OUTCOMES RESEARCH Providing the evidence for evidence-based medicine© Infection Prevention Prophylactic Antibiotics Supplemental Oxygen Normothermia Normoglycemia Smoking www.OR.org Surgical Site Infections Common • >500,000 surgical site infections per year in the States • 1-3% incidence overall; ≈10% after colon surgery Serious • Increases hospital duration ≈1 week • Doubles ICU admission and mortality Costly • $1.6 billion annually in the United States • 3.7 million excess hospital days yearly in the States CMS priority • Probable “pay-for-performance” measure Decisive Period All wounds become contaminated Infections established within 2 h of contamination • Interventions most effective during “Decisive Period” Progression to infection determined by • Prophylactic antibiotics • Host defense Prophylactic Antibiotics Effective only during the decisive period • Subsequent administration useless (or harmful) Should be given within 1 hour before incision • Repeat after 4-6 hours for long operations • Discontinue within 24-48 hours Various guidelines for type of antibiotic • In practice, surgeons choose antibiotics • Our mission is to give them — on time Host Defense Oxidative killing by neutrophils • Primary defense against surgical pathogens Oxygen is transformed to superoxide radical – Killing determined by tissue oxygen Measuring Tissue Oxygen Tissue oxygenation ≠ saturation; much lower than arterial PO2 Tissue Oxygen Correlates with Infection O b s e rv e d - E x p e c te d In fe c tio n R a te (% ) 20 10 0 -1 0 45 55 65 P s q O 2 75 (m m 85 95 H g ) Hopf, et al., 1996, Arch Surg Supplemental Oxygen Supplemental Oxygen • Easy to provide • Inexpensive (a few cents/patient) Recent utilization • Usually 30% in Europe • Essentially random concentrations in the States Rationale for various concentrations unclear Atelectasis: Pulmonary Function 30% 80% 14 16 AaDO2 (mmHg) 29 ± 13 30 ± 8 0.73 Saturation (%) 95 ± 2 95 ± 2 0.45 Number P Akça, et al. 1999, Anesthesiology Postoperative Atelectasis 10 8 6 Atelectasis 4 (%) 2 These data provide a 99% power to detect a 2% difference in the atelectasis rate, at an alpha level of 0.05 0 30 80 FiO2 (%) Hemodynamic Effects 40% 100% 1860 2300 CI 2.8 2.5 MAP 69 69 SVR Harten, et al 2005, JCVTA Greif, et al. NEJM, 2000 Hypothesis: 80% O2 reduces wound infection risk 500 patients having elective colon resection • Standardized antibiotic, anesthetic, & fluid management • Intraoperative core temperature maintained at 36oC Randomization • 30% oxygen (balance nitrogen); PaO2 ≈ 120 • 80% oxygen (balance nitrogen) ; PaO2 ≈ 350 Wound infections • Wounds evaluated daily by a blinded observer • Pus and positive culture required for diagnosis Subcutaneous Oxygen Tension (n=30) 200 PsqO2 (mmHg) 150 80% FiO2 100 30% FiO2 50 0 Intra-op 1 2 3 Post-op 4 0 1 Time (h) 2 3 Surgical Wound Infections (n=500) Hospitalization (days) Infection (%) 30% Oxygen 80% Oxygen P 11.9 ± 4 12.2 ± 6.1 0.26 11 5 0.01 Oxygen is as effective as antibiotics! Effect of Infections Number Hospitalization (days) Infected Uninfected 40 460 18 ± 9 11 ± 4 P <0.001 Infections prolong hospitaliation by a full week Pryor, et al. JAMA, 2004 Protocol • 160 patients randomized to 35% or 80% oxygen – 30% at low risk of infection – Inadequate sample size; stopped early • Anesthetic, fluid, and pain management uncontrolled • Unblinded, retrospective evaluation of wound infection Results • Five patients dropped from 80% oxygen group • Patients assigned to 80% oxygen were – Twice as likely to have BMI >30 kg/m2 – Lost more blood, received more fluid – More likely to require postoperative intubation (5 vs. 1 pt) • 80% oxygen increased infection risk from 11% to 25% Belda, et al. 2005, JAMA Standardized antibiotic, anesthetic, & fluid management Randomization • 30% vs. 80% oxygen (balance nitrogen) Wound infections: CDC criteria by blinded observer Hospitalization (days) Infection (%) 30% Oxygen 80% Oxygen P 10.5 ± 4.4 11.7 ± 7.0 0.09 35 22 0.04 Adjusted odds ratio 0.46 (95 CI 0.22-0.95, P = 0.04) Additional Evidence Myles, et al. (n = 2,000) Infection (%) Fleischmann, et al. (n = 418) Infection (%) 80% Oxygen, 20% Nitrogen 70% Nitrous, 30% Oxygen P 7.7 10.0 0.03 65% Nitrous, 35% Oxygen 65% Nitrogen, 35% Oxgyen 20 15 0.21 Temperature and Infection Hypothermia • Decreases tissue oxygen • Impairs numerous immune functions Hypothesis: normothermia reduces infection risk 200 patients having elective colon resection • Standardized antibiotic, anesthetic, & fluid management • Randomized to normothermia or ≈2°C hypothermia Wound infections • Wounds evaluated daily by a blinded observer • Pus and positive culture required for diagnosis Kurz, et al., 1996, NEJM N o rm o the rm ic Hyp o the rm ic P Te m p e rature 36.6 ± 0.5 34.7 ± 0.6 <0.001 Infe ctio ns (%) 6 19 <0.01 12.1 ± 4.4 14.7 ± 6.5 =0.001 Ho s p italizatio n (d ays ) (n = 200) Normothermia is more effective than antibiotics! Beneficial effect of active warming on infection confirmed by Melling, et al. Lancet, 2001 Forced-Air vs. Circulating-Water 38 Forced-Air 36 3.5°C T em p (°C) 3 4 Circulating-Water 0 4 8 Time (h) 12 Kurz, et al. 1993, Anesth Analg Fluid Warming Cooling by intravenous fluids • 0.25°C per liter crystalloid at ambient temperature • 0.25°C per unit of blood from refrigerator Cooling prevented by warming solutions • Type of warmer usually unimportant Fluid warming does not prevent hypothermia! • Most core cooling from redistribution • 90% of heat loss is from anterior skin surface Smoking Decreases Tissue Oxygen Tissue oxygen decreases: 65 ± 7 to 44 ± 3 mmHg • Jensen, et al. Arch Surg, 1991 Tissue oxygen 40-50 mmHg —> infection • Hopf, et al. Arch Surg, 1997 "Pack-a-day" smokers hypoxic most of the time Hypothesis: smoking • Increases the risk of surgical wound infection Subjects: 200 patients having colon resection Smoking and Infection (1996) N Infections (%) Hospital Duration (days) Smokers Nonsmokers 76 148 22% 7% <0.001 15 ± 7 13 ± 5 0.02 P Kurz et al., 1996, NEJM Smoking and Infection (≥2000) Greif, et al., 2000, NEJM, n=500 • No effect of smoking on infection risk Fleischmann, et al., 2005, Lancet, n=400 • No effect of smoking on infection risk Belda, et al., 2005, JAMA, n=300 • No effect of smoking on infection risk Conclusion • No effect of smoking on infection now… • Because smoking is no longer allowed in hospitals Hyperglycemia and Infection Tight control of glucose improves immunity – [Gallacher et al. Diabet Med 1995] Glucose control maintains neutrophil phagocytosis – [Athos et al. Anesth Analg 1999] Mortality reduced by intensive insulin therapy in critical care patients (including cardiac surgery) – [Van Den Berghe et al., N Engl J Med 2001] Summary Prophylactic antibiotics: • Most effective when given within one hour before incision Supplemental oxygen: • Does not cause atelectasis • Halves the risk of surgical wound infection Maintaining perioperative normothermia: • Reduces the risk of surgical wound infection 3-fold • Reduces the duration of hospitalization 20% Smoking: • No longer increases infection risk • Many other harmful effects Hyperglycemia: • Importance of intraoperative glucose control remains unknown Recommendations Timely antibiotic administration Provide 80% oxygen when practical Maintain Normothermia • Forced-air • Fluid warming Euglycemia • Probably prudent OUTCOMES RESEARCH Providing the evidence for evidence-based medicine©