Chapter 19 Bandages and Drains

Question 1

Whan shoudl primarylayer be changed?

Answer 1

When absorbtive capacity reached or when its properties ar eno longer appropriate for stage of wound healing.

Question 2

List 4 reasons a dressing may adhere to wound

Answer 2

1. Absorbtive ability of dressing is greater than the amount of wound fluid produced
2. Gelling dressing that has not been in place long enougn (initial non-gelled form may adhere to wound)
3. Dressing left in plae so long ot has dreid out
4. Dried exudate, granulation tissue or new epithelium has invaded the pores of dressing.

Question 3

Laplace’s law describes the pressure applied at each point under a bandage. What is the formula?

Answer 3

proportional to

(N × T)/(R × W)

where N is the number of bandage layers, T is the bandage tension, R is the radius of curvature of the body part being bandaged, and W is the width of the bandage material under tension.

Because limb circumference and thus the radius of curvature (R) generally increase in a distal-to-proximal direction, the pressure gradient under an evenly applied bandage naturally decreases proximally. Exceptions arise when a proximal area is narrower than a more distal site, such as the regions just proximal to the digits, carpi, and tarsi.1 These sites are at risk for a tourniquet effect and were the most commonly affected locations in a case series of ischemic bandage injuries in dogs and cats.1 Additional padding placed to effectively increase the diameter of narrow sites helps restore a gradual, proximally directed decrease in the pressure gradient

Question 4

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

Answer 4

30 mmHg in skin

50 mmHg in muscle

N.B. Initial application pressure of RJB 50-60 mmHg, declined rapidly in first 15 minutes to around 20 mmHg

Question 5

List 6 benefits of appropriate pressure dressing

Answer 5

1. Controls haemorrhage
2. Limits intercellular fluid accumulation and dead space
3. Prevents seroma/haematoma
4. Counters centrifugal expansion of wound edges
5. Decreases spread of wound microflora
6. Supports underlying tissue

Question 6

List three techniques for pressure relief

Answer 6

1. Doughnut
2. Bandage window
3. Splint (e.g. to prevent limb bending)

Question 7

Ina group of 60 dogs and cats that had casts to manage ortho condition, how may developed ST injury and how many of those moderate/severe?

Answer 7

63% developed St injury

40% of those moderate/severe

Question 8

What is the temperature difference between normal body temp and surface temp of exposed wound?

Answer 8

Wound 16°C lower –> suppressed healing activity

Question 9

How long do dispersed bacteria remain aerosolised for?

Answer 9

30 minutes

Question 10

List 3 benefits of drains

Answer 10

1. Removal of serum/blood accumulations
2. Relief of pressure
3. Evacuation of inflammatory mediators, bacteria, necrotic tissue, debris

Question 11

What are penrose drains made of?

Answer 11

Latex.

radio-opaque, can be steam sterilized.

Question 12

What are recommended drain vacuum levels in humans?

Answer 12

24-400 mmHg

Question 13

Laminar flow through drain described by Poiseuilles law. What is formula?

Answer 13

F = dPπr4/8nL

where F is the flow of fluid through the drain lumen, dP is the pressure difference between the two ends of the drain, r is the radius of the tube, n is the viscosity of the fluid, and L is the drain length.

Thus, doubling the drain diameter increases flow 16-fold, and halving the drain length increases flow two-fold.

Question 14

Study of dogs with sc closed suction drain found reduced incidence of seroma if drain removed once production fell below what rate?

Answer 14

0.2 ml/kg/hr

Question 15

List5 ways to minimize risk of drain associated infection

Answer 15

1. As small and few drains as possible
2. Remove when no longer necessary
3. Use flexible drain (less trauma)
4. Used closed, active drain
5. Proper placement and handling technique (sterile)