Are children undergoing cardiac surgery receiving antibiotics at subtherapeutic levels?

Plasma concentrations of cefazolin in pediatric patients undergoing cardiac surgery

Background

The guideline for antibiotic prophylaxis in pediatric cardiac surgery is currently unavailable, and the effects of cardiopulmonary bypass (CPB) may result in low plasma cefazolin concentrations and subsequent postoperative surgical site infections (SSIs).

Aims

To demonstrate the calculated-unbound plasma concentrations of cefazolin during uncomplicated pediatric cardiac surgery.

Settings and Design

A prospective observational study that included 18 patients <seven years of age, undergoing elective cardiac surgery with CPB.

Materials and Methods

An intravenous infusion of cefazolin (25 mg.kg^-1) was administered to patients over 30 minutes within 1 hour before skin incision (first dose). Another 25 mg.kg^-1 infusion was administered to the CPB prime volume (second dose). Blood samples were obtained at eight time points: 15 minutes after the first dose (T1); before aortic cannulation (T2); immediately after CPB initiation (T3); 30 (T4), 60 (T5), and 120 (T6) minutes after CPB; 15 minutes after CPB discontinuation (T7), and at skin closure (T8). The total plasma cefazolin concentrations were measured using liquid chromatography tandem mass spectrometry.

Results

The unbound cefazolin concentrations were calculated assuming 80%-protein binding. The median cefazolin levels were 18.1 (range 4.3-27.0), 11.9 (2.8-24.1), 31.4 (18.3-66.1), 23.4 (13.7-35.9), 20.2 (15.4-24.9), 17.7 (14.8-18.0), 15.6 (9.8-26.2), and 13.3 (8.3-24.6) μg.mL^-1 from T1-T8, respectively. The cefazolin levels remained four times above the minimum inhibitory concentrations (MICs) for Methicillin-sensitive S. aureus (MSSA) and S. epidermidis in most patients, but they were inadequate for Enterobacter and E. coli.

Conclusion

This regimen produced adequate plasma cefazolin concentrations for common organisms that cause SSIs after cardiac surgery.

Population Pharmacokinetics of Cefoxitin Administered for Pediatric Cardiac Surgery Prophylaxis

BACKGROUND

Available data about pharmacokinetics (PK) of antimicrobials administered as surgical prophylaxis to children undergoing cardiac surgery with cardiopulmonary bypass (CPB) showed that drug concentrations during CPB may be supra or subtherapeutic. The aim of this study was to determine the population PK and pharmacodynamic target attainment (PTA) of cefoxitin during pediatric CPB surgery.

METHODS

A prospective interventional study was conducted. Cefoxitin (40 mg/kg, up to max 1000 mg) was administered before skin incision. Blood samples were obtained in the operatory room throughout surgery. Population PK, PTA, and safety of cefoxitin were evaluated in neonates, infants, children <10 and >10 years old.

RESULTS

Forty patients were enrolled. Cefoxitin levels correlated with time from bolus administration (r = -0.6, P = 0.0001) and, after 240 minutes from bolus, drug values below the target (8 mg/L) were shown. Cefoxitin concentrations were best described by a one-compartment model with first order elimination. A significant relationship was identified between body weight, age, body mass index, and serum creatinine on drug clearance and age, body weight, and body mass index on cefoxitin volume of distribution. The PTA for free drug concentration being above the minimum inhibitory concentration of 8 mg/L for at least 240 minutes was >90% in all age groups except in patients >10 years of age (PTA = 62%).

CONCLUSIONS

Cefoxitin PK appears to be significantly influenced by CPB with generally reduced drug clearance. The PTA was adequately achieved in the majority of patients except in patients >10 years old or longer surgeries.

Cefoxitin Prophylaxis During Pediatric Cardiac Surgery: Retrospective Exploration of Postoperative Trough Levels

BACKGROUND

This study aimed to explore inter-individual variability of cefoxitin trough levels, predictors of serum cefoxitin concentration and the probability of target attainment of drug levels above 4 mg/L after pediatric cardiac surgery.

METHODS

Retrospective study on children scheduled for elective cardiac surgery and having cefoxitin trough levels available up to 24 hours postsurgery.

RESULTS

Overall, 68 children (9 neonates, 34 infants, 15 children below or equal to 10 years old and 10 patients above this age) were included. Of these, 16 surgeries were performed off cardiopulmonary bypass and 52 were performed on cardiopulmonary bypass. The free cefoxitin concentrations showed a median (interquartile range) concentration of 1.7 (0.6-4.2) mg/L. The range of cefoxitin concentrations showed a 150-fold and 340-fold variability at cardiac intensive care unit admission and after 24 hours, respectively. The pharmacodynamics (PD) targets of free cefoxitin at 100% of the dosing interval, considering Eucast breakpoints for Methicillin Sensitive Staphylococcus Aureus (4 mg/L) and E.Coli (8 mg/L), were obtained in 28% and 16% of patients, respectively. Patient weight (odds ratio, 0.7; 95% confidence interval, 0.62-0.92; P = 0.006) and serum creatinine concentrations (odds ratio, 25; 95% confidence interval, 18-36; P = 0.004) showed a significant relationship with the PD targets.

CONCLUSIONS

Cefoxitin trough concentrations vary significantly in the first 24 hours after pediatric cardiac surgery. Both serum creatinine and body weight showed independent associations with cefoxitin concentration. The PD target was not obtained in the vast majority of the explored population, regardless of the target bacteria.

Fluid Overload and Cumulative Thoracostomy Output Are Associated With Surgical Site Infection After Pediatric Cardiothoracic Surgery

OBJECTIVES

To determine the impact of cumulative, postoperative thoracostomy output, amount of bolus IV fluids and peak fluid overload on the incidence and odds of developing a deep surgical site infection following pediatric cardiothoracic surgery.

DESIGN

A single-center, nested, retrospective, matched case-control study.

SETTING

A 26-bed cardiac ICU in a 303-bed tertiary care pediatric hospital.

PATIENTS

Cases with deep surgical site infection following cardiothoracic surgery were identified retrospectively from January 2010 through December 2013 and individually matched to controls at a ratio of 1:2 by age, gender, Risk Adjustment for Congenital Heart Surgery score, Society of Thoracic Surgeons-European Association for Cardiothoracic Surgery category, primary cardiac diagnosis, and procedure.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twelve cases with deep surgical site infection were identified and matched to 24 controls without detectable differences in perioperative clinical characteristics. Deep surgical site infection cases had larger thoracostomy output and bolus IV fluid volumes at 6, 24, and 48 hours postoperatively compared with controls. For every 1 mL/kg of thoracostomy output, the odds of developing a deep surgical site infection increase by 13%. By receiver operative characteristic curve analysis, a cutoff of 49 mL/kg of thoracostomy output at 48 hours best discriminates the development of deep surgical site infection (sensitivity 83%, specificity 83%). Peak fluid overload was greater in cases than matched controls (12.5% vs 6%; p < 0.01). On receiver operative characteristic curve analysis, a threshold value of 10% peak fluid overload was observed to identify deep surgical site infection (sensitivity 67%, specificity 79%). Conditional logistic regression of peak fluid overload greater than 10% on the development of deep surgical site infection yielded an odds ratio of 9.4 (95% CI, 2-46.2).

CONCLUSIONS

Increased postoperative peak fluid overload and cumulative thoracostomy output were associated with deep surgical site infection after pediatric cardiothoracic surgery. We suspect the observed increased thoracostomy output, fluid overload, and IV fluid boluses may have altered antimicrobial prophylaxis. Although analysis of additional pharmacokinetic data is warranted, providers may consider modification of antimicrobial prophylaxis dosing or alterations in fluid management and diuresis in response to assessment of peak fluid overload and fluid volume shifts in the immediate postoperative period.

Dosing antibiotic prophylaxis during cardiopulmonary bypass-a higher level of complexity? A structured review

In highly invasive procedures such as open heart surgery, the risk of post-operative infection is particularly high due to exposure of the surgical field to multiple foreign devices. Adequate antibiotic prophylaxis is an essential intervention to minimise post-operative morbidity and mortality. However, there is a lack of clear understanding on the adequacy of traditional prophylactic dosing regimens, which are rarely supported by data. The aim of this structured review is to describe the relevant pharmacokinetic/pharmacodynamic (PK/PD) considerations for optimal antibiotic prophylaxis for major cardiac surgery including cardiopulmonary bypass (CPB). A structured review of the relevant published literature was performed and 45 relevant studies describing antibiotic pharmacokinetics in patients receiving extracorporeal CPB as part of major cardiac surgery were identified. Some of the studies suggested marked PK alterations in the peri-operative period with increases in volume of distribution (V_d) by up to 58% and altered drug clearances of up to 20%. Mechanisms proposed as causing the PK changes included haemodilution, hypothermia, retention of the antibiotic within the extracorporeal circuit, altered physiology related to a systemic inflammatory response, and maldistribution of blood flow. Of note, some studies reported no or minimal impact of the CPB procedure on antibiotic pharmacokinetics. Given the inconsistent data, ongoing research should focus on clarifying the influence of CPB procedure and related clinical covariates on the pharmacokinetics of different antibiotics during cardiac surgery. Traditional prophylactic dosing regimens may need to be re-assessed to ensure sufficient drug exposures that will minimise the risk of surgical site infections.