Surgical site infection and use of antimicrobials

Question 1

What are 6 recommendations regarding reducing risk of SSI resulting from the operating suit?

Answer 1

1.  locating the operating room in a low-traffic location of the hospital 2. minimizing the number and activity of personnel.
2.  maintaining positive air pressure in the  operating room, 
3. filtering greater than 90% of the air, 
4. exchanging air 15 times per hour, 
5.  ensuring that air is introduced  from the ceiling and exhausted at the floor. 

Question 2

T/F: The CDC recommends the use of ultraviolet light in surgical suits to reduce SSIs.

Answer 2

False; It does not recommend the use of ultraviolet light to reduce SSIs.

Question 3

T/F: Infection of a surgical wound occurs most commonly as a  result of direct inoculation of the surgeon’s endogenous flora from the skin or mucous membranes. 

Answer 3

False; Infection of a surgical wound occurs most commonly as a  result of direct inoculation of the patient’s endogenous flora from  the  skin,  mucous  membranes,  or  hollow  viscera. 

Question 4

T/F: Polyglactin 910 is more likely to be correlated with SSI compared to silk suture.

Answer 4

False;  Silk suture  material is 3.4 times more likely than polyglactin 910 (Vicryl)  to be correlated with an infection.

Question 5

T/F:  Skin incisions made with  steel  scalpels  heal  faster than those made with laser tools or electrosurgical devices.

Answer 5

True; A benefit of laser and  electrosurgical  devices  is  improved  hemostasis  compared  to  the traditional scalpel. However, these devices also cause  collateral  tissue  damage,  resulting  in  eschar  formation. The  LigaSure  unit  and  harmonic  scalpel  are  associated  with  less  lateral  thermal  damage  compared  to  cautery  devices  and  thus  are  less  likely  to  produce  necrotic  tissue that may serve as a focus for infection.

Question 6

T/F:  The near-far-far-near suture pattern is associated with an increased rate of SSI  compared to a simple interrupted pattern.

Answer 6

True

Question 7

T/F:  A difference in peritoneal and peripheral serum glucose of greater than  25 mg/dL has been shown to be a good indicator of septic  peritonitis.

Answer 7

False;  A difference in peritoneal and peripheral serum glucose of greater than  50 mg/dL has been shown to be a good indicator of septic  peritonitis.

Question 8

T/F:  Blood  culture media are excellent for anaerobic culture and are superior  to directly plating onto agar plates.

Answer 8

False;  Blood  culture media are excellent for aerobic culture and are superior  to directly plating onto agar plates.

Question 9

What are two key considerations when selecting perioperative antibiotics?

Answer 9

Antimicrobials should achieve effective  tissue concentrations at the time of surgery, and act against  likely pathogens.

Question 10

Which of the following does not describe penicillins?

1. bactericidal
2. concentration-dependent
3. inhibits cell wall synthesis by binding to penicillin-binding proteins, leading to cell  lysis
4. may cause autoimmune hemolytic anemia, anaphylaxis,  transient hypotension, increased large  intestinal motility, cardiac arrhythmia
5. readily inactivated by bacteria that produce beta-lactamase

Answer 10

2. penicillins are time-dependent antimicrobials.

Question 11

Which of the following does not describe cephalosporins?

1. bactericidal
2. time-dependent
3. disrupt bacterial DNA by free radicals and  unstable intermediate compounds after  structural change once in target organism
4. may cause enterocolitis
5. readily inactivated by bacteria that produce beta-lactamase

Answer 11

3. cephalosporins are beta-lactams and work by inhibiting cell wall synthesis by binding to  penicillin-binding proteins, leading to cell  lysis.

Question 12

Which of the following does not describe aminoglycosides?

1. bactericidal
2. time-dependent
3. inhibit protein synthesis by binding to 30S  ribosomal subunit
4. may cause ribosomal subunit nephrotoxicity, neuromuscular blockade, ototoxicity
5. must be transported into the bacterial  cell, which requires energy and oxygen; as a result, anaerobic  bacteria  are  commonly  resistant. 

Answer 12

2. Aminoglycosides are concentration-dependent antimicrobials.

Question 13

Which of the following does not describe fluoroquinolones?

1. bactericidal
2. concentration-dependent
3. inhibit protein synthesis by reversibly binding  to 30S ribosomal subunit
4. may cause cartilage disorders in young (<3 yr) horses,  oral ulceration
5. has been linked to detrimental  effects  on  tendon,  cartilage,  and  bone

Answer 13

3. Fluoroquinolones inhibit bacterial DNA gyrase

Question 14

Which of the following does not describe metronidazole?

1. bacteriostatic
2. concentration-dependent
3. disrupts bacterial DNA by free radicals and  unstable intermediate compounds after structural change once in target organism.
4. may cause enterocolitis, inappetence

Answer 14

1. Metronidazole is bactericidal

Question 15

Which of the following does not describe trimethoprim/sulfonamides?

1. bacteriostatic
2. concentration-dependent
3. sulfonamides prevent conversion of PABA to dihydrofolic acid (1st step in folic acid synthesis) 
4. trimethoprim inhibits dihydrofolic acid reductace, inhibiting the conversion of dihydrofolic acid to tetrahydrofolic acid (2nd step in folic acid synthesis)
5. may cause idiosyncratic reactions

Answer 15

1. when  sulfonamides  are  used  alone, they were bacteriostatic. The  combined  activity  of  trimethoprim-sulfonamide as a result inhibits two successive  steps in the folic acid pathway, producing a bactericidal effect.

Question 16

Which of the following does not describe tetracyclines?

1. bacteriostatic
2. time-dependent
3. inhibit protein synthesis by reversibly binding  to 50S ribosomal subunit
4. may cause nephrotoxicity, discoloration of urine and  erupting teeth

Answer 16

3. tetracyclines inhibit protein synthesis by reversibly binding  to 30S ribosomal subunit

Question 17

Which of the following does not describe chloramphenicol?

1. bacteriostatic
2. time-dependent
3. inhibits protein synthesis by reversibly binding  to 50S ribosomal subunit
4. may cause nephrotoxicity, neuromuscular blockade,  ototoxicity

Answer 17

4. Chloramphenicol may cause Reversible aplastic anemia (use carefully; it  may causes idiosyncratic anemia in  humans)

Question 18

Which of the following does not describe macrolides?

1. bactericidal
2. time-dependent
3. inhibit protein synthesis by reversibly binding  to 50S ribosomal subunit
4. May be an intestinal prokinetic

Answer 18

1. Macrolides are bacteriostatic

Question 19

____________-dependent  antimicrobials are reliant on the ratio of the peak  plasma concentration of the antibiotic to the minimum inhibitory concentration (MIC) for the bacteria.

Answer 19

Concentration;  A ratio of greater  than 10:1 (more than 10 times MIC) or 12:1 is optimal for concentration-dependent antimicrobial effect.

Question 20

___________-dependent antimicrobials have a saturable concentration dependent  effect  on  bacterial  killing. 

Answer 20

Time; This  means  that  at  a  certain point above MIC, there is no additional benefit to higher  concentrations of the antimicrobial. Bacterial killing is optimized for these types of antibiotics by maintaining the concentration above the MIC for a longer period.

Question 21

 Four basic principles must be  followed to maximize the benefits of prophylactic antibiotics  and avoid potential complications: 

Answer 21

(1)  antimicrobials should  only be used when the benefits have been demonstrated by clinical trials or when an SSI would have catastrophic results. 
(2)  a safe, inexpensive,  and  bactericidal  antibiotic  that  covers the most commonly occurring contaminants of the operation 
(3)  time to achieve an effective tissue concentration at the time of surgery;   
(4)  tissue levels of antimicrobials maintained  throughout the procedure and at most for a few hours after the  skin incision is closed.

Question 22

Overall, antibiotic use should be restricted to patients in which  the  incidence  of  infection  exceeds ____%  without  prophylactic  antimicrobial use or when an infection would have devastating  results.

Answer 22

5%;  In equine arthroscopy, the use of antibiotics is probably not indicated with the infection rate being  reported to be 1.5%. General clean orthopedic procedures  with  a  reported  rate  of  SSIs  of  8%  and  clean-contaminated  procedures with a rate of 52% to 57% are obviously clear indications for prophylactic antimicrobial use. Similarly, abdominal surgery in the horse (emergency SSI of 39%; elective SSI of  7%)  has  good  evidence  to  support  the  use  of  prophylactic  antimicrobials.

Question 23

The use of antibiotics is probably not indicated in which surgical procedure?

1. elective arthroscopy
2. umbilical hernia repair
3. medial condylar fracture repair
4. enucleation 

Answer 23

 In equine arthroscopy, the use of antibiotics is probably not indicated with the infection rate being  reported to be 1.5%

Question 24

According to Auer and Stick, which surgical procedures have a SSI rate less than 5%?

Answer 24

routine castration and laparoscopic cryptorchidectomy, laryngoplasty, and arthroscopy

Question 25

The ______________________ refers to the period of time after  which  the  antimicrobial  concentration  has  fallen  below  the  MIC, during which growth of  the  target bacteria  is suppressed.

Answer 25

postantibiotic effect (PAE)

Question 26

What 4 factors determine PAE?

Answer 26

the antibiotic concentration, the duration of exposure to the antibiotic, the bacterial  species, and the antimicrobial used. 

Question 27

 All antibiotics appear to be  able to produce a PAE against ___________,  but β-lactam  antibiotics induce almost no prolonged effects against __________________.

Answer 27

gram-positive cocci; gram-negative bacilli

Question 28

Which drugs exhibit the most pronounced PAEs?

Answer 28

 Aminoglycosides, fluoroquinolones, and  protein-synthesis inhibitors ( [aminoglycosides], tetracyclines, chloramphenicol, macrolides) exhibit the most pronounced PAEs.

Question 29

T/F: The greater the magnitude above the MIC, the longer the PAE  is for time-dependent antimicrobials.

Answer 29

False; The greater the magnitude above the MIC, the longer the PAE  is for concentration-dependent antimicrobials.

Question 30

T/F:   The renal toxicity is  linked to aminoglycoside accumulation in proximal tubule cells  following uptake via the organic ion transport system.

Answer 30

 True

Question 31

In which of the following sets of surgical procedures are all of the procedures classified as “clean-contaminated”?

1. elective, primary closed, and undrained; gastrointestinal or respiratory tract entered without significant spillage; vagina entered; minor break in sterile technique.
2. traumatic wound (< 4 hours old); oropharynx entered; gastrointestinal or respiratory tract entered without significant spillage; acute bacterial infection encountered.
3. gastrointestinal or respiratory tract entered without significant spillage; vagina entered; minor break in sterile technique; genitourinary tract entered in absence of infected urine.
4. gastrointestinal or respiratory tract entered without significant spillage; acute bacterial inflammation encountered; minor break in sterile technique; genitourinary tract enteres in absence of infected urine.

Answer 31

3. all are clean-contaminated
4. elective, primarily closed, and undrained = “clean”
5. traumatic wound (< 4 hours old) = “contaminated”; acute bacterial infection encountered = “dirty”
6. acute bacT infection = “dirty”