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Laplace's law for bandaging pressure

p = # T/ RWP= pressure# number of layersT tensionR radiusW width


normal closing pressure of skin vs muscle arterioles

30 mm Hg skin arterioles50 mm Hg muscle arteriolesskin can be easily compromised with too much P on bandage


degree of bacterial aerolization during bandage change with dry dressings

aerolization of bacT was 20% higher when a dry gauze was removed vs a moisture retentive dressing was removedremains in air ~ 30 min


types of drain material that incites the MOST inflammation

MOST red rubber and latexLEAST polyethylene, polyvinyl chloride, silastic (silicone)


open passive drain characteristics

PENROSEsoft, pliable, latex, radio opaquedrainage occurs via capillary action (outside), gravity dep, overflow from wound or fluctuation of pressure in wounddrainage is proportional to surface area of drainnot for body cavity


closed active drain characteristics

vacuum pulls fluid into tube systemfenestrationsno gravity depdecreases risk infectionprevents skin excoriation by drain fluidcontinuous or intermittent


rule to follow when adding fenestrations to a drain

make fenestrations < 1/3 tube diameter to prevent kinking/breakage


types of closed suction active drains

compressible reservoirs: JP drainRigid reservoirs: Synder drainSump pump drainsneedle/syringe/tubebutterfly cathetervacuum assisted drains


VAC guidelines (TJ) for draining tissues

60-125 mm Hg25-75 mm Hg delicate tissues75-250 mm Hg heavy exudate/dead space200-400 mm Hg to encourage adhesion250-350 mm Hg large volume fluid


Poiseuille's law of laminar flow

flow = dPpir^4/8nLdP = pressure difference btwn to ends of drainr = radius of drainn = viscosity of fluidL =drain length


doubling drain diameter does what to flow

2x drain diameterincreases flow ^ 4 power (16 x)flow is directly proportional to radius to fourth power


halving the drain length does what to flow

1/2 drain lengthincreases flow 2xflow is indirectly to drain length


compare grenade compression pressure generated one hand vs two hands vs roll base to apex

one hand 84 mm Hgtwo hands 110 mm Hgroll base to apex 170 mm Hg******


when does grenade lose suction

loses suction as it fills (20-30%)therefor empty grenades before they become half full


reasons why a drain should NOT exit the main incision

1. provides an entry point for bacteria2. increases the risk for incisional infection/dehiscence3. increases the risk of herniation4. FOR PENROSE, leads to spread of drainage fluid along incision line


reasons for drain failure

1. inadequate tube diameter2.improper placement3. plugging/kinking4.retrograde contamination5. loss of negative pressure6. premature removal/self mutilation