Transcutaneous P<Emphasis Type="SmallCaps">tc</Emphasis>CO<Subscript>2</Subscript> measurement in combination with arterial blood gas analysis provides superior accuracy and reliability in ICU patients

Hyper or hypoventilation may have serious clinical consequences in critically ill patients and should be generally avoided, especially in neurosurgical patients. Therefore, monitoring of carbon dioxide partial pressure by intermittent arterial blood gas analysis (PaCO₂) has become standard in intensive care units (ICUs). However, several additional methods are available to determine PCO₂ including end-tidal (PetCO₂) and transcutaneous (PtcCO₂) measurements. The aim of this study was to compare the accuracy and reliability of different methods to determine PCO₂ in mechanically ventilated patients on ICU. After approval of the local ethics committee PCO₂ was determined in n = 32 ICU consecutive patients requiring mechanical ventilation: (1) arterial PaCO₂ blood gas analysis with Radiometer ABL 625 (ABL; gold standard), (2) arterial PaCO₂ analysis with Immediate Response Mobile Analyzer (IRMA), (3) end-tidal PetCO₂ by a Propaq 106 EL monitor and (4) transcutaneous PtcCO₂ determination by a Tina TCM4. Bland–Altman method was used for statistical analysis; p < 0.05 was considered statistically significant. Statistical analysis revealed good correlation between PaCO₂ by IRMA and ABL (R² = 0.766; p < 0.01) as well as between PtcCO₂ and ABL (R² = 0.619; p < 0.01), whereas correlation between PetCO₂ and ABL was weaker (R² = 0.405; p < 0.01). Bland–Altman analysis revealed a bias and precision of 2.0 ± 3.7 mmHg for the IRMA, 2.2 ± 5.7 mmHg for transcutaneous, and ?5.5 ± 5.6 mmHg for end-tidal measurement. Arterial CO₂ partial pressure by IRMA (PaCO₂) and PtcCO₂ provided greater accuracy compared to the reference measurement (ABL) than the end-tidal CO₂ measurements in critically ill in mechanically ventilated patients patients.     

Near-infrared spectroscopy assessed cerebral oxygenation during open abdominal aortic aneurysm repair: relation to end-tidal CO<Subscript>2</Subscript> tension

During open abdominal aortic aneurism (AAA) repair cerebral blood flow is challenged. Clamping of the aorta may lead to unintended hyperventilation as metabolism is reduced by perfusion of a smaller part of the body and reperfusion of the aorta releases vasodilatory substances including CO₂. We intend to adjust ventilation according end-tidal CO₂ tension (EtCO₂) and here evaluated to what extent that strategy maintains frontal lobe oxygenation (S_cO₂) as determined by near infrared spectroscopy. For 44 patients [5 women, aged 70 (48–83) years] S_cO₂, mean arterial pressure (MAP), EtCO₂, and ventilation were obtained retrospectively from the anesthetic charts. By clamping the aorta, S_cO₂ and EtCO₂ were kept stable by reducing ventilation (median, ?0.8 l min^?1; interquartile range, ?1.1 to ?0.4; P < 0.001). During reperfusion of the aorta a reduction in MAP by 8 mmHg (?15 to ?1; P < 0.001) did not prevent an increase in S_cO₂ by 2 % (?1 to 4; P < 0.001) as EtCO₂ increased 0.5 kPa (0.1–1.0; P < 0.001) despite an increase in ventilation by 1.8 l min^?1 (0.9–2.7; P < 0.001). Changes in S_cO₂ related to those in EtCO₂ (r = 0.41; P = 0.0001) and cerebral deoxygenation (?15 %) was noted in three patients while cerebral hyperoxygenation (+15 %) manifests in one patient. Thus changes in ScO₂ were kept within acceptable limits (±15 %) in 91 % of the patients. For the majority of the patients undergoing AAA repair S_cO₂ was kept within reasonable limits by reducing ventilation by approximately 1 l min^?1 upon clamping of the aorta and increasing ventilation by approximately 2 l min^?1 when the lower body is reperfused.     

Measuring gas exchange with step changes in inspired oxygen: an analysis of the assumption of oxygen steady state in patients suffering from COPD

Bedside estimation of pulmonary gas exchange efficiency may be possible from step changes in FiO₂ and subsequent measurement of arterial oxygenation at steady state conditions. However, a steady state may not be achieved quickly after a change in FiO₂, especially in patients with lung disease such as COPD, rendering this approach cumbersome. This paper investigates whether breath by breath measurement of respiratory gas and arterial oxygen levels as FiO₂ is changed can be used as a much more rapid alternative to collecting data from steady state conditions for measuring pulmonary gas exchange efficiency. Fourteen patients with COPD were studied using 4–5 step changes in FiO₂ in the range of 0.15–0.35. Values of expired respiratory gas and arterial oxygenation were used to calculate and compare the parameters of a mathematical model of pulmonary gas exchange in two cases: from data at steady state; and from breath by breath data prior to achievement of a steady state. For each patient, the breath by breath data were corrected for the delay in arterial oxygen saturation changes following each change in FiO₂. Calculated model parameters were shown to be similar for the two data sets, with Bland–Altman bias and limits of agreement of ?0.4 and ?3.0 to 2.2 % for calculation of pulmonary shunt and 0.17 and ?0.47 to 0.81 kPa for alveolar to end-capillary PO₂, a measure of oxygen abnormality due to shunting plus regions of low \({\dot{\text{V}}}\) a/\({\dot{\text{Q}}}\) ratio. This study shows that steady state oxygen levels may not be necessary when estimating pulmonary gas exchange using changes in FiO₂. As such this technique may be applicable in patients with lung disease such as COPD.     

Performance of an active inspired hypoxic guard

Current hypoxic guards systems fail to maintain the inspired O₂ concentration (F_IO₂) ≥ 21 % across the entire fresh gas flow (FGF) range when a second carrier gas is used (N₂O or air). We examined the performance of the Maquet O₂ Guard^®, a smart hypoxic guard that increases O₂ delivery if an inspired hypoxic mixture is formed. After obtaining IRB approval and informed consent, 12 ASA I-II patients were enrolled. During anesthesia with sevoflurane in O₂/air, the O₂ Guard^® was tested by administering O₂/air at the following delivered hypoxic guard limits [expressed as (total FGF in L min^?1; F_DO₂ in %)] for 4 min each: [0.3;67], [0.4;50], [0.6;34], [0.8;25], [1.0;21], [1.2;21], [1.5;21], [2;21], [3;21], and [5;21]. The following data were collected: (1) time from F_IO₂ = 30 to 20 %; (2) time from F_IO₂ = 20 % to O₂ Guard^® activation; (3) time from O₂ Guard^® activation to F_IO₂ = 25 %; (4) FGF and F_DO₂ used by the O₂ Guard. If SpO₂ was <90 % for 10 s or longer at any time, the patient was excluded. Three patients were excluded for low SpO₂. The incidence of F_IO₂ < 21 % was 100 % within the 1–2 L min^?1 FGF range. The O₂ Guard^® was activated within 20 s after F_IO₂ became 20 %, except in one patient where F_IO₂ oscillated between 20 and 21 %. F_DO₂ was increased to 60 % and FGF to 1 L min^?1 (the latter only if it was lower than 1 L min^?1 prior to activation of the O₂ Guard). F_IO₂ increased to 25 % within 55 s after O₂ Guard activation in all patients. The O₂ Guard^®, an active inspired hypoxic guard, rapidly reverses and limits the duration of inspired hypoxic episodes when the delivered hypoxic guard fails to do so.     

Safety and efficacy of a fully closed-loop control ventilation (IntelliVent-ASV<Superscript>®</Superscript>) in sedated ICU patients with acute respiratory failure: a prospective randomized crossover study

Purpose

IntelliVent-ASV^® is a development of adaptive support ventilation (ASV) that automatically adjusts ventilation and oxygenation parameters. This study assessed the safety and efficacy of IntelliVent-ASV^® in sedated intensive care unit (ICU) patients with acute respiratory failure.

Methods

This prospective randomized crossover comparative study was conducted in a 12-bed ICU in a general hospital. Two periods of 2 h of ventilation in randomly applied ASV or IntelliVent-ASV^® were compared in 50 sedated, passively ventilated patients. Tidal volume (V _T), respiratory rate (RR), inspiratory pressure (P _INSP), SpO₂ and E_TCO₂ were continuously monitored and recorded breath by breath. Mean values over the 2-h period were calculated. Respiratory mechanics, plateau pressure (P _PLAT) and blood gas exchanges were measured at the end of each period.

Results

There was no safety issue requiring premature interruption of IntelliVent-ASV^®. Minute ventilation (MV) and V _T decreased from 7.6 (6.5–9.5) to 6.8 (6.0–8.0) L/min (p < 0.001) and from 8.3 (7.8–9.0) to 8.1 (7.7–8.6) mL/kg PBW (p = 0.003) during IntelliVent-ASV^® as compared to ASV. P _PLAT and FiO₂ decreased from 24 (20–29) to 20 (19–25) cmH₂O (p = 0.005) and from 40 (30–50) to 30 (30–39) % (p < 0.001) during IntelliVent-ASV^® as compared to ASV. RR, P _INSP, and PEEP decreased as well during IntelliVent-ASV^® as compared to ASV. Respiratory mechanics, pH, PaO₂ and PaO₂/FiO₂ ratio were not different but PaCO₂ was slightly higher during IntelliVent-ASV^® as compared to ASV.

Conclusions

In passive patients with acute respiratory failure, IntelliVent-ASV^® was safe and able to ventilate patients with less pressure, volume and FiO₂ while producing the same results in terms of oxygenation.

     

Accuracy of simple approaches to assessing liver volume in radiological imaging

Objectives

The purpose of the study was to evaluate the accuracy of measured diameters and calculated volume indices for determining liver size and to derive a simple approach for estimating liver volume.

Methods

Three hundred twenty-nine volunteers (cohort A) were grouped according to liver volume: small (n = 109), medium (n = 110), and large (n = 110). True liver volume was determined by magnetic resonance imaging (MRI) using manual segmentation. Maximum diameters (maxdiam) of the liver and distances in midclavicular line (MCL) were measured. Volume indices were calculated as a simple product of the measured diameters. The calculated volume indices were calibrated to predict true liver volume. Performance of the calibrated method was evaluated in a control group (cohort B) including randomly selected volunteers (n = 110) and a patient group with histopathologically proven parenchymal liver diseases (n = 28).

Results

In cohort A, there was strong correlation between diameters and true liver volume (r _s = 0.631–0.823). Calculated volume indices had slightly better correlation (maxdiam r _s = 0.903, MCL r _s = 0.920). A calibration index was calculated from the volumes and diameters determined in cohort A. Application of this calibration on cohort B verified a very strong correlation between calibrated volume indices and true liver volume (maxdiam r _s = 0.920, MCL r _s = 0.909). In addition, the low mean difference between predicted liver volume (maxdiam = ?70.9 cm³;MCL = ?88.4 cm³) and true liver volume confirms that the calibrated method allows accurate assessment of liver volume.

Conclusions

Both simple diameters and volume indices allow estimating liver size. A simple calibration formula enables prediction of true liver volume without significant expense.

     

Quantification of Tumor Hypoxic Fractions Using Positron Emission Tomography with [<Superscript>18</Superscript>F]Fluoromisonidazole ([<Superscript>18</Superscript>F]FMISO) Kinetic Analysis and Invasive Oxygen Measurements

Purpose

The purpose of this study is to use dynamic [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO) positron emission tomography (PET) to compare estimates of tumor hypoxic fractions (HFs) derived by tracer kinetic modeling, tissue-to-blood ratios (TBR), and independent oxygen (pO₂) measurements.

Procedures

BALB/c mice with EMT6 subcutaneous tumors were selected for PET imaging and invasive pO₂ measurements. Data from 120-min dynamic [¹⁸F]FMISO scans were fit to two-compartment irreversible three rate constant (K ₁, k ₂, k ₃) and Patlak models (K _i). Tumor HFs were calculated and compared using K _i, k ₃, TBR, and pO₂ values. The clinical impact of each method was evaluated on [¹⁸F]FMISO scans for three non-small cell lung cancer (NSCLC) radiotherapy patients.

Results

HFs defined by TBR (≥1.2, ≥1.3, and ≥1.4) ranged from 2 to 85 % of absolute tumor volume. HFs defined by K _i (>0.004 ml min cm^?3) and k ₃ (>0.008 min^?1) varied from 9 to 85 %. HF quantification was highly dependent on metric (TBR, k ₃, or K _i) and threshold. HFs quantified on human [¹⁸F]FMISO scans varied from 38 to 67, 0 to 14, and 0.1 to 27 %, for each patient, respectively, using TBR, k ₃, and K _i metrics.

Conclusions

[¹⁸F]FMISO PET imaging metric choice and threshold impacts hypoxia quantification reliability. Our results suggest that tracer kinetic modeling has the potential to improve hypoxia quantification clinically as it may provide a stronger correlation with direct pO₂ measurements.

     

Quantification of stenotic mitral valve area and diagnostic accuracy of mitral stenosis by dual-source computed tomography in patients with atrial fibrillation: comparison with cardiovascular magnetic resonance and transthoracic echocardiography

This study aimed to evaluate the utility of dual-source computed tomography (DSCT) for quantification of the mitral valve area (MVA) in patients with atrial fibrillation (AF) and mitral stenosis (MS) and to compare the results of DSCT with those of cardiovascular magnetic resonance (CMR) and transthoracic echocardiography (TTE). One hundred-two patients with AF and MS who had undergone electrocardiography-gated DSCT, TTE and CMR prior to operation were retrospectively enrolled. The MVA was planimetrically determined by DSCT, CMR, and TTE, as well as by Doppler TTE using the pressure half-time method (TTE–PHT). Agreement, relationship between measurements, and the highest accuracy were evaluated using Bland–Altman, Pearson correlation, and receiver operating characteristic analyses. The MVA on DSCT (mean, 1.27 ± 0.27 cm²) was significantly larger than that on CMR (1.15 ± 0.28 cm², P < 0.05), TTE-planimetry and TTE–PHT (1.16 ± 0.28 and 1.07 ± 0.30 cm², respectively; P < 0.05). TTE-planimetry had better correlation with planimetry on DSCT and CMR (r = 0.65 and 0.67, respectively; P < 0.05) than TTE–PHT (r = 0.51 and 0.55, respectively; P < 0.05). Using an MVA of 1.0 cm² on TTE-planimetry and TTE–PHT as the reference, the optimal thresholds for detecting severe MS on DSCT was 1.19 cm². The planimetry of the MVA measured by DSCT may be a reliable, alternative method for the quantification of MS in patients with AF.     

Accuracy of pleth variability index to predict fluid responsiveness in mechanically ventilated patients: a systematic review and meta-analysis

To systemically evaluate the accuracy of pleth variability index to predict fluid responsiveness in mechanically ventilated patients. A literature search of PUBMED, OVID, CBM, CNKI and Wanfang Data for clinical studies in which the accuracy of pleth variability index to predict fluid responsiveness was performed (last update 5 April 2015). Related journals were also searched manually. Two reviewers independently assessed trial quality according to the modified QUADAS items. Heterogeneous studies and meta-analysis were conducted by Meta-Disc 1.4 software. A subgroup analysis in the operating room (OR) and in intensive care unit (ICU) was also performed. Differences between subgroups were analyzed using the interaction test. A total of 18 studies involving 665 subjects were included. The pooled area under the receiver operating characteristic curve (AUC) to predict fluid responsiveness in mechanically ventilated patients was 0.88 [95 % confidence interval (CI) 0.84–0.91]. The pooled sensitivity and specificity were 0.73 (95 % CI 0.68–0.78) and 0.82 (95 % CI 0.77–0.86), respectively. No heterogeneity was found within studies nor between studies. And there was no significant heterogeneity within each subgroup. No statistical differences were found between OR subgroup and ICU subgroup in the AUC [0.89 (95 % CI 0.85–0.92) versus 0.90 (95 % CI 0.82–0.94); P = 0.97], and in the specificity [0.84 (95 % CI 0.75–0.86) vs. 0.84 (95 % CI 0.75–0.91); P = 1.00]. Sensitivity was higher in the OR subgroup than the ICU subgroup [0.84 (95 % CI 0.78–0.88) vs. 0.56 (95 % CI 0.47–0.64); P = 0.00004]. The pleth variability index has a reasonable ability to predict fluid responsiveness.     

Dead space reduction by Kolobow’s endotracheal tube does not justify the waiving of volume monitoring in small,ventilated lungs

In ventilated preterm infants the flow sensor contributes significantly to the total apparatus dead space, which may impair gas exchange. The aim of the study was to quantify to which extent a dead space reduced Kolobow tube (KB) without flow sensor improves the gas exchange compared with a conventional ventilator circuit with flow sensor [Babylog 8000 (BL)]. In a cross-over trial in 14 tracheotomized, surfactant-depleted (saline lavage) and mechanically ventilated newborn piglets (age <12 h; body weight 705–1200 g) BL and KB was applied alternately for 15 min and blood gases were recorded. The inner diameter of the endotracheal tube was 3.6 mm and the apparatus dead space of BL and KB including the endotracheal tube were 3.0 and 1.34 mL. Despite a 50 % apparatus dead space reduction with KB compared to BL statistically significant improvements were only observed for body weights <900 g. In this weight group median paCO₂ was decreased by 5 mmHg (p < 0.01), whereas the improvement decreased with decreasing baseline paCO₂. Furthermore, median paO₂ was increased by 4 mmHg (p < 0.05) and O₂ saturation was increased by 2.5 % (p < 0.05). No significant changes were seen in the circulatory parameters. In very small, ventilated lungs the use of KB improved the gas exchange; however, the improvement was moderate and does not justify the waiving of volume monitoring.     

Comparison of non-invasive peripheral venous saturations with venous blood co-oximetry

The estimation of venous oxygen saturations using photoplethysmography (PPG) may be useful as a noninvasive continuous method of detecting changes in regional oxygen supply and demand (e.g. in the splanchnic circulation). The aim of this research was to compare PPG-derived peripheral venous oxygen saturations directly with venous saturation measured from co-oximetry blood samples, to assess the feasibility of non-invasive local venous oxygen saturation. This paper comprises two similar studies: one in healthy spontaneously-breathing volunteers and one in mechanically ventilated anaesthetised patients. In both studies, PPG-derived estimates of peripheral venous oxygen saturations (SxvO₂) were compared with co-oximetry samples (ScovO₂) of venous blood from the dorsum of the hand. The results were analysed and correlation between the PPG-derived results and co-oximetry was tested for. In the volunteer subjects,moderate correlation (r = 0.81) was seen between SxvO₂ values and co-oximetry derived venous saturations (ScovO₂), with a mean (±SD) difference of +5.65 ± 14.3% observed between the two methods. In the anaesthetised patients SxvO₂ values were only 3.81% lower than SpO₂ and tended to underestimate venous saturation (mean difference = –2.67 ± 5.89%) while correlating weakly with ScovO₂ (r = 0.10). The results suggest that significant refinement of the technique is needed to sufficiently improve accuracy to produce clinically meaningful measurement of peripheral venous oxygen saturation. In anaesthetised patients the use of the technique may be severely limited by cutaneous arteriovenous shunting.     

A mesenteric traction syndrome affects near-infrared spectroscopy evaluated cerebral oxygenation because skin blood flow increases

During abdominal surgery manipulation of internal organs may induce a “mesenteric traction syndrome” (MTS) including a triad of flushing, hypotension, and tachycardia that lasts for about 30 min. We evaluated whether MTS affects near-infrared spectroscopy (NIRS) assessed frontal lobe oxygenation (S_cO₂) by an increase in forehead skin blood flow (SkBF). The study intended to include 10 patients who developed MTS during pancreaticoduodenectomy and 22 patients were enrolled (age 61?±?8 years; mean?±?SD). NIRS determined ScO₂, laser Doppler flowmetry determined SkBF, cardiac output (CO) was evaluated by pulse-contour analysis (Modelflow), and transcranial Doppler assessed middle cerebral artery mean flow velocity (MCA V_mean). MTS was identified by flushing within 60 min after start of surgery. MTS developed 20 min (12–24; median with range) after the start of surgery and heart rate (78?±?16 vs. 68?±?17 bpm; P?=?0.0032), CO (6.2?±?1.4 vs. 5.3?±?1.1 L min^?1; P?=?0.0086), SkBF (98?±?35 vs. 80?±?23 PU; P?=?0.0271), and S_cO₂ (71?±?6 vs. 67?±?8%; P?<?0.0001), but not MCA V_mean (32?±?8 vs. 32?±?7; P?=?0.1881) were largest in the patients who developed MTS. In some patients undergoing abdominal surgery NIRS-determined S_cO₂ is at least temporarily affected by an increase in extra-cranial perfusion independent of cerebral blood flow as indicated by MCA V_mean. Thus, NIRS evaluation of S_cO₂ may overestimate cerebral oxygenation if patients flush during surgery.     

Utility of stroke volume variation measured using non-invasive bioreactance as a predictor of fluid responsiveness in the prone position

The aim of this prospective study was to evaluate the usefulness of stroke volume variation (SVV) derived from NICOM^® to predict fluid responsiveness in the prone position. Forty adult patients undergoing spinal surgery in the prone position were included in this study. We measured SVV from NICOM^® (SVV_NICOM) and FloTrac?/Vigileo? systems (SVV_Vigileo), and pulse pressure variation (PPV) using automatic (PPV_auto) and manual (PPV_manual) calculations at four time points including supine and prone positions, and before and after fluid loading of 6 ml kg^?1 colloid solution. Fluid responsiveness was defined as an increase in the cardiac index from Vigileo? of ≥12 %. There were 19 responders and 21 non-responders. Prone positioning induced a significant decrease in SVV_NICOM, SVV_Vigileo, PPV_auto, and PPV_manual. However, all of these parameters successfully predicted fluid responsiveness in the prone position with area under the receiver-operator characteristic curves for SVV_NICOM, SVV_Vigileo, PPV_auto, and PPV_manual of 0.78 [95 % confidence interval (CI) 0.62–0.90, P = 0.0001], 0.79 (95 % CI 0.63–0.90, P = 0.0001), 0.76 (95 % CI 0.6–0.88, P = 0.0006), and 0.84 (95 % CI 0.69–0.94, P < 0.0001), respectively. The optimal cut-off values were 12 % for SVV_NICOM, SVV_Vigileo, and PPV_auto, and 10 % for PPV_manual. SVV from NICOM^® successfully predicts fluid responsiveness during surgery in the prone position. This totally non-invasive technique for assessing individual functional intravenous volume status would be useful in a wide range of surgeries performed in the prone position.     

Midregional pro-atrial natriuretic peptide: a novel marker of myocardial fibrosis in patients with hypertrophic cardiomyopathy

We aimed to determine the diagnostic performance of biomarkers in predicting myocardial fibrosis assessed by late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) in patients with hypertrophic cardiomyopathy (HCM). LGE CMR was performed in 40 consecutive patients with HCM. Left and right ventricular parameters, as well as the extent of LGE were determined and correlated to the plasma levels of midregional pro-atrial natriuretic peptide (MR-proANP), midregional pro-adrenomedullin (MR-proADM), carboxy-terminal pro-endothelin-1 (CT-proET-1), carboxy-terminal pro-vasopressin (CT-proAVP), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and interleukin-8 (IL-8). Myocardial fibrosis was assumed positive, if CMR indicated LGE. LGE was present in 26 of 40 patients with HCM (65%) with variable extent (mean: 14%, range: 1.3–42%). The extent of LGE was positively associated with MR-proANP (r = 0.4; P = 0.01). No correlations were found between LGE and MR-proADM (r = 0.1; P = 0.5), CT-proET-1 (r = 0.07; P = 0.66), CT-proAVP (r = 0.16; P = 0.3), MMP-9 (r = 0.01; P = 0.9), TIMP-1 (r = 0.02; P = 0.85), and IL-8 (r = 0.02; P = 0.89). After adjustment for confounding factors, MR-proANP was the only independent predictor associated with the presence of LGE (P = 0.007) in multivariate analysis. The area under the ROC curve (AUC) indicated good predictive performance (AUC = 0.882) of MR-proANP with respect to LGE. The odds ratio was 1.268 (95% confidence interval 1.066–1.508). The sensitivity of MR-proANP at a cut-off value of 207 pmol/L was 69%, the specificity 94%, the positive predictive value 90% and the negative predictive value 80%. The results imply that MR-proANP serves as a novel marker of myocardial fibrosis assessed by LGE CMR in patients with HCM.     

Central venous-to-arterial carbon dioxide difference and the effect of venous hyperoxia: A limiting factor,or an additional marker of severity in shock?

Central venous-to-arterial carbon dioxide difference (P_cvaCO₂) has demonstrated its prognostic value in critically ill patients suffering from shock, and current expert recommendations advocate for further resuscitation interventions when P_cvaCO₂ is elevated. P_cvaCO₂ combination with arterial–venous oxygen content difference (P_cvaCO₂/C_avO₂) seems to enhance its performance when assessing anaerobic metabolism. However, the fact that PCO₂ values might be altered by changes in blood O₂ content (the Haldane effect), has been presented as a limitation of PCO₂-derived variables. The present study aimed at exploring the impact of hyperoxia on P_cvaCO₂ and P_cvaCO₂/C_avO₂ during the early phase of shock. Prospective interventional study. Ventilated patients suffering from shock within the first 24 h of ICU admission. Patients requiring FiO₂ ≥ 0.5 were excluded. At inclusion, simultaneous arterial and central venous blood samples were collected. Patients underwent a hyperoxygenation test (5 min of FiO₂ 100%), and arterial and central venous blood samples were repeated. Oxygenation and CO₂ variables were calculated at both time points. Twenty patients were studied. The main cause of shock was septic shock (70%). The hyperoxygenation trial increased oxygenation parameters in arterial and venous blood, whereas PCO₂ only changed at the venous site. Resulting P_cvaCO₂ and P_cvaCO₂/C_avO₂ significantly increased [6.8 (4.9, 8.1) vs. 7.6 (6.7, 8.5) mmHg, p 0.001; and 1.9 (1.4, 2.2) vs. 2.3 (1.8, 3), p < 0.001, respectively]. Baseline P_cvaCO₂, P_cvaCO₂/C_avO₂ and S_cvO₂ correlated with the magnitude of PO₂ augmentation at the venous site within the trial (ρ ?0.46, p 0.04; ρ 0.6, p < 0.01; and ρ 0.7, p < 0.001, respectively). Increased P_cvaCO₂/C_avO₂ values were associated with higher mortality in our sample [1.46 (1.21, 1.89) survivors vs. 2.23 (1.86, 2.8) non-survivors, p < 0.01]. P_cvaCO₂ and P_cvaCO₂/C_avO₂ are influenced by oxygenation changes not related to flow. Elevated P_cvaCO₂ and P_cvaCO₂/C_avO₂ values might not only derive from cardiac output inadequacy, but also from venous hyperoxia. Elevated P_cvaCO₂/C_avO₂ values were associated with higher PO₂ transmission to the venous compartment, suggesting higher shunting phenomena.     

In-stent area stenosis on 64-slice multi-detector computed tomography coronary angiography: optimal cutoff value for minimum lumen cross-sectional area of coronary stents compared with intravascular ultrasound

We aimed to prospectively assess the optimal cutoff value for a minimum lumen cross-sectional area (CSA) on a 64-slice multidetector computed tomography (MDCT) compared with an intravascular ultrasound (IVUS). In 39 patients with 43 stents, the minimum lumen diameter, stent diameter, diameter stenosis, minimum lumen CSA, stent CSA, and area stenosis at the narrowest point were measured independently on 64-slice MDCT and IVUS images. For the assessment of diameter and CSA, 64-slice MDCT showed good correlations with IVUS (r = 0.82 for minimum lumen diameter, r = 0.66 for stent diameter, r = 0.79 for minimum lumen CSA, and r = 0.75 for stent CSA, respectively, P < 0.0001). For the assessment of diameter and area stenoses, a 64-slice MDCT showed good correlations with IVUS (r = 0.89 and 0.91, respectively, P < 0.0001). The overall sensitivity, specificity, positive predictive value, and negative predictive value to detect in-stent area restenosis (≥50 % area stenosis) of a 64-slice MDCT were 77, 100, 100, and 91 %, respectively. The cutoff value of a 64-slice MDCT, determined by receiver operator characteristic (ROC) analysis, was 5.0 mm² with 76.5 % sensitivity and 92.3 % specificity for significant in-stent area restenosis; the area under the ROC curve was 0.902 (P < 0.0001). A good correlation was found between a 64-slice MDCT and the IVUS, regarding the assessment of diameter and area stenoses of coronary stents in selected patients implanted with stents of more than 3 mm in diameter. Optimal cutoff value for the minimum lumen CSA of coronary stents on the 64-slice MDCT is 5 mm² to predict a CSA of 4 mm² on IVUS.     

<Emphasis Type="Italic">In Vivo</Emphasis> DCE-MRI for the Discrimination Between Glioblastoma and Radiation Necrosis in Rats

Purpose

In this study, the potential of semiquantitative and quantitative analysis of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) was investigated to differentiate glioblastoma (GB) from radiation necrosis (RN) in rats.

Procedures

F98 GB growth was seen on MRI 8–23 days post-inoculation (n = 15). RN lesions developed 6–8 months post-irradiation (n = 10). DCE-MRI was acquired using a fast low-angle shot (FLASH) sequence. Regions of interest (ROIs) encompassed peripheral contrast enhancement in GB (n = 15) and RN (n = 10) as well as central necrosis within these lesions (GB (n = 4), RN (n = 3)). Dynamic contrast-enhanced time series, obtained from the DCE-MRI data, were fitted to determine four function variables (amplitude A, offset from zero C, wash-in rate k, and wash-out rate D) as well as maximal intensity (Imax_F) and time to peak (TTP_F). Secondly, maps of semiquantitative and quantitative parameters (extended Tofts model) were created using Olea Sphere (_O). Semiquantitative DCE-MRI parameters included wash-in_O, wash-out_O, area under the curve (AUC_O), maximal intensity (Imax_O), and time to peak (TTP_O). Quantitative parameters included the rate constant plasma to extravascular-extracellular space (EES) (K _trans), the rate constant EES to plasma (K _ep), plasma volume (V _p), and EES volume (V _e). All (semi)quantitative parameters were compared between GB and RN using the Mann-Whitney U test. ROC analysis was performed.

Results

Wash-in rate (k) and wash-out rate (D) were significantly higher in GB compared to RN using curve fitting (p = 0.016 and p = 0.014). TTP_F and TTP_O were significantly lower in GB compared to RN (p = 0.001 and p = 0.005, respectively). The highest sensitivity (87 %) and specificity (80 %) were obtained for TTP_F by applying a threshold of 581 s. K _trans, K _ep, and V _e were not significantly different between GB and RN. A trend towards higher V _p values was found in GB compared to RN, indicating angiogenesis in GB (p = 0.075).

Conclusions

Based on our results, in a rat model of GB and RN, wash-in rate, wash-out rate, and the time to peak extracted from DCE-MRI time series data may be useful to discriminate GB from RN.

     

Automated gas control with the Maquet FLOW-i

The FLOW-i anesthesia machine (Maquet, Solna, Sweden) can be equipped with automated gas control (AGC), an automated low flow tool with target control of the inspired oxygen concentration (F_IO₂) and end-expired concentration (F_A) of a potent inhaled anesthetic. We examined the performance and quantitative aspects of the AGC. After IRB approval and individual informed consent, anesthesia in 24 ASA I–II patients undergoing abdominal or gynecological surgery was maintained with sevoflurane in O₂/air with a target F_IO₂ of 40 % and a target sevoflurane F_A (F_Asevo) of 2.0 %. The AGC tool also allows the user to select 1 out of 9 different speeds with which the target F_Asevo can be reached (with 9 being the fastest speed). Eight patients each were randomly assigned to speed 2, 4, and 6 (= group 2, group 4, and group 6, respectively); these three speeds were chosen arbitrarily. AGC was activated immediately after securing the airway, which defined the start of the study, and the study ended 60 min later. The following parameters were compared among the three groups: age, height, weight, F_IO₂, F_Asevo, BIS values, heart rate, mean arterial blood pressure, fresh gas flow, and sevoflurane usage. Agent usage as reported by the FLOW-i was compared among the three groups. Patient demographics and maintenance FGF did not differ among groups. A very short-lived very high FGF (≈20 L min^?1 for 8–12 s) ensured that the target F_IO₂ was attained within 1–2 min in all patients. F_Asevo was 1.8 % after 15, 10, and 6 min, and 1.9 % after 30, 20 and 15 min in groups 2, 4, and 6, respectively. Blood pressure, heart rate, and BIS values did not differ among the three groups. BIS values remained acceptable in all patients, even with the slowest speed. Cumulative agent usage differed among all three groups between 2 and 30 min (lower with the lower speed), and between group 2 and 6 between 35 and 60 min. AGC combines an exponentially decreasing FGF pattern with a choice of ramp functions for the end-expired target concentration of the inhaled anesthetic. Consequently, both FGF and the choice of speed become factors that influence agent usage. After 15 min, a 300 mL min^?1 maintenance FGF reduces agent usage to near closed-circuit conditions. This new addition to our automated low flow armamentarium helps to reduce anesthetic waste, cost, and pollution, while minimizing the ergonomic burden of low flow anesthesia.     

Utility and safety of draining pleural effusions in mechanically ventilated patients: a systematic review and meta-analysis

Introduction

Pleural effusions are frequently drained in mechanically ventilated patients but the benefits and risks of this procedure are not well established.

Methods

We performed a literature search of multiple databases (MEDLINE, EMBASE, HEALTHSTAR, CINAHL) up to April 2010 to identify studies reporting clinical or physiological outcomes of mechanically ventilated critically ill patients who underwent drainage of pleural effusions. Studies were adjudicated for inclusion independently and in duplicate. Data on duration of ventilation and other clinical outcomes, oxygenation and lung mechanics, and adverse events were abstracted in duplicate independently.

Results

Nineteen observational studies (N = 1,124) met selection criteria. The mean P_aO₂:F_iO₂ ratio improved by 18% (95% confidence interval (CI) 5% to 33%, I ² = 53.7%, five studies including 118 patients) after effusion drainage. Reported complication rates were low for pneumothorax (20 events in 14 studies including 965 patients; pooled mean 3.4%, 95% CI 1.7 to 6.5%, I ² = 52.5%) and hemothorax (4 events in 10 studies including 721 patients; pooled mean 1.6%, 95% CI 0.8 to 3.3%, I ² = 0%). The use of ultrasound guidance (either real-time or for site marking) was not associated with a statistically significant reduction in the risk of pneumothorax (OR = 0.32; 95% CI 0.08 to 1.19). Studies did not report duration of ventilation, length of stay in the intensive care unit or hospital, or mortality.

Conclusions

Drainage of pleural effusions in mechanically ventilated patients appears to improve oxygenation and is safe. We found no data to either support or refute claims of beneficial effects on clinically important outcomes such as duration of ventilation or length of stay.