SummaryA 47-year-old female patient had a subclinical superior vena caval syndrome which developed into the 'full blown' acute condition when she was placed into the left lateral position after mediastinoscopy. She developed airway obstruction requiring urgent re-intubation and subsequent admission to the intensive care unit. This subclinical condition might have been suspected pre-operatively if closer attention had been paid to the history, physical examination and review of the computerised axial tomography scan: she had a history of intermittent dyspnoea, wheeze and cough which was worse on waking and improved as the day progressed, she had a positive Pemberton's sign and the computerised axial tomography scan showed that the lesion was encroaching on the superior vena cava. Vincent's Hospital, Elm Park, Dublin 4, Ireland Accepted: 14 April 1997 There is an increasing emphasis on the role of the anaesthetist as a peri-operative physician [1]. Patients with significant medical pathology regularly undergo complex surgical interventions and the anaesthetist may be involved in the pre-operative evaluation and in the planning of intensive or high-dependency care and postoperative pain management. Given the escalating costs incurred in the provision of intensive care, it is likely that strategies leading to a reduction in admission to the intensive care unit will receive more attention in the future. One such strategy is the improved quality of pre-operative evaluation. Possibly contrary to this, many patients, particularly if admitted as a daycase, now complete questionnaires to identify peri-operative problems and assist speedy pre-operative assessment. Such questionnaires give information that is factually correct but without the details which would have been forthcoming from a complementary medical interview.Pre-operative patients are usually seen by the anaesthetist on the night before surgery. To aid this process in our hospital, a patient proforma is completed by the house officer highlighting essential pre-operative information. This is an efficient alternative to perusal of the patient's chart but it is not foolproof. In the case that we report, the information provided formed the basis for a brief factual interview, the patient was examined, anxieties were allayed and premedication was prescribed. The interview had proceeded in standard fashion. However, as a consequence of this system of assessment, several useful pieces of clinical information were not obtained. Case historyA 47-year-old female was booked for elective mediastinoscopy and biopsy. At the pre-operative visit, the following details were noted: she had a 6-week history of intermittent dyspnoea, wheeze and cough with no past medical history; there was a strong family history of asthma; she was not taking any medication; she had had a significant allergic reaction to contrast medium during the computerised axial tomography (CT) scan 1 week previously with extensive erythema lasting 24 h. On examination she weighed 86 kg, her airway was c...

With large numbers of COVID-19 patients requiring mechanical ventilation and ventilators being in short supply, in extremis two patients are having to share one ventilator. This possibility has been discussed for at least two decades, and careful matching of patient ventilation requirements is advised. However, with a large range of lung compliance and other characteristics, which may also vary with time, good matching is difficult to achieve. Adjusting the impedance of the flow path between ventilator and patient gives the opportunity to control the airway pressure and hence flow and volume individually for each patient. Several groups are now investigating this, in particular the addition of a flow restrictor in the inspiration tube for the patient who is more compliant, or requires a lower tidal volume. In this paper, we show that a simple linear resistance-compliance model, termed the BathRC model, of the ventilator tubing system and lung allows direct calculation of the relationships between pressures, volumes, and required flow restriction. The BathRC model is experimentally validated using a GE Aisys CS2 ventilator connected to two test lungs. The pressureflow relationships for two restrictors are experimentally determined, and despite the need to approximate them with a linear resistance characteristic, their effect in the breathing circuit is accurately predicted by the simple model. The BathRC model is freely available for download; we do not condone dual ventilation, but this tool is provided to demonstrate that flow restriction can be readily estimated. This research is part of a larger test, simulation and design investigation on dual ventilation being undertaken at the UoB and RUH.

When supplementary oxygen is necessary with nasal intermittent positive pressure ventilation (NIPPV), the optimal route by which it should be added to the ventilator circuit is unknown. We investigated the oxygen concentration received when oxygen was supplied at flow rates between 0 and 6 L·min -1 into the proximal ventilator tubing or the nasal mask whilst patients were ventilated with air.Eleven patients with stable chronic hypercapnic respiratory failure were studied. A calibration curve was produced for each by supplying different known oxygen concentrations through a Monnal D or DCC ventilator and measuring the arterial oxygen saturations achieved. Oxygen was then supplied into the ventilator tubing or nasal mask and arterial saturation again measured. The oxygen concentration received was estimated using the calibration curve. Tracheal oxygen concentration throughout the respiratory cycle was studied in one patient when oxygen was supplied by both routes.Peak inspired oxygen concentration occurred at end-inspiration when oxygen was supplied into the ventilator tubing, but at mid-inspiration when supplied into the nasal mask. However, there was no significant difference between the two routes in the inspired oxygen concentration achieved at all flow rates: 1 L·min -1 supplied approximately 31% oxygen; 2 L·min -1 37%; 3 L·min -1 40%; and 4 L·min -1 44%. Flow rates above 4 L·min -1 had little additional effect.In conclusion, oxygen supplementation during nasal intermittent positive pressure ventilation can be provided into the ventilator tubing or the nasal mask with equal efficiency.