Lithium dilution cardiac output measurements in isoflurane-anaesthetised goats: Jugular versus cephalic lithium chloride administration

The administration of lithium chloride (LiCl) for cardiac output (CO) measurement via a peripheral instead of a central vein has been described previously as a valid alternative route in pigs and dogs. The aim of the study was to compare CO measurements after administration of LiCl using two peripheral veins, cephalic or jugular, in goats. Ten adult, female, experimental goats undergoing bilateral stifle arthrotomy were recruited for the study. Paired CO measurements were taken two minutes apart during stable conditions in isoflurane-anaesthetised goats. Forty-two paired CO measurements were taken in total, and the median (range) of paired CO measurement per goat were 4.5 (3-6). The mean (SD) CO using the cephalic and jugular vein for injection of LiCl was 5.28 (1.29) L min^-1 and 5.20 (1.24) L min^-1 respectively. The Bland-Altman analysis showed an acceptable agreement with a mean bias of 1.33% with limits of agreement (LoA) of -18.43 to 21.09%. The percentage of error was 25%. The four-quadrant plot analysis showed a poor agreement (71%) between the two routes. The polar plot showed a poor trending ability. An 86% inclusion rate (18/21 points) was reached with a ± 35° radial sector size. The findings revealed that the agreement between the two routes is not as precise as the authors expected, however the results are comparable with studies published previously.

The use of LiDCO based fluid management in patients undergoing hip fracture surgery under spinal anaesthesia: neck of femur optimisation therapy - targeted stroke volume (NOTTS): study protocol for a randomized controlled trial

BACKGROUND

Approximately 70,000 patients/year undergo surgery for repair of a fractured hip in the United Kingdom. This is associated with 30-day mortality of 9% and survivors have a considerable length of acute hospital stay postoperatively (median 26 days). Use of oesophageal Doppler monitoring to guide intra-operative fluid administration in hip fracture repair has previously been associated with a reduction in hospital stay of 4-5 days. Most hip fracture surgery is now performed under spinal anaesthesia. Oesophageal Doppler monitoring may be unreliable in the presence of spinal anaesthesia and most patients would not tolerate the probes. An alternative method of guiding fluid administration (minimally-invasive arterial pulse contour analysis) has been shown to reduce length of stay in high-risk surgical patients but has never been studied in hip fracture surgery.

METHODS

Single-centre randomised controlled parallel group trial. Randomisation by website using computer generated concealed tables.

SETTING

University hospital in UK.

PARTICIPANTS

128 patients with acute primary hip fracture listed for operative repair under spinal anaesthesia and aged > 65 years.

INTERVENTION

Stroke volume guided intra-operative fluid management. Continuous measurement of SV recorded by a calibrated cardiac output monitor (LiDCOplus). Maintenance fluid and 250 ml colloid boluses given to achieve sustained 10% increases in stroke volume.

CONTROL GROUP

fluid administration at the responsible (blinded) anaesthetist's discretion. The intervention terminates at the end of the surgical procedure and post-operative fluid management is at the responsible anaesthetist's discretion.

PRIMARY OUTCOME

length of acute hospital stay is determined by a blinded team of clinicians. Secondary outcomes include number of complications and total cost of care. Funding NIHR/RfPB: PB-PG-0407-13073.

TRIAL REGISTRATION NUMBER

TRIAL REGISTRATION

Current Controlled Trials ISRCTN88284896.

Emerging technologies

Hemodynamic monitoring in critically ill patients has been considered part of the standard of care in managing patients with shock and/or acute lung injury, but outcome benefit, particularly in pediatric patients, has been questioned. There is difficulty in validating the reliability of monitoring devices, especially since this validation requires comparison to the pulmonary artery catheter, which has its own problems as a measurement tool. Interpretation of the available evidence reveals advantages and disadvantages of the available hemodynamic monitoring devices.

Methods in pharmacology: measurement of cardiac output

Many methods of cardiac output measurement have been developed, but the number of methods useful for human pharmacological studies is limited. The 'holy grail' for the measurement of cardiac output would be a method that is accurate, precise, operator independent, fast responding, non-invasive, continuous, easy to use, cheap and safe. This method does not exist today. In this review on cardiac output methods used in pharmacology, the Fick principle, indicator dilution techniques, arterial pulse contour analysis, ultrasound and bio-impedance are reviewed.

The effect of anaesthesia and aortic clamping on cardiac output measurement using arterial pulse power analysis during aortic aneurysm repair

The LiDCO plus monitor (LiDCO Ltd, Cambridge, UK) uses pulse contour analysis of the arterial pressure waveform to indicate changes in stroke volume and cardiac output. Calibration against a lithium indicator dilution method is required to permit display of absolute values in addition to trends. The effect of haemodynamic changes during anaesthesia and surgery on this calibration factor has not previously been studied. Therefore, we investigated whether it remained constant during elective abdominal aortic aneurysm surgery in 15 patients. Comparison between the calibration factor values at different time points was made by repeated recalibration throughout the peri-operative period. Calibration factor increased by a mean of 53% after anaesthesia (epidural plus general) (p = 0.03) and decreased by a mean of 40% after aortic clamping (p = 0.0001). Recalibration should be undertaken after induction of anaesthesia and after aortic clamping if absolute values of cardiac output and stroke volume are required.

Physiological changes of pregnancy and monitoring

Advances in medical care have led to increasing numbers of complex, high-risk obstetric patients. Specialist training and a sound knowledge of normal maternal physiology are essential to optimize outcomes. One of the earliest observed changes is peripheral vasodilatation; this causes a fall in systemic vascular resistance and triggers physiological changes in the cardiovascular and renal systems, with 40-50% increases in cardiac output and glomerular filtration rates. Safety concerns over Swan Ganz catheters have driven the increasing interest in alternative techniques, such as echocardiography, thoracic bioimpedance and pulse contour analysis, although their exact roles in future obstetric high-dependency care have yet to be established. Analysis of arterial blood gases is fundamental to the management of sick patients, and correct interpretation can be aided by a systematic approach. Observation charts are almost ubiquitous in all aspects of medicine, but little evidence exists to support their use in the high-dependency setting.

Lithium dilution measurement of cardiac output and arterial pulse waveform analysis: an indicator dilution calibrated beat-by-beat system for continuous estimation of cardiac output

Lithium dilution cardiac output (LiDCO trade mark; LiDCO, London, UK) is a minimally invasive indicator dilution technique for the measurement of cardiac output. It was primarily developed as a simple calibration for the PulseCO trade mark (LiDCO, London, UK) continuous arterial waveform analysis monitor. The technique is quick and simple, requiring only an arterial line and central or peripheral venous access. These lines would probably already have been inserted in critical care patients. A small dose of lithium chloride is injected as an intravenous bolus, and cardiac output is derived from the dilution curve generated by a lithium-sensitive electrode attached to the arterial line. Studies in humans and animals have shown good agreement compared with results obtained with other techniques, and the efficacy of LiDCO trade mark in pediatric patients has also been proven. Compared with thermodilution, lithium dilution showed closer agreement in clinical studies with electromagnetic flow measurement.PulseCO trade mark is a beat-to-beat cardiac output monitor that calculates stroke volume from the arterial pressure waveform using an autocorrelation algorithm. The algorithm is not dependent on waveform morphology, but, rather, it calculates nominal stroke volume from a pressure-volume transform of the entire waveform. The nominal stroke volume is converted to actual stroke volume by calibration of the algorithm with LiDCO trade mark. Initial studies indicate good fidelity, and the results from centers in the United States and the United Kingdom are extremely encouraging. The PulseCO trade mark monitor incorporates software for interpretation of the hemodynamic data generated and provides a real-time analysis of arterial pressure variations (ie, stroke volume variation, pulse pressure variation, and systolic pressure variation) as theoretical guides to intravascular and cardiac filling.