title: Noninvasive cardiac output and blood pressure monitoring cannot replace an invasive monitoring system in critically ill patients.
abstract: BACKGROUND
  Monitoring of cardiac output and blood pressure are standard procedures in critical care medicine. Traditionally, invasive techniques like pulmonary artery catheter (PAC) and arterial catheters are widely used. Invasiveness bears many risks of deleterious complications. Therefore, a noninvasive reliable cardiac output (CO) and blood pressure monitoring system could improve the safety of cardiac monitoring. The aim of the present study was to compare a noninvasive versus a standard invasive cardiovascular monitoring system.
  
  
  METHODS
  Nexfin HD is a continuous noninvasive blood pressure and cardiac output monitor system and is based on the development of the pulsatile unloading of the finger arterial walls using an inflatable finger cuff. During continuous BP measurement CO is calculated. We included 10 patients with standard invasive cardiac monitoring system (pulmonary artery catheter and arterial catheter) comparing invasively obtained data to the data collected noninvasively using the Nexfin HD.
  
  
  RESULTS
  Correlation between mean arterial pressure measured with the standard arterial monitoring system and the Nexfin HD was r2 = 0.67 with a bias of -2 mmHg and two standard deviations of +/- 16 mmHg. Correlation between CO derived from PAC and the Nexfin HD was r2 = 0.83 with a bias of 0.23 l/min and two standard deviations of +/- 2.1 l/min; the percentage error was 29%.
  
  
  CONCLUSIONS
  Although the noninvasive CO measurement appears promising, the noninvasive blood pressure assessment is clearly less reliable than the invasively measured blood pressure. Therefore, according to the present data application of the Nexfin HD monitoring system in the ICU cannot be recommended generally. Whether such a tool might be reliable in certain critically ill patients remains to be determined.
authors.affiliation: Surgical Intensive Care Unit, University Hospital of Zurich, CH 8091 Zurich, Switzerland. markus.bechir@usz.ch.
authors.forename: John F
authors.initials: JF
authors.lastname: Stover
authors.forename: Reto
authors.initials: R
authors.lastname: Stocker
authors.forename: Renato
authors.initials: R
authors.lastname: Lenherr
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Neff
authors.forename: Silvia R
authors.initials: SR
authors.lastname: Cottini
authors.forename: Bernhard
authors.initials: B
authors.lastname: Zoller
authors.forename: Markus
authors.initials: M
authors.lastname: Béchir