Sasse S A, Chen P A, Berry R B, Sassoon C S, Mahutte C K
Department of Medicine, Long Beach Veterans Affairs Medical Center, CA.
Crit Care Med. 1994 Feb;22(2):225-32. doi: 10.1097/00003246-199402000-00012.
To determine the amount of spontaneous variability of cardiac output over time in critically ill patients, and to determine the effect of mechanical ventilation on cardiac output variability over time.
Case series.
Medical intensive care unit in a Veterans Affairs Medical Center.
Twenty-two patients with indwelling pulmonary artery flotation catheters were studied. Two patients were studied twice.
During a 1-hr time period in which no interventions were required or made, thermodilution cardiac output was determined at baseline and then every 15 mins for 1 hr. At each time point, five individual cardiac output measurements were made and a mean was computed. The covariables of heart rate, respiration rate, mean arterial pressure, mean pulmonary arterial pressure, pulmonary artery occlusion pressure, and temperature were also recorded at each time point.
The variability of the five cardiac output measurements made at each time point was expressed by calculating for each patient a coefficient of variation of the measurements. The overall mean coefficient of variation of the measurements was 5.8%. The variability of the cardiac output measurements over time was expressed by calculating for each patient a coefficient of variation over time. The overall mean coefficient of variation over time was 7.7%. A subgroup of 15 "covariable stable" patients (defined as those patients with covariables within +/- 5% of the mean covariable values during the hour) had a mean coefficient of variation over time of 6.4%, whereas "covariable unstable" patients (with > +/- 5% changes in any covariable) had a mean coefficient of variation over time of 9.9% (p < .05). Patients breathing spontaneously had a mean coefficient of variation over time of 10.1%, whereas mechanically ventilated patients had a mean coefficient of variation over time of 6.3% (p < .05).
The spontaneous variability of cardiac output should be considered when interpreting two cardiac output determinations made at separate times. Due to spontaneous variability alone, a patient with a baseline cardiac output of 10.0 L/min would be expected (95% confidence interval) to have a cardiac output range of 9.2 to 10.8 L/min if covariables were stable, and a range of at least 8.8 to 11.2 L/min if covariables were unstable. Patients who were mechanically ventilated displayed less variability than patients who were breathing spontaneously.
确定重症患者心输出量随时间的自发变异性，并确定机械通气对心输出量随时间变异性的影响。
病例系列研究。
退伍军人事务医疗中心的医学重症监护病房。
对22例留置肺动脉漂浮导管的患者进行研究。2例患者接受了两次研究。
在1小时内，无需进行或未进行任何干预，在基线时测定热稀释法心输出量，然后每15分钟测定1次，共1小时。在每个时间点，进行5次心输出量的单独测量并计算平均值。在每个时间点还记录心率、呼吸频率、平均动脉压、平均肺动脉压、肺动脉闭塞压和体温等协变量。
通过计算每个患者测量值的变异系数来表示每个时间点5次心输出量测量的变异性。测量值的总体平均变异系数为5.8%。通过计算每个患者随时间的变异系数来表示心输出量测量值随时间的变异性。随时间的总体平均变异系数为7.7%。15例“协变量稳定”患者（定义为在1小时内协变量在平均协变量值的±5%范围内的患者）随时间的平均变异系数为6.4%，而“协变量不稳定”患者（任何协变量变化>±5%）随时间的平均变异系数为9.9%（p<0.05）。自主呼吸患者随时间的平均变异系数为10.1%，而机械通气患者随时间 的平均变异系数为6.3%（p<0.05）。
在解释不同时间点进行的两次心输出量测定时，应考虑心输出量的自发变异性。仅由于自发变异性，如果协变量稳定，基线心输出量为10.0L/min的患者预期（95%置信区间）心输出量范围为9.2至10.8L/min；如果协变量不稳定，则范围至少为8.8至11.2L/min。机械通气患者的变异性低于自主呼吸患者。
