The true value of continuous hemodynamic monitoring in critically ill patients becomes clear in the light of beat-to-beat changing hemodynamics due to either continuously improving or deteriorating cardiac and disease status [
We prospectively studied 47 critically ill patients admitted to the intensive care units of our hospital. Inclusion criteria were hemodynamic instability with need for continuous hemodynamic monitoring and the presence of a central venous (jugular or subclavian) catheter and a PiCCO femoral arterial catheter already in place before inclusion in the study.
The Nexfin (BMEYE, Amsterdam, The Netherlands) method is based on the measurement of finger arterial pressure by an inflatable cuff around the middle phalange of the finger. The pulsating finger artery is clamped to a constant volume by applying a varying counter pressure equivalent to the arterial pressure using a built-in photoelectric plethysmograph and an automatic algorithm (Physiocal). The resulting finger arterial pressure waveform is reconstructed into a brachial artery pressure waveform by a generalized algorithm. NexCO is calculated by a pulse contour method (CO-TREK) using the measured systolic pressure time integral and the heart’s afterload determined from the Windkessel model [
In an 8-hour period, simultaneous CCO and NexCO measurements were obtained every 2 hours (0–2–4–6–8 hrs, in total 225 paired measurements) while simultaneous TDCO and NexCO were obtained every 4 hours (0–4–8 hrs, in total 135 paired measurements). The CCO and NexCO values were recorded simultaneously by hand 5 min before TDCO was determined by 3 repeated injections of 20 mL of sterile ice-cold saline via the central venous line. Blood pressure measurements were recorded continuously by Nexfin and PiCCO and were by each device used to calculate the continuous CO. Subanalysis was performed for patients with a low MAP (defined as MAP ≤ 70 mmHg), low and high TDCO (defined as ≤ 4 L/min and ≥ 8 L/min), low and high SVRI (defined as an SVRI obtained by PiCCO ≤ 1700 dyne·s·cm−5/m² and ≥ 3000 dyne·s·cm-5/m²), and patients on high dose norepinephrine (≥0.3
Results are presented as mean (±SD) unless otherwise stated. Mean values were compared using student’s
The study was conducted in accordance with the ICU protocol, the declaration of Helsinki, and applicable regulatory requirements as approved by the institutional review board and the local institutional ethics committee (approval number 3789). In view of the nature of the study being purely observational, not demanding a deviation from standard clinical ICU care and since the results obtained by Nexfin were not used for clinical decision making, informed consent from the patient or the next of kin was not deemed essential. We merely analysed the existing situation and did nothing to influence events. Only treating ICU physicians accessed the medical records. All data were pseudonymized before analysis.
In 2 patients (4.3%) it was impossible to obtain Nexfin values from any of 10 fingers, and they were therefore excluded from final analysis. Baseline characteristics of the 45 remaining patients are summarized in Table
Patient characteristics.
Mean |
| |
---|---|---|
Demographics | ||
Age (yrs) |
|
|
Male | 32 (71%) | |
Reason of admission | ||
Medical | 27 (60%) | |
Surgical | 9 (20%) | |
Trauma | 5 (11%) | |
Burns | 4 (9%) | |
Shock | 31 (69%) | |
Septic | 18 (58%) | |
Cardiogenic | 6 (19%) | |
Other | 7 (23%) | |
ICU scores | ||
APACHE II |
|
|
SOFA |
|
|
SAPS II |
|
APACHE II: acute physiology and chronic health evaluation.
SAPS II: simplified acute physiology score.
SOFA: sequential organ failure assessment.
Comparison of several neurological, respiratory, and hemodynamic variables and dose of the used drugs between the start and the end (at 8 hours) of the study period.
Number (%) | Start | 8 hours |
| |
---|---|---|---|---|
Neurological | ||||
Propofol (mg/kg/hr) | 35 (71%) |
|
|
0.99 |
Midazolam (mg/kg/hr) | 31 (69%) |
|
|
0.81 |
Remifentanil ( |
39 (87%) |
|
|
0.80 |
Cisatracurium (mg/kg/hr) | 9 (20%) |
|
|
0.77 |
SAS (1–7) | 45 (100%) |
|
|
0.28 |
GCS (3–15) | 45 (100%) |
|
|
0.67 |
Respiratory system | ||||
pO2/FIO2 | 45 (100%) |
|
|
0.64 |
Minute ventilation (L/min) | 45 (100%) |
|
|
0.92 |
pH | 45 (100%) |
|
|
0.45 |
EVLWI (mL/kg) | 45 (100%) |
|
|
0.89 |
Hemodynamics | ||||
Norepinephrine ( |
35 (78%) |
|
|
0.90 |
Dobutamine ( |
27 (60%) |
|
|
0.49 |
MAP (mmHg) | 45 (100%) |
|
|
0.41 |
Heart rate (BPM) | 45 (100%) |
|
|
0.66 |
CVP (mmHg) | 45 (100%) |
|
|
0.65 |
TDCO (L/min) | 45 (100%) |
|
|
0.14 |
GEF (%) | 45 (100%) |
|
|
0.45 |
GEDVI (mL/BSA) | 45 (100%) |
|
|
0.56 |
SVRI (dyne·s·cm−5/m²) | 45 (100%) |
|
|
0.56 |
SVV (%) | 45 (100%) |
|
|
0.12 |
PPV (%) | 45 (100%) |
|
|
0.17 |
Other | ||||
IAP (mmHg) | 45 (100%) |
|
|
0.15 |
Body Temperature (°C) | 45 (100%) |
|
|
0.76 |
CVP: central venous pressure.
EVLWI: extravascular lung water index.
GCS: Glasgow coma scale.
GEDVI: global end-diastolic volume index.
GEF: global ejection fraction.
IAP: intra-abdominal pressure.
MAP: mean arterial pressure.
PPV: pulse pressure variation.
SAS: sedation and agitation scale.
SVRI: systemic vascular resistance index.
SVV: stroke volume variation.
TDCO: thermodilution cardiac output.
Mean NexCO was comparable to mean TDCO (6.1 ± 2.3 versus 6.6 ± 2.2 L/min,
Comparison of TDCO versus NexCO including subgroup analysis for patients with low MAP, low and high TDCO, low and high SVRI, and high dose norepinephrine and hypothermia.
Overall | Low MAP | Low TDCO | High TDCO | Low SVRI | High SVRI | Norepinephrine | Hypothermia | ||
---|---|---|---|---|---|---|---|---|---|
≤70 mmHg | ≤4 L/min | ≥8 L/min | ≤1700 dyne·s·cm−5/m² | ≥3000 dyne·s·cm−5/m² | ≥0,3 µg/kg/min | ≤35°C | |||
No. of patients | 45 | 19 | 9 | 18 | 29 | 6 | 11 | 22 | |
No. of paired measurements | 135 | 27 | 16 | 32 | 58 | 14 | 27 | 63 | |
| |||||||||
Mean TDCO | L/min | 6.6 | 6.2 | 3.8 | 8.2 | 7.2 | 4.5 | 6.7 | 6.5 |
| |||||||||
|
0.67 | 0.82 | 0.01 | 0.67 | 0.74 | 0.81 | 0.89 | 0.70 | |
|
<0.001 | <0.001 | NS | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | |
| |||||||||
Bias | L/min | 0.4 | 0.9 |
|
0.9 | 0.6 |
|
0.4 | 0.1 |
Precision | L/min | 1.2 | 1.1 | 1.5 | 1.1 | 1.3 | 1.3 | 1 | 1.3 |
Lower LA | L/min |
|
|
|
|
|
|
|
|
Upper LA | L/min | 2.7 | 3 | 2.5 | 3 | 3.2 | 2.4 | 2.3 | 2.6 |
| |||||||||
Percentage error | % | 36 | 34 | 78 | 26 | 37 | 57 | 29 | 39 |
TDCO: thermodilution cardiac output.
LA: limits of agreement.
MAP: mean arterial pressure.
SVRI: systemic vascular resistance index.
Comparison of CCO versus NexCO including subgroup analysis for patients with low MAP, low and high TDCO, low and high SVRI, and high dose norepinephrine or hypothermia.
|
|
Overall | Low MAP | Low TDCO | High TDCO | Low SVRI | High SVRI | Norepinephrine | Hypothermia |
---|---|---|---|---|---|---|---|---|---|
≤70 mmHg | ≤4 L/min | ≥8 L/min | ≤1700 dyne·s·cm−5/m² | ≥3000 dyne·s·cm−5/m² | ≥0.3 |
≤35°C | |||
No. of patients | 45 | 19 | 9 | 18 | 29 | 6 | 11 | 22 | |
No. of paired measurements | 135 | 50 | 27 | 51 | 104 | 22 | 44 | 63 | |
| |||||||||
Mean TDCO | L/min | 6.4 | 5.9 | 3.8 | 7.8 | 7.0 | 4.5 | 6.4 | 6.3 |
| |||||||||
|
0.71 | 0.87 | 0.1 | 0.73 | 0.81 | 0.78 | 0.94 | 0.67 | |
|
<0.001 | <0.001 | NS | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 | |
| |||||||||
Bias | L/min | 0.2 | 0.4 | 0.0 | 0.6 | 0.4 | 0.0 | 0.0 | 0.0 |
Precision | L/min | 1.2 | 0.9 | 1.4 | 1.1 | 1.0 | 1.2 | 0.5 | 1.3 |
Lower LA | L/min |
|
|
|
|
|
|
|
|
Upper LA | L/min | 2.5 | 2.2 | 2.7 | 2.8 | 2.3 | 2.3 | 1.0 | 2.6 |
| |||||||||
Percentage error | % | 36 | 30 | 71 | 29 | 29 | 53 | 16 | 42 |
TDCO: thermodilution cardiac output.
LA: limits of agreement.
MAP: mean arterial pressure.
SVRI: systemic vascular resistance index.
Cardiac output measurements: TDCO versus NexCO. Only one average value per patient is plotted. (a) Regression analysis. (b) Bland-Altman analysis. Patient averages with the mean cardiac output ranges (
Cardiac output measurements: CCO versus NexCO. Only one average value per patient is plotted. (a) Regression analysis. (b) Bland-Altman analysis. Patient averages with the mean cardiac output ranges (
Subanalysis for patients with a low MAP, high TDCO, low SVRI, and high dose norepinephrine consistently showed a very good correlation between NexCO and TDCO or CCO. NexCO was less reliable in patients with hypothermia and not reliable in patients with low TDCO and high SVRI (Tables
The four quadrants concordance plots are shown in Figure
Four quadrants trend plot. (a) Plot for 90 paired measurements of
The polar trending plots are shown in Figure
Polar plot. The distance from the center of the plot represents the mean change in cardiac output (
Data on ease of use were collected in 27 patients. There were no local signs of disturbed circulation in the middle finger due to the application of the finger cuff. The time between the decision to apply Nexfin and the first measurement was less than 5 minutes in 23/27 patients (85%) and between 5 and 10 minutes in 4/27 patients (15%). In 9/27 patients (33%) we were able to do measurements with the first application, while 13/27 patients (48%) needed 1–5 and 5/27 (19%) needed more than 5 repositions. Nurse questionnaires revealed a mean score of 1.4 ± 0.5 for the set-up of the device, 1.7 ± 0.7 for set-up placement, 1.8 ± 0.5 for measurements, and 1.9 ± 0.5 for ease of use (1 = very easy to 4 = very difficult).
We performed an open observational study in 45 mixed surgical/medical and burns critically ill patients to validate the Nexfin against transpulmonary thermodilution and continuous femoral arterial pulse contour derived CO by the PiCCO. To the best of our knowledge, this is the second Nexfin CO validation study conducted in mainly medical ICU patients, the first being published last year by Monnet and coworkers [
First, we found moderate to good CO correlation coefficients with TDCO (
Based on these results and review of the literature, we think that the Nexfin device can be applied in ICU or ER patients, potentially also on the regular wards and even out of hospital (if the manufacturer would provide a battery), for an initial quick hemodynamic assessment as a bridge to installation of a more advanced invasive monitoring system. Differentiation of the different types of shock on a clinical basis showed to be a major challenge and often inaccurate even in hands of experienced ICU and ER physicians [
However, in our opinion there are 5 main reasons why Nexfin cannot always be used as a first choice in the general ICU population with good IV and IA access requiring prolonged advanced hemodynamic monitoring. First, not only is the overall calculated PE too high but we also think that the LA are too broad to be clinically acceptable. If a CO is measured at 8 L/min, the true value can be between 5.7 and 10.3 L/min. Of note; however, is that the obtained correlation coefficients and LA are comparable to previous validation studies with PiCCO against PAC [
Some limitations of this study need to be considered. First, this is a validation study of CO by Nexfin against PiCCO. PAC is still considered by some clinicians as a golden standard. Although highly validated and widely used, PiCCO obtained CO shows some error against PAC. Second, the patient sample size and the size of the subgroups are probably too small to allow extensive further subgroup analysis. Third, we did not perform therapeutic intervention to assess the trending capabilities of the Nexfin. Fourth, we need to be aware that these results were obtained in an ICU patient group already receiving a lot of vasopressors and inotropic hemodynamic support thereby possibly not representing the initial hemodynamic pattern. Future studies should be performed to confirm that these results can be extrapolated to ER patients. Finally, the number of patients was determined on a random basis and no power analysis was performed.
In conclusion, Nexfin is a totally noninvasive, easy to use blood pressure and CO monitor based on finger arterial blood pressure pulse contour analysis. Nexfin obtained CO showed a moderate to good correlation with CO measured by PiCCO although the PE was too high. The Nexfin can be used for keeping track of changes in CO over time (e.g., to assess the therapeutic effect of a given treatment), although the absolute criteria for full interchangeability were not met in this population of mixed ICU patients.
Nexfin is a totally noninvasive, easy to use blood pressure and cardiac output monitor. Nexfin shows a moderate to good cardiac output correlation with transcardiopulmonary thermodilution (TDCO) and continuous pulse contour CO (CCO) obtained by PiCCO in a mixed ICU population although the obtained percentage error was too high to allow full interchangeability. Changes in NexCO correlate well with changes in TDCO and CCO although the obtained concordance coefficient was too high to allow full trending interchangeability.
Continuous cardiac output by PiCCO
Thermodilution
Nexfin obtained cardiac output
Central venous pressure
Extravascular lung water index
Glasgow coma scale
Global end-diastolic volume index
Global ejection fraction
Intra-abdominal pressure
Mean arterial pressure
Pulse pressure variation
Percentage error
Sedation and agitation scale
Systemic vascular resistance index
Stroke volume variation
Simplified acute physiology score
Sequential organ failure assessment
Acute physiology and chronic health evaluation.
Manu Malbrain and Berthold Bein are members of the medical advisory board of Pulsion Medical Systems (Munich, Germany) but have no direct financial relation with the commercial identities mentioned in the paper that might lead to a conflict of interests. The other authors have no competing interests.
Part of this paper has been presented previously in abstract and poster form at the 31st International Symposium on Intensive Care and Emergency Medicine (ISICEM) held in Brussels in 2011 [