Ch. 19 Bandages and Drains

Question 1

Functions of the primary layer of a bandage

Answer 1

final barrier between wound and outside contaminants
absorbs and transfers exudate to next layer
maintain moist wound environment that supports selective autolytic debridement, granulation, epithelialization, and or contraction

Question 2

four reasons why a primary dressing layer may adhere to a wound

Answer 2

1. its absorptive ability is greater than the amount of wound fluid produced
2. a gelling dressing has not been left in place long enough to become a gel
3. the dressing has been left so long that it is not dried out
4. dried exudate, granulation tissue, or new epithelium has invaded the pores or open weave of a dressing

Question 3

Laplace’s law for bandages:

NT = RW

Answer 3

N is the number of bandage layers
T is the bandage tension
R is the radius of the curvature of the body party getting wrapped
W is the width of the bandage material
*because limb circumference and therefore R increases in a distal to proximal direction, the pressure gradient under an evenly applied bandage naturally increases proximally

Question 4

Tension to extension ratio in regards to bandages

Answer 4

This describes the amount of tension generated relative to the extent to which a bandage material is stretched
ex. cast padding generates low tension even when fully extended
but vet wrap is elastic and has high tension even when only partially stretched

Question 5

What is the normal closing pressure of arterioles in the skin versus the muscle?

Answer 5

30 mmHg for the skin

50 mmHg for muscle

Question 6

Second intention wounds heal by contraction and epithelialization. Why is this important to remember for a wound over a joint?

Answer 6

For a wound that overlies the flexion surface of a joint, joint immobilization favors epithelialization and joint movement favors contraction

Question 7

Three benefits of drains

Answer 7

1. removal of accumulations of serum and blood that provide a media for bacteria
2. relief of pressure that can compromise tissue perfusion and cause pain
3. evacuation of inflammatory mediators, bacteria, necrotic tissue, and foreign matter that perpetuate tissue compromise

Question 8

Drain materials

Answer 8

latex (can be steam sterilized)
red rubber
polyethylene
polyvinyl chloride
silicone rubber

Question 9

polyethylene drain

Answer 9

thermoplastic polymer with a low coefficient of friction and good wear resistance
has a low melting point so it requires steam sterilization

Question 10

polyvinyl chloride drain material

Answer 10

made with a plasticizer that ultimately can leach into tissues
binds with ethylene oxide so cannot be sterilized that way as this can lead to hemolysis in the body

Question 11

silicone rubber (Silastic) drain tubing

Answer 11

highly biocompatible

can be steam sterilized

Question 12

how do penrose drains work?

Answer 12

passive drain
a combination of capillary action, gravity, overflow, and/or fluctuation of pressure within the space occupied by the drain
the amount flowing is proportional to its surface area, therefore, the cylindrical shape provides a high surface area to volume ratio and then allows significant drainage in a compact package

Question 13

What are the recommended pressures for wound vacuums on drains?

Answer 13

25-74 mmHg for delicate tissue
75-250 mmHg for heavier exudate
200-400 mmHg to encourage active adhesion between surfaces
250-350 mmHg to open drain occlusions or move large fluid volumes quickly

Question 14

Poiseuille’s law

F = dPπr^4/8nL

Answer 14

F is the flow of fluid through the drain lumen
dP is the pressure difference between the ends of the drain
r is the radius of the tube
n is the viscosity of the fluid
L is the length of the drain tube
Therefore, doubling the drain diameter will increase flow 16 fold
Having the drain length will increase flow 2 fold

Question 15

Name four reasons why a drain should not exit the main incision site

Answer 15

1. provides an entry point for bacteria, which can migrate all along the incision
2. increases the risk for incisional infection and dehiscence
3. increases the risk for herniation
4. for passive drains, leads to a spread of drain fluid along the incision line