Non-invasive measurements of pulse pressure variation and stroke volume variation in anesthetized patients using the Nexfin blood pressure monitor

Nexfin beat-to-beat arterial blood pressure monitoring enables continuous assessment of hemodynamic indices like cardiac index (CI), pulse pressure variation (PPV) and stroke volume variation (SVV) in the perioperative setting. In this study we investigated whether Nexfin adequately reflects alterations in these hemodynamic parameters during a provoked fluid shift in anesthetized and mechanically ventilated patients. The study included 54 patients undergoing non-thoracic surgery with positive pressure mechanical ventilation. The provoked fluid shift comprised 15° Trendelenburg positioning, and fluid responsiveness was defined as a concomitant increase in stroke volume (SV) >10 %. Nexfin blood pressure measurements were performed during supine steady state, Trendelenburg and supine repositioning. Hemodynamic parameters included arterial blood pressure (MAP), CI, PPV and SVV. Trendelenburg positioning did not affect MAP or CI, but induced a decrease in PPV and SVV by 3.3 ± 2.8 and 3.4 ± 2.7 %, respectively. PPV and SVV returned back to baseline values after repositioning of the patient to baseline. Bland–Altman analysis of SVV and PPV showed a bias of ?0.3 ± 3.0 % with limits of agreement ranging from ?5.6 to 6.2 %. The SVV was more superior in predicting fluid responsiveness (AUC 0.728) than the PVV (AUC 0.636), respectively. The median bias between PPV and SVV was different for patients younger [?1.5 % (?3 to 0)] or older [+2 % (0–4.75)] than 55 years (P < 0.001), while there were no gender differences in the bias between PPV and SVV. The Nexfin monitor adequately reflects alterations in PPV and SVV during a provoked fluid shift, but the level of agreement between PPV and SVV was low. The SVV tended to be superior over PPV or Ea_dyn in predicting fluid responsiveness in our population.     

Systolic pressure variation and pulse pressure variation during modifications of arterial pressure

OBJECTIVE: This study was performed to investigate the effect of vasopressor therapy on systolic pressure variation (SPV) and pulse pressure variation (PPV) compared to experimentally measured left ventricular stroke volume variation (SVV). DESIGN AND SETTING: Prospective study in a university laboratory. SUBJECTS: Twelve anesthetized and mechanically ventilated pigs. INTERVENTIONS: Increase in mean arterial pressure (by 100%) using phenylephrine and decrease (by 38%) using adenosine. MEASUREMENTS AND RESULTS: SPV and PPV were calculated and compared to SVV derived from aortic blood flow measurements. SPV was significantly affected by changes in arterial pressure [4.6% (1.5) vs. 6.3% (2.1), p[Symbol: see text]<[Symbol: see text]0.05, increased vs. decreased arterial pressure], whereas PPV did not change during modifications of arterial pressure. During baseline conditions and decreased afterload, correlation with SVV was good both for SPV (r[Symbol: see text]=[Symbol: see text]0.892 and r[Symbol: see text]=[Symbol: see text]0.859, respectively) and for PPV (r[Symbol: see text]=[Symbol: see text]0.870 and r[Symbol: see text]=[Symbol: see text]0.871, respectively) (all p[Symbol: see text]<[Symbol: see text]0.001). Correlation with SVV was only moderate during increased arterial pressure (r[Symbol: see text]=[Symbol: see text]0.683 for SPV and r[Symbol: see text]=[Symbol: see text]0.732 for PPV, p[Symbol: see text]<[Symbol: see text]0.05). CONCLUSION: For guiding fluid therapy in patients under vasopressor support, PPV seems superior to SPV.     

Predictive values of pulse pressure variation and stroke volume variation for fluid responsiveness in patients with pneumoperitoneum

Animal studies suggest that dynamic predictors remain useful in patients with pneumoperitoneum, but human data is conflicting. Our aim was to determine predictive values of pulse pressure variation (PPV) and stroke volume variation (SVV) in patients with pneumoperitoneum using LiDCORapid? haemodynamic monitor. Standardised fluid challenges of colloid were administered to patients undergoing laparoscopic procedures, one fluid challenge per patient. Intra-abdominal pressure was automatically held at 12 mmHg. Fluid responsiveness was defined as an increase in nominal stroke index (nSI)?≥?10%. Linear regression was used to assess the ability of PPV and SVV to track the changes of nSI and logistic regression and area under the receiver operating curve (AUROC) to assess the predictive value of PPV and SVV for fluid responsiveness. Threshold values for PPV and SVV were obtained using the “gray zone” approach. A p?<?0.05 was considered as statistically significant. 56 patients were included in analysis. 41 patients (73%) responded to fluids. Both PPV and SVV tracked changes in nSI (Spearman correlation coefficients 0.34 for PPV and 0.53 for SVV). Odds ratio for fluid responsiveness for PPV was 1.163 (95% CI 1.01–1.34) and for SVV 1.341 (95% CI 1.10–1.63). PPV achieved an AUROC of 0.674 (95% CI 0.518–0.830) and SVV 0.80 (95% CI 0.668–0.932). The gray zone of PPV ranged between 6.5 and 20.5% and that of SVV between 7.5 and 13%. During pneumoperitoneum, as measured by LiDCORapid?, PPV and SVV can predict fluid responsiveness, however their sensitivity is lower than the one reported in conditions without pneumoperitoneum. Trial registry number: (with the Australian New Zealand Clinical Trials Registry): ACTRN12612000456853.     

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.     

The effects of vasoactive drugs on pulse pressure and stroke volume variation in postoperative ventilated patients

Introduction

Although pulse pressure variation (PPV) and stroke volume variation (SVV) during mechanical ventilation have been shown to predict preload responsiveness, the effect of vasoactive therapy on PPV and SVV is unknown.

Methods

Pulse pressure variation and SVV were measured continuously in 15 cardiac surgery patients for the first 4 postoperative hours. Pulse pressure variation was directly measured from the arterial pressure waveform, and both PPV and SVV were also calculated by LiDCO Plus (LiDCO Ltd, Cambridge, United Kingdom) before and after volume challenges or changes in vasoactive drug infusions done to sustain cardiovascular stability.

Results

Seventy-one paired events were studied (38 vasodilator, 10 vasoconstrictor, 14 inotropes, and 9 volume challenges). The difference between the measured and LiDCO-calculated PPV was 1% ± 7% (1.96 SD, 95% confidence interval, r² = 0.8). Volume challenge decreased both PPV and SVV (15% to 10%, P < .05 and 13% to 9%, P = .09, respectively). Vasodilator therapy increased PPV and SVV (13% to 17% and 9% to 15%, respectively, P < .001), whereas increasing inotropes or vasoconstrictors did not alter PPV or SVV. The PPV/SVV ratio was unaffected by treatments.

Conclusion

Volume loading decreased PPV and SVV; and vasodilators increased both, consistent with their known cardiovascular effects. Thus, SVV and PPV can be used to drive fluid resuscitation algorithms in the setting of changing vasoactive drug therapy.     

The effect of fluid resuscitation on the effective circulating volume in patients undergoing liver surgery: a post-hoc analysis of a randomized controlled trial

To assess the significance of an analogue of the mean systemic filling pressure (Pmsa) and its derived variables, in providing a physiology based discrimination between responders and non-responders to fluid resuscitation during liver surgery. A post-hoc analysis of data from 30 patients undergoing major hepatic surgery was performed. Patients received 15 ml kg^?1 fluid in 30 min. Fluid responsiveness (FR) was defined as an increase of 20% or greater in cardiac index, measured by FloTrac-Vigileo^®. Dynamic preload variables (pulse pressure variation and stroke volume variation: PPV, SVV) were recorded additionally. Pvr, the driving pressure for venous return (=Pmsa–central venous pressure) and heart performance (E_H; Pvr/Pmsa) were calculated according to standard formula. Pmsa increased following fluid administration in responders (n?=?18; from 13?±?3 to 17?±?4 mmHg, p?<?0.01) and in non-responders (n?=?12; from 14?±?4 to 17?±?4 mmHg, p?<?0.01). Pvr, which was lower in responders before fluid administration (6?±?1 vs. 7?±?1 mmHg; p?=?0.02), increased after fluid administration only in responders (from 6?±?1 to 8?±?1 mmHg; p?<?0.01). E_H only decreased in non-responders (from 0.56?±?0.17 to 0.45?±?0.12; p?<?0.05). The area under the receiver operating characteristics curve of Pvr, PPV and SVV for predicting FR was 0.75, 0.73 and 0.72, respectively. Changes in Pmsa, Pvr and E_H reflect changes in effective circulating volume and heart performance following fluid resuscitation, providing a physiologic discrimination between responders and non-responders. Also, Pvr predicts FR equivalently compared to PPV and SVV, and might therefore aid in predicting FR in case dynamic preload variables cannot be used.     

Applicability of stroke volume variation in patients of a general intensive care unit: a longitudinal observational study

Sinus rhythm (SR) and controlled mechanical ventilation (CV) are mandatory for the applicability of respiratory changes of the arterial curve such as stroke volume variation (SVV) to predict fluid-responsiveness. Furthermore, several secondary limitations including tidal volumes <8 mL/kg and SVV-values within the “gray zone” of 9–13% impair prediction of fluid-responsiveness by SVV. Therefore, we investigated the prevalence of these four conditions in general ICU-patients. This longitudinal observational study analyzed a prospectively maintained haemodynamic database including 4801 transpulmonary thermodilution and pulse contour analysis measurements of 278 patients (APACHE-II 21.0 ± 7.4). The main underlying diseases were cirrhosis (32%), sepsis (28%), and ARDS (17%). The prevalence of SR and CV was only 19.4% (54/278) in the first measurements (primary endpoint), 18.8% (902/4801) in all measurements and 26.5% (9/34) in measurements with MAP < 65 mmHg and CI < 2.5 L/min/m² and vasopressor therapy. In 69.1% (192/278) of the first measurements and in 65.9% (3165/4801) of all measurements the patients had SR but did not have CV. In 1.8% (5/278) of the first measurements and in 2.5% (119/4801) of all measurements the patients had CV but lacked SR. In 9.7% (27/278) of the first measurements and in 12.8% (615/4801) of all measurements the patients did neither have SR nor CV. Only 20 of 278 (7.2%) of the first measurements and 8.2% of all measurements fulfilled both major criteria (CV, SR) and both minor criteria for the applicability of SVV. The applicability of SVV in ICU-patients is limited due to the absence of mandatory criteria during the majority of measurements.     

Diagnostic accuracy of stroke volume variation measured with uncalibrated arterial waveform analysis for the prediction of fluid responsiveness in patients with impaired left ventricular function: a prospective,observational study

Uncalibrated arterial waveform analysis enables dynamic preload assessment in a minimally invasive fashion. Evidence about the validity of the technique in patients with impaired left ventricular function is scarce, while adequate cardiac preload assessment would be of great value in these patients. The aim of this study was to investigate the diagnostic accuracy of stroke volume variation (SVV) measured with the FloTrac/Vigileo? system in patients with impaired left ventricular function. In this prospective, observational study, 22 patients with a left ventricular ejection fraction of 40 % or less undergoing elective coronary artery bypass grafting were included. Patients were considered fluid responsive if cardiac output increased with 15 % or more after volume loading (7 ml kg^?1 ideal body weight). The following variables were calculated: area under the receiver operating characteristics (ROC) curve, ideal cut-off value for SVV, sensitivity, specificity, positive and negative predictive values, and overall accuracy. In addition, SVV cut-off points to obtain 90 % true positive and 90 % true negative predictions were determined. ROC analysis revealed an area under the curve of 0.70 [0.47; 0.92]. The ideal SVV cut-off value was 10 %, with a corresponding sensitivity and specificity of 56 and 69 % respectively. Overall accuracy was 64 %, positive and negative predictive values were 69 and 56 % respectively. SVV values to obtain more than 90 % true positive and negative predictions were 16 and 6 % respectively. The ability of uncalibrated arterial waveform analysis SVV to predict fluid responsiveness in patients with impaired LVF was low.     

Goal-directed intraoperative fluid therapy guided by stroke volume and its variation in high-risk surgical patients: a prospective randomized multicentre study

Perioperative hemodynamic optimisation improves postoperative outcome for patients undergoing high-risk surgery (HRS). In this prospective randomized multicentre study we studied the effects of an individualized, goal-directed fluid management based on continuous stroke volume variation (SVV) and stroke volume (SV) monitoring on postoperative outcomes. 64 patients undergoing HRS were randomized either to a control group (CON, n = 32) or a goal-directed group (GDT, n = 32). In GDT, SVV and SV were continuously monitored (FloTrac/Vigileo) and patients were brought to and maintained on the plateau of the Frank-Starling curve (SVV <10 % and SV increase <10 % in response to fluid loading). Organ dysfunction was assessed using the SOFA score and resource utilization using the TISS score. Patients were followed up to 28 days for postoperative complications. Main outcome measures were the number of complications (infectious, cardiac, respiratory, renal, hematologic and abdominal post-operative complications), maximum SOFA score and cumulative TISS score during ICU stay, duration of mechanical ventilation, length of ICU stay, and time until fit for discharge. 12 patients had to be excluded from final analysis (6 in each group). During surgery, GDT received more colloids than CON (1,589 vs. 927 ml, P < 0.05) and SVV decreased in GDT (from 9.0 to 8.0 %, P < 0.05) but not in CON. The number of postoperative wound infections was lower in GDT (0 vs. 7, P < 0.01). Although not statistically significant, the proportion of patients with at least one complication (46 vs. 62 %), the number of postoperative complications per patient (0.65 vs. 1.40), the maximum sofa score (5.9 vs. 7.2), and the cumulative TISS score (69 vs. 83) tended to be lower. This multicentre study shows that fluid management based on a SVV and SV optimisation protocol is feasible and decreases postoperative wound infections. Our findings also suggest that a goal-directed strategy might decrease postoperative organ dysfunction.     

Pre-anesthetic stroke volume variation can predict cardiac output decrease and hypotension during induction of general anesthesia

This study aimed to assess the reliability of stroke volume variation (SVV) in predicting cardiac output (CO) decrease and hypotension during induction of general anesthesia. Forty-five patients undergoing abdominal surgery under general anesthesia were enrolled. Before induction of anesthesia, patients were required to maintain deep breathing (6–8 times/min), and pre-anesthetic SVV was measured for 1 min by electrical cardiometry. General anesthesia was induced with propofol, remifentanil, rocuronium, and sevoflurane. Study duration was defined from the start of fluid administration till 5 min after tracheal intubation. Blood pressure (BP) was measured every minute. Cardiac output was measured continuously by electrical cardiometry. Receiver operating characteristics (ROC) curves were made regarding the incidence of decreased CO (less than 70% of the baseline) and hypotension (mean BP <65 mmHg). The risk of developing decreased CO and hypotension was evaluated by multivariate logistic regression analysis. The time from the start of the procedure to onset of decreased CO was analyzed by the Kaplan–Meier method. The area under the ROC curve and optimal threshold value of pre-anesthetic SVV for predicting decreased CO and hypotension were 0.857 and 0.693. Patients with lower SVV exhibited a significantly slower onset and lower incidence of decreased CO than those with higher SVV (p?=?0.003). Multivariate logistic regression analysis indicated high pre-anesthetic SVV as being an independent risk factor for decreased CO and hypotension (odds ratio, 1.43 and 1.16, respectively). In conclusions, pre-anesthetic SVV can predict incidence of decreased CO and hypotension during induction of general anesthesia.     

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.     

A systematic review of pulse pressure variation and stroke volume variation to predict fluid responsiveness during cardiac and thoracic surgery

This systematic review aims to summarize the published data on the reliability of pulse pressure variation (PPV) and stroke volume variation (SVV) to predict fluid responsiveness in an open-chest setting during cardio-thoracic surgery. The analysis included studies reporting receiver operating characteristics or correlation coefficients between PPV/SVV and change in any hemodynamic variables after a fluid challenge test in open-chest conditions. The literature search included seven studies. Increase in cardiac index and stroke volume index after a fluid challenge were the most adopted end-point variables. PPV and SVV showed similar area under the receiver operating characteristic curve values but high heterogeneity among studies. Cardiac and thoracic studies did not differ between PPV/SVV pooled area under the receiver operating characteristic curve. Studies exploring correlation between dynamic indices and end-point variable increase after fluid challenge showed conflicting results. The great heterogeneity between studies was due to small sample size and differences among protocol designs (different monitor devices, mechanical ventilation settings, fluid challenge methodologies, surgical incisions, and end-point variables). PPV and SVV seem to be inaccurate in predicting fluid responsiveness in an open-chest setting during cardio-thoracic surgery. Given the high heterogeneity of published data, more studies are needed to define the role of PPV/SVV in this context.     

Intraoperative TTE inferior vena cava monitoring in elderly orthopaedic patients with cardiac disease and spinal-induced hypotension

Objective To address the role of transthoracic echocardiography in inferior vena cava (IVC) monitoring in the management of haemodynamically unstable elderly patients subjected to lower limb orthopaedic surgery under spinal anesthesia. Possible implications in the postoperative care unit (PACU) length of stay (LOS) are investigated. Methods 41 elderly patients with cardiac diseases were recruited. Patients experiencing intraoperative haemodynamic instability (diastolic blood pressure ≤ 60 mmHg) were divided into two groups according to right atrial pressure (RAP), (RAP < 5 mmHg and RAP between 5 and 10 mmHg) as measured by inferior vena cava collapsibility index (IVCCI). Haemodynamic instability was treated with normal saline infused at a constant rate supplemented by phenylephrine (PHE) infusions titrated to normal blood pressure values. Intraoperatively comparisons of peak PHE infusion rates and all episodes of hypotension, including in the PACU, were recorded among groups. The patients’ PACU LOS and associated factors were assessed. Results The intraoperative peak PHE infusion rate and the incidence of haemodynamic instability in the postoperative period were significantly higher in patients with RAP < 5 mmHg. The total PHE consumption was also higher in patients with RAP < 5 mmHg postoperatively. The primary risk factor for a prolonged stay in PACU, as determined by multiple regression analysis was RAP. Conclusions Patients with high dynamic collapsibility of the IVC may require aggressive treatment to restore their haemodynamic status. Additionally, intraoperative levels of RAP, as measured by IVCCI, can act as a predictor for increased LOS in the PACU.     

Outcome impact of goal directed fluid therapy during high risk abdominal surgery in low to moderate risk patients: a randomized controlled trial

Intraoperative goal directed fluid therapy (GDT) guided by an arterial pressure-based cardiac output system has been reported to improve gastrointestinal (GI) recovery in high-risk patients. This study evaluates the impact of this approach on GI recovery in low to moderate risk patients undergoing major abdominal surgery. IRB approved randomized controlled trial in low to moderate risk adults scheduled for major surgery. Patients were randomized to standard (n = 20) or GDT (n = 18) groups, whose fluids were managed to maintain stroke volume variation (SVV) <12 %. The primary outcome measure was GI recovery. Additional measures included quality of recovery score. Continuous, non-normally distributed by Mann–Whitney test; ordinal and nominal by Chi square analysis. GDT patients had lower average intraoperative SVV. The GDT group had faster return of GI function (p = 0.004) and higher quality of recovery scores. In low to moderate risk patients undergoing major abdominal surgery, intraoperative GDT guided by SVV optimization was associated with faster restoration of GI recovery and higher quality of recovery scores. These results suggest that outcome benefits related to the use of an intraoperative goal directed fluid protocol guided by SVV are not limited to high-risk patients.     

Inferior vena cava diameter variation compared with pulse pressure variation as predictors of fluid responsiveness in patients with sepsis

BackgroundCurrently, physicians employ pulse pressure variation (PPV) as a gold standard for predicting fluid responsiveness. However, employing ultrasonography in intensive care units is increasing, including using the ultrasonography for assessment of fluid responsiveness. Data comparing the performance of both methods are still lacking. This is the reason for the present study.Materials and methodsWe conducted a prospective observational study in patients with sepsis requiring fluid challenge. The PPV, inferior vena cava diameter variation (IVDV), stroke volume variation (SVV), and the other hemodynamic variables were recorded before and after fluid challenges. Fluid responders were identified when cardiac output increased more than 15% after fluid loading.ResultsA total of 29 patients with sepsis were enrolled in this study. Sixteen (55.2%) were fluid responders. Threshold values to predict fluid responsiveness were 13.8% of PPV (sensitivity 100% and specificity 84.6%), 10.2% of IVDV (sensitivity 75% and specificity 76.9%) and 10.7% of SVV (sensitivity 81.3% and specificity 76.9%). The area under the curves of receiver operating characteristic showed that PPV (0.909, 95% confidence interval [CI], 0.784-1.00) and SVV (0.812, 95% CI, 0.644-0.981) had greater performance than IVDV (0.688, 95% CI, 0.480-0.895) regarding fluid responsiveness assessment.ConclusionsThe present study demonstrated better performance of the PPV than the IVDV. A threshold value more than 10% may be used for identifying fluid responders.     

The effect of variable arterial transducer level on the accuracy of pulse contour waveform-derived measurements in critically ill patients

We know that a 10 cm departure from the reference level of pressure transducer position is equal to a 7.5 mmHg change of invasive hemodynamic pressure monitoring in a fluid-filled system. However, the relationship between the site level of a variable arterial pressure transducer and the pulse contour-derived parameters has yet to be established in critically ill patients. Moreover, the related quantitative analysis has never been investigated. Forty-two critically ill patients requiring PiCCO-Plus cardiac output monitoring were prospectively studied. The phlebostatic axis was defined as the zero reference level; the arterial pressure transducer was then vertically adjusted to different positions (+5, +10, +15, +20, ?20, ?15, ?10, ?5 cm) of departure from the zero reference site. The pulse contour waveform-derived parameters were recorded at each position. Elevation of the pressure transducer caused significantly positive changes in the continuous cardiac index (+CCI), stroke volume index (+SVI), and stroke volume variation (+SVV), and negative changes in the rate of left ventricular pressure rise during systole (?dP/dtmax), the systemic vascular resistance index (?SVRI), and vice versa. At the 5 cm position, the SVRI changes reached statistical significance with error. At the 10 cm position, the changes in CCI and dP/dtmax reached statistical significance with error, while the change in SVV reached statistical significance at 15 cm. The change rate of CCI was more than 5 % at the 15 cm position and approximately 10 % at the 20 cm position. On average, for every centimeter change of the transducer, there was a corresponding 0.014 L/min/m² CCI change and 0.36 % change rate, a 1.41 mmHg/s dP/dtmax change and 0.13 % change rate, and a 25 dyne/s/cm⁵ SVRI change and 1.2 % change rate. The variation of arterial transducer position can result in inaccurate measurement of pulse contour waveform-derived parameters, especially when the transducer’s vertical distance is more than 10 cm from the phlebostatic axis. These findings have clinical implications for continuous hemodynamic monitoring.     

Automated titration of propofol and remifentanil decreases the anesthesiologist’s workload during vascular or thoracic surgery: a randomized prospective study

Closed loop target-control infusion systems using a Bispectral (BIS) signal as an input (TCI Loop) can automatically maintain intravenous anesthesia in a BIS range of 40–60 %. Our purpose was to assess to what extent such a system could decrease anesthesia workload in comparison to the use of a stand alone TCI system manually adjusted to fit the same BIS range of 40–60 % (TCI Manual). Patients scheduled for elective vascular or thoracic surgery were randomized to the TCI Loop or TCI Manual method for administering propofol and remifentanil during both induction and maintenance of general anesthesia. Assessment of workload was performed by an independent observer who quoted each time the physician looked at the BIS monitor. The number of propofol and remifentanil target modifications, the percentage of time of adequate anesthesia i.e. BIS in the range 40–60 and hemodynamic data were recorded. Eighteen patients per group were enrolled. Characteristics, duration of surgery and propofol-remifentanil consumption were similar between groups. However, the percentage of time in the BIS range 40–60 % was higher in the TCI Loop versus TCI Manual groups (94 % ± 12 vs. 74 % ± 19, p < 0.001). Mean arterial pressure was lower with TCI Manual (78 ± 6 vs. 88 ± 13 mmHg, p < 0.001). The number of times the anesthesiologist watched the controller or BIS monitor (p < 0.05) and the number of manual adjustments (p < 0.001) performed in each group was lower with TCI Loop group during induction and maintenance of anesthesia. An automated controller strikingly frees the anesthesiologist from manual intervention to adjust drug delivery.     

Extracellular volume fraction in dilated cardiomyopathy patients without obvious late gadolinium enhancement: comparison with healthy control subjects

To evaluate whether the extracellular volume fraction (ECV) measured using cardiac magnetic resonance (CMR) imaging can detect myocardial tissue changes in dilated cardiomyopathy (DCM) without late gadolinium enhancement (LGE). Forty-one DCM patients and 10 healthy volunteers underwent pre- and post-T1 mapping using a modified Look-Locker Inversion recovery sequence, LGE, and cine MRI on a 3-T CMR system. LGE-MR findings were used to divide DCM patients into two groups: Group A had no apparent LGE, and Group B had LGE apparent in at least one segment. The ECV of the left ventricle (LV) myocardium (16 segments) was calculated in the short-axis view as follows: ECV = [(ΔR1 of myocardium/ΔR1 of LV blood pool)] × (1 ? hematocrit), where R1 = 1/T1, ΔR1 = post-contrast R1 ? pre-contrast R1. The LV ejection fraction (LVEF) was obtained from cine MRI images. The mean myocardial ECV in LGE (?) segments in Group A + B was compared to that of controls. The mean myocardial ECV in Group A was compared to that of LGE (?) segments in Group B. The correlation between LV systolic function and the mean myocardial ECV of the whole myocardium was evaluated in all groups. Among the 41 DCM patients, 22 were in Group A, and 19 were in Group B. The mean ECV of DCM patents (n = 41, 568 segments, 30.7 % ± 5.9) was significantly higher (P < 0.001) than that of the control group (n = 10, 157 segments, 25.6 % ± 3.2). The ECV was inversely related to LVEF in Group A (r = ?0.551, P = 0.008), Group B (r = ?0.525, P = 0.021), and Group A + B (r = ?0.550, P < 0.001). The ECV measured by MRI could be a useful parameter in evaluating diffuse myocardial changes in DCM patients.     

Typical patterns of expiratory flow and carbon dioxide in mechanically ventilated patients with spontaneous breathing

Incomplete expiration of tidal volume can lead to dynamic hyperinflation and auto-PEEP. Methods are available for assessing these, but are not appropriate for patients with respiratory muscle activity, as occurs in pressure support. Information may exist in expiratory flow and carbon dioxide measurements, which, when taken together, may help characterize dynamic hyperinflation. This paper postulates such patterns and investigates whether these can be seen systematically in data. Two variables are proposed summarizing the number of incomplete expirations quantified as a lack of return to zero flow in expiration (IncExp), and the end tidal CO₂ variability (varetCO₂), over 20 breaths. Using these variables, three patterns of ventilation are postulated: (a) few incomplete expirations (IncExp < 2) and small varetCO₂; (b) a variable number of incomplete expirations (2 ≤ IncExp ≤ 18) and large varetCO₂; and (c) a large number of incomplete expirations (IncExp > 18) and small varetCO₂. IncExp and varetCO₂ were calculated from data describing respiratory flow and CO₂ signals in 11 patients mechanically ventilated at 5 levels of pressure support. Data analysis showed that the three patterns presented systematically in the data, with periods of IncExp < 2 or IncExp > 18 having significantly lower variability in end-tidal CO₂ than periods with 2 ≤ IncExp ≤ 18 (p < 0.05). It was also shown that sudden change in IncExp from either IncExp < 2 or IncExp > 18 to 2 ≤ IncExp ≤ 18 results in significant, rapid, change in the variability of end-tidal CO₂ p < 0.05. This study illustrates that systematic patterns of expiratory flow and end-tidal CO₂ are present in patients in supported mechanical ventilation, and that changes between these patterns can be identified. Further studies are required to see if these patterns characterize dynamic hyperinflation. If so, then their combination may provide a useful addition to understanding the patient at the bedside.     

Prediction of hypotension in the beach chair position during shoulder arthroscopy using pre-operative hemodynamic variables

Since hypotension in beach chair position (BCP) can lead to catastrophic neurologic complications, the prediction of hypotension is a matter of concern in the BCP under general anesthesia. We investigated whether pre-induction values of mean arterial pressure (MAP), stroke volume variation (SVV), cardiac index (CI), and stroke volume index (SVI) can predict hypotension in BCP during general anesthesia. Forty healthy adult patients, aged 18–65 years, undergoing elective arthroscopic shoulder surgery, were enrolled. At 5 min after anesthesia induction, patients were placed in the 70° upright position. Receiver operating characteristic (ROC) curves were plotted for preoperative hemodynamic variables, including MAP, SVV, CI and SVI, and their abilities to predict hypotension were investigated. Fifteen patients developed hypotension after being moved from the supine to the BCP. The areas under the ROC curves for pre-induction values of MAP, CI, and SVI and post-induction value of SVV before a positional change were 0.556 (95 % CI 0.373–0.739; p = 0.557), 0.735 (0.576–0.894; p = 0.014), 0.787 (0.647–0.926; p = 0.003), and 0.691 (0.525–0.857; p = 0.046), respectively. In this study, pre-induction values of CI and SVI and post-induction value of SVV before a positional change predicted hypotension in the BCP under general anesthesia. Our findings suggest that not only preload but also preoperative cardiac performances might be the important factors for the development of hypotension after a repositioning supine to the sitting during general anesthesia.