Fluid responsiveness is about stroke volume, and not pulse pressure Yogi: the power of Doppler fluid management and cardiovascular monitoring

The cardiovascular effects of crystalloid administration in endoscopy patients

Intravenous fluids are commonly administered for patients having colonoscopy despite relatively little data to support this practice. It is unclear what, if any, effect crystalloid administration has on stroke volume and cardiac output in patients who are fasting and have had bowel preparation agents. We aimed to assess the physiological effect of 10 ml/kg of crystalloid administration in colonoscopy patients on haemodynamic parameters including stroke volume, stroke volume variation and cardiac output, as measured with transthoracic echocardiography. Our secondary aims were to determine whether stroke volume variation predicted fluid responsiveness in gastrointestinal endoscopy patients and whether these haemodynamic measures are different in fasting patients with bowel preparation (colonoscopy patients) compared to fasting patients alone (gastroscopy patients). We recruited 54 patients having elective gastrointestinal endoscopy (25 colonoscopy, 29 gastroscopy). All patients had stroke volume, cardiac output and stroke volume variation measured with transthoracic echocardiography at baseline. In colonoscopy patients, stroke volume, cardiac output and stroke volume variation were remeasured after 10 ml/kg of intravenous crystalloid. Administration of 10 ml/kg of crystalloid increases stroke volume by 19.6 ml ( p < 0.00005) and cardiac output by 0.81 l/min ( p < 0.001). Stroke volume variation reduced from 23% to 14% after fluid administration ( p < 0.0011). The optimum threshold of stroke volume variation to predict fluid responsiveness was 21% with a sensitivity of 77.8% and specificity of 62.5%. Administration of 10 ml/kg of crystalloid increases stroke volume and cardiac output, and reduces stroke volume variation in fasting elective colonoscopy patients.

Carotid Doppler flowmetry correlates poorly with thermodilution cardiac output following cardiac surgery

BACKGROUND

It remains unclear whether measuring carotid arterial flow by the time velocity integral using vascular Doppler ultrasound can be used to monitor cardiac output and volume responsiveness.

METHODS

The carotid Doppler flow (time velocity integral and peak flow velocity variation) was assessed in triplicate by an intensivist with formal vascular ultrasound training. Thirty-three patients admitted following coronary by-pass surgery were studied before and after a passive leg-raising manoeuvre to investigate volume responsiveness (more than 10% increase in cardiac output) along with indices of arterial load measuring cardiac output by thermodilution. Pearson's correlation coefficient and area under the curve (AUC) by receiver operating characteristics were calculated.

RESULTS

A significant correlation between carotid Doppler flow and cardiac output was demonstrated in post-operative cardiac surgery patients (r = 0.80 [95%CI 0.61-0.89]), including relative changes following passive leg raising (r = 0.79 [95%CI 0.60-0.89]) that showed a mean difference of 2% with wide limits of agreements (-19% to 16%). Changes in carotid Doppler flow following passive leg raising correlated with the baseline arterial resistance but not with compliance or effective elastance. A peak flow variation > 10% before passive leg raising discriminated responders to the manoeuvre with an AUC of 0.81 [95% CI 0.55-0.95].

CONCLUSIONS

Weak correlations between common carotid Doppler flow and cardiac output mean that the methods cannot be used interchangeably in post-operative cardiac surgery patients.