Complications after major surgery are a leading cause of morbidity and mortality. The etiology of postoperative complications is complex, but poor cardiorespiratory reserve appears to be a key factor. There is increasing interest in the use of central and mixed venous oxygen saturation to guide therapeutic interventions during the perioperative period. However, a detailed understanding of the physiologic principles of venous oximetry is essential for safe and effective use in clinical practice. Venous oxygen saturation reflects the balance between global oxygen delivery and oxygen consumption, which may be affected by a wide range of factors during the perioperative period. The purpose of this article is to describe the physiology and measurement of mixed and central venous oxygen saturation and to explore the findings of clinical investigations of their use in perioperative care.

SummaryWe conducted a single-centre observational study of retrievals for severe respiratory failure over 12 months. Our intensivist-delivered retrieval service has mobile extracorporeal membrane oxygenation capabilities. Sixty patients were analysed: 34 (57%) were female and the mean (SD) age was 44.1 (13.6) years. The mean (SD) PaO 2 /F I O 2 ratio at referral was 10.2 (4.1) kPa and median (IQR [range]) Murray score was 3.25 (3.0-3.5 [1.5-4.0]). Forty-eight patients (80%) required veno-venous extracorporeal membrane oxygenation at the referring centre. There were no cannulation or extracorporeal membrane oxygenation-related complications. The median (IQR [range]) retrieval distance was 47.2 (14.9-77.0 [2.3-342.0]) miles. There were no major adverse events during retrieval. Thirty-seven patients (77%) who received extracorporeal membrane oxygenation survived to discharge from the intensive care unit and 36 patients (75%) were alive after six months. Senior intensivist-initiated and delivered mobile extracorporeal membrane oxygenation is safe and associated with a high incidence of survival.

The role of the neurointensivist in outcome for patients who suffer severe traumatic brain injury is key. Targeted therapies are allowing early detection and manipulation of brain ischaemia leading to more individualized treatment.

At present, no pharmacological intervention can be recommended to prevent or treat ICU-acquired weakness. Further research is required into this field to include more novel agents such as myostatin inhibitors. Challenges in the conduct of research in this area are highlighted.

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This study investigated the role of sympathetic withdrawal on blood flow responses in cutaneous arteriovenous anastomoses (AVAs) and capillaries to direct and indirect heat stress. This was achieved by clamping sympathetic activity (SC) to the tail of anesthetized rats so that constrictor tone remained invariant during exposure of either the animal's tail (direct heating) or body (indirect heating) to a 35 degrees C environment. Flow through the AVAs in the tail was evaluated by laser-Doppler flowmetry (LDF), while capillary flow was investigated by videodensitometry measurements of blood cell velocity (CBV) in single capillaries within the subepidermal vascular plexus. Both direct and indirect heating significantly increased LDF and CBV. In comparison to blood flow responses in sham-operated control rats, the SC procedure resulted in significantly lower LDF responses to both direct and indirect heat stress. By contrast, the response of CBV was not significantly affected by SC during either mode of heating. These results indicate that the withdrawal of sympathetic constrictor tone plays a role in the response of cutaneous AVAs, but not precapillary arterioles, to direct as well as indirect heat stress. Additional studies on unanesthetized animals showed that superimposing body heating on a base of local heating elicited a further increase in LDF, suggesting that local heating does not deplete neural mediated dilatory reserve.

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