Sven-Olov Nyström

Sternal wound complications-incidence, microbiology and risk factors

OBJECTIVE Sternal wound complications, i.e. instability and/or infection (mediastinitis), are important causes of morbidity in patients undergoing cardiac surgery via median sternotomy. Coagulase negative staphylococci, a normal inhabitant of the skin, have evolved as a cause of sternal wound infections. Since these opportunistic pathogens often are multiresistant, they can cause therapeutic problems. METHODS From 1980 through 1995 open heart surgery, was performed on 13,285 adult patients. Reoperation necessitated by sternal wound complications occurerd in 203 patients (1.5%). The incidence was 1.7% (168/9987) after coronary artery bypass grafting (CABG group) and 0.7% (35/3413) after heart valve surgery with or without concomitant CABG (HVR group). RESULTS Factors independently related to sternal complications in the CABG group (variable odds ratio [95% C.I.]): year of surgery, 1.9 [1.3-2.8] in 1990-1992, 2.0 [1.4-2.9] in 1993-1995; female sex, 0.4 [0.2-0.6]; diabetic disease, 1.8 [1.2-2.5]; bilateral ITA procedure, 3.3 [1.1-7.7]; and postoperative dialysis, 3.1 [1.4-6.9]. In the HVR group they were: use of ITA graft, 3.7 [1.7-7.7]; early re-exploration because of bleeding 3.0 [1.1-8.2]; and postoperative dialysis 3.1, [1.4-9.3]. Multivariate models were used to compute the risk for sternal complications in each patient. However, the prognostic models based on these risk scores provided low sensitivity and low predictive value. Patients with sternal wound complications showed no increased early mortality but worse long-term survival even after adjustment for other factors (relative hazard in CABG group 1.9 [1.2-2.8]; in HVR group 2.1 [1.1-4.3]. CONCLUSIONS The use of ITA grafts seems to be one of the most important factors related to sternal wound complications. However, patients at truly increased risk for this complication could not be identified on the basis of the risk factors considered in this study.

Ventilation-perfusion inequality in patients undergoing cardiac surgery.

BackgroundImpaired gas exchange is a major complication after cardiac surgery with the use of extracorporeal circulation. Blood gas analysis gives little information on underlying mechanisms, in particular if the impairment is multifactorial. In the current study we used the multiple inert gas technique with recordings of hemodynamics to analyze the separate effects of intrapulmonary shunt (&OV0422;s/&OV0422;r), ventilation-perfusion (&OV0312;A/&OV0422;) mismatch, and low mixed venous oxygen tension on arterial oxygenation during cardiac surgery. Methods&OV0312;A/&OV0422; distribution was studied in nine patients undergoing coronary artery revascularization surgery. The obtained data related to &OV0312;A/&OV0422; distribution were perfusion of lung regions with &OV0312;A/&OV0422; < 0.005 (&OV0422;s/&OV0422;r), perfusion of lung regions with 0.005 < &OV0312;A/&OV0422; < 0.1 (“low”-&OV0312;A/&OV0422; regions), ventilation of lung regions with 10 < &OV0312;A/&OV0422; < 100 (“high”-&OV0312;A/&OV0422; regions), and ventilation of lung regions with &OV0312;A/&OV0422; > 100 (dead space [&OV0312;D/&OV0312;T]). In addition, arterial and mixed venous oxygen and carbon dioxide tensions and systemic and pulmonary hemodynamics were analyzed. Recordings were made before and after induction of anesthesia, after sternotomy, 45 min after separation from extracorporeal circulation, 4 h postoperatively during mechanical ventilation, and on the 1st postoperative day during spontaneous breathing. ResultsIn the awake state, &OV0422;s/&OV0422;r was 4 ± 4%, and perfusion of low-&OV0312;A/&OV0422; regions was 3 ± 5%. The sum of &OV0422;s/&OV0422;r and low-&OV0312;A/&OV0422; units correlated with the alveolar-arterial oxygen tension gradient (PA-ao2) (r = 0.63, P < 0.05). After induction of anesthesia, &OV0422;s/&OV0422;r increased to 10 ± 9% (P = 0.069). Sternotomy had little effect on shunt, but &OV0422;s/&OV0422;r increased to 22 ± 8% (P < 0.01) after separation from extracorporeal circulation, which was correlated with a significantly higher PA-ao2 (r = 0.77, P < 0.05). Postoperatively, gas exchange improved rapidly, as assessed by a decrease of PA-ao2 from 341 ± 77 to 97 ± 36 mmHg (P < 0.01) and a reduced &OV0422;s/&OV0422;r (5 ± 4%, P < 0.05). On the 1st postoperative day, arterial oxygen tension was significantly lower than preanesthesia values (58 ± 6 vs. 68 ± 8 mmHg, P < 0.05). &OV0422;s/&OV0422;r had increased to 11 ± 6% (P < 0.05), but little perfusion of low-&OV0312;A/&OV0422; units was observed. A correlation was found between PA-ao2 and &OV0422;s/&OV0422;r (r = 0.82, P < 0.03). Conclusions&OV0422;s/&OV0422;r is a major component of impaired gas exchange before, during, and after cardiac surgery. &OV0422;s/&OV0422;r increases after induction of general anesthesia, probably because of development of atelectasis. After separation from extracorporeal circulation, accumulation of extravascular lung water or further collapse of lung tissue may aggravate &OV0422;s/&OV0422;r-Postoperatively, oxygenation improves, possibly because of recruitment of previously nonventilated alveoli or resolution of extravascular lung water. During spontaneous breathing, additional mechanisms such as altered mechanics of the chest, perfusion of low-&OV0312;A/&OV0422; regions, and decreased mixed venous oxygen tension may contribute to impaired gas exchange.

Early extubation after coronary artery surgery in efficiently rewarmed patients: A postoperative comparison of opioid anesthesia versus inhalational anesthesia and thoracic epidural analgesia

Twenty-eight patients were studied after uncomplicated aortocoronary bypass surgery with hypothermic cardiopulmonary bypass (CPB). In all patients residual hypothermia was effectively treated by the use of extended rewarming during CPB and postoperatively by an external heat source. This treatment almost eliminated postoperative shivering, and it resulted in the lowering of oxygen uptake, carbon dioxide production, and required ventilatory volumes to stable levels where spontaneous breathing could be used safely. The patients were divided into two groups. In group I (n = 12), intraoperative anesthesia was based on an intravenous (IV) opioid (phenoperidine), which caused persistent respiratory depression and made mechanical ventilation necessary for a mean postoperative time period of 10.7 +/- 3.8 hours even with the rewarming. In group II (n = 16), thoracic epidural analgesia and intraoperative general anesthesia with enflurane were used. In this group, postoperative metabolic and ventilatory requirements were stable and low, finger skin temperature was normalized earlier, systemic vascular resistance was lower, and stroke index was higher. Emergence from anesthesia was uneventful and was achieved early postoperatively in Group II. The patients had good pain relief and were mentally alert. Adequate spontaneous breathing was resumed quickly and endotracheal extubation was performed within the first two postoperative hours (1.6 +/- 0.5 hours). No complications or increased morbidity occurred, and no patient needed to be reintubated in Group II.

Thoracic Intravascular and Extravascular Fluid Volumes in Cardiac Surgical Patients

BackgroundOne possible mechanism of impaired oxygenation in cardiac surgery with extracorporeal circulation (ECC) is the accumulation of extravascular lung water (EVLW). Intrathoracic blood volume (ITBV) and pulmonary blood volume (PBV) also may increase after separation from ECC, which can influence both cardiac performance and pulmonary capillary fluid filtration. This study tested whether there were any relationships between lung fluid accumulation and pulmonary gas exchange during the perioperative period of cardiac surgery and ECC. MethodsTen patients undergoing myocardial revascularization were studied. ITBV, PBV, and EVLW were determined from the mean transit times and decay times of the dye and thermal indicator curves obtained simultaneously in the descending aorta. Gas exchange was assessed by arterial and mixed venous partial pressure of oxygen (Po2) and carbon dioxide (Pco2), and calculation of alveolo-arterial Po2 gradient (Pa-ao2) and venous admixture (Qva/Qt). Recordings were made after Induction of anesthesia, after sternotomy, 15 min after separation from ECC, and 4 and 20 h postoperatively. ResultsAfter induction of anesthesia, EVLW (6.0 ± 1.0 ml/kg, ± ± SD), PBV (3.6 ± 1.3 ml/kg), and ITBV (18.4 ± 2.7 ml/kg) were within normal ranges. Oxygenation was moderately impaired, as indicated by an increased Pa-ao2 (144 ± 46 mmHg) and Qva/Qt (11 ± 4%). After separation from ECC, EVLW had increased to 9.1 ± 2.6 ml/kg, which was accompanied by an increase of ITBV (26.0 ± 4.4 ml/kg) and PBV (5.6 ± 1.9 ml/kg). Paa-02 (396 ± 116 mmHg) and Qva/Qt (29 ± 7%) also were increased. ITBV and PBV remained increased 4 and 20 h post-operatively, but EVLW decreased to presurgery values. No correlations were found between thoracic intravascular and extravascular fluid volumes and gas exchange. ConclusionsCardiac surgery with the use of ECC induces alterations of thoracic intravascular and extravascular fluid volumes. Postoperatively, increased ITBV and PBV need not be associated with higher EVLW. Thus, sufficient mechanisms protecting against lung edema formation or providing resolution of EVLW probably are maintained after ECC. Since oxygenation is impaired during and after cardiac surgery, it is concluded that mechanisms other than or in addition to changes of ITBV, PBV, and EVLW predominantly influence gas exchange.

Coagulation, fibrinolysis and bleeding after open-heart surgery

To investigate the disputed pathogenesis of excessive bleeding after open-heart surgery, variables representing different hemostatic systems were correlated to postoperative blood loss in 29 patients. The general bleeding tendency in the early postoperative phase was probably attributable to depletion of hemostatic agents due to hemodilution, decreased antiplasmin activity, instantaneous but reversible platelet dysfunction following protaminization, and the natural interval to development of complete hemostasis. Heavy bleeding (greater than 800 ml/16 h) occurred in ten patients, who had significantly reduced levels of von Willebrand factor and lower active platelet count than in eight patients with minor bleeding. Defective primary hemostasis thus seemed to be the main cause of increased postoperative bleeding in these patients. Determination of platelet function by glass retention test showed good clinical relevance and gave considerably more reliable diagnosis than conventional platelet count alone. The patient with the greatest blood loss also showed drastic decrease in the plasminogen-binding form of alpha 2-antiplasmin, suggesting that additionally impaired fibrinolysis inhibition may contribute to development of severe hemorrhagic complications.

Bubble and Membrane Oxygenators—Comparison of Postoperative Organ Dysfunction with Special Reference to Inflammatory Activity

Bubble and membrane oxygenators (2 types of each) were compared in a randomized study of 96 patients undergoing coronary bypass grafting. Cardiac performance, assessed from postoperative need of inotropic support, was significantly better in the membrane oxygenator group. After perfusion lasting more than 2 hours, respiratory function, measured as alveolar-arterial oxygen pressure gradient, was less compromised in that group and renal function, quantified as postoperative rise of serum creatinine was less disturbed. Cerebral function, studied in terms of psychometric test results and concentration of adenylate kinase in cerebrospinal fluid, did not differ between the bubble and membrane oxygenator groups. In investigations concerning changes in inflammatory activity during bypass, complement activation could not be related to the mentioned clinical parameters. Release of the neutrophil granulocyte factors lactoferrin and myeloperoxidase was greater in the bubble oxygenator group and correlated to impaired cardiac and renal performance, but not to pulmonary or cerebral dysfunction.

Inflammatory System Activation During Cardiopulmonary Bypass as an Indicator of Biocompatibility: A Randomized Comparison of Bubble and Membrane Oxygenators

As the exposure of blood to foreign material during cardiopulmonary bypass (CPB) leads to triggering of inflammatory systems, the inflammatory response was used as an indicator of the biocompatibility of oxygenators. Activation of complement and neutrophil granulocytes during CPB was studied in 96 patients undergoing coronary bypass, with randomized comparisons between four different oxygenators, two of bubble and two of membrane type. Seven patients undergoing thoracotomy without CPB served as controls. During CPB there was significant complement activation, measured as changes in the ratio C3d/C3, with no demonstrable difference between the bubble and membrane oxygenator groups. Such change was not seen in the controls. Neutrophil granulocytes released significant amounts of the granule proteins lactoferrin and myeloperoxidase during CPB, but not during thoracotomy without CPB. The plasma concentrations of lactoferrin and myeloperoxidase were significantly lower in the membrane oxygenator groups, possibly indicating better biocompatibility. The strong inflammatory response with both oxygenator types, however, indicates that presently used CPB devices have unsatisfactory biocompatibility.

Early Results of Aortic Valve Replacement with or Without Concomitant Coronary Artery Bypass Grafting

Early results of aortic valve replacement were reviewed in 962 unselected patients, 659 without concomitant coronary bypass surgery (AVR group) and 303 with combined valve replacement and coronary artery bypass grafting (AVR + CABG). The early (less than 30-day) mortality was 4.6% in the AVR, and 5.9% in the AVR + CABG group. Multivariate analysis showed coronary artery stenoses and NYHA functional class to be independent predictors of early mortality in the AVR group, and the number of distal anastomoses as the strongest predictor in AVR + CABG. The incidence of peroperative technical complications in the cases with fatal outcome was 27% in the AVR and 6% in the AVR + CABG group. The incidence of myocardial injury (new Q wave or evidence of increased enzyme leakage) was 11% in AVR and 21% in AVR + CABG. Independent predictors of postoperative myocardial injury were aortic cross-clamp time, year of surgery, coronary artery stenoses and NYHA class in AVR and aortic cross-clamp time and year of surgery in AVR + CABG. The study suggests that coronary artery disease increases risk in aortic valve replacement with or without CABG. Replacement should be undertaken before endstage of the disease (NYHA IV), with CABG if significant coronary disease is present, and in multivessel disease the number of distal anastomoses should be restricted in order to shorten aortic cross-clamp time.

Long-term relative survival after primary heart valve replacement.

OBJECTIVE Determination of the optimal timing of primary heart valve replacement is an important issue. The present paper provides a synopsis over early and late survival after primary heart valve replacement, including an evaluation of the excess mortality among heart valve replacement patients compared with the general population. METHODS Survival was analyzed in 2365 patients (1568 without and 797 with concomitant coronary artery bypass grafting (CABG)) who underwent their first heart valve replacement. Observed survival was related to that expected among persons from the general Swedish population stratified by age, sex, and 5-year calendar period, to calculate the relative survival and estimate the disease-specific survival. RESULTS Early mortality (death within 30 days after surgery) was 5.9% after aortic valve replacement, 10.4% after mitral valve replacement and 10.6% after combined aortic and mitral valve replacement. Relative survival rates (excluding early deaths) were 84% 10 years after aortic, 68.5% after mitral and 80.9% after both aortic and mitral valve replacement. A multivariate model based on observed survival rates was produced for each group, using the Cox proportional hazards model. Concomitant CABG, advanced New York Heart Association (NYHA) class, preoperative atrial fibrillation, pure aortic regurgitation and higher age increased the late observed survival after aortic valve replacement. NYHA class was the only factor independently related to observed late deaths after mitral valve replacement, and mitral insufficiency the only corresponding factor after both aortic and mitral valve surgery. CONCLUSION The use of relative survival rates tended to modify the difference between subgroups compared with observed survival rates. Relative survival rates reduced the effect of concomitant CABG on survival, but enhanced for example the effect of aortic regurgitation. In patients > or = 70 years of age and patients submitted to aortic or mitral valve replacement with mild or no symptoms, the survival rate was similar for many years to that in the Swedish population at large.

Heating efficacy of external heat supply during and after open-heart surgery with hypothermia

Heat balance after cardiac surgery with hypothermic cardiopulmonary bypass (CPB) was studied in 156 patients. In spite of rewarming during CPB there was residual hypothermia at the end of operation. This heat deficit could not be prevented by intraoperative use of a heating mattress at 38°C and/or heated (39°C) humidified inspired gases. Postoperatively, in four groups of patients, the core and finger skin temperatures were recorded and the mean skin and mean body temperatures and heat balance were calculated. Heating of humidified inspired gases (n = 22) gave little improvement in the time course of the temperatures and heat balance as compared with that in a control group with no external warming postoperatively (n = 49). A thermal ceiling (a low‐temperature radiator suspended above the bed and providing radiant heat (n = 35)) significantly increased the measured temperatures, which were restored to normal earlier than those in the controls. Also, with this radiant heat postoperative shivering was almost abolished. With a combination of radiant heat and heated, humidified gases (n = 50), the postoperative heat balance was improved somewhat further. For patients treated with radiant heat, postoperative rewarming was accomplished in a shorter time and almost without active endogenous muscular thermogenesis, as was evident by the great reduction in postoperative shivering.