The use of a vascular occlusion test combined with near-infrared spectroscopy in perioperative care: a systematic review.

In the perioperative phase oxygen delivery and consumption can be influenced by different factors, i.e. type of surgery, anesthetic and cardiovascular drugs, or fluids. By combining near-infrared spectroscopy (NIRS) monitoring of regional tissue oxygen saturation (StO2) with an ischemic provocation test, the vascular occlusion test (VOT), local tissue oxygen consumption and vascular reactivity at the microcirculatory level can be assessed. This systematic review aims to give an overview of the clinical information that VOT-derived NIRS values can provide in the perioperative period. After performing a systematic literature search, we included 29 articles. It was not possible to perform a meta-analysis because of the lack of comparable data and the observational nature of the majority of the included articles. We have clustered the found articles in two groups: non-cardiac surgery and cardiac surgery. We found that VOT-derived NIRS values show a wide variability and are influenced by the effects of anesthetics, cardiovascular drugs, fluids, and by the type of surgery. Additionally, deviations in VOT-derived NIRS values are also associated with adverse patients' outcomes, such as postoperative complications, prolonged mechanical ventilation and prolonged hospital length of stay. However, given the variability in VOT-derived NIRS values, clinical applicability remains elusive. Future clinical interventional trials might provide additional insight into the potential of VOT associated with NIRS to optimize perioperative care by targeting specific interventions to optimize the function of the microvasculature.

The effect of compliance with a perioperative goal-directed therapy protocol on outcomes after high-risk surgery: a before-after study.

Perioperative goal-directed therapy is considered to improve patient outcomes after high-risk surgery. The association of compliance with perioperative goal-directed therapy protocols and postoperative outcomes is unclear. The purpose of this study is to determine the effect of protocol compliance on postoperative outcomes following high-risk surgery, after implementation of a perioperative goal-directed therapy protocol. Through a before-after study design, patients undergoing elective high-risk surgery before (before-group) and after implementation of a perioperative goal-directed therapy protocol (after-group) were included. Perioperative goal-directed therapy in the after-group consisted of optimized stroke volume variation or stroke volume index and optimized cardiac index. Additionally, the association of protocol compliance with postoperative complications when using perioperative goal-directed therapy was assessed. High protocol compliance was defined as ≥ 85% of the procedure time spent within the individual targets. The difference in complications during the first 30 postoperative days before and after implementation of the protocol was assessed. In the before-group, 214 patients were included and 193 patients in the after-group. The number of complications was higher in the before-group compared to the after-group (n = 414 vs. 282; p = 0.031). In the after-group, patients with high protocol compliance for stroke volume variation or stroke volume index had less complications compared to patients with low protocol compliance for stroke volume variation or stroke volume index (n = 187 vs. 90; p = 0.01). Protocol compliance by the attending clinicians is essential and should be monitored to facilitate an improvement in postoperative outcomes desired by the implementation of perioperative goal-directed therapy protocols.

Journal of Clinical Monitoring and Computing 2019 end of year summary: monitoring tissue oxygenation and perfusion and its autoregulation.

Tissue perfusion monitoring is increasingly being employed clinically in a non-invasive fashion. In this end-of-year summary of the Journal of Clinical Monitoring and Computing, we take a closer look at the papers published recently on this subject in the journal. Most of these papers focus on monitoring cerebral perfusion (and associated hemodynamics), using either transcranial doppler measurements or near-infrared spectroscopy. Given the importance of cerebral autoregulation in the analyses performed in most of the studies discussed here, this end-of-year summary also includes a short description of cerebral hemodynamic physiology and its autoregulation. Finally, we review articles on somatic tissue oxygenation and its possible association with outcome.

Journal of Clinical Monitoring and Computing 2017/2018 end of year summary: monitoring-and provocation-of the microcirculation and tissue oxygenation.

The microcirculation is the ultimate goal of hemodynamic optimization in the perioperative and critical care setting. In this fourth end-of-year summary of the Journal of Clinical Monitoring and Computing on this topic, we take a closer look at papers published in the last 2 years that focus on this important aspect. The majority of these papers investigated the use of either cerebral or peripheral tissue oxygen saturation, derived non-invasively using near infrared spectroscopy (NIRS). In some of these studies, the microcirculation was "provocated" by inducing short-term tissue hypoxia, allowing the assessment of functional microvascular reserve. Additionally, studies on technical differences between NIRS monitors are summarized, as well as studies investigating the feasibility of NIRS monitoring, mainly in the pediatric patient population. Last but not least, novel monitoring tools allow assessing oxygenation at a (sub)cellular level, and those papers incorporating these techniques are also reviewed here.

Phenylephrine increases cardiac output by raising cardiac preload in patients with anesthesia induced hypotension.

Induction of general anesthesia frequently induces arterial hypotension, which is often treated with a vasopressor, such as phenylephrine. As a pure α-agonist, phenylephrine is conventionally considered to solely induce arterial vasoconstriction and thus increase cardiac afterload but not cardiac preload. In specific circumstances, however, phenylephrine may also contribute to an increase in venous return and thus cardiac output (CO). The aim of this study is to describe the initial time course of the effects of phenylephrine on various hemodynamic variables and to evaluate the ability of advanced hemodynamic monitoring to quantify these changes through different hemodynamic variables. In 24 patients, after induction of anesthesia, during the period before surgical stimulus, phenylephrine 2 µg kg-1 was administered when the MAP dropped below 80% of the awake state baseline value for > 3 min. The mean arterial blood pressure (MAP), heart rate (HR), end-tidal CO2 (EtCO2), central venous pressure (CVP), stroke volume (SV), CO, pulse pressure variation (PPV), stroke volume variation (SVV) and systemic vascular resistance (SVR) were recorded continuously. The values at the moment before administration of phenylephrine and 5(T5) and 10(T10) min thereafter were compared. After phenylephrine, the mean(SD) MAP, SV, CO, CVP and EtCO2 increased by 34(13) mmHg, 11(9) mL, 1.02(0.74) L min-1, 3(2.6) mmHg and 4.0(1.6) mmHg at T5 respectively, while both dynamic preload variables decreased: PPV dropped from 20% at baseline to 9% at T5 and to 13% at T10 and SVV from 19 to 11 and 14%, respectively. Initially, the increase in MAP was perfectly aligned with the increase in SVR, until 150 s after the initial increase in MAP, when both curves started to dissociate. The dissociation of the evolution of MAP and SVR, together with the changes in PPV, CVP, EtCO2 and CO indicate that in patients with anesthesia-induced hypotension, phenylephrine increases the CO by virtue of an increase in cardiac preload.

Light damage to the retina: an historical approach.

A brief review of retinal light damage is presented. Thermal damage requires a local rise in temperature of at least 10 °C, causing an instant denaturation of proteins. The primary absorber is melanin. Photochemical damage occurs at body temperature and involves cellular damage by reactive forms of oxygen. The photosensitizers are photoproducts of the visual pigments. First indications that non-thermal damage might exist, in particular in the case of eclipse blindness, was presented by Vos in 1962. Attribution thereof to photochemical action was presented in 1966 by Noell et al who also measured the first action spectrum, in rat. It turned out to be identical to the absorption spectrum of rhodopsin. However, in 1976 and 1982 Ham et al found a quite different spectrum in monkeys, peaking at short wavelengths. The latter spectrum, but not the former, was confirmed since in numerous publications with animal models including rat. In ophthalmological practice a 'sunburn' was at first the only complaint caused by light damage. To avoid this, patients with dilated pupils should always be advised to wear sunglasses. Since the invention of the laser accidents have been reported, the most recent development is youth playfully pointing a strong laser pen in their eyes with marked consequences. The operation microscope and endoilluminators should always be used as brief as possible to avoid photochemical damage. Arguments for implant lenses that block not only the UV but also part of the visible spectrum seem too weak to justify extra costs.

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.

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.

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).

Intraoperative ICG plasma disappearance rate helps to predict absence of early postoperative complications after orthotopic liver transplantation.

Early postoperative complications after orthotopic liver transplantation (OLT) are a common problem in intensive care medicine. Adequate assessment of initial graft function remains difficult, however, plasma disaperance rate of indocyanine green (PDRICG) may have an additional diagnostic and prognostic value in this setting. We retrospectively evaluated the ability of intraoperative PDRICG values to predict absence of early postoperative complications in 62 subjects. PDRICG was measured non-invasively by pulse dye densitometry during surgery and was correlated with initial graft function. At the end of surgery, PDRICG was higher in patients without complications: 24.9 % min(-1) (n = 40) versus 21.0 % min(-1), (n = 22; p = 0.034). An area under the ROC curve (AUROC) for PDRICG was 0.70, while the AUROC for pH, lactate and PT at ICU admission were 0.53, 0.50 and 0.46, respectively. The AUROC of serum bilirubin and PT at postoperative day 5 were 0.68 and 0.49, respectively. The optimal cut-off PDRICG value for predicting absence of development early postoperative complications was determined to be 23.5 % min(-1) with 72.4 % sensitivity and 71.0 % specificity. Intraoperative point-of-care PDRICG measurement during OLT already predicts absence of early postoperative complications, better and earlier than clinically used laboratory parameters.

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.

From lower to higher colour metrics: a historical account.

BACKGROUND: 'Lower colour metrics' describes the laws of colour mixture as manifest in trichromatic colour space and best known in its two-dimensional projection, the chromaticity diagram. 'Higher colour metrics' describes how distance in this colour space translates into perceptual difference. It is higher in the sense that it builds on the fundamentals of lower colour metrics. METHODS: A historical account is given of the development of higher colour metrics, with many ups and downs, since Helmholtz started it at the end of the 19th Century. RESULTS: Despite long periods of silence, Helmholtz's basic ideas have survived by successfully extended modelling, which could also account for seemingly paradoxical effects of luminance and saturation on colour discrimination. CONCLUSION: The subject theme, which presently is at a low tide of interest, deserves the renewed interest of colour vision researchers.

Retinal damage by optical radiation. An alternative to current, ACGIH-inspired guidelines.

BACKGROUND: The ACGIH guidelines for protection against retinal damage by optical radiation are often difficult to apply due to their lack of transparency. The less known guidelines by the Netherlands Health Council (HCN), dating from 1978 and updated in 1993, might offer a way out in many cases. METHODS: A comparison is made of these guidelines, embedded in a short sketch of the history. They are illustrated by examples of applications. RESULTS: In most cases the HCN guidelines produce results that hardly deviate from those obtained with the ACGIH guidelines but in some cases the results diverge and in other cases HCN gives an answer where ACGIH seems to fall short. CONCLUSIONS: The HCN guidelines form a good alternative to those of ACGIH.

[The laser pointer: no demonstrated danger to the eyes]. / De laserpen als aanwijsstok niet aangetoond gevaarlijk voor de ogen.

If laser pointers are powerful enough (> 5 mW), they can cause ocular damage. Most laser pointers in use, however, have low power, viz. 1 mW. In the peer-reviewed scientific literature worldwide not a single case of eye damage due to laser pointers is described. A review among Dutch ophthalmologists up to June 1998 revealed no cases of permanent damage caused by laser pointers. In view of the widespread use of laser pointers, the risk of retinal damage must be minimal, even with the types now banned. Laser pointers of 1 mW emitting light red or green light have sufficient visibility on projection screens. It is advisable to prohibit the sale of more powerful pointers to prevent excesses.

On the Stiles-Crawford effect with age.

PURPOSE: To determine whether the Stiles-Crawford effect remains stable after subjects have aged 30 years. METHODS: The relative luminous efficiency as a function of pupil position (Stiles-Crawford effect) was determined for the same seven subjects on the same apparatus in the 1960s and in 1995. The pupil opening was traversed nine times, at 20 degrees azimuth intervals. Data were fit with a revolution paraboloid yielding a peak position (x0, y0) and a peakedness (rho). RESULTS: Two of seven subjects showed a significant, but small, decrease in rho, and the other five showed, no change. No clear outcome in x0, y0 changes could be reported because of differences in pupil dilation then and now. CONCLUSIONS: Although exceptions are found on the stability of the Stiles-Crawford effect with age, the authors can still conclude that it is stable.