Jaap Jan Vos

Comparison of continuous non-invasive finger arterial pressure monitoring with conventional intermittent automated arm arterial pressure measurement in patients under general anaesthesia

BACKGROUND For a majority of patients undergoing anaesthesia for general surgery, mean arterial pressure (MAP) is only measured intermittently by arm cuff oscillometry (MAPiNIAP). In contrast, the Nexfin(®) device provides continuous non-invasive measurement of MAP (MAPcNIAP) using a finger cuff. We explored the agreement of MAPcNIAP and MAPiNIAP with the gold standard: continuous invasive MAP measurement by placement of a radial artery catheter (MAPinvasive). METHODS In a total of 120 patients undergoing elective general surgery and clinically requiring MAPinvasive measurement, MAPiNIAP and MAPcNIAP were measured in a 30 min time period at an arbitrary moment during surgery with stable haemodynamics. MAPiNIAP was measured every 5 min. RESULTS Data from 112 patients were analysed. Compared with MAPinvasive, modified Bland-Altman analysis revealed a bias (sd) of 2 (9) mm Hg for MAPcNIAP and -2 (12) mm Hg for MAPiNIAP. Percentage errors for MAPcNIAP and MAPiNIAP were 22% and 32%, respectively. CONCLUSIONS In a haemodynamically stable phase in patients undergoing general anaesthesia, the agreement with invasive MAP of continuous non-invasive measurement using a finger cuff was not inferior to the agreement of intermittent arm cuff oscillometry. Continuous measurements using a finger cuff can interchangeably be used as an alternative for intermittent arm cuff oscillometry in haemodynamically stable patients, with the advantage of beat-to-beat haemodynamic monitoring. CLINICAL TRIAL REGISTRATION NCT 01362335 (clinicaltrials.gov).

Comparison of arterial pressure and plethysmographic waveform-based dynamic preload variables in assessing fluid responsiveness and dynamic arterial tone in patients undergoing major hepatic resection

BACKGROUND Dynamic preload variables to predict fluid responsiveness are based either on the arterial pressure waveform (APW) or on the plethysmographic waveform (PW). We compared the ability of APW-based variations in stroke volume (SVV) and pulse pressure (PPV) and of PW-based plethysmographic variability index (PVI) to predict fluid responsiveness and to track fluid changes in patients undergoing major hepatic resection. Furthermore, we assessed whether the PPV/SVV ratio, as a measure of dynamic arterial elastance (Eadyn), could predict a reduction in norepinephrine requirement after fluid administration. METHODS Thirty patients received i.v. fluid (15 ml kg(-1) in 30 min) after hepatic resection and were considered responders when stroke volume index (SVI) increased ≥20% after fluid administration. SVV and SVI were measured by the FloTrac-Vigileo(®) device, and PVI was measured by the Masimo Radical 7 pulse co-oximeter(®). RESULTS The areas under a receiver operating characteristic curve for SVV, PPV, and PVI were 0.81, 0.77, and 0.78, respectively. In responders, all dynamic variables, except PVI, decreased after fluid administration. Eadyn predicted a reduced norepinephrine requirement (AUC = 0.81). CONCLUSIONS In patients undergoing major hepatic resection, both APW- and PW-based dynamic preload variables predict fluid responsiveness (preload) to a similar extent. Most variables (except PVI) also tracked fluid changes. Eadyn, as a measure of arterial elastance (afterload), might be helpful to distinguish the origin of hypotension. CLINICAL TRIAL REGISTRATION ClinicalTrials.gov, NCT01060683.

Accuracy of non-invasive measurement of haemoglobin concentration by pulse co-oximetry during steady-state and dynamic conditions in liver surgery

BACKGROUND The Masimo Radical 7 (Masimo Corp., Irvine, CA, USA) pulse co-oximeter(®) calculates haemoglobin concentration (SpHb) non-invasively using transcutaneous spectrophotometry. We compared SpHb with invasive satellite-lab haemoglobin monitoring (Hb(satlab)) during major hepatic resections both under steady-state conditions and in a dynamic phase with fluid administration of crystalloid and colloid solutions. METHODS Thirty patients undergoing major hepatic resection were included and randomized to receive a fluid bolus of 15 ml kg(-1) colloid (n=15) or crystalloid (n=15) solution over 30 min. SpHb was continuously measured on the index finger, and venous blood samples were analysed in both the steady-state phase (from induction until completion of parenchymal transection) and the dynamic phase (during fluid bolus). RESULTS Correlation was significant between SpHb and Hb(satlab) (R(2)=0.50, n=543). The modified Bland-Altman analysis for repeated measurements showed a bias (precision) of -0.27 (1.06) and -0.02 (1.07) g dl(-1) for the steady-state and dynamic phases, respectively. SpHb accuracy increased when Hb(satlab) was <10 g dl(-1), with a bias (precision) of 0.41 (0.47) vs -0.26 (1.12) g dl(-1) for values >10 g dl(-1), but accuracy decreased after colloid administration (R(2)=0.25). CONCLUSIONS SpHb correlated moderately with Hb(satlab) with a slight underestimation in both phases in patients undergoing major hepatic resection. Accuracy increased for lower Hb(satlab) values but decreased in the presence of colloid solution. Further improvements are necessary to improve device accuracy under these conditions, so that SpHb might become a sensitive screening device for clinically significant anaemia.

Green light for liver function monitoring using indocyanine green? An overview of current clinical applications

The dye indocyanine green is familiar to anaesthetists, and has been studied for more than half a century for cardiovascular and hepatic function monitoring. It is still, however, not yet in routine clinical use in anaesthesia and critical care, at least in Europe. This review is intended to provide a critical analysis of the available evidence concerning the indications for clinical measurement of indocyanine green elimination as a diagnostic and prognostic tool in two areas: its role in peri‐operative liver function monitoring during major hepatic resection and liver transplantation; and its role in critically ill patients on the intensive care unit, where it is used for prediction of mortality, and for assessment of the severity of acute liver failure or that of intra‐abdominal hypertension. Although numerous studies have demonstrated that indocyanine green elimination measurements in these patient populations can provide diagnostic or prognostic information to the clinician, ‘hard’ evidence – i.e. high‐quality prospective randomised controlled trials – is lacking, and therefore it is not yet time to give a green light for use of indocyanine green in routine clinical practice.

Differential effects of phenylephrine and norepinephrine on peripheral tissue oxygenation during general anaesthesia: A randomised controlled trial

BACKGROUND Phenylephrine and norepinephrine are two vasopressors commonly used to counteract anaesthesia-induced hypotension. Their dissimilar working mechanisms may differentially affect the macro and microcirculation, and ultimately tissue oxygenation. OBJECTIVES We investigated the differential effect of phenylephrine and norepinephrine on the heart rate (HR), stroke volume (SV), cardiac index (CI), cerebral tissue oxygenation (SctO2) and peripheral tissue oxygenation (SptO2), and rate-pressure product (RPP). DESIGN A randomised controlled study. SETTING Single-centre, University Medical Center Groningen, The Netherlands. PATIENTS Sixty normovolaemic patients under balanced propofol/remifentanil anaesthesia. INTERVENTIONS If the mean arterial pressure (MAP) dropped below 80% of the awake state value, phenylephrine (100 &mgr;g + 0.5 &mgr;g kg−1 min−1) or norepinephrine (10 &mgr;g + 0.05 &mgr;g kg−1 min−1) was administered in a randomised fashion. MAIN OUTCOME MEASURES MAP, HR, SV, CI, SctO2, SptO2 and rate-pressure product (RPP) analysed from 30 s before drug administration until 240 s thereafter. RESULTS Phenylephrine and norepinephrine caused an equivalent increase in MAP [&Dgr; = 13 (8 to 22) and &Dgr; = 13 (9 to 19) mmHg, respectively] and SV [&Dgr; = 6 ± 6 and &Dgr; = 5 ± 7 ml, respectively], combined with a significant equivalent decrease in HR (both &Dgr; = −8 ± 6 bpm), CI (both &Dgr; = −0.2 ± 0.3 l min−1 m−2) and SctO2 and an unchanged RPP (&Dgr; = 345 ± 876 and &Dgr; = 537 ± 1076 mmHg min−1). However, SptO2 was slightly but statistically significantly (P < 0.05) decreased after norepinephrine [&Dgr; = −3 (−6 to 0)%] but not after phenylephrine administration [&Dgr; = 0 (−1 to 1)%]. In both groups, SptO2 after vasopressor was still higher than the awake value. CONCLUSION In normovolaemic patients under balanced propofol/remifentanil anaesthesia, phenylephrine and norepinephrine produced similar clinical effects when used to counteract anaesthesia-induced hypotension. After norepinephrine, a fall in peripheral tissue oxygenation was statistically significant, but its magnitude was not clinically relevant.

Minimally invasive cardiac output technologies in the ICU : putting it all together

Purpose of review Haemodynamic monitoring is a cornerstone in the diagnosis and evaluation of treatment in critically ill patients in circulatory distress. The interest in using minimally invasive cardiac output monitors is growing. The purpose of this review is to discuss the currently available devices to provide an overview of their validation studies in order to answer the question whether these devices are ready for implementation in clinical practice. Recent findings Current evidence shows that minimally invasive cardiac output monitoring devices are not yet interchangeable with (trans)pulmonary thermodilution in measuring cardiac output. However, validation studies are generally single centre, are based on small sample sizes in heterogeneous groups, and differ in the statistical methods used. Summary Minimally and noninvasive monitoring devices may not be sufficiently accurate to replace (trans)pulmonary thermodilution in estimating cardiac output. The current paradigm shift to explore trending ability rather than investigating agreement of absolute values alone is to be applauded. Future research should focus on the effectiveness of these devices in the context of (functional) haemodynamic monitoring before adoption into clinical practice can be recommended.

How to "validate" newly developed cardiac output monitoring devices

In the past decade, technological advances have catalyzedthe development of (advanced) hemodynamic monitoringdevices from invasive towards less invasive methods.Almost every month a new device appears on the marketclaiming to measure or estimate hemodynamic variables ina minimal or non-invasive fashion. These devices allowclinicians to broaden the scope beyond traditional pressure-based hemodynamic monitoring and by now, flow(-related)variables such as cardiac output (CO) can be assessed thisway in almost all patients in the anesthetic or critical caresetting. Hopefully, these technological advancements proveadvantageous in terms of patient outcome in the (near)future. However, an accurate and precise estimation of theassumed-to-be-measured hemodynamic variable is anabsolute prerequisite before such new devices can beclinically implemented, or even before outcome-relatedstudies can be performed. Additionally, given the (hemo-dynamic) heterogeneity of various patient populations (e.g.patients with septic shock versus patients with cardiogenicshock), both accuracy and precision should be investigatedin the relevant patient population(s). Therefore, researchersall over the world are stimulated to perform comparisonstudies in which new devices, software versions or sensorrevisions are compared with their clinical reference meth-ods or ‘‘gold standards’’, and journals are overflooded withmanuscripts on such evaluation studies.The basis for statistical reporting for such studies wasset almost 30 years ago by Bland and Altman in their land-mark paper [1], in which they introduced their famous‘‘Bland–Altman plot’’. In this (scatter)plot, agreementbetween two measurement methods is assessed by plottingthe mean of the measurements against the difference of themeasurements and it allows the calculation of the limits ofagreement (LOA; 1.96 9 SD of the bias) as a measure ofreproducibility.Assuch,theBland–Altmanplotappreciatestwo important aspects: it assesses method agreement basedon the ‘‘closeness’’ of individual data points and it does notrequire the definition of a gold standard, i.e. it assumes nofixed‘‘true’’value.Sinceitsintroduction,theBland–Altmanplot (initially developed for comparing CO measurements)has become the minimal standard for statistical reporting ofmethod comparison studies in general [2].While the Bland–Altman plot remains highly popular, itbears some important limitations that are especially rele-vant for CO method agreement studies. At first, the plotonly provides an estimation of agreement in the light of alinear relationship between the two measurement methods,and it does not take the magnitude of these observationsinto consideration, while this is highly important as a‘‘closer’’ agreement is required for a CO value of 1.5 L/mincompared to a CO of 3.5 L/min. To overcome this issue,Critchley and Critchley [3] introduced percentage errors(calculated as the LOA divided by the mean of the mea-surements) to compensate agreement for the magnitude ofmeasurement. In CO agreement studies, the calculation ofpercentage errors is well adopted and there is generalconsensus for accepting new CO measurement methods ifthese devices meet the so-called Critchley criteria, whichmeans that the percentage error is below 30 %.As all clinicians will be aware of, CO is not a staticvariable and changes continuously secondary to complex

Do intravascular hypo- and hypervolaemia result in changes in central blood volumes?

BACKGROUND Hypovolaemia is generally believed to induce centralization of blood volume. Therefore, we evaluated whether induced hypo- and hypervolaemia result in changes in central blood volumes (pulmonary blood volume (PBV), intrathoracic blood volume (ITBV)) and we explored the effects on the distribution between these central blood volumes and circulating blood volume (Vd circ). METHODS Six anaesthetized, spontaneously breathing Foxhound dogs underwent random blood volume alterations in steps of 150 ml (mild) to 450 ml (moderate), either by haemorrhage, retransfusion of blood, or colloid infusion. PBV, ITBV and Vd circ were measured using (transpulmonary) dye dilution. The PBV/Vd circ ratio and the ITBV/Vd circ ratio were used as an assessment of blood volume distribution. RESULTS 68 blood volume alterations resulted in changes in Vdcirc ranging from -33 to +31%. PBV and ITBV decreased during mild and moderate haemorrhage, while during retransfusion, PBV and ITBV increased during moderate hypervolaemia only. The PBV/Vd circ ratio remained constant during all stages of hypo- and hypervolaemia (mean values between 0.20-0.22). This was also true for the ITBV/Vd circ ratio, which remained between 0.31 and 0.32, except for moderate hypervolaemia, where it increased slightly to 0.33 (0.02), P<0.05. CONCLUSIONS Mild to moderate blood volume alterations result in changes of Vd circ, PBV and ITBV. The ratio between the central blood volumes and Vd circ generally remained unaltered. Therefore, it could be suggested that in anaesthetized spontaneously breathing dogs, the cardiovascular system maintains the distribution of blood between central and circulating blood volume.

The Validity of Eadyn in Spontaneously Breathing Patients.

To the Editor Recently, Cecconi et al. 1 showed that in spontaneously breathing patients in the intensive care unit, noninvasively derived dynamic arterial elastance (Eadyn) can predict an increase in arterial blood pressure after fluid administration. Included patients were assumed preloaddependent, and hemodynamics were assessed using the volume clamp technique (Nexfin®, BMEYE, Amsterdam, The Netherlands). Eadyn, assumed as a functional measure of arterial elastance, represents the ratio of pulse pressure specifically examining whether the arterial pressure pulsatility in the brain (especially in the periresection bed that may have impaired autoregulation to systemic blood pressure) is associated with postoperative intracranial bleeding. IV nicardipine effectively controls systemic hypertension without increasing intracranial pressure.3 Because (fortunately) the overall incidence of postoperative intracranial hematoma is low (1.1%),4 our study was not designed a priori to determine whether hypertension itself or the specific antihypertensive used during emergence from anesthesia is related to the development of postoperative intracranial hemorrhage. With the widespread use of electronic medical records, it may be possible to retrospectively calculate systemic arterial pulsatility over the initial hours after emergence from anesthesia and thereby explore whether there is a relationship between the systemic arterial pulsatility and the development of postoperative intracranial hemorrhage after resection of brain tumors.

Pulse Dye Densitometry and Indocyanine Green Plasma Disappearance: The Issue of "Normal" Values

We agree with Kopp et al. that the ALARA (as low as reasonably achievable) concept must be considered in pediatric fluoroscopic imaging. Of course, in our study we obtained consent from the parents of the children after explaining details of the study and radiation exposure. The genital area was protected from radiation by a lead plate during fluoroscopy using a new pulsed unit from Phillips (Eindhoven, The Netherlands). The study by Cohen described possible radiation exposure variations as much as 3486% and 4479% with the maximum magnification, greatest pulse rate, intensifier high, grid in, and greatest intensifier exposure rate. We believe that the exposure variations were not as great because we did not alter the basal magnification setting and used the lowest pulse rate, grid out, and lowest intensifier exposure rate. The exposure frequency to obtain 1 image (exposure rate) was 1 or 2, and overall duration of fluoroscopy was 30 seconds. However, because the average estimated entrance surface dose (ESD) and dose area product increases with age, the ESD also increases in children in comparison with adults; we investigated the ESD in 5 randomly selected children in our previous study. The ESD was 0.05 to 0.26 mSv, which was less than the results of a United Kingdom nationwide survey in 2005. Although our procedures did not diverge from the ALARA concept when we substituted the procedure to the flow diagram for managing patient dose by Strauss and Kaste, we believe that the radiation exposure should be strictly limited in children.