A comparison between continuous central venous pressure measurement from right atrium and abdominal vena cava or common iliac vein

The intricate physiology of veno-venous extracorporeal membrane oxygenation: an overview for clinicians

During veno-venous extracorporeal membrane oxygenation (V-V ECMO), blood is drained from the central venous circulation to be oxygenated and decarbonated by an artificial lung. It is then reinfused into the right heart and pulmonary circulation where further gas-exchange occurs. Each of these steps is characterized by a peculiar physiology that this manuscript analyses, with the aim of providing bedside tools for clinical care: we begin by describing the factors that affect the efficiency of blood drainage, such as patient and cannulae position, fluid status, cardiac output and ventilatory strategies. We then dig into the complexity of extracorporeal gas-exchange, with particular reference to the effects of extracorporeal blood-flow (ECBF), fraction of delivered oxygen (FdO2) and sweep gas-flow (SGF) on oxygenation and decarbonation. Subsequently, we focus on the reinfusion of arterialized blood into the right heart, highlighting the effects on recirculation and, more importantly, on right ventricular function. The importance and challenges of haemodynamic monitoring during V-V ECMO are also analysed. Finally, we detail the interdependence between extracorporeal circulation, native lung function and mechanical ventilation in providing adequate arterial blood gases while allowing lung rest. In the absence of evidence-based strategies to care for this particular group of patients, clinical practice is underpinned by a sound knowledge of the intricate physiology of V-V ECMO.

Noninvasive Assessment of Jugular Venous Pressure via Force-Coupled Single Crystal Ultrasound

OBJECTIVE

we have developed a handheld device for noninvasive quantitative assessment of jugular venous pressure (JVP).

METHODS

we used a single crystal ultrasound coupled to a force-sensing load cell to measure JVP based on the force necessary to collapse the internal jugular vein (IJV) walls. We used a gelatin-based model system of the IJV to test the ability of single crystal ultrasound to identify the IJV and verified the cross-sectional position and diameter of the vessels with conventional imaging ultrasound. We also tested our prototype device on healthy human volunteers.

RESULTS

experiments on model system demonstrated that vessel diameters determined with single crystal ultrasound were in close agreement with the diameters derived from conventional 2-D ultrasound. Proof-of-concept human experiments demonstrate that single crystal ultrasound can detect the IJV in basal and collapsed states, as compared to gold-standard sonography (insert stats). Assessment of JVP in human volunteers was physiologically consistent with and sensitive to postural changes (supine JVP 6.6 ± 2.4 mmHg; standing JVP 4.2 ± 1.9 mmHg (p < 0.0001).

CONCLUSION

noninvasive assessment of JVP could prove valuable in informing rapid clinical decision-making across various pathologies and conditions leading to derangements in intravascular volume status.

Predicting Central Venous Pressure by Measuring Femoral Venous Diameter Using Ultrasonography

Objectives

The objective of this exploratory study was to find out the correlation of femoral vein diameter (FVD) to central venous pressure (CVP) measurements and to derive a prediction equation to help ascertain the fluid volume status in a critical patient.

Patients and methods

This was a single-centered prospective cohort study designed and conducted by the critical care department of Shifa International hospital in Islamabad, Pakistan. Patients were enrolled from the medical and surgical intensive care units. The inclusion criteria consisted of patients > 18 years of age, and an intrathoracic central venous catheterization (CVC) in place for producing CVP waveform through the transducer. Patients having contraindications to CVP placement and those unable to lie supine were excluded from the study. Critical Care fellows with sufficient training in performing venous ultrasonography measured the FVD. They were blinded to the CVP values of the same patients.

Results

The study included 108 patients. Among these 70/108 (64.8%) were males. Mean age was 53.85 (SD=16.74). The CVP and femoral vein diameter were measured in all patients. Mean CVP was 9.89 cmH2O (SD=3.46) and mean femoral vein diameter was 0.92 cm (SD=0.27). Multiple regression was used to generate a prediction model. FVD, age and sex of the patient were used as predictor variables to predict CVP diameter. The model was statistically significant with a p-value of < 0.000 and an F-value of 104.806. R-squared value for this model came out to be 0.744, thus the model was able to explain about 74.4% of the variance in the values observed for CVP. When controlled for age and sex, FVD was found highly correlated with CVP diameter with a p-value of < 0.000. A regression equation was derived that can be used to generate predicted values of CVP in millimeters of mercury with an R-square of 0.745 if FVD in centimeters is provided; CVP (cmH2O) = -0.039 + 10.718* FVD.

Conclusions

FVD was found highly correlated to CVP measurements and it suggests an alternate non-invasive method of ascertaining the volume status in the critically ill.

Measurement of Femoral Vein Diameter by Ultrasound to Estimate Central Venous Pressure

RATIONALE

Central venous pressure (CVP) can be estimated by ultrasound of the inferior vena cava (IVC), but imaging the IVC is sometimes challenging. The femoral vein is easily imaged by ultrasound and might therefore provide an alternate target for estimating CVP.

OBJECTIVES

To assess femoral vein diameter (FVD) measured by ultrasound imaging for estimating CVP.

METHODS

We prospectively measured CVP and FVD in 97 patients. Receiver operating characteristic curves were used to assess the ability of FVD to predict specific CVP values: less than 10 mm Hg, less than 8 mm Hg (low CVP), and greater than 12 mm Hg (high CVP). Interobserver variability of FVD measurement was assessed in 20 patients.

MEASUREMENTS AND MAIN RESULTS

There was moderate correlation between FVD and CVP (r = 0.66, P < 0.001). FVD less than or equal to 0.8 cm was the best predictor of CVP < 10 mm Hg, with an area under the curve (AUC) of 0.894 and a 95% confidence interval (CI) of 0.82 to 0.97. FVD less than or equal to 0.7 cm performed best for predicting low CVP (AUC = 0.97; 95% CI, 0.94-0.99) and FVD greater than or equal to 1.0 cm for high CVP (AUC = 0.80; 95% CI, 0.72-0.89). However, FVD greater than or equal to 1.2 cm had the greatest specificity (94%) for high CVP. Interobserver variability in FVD measurements was 8.3 ± 7.2%.

CONCLUSIONS

The results of this exploratory study suggest that the accuracy of FVD measured by ultrasound imaging for estimating CVP is comparable to that which has been reported for ultrasound measurement of IVC diameter. FVD may provide an alternative approach when the IVC is difficult to image. Additional studies on other cohorts of patients are warranted to validate our proposed FVD cutoff values for predicting low and high CVP.

Iliac venous pressure estimates central venous pressure after laparotomy

BACKGROUND

Central venous pressure (CVP) is traditionally obtained through subclavian or internal jugular central catheters; however, many patients who could benefit from CVP monitoring have only femoral lines. The accuracy of illiac venous pressure (IVP) as a measure of CVP is unknown, particularly following laparotomy.

METHODS

This was a prospective, observational study. Patients who had both internal jugular or subclavian lines and femoral lines already in place were eligible for the study. Pressure measurements were taken from both lines in addition to measurement of bladder pressure, mean arterial pressure, and peak airway pressure. Data were evaluated using paired t-test, Bland-Altman analysis, and linear regression.

RESULTS

Measurements were obtained from 40 patients, 26 of which had laparotomy. The mean difference between measurements was 2.2 mm Hg. There were no significant differences between patients who had laparotomy and nonsurgical patients (P = 0.93). Bland-Altman analysis revealed a bias of 1.63 ± 2.44 mm Hg. There was no correlation between IVP accuracy and bladder pressure, mean arterial pressure, or peak airway pressure.

CONCLUSIONS

IVP is an adequate measure of CVP, even in surgical patients who have had recent laparotomy. Measurement of IVP to guide resuscitation is encouraged in patients who have only femoral venous catheter access.

Comparison of superior vena cava and femoroiliac vein pressure according to intra-abdominal pressure

Background

Previous studies have shown a good agreement between central venous pressure (CVP) measurements from catheters placed in superior vena cava and catheters placed in the abdominal cava/common iliac vein. However, the influence of intra-abdominal pressure on such measurements remains unknown.

Methods

We conducted a prospective, observational study in a tertiary teaching hospital. We enrolled patients who had indwelling catheters in both superior vena cava (double lumen catheter) and femoroiliac veins (dialysis catheter) and into the bladder. Pressures were measured from all the sites, CVP, femoroiliac venous pressure (FIVP), and intra-abdominal pressure.

Results

A total of 30 patients were enrolled (age 62 ± 14 years; SAPS II 62 (52–76)). Fifty complete sets of measurements were performed. All of the studied patients were mechanically ventilated (PEP 3 cmH₂0 (2–5)). We observed that the concordance between CVP and FIVP decreased when intra-abdominal pressure increased. We identified 14 mmHg as the best intra-abdominal pressure cutoff, and we found that CVP and FIVP were significantly more in agreement below this threshold than above (94% versus 50%, P = 0.002).

Conclusions

We reported that intra-abdominal pressure affected agreement between CVP measurements from catheter placed in superior vena cava and catheters placed in the femoroiliac vein. Agreement was excellent when intra-abdominal pressure was below 14 mmHg.

Correlation of sonographic measurements of the internal jugular vein with central venous pressure

Determination of volume status is crucial in treating acutely ill patients. This study examined bedside ultrasonography of the internal jugular vein (IJV) to predict central venous pressure (CVP). Ultrasonography was performed on 34 nonventilated patients with monitored CVPs. The IJV was measured during the respiratory cycle and with the patient in different positions. Mean IJV diameter in patients with CVP less than 10 cm H2O was 7.0 mm (95% confidence interval [CI], 5.7-8.3) vs 12.5 mm (95% CI, 11.2-13.8) in patients with CVP of 10 cm H2O and greater. Measurement of end expiratory diameter with the patient supine had the highest correlation coefficient: 0.82 (95% CI). There was strong agreement among ultrasonographers: correlation coefficient, 0.92 (95% CI). This pilot study shows promise that ultrasonography of the IJV can be a noninvasive tool to predict CVP. Measurement of end expiratory diameter in supine patients exhibited a high correlation to CVP.

Estimation of central venous pressure by ultrasound

INTRODUCTION

Increasing blood volume and cardiac output is one of the most commonly needed intervention in the primary care of traumatized and severely ill patients. Although cardiac filling pressures have severe limitations in assessing the preload, central venous pressure (CVP) is the invasive measure most frequently used in clinical practice for the assessment of volume status and cardiac preload. We combined ultrasound and tissue pressure measurement for non-invasive jugular and brachial venous pressure estimation.

MATERIALS AND METHODS

CVP was measured invasively and non-invasively using the new technique in 32 critically ill patients. In six volunteers, increasing PEEP was used for the assessment of changes in non-invasive CVP.

RESULTS

Non-invasive CVP increased linearly with increasing PEEP, independent of the investigator. Median (range) coefficient of variation (CV) for five consecutive measurements performed by three investigators in volunteers was 15% (6-31%), 14% (4-31%), and 21% (8-42%). Absolute differences between the average non-invasive CVP between investigators was 1.7 cm H2O (0.4-6.6 cm H2O), and the inter-examiner CVP was high (182%, 40-415%). In patients, invasive CVP was 10 mmHg (5-18 mmHg), and the corresponding non-invasive venous pressures were 8 mmHg (3-14 mmHg, basilic vein, p<0.01) and 6 mmHg (3-13 mmHg, jugular vein, p<0.01). The coefficients of variation were 4% (<1%-64%, invasive CVP), 22% (5%-51%, non-invasive basilic vein pressure), and 17% (7%-34%, non-invasive jugular vein pressure).

CONCLUSION

Ultrasound-based, non-invasive measurement of venous pressure provides a relatively easy method rapid estimation of changes in CVP, although absolute values may differ substantially from invasive CVP and between different investigators.

Low inferior vena caval catheters for hemodynamic and pulmonary function monitoring in pediatric critical care patients

OBJECTIVE

To assess the value of low inferior vena caval (LIVC) catheters for estimating central venous pressure in pediatric intensive care patients and to assess influences of intra-abdominal pressures and mean airway pressure on these measurements.

DESIGN

Prospective cohort of consecutive patients.

SETTING

Pediatric intensive care unit.

PATIENTS

Thirty patients ranging in age (18, 0-1 yrs; four, 1-3 yrs; four, 3-10 yrs; four, > or =10 yrs).

INTERVENTIONS

Interventions included catheterizations via internal jugular, subclavian, and common femoral veins, as well as direct right atrial catheterization during surgery; arterial catheter placement; airway pressure monitoring during mechanical ventilation; indirect intra-abdominal pressure monitoring via bladder catheter pressure readings; and arterial and central venous blood gas analysis. LIVC vein catheters were placed below the origin of the renal veins.

MEASUREMENTS AND MAIN RESULTS

LIVC pressure was highly correlated with central venous pressure (n=30, r2=.965, p=.0001). LIVC pressure did not correlate with intra-abdominal pressure (n=18, r2=.000). Mean airway pressure did not correlate with central venous pressure (n=11, r2=.106). The pH of LIVC blood was similar to that of central venous blood (n=18, r2=.941, p=.0001). PCO2 values of inferior vena cava and central venous blood correlated (r2=.945, p=.0001). However, agreement between inferior vena cava and central venous PO2 and oxyhemoglobin saturation was poor (PO2, r2=.066; oxyhemoglobin saturation, r2=.000).

CONCLUSIONS

LIVC catheters whose tips lie below the origin of the renal veins predict central venous pressure in pediatric intensive care unit patients. Intra-abdominal pressure and mean airway pressure do not affect this relationship, within the wide range of values for these variables included in this study. Blood samples drawn from femoral venous catheters can be used to monitor acid-base balance and partial pressure of carbon dioxide.

Comparison of superior vena caval and femoroiliac venous pressure measurements during normal and inverse ratio ventilation

OBJECTIVE

The aim of this study was to estimate the agreement between superior vena caval pressure (SVCP) and femoroiliac venous pressure (FIVP) measurements by using short (<20 cm) femoral catheters commonly used in an adult intensive care unit. In addition, the effects of two modes of ventilation on agreement were assessed.

DESIGN

Measurements of central venous pressure were recorded from both sites by using the same pressure transducer connected to the catheters via a three-way stopcock. SVCP and FIVP were recorded at 5-min intervals for 40 mins with the patient in the supine position. Recordings were taken from ventilated patients during a randomized crossover sequence of normal and inverse ratio ventilation (IRV). Analyses included Pearson's correlation (r), intraclass correlation (ri), Bland-Altman plots, and repeated measures analysis of variance with crossover tests for period and period-treatment interactions.

SETTING

Adult intensive care unit.

PATIENTS

Adult intensive care patients.

MEASUREMENTS

Central venous pressure.

RESULTS

Twenty-two patients were enrolled in the study, giving 162 paired measurements; r was .97 (p < .0001), and ri was .96. The bias for SVCP-FIVP measurements was -0.75 mm Hg (95% confidence interval = -1.31 to -0.18), with 95% limits of agreement of -3.30 to 1.81 mm Hg. Seventeen patients were suitable for randomization to normal ratio ventilation and IRV. IRV significantly increased SVCP and FIVP (p < .002). Tests for the effect of mode of ventilation on agreement (p = .36), for period (p = .26), and for period-treatment interaction (p = .84) were not significant.

CONCLUSION

The study showed excellent overall agreement with acceptable clinical agreement for SVCP and FIVP measurements that was not affected by changing the mode of ventilation. IRV significantly increased central venous pressure measurements from both catheter sites but had no effect on overall agreement.

Central venous pressure from common iliac vein reflects right atrial pressure

PURPOSE

To determine whether central venous pressure at the common iliac vein reflects right atrial pressure in adult patients.

METHODS

In this prospective, non-blinded study 26 mechanically-ventilated adult patients were studied. Simultaneous pressure readings were obtained from the right atrium (TCVP) and the common iliac vein (ACVP).

RESULTS

There was a correlation between TCVP and ACVP (r = 0.987; P < 0.0001). The mean difference between TCVP and ACVP was 0.93 mm Hg. And the limits of agreement were: -1.93 to 1.77 mm Hg.

CONCLUSION

Venous pressure recorded from the common iliac vein reflects that in the right atrium. Adopting a femoral route for central venous pressure measurement may avoid some of the complications associated with the subclavian route.

A comparison of central venous pressure and common iliac venous pressure in critically ill mechanically ventilated patients

OBJECTIVE

To investigate the possibility of using common iliac venous pressure (CIVP) as an alternative to superior vena cava pressure (SVCP) in mechanically ventilated, critically ill, adult patients.

DESIGN

A randomized, blinded comparison.

SETTING

Multidisciplinary intensive care unit at a university teaching hospital.

PATIENTS

Twenty mechanically ventilated, critically ill, adult patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

All patients had a catheter in situ for measuring the SVCP. A new triple-lumen catheter, with a length ranging from 15 to 20 cm, was placed into the common iliac vein via the femoral route. The SVCP and CIVP were simultaneously measured at hourly intervals for 6 hrs. Positive end-expiratory pressure, mean airway pressure, and intra-abdominal pressure were measured at the same time intervals. For 140 paired measurements of CIVP and SVCP in 20 patients, the mean difference was 0.1 +/- 1.06 (SD) mm Hg (95% confidence interval -0.10 to 0.25); the limits of agreement were -2.04 to 2.20 mm Hg (95% confidence interval -2.34 to 2.50). Mean airway pressure, intra-abdominal pressure, and positive end-expiratory pressure had no measurable effect on the difference between SVCP and CIVP. Serious complications arising from insertion of the catheter through the femoral route were not observed.

CONCLUSION

For clinical purposes, CIVP measured by a catheter of 15 to 20 cm placed through the femoral route is interchangeable with SVCP in mechanically ventilated adult patients. This finding provides an alternative route for assessment of central venous pressure when other routes are not appropriate.