplished via surgical, autolytic, mechanical or enzymatic or biological methods. The general goal is to remove all devitalized tissue without damaging viable structures/tissues, so each method has advantages/disadvantages.
- Moist Wound Healing: A moist wound environment promotes wound selective autolytic debridement, granulation tissue formation and epithelialization. WBC’s migrate more readily in moist environment, making it more resilient to infection (improved phagocytosis, lower pH). Scabs are not formed, therapy preventing the “trapping” of WBC’s. The low O2 environment under occlusive dressings promote macrophage activity, fibroblast proliferation and capillary ingrowth. The rate of re-epithelialization can be up to 2x faster as compared to air-exposed wounds.
- Systemic antibiotic therapy: the selective use of antibiotics may help prevent or control infections. Minimally contaminated wounds withing the “golden period” or 6-8 hours don’t typically require antibiotics. Heavily contaminated wounds and those with clear signs of infection should be cultured. A broad-spectrum antibiotic can be administered while awaiting culture results.
- Topical antibiotic therapy: may eliminate or reduce the numbers of microorganisms that destroy tissue, and are preferred over systemic antibiotics. Usually applied every 1 to 3 hours to prevent infection, but no longer effective once infection is well-established (wound coagulum prevents Abx from reaching superficial bacteria).
- Topical wound-healing enhancers: Compounds like Aloe Vera, Acemannan, Honey, Maltodextrin and others have been shown to improve wound healing. Unfortunately well-controlled prospective trials are still lacking in Veterinary Medicine.
a) Briefly define shock.
Shock is defined as inadequate cellular energy production, typically as a result of poor tissue perfusion leading to decreased oxygen delivery.
b) List four (4) different types of shock. For each type, briefly describe the mechanism and give one (1) example.
- Hypovolemic – Caused by a severe decrease in circulating blood volume. Secondary to hemorrhage, severe dehydration, or trauma.
- Distributive - Caused by marked decease or increase in systemic vascular resistance or maldistribution of blood. Examples may include sepsis, neurogenic and anaphylaxis.
- Cardiogenic – Caused by a decrease in cardiac output. Examples may include cardiac tamponade, cardiac arrhythmias, CHF or drug overdosage (B-blockers, Ca-channel blockers, anesthetics).
- Obstructive – Caused by obstruction of cardiac preload or afterload. Causes may include catecholamine excess (pheochromocytoma), GDV and thromboembolism.
c) Discuss how the body detects an acute reduction of circulating blood volume due to hemorrhage.
Acute drop in circulating blood volume is detected by arterial and cardiopulmonary baroceptors. These are stretch receptors located in the caudal vena cava, right atrium and pulmonic artery. These receptors provide a vagal-mediated signal to the brainstem.
d) Discuss how the body attempts to maintain cardiac output and blood pressure in the face of acute blood loss greater than 30%. Include in your answer both neural and hormonal responses.
- Increased sympathetic activity (neuronal): Increased release of catecholamines cause vasoconstriction, increased cardiac contractility and tachycardia, leading to increased cardiac output.
- Activation of the Renin-Angiotensin-Aldosterone system (hormonal): triggered by reduction of renal blood flow. Further contribute to sympathetic activation and cause water and sodium retention via ADH and aldosterone, respectively.
e) Describe how to calculate the quantity of whole blood needed to transfuse an anemic patient.
Volume to be infused = Blood Volume X (desired PCV – Current PCV)
Donor PCV
For practical purposes transfusions are administered at 2.2 ml/kg of whole blood to increase the recipient’s PCV by 1%
