Accuracy and trending abilities of finger plethysmographic blood pressure and cardiac output compared with invasive measurements during caesarean delivery in healthy women. An observational study.

Abstract

Background: In women presenting for caesarean section under spinal anaesthesia, continuous measurement of circulatory aspects, such as blood pressure and cardiac output, is often needed. At present, invasive techniques are used almost exclusively. Reliable non-invasive monitors would be welcome, as they could be safer and less uncomfortable, while easy and quick to apply. We aimed to evaluate whether a non-invasive, finger plethysmographic device, the ccNexFin monitor, can replace invasively measured blood pressure in the radial artery, and whether cardiac output measurements from this device can be used interchangeably with measurements from the mini-invasive LiDCO monitor, currently in use at our institution. Methods: Simultaneous invasive measurements were compared with ccNexFin in 23 healthy women during elective caesarean section under spinal anaesthesia. We used Bland Altman statistics for assessing agreement, and polar plot methodology for judging trending abilities with pre-defined limits. Results: Mean arterial and systolic pressures showed biases (invasive – ccNexFin) of -4.3 and 12.2 mmHg, with limits of agreement of -15.9 – 7.4 and -11.1 – 35.6, respectively. The ccNexFin trending abilities were within suggested limits for mean pressure, but insufficient for systolic pressure compared with invasive measurements. Cardiac output had a small bias of 0.2 L/min, but wide limits of agreement of -2.6 – 3.0. The ccNexFin trending abilities compared with the invasive estimated values (LiDCO) were unsatisfactory. Conclusions: We consider the ccNexFin monitor to have sufficient accuracy in measuring mean arterial pressures. The limits of agreement for systolic measurements were wider, and the trending ability, compared with invasive measurements, was outside the recommended limit. The ccNexFin is not reliable for cardiac output measurements or trend in pregnant women for caesarean delivery under spinal anaesthesia.

Beat-to-beat blood pressure variability: an early predictor of disease and cardiovascular risk

“…Thus, future researchers ought to vary the techniques used to include more often pulse transit time and tonometry [30,31,92]. Moreover, validity studies have shown that some measures of noninvasive BP, that is mean arterial pressure and SBP, are more representative of invasive values [93,94]. So, although beat-to-beat BP monitoring can be suitable for quantification of very-short term variability, its diagnostic capacity in terms of BP level remains limited.…”