May 12th, 2009
Airway Pressure Release Ventilation (APRV)
This mode of ventilation became commercially available in the United States in the mid 1990s. It uses a different mode of ventilation than other methods.
Conventional modalities use a strategy that begins the ventilation cycle at a lower baseline pressure and with an increase in airway pressure to open the alveoli and produce ventilation.
APRV begins the ventilation cycle at an elevated airway pressure and intermittently releases the pressure (i.e., deflates the lungs) to create tidal ventilation and allow removal of carbon dioxide.
APRV has been described as continuous positive airway pressure with brief releases of pressure. While teleologically similar, APRV differs from CPAP in that it allows for both ventilation (i.e., CO2 removal) and oxygenation.
APRV is now used commonly in acute lung injury to ventilate using maximum lung protection strategies.
Some advantages of its use include the reduction of patient sedation, the ability to breath spontaneously throughout the cycle, lower airway pressures, minimal effects on the cardiovascular system (e.g., mimimal effects on venous return), and elimination of neuromuscular blockade.
May 11th, 2009
Dorsalis Pedis (DP) Artery
This small artery runs on top of the foot. The ability to palpate a pulse in this vessel is very important (along with the posterior tibial artery) in clinical exams to determine blood flow to the foot.
It forms as a continuation of the anterior tibial artery after it passes through the inferior extensor retinaculum. The DP runs on top of the foot slightly medially (toward the toe) to the first interosseus space (space between the big toe and second toe). As it passes through the first dorsal interosseus muscle, it becomes the deep plantar artery.
In the ICU the DP is a site where an arterial line can easily be placed for second-to-second blood pressure monitoring.
May 10th, 2009
This small sesamoid bone is found buried in gastrocnemius close to the proximal attachment behind the knee at the level of the mid-patella and posterior to the distal femur. It has no bony attachments.
Fabella is the Latin word for bean. It occurs in 3 to 5% of the population and is readily appreciable on lateral radiograph (X-ray) of the knee. It is sometimes mistaken for a bone chip off the femur in the inexperienced.
March 19th, 2009
Z-plasty For Treatment of Chronic, Refractory Pilonidal Disease
Pilonidal disease is inflammation with abscess formation and very often chronic drainage from the natal cleft at the tip of the coccyx. First line techniques such as drainage, excision, fibrin glue, and marsupialization are often unsatisfactory and do not provide definitive repair. One technique used by plastic surgeons and some general surgeons as a second line treatment when earlier attempts at treatment have failed is the Z-plasty.
Z-plasty is a surgical technique that is used widely in plastic surgery to close large wounds and to release contractures. In pilonidal disease, it has the advantage of eliminating the deep natal cleft and replacing the tissue defect with healthy, sinus free tissue from the lateral lower back.
Typically the pilonidal sinus is excised down to the presacral fascia (i.e., close to the sacral bone). Then two parallel incisions are made at the superior and inferion edges of the wound. The subcutaneous tissue (i.e., the fat layer beneath the skin) is raised to form skin flaps and the hook retractors are used to transpose the edges of the initial resection from the horizontal to the vertical.
The skin is then closed using nylon mattress sutures after a drain is placed. Generally, the patients tolerate the procedure well and have a fairly rapid recovery.
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March 19th, 2009
Bone, cartilage, and vascular implants and prosthetics used by surgeons all have very carefully engineered levels of collagen cross-linking. This chemical manipulation confers both advantages and disadvantages.
The advantage of an increased degree of cross-linking is a greater degree of fibroblast encapsulation and therefore and increased resistance to enzymatic breakdown. In layman’s terms, it is harder for the body “to digest the implant.”
The disadvantage is that cross-linking prevents cellular infiltration of the implant, thus preventing incorporation and the body from remodeling tissues to incorporate. In layman’s terms, it is less likely the implant “will take.”
The optimum level of collagen cross-linking is unfortunately unclear due to the absence of long-term clinical experience and research data.
March 2nd, 2009
Biologic Prosthetic Materials for Hernia Repair: Human
Human tissue prosthetics have found a use in the setting of a contaminated or infected abdominal wall. Although they are approved by the FDA for use in inguinal hernia repair they are rarely used, except in contaminated fields, do to their lack of strength of the repair. Use of a sterilized human tissue prosthetic carries the risk of human disease transmission, although no reports of this exist. Human tissue prosthestics are listed below:
AlloDerm – manufactured by LifeCell, widely used hand harvested human dermis, processed by complete removal of all cellular tissue and freeze drying of the dermis without end gas sterilization to avoid structural degradation. The product is refrigerated and needs to be rehydrated prior to use.
FlexHD – manufactured by Musculoskeletal Tissue Foundation, human dermis with the cells removed, has long storage time, no preparation required before it is placed in the patient.
Bard AlloMax Surgical Graft – Davol, Inc., Sterilized using low dose gamma radiation, proprietary process used to remove cells and pathogens.
Copyright 2008 InsideSurgery.com®. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
March 1st, 2009
Biologic Prosthetic Materials for Hernia Repair: Non-Human
Biological prosthetics are useful when the surgeon is faced with a infected or contaminated wound but must cover a fascial defect. Their goal is to create a scaffold that will allow cells to attach but will not serve as a continuing source of infection. The disadvantage of these prosthetics is their lack of strength in effecting a long-term repair. Because of this, they are not routinely used in elective abdominal hernia repair and many surgeons have abandoned them and have opted for placing a Wittman patch with staged closure.
Surgisis – Cook, made from the submucosal of pig intestine, decellularization reduces risk of immune-mediated rejection, scar tissue encapsulation does not occur because of lack of collagen cross-linking.
Permacol – Tissue Science Laboratories, made from collagen harvested from pig dermis, can be used in infected site, cross-linked to improve durability and strength.
Bard CollaMend – Davol, Inc., made from acellular collagen from pig dermis, cross-linked fibers require rehydration before use, retains good elasticity.
FortaGen – Organogenesis, Inc, made from pig intestines, non-cross linked, not widely used.
Veritas Collagen Matrix – Synovis Surgical, Inc., made from cow pericardium (sac surrounding the heart), more commonly used to reinforce anastomotic staple lines (Peri strips) than hernia repair
SurgiMend – TEI Bioscience, made from fetal cow dermis, not cross-linked, requires rehydration, has extended shelf-life.
Tutumesh – Tutogen Medical, Inc., made from cow pericardium, susceptible to shrinkage, relatively non-inflammatory.
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February 28th, 2009
Prosthetic Materials for Hernia Repair: PTFE (polytetraflouroethylene)
These meshes are widely used in ventral hernia repair. They are usually solid but are available in woven models. They have a lesser degree of inflammation than polypropylene meshes. The mesh can interact with surrounding tissue to form a persistent seroma. PTFE generally should not be placed in a wound with a risk of infection and must be completely removed if a sterile wound subsequently becomes infected. Some types of PTFE with associated characteristics are listed below:
DualMesh, DualMesh Plus – W.L. Gore, the Plus material differs from the plain DualMesh because it is impregnated with antimicrobial silver carbonate and chlorhexidine diacetate to inhibit bacterial colonization.
Bard Dulex Mesh – Davol, two-sided mesh with a smooth side to be placed next to the bowel and a microporous side to be placed against the abdominal wall to promote tissue ingrowth.
MotifMESH – Proxy, has high porosity that facilitates tissue ingrowth, has low tissue inflammation.
Composix – Bard, combination PTFE and polypropylene with the PTFE side placed against the bowel wall, widely used
Composix Kugel Patch – Bard, combination PTFE and Polypropylene, some sizes recalled by the FDA.
Copyright 2008 InsideSurgery.com®. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
February 24th, 2009
Prosthetic Materials for Hernia Repair: Polyester
In addition to polypropylene and PTFE, polyester is a widely used synthetic for mesh repair of hernias. Polyester is somewhat easier to handle than polypropylene and PTFE as it sticks less to tissue and is softer. It is hydrophilic and produces less scar-tissue contraction than heavier materials.
Polyester performs well in a contaminated environment, although material that does not incorporate is usually removed. Granulation tissue will form through the pores even when exposed.
Polyester meshes are not typically used in inguinal hernia repair. They are occasionally used in ventral hernia repair as described below
Parietex – manufactured by Sofradim Corporation, composite mesh with polyester on one side and a combination of polyethylene glycol, glycerol, and oxidized collagen on the other side.
Copyright 2008 InsideSurgery.com®. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
February 23rd, 2009
Prosthetic Materials for Hernia Repair: Polypropylene
In the United States, general surgeons perform about 900,000 hernia repairs every year. There has been an explosion of new synthetic materials available to aid in closing these anatomic defects. These polymers fall into the following three categories – polypropylene, polyester, and polytetraflouroethylene (PTFE).
Polypropylene prosthetics are widely used. They can vary siginificantly in porosity, weave, and density. Products with lower density and larger pore size may cause less inflammatory response and less contracture because of the relatively thinner scar formed, with a comcomitant improvement in outcomes. However, this lesser inflammatory response must be balanced against rates of recurrence.
Some commonly used brands of polypropylene mesh for inguinal hernia repair are listed below:
Bard 3D Max – manufactured by Davol, Inc., relatively heavyweight material.
PerFix Plug – manufactured by Davol, Inc., prone to contracture and migration as a relatively large amount of scar tissue decreases its size.
Kugel Patch – manufactured by Davol, Inc, has a flat surface with an attached ring.
Prolene Hernia System – manufactured by Ethicon, heavyweight mesh that has an on-lay sheet with an attached plug that is placed in the preperitoneal position to reduce plug migration. Used only in open hernia repair.
Prolite Mesh and Plug – manufactured by Atrium Medical Corporation, this is relatively porous, lightweight material.
Proloop Mesh Plug – manufactured by Atrium Medical Corporation, relatively porous, lightweight material.
Surgipro – manufactured by US Surgical, comes in open-weave, and mono- and multi-filament.
Some commonly used brands of polypropylene mesh for ventral hernia repair are listed below:
Supramesh-IP - manufactured by Genzyme, composite material of polypropylene and polyglycolic acid woven together, also coated on one side with a gel mixture of sodium hyaluronate, carboxymethylcellulose, and polyethylene glycol.
Proceed – manufactured by Ethicon, coated with a proprietary cellulose based polymer.
C-Qur – manufactured by Atrium Medical, absorbs in 10-12 weeks, coated with processed fish oil on both sides
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