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on the degree of hypovolemia and the severity of the inflammatory insult. Further, the hyperinflammatory response is characterized by increased cellular metabolism and oxygen demand with decreased efficiency for mitochrondrial oxygen utilization. Cellular hypoperfusion and anaerobic metabolism are common and are associated with organ dysfunction and death.

Obstructive shock. A physical obstruction resulting in decreased cardiac output is the hallmark of this form of shock. Examples include tension pneumothorax, cardiac tamponade, massive pulmonary embolism, venous air embolism, and severe cardiac valvular stenosis. All result in decreased cardiac output with elevated central venous pressure resulting in tissue hypoperfusion.

Tension pneumothorax develops when injured lung develops a one -way valve that allows air into but not out of the pleural space. The trapped air creates an increase in unilateral pleural pressure, causing the heart and other mediastinal structures (e.g., vena cava, aorta) to be displaced to the contralateral side with compression of the vena cava and decreased venous return to the heart. Placement of a chest tube on the affected side relieves the problem and restores perfusion.

Cardiac tamponade develops when blood or fluid accumulates around the heart in the pericardium space. The resulting increased pressure in the pericardial sac impairs venous return into the right atrium, and cardiac output is decreased. The treatment is to drain the pericardium, usually operatively, to allow venous return to increase and cardiac output to normalize.

Pulmonary embolism causes blockage of blood flow through the pulmonary artery, resulting in decreased cardiac output and hypoxia.

Miscellaneous shock. Other diverse derangements can result in cellular hypoperfusion and shock. Examples include cyanide toxicity, severe hypoxia, normovolemic severe anemia, profound hypoglycemia, and anaphylaxis. All result in damage to cells and organ dysfunction, leading to death if untreated.

C Management of shock

Fundamental to the treatment of shock is knowing the underlying etiology. Rapid volume replacement is essential for hypovolemic and vasodilatory shock states. Blood products should be administered if significant blood loss has occurred or when shock is associated with a hematocrit of less than 30%. Inotropic support is indicated if cardiac performance is

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depressed. Shock related to vasodilatation and unresponsive to volume loading should have vasoconstrictors administered. Caution should be used when administering vasoconstrictors, as perfusion may be negatively affected by these agents. In general, a mean arterial pressure of 65 mm Hg or greater is adequate for tissue perfusion. Monitoring adequacy of resuscitation is critical to correcting shock. Return of normal blood pressure, heart rate, and urine output are simple measures for assessing adequacy. Normalization of lactate levels and mixed venous oxygen saturation are more sophisticated and accurate measures of assessing resuscitation, especially in occult hypoperfusion conditions. Specific management for different shock types include:

Hypovolemic. Aggressive volume administration, preferably through two large-bore intravenous catheters. Stop ongoing blood loss. Consider central venous access for monitoring and high-flow fluid administration.

Cardiogenic. Inotropic support with dobutamine or dopamine. Nitroglycerine to reverse cardiac ischemia if blood pressure will tolerate.

Neurogenic. Volume resuscitation, consider vasoconstrictor administration with phenylephrine or norepinephrine if unresponsive to volume resuscitation.

Septic. Volume resuscitation, consider placement of central venous access for volume resuscitation and SvO 2 monitoring (goal SvO 2 >70%). Consider dobutamine if adequately volume resuscitated and SvO 2 <70%, consider norepinephrine or dopamine if adequately resuscitated and MAP <65 mm Hg.

Obstructive. Volume resuscitation and correction of the underlying condition.

Chapter 2

Essential Topics in General Surgery

Michael J. Moritz

Section A: Essentials of Normal Surgical Practice

I Wound Closure

Wounds, whether traumatic or surgical, must be appropriately closed, layer by layer.

A

There are three types of wound closure and healing; the choice of technique is determined by the degree of bacterial contamination in the wound (see Chapter 1, V C, D)

Primary intention. Clean and clean-contaminated wounds can be closed in this manner. All layers are closed.

This produces the most cosmetic scar.

With the skin closed, bacteria in the subcutaneous layer can result in a wound infection.

Secondary intention. Infected wounds are closed in this manner. The deep layers are closed, while the subcutaneous layer and the skin are left open.

Wound care consists of 1 to 3 dressing changes daily, including wound irrigation, packing, and sterile dressings.

The open portion of the wound granulates and slowly re-epithelializes with a broad scar.

Because the skin is not closed, a wound infection cannot occur.

Delayed primary intention. Contaminated wounds can be closed in this manner. The deep layers are closed, while the subcutaneous layer and skin are left open and packed.

At postoperative day 4 or 5, the wound is unpacked and inspected.

If the subcutaneous tissue is clean and just beginning to granulate, then the skin edges are closed, either with sutures placed and left untied at the initial procedure or with adhesive paper tapes.

If there is purulence in the subcutaneous layer, then the wound is left open to heal by secondary intention.

B The skin

The integumentary system is the largest organ in the body

Skin layers. The two principal layers, the dermis and epidermis, have specialized functions.

The epidermis is composed of stratified squamous epithelium, which covers the entire body and provides protection. Living cells migrate from the innermost level of the epidermis to the surface to form the dead, desquamating layer. The migration takes approximately 19 days.

The dermis , which serves in a nutritive capacity to the epidermis, is itself composed of two layers.

The papillary layer is composed of fine collagen fibers, ground substance, and capillaries.

The deeper reticular layer is composed of dense collagen, hair follicles, sebaceous glands, and sweat glands.

The hypodermis or subcutaneous tissue, which lies deep to the dermis, contains fat and nutrient vessels and can contain hair follicles and sweat glands.

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A cosmetically acceptable appearance is a goal of all closures.

Atraumatic handling of tissue minimizes necrosis and decreases scarring.

Eversion of the wound edges results in a level scar with time, whereas inversion of the edges may result in an uneven or concave scar.

Early removal of skin sutures or skin staples decreases the scarring.

C

Deeper fascial layers vary with location and the type of incision (i.e., transverse vs. vertical).

Fascia generally has greater strength than other layers, and the fascial closure should assume most of the tension distracting the wound, rather than the skin.

Where multiple deep layers exist, they can be closed as individual layers or in combination. For example, a transverse abdominal incision will have four deep layers: peritoneum and transversus abdominus, internal oblique, and external oblique muscles. Often, the deepest two or three layers are closed with a single suture line, and the shallowest one or two layers are closed with a second suture line.

When the integrity of the deep layers has been violated (or they are at high risk of disruption), as in the case of wound dehiscence, then all layers—deep and superficial, including the skin—can be included in a single suture line, a so-called mass closure, usually using interrupted retention sutures.

D Closure techniques

Suture lines can either be interrupted (a new knot every one or two stitches) or continuous (many stitches between knots). Continuous sutures are also called running sutures (Fig. 2-1).

Interrupted closures

The advantages. These closures have the potential for better vascular supply to the wound edges.

The disadvantages include the greater time it takes to close with this method, the inconsistency of tension on individual sutures, and the large number of knots required.

FIGURE 2-1 Suturing techniques. A: Simple interrupted suture. B: Interrupted vertical mattress suture. C: Interrupted horizontal mattress suture. D: Continuous (running) simple suture.

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Running closures

The advantages. Running closures take less time, have greater water -tightness, and the tension is equal along the entire suture line.

The disadvantages include the potential to strangulate the tissues if the suture is placed too tightly. Also, the integrity of the closure is dependent on one or two sutures and only a few knots, disruption of which will unravel the entire closure.

Sutures, whether continuous or interrupted, can be sewn in a simple or a complex fashion.

Simple sutures are also called “over and over” sutures.

Complex suture techniques include vertical and horizontal mattress sutures and their variations (Fig. 2-1).

Simple interrupted sutures are created with equal full -thickness bites of tissue.

Vertical mattress sutures are similar to simple sutures, but an additional bite close to each wound edge is used to ensure edge coaptation (far-far, reverse direction, near -near).

Horizontal mattress sutures are similar to simple sutures, but additional parallel bites are taken (far-far, move along incision, and reverse direction, far -far).

Subcuticular sutures are intradermal closures that are usually continuous horizontal mattress sutures; the suture material is usually absorbable. The advantages are the avoidance of suture marks on the skin, and there is no need to remove sutures (especially important in pediatric cases).

E Knot tying

The standard knot is a square knot (overhand throw, then underhand throw).

To create a secure knot, braided sutures (e.g., silk, polyester, polyglycolic acid) require three or four throws, whereas monofilament sutures (e.g., nylon, polypropylene, polydioxanone) require six to eight throws.

More throws are required for thicker suture sizes, running (as opposed to interrupted) closures, and more slippery suture materials (e.g., expanded dedpolytetraflouroethylene [ePTFE]).

When there is tension on the suture, a surgeon's knot can be used, which begins with a double -overhand throw to secure the first throws. Standard square knot throws follow. This knot is slightly weaker than a square knot.

A granny knot begins with overhand throw–overhand throw, creating a slip knot, which is then cinched down to the

appropriate tightness. Standard square knot throws follow. This knot is slightly weaker than a square knot.

F Suture materials

Strength of tissue. Although the gain in tensile strength varies from one type of tissue to another, as a general principle, the strength of tissue closed primarily returns toward normal, unincised tissue (100%) at the following pace:

At 20 days, 20% of normal.

At 40 days, 40% of normal.

At 90 days, 60% of normal.

At 1 year, 70% of normal.

The first factor in classifying suture material is nonabsorbable versus absorbable (Table 2-1). The second factor to include is whether the suture material is braided or monofilament.

Nonabsorbable sutures have enduring strength and last for years. They are permanent foreign bodies.

They can serve as a nidus for harboring bacteria, resulting in infection.

When the knots are prominent and just deep to the skin, they are noticeable, and patients may complain.

Examples of situations in which to use nonabsorbable sutures include:

Prosthetic heart valves

Vascular suture lines

Hernia repairs

Any difficult closure or where the patient's ability to heal at the usual pace is compromised (e.g., radiation therapy, corticosteroid therapy).

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TABLE 2-1 Types of Suture Materials