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Intravenous infusions are required when a drug has a short half-life or a narrow therapeutic window. Pharmacokinetic models are employed to calculate the infusion rate for a particular target plasma concentration. While the one-compartment model is based on relatively simple mathematics, it is of little practical use. Multi-compartment models involve complex mathematics: a bolus-infusion regimen requires a variable-infusion rate. In clinical practice, this means incorporating the pharmacokinetic models into specially designed target-controlled infusion pumps. The physicochemical properties of different drugs result in very different behaviours, especially following cessation of intravenous infusion.

Older people are undergoing increasingly complex surgery with much greater mortality and morbidity than the younger adult population. In this article, we discuss the physiological changes that take place in the older patient, and how these may affect anaesthetic technique. Perioperative risk in the elderly is discussed, with focus on emergency surgery and frailty.

The aim of this study was to compare several methods of hypothermic heart preservation.We preserved isolated pig hearts for 24 hours in cold cardioplegia (4 degrees C), using either continuous microperfusion (Group I) or simple storage (Group II), and with a new preservative solution (NPS, groups IA and IIA) vs St. Thomas' solution (groups IB and IIB). The main characteristics of the NPS include (1) prevention of cell swelling with polyethelene glycol (PEG), (2) low calcium and magnesium, and (3) presence of metabolic substrates, such as glucose, insulin, pyruvate, aspartate, alanyl-glutamine, and membrane stabilization compounds such as ethanol and chlorpromazine.The 4 above groups were compared with hearts harvested and immediately reperfused (control group). During preservation, only Group IB showed significant edema (40% +/- 8.4% water gain). Adenylate charge was 25% to 50% higher in microperfused Groups IA and IB (0.678 +/- 0.049 and 0.795 +/- 0.071, respectively) as compared with simple-storage groups IIA and IIB (0.605 +/- 0.048 and 0.524 +/- 0.160, respectively). Ultrastructural analysis showed that tissue injury occurred mainly in Group IIB (altered mitochondria, chromatin clumping). Functional data showed better recovery of NPS groups as compared with St. Thomas groups: coronary flow was identical in Group IB and control (57.8 +/- 22 and 56.6 +/- 14 ml/min/100 g, respectively), and in IAIB (p0.001) and IIAIIB (p0.01); the rate pressure products were higher in NPS groups compared with St. Thomas groups (IAIB, p0.01); IIAIIB, p0.05).The microperfusion method associated with the NPS provides excellent protection in long-term hypothermic heart preservation.