Comparing invasive blood pressure measurements with both classic intermittent and novel continuous, non-invasive measurements in patients undergoing cardiac surgery

Background and Goal of Study: Measuring blood pressure (BP) invasively via an arterial catheter (ABP) is widely used but may cause complications [1]. Classic non-invasive measurement by arm cuff (NIBP) measures BP intermittently (BPNIBP), presenting a major shortcoming, but with minor risk of complications. Novel non-invasive BP measurements (e.g. Nexfin™) (BPNEX) are continuous and show little risk of complications. We recently showed promising results comparing BPNEX with ABP in haemodynamic stable patients [2]. This study compares BPNEX and BPNIBP with ABP in unstable haemodynamic conditions during cardiac surgery. Materials and Methods:  This prospective, observational single center study includes seventy patients undergoing off-pump coronary artery bypass surgery. Measurements were obtained intermittently (BPNIBP) and continuously (ABP, BPNEX) and analyzed in 30 minute intervals. Bland-Altman and polar plot methodology were used to compare accuracy, precision and trending ability.  Results and Discussion:  Agreement analysis of BPNIBP (Fig. 1A) and BPNEX (Fig.1B) versus ABP showed a bias of respectively -4 and -2 mmHg and 95% limits of agreement (LoA) of ± 22 and 12 mmHg. This results in a percentage error of 118%error for the BPNIBP and 64%error for the BPNEX. Trending ability analysis with an exclusion zone of 8 mmHg showed a percentage within LoA of 47% for the BPNIBP (Fig. 2A) and 68% for the BPNEX (Fig. 2B). Conclusion(s): In contrast to BPNIBP, BPNEX shows a promising agreement with ABP in patients undergoing surgery involving haemodynamic instability, yet it is not interchangeable.  References:  1. Scheer et al, Critical Care 2002; 6: 199-204 2. Vos et al, 2014; 113: 67-7