Radial to femoral arterial blood pressure differences during liver transplantation

Comparison of Central and Peripheral Arterial Blood Pressure Gradients in Critically Ill Patients: A Systematic Review and Meta-Analysis

OBJECTIVES

Measurement of blood pressure taken from different anatomical sites, are often perceived as interchangeable, despite them representing different parts of the systemic circulation. We aimed to perform a systematic review and meta-analysis on blood pressure differences between central and peripheral arterial cannulation in critically ill patients.

DATA SOURCES

We searched MEDLINE, Cochrane Central Register of Controlled Trials, and Embase from inception to December 26, 2023, using Medical Subject Headings (MeSH) terms and keywords.

STUDY SELECTION

Observation study of adult patients in ICUs and operating rooms who underwent simultaneous central (femoral, axillary, or subclavian artery) and peripheral (radial, brachial, or dorsalis pedis artery) arterial catheter placement in ICUs and operating rooms.

DATA EXTRACTION

We screened and extracted studies independently and in duplicate. We assessed risk of bias using the revised Quality Assessment for Studies of Diagnostic Accuracy tool.

DATA SYNTHESIS

Twenty-four studies that enrolled 1598 patients in total were included. Central pressures (mean arterial pressure [MAP] and systolic blood pressure [SBP]) were found to be significantly higher than their peripheral counterparts, with mean gradients of 3.5 and 8.0 mm Hg, respectively. However, there was no statistically significant difference in central or peripheral diastolic blood pressure (DBP). Subgroup analysis further highlighted a higher MAP gradient during the on-cardiopulmonary bypass stage of cardiac surgery, reperfusion stage of liver transplant, and in nonsurgical critically ill patients. SBP or DBP gradient did not demonstrate any subgroup specific changes.

CONCLUSIONS

SBP and MAP obtained by central arterial cannulation were higher than peripheral arterial cannulation; however, clinical implication of a difference of 8.0 mm Hg in SBP and 3.5 mm Hg in MAP remains unclear. Our current clinical practices preferring peripheral arterial lines need not change.

Anaesthesia management for liver transplantation: A narrative review

Orthotopic liver transplantation is the definitive standard treatment for end-stage liver disease. Orthotopic liver transplantation anaesthesia management is a complex procedure that requires a multidisciplinary team approach. Understanding the complex pathophysiology of end-stage liver disease and its complications in the affected systems is essential for proper anaesthesia management in orthotopic liver transplantation. Orthotopic liver transplantation is a dynamic process, and preoperative optimisation is essential in these patients. Therefore, anaesthesiologists should focus on rapidly fluctuating physiology, haemodynamics, metabolic, and coagulation status in the anaesthesia management of these patients. Perioperative care and anaesthesia for orthotopic liver transplantation can be divided into preoperative evaluation, anaesthesia induction and management, dissection, anhepatic, neo-hepatic, and postoperative care, with essential anaesthetic considerations at each point. Considering the clinical situation, haemodynamic changes, misapplications, knowledge, attitude, and multimodal and multidisciplinary approach are vital in anaesthesia and the perioperative period. In our review, in line with the literature, we aimed to present the perioperative and anaesthesia management in orthotopic liver transplantation patients.

Discrepancy between two invasive blood pressure measurements in patients receiving intra-aortic balloon pump therapy

BACKGROUND

Hemodynamic monitoring is imperative for patients with cardiogenic shock undergoing Intra-aortic Balloon Pump (IABP) therapy. Blood pressure monitoring encompasses non-invasive, invasive peripheral arterial pressure (IPAP), and invasive central aortic pressure (ICAP) methods. However, marked disparities exist between IPAP and ICAP. This study examined the discrepancies between IPAP and ICAP and their clinical significance.

METHODS

A retrospective analysis was conducted on cardiogenic shock patients who underwent IABP therapy and were admitted to the Coronary Care Unit (CCU) of a tertiary hospital in China from March 2017 to November 2022. The Bland-Altman plot illustrated the discrepancy between IPAP and ICAP. A clinically significant difference between ICAP and IPAP measurements was defined as ≥ 10 mmHg, which could necessitate alterations in blood pressure management according to current guidelines that recommend maintaining a mean arterial pressure (MAP) ≥ 70 mmHg.

RESULTS

In total, 162 patients were included in the final analysis. In patients without vasopressors, the difference between ICAP and IPAP was 5.73 mmHg (95% limits of agreement [LOA], -16.98 to 28.44), whereas, in patients with vasopressors, it was 4.36 mmHg (95% LOA, -17.31 to 26.03). ICAP measurements exceeded IPAP in patients undergoing IABP therapy. However, the difference was not statistically significant between the two groups. Multivariate logistic regression revealed that higher serum lactate levels (Odds ratio [OR], 1.14; 95% confidence interval [CI], 1.03-1.27; p = 0.013) and age ≥ 60 years (OR, 13.20; 95% CI, 1.50-115.51; p = 0.020) were associated with an increased likelihood of a clinically significant MAP discrepancy. Conversely, a history of coronary heart disease was associated with a decreased likelihood (OR, 0.34; 95% CI, 0.13-0.90; p = 0.031).

CONCLUSIONS

Notable discrepancies between ICAP and IPAP measurements exist in cardiogenic shock patients undergoing IABP therapy. ICAP exceeds IPAP, and factors such as age ≥ 60 years, elevated lactic acid levels, and absence of coronary heart disease contribute to this discrepancy. Enhanced vigilance is warranted for these patients, and the consideration of peripheral invasive monitoring in conjunction with IABP therapy is advised.

Arterial site selection for measurement of mean arterial pressure in septic shock patients on high-dose norepinephrine

Background

The guidelines of the Surviving Sepsis Campaign suggest using invasive blood pressure (IBP) measurement in septic shock patients, without specifying for a preferred arterial site for accuracy in relation to the severity of septic shock. The objective of this study was to determine the mean arterial pressure (MAP) gradient between the femoral and radial artery sites in septic shock patients.

Method

This prospective study was carried out at a 20-bed ICU in a university hospital. Simultaneous MAP measurements at femoral and radial arterial sites were obtained in septic shock patients receiving norepinephrine (≥0.1 μg/kg/min), with a pre-planned subgroup analysis for those receiving a high dose of norepinephrine (≥0.3 μg/kg/min).

Results

The median norepinephrine dose across all 80 patients studied, including 59 patients on a high dose, was 0.4 (0.28-0.7) μg/kg/min. Overall, simultaneous measurement of MAP (mmHg) at the femoral and radial arterial sites produced mean (95% CI) MAP values of 81 (79-83) and 78 (76-80), respectively, with a mean difference of 3.3 (2.67-3.93), p < 0.001. In Bland-Altman analysis of MAP measurements, the detected effect sizes were 1.14 and 1.04 for the overall and high-dose cohorts, respectively, which indicates a significant difference between the measurements taken at each of the two arterial sites. The Pearson correlation coefficient indicated a weak but statistically significant correlation between MAP gradient and norepinephrine dose among patients receiving a high dose of norepinephrine (r = 0.289; p = 0.026; 95% CI 0.036-0.508).

Conclusion

In septic shock patients, MAP readings were higher at the femoral site than at the radial site, particularly in those receiving a high dose of norepinephrine.

Clinical trial registration

[ClinicalTrials.gov], identifier [NCT03475667].

Central Versus Peripheral Invasive Arterial Blood Pressure Monitoring in Liver Transplant Surgery

Introduction Invasive blood pressure monitoring is essential in liver transplant surgery due to expected major hemodynamic shifts. The use of central versus peripheral arterial access, however, is institution-dependent, which can affect clinical decisions regarding vasopressor therapy. Although there are studies that demonstrate inconsistencies based on arterial cannulation sites, few studies have compared femoral and radial artery blood pressures in patients undergoing liver transplant surgery. To our knowledge, there are no studies investigating the differences between continuous minute-to-minute femoral and radial artery measurements during all three phases of liver transplant surgery. Objective The main objective of this study was to evaluate for any differences between central and peripheral blood pressure measurements in liver transplant surgery and to assess for any correlation between vasopressor infusion dose and femoral-arterial pressure differences. Methods In this retrospective study, we reviewed and studied the data of 61 patients with American Society of Anesthesiologists (ASA) grade 4 who underwent liver transplant surgery at Loma Linda University Medical Center between January and December of 2019. All patients had both femoral and radial arterial lines placed for liver transplant surgery. Femoral and radial arterial blood pressure values were obtained continuously over 60 minutes in the pre-anhepatic phase, 45 minutes during the anhepatic phase, and 60 minutes into the neo-hepatic phase. Vasopressor infusion doses were also recorded for each patient during these time frames. Results This pilot study found statistically significant differences between the mean femoral and radial systolic blood pressure (SBP; p < 0.0001), diastolic blood pressure (DBP; p < 0.0001), and mean arterial pressure (MAP; p < 0.0001) during all phases of liver transplantation. The meanSBP and MAP differences between femoral and radial arteries were highest (femoral blood pressure reading higher than radial blood pressure measurements) in the late anhepatic and early neo-hepatic phases with SBP differences of 20.8 ± 0.8 mmHg and 22.8 ± 0.8 mmHg, respectively, and MAP differences of 10.0 ± 0.4 mmHg and 9.8 ± 0.4 mmHg, respectively. Higher vasopressor infusion doses were strongly associated with greater differences in femoral-radial SBP and MAP measurements (r = 0.69 for vasopressin, 0.68 for norepinephrine, and 0.68 for epinephrine; p < 0.0001) during the anhepatic phase. Conclusions Peripheral invasive blood pressure monitoring may result in underestimation of the central blood pressure, as was seen in all phases of liver transplantation. This may lead to excessive vasopressor use with potentially adverse effects. Although the cause for the difference between femoral and radial artery measurements is unclear, increasing vasopressor infusion dosages appears to contribute. Femoral artery blood pressure monitoring allows clinicians to interpret hemodynamic status and administer appropriate vasopressors more accurately.

What is the optimal anesthetic monitoring regarding immediate and short-term outcomes after liver transplantation?-A systematic review of the literature and expert panel recommendations

BACKGROUND

Liver transplant centers vary in approach to intraoperative vascular accesses, monitoring of cardiac function and temperature management. Evidence is limited regarding impact of selected modalities on postoperative outcomes.

OBJECTIVES

To review the literature and provide expert panel recommendations on optimal intraoperative arterial blood pressure (BP), central venous pressure (CVP), and vascular accesses, monitoring of cardiac function and intraoperative temperature management regarding immediate and short-term outcomes after orthotopic liver transplant (OLT).

METHODS

Systematic review following PRISMA guidelines and recommendations using the GRADE approach derived from an international expert panel. Recommendations made for: (1) Vascular accesses, arterial BP and CVP monitoring, (2) cardiac function monitoring, and (3) Intraoperative temperature management (CRD42021239908).

RESULTS

Of 2619 articles screened 16 were included. Studies were small, retrospective, and observational. Vascular access studies demonstrated low rates of insertion complications. TEE studies demonstrated low rates of esophageal hemorrhage. One study found lower hospital-LOS and 30-day mortality in patients monitored with both PAC and TEE. Other monitoring studies were heterogenous in design and outcomes. Temperature studies showed increased blood transfusion and ventilation times in hypothermic groups.

CONCLUSIONS

Recommendations were made for; routine arterial and CVP monitoring as a minimum standard of practice, consideration of discrepancy between peripheral and central arterial BP in patients with hemodynamic instability and high vasopressor requirements, and routine use of high flow cannulae while monitoring for extravasation and hematoma formation. Availability and expertise in PAC and/or TEE monitoring is strongly recommended particularly in hemodynamic instability, portopulmonary HT and/or cardiac dysfunction. TEE use is recommended as an acceptable risk in patients with treated esophageal varices and is an effective diagnostic tool for emergency cardiovascular collapse. Maintenance of intraoperative normothermia is strongly recommended.

Femoral Pulse Pressure Variation Is Not Interchangeable with Radial Pulse Pressure Variation during Living Donor Liver Transplantation

The radial artery is commonly used as the site measuring pulse pressure variation (PPV) during surgery. Accurate measurement of circulating blood volume and timely interventions to maintain optimal circulating blood volume is important to deliver sufficient oxygen to tissues and organs. It has not rather than never studied in patients undergoing liver transplantation whether PPV measured at peripheral sites, such as the radial artery, do represent central PPV for evaluating blood volume. In this retrospective study, 51 liver transplant recipients were enrolled. The two PPVs had been automatically recorded every minute in electrical medical records. A total 1878 pairs of the two PPVs were collected. The interchangeability of PPV measured at the radial and the femoral artery was analyzed by using the Bland−Altman plot, four-quadrant plot, Cohen’s kappa (k), and receiver operating curve. The bias and limits of agreement of the two PPVs were −1.3% and −8.8% to 6.2%, respectively. The percentage error was 75%. The concordance rate was 65%. The Kappa of PPV-radial determining whether PPV-femoral was >13% or ≤13% was 0.64. We found that PPV-radial is not interchangeable with PPV-femoral during liver transplantation. Additionally, PPV-radial failed to reliably track changes of PPV-femoral. Lastly, the clinical decision regarding blood volume status (depletion or not) is significantly different between the two PPVs. Therefore, PPV-femoral may help maintain blood volume circulating to major organs including the newly transplanted liver graft for liver transplant recipients.

Agreements between mean arterial pressure from radial and femoral artery measurements in refractory shock patients

Radial and femoral artery catheterization is the most common procedure for monitoring patients with shock. However, a disagreement in mean arterial pressure (MAP) between the two sites has been reported. Hence, the aim of this study was to compare the MAP from the radial artery (MAP_radial) with that of the femoral artery (MAP_femoral) in patients with refractory shock. A prospective study was conducted in the medical intensive care unit. The radial and femoral were simultaneously measured MAP in the patients every hour, for 24 h. In total, 706 paired data points were obtained from 32 patients. MAP_radial strongly correlated with MAP_femoral (r = 0.89, p < 0.0001). However, overall MAP_radial was significantly lower than MAP_femoral 7.6 mmHg. The bias between MAP_radial and MAP_femoral was − 7.6 mmHg (95% limits of agreement (LOA), − 24.1 to 8.9). In the subgroup of patients with MAP_radial < 65 mmHg, MAP_radial moderately correlated with MAP_femoral (r = 0.63) and the bias was increased to − 13.0 mmHg (95% LOA, − 28.8 to 2.9). There were 414 (58.6%) measurements in which the MAP gradient between the two sites was > 5 mmHg. In conclusion, the radial artery significantly underestimated MAP compared with the femoral artery in patients with refractory shock.

Ability of dynamic preload indices to predict fluid responsiveness in a high femoral-to-radial arterial pressure gradient: a retrospective study

Background

Dynamic preload indices may predict fluid responsiveness in end-stage liver disease. However, their usefulness in patients with altered vascular compliance is uncertain. This study is the first to evaluate whether dynamic indices can reliably predict fluid responsiveness in patients undergoing liver transplantation with a high femoral-to-radial arterial pressure gradient (PG).

Methods

Eighty liver transplant recipients were retrospectively categorized as having a normal (n = 56) or high (n = 24, difference in systolic pressure ≥ 10 mmHg and/or mean pressure ≥ 5 mmHg) femoral-to-radial arterial PG, measured immediately after radial and femoral arterial cannulation. The ability of dynamic preload indices (stroke volume variation, pulse pressure variation [PPV], pleth variability index) to predict fluid responsiveness was assessed before the surgery. Fluid replacement of 500 ml of crystalloid solution was performed over 15 min. Fluid responsiveness was defined as ≥ 15% increase in the stroke volume index. The area under the receiver-operating characteristic curve (AUC) indicated the prediction of fluid responsiveness.

Results

Fourteen patients in the normal, and eight in the high PG group were fluid responders. The AUCs for PPV in the normal, high PG groups and total patients were 0.702 (95% confidence interval [CI] 0.553–0.851, P = 0.008), 0.633 (95% CI 0.384–0.881, P = 0.295) and 0.667 (95% CI 0.537–0.798, P = 0.012), respectively. No other index predicted fluid responsiveness.

Conclusion

PPV can be used as a dynamic index of fluid responsiveness in patients with end-stage liver disease but not in patients with altered vascular compliance.

Correlation between radial and femoral arterial blood pressure during reperfusion in living donor liver transplantation

Background and Aims

Accurate blood pressure measurements are the mainstay for the efficient management of abrupt cardiovascular changes during reperfusion in liver transplant. We sought to compare the femoral and radial pressures during reperfusion and at T1:baseline, T2: 1 h in dissection: T3:portosystemic shunt, T4:reperfusion, T5: at bile duct anastomosis.

Methods

A retrospective study was performed amongst 102 adult patients who underwent R lobe living donor liver transplantation. Mean arterial pressure (MAP) and systolic arterial pressure (SAP) at 10 s intervals at reperfusion and at five fixed time points were compared by intraclass correlation coefficient (ICC) and limits of agreement by Bland-Altman statistics.

Results

MAP by both routes had a good correlation at all time points during reperfusion (overall ICC: 0.946 [0.938, 0.949]) in comparison with SAP (overall ICC: 0.650 [0.6128, 0.684]). At the lowest reperfusion pressure (reperfusion point), MAP showed high levels of agreements (ICC: 0.833 [0.761, 0.885]), whereas SAP showed only a poor level of agreement (ICC 0.343 [0.153, 0.508]). The Bland-Altman analysis for MAP showed a bias of 7.18 (5.94) mmHg and limits of agreement of - 4.5 mmHg to + 18.8 mmHg and for SAP a bias of 25.2 (22.04) mmHg and limits of agreement of - 18.0 mmHg to + 68.4 mmHg at the reperfusion point. The incidence of post-reperfusion syndrome (PRS) was 52.94% by femoral and 57.84% by radial routes.

Conclusions

Radial MAP correlated well with femoral MAP during reperfusion and at predefined time points and can be used interchangeably for intraoperative monitoring. A high incidence of PRS was noted by our technique of measurement.

Clinical Evaluation of a High-fidelity Upper Arm Cuff to Measure Arterial Blood Pressure during Noncardiac Surgery

BACKGROUND

In most patients having noncardiac surgery, blood pressure is measured with the oscillometric upper arm cuff method. Although the method is noninvasive and practical, it is known to overestimate intraarterial pressure in hypotension and to underestimate it in hypertension. A high-fidelity upper arm cuff incorporating a hydraulic sensor pad was recently developed. The aim of the present study was to investigate whether noninvasive blood pressure measurements with the new high-fidelity cuff correspond to invasive measurements with a femoral artery catheter, especially at low blood pressure.

METHODS

Simultaneous measurements of blood pressure recorded from a femoral arterial catheter and from the high-fidelity upper arm cuff were compared in 110 patients having major abdominal surgery or neurosurgery.

RESULTS

550 pairs of blood pressure measurements (5 pairs per patient) were considered for analysis. For mean arterial pressure measurements, the average bias was 0 mmHg, and the precision was 3 mmHg. The Pearson correlation coefficient was 0.96 (P < 0.0001; 95% CI, 0.96 to 0.97), and the percentage error was 9%. Error grid analysis showed that the proportions of mean arterial pressure measurements done with the high-fidelity cuff method were 98.4% in zone A (no risk), 1.6% in zone B (low risk) and 0% in zones C, D, and E (moderate, significant, and dangerous risk, respectively). The high-fidelity cuff method detected mean arterial pressure values less than 65 mmHg with a sensitivity of 84% (95% CI, 74 to 92%) and a specificity of 97% (95% CI, 95% to 98%). To detect changes in mean arterial pressure of more than 5 mmHg, the concordance rate between the two methods was 99.7%. Comparable accuracy and precision were observed for systolic and diastolic blood pressure measurements.

CONCLUSIONS

The new high-fidelity upper arm cuff method met the current international standards in terms of accuracy and precision. It was also very accurate to track changes in blood pressure and reliably detect severe hypotension during noncardiac surgery.

EDITOR’S PERSPECTIVE

Oscillometric versus invasive blood pressure measurement in patients with shock: a prospective observational study in the emergency department

In emergency medicine, blood pressure is often measured by an oscillometric device using an upper arm cuff. However, measurement accuracy of this technique in patients suffering from hypotensive shock has not been sufficiently evaluated. We designed a prospective observational study investigating the accuracy of an oscillometric device in hypotensive patients admitted to the resuscitation area of the emergency department. Patients admitted to the resuscitation area of a university hospital, who were equipped with an arterial catheter and found to be hypotensive (mean arterial pressure (MAP) < 60 mmHg) were eligible for the study. Blood pressure was measured simultaneously via upper arm cuff and invasively under routine clinical conditions. After data extraction, Bland–Altman analysis, correlation coefficient and percentage error of mean and systolic blood pressure pairs were performed. We analysed 75 simultaneously obtained blood pressure measurements of 30 patients in hypotension, 11 (37%) were female, median age was 76.5 years (IQR 63–82). Oscillometric MAP was markedly higher than invasive MAP with a mean of the differences of 13 ± 15 mmHg (oscillometric—invasive), 95% limits of agreement − 16 to 41 mmHg, percentage error was 76%. In 64% of readings, values obtained by the upper arm cuff were not able to detect hypotension. Oscillometric blood pressure measurement is not able to reliably detect hypotension in emergency patients. Therefore, direct measurement of blood pressure should be established as soon as possible in patients suffering from shock.

Risk Factors Involved in Central-to-Radial Arterial Pressure Gradient During Cardiac Surgery

BACKGROUND

A central-to-radial arterial pressure gradient may occur after cardiopulmonary bypass (CPB), which, in some patients, may last for a prolonged time after CPB. Whenever there is a pressure gradient, the radial artery pressure measure may underestimate a more centrally measured systemic pressure, which may result in a misguided therapeutic strategy. It is clinically important to identify the risk factors that may predict the appearance of a central-to-radial pressure gradient, because more central sites of measurements might then be considered to monitor systemic arterial pressure in high-risk patients. The objective of this study was to assess preoperative and intraoperative risk factors for central-to-radial pressure gradient.

METHODS

Seventy-three patients undergoing cardiac surgery using CPB were included in this prospective observational study. A significant central-to-radial arterial pressure gradient was defined as a difference of 25 mm Hg in systolic pressure or 10 mm Hg in mean arterial pressure for a minimum of 5 minutes. Preoperative data included demographics, presence of comorbidities, and medications. Intraoperative data included type of surgery, CPB and aortic clamping time, use of inotropic drugs, and vasodilators or vasopressors agents. The diameter of the radial and femoral artery was measured before the induction of anesthesia using B-mode ultrasonography.

RESULTS

Thirty-three patients developed a central-to-radial arterial pressure gradient (45%). Patients with a significant pressure gradient had a smaller weight (71.0 ± 16.9 vs 79.3 ± 17.3 kg, P = 0.041), a smaller height (162.0 ± 9.6 vs 166.3 ± 8.6 cm, P = 0.047), a smaller radial artery diameter (0.24 ± 0.03 vs 0.29 ± 0.05 cm, P < 0.001), and were at a higher risk as determined by the Parsonnet score (30.3 ± 24.9 vs 17.0 ± 10.9, P = 0.007). In addition, a longer aortic clamping time (85.8 ± 51.0 vs 64.2 ± 29.3 minutes, P = 0.036), mitral and complex surgery (P = 0.007 and P = 0.017, respectively), and administration of vasopressin (P = 0.039) were identified as potential independent predictors of a central-to-radial pressure gradient. By using multivariate logistic regression analysis, the following independent risk factors were identified: Parsonnet score (odds ratio [OR], 1.076; 95% confidence interval [CI], 1.027-1.127, P = 0.002), aortic clamping time >90 minutes (OR, 8.521; 95% CI, 1.917-37.870, P = 0.005), and patient height (OR, 0.933, 95% CI, 0.876-0.993, P = 0.029). The relative risk (RR) estimates remained statistically significant for the Parsonnet score and the aortic clamping time ≥90 minutes (RR, 1.010; 95% CI, 1.003-1.018, P = 0.009 and RR, 2.253; 95% CI, 1.475-3.443, P < 0.001 respectively) while showing a trend for patient height (RR, 0.974; 95% CI, 0.948-1.001, P = 0.058).

CONCLUSIONS

Central-to-radial gradients are common in cardiac surgery. The threshold for using a central site for blood pressure monitoring should be low in small, high-risk patients undergoing longer surgical interventions to avoid inappropriate administration of vasopressors and/or inotropic agents.

The comparison of femoral and radial arterial blood pressures during pediatric liver transplantation

BACKGROUND

Orthotopic liver transplantation (OLT) is frequently associated with dramatic hemodynamic changes; thus, it is critical to accurately monitor blood pressure. Although comparisons between femoral arterial blood pressure (FABP) and radial arterial blood pressure (RABP) have been reported in adult liver recipients, we compared FABP with RABP in pediatric recipients.

METHODS

Thirty-five pediatric liver recipients younger than 13 years of age were included in this prospective, observational study. We measured simultaneous FABP and RABP in the femoral and radial arteries at nine time points during the procedure, including: baseline (after anesthetic induction); 1 hour thereafter; 30 minutes after the beginning of the anhepatic period as well as 0, 1, 3, 5, 15, and 60 minutes after graft reperfusion.

RESULTS

Of the 35 pediatric liver recipients, 2 infants and 1 13-month-old child were excluded from the analysis because of radial arterial catheter malfunction. The remaining 32 patients including 16 infants and 16 children all showed significantly higher systolic and mean FABP than RABP during most stages of pediatric OLT. Overall diastolic FABP measurements were similar to diastolic RABP throughout the study.

CONCLUSIONS

Systolic and mean FABP were significantly higher than RABP during most stages of pediatric OLT. Radial arterial catheter malfunctions were not uncommon during pediatric OLT. Our results indicated that it is useful to cannulate the femoral artery to accurately and reliably measure arterial blood pressure to detect hemodynamic instability during pediatric OLT.

Microsystems for biomimetic stimulation of cardiac cells

The heart is a complex integrated system that leverages mechanoelectrical signals to synchronize cardiomyocyte contraction and push blood throughout the body. The correct magnitude, timing, and distribution of these signals is critical for proper functioning of the heart; aberrant signals can lead to acute incidents, long-term pathologies, and even death. Due to the heart's limited regenerative capacity and the wide variety of pathologies, heart disease is often studied in vitro. However, it is difficult to accurately replicate the cardiac environment outside of the body. Studying the biophysiology of the heart in vitro typically consists of studying single cells in a tightly controlled static environment or whole tissues in a complex dynamic environment. Micro-electromechanical systems (MEMS) allow us to bridge these two extremes by providing increasing complexity for cell culture without having to use a whole tissue. Here, we carefully describe the electromechanical environment of the heart and discuss MEMS specifically designed to replicate these stimulation modes. Strengths, limitations and future directions of various designs are discussed for a variety of applications.

Direct pressure measurement in the hepatic artery during liver transplantation: can it prevent the "steal" syndrome?

Splenic artery "steal" syndrome after orthotopic liver transplantation (OLT) is an important cause of graft dysfunction. Direct pressure measurement in the hepatic (HA) and radial artery (RA) may identify patients at risk allowing its prevention. This observational study compared radial and hepatic mean arterial pressures (MAP) measured during 100 OLTs performed in 99 recipients, in whom the HA was considered suitable for the anastomosis. A difference of ≥5 mmHg between the radial and hepatic MAP was arbitrarily chosen as the criterion for inflow modulation. Seven patients fulfilled this criterion showing a MAP gradient that was significantly different compared to the others (-10.8±3.3 vs. 2.6±5.0; p<0.0001). They underwent splenic artery ligation (n=5), arcuate ligament division (n=1) and aortohepatic bypass grafting (n=1) that all resulted in immediate normalization of the arterial inflow pressure to the graft. The splenic artery "steal" syndrome occurred in one patient (day 2 after OLT) in whom the mean HA pressure normalized during OLT following arcuate ligament division, suggesting pathology within the graft as the most likely etiology. Our results indicate that radial MAP can reflect the hepatic MAP during OLT. If a substantial pressure gradient is found, it can be corrected by intraoperative splenic artery ligation or arcuate ligament division.

Utility of uncalibrated femoral stroke volume variation as a predictor of fluid responsiveness during the anhepatic phase of liver transplantation

We evaluated the value of the stroke volume variation (SVV) calculated with the Vigileo monitor, which recently has been increasingly advocated for fluid management, as a predictor of fluid responsiveness during the anhepatic phase of liver transplantation (LT). We also compared SVV to the central venous pressure (CVP) and pulmonary arterial occlusion pressure (PAOP) in patients. Thirty-three adult recipients scheduled for elective living donor LT were enrolled in this study. Twenty minutes after the start of the anhepatic phase, the CVP, PAOP, approximate inferior vena caval pressure, femoral SVV, and cardiac output values were measured before and 12 minutes after fluid loading. Fluid loading was performed with a 6% hydroxyethyl starch solution (10 mL/kg). The responders were defined as patients whose cardiac index increased ≥ 15% after fluid loading. Receiver operating characteristic (ROC) analysis showed that only femoral SVV (area under the curve = 0.894, P = 0.0001) could be used to predict fluid responsiveness during the anhepatic phase of LT. The area under the ROC curve for femoral SVV was 0.894 (P = 0.0001), and it was significantly larger than those for CVP (area under the curve = 0.576, P = 0.004) and PAOP (area under the curve = 0.670, P = 0.021). Femoral SVV >8% identified the responders with a sensitivity of 89% and a specificity of 80%. Our results suggest that femoral SVV derived with the Vigileo monitor would be useful for fluid management during the anhepatic phase in LT recipients.

Complications related to less-invasive haemodynamic monitoring

BACKGROUND

The aim of this study was to evaluate the type and incidence of complications during insertion, maintenance, and withdrawal of central arterial catheters used for transpulmonary thermodilution haemodynamic monitoring (PiCCO™).

METHODS

We conducted a prospective, observational, multicentre study in 14 European intensive care units (six countries). A total of 514 consecutive patients in whom haemodynamic monitoring by PiCCO™ was indicated were studied.

RESULTS

Five hundred and fourteen PiCCO catheters (475 in femoral, 26 in radial, nine in axillary, and four in brachial arteries) were inserted. Arterial access was obtained on the first attempt in 86.4% of the patients. Minor problems such as oozing after insertion (3.3%) or removal of the catheter (3.5%) were observed, but no episodes of serious bleeding (more than 50 ml) were recorded. Small local haematomas were observed after insertion (4.5%) and after removal (1.2%) of the catheter. These complications were not more frequent in patients with coagulation abnormalities. The incidence of site inflammation and catheter-related infection was 2% and 0.78%, respectively. Other complications such as ischaemia (0.4%), pulse loss (0.4%), or femoral artery thrombosis (0.2%) were rare, transient, and all resolved with catheter removal or embolectomy, respectively.

CONCLUSIONS

In this series of patients, central arterial catheters used for PiCCO™ monitoring were demonstrated to be a safe alternative for advanced haemodynamic monitoring.

Comparison of stroke volume variations derived from radial and femoral arterial pressure waveforms during liver transplantation

BACKGROUND

Stroke volume variation (SVV) is being increasingly used to predict fluid responsiveness. Since radial arterial pressure (RAP) and femoral arterial pressure (FAP) frequently showing discrepancies during liver transplantation (LT), we sought to investigate the effect of differing arterial waveforms on SVV and cardiac output (CO) derived from the Vigileo device, by comparing SVV and CO values derived from RAP (SVV(RAP), CO(RAP)) and FAP (SVV(FAP), CO(FAP)) during LT.

METHODS

The linear associations and agreements between SVV(RAP) and SVV(FAP) and between CO(RAP) and CO(FAP) were assessed during LT. Hemodynamic variables were measured at nine predefined time points in all 32 recipients, resulting in 288 data pairs.

RESULTS

Correlations were observed between SVV(RAP) and SVV(FAP) (r = .961) and between CO(RAP) and CO(FAP) (r = .848) at all time points. These correlations between SVV(RAP) and SVV(FAP) (r = .923) and between CO(RAP) and CO(FAP) (r = .902) existed even during the period when mean RAP and FAP values differed (10 minutes after reperfusion). Bland-Altman analysis for SVV(RAP) versus SVV(FAP) and for CO(RAP) versus CO(FAP) showed weak biases (-0.2% and -0.5 L/min) and reasonable limits of agreement (-2.2 to 1.8% and -1.9 to 0.9 L/min). The percentage errors for SVV and CO values were 27.0% and 22.2%.

CONCLUSIONS

There was no significant difference between SVV(RAP) and SVV(FAP) when measured using the Vigileo device during LT. This finding indicated that SVV obtained using the Vigileo device offered relatively consistent information regardless of the catheterization site.

Pitfalls in haemodynamic monitoring based on the arterial pressure waveform

The accuracy of the arterial pressure-based cardiac output FloTrac-Vigileo system remains unacceptably low during haemodynamic instability. Data show that the measurement of cardiac output (CO) is strongly influenced by changes in factors that affect arterial blood pressure (ABP) - for example, vascular tone and compliance and the arterial site - independently of true changes in CO. Although in theory the autocalibration algorithm of FloTrac-Vigileo should adjust for those changes, the model undercompensates (or overcompensates) for prominent increases (or decreases) in vascular tone and compliance, making the system largely dependent on changes in ABP. These limitations make FloTrac-Vigileo accurate in stable haemodynamic conditions only, and until more robust algorithms and further validation studies become available, we should be aware that during haemodynamic instability or in extreme conditions of vasodilation or vasoconstriction, the measured CO may diverge from an independent bolus indicator dilution measurement, particularly if a peripheral artery is used. In these conditions, we advocate the use of transpulmonary indicator dilution via a femoral artery.

Techniques of cardiac output measurement during liver transplantation: arterial pulse wave versus thermodilution

In this study, we compared continuous cardiac output (CO) obtained from the femoral arterial pressure by simulation of an aortic input impedance model [model-simulated cardiac output (MCO)] to thermodilution cardiac output (TDCO) determined by bolus injection during liver transplantation. Both variables were measured in 39 adult patients (13 females) every 10th minute during liver transplant surgery. Paired measurements were compared during the 4 phases of surgery-dissection, anhepatic phase, early reperfusion (the first 15 minutes after reperfusion), and late reperfusion (15-60 minutes after reperfusion)-without the detection of any significant difference between the 2 estimates of CO. TDCO ranged from 2.3 to 17.2 L/minute, and the bias (the mean difference between MCO and TDCO) prior to calibration was -0.4 +/- 1.6 L/minute (mean +/- standard deviation; 1309 paired measurements; 95% limits of agreement: -3.4 to 2.6 L/minute). After calibration of the first determined MCO by the simultaneously determined TDCO, the bias was 0.1 +/- 1.5 L/minute, with 57% (n = 744) of the comparisons being less than 1 L/minute and 35% (n = 453) being less than 0.5 L/minute; this was independent of the level of CO, and the mutual correlation coefficient was 0.812 (P < 0.001). This study indicates that during liver transplantation surgery, MCO reflects TDCO throughout the operation. Thus, for CO, this less invasive method appears to provide a reliable uninterrupted measurement during orthotopic liver transplantation.

Anesthetic management of hepatic transplantation

PURPOSE OF REVIEW

The present review describes new trends and ongoing controversies in the anesthetic care of liver transplant recipients.

RECENT FINDINGS

Recent studies have improved our knowledge of conditions increasing perioperative risk, such as portopulmonary hypertension and renal failure. Improved surgical and anesthetic management has reduced intraoperative blood loss, as more studies identify an independent association between blood transfusion and poor outcome. New concepts in the coagulopathy of liver failure are emerging, with clear implications for clinical practice, including greater awareness of the risks of intraoperative thromboembolism. Less invasive intraoperative hemodynamic monitoring has been advocated, as has wider use of transoesophageal echocardiography. Early extubation is becoming more routinized.

SUMMARY

Anesthetic management still varies widely between liver transplant centers with little data to indicate best practice. Future research should focus on fluid replacement, prevention and treatment of coagulopathy, care of the acutely ill patient and the safety and benefits of early extubation.

Reliability of a new ultrasonic cardiac output monitor in recipients of living donor liver transplantation

The ultrasonic cardiac output monitor (USCOM) is a new Doppler device for noninvasive hemodynamic monitoring. The aim of this prospective nonrandomized study was to test the feasibility, perioperative reliability, and clinical applicability of using USCOM as an alternative to pulmonary artery catheterization in recipients of living donor liver transplantation. Thirteen patients scheduled to receive living donor liver transplants were initially recruited. Three were subsequently excluded prior to the commencement of surgery because of technical difficulties in obtaining diagnostic-quality images with USCOM. Ten patients proceeded to be studied. Cardiac output measurements by thermodilution and USCOM were compared at 30-minute intervals throughout the procedure and at 10 specific procedural reference points during the surgery when hemodynamic changes were most likely to be observed. The data were analyzed with Lin's concordance coefficient and Bland-Altman analysis. Two hundred ninety paired cardiac output values were obtained from the 10 patients. The concordance between both methods was excellent in 8 patients and satisfactory in 2. Bland-Altman analysis of all data produced a mean bias of - 0.02 L/minute for USCOM, and the 95% limits of agreement were -1.06 to +1.10 L/minute. Further analysis of the 10 reference time points showed minimal bias and high levels of agreement between the methods. We conclude that USCOM provides an accurate and noninvasive method for cardiac output measurement during liver transplantation. It may therefore represent an alternative to pulmonary artery catheter placement with consequent reduction in patient's risk and morbidity associated with catheterization. Liver Transpl 14:1029-1037, 2008. (c) 2008 AASLD.

Comparison of femoral arterial blood pressure with radial arterial blood pressure and noninvasive upper arm blood pressure in the reperfusion period during liver transplantation

PURPOSE

The reperfusion period during liver transplantation is hemodynamically unstable. Accurate blood pressure measurements are the mainstay for the efficient management of abrupt cardiovascular changes. We sought to compare femoral arterial blood pressure (FABP) with radial arterial blood pressure (RABP) and noninvasive upper arm blood pressure (NIBP) in the reperfusion period.

METHODS

Thirty-six adult living donor liver recipients were enrolled in this prospective study. Blood pressures in 3 locations were simultaneously recorded from 1 minute before reperfusion to 15 minutes after reperfusion. We evaluated agreements between FABP and RABP and between FABP and NIBP using intraclass correlation coefficients. Also, we investigated the rates of postreperfusion syndrome (PRS) based on the measurements from 3 locations.

RESULTS

After reperfusion, the mean and diastolic RABP agreed more with the corresponding FABP than NIBP. However, systolic NIBP showed high agreement with FABP from 3 to 10 minutes after reperfusion in contrast with the moderate agreement between systolic RABP with FABP, and systolic values of NIBP than RABP were closer to FABP. The rates of PRS based on FABP, RABP, and NIBP measurements were 50.0% (18/36), 80.6% (29/36), and 50.0% (18/36), respectively.

CONCLUSIONS

We believe that NIBP in addition to RABP may be considered to be a reliable alternative when FABP is not available to evaluate hemodynamic instability in the reperfusion period during liver transplantation.