In vivo effects on human skeletal muscle oxygen delivery and metabolism of cardiopulmonary bypass and perioperative hemodilution.

PURPOSE: To investigate the in vivo effects of cardiopulmonary bypass (CPB) and perioperative hemodilution on human skeletal muscle oxygen delivery and metabolism and to determine the dilution state at which these effects arise. METHODS: We conducted this observational study in adult patients undergoing CPB surgery. Microcirculatory data were obtained by near-infrared spectroscopy from the brachioradial muscle in 20 consecutive patients undergoing hemodilution for CPB. Outcome variables included tissue oxy- and deoxyhemoglobin concentration ([HbO(2)], [HHb]), oxygen content, blood flow, oxygen delivery, and oxygen consumption. RESULTS: Although CPB left tissue blood flow and oxygen delivery unchanged, both microcirculatory variables correlated significantly and inversely with hematocrit (Hct) (r = -0.39, p < 0.001; r = -0.50, p < 0.001). CPB also left muscle oxygen consumption (mVO(2)) unchanged and this variable correlated with the tissue hemoglobin concentration and tissue oxygen delivery (r = 0.40, p = 0.001; r = 0.35, p = 0.005). During CPB most of the systemic cardiovascular variables remained unchanged. Conversely at Hct lower than 30%, mean arterial pressure and pH decreased and lactate values increased twofold, whereas microvascular blood volume and oxygen delivery increased. At Hct lower than 20% blood flow and oxygen delivery increased, whereas hemoglobin and oxygen content variables decreased. CONCLUSIONS: CPB leaves skeletal muscle oxygen delivery and metabolism as measured by near-infrared spectroscopy unchanged. The only factor that correlates directly with the oxygen content variables and inversely with blood flow, and induces significant changes in tissue hemoglobin content and oxygen delivery, is hemodilution.

Effects of sternotomy on heart-lung interaction in patients undergoing cardiac surgery receiving pressure-controlled mechanical ventilation.

BACKGROUND: The key concept underlying the dynamic indexes of preload dependence is the physiological heart-lung interaction. During sternotomy this interaction undergoes various changes, some of which remain unclear. Our primary aim was to investigate how the interaction changes during sternotomy by evaluating pulse pressure variations (PPV) with the chest closed and after sternotomy in patients ventilated using the pressure-controlled mode. METHODS: We prospectively studied 25 patients undergoing coronary artery bypass grafting (CABG) receiving pressure-controlled ventilation. Standard hemodynamic data, PPV and tidal volume delivered were recorded before and after sternotomy, and, with the chest open, before and after positive end-expiratory pressure (PEEP) was applied and inspiratory pressure was increased. RESULTS: Sternotomy left all variables statistically unchanged from values before thoracotomy although in the subgroup of patients with a PPV > 8% (56%) sternotomy significantly reduced PPV (from 14.4 +/- 5.2% to 8.9 +/- 4.5%). With the chest open, when PEEP was applied at 5 cm H(2)O, tidal volume decreased (from 643 +/- 83 to 587 +/- 104 ml) and stroke volume decreased (from 77 +/- 17 to 72 +/- 15 ml) but PPV remained unchanged. When PEEP was discontinued and inspiratory pressure was increased by 5 cm H(2)O, tidal volume increased (from 643 +/- 83 to 814 +/- 89 ml) and PPV increased (from 8.2 +/- 3.9% to 12.3 +/- 6.8%) but stroke volume remained unchanged. CONCLUSIONS: In patients ventilated in the pressure-controlled mode, except those with a pre-sternotomy PPV > 8% (fluid responders), sternotomy leaves standard hemodynamic data and PPV unchanged. When the chest wall is open, cyclic changes (tidal volume) but not continuous changes (PEEP) in intrathoracic pressure directly influence PPV.

Hormone metabolism in the pulmonary circulation.

We measured hormonal levels in blood samples from pulmonary and radial arteries in 117 patients undergoing aorto-coronary by-pass surgery with the aim of investigating the role of the pulmonary vessel endothelium in hormone metabolism. Insulin and glucagon concentrations were significantly higher in pulmonary artery blood with respect to radial artery blood (73 +/- 65 vs. 65 +/- 47 pmol/l, p < 0.005, and 80 +/- 49 vs. 73 +/- 51 ng/l, p < 0.01, respectively), while no difference was found for growth hormone, prolactin, C peptide, insulin-like growth factor I, follicle stimulating hormone, luteinizing hormone, thyroid stimulating hormone, parathyroid hormone, thyroglobulin, triiodothyronine, thyroxine, free triiodothyronine, and free thyroxine. Moreover, prolactin concentrations were more than twice the normal levels, this being an effect of propafol and the opiate fentanyl used for the general anesthesia. Assuming that the arteriovenous differences observed are a marker of peptide hormone degradation, our study has demonstrated that with similar kinetics insulin and glucagon secreted into portal circulation and escaping from hepatic extraction undergo further homeostatic removal of about 9-10 % in the pulmonary circulation before entering the general circulation.

Osteocalcin metabolism in the pulmonary circulation.

The aim of this study was to evaluate the role of the pulmonary vessel endothelium in the removal of circulating osteocalcin, by measuring the osteocalcin levels in serum from pulmonary and radial artery blood from 39 patients undergoing aorto-coronary bypass. Because of the discrepancies between methods of measurement, two methods were used. Significant differences were observed in group A (n = 18), tested with heterologous radioimmunoassay (2.85 +/- 0.67 microg l-1 in the pulmonary versus 2.69 +/- 0.67 microg l-1 in the radial artery serum, P<0.001) and in group B (n = 21), tested with a two-site immunoradiometric assay (5.22 +/- 1.46 versus 4.93 +/- 1.36 microg l-1, P<0.01). The percentage differences were -5.54 +/- 4.76% (P<0.001) in group A and -4.99 +/- 8.13% (P<0.01) in group B; the comparison between the percentage differences was not significant. These different osteocalcin concentrations between the two vascular compartments were considered a marker of osteocalcin degradation. Therefore, the study seems to demonstrate that, as well as kidney, liver and bone, the lung is a relevant site of osteocalcin catabolism. The proteolytic activity of pulmonary vessel endothelium seems to involve about 5% of the circulating peptide.

[Anesthesia using high doses of fentanyl in coronary patients subjected to myocardial revascularization. Comparison of 2 administration methods]. / Anestesia con fentanyl ad alti dosaggi nei pazienti coronaropatici sottoposti ad intervento di rivascolarizzazione miocardica. Confronto tra due metodiche di somministrazione.

Eighteen patients to be submitted to heart surgery for myocardial revascularization have been considered. The patients were subdivided into two groups, A and B, and a high dose morphinic was administered for the induction and maintenance of the anaesthetic without further analgesic and/or narcotic supplement. The haemodynamic data obtained pointed to excellent stability in patient cardiocirculatory condition: preservation of IC within acceptable values was very interesting, owing to the fact that the high dose morphinic employed triggers very limited myocardiodepression. To conclude, the anaesthesiological techniques adopted seemed reliable and sufficiently protective with regard to exaggerated hyperdynamic responses to algogenic stimuli that trigger harmful haemodynamic conditions in coronary patients.