After approval by the institutional board and after having obtained informed consent 24 patients having heart surgery with ECC were enrolled into the study. All patients had to be older than 18 years, and all patients had indwelling pulmonary artery catheters for reasons of underlying diseases or kind of surgery. 13 patients were female and 11 male, the mean age was 69 years (range 55 – 80),16 suffered from coronary heart disease (CAD) and were scheduled for coronary artery bypass grafting (CABG), 2 of these had additional aortic valve stenosis, one had left ventricular aneurysm and one had stenosis of carotid artery. In these patients surgery was extended according to diagnoses. Four patients had aortic valve replacement, two had mitral valve replacement and two had combined mitral and aortic valve replacement. In 18 patients cardiac surgery was performed for the first time, 6 patients had recurrent surgery.
In each patient age, body mass index, medical history (diabetes, lipid disorders, COPD) and actual medications (statins, corticosteroids) were recorded. 12 patients suffered from diabetes. 7 of them were insulin dependent. 4 patients had COPD.
In addition, the following serum parameters were determined: K+, Na+, Ca2+, PT, PTT, hemoglobin, hematocrit, platelets, leucocytes, bilirubine, urea, dextrose, CRP, PcapO2, PcapCO2. Before surgery patients underwent thorough cardiac diagnostics, including determination of ejection fraction.
Preparation for surgery, anesthesia and perioperative vital data monitoring (5 channel ECG, pulse oximetry, arterial blood pressure measurement, 7F pulmonary artery catheter (Arrow, Erdingen, Germany)) was done in the same standardized way for any patient. Before anesthesia was begun patients got 250 mg of methyl prednisolone intravenously. Anesthesia was induced with sufentanil, etomidate and cis-atracurium and maintained with midazolam, sufentanil and cis-atracurium. Ventilation during anesthesia was performed in volume controlled mode. Respiratory rate and tidal volume were adjusted in the way that normocapnia was achieved. 22 patients got 2 g cefazoline, 6 patients other antimicrobial drugs as perioperative prophylaxis.
For skin incision always a scalpel was used. Electrocautery was employed for dissection of subcutaneous tissues and for bleeding control. When patients underwent cardiac surgery for the first time sternotomy was performed by means of a jigsaw, in the case of recurrent surgery an oscillating saw was used. After sternotomy all patients got 2 millions IU of aprotinine and 400 IU/kg of heparine intravenously before start of cardio pulmonary bypass (CPB). For CPB continuous, non pulsatile flow was employed, oxygenation was achieved by means of uncoated membrane oxygenators. Priming of heart and lung machine consisted of 1000 mL of gelatine solution, 500 mL of normal electrolyte solution, 5000 IE heparine, 250 mg methyl prednisolone and 1000 mg vitamin C.
During surgery duration of aortic clamping and CPB, volume of cardioplegic solution used, volume of hemodilution and infusions, diuresis and minimum body temperature and dose of catecholamines at the moment of weaning from CPB were recorded.
After surgery patients were transferred to the intensive care unit (ICU). All patients were sedated and mechanically ventilated beyond the end of the last breath gas analysis performed within the study. On arrival in the ICU, an arterial blood gas analysis was done, and hemoglobin, hematocrit, platelets, creatinine, dextrose, K+, Na+, Ca2+ were determined in patients' blood. About four hours after the end of surgery blood was taken again to determine creatinine kinase (CK), CK-myocardium/brain (CK-MB) and troponine T (TNT). Diuresis, dose of catecholamines and transfusion of blood or blood products during stay in ICU were recorded.
Breath samples were taken after induction of anesthesia, after sternotomy, 5 min after end of ECC, and 30, 60, 90, 120 and 150 min after end of surgery. For that purpose, a sterilized stainless steel T-piece and the measuring cuvette of a commercially available capnometer had been incorporated into the respiratory circuit near the endotracheal tube (ETT). Contamination of respiratory circuits with volatile anesthetics was meticulously excluded. Breath samples (10 mL) were drawn from the respiratory circuits into a gas tight syringe and transferred immediately into evacuated 20 mL glass vials. Alveolar breath samples were taken manually from the expiratory limb of the respiratory circuit by means of a gas tight syringe in a CO2 controlled way as described before [10–12].
For that purpose, the sensor of a fast responding mainstream CO2 analyzer (Capnogard, Novametrix Medical Systems Inc., Wallingford, CT, USA) was inserted into the respiratory circuit near the ETT. Alveolar gas samples were withdrawn from the circuit under visual control of expired CO2 in the way that gas collection only took place during the alveolar phase of expiration. Inspiratory samples were taken near the ventilator inlet. The access to the respiratory circuit was realized through sterilized stainless steel T-pieces. At least two samples for each measurement were collected. Inspired samples were withdrawn from the inspiratory limb of the ventilator tubing . Although it was known from pre-study experiments that samples in the vials remain stable for at least 8 h, preconcentration and analysis was begun immediately after sampling.
Preconcentration and analysis of volatile substances
Volatile substances in breath were preconcentrated by means of solid phase micro extraction (SPME) [14–16]. Preconcentration and desorption of the volatile organic compounds were done automatically by means of a SPME autosampler (CTC Multi Purpose Sampler, PAL, Zwingen, Switzerland). Before the SPME procedure, the PDMS/Carboxen-coated fiber was pre-treated in the injection port of a gas chromatograph at 285°C for 30 min. Internal standard (2,3-dimethylbutadiene) was added through the septum by means of a micro syringe. The vial was vortexed for 5 min at 40°C in the heating block of the CTC autosampler. Then, the syringe needle of the SPME device was inserted into the vial for 5 min. The needle containing the SPME fiber was withdrawn and introduced into the port of a capillary gas chromatograph (Varian, Walnut Creek, CA, USA). Port temperature was 280°C. The SPME device was held in the port for 2 min to allow complete desorption of the components.
Substances were separated on a 30 m (0.32 mm ID.) Porabond Q column (Varian/Chrompack, Middleburg, The Netherlands), detected and identified by mass spectrometry (Saturn 2000, Varian, Walnut Creek, CA, USA) and quantified via calibration curves. Precision, variation and limits of detection of SPME procedures have been extensively studied in previous work [11, 16–19]. Limits of detection (LODs) for the analysis of isoprene, pentane and acetone in exhaled gas were 0.01, 0.02 and 0.1 nmol/L. Intraday variation was < 5% relative standard deviation (RSD) (n = 8) for all substances.
Results are given as medians and 25–75% percentiles or as means and 95% confidence intervals, as appropriate. Correlation between different variables was assessed by means of Spearman correlation coefficients for not parametric data. Multiple comparisons between data from different measurements during and after surgery were done by means of One Way Repeated Measures Analysis of Variance for normally distributed values or by means of Friedman Repeated Measures Analysis of Variance on Ranks for non parametric data. The Student-Newman-Keuls test was used for post-hoc analysis. Comparison between only two patient groups was done by Wilcoxon signed rank test.
In order to render results comparable between different patients exhaled substance concentrations were normalized to respective concentrations at 120 min after end of surgery (Ci/C120). By means of that normalization effects of inspiratory substance concentrations were also eliminated as each patient served as his own control.
P < 0.05 was considered to be statistically significant. For statistical testing the computer program SPSS 11.0 for Windows was used.