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SummaryThe hypothesis that anaesthetic uptake during maintenance of anaesthesia is related to cardiac output was tested on 21 patients undergoing cardiac surgery. Using a computer-controlled closed breathing system, enjlurane was administered to maintain an end-expired concentration of 1 YO. Cardiac output was measured by thermodilution using a pulmonary artery catheter. A clear qualitative but not quantitative relationship was demonstrated. Changes in anaesthetic requirements at a constant end-expired concentration are a better guide to changes in cardiac output than changes in end-expired carbon dioxide with constant ventilation in patients undergoing cardiac surgery. Key wordsAnaesthetics, volatile; enflurane. Heart; cardiac output. Pharmacokinetics; uptake.It is well known that induction of inhalational anaesthesia is delayed when cardiac output is large because of uptake of anaesthetic by blood. This is seen by application of the Fick principle:Where Ublad is uptake into blood, Q is cardiac output, lB,G is the blood gas partition coefficient and Pa and PB are the partial pressures in arterial and mixed venous blood respectively.There are established techniques for the non-invasive quantification of cardiac output based on this principle, commonly using acetylene as the tracer [I], though nitrous oxide has been used [2] and a recent theoretical study has advocated the use of enflurane [3]. These techniques succeed because the concentration of the tracer in mixed venous blood can be neglected during the investigation so the uptake of the agent by blood is the product of its partial pressure in arterial blood, its blood solubility and the cardiac output. Partial pressure in arterial blood and uptake are inferred from continuous measurements of inspired and expired concentrations.If an inhalational anaesthetic is used as the tracer during anaesthesia maintained with that same agent, its concentration in mixed venous blood can no longer be ignored and this confounds attempts at quantification of cardiac output. Nevertheless, an acute reduction in cardiac output should cause an acute reduction in anaesthetic uptake. Redistribution of blood flow to the already saturated vessel-rich tissue group will reduce the arterial to mixed venous partial pressure gradient, compounding this effect. It might therefore be expected that continuous measurement of uptake of a volatile agent during inhalational anaesthesia will be a sensitive guide to trends in cardiac output. We have compared the rate of uptake of enflurane at a constant end-expired concentration of 1 YO with repeated thermodilution cardiac output measurements in patients undergoing cardiac surgery. MethodTwenty-one patients undergoing coronary artery bypass grafting were studied. The patients gave their informed consent and local ethics committee approval had been granted for another study necessitating invasive monitoring and from which the data were collected. Patients were prernedicated with lorazepam 0.04 mg.kg-I . Peripheral venous access and intra-arterial p...

1. The effects of single oral doses of various sympatholytic drugs on the heart rate and blood pressure increases during isometric handgrip contraction were studied in six healthy subjects. 2. Bethanidine reduced both the systolic and diastolic increases in pressure. Clonidine reduced the systolic but not the diastolic increase. Oxprenolol alone or in combination with phentolamine or phenyoxybenzamine failed to influence the pressor response. 3. The increase in systemic blood pressure associated with sustained contraction of voluntary muscle appears to be relatively resistant to acute sympathetic adrenoreceptor blockade in man.

To exploit to the full the diagnostic potential of the absolute velocity measurement, a 2 MHz continuous wave Doppler instrument has been used with a new on-line spectral display of blood velocities. Continuous wave Doppler retrieves velocity information from the full length of the ultrasound beam. As it is the high-velocity jets that carry diagnostic information, the lowfrequency Doppler signals from slow-moving blood and intracardiac structures are filtered out and the Doppler signals from high-velocity jets are displayed in the form of a sonagram.Where the Doppler probe can be aligned with the intracardiac jet, the peak absolute velocity (as much as 6 m/s) can be measured and an approximate pressure gradient calculated. When accurate alignment cannot be achieved, the anatomical location of the jet, its direction, width and timing give useful diagnostic clues.Jet velocities in pulmonary, tricuspid, aortic and mitral valve disease, ventricular septal defects and coarctation of the aorta have been measured and accurate differential diagnoses made, despite the lack of simultaneous echocardiographic display. This technique promises to be a useful complement to echocardiography, particularly for regurgitant and pulmonary valve disease and ventricular septal defects where echocardiography is often unhelpful. CIRCULATORY RESPONSE TO SKIN COOLING