The National Nosocomial Infection Surveillance (NNIS) System Risk Index is a simple additive scale which can give an estimate of a patient's risk for surgical site infection.
Parameters:
(1) American Society for Anesthesiologists (ASA) preoperative assessment: This reflects the patient's preoperative physical status.
(2) duration of procedure: Rather than using a single time, the NNIS risk index indicates a prolonged case as one taking more than the 75th percentile for all such cases
(3) surgical wound class
Parameter
Finding
Points
ASA preoperative assessment
1 or 2
0
3, 4 or 5
1
duration operative procedure
<= 75th percentile for procedure
0
> 75th percentile for procedure
1
surgical wound class
clean or clean-contaminated
0
contaminated or dirty
1
NNIS risk index =
= (points for ASA preoperative assessment) + (points for duration of procedure) + (points for surgical wound class)
Interpretation:
• minimum score: 0
• maximum score: 3
NNIS Risk Index
Risk of Surgical Site Infection
0
1.5%
1
2.9%
2
6.8%
3
13%
Limitations:
• Since this is a general risk index, it may be not be accurate due to the number of possible procedures and the full range of patient diversity.
• It has been found to be inaccurate with certain procedures such as cesarean sections, craniotomies, ventricular shunt placement and cardiothoracic operative procedures.
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