Central venous pressure: physiological significance and clinical implications

Gravitational effects on carotid and jugular characteristics in graded head-up and head-down tilt

Altered gravity affects hemodynamics and blood flow in the neck. At least one incidence of jugular venous thrombosis has been reported in an astronaut on the International Space Station. This investigation explores the impact of changes in the direction of the gravitational vector on the characteristics of the neck arteries and veins. Twelve subjects underwent graded tilt from 45° head-up to 45° head-down in 15° increments in both supine and prone positions. At each angle, the cross-sectional area of the left and right common carotid arteries (ACCA) and internal jugular veins (AIJV) were measured by ultrasound. Internal jugular venous pressure (IJVP) was also measured by compression sonography. Gravitational dose-response curves were generated from experimental data. ACCA did not show any gravitational dependence. Conversely, both AIJV and IJVP increased in a nonlinear fashion with head-down tilt. AIJV was significantly larger on the right side than the left side at all tilt angles. In addition, IJVP was significantly elevated in the prone position compared with the supine position, most likely because of raised intrathoracic pressure while prone. Dose-response curves were compared with existing experimental data from parabolic flight and spaceflight studies, showing good agreement on an acute timescale. The quantification of jugular hemodynamics as a function of changes in the gravitational vector presented here provides a terrestrial model to reference spaceflight-induced changes, contributes to the assessment of the pathogenesis of spaceflight venous thromboembolism events, and informs the development of countermeasures.NEW & NOTEWORTHY Flow stasis and thrombosis have been identified in the jugular vein during spaceflight. We measured the area and pressure of the internal jugular vein and the area of the common carotid artery in graded head-up and head-down tilt. Experimental data are used to generate gravitational dose-response curves for the measured variables, demonstrating that jugular vein area and pressure exhibit a nonlinear response to altered gravity. Gravitational dose-response curves show good agreement with spaceflight and parabolic flight studies.

Pathophysiology of fluid administration in critically ill patients

Fluid administration is a cornerstone of treatment of critically ill patients. The aim of this review is to reappraise the pathophysiology of fluid therapy, considering the mechanisms related to the interplay of flow and pressure variables, the systemic response to the shock syndrome, the effects of different types of fluids administered and the concept of preload dependency responsiveness. In this context, the relationship between preload, stroke volume (SV) and fluid administration is that the volume infused has to be large enough to increase the driving pressure for venous return, and that the resulting increase in end-diastolic volume produces an increase in SV only if both ventricles are operating on the steep part of the curve. As a consequence, fluids should be given as drugs and, accordingly, the dose and the rate of administration impact on the final outcome. Titrating fluid therapy in terms of overall volume infused but also considering the type of fluid used is a key component of fluid resuscitation. A single, reliable, and feasible physiological or biochemical parameter to define the balance between the changes in SV and oxygen delivery (i.e., coupling “macro” and “micro” circulation) is still not available, making the diagnosis of acute circulatory dysfunction primarily clinical.

Fluids are drugs used in patients with shock to increase the cardiac output with the aim to improve oxygen delivery to the cells. The response to fluid administration is determined by the physiological interaction of cardiac function and venous return. In septic shock, the beneficial clinical response of fluid administration is rapidly reduced after few hours and fluid titration is crucial to avoid detrimental fluid overload. The fluid challenge is a fluid bolus given at a defined quantity and rate to assess fluid responsiveness.

The ideal fluid for critically ill patients does not exist; however, crystalloids should be used as first choice. Balanced crystalloid solutions may be associated with better outcomes but the evidence is still low. Albumin infusion may have a role in already fluid resuscitated patients at risk of fluid overload.

Fluid administration is integrated into the complex management of pressure and flow “macro” hemodynamic variables, coupled to the “micro” local tissue flow distribution and regional metabolism. Macro-variables are managed by measuring systemic blood pressure and evaluating the global cardiac function. The critical threshold of oxygen delivery to the cells is difficult to estimate, however, several indexes and clinical signs may be considered as surrogate of that, and integrated in a decision-making process at the bedside.

Pharmacodynamic analysis of a fluid challenge with 4 ml kg-1 over 10 or 20 min: a multicenter cross-over randomized clinical trial

Purpose

A number of studies performed in the operating room evaluated the hemodynamic effects of the fluid challenge (FC), solely considering the effect before and after the infusion. Few studies have investigated the pharmacodynamic effect of the FC on hemodynamic flow and pressure variables. We designed this trial aiming at describing the pharmacodynamic profile of two different FC infusion times, of a fixed dose of 4 ml kg⁻¹.

Methods

Forty-nine elective neurosurgical patients received two consecutive FCs of 4 ml kg⁻¹ of crystalloids in 10 (FC₁₀) or 20 (FC₂₀) minutes, in a random order. Fluid responsiveness was defined as stroke volume index increase ≥ 10%. We assessed the net area under the curve (AUC), the maximal percentage difference from baseline (d_max), time when the d_max was observed (t_max), change from baseline at 1-min (d₁) and 5-min (d₅) after FC end.

Results

After FC₁₀ and FC_20, 25 (51%) and 14 (29%) of 49 patients were classified as fluid responders (p = 0.001). With the exception of the AUCs of SAP and MAP, the AUCs of all the considered hemodynamic variables were comparable. The d_max and the t_max were overall comparable. In both groups, the hemodynamic effects on flow variables were dissipated within 5 min after FC end.

Conclusions

The infusion time of FC administration affects fluid responsiveness, being higher for FC₁₀ as compared to FC₂₀. The effect on flow variables of either FCs fades 5 min after the end of infusion.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10877-021-00756-3.

Renal Dysfunction and Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) and chronic kidney disease (CKD) constitute a high-risk phenotype with significant morbidity and mortality and poor prognosis. Multiple proinflammatory comorbid conditions influence the pathogenesis of HFpEF and CKD. Renal dysfunction in HFpEF is a consequence of the complex interplay between hemodynamic factors, systemic congestion, inflammation, endothelial dysfunction, and neurohormonal mechanisms. In contrast to heart failure with reduced ejection fraction, there is a dearth of effective targeted therapies for HFpEF. Tailoring study design toward the different phenotypes and delving into their pathophysiology may be fruitful in development of effective phenotype-specific targeted pharmaceutical therapies.

Multivariable haemodynamic approach to predict the fluid challenge response: A multicentre cohort study

BACKGROUND

Beat-to-beat stroke volume (SV) results from the interplay between left ventricular function and arterial load. Fluid challenge induces time-dependent responses in cardiac performance and peripheral vascular and capillary characteristics.

OBJECTIVE

To assess whether analysis of the determinants of the haemodynamic response during fluid challenge can predict the final response at 10 and 30 min.

DESIGN

Observational multicentric cohort study.

SETTING

Three university ICUs.

PATIENTS

85 ICU patients with acute circulatory failure diagnosed within the first 48 h of admission.

INTERVENTION(S)

The fluid challenge consisted of 500 ml of Ringer's solution infused over 10 min. A SV index increase at least 10% indicated fluid responsiveness.

MAIN OUTCOME MEASURES

The SV, pulse pressure variation (PPV), arterial elastance, the systolic-dicrotic pressure difference (SAP-Pdic) and cardiac cycle efficiency (CCE) were measured at baseline, 1, 2, 3, 4, 5, 10, 15 and 30 min after the start of the fluid challenge. All haemodynamic data were submitted to a univariable logistic regression model and a multivariable analysis was then performed using the significant variables given by univariable analysis.

RESULTS

The multivariable model including baseline PPV, and the changes of arterial elastance at 1 min and of the CCE and SAP-Pdic at 5 min when compared with their baseline values, correctly classified 80.5% of responders and 90.7% of nonresponders at 10 min. For the response 30 min after starting the fluid challenge, the model, including the changes of PPV, CCE, SAP-Pdic at 5 min and of arterial elastance at 10 min compared with their baseline values, correctly identified 93.3% of responders and 91.4% of nonresponders.

CONCLUSION

In a selection of mixed ICU patients, a statistical model based on a multivariable analysis of the changes of PPV, CCE, arterial elastance and SAP-Pdic, with respect to baseline values, reliably predicts both the early and the late response to a standardised fluid challenge.

TRIAL REGISTRATION

ACTRN12617000076370.

Chest radiography for simplified evaluation of central venous catheter tip positioning for safe and accurate haemodynamic monitoring: a retrospective observational study

OBJECTIVES

The tip-to-carina (TC) distance on a simple chest X-ray (CXR) has proven value in the determination of correct central venous catheter (CVC) positioning. However, previous studies have mostly focused on preventing the atrial insertion of the CVC tip, and not on appropriate positioning for accurate haemodynamic monitoring. We aimed to assess whether the TC distance could detect the passage of the CVC tip into the superior vena cava (SVC) and the right atrium (RA), and to accordingly suggest cut-off reference values for these two aspects.

DESIGN

Retrospective observational cohort study.

SETTING

Single urban tertiary level academic hospital.

PARTICIPANTS

479 patients who underwent CXR and chest CT scan after the insertion of a CVC with a 24-hour interval during the study period.

INTERVENTION

The TC distance was measured on CXR, and the position of the CVC tip was assessed on the chest CT images. The TC distance was described as a negative or positive number if the CVC tip was above or below the carina, respectively. Receiver-operating characteristics curve analyses were conducted to ascertain the TC distance to detect SVC entrance and RA insertion of CVC tip.

RESULTS

The TC distance could significantly detect both SVC entrance and RA insertion (p<0.001 for both; area under curve 0.987 and 0.965, respectively), with a reference range of -6.69 to 15.61 mm.

CONCLUSION

The TC distance in CXR is a simple and precise method to confirm not only the safe placement of the CVC tip but also its optimal positioning for accurate haemodynamic monitoring.

Impact of increased venous pressure on kidney function and mortality in cardiovascular patients with preserved ejection fraction

Background: Right but not left ventricular hemodynamic parameters have been found to be independently associated with adverse renal outcomes in patients with acute decompensated heart failure (HF).Aim: To investigate the hemodynamic profile of patients without acute decompensated heart failure and left ventricular ejection fraction >50% referred for elective left and right heart catheterization and to correlate left and right filling pressures, stroke volume and arterial blood pressure to renal function parameters. Subsequently, we tested the hypothesis that right ventricle and left ventricle hemodynamic parameters can predict all-cause mortality in our non-HF subjects.Methods: Between October 2009 and November 2010, 151 consecutive patients referred for elective left and right heart catheterization were studied and consequently followed up for a mean period of 8 years in order to identify all-cause mortality. Patient's initial cohort was subdivided in two groups according to right atrial pressure. The RAPR_LOW group (Right Atrium Pressure ≤ 9 mmHg) and the RAPR_HIGH group (Right Atrium Pressure > 9mmHg)Results: No correlation between blood pressure, pulmonary capillary wedges pressure, cardiac index, stroke volume and stroke volume index (SVI), and parameters of kidney function was observed. However, a weak, although, significant correlation between right atrial pressure (RAP) and modification of diet in renal disease (MDRD) (r = -0.202; p = .014) could be detected. RAPR_LOW patients had a statistically significant lower MDRD value of 16.6 mL/min/1.73 m² than RAPR_HIGH patients. Increased RAP (HR = 2.03; 95% [CI]: 1.05 to 3.9; p = .025) and age (HR = 1.08, 95% [CI] 1.04-1.12, p < .001) independently predicted all-cause mortality during follow up.Conclusions: Our study demonstrates that right ventricular preload affects renal function in patients with preserved systolic function and that neither aortic systolic pressure nor left ventricle pressure indices were related to estimated glomerular filtration rate. Furthermore, we demonstrate for the first time that an increased RAP is able to predict a worse prognosis in patients with preserved ejection fraction independently of well-established risk factors, such as blood pressure and SVI.

High central venous pressure is associated with acute kidney injury and mortality in patients underwent cardiopulmonary bypass surgery

PURPOSE

We sought to investigate the relationship between high CVP, AKI, and mortality in patients undergoing cardiac surgery with cardiopulmonary bypass.

MATERIALS

All patients aged 18 years or older who underwent cardiac surgery with CPB were prospectively reviewed. Patients were excluded when renal artery were involved before and during surgery. Patients were dichotomized into high CVP group(>10 mmHg) and low CVP group(<10 mmHg). All patients were followed by telephone.

RESULTS

A total of 1941 patients were included in observed study. In high CVP group, three hundred forty-seven patients (43.32%) developed AKI, while eighty-six (7.543%) in low CVP group(P <0.0001). Furthermore, in every KDIGO stage, patients of AKI in high CVP group were more than those in low CVP group(P <0.0001). The incidence of AKI increased as CVP increased, especially when CVP was higher than 10cmH2O. In a median follow-up time of 9.2 months, Crude mortality is 8.365% in the high CVP group compared to 1.929% in the low CVP group (p<0.0001). In multivariate analysis, CVP remained the independent predictor of survival.

CONCLUSIONS

High CVP is associated with AKI , and it is independently related to all-cause mortality in patients underwent cardiovascular surgery with cardiopulmonary bypass.

Clearsight™ use for haemodynamic monitoring during the third trimester of pregnancy - a validation study

BACKGROUND

We assessed the validity of Clearsight™ as a non-invasive cardiac output and stroke volume monitoring device, comparing it with transthoracic echocardiography measurements during the third trimester of pregnancy.

METHODS

Measurements obtained from Clearsight™ were compared with those from echocardiography as the gold standard. The precision and accuracy of the Clearsight™ was measured using the Bland and Altman method. Clinical agreement with echocardiography was assessed using the agreement tolerability index.

RESULTS

Measurements were recorded from 44 pregnant women with a median [IQR range] gestational age of 33 [30-37] weeks. We found that Clearsight™ measurements presented a systematic overestimation of cardiac output, with mean bias [CI 95%] of 2.7 [2.3-3.0] L/min, with limits of agreement of  -0.1 to 5.4 L/min. It overestimated stroke volume, with a bias of 29.5 [25.0-33.4] mL and a limit of agreement of -1.6 to 60.1 mL. In addition, the analysis of cardiac output showed a percentage of error of 41% and intra-class correlation [CI 95%] of 0.37 [0.17 to 0.53, P <0.001]. For stroke volume, the percentage of error was 40% and intra-class correlation 0.16 [-0.1 to 0.34; P=0.27]. We found that agreement tolerability index scores were unacceptable. We evaluated the ability of the device to track changes in cardiac output by inducing a left lateral decubitus position, but the analysis was inconclusive.

CONCLUSION

The agreement between Clearsight™ and the echocardiography measurements of cardiac output and stroke volume were not within an acceptable range in the third trimester of pregnancy.

Chronic iliofemoral vein obstruction - an under-recognized cause of exercise limitation

Local symptoms of chronic venous insufficiency after deep vein thrombosis (DVT) are well described, but little is known about the effect of residual venous obstruction on exercise capacity. We tested our hypothesis that chronic residual iliofemoral vein occlusion (IFVO) after DVT may impair exercise capacity. Nine post-DVT patients with residual IFVO and effort intolerance were studied; a comparison cohort consisted of 11 healthy volunteers. Exercise tolerance was assessed by bimodality incremental symptom-limited cardiopulmonary testing, using leg and arm ergometers. In healthy subjects, leg vein obstruction was modelled by application to the thighs of cuff tourniquets inflated to 30-40 mmHg. Leg exercise tolerance as measured by oxygen uptake at peak exercise (peak ⩒'O₂) was reduced in patients (median 50% predicted (range 36-83%) vs. 88% predicted (67-129%) in normal subjects, p < 0.001). Arm exercise tolerance was also reduced in patients, but less severely than in the legs - the median arm: leg ratio of peak ⩒'O₂ was 0.95 (0.77-1.43) in patients vs. a normal ratio of 0.73 (0.6-1.0) in healthy subjects (p < 0.003). In healthy subjects, bilateral leg vein obstruction by tourniquets reduced peak ⩒'O₂ in leg exercise to 76% predicted (range 55-108%; p < 0.001 vs. standard test). In conclusion, the comparison of arm vs. leg exercise capacity in post-DVT patients with residual IFVO and the effect of experimental venous obstruction (thigh tourniquets) in healthy subjects suggest that reduced exercise capacity in patients was at least partially caused by reduced venous return. Chronic venous obstruction should be recognized as a cause of exercise limitation.

Central Venous Catheterization: A Comprehensive Review, Part I

Central venous catheterization is an indispensable tech nique in today's practice of medicine. It was initially used to monitor central venous pressure; however, this method has become obsolete. Central venous access is now more commonly established to administer hyper tonic intravenous alimentation or to insert pulmonary artery catheters. The sites available for central venous catheterization include the antecubital veins, external and internal jugular veins, subclavian vein, and femoral vein. Many of these sites offer more than one method of insertion. Although the indications for central venous access are well known, there is a general lack of respect for the considerable incidence of associated complica tions. It is useful to separate complications into two categories: those associated with venipuncture and catheter insertion, which will vary greatly depending on the route chosen, and those associated with catheter maintenance, which tend to be similar. The various methods of central venous catheterization are com prehensively reviewed with regard to specific indica tions, technique, and complications.

Measurement of Central Venous Pressure Using Ultrasound in Emergency Department

Background:

In order to assessment of intravascular fluid measurement of central venous pressure (CVP) is used via central venous catheterization (CVC). This procedure is highly invasive and may cause serious complications such as pneumothorax, infection, hematoma and etc. It is so valuable procedure if we can uses a less invasive or noninvasive procedure to assess patients intravascular fluid in critical positions.

Objectives:

In this study, the ultrasound was used to measure the central venous pressure (CVP).

Patients and Methods:

In this study, patients with Central venous catheterization were selected using simple random sampling. The largest diameter of longitudinal, transverse views and the cross-section of inferior vena cava (IVC) and internal jugular vein (IJV) were measured using the ultrasound in the bedside of the patients. Central venous pressure was measured using routine methods. Correlations between variables were analyzed using SPSS and linear regression.

Results:

Twenty patients with the mean age of 60.3 were studied. The main reason for cardiac catheterization was shock. There are no relationship between anterior posterior diameter of inferior vena cava and CVP of patients (P = 0.257). The longest diameter of IVC in ultrasonographic transverse view had significant association with CVP of patients (P = 0.045) but in patients with BMI > 25 it was not significant. Cross section of internal jugular vein had significant association with CVP of patients (P = 0.003). Longitudinal diameter of internal jugular vein had no significant association with CVP of patients (P = 0.052), but transverse diameter of internal jugular generally had significant association with CVP of patients (P = 0.003). Cross section of internal jugular had significant association with CVP (P = 0.001).

Conclusions:

Noninvasive assessment of the patient hydration condition using the ultrasound is a simple and practicable measure in emergency. With regard to the considerations, it is possible to estimate CVP via diameter measurement and cross-section of the central veins.

Central venous catheterization -- an anatomical review of a clinical skill -- Part 1: subclavian vein via the infraclavicular approach

The safe and successful performance of a central venous catheterization (CVC) requires a specific knowledge of anatomy in addition to a working knowledge. Misunderstanding the anatomy may result in failure or complications. This review aims to aid understanding of the anatomical framework, pitfalls, and complications of CVC of the subclavian (SCV). CVC is common practice amongst surgeons, anesthesiologists, and emergency room physicians during the preparations for major surgical procedures such as open-heart surgery, as well as, for intensive care monitoring and rapid restoration of blood volume. Associated with this technique are certain anatomical pitfalls and complications that can be successfully avoided if one possesses a thorough knowledge of the contraindications, regional anatomy, and rationale of the technique.

Blind placements of peripherally inserted antecubital central catheters: initial catheter tip position in relation to carina

BACKGROUND

We investigated how often blind placement of peripherally inserted central catheters (PICCs) through the antecubital veins results in a correct tip location in relation to carina and evaluated the inter-observer agreement in locating the tip of PICCs in plain radiography with digital imaging.

METHODS

In this study, 202 suitable chest radiographs with PICCs out of 803 patients were identified. An initial audit on the tip of these catheters in relation to carina was done by a consultant anaesthetist and was recorded as the first observer. The same sets of CXRs were examined by a consultant radiologist and the tips were identified and recorded as the second observer. Inter-observer agreement was assessed.

RESULTS

In 75 of 202 (37%), PICCs had a central tip location in relation to the carina. Fifty-five of 131 (42%) right-sided catheters had a central location compared with 20 of 71 (28%) of the left-sided catheters. The tip position for right-sided catheters was most frequently centrally located whereas the tip for left-sided catheters was most commonly positioned in the ipsilateral innominate vein. There was excellent agreement between the observers in reporting the tip of PICCs at all positions (kappa=0.87) including central locations (kappa=0.83).

CONCLUSIONS

Right antecubital PICCs are more likely to be placed in the central location in relation to the carina. PICCs inserted through the left antecubital veins need to be pushed further down to aim for a central location. Inter-observer variability in identifying the tip of PICCs is least with the introduction of digital imaging.

Pressão venosa central em bezerros neonatos hígidos

Com o propósito de estabelecer valores-padrão da pressão venosa central (PVC), utilizaram-se 24 bezerros sadios, da raça Holandesa, com idade entre oito e 30 dias, e peso entre 37 e 50kg. A PVC foi medida, no átrio direito, com uso de cateter intravenoso e equipo próprio usando-se como via de acesso a veia jugular esquerda. O átrio direito foi considerado o ponto zero de referência para as leituras, estando topograficamente em correspondência externa à articulação escapuloumeral no animal em estação e à região do esterno, quando em decúbito lateral direito. Estabeleceram-se os valores médios da PVC, em centímetros de água, de 0,81±1,40 e 0,88±1,76, respectivamente, nos animais em estação e em decúbito lateral, e não houve diferença estatística entre os valores. A metodologia empregada para mensurar a PVC de bezerros revelou-se segura e exeqüível, não necessitando de aparelhagem sofisticada para a sua determinação.

Proteolytic N-terminal Truncation of Cardiac Troponin I Enhances Ventricular Diastolic Function

Besides the core structure conserved in all troponin I isoforms, cardiac troponin I (cTnI) has an N-terminal extension that contains phosphorylation sites for protein kinase A under beta-adrenergic regulation. A restricted cleavage of this N-terminal regulatory domain occurs in normal cardiac muscle and is up-regulated during hemodynamic adaptation (Z.-B. Yu, L.-F. Zhang, and J.-P. Jin (2001) J. Biol. Chem. 276, 15753-15760). In the present study, we developed transgenic mice overexpressing the N-terminal truncated cTnI (cTnI-ND) in the heart to examine its biochemical and physiological significance. Ca(2+)-activated actomyosin ATPase activity showed that cTnI-ND myofibrils had lower affinity for Ca(2+) than controls, similar to the effect of isoproterenol treatment. In vivo and isolated working heart experiments revealed that cTnI-ND hearts had a significantly faster rate of relaxation and lower left ventricular end diastolic pressure compared with controls. The higher baseline relaxation rate of cTnI-ND hearts was at a level similar to that of wild type mouse hearts under beta-adrenergic stimulation. The decrease in cardiac output due to lowered preload was significantly smaller for cTnI-ND hearts compared with controls. These findings indicate that removal of the N-terminal extension of cTnI via restricted proteolysis enhances cardiac function by increasing the rate of myocardial relaxation and lowering left ventricular end diastolic pressure to facilitate ventricular filling, thus resulting in better utilization of the Frank-Starling mechanism.

Stretch-induced changes in heart rate and rhythm: clinical observations, experiments and mathematical models

Clinical and research data indicate that active and passive changes in the mechanical environment of the heart are capable of influencing both the initiation and the spread of cardiac excitation via pathways that are intrinsic to the heart. This direction of the cross-talk between cardiac electrical and mechanical activity is referred to as mechano-electric feedback (MEF). MEF is thought to be involved in the adjustment of heart rate to changes in mechanical load and would help to explain the precise beat-to-beat regulation of cardiac performance as it occurs even in the recently transplanted (and, thus, denervated) heart. Furthermore, there is clinical evidence that MEF may be involved in mechanical initiation of arrhythmias and fibrillation, as well as in the re-setting of disturbed heart rhythm by 'mechanical' first aid procedures. This review will outline the clinical relevance of cardiac MEF, describe cellular correlates to the responses observed in situ, and discuss the role that quantitative mathematical models may play in identifying the involvement of cardiac MEF in the regulation of heart rate and rhythm.

Intraocular pressure difference in Goldmann applanation tonometry versus Perkins hand-held applanation tonometry in overweight patients

OBJECTIVE

To analyze the increase in intraocular pressure (IOP) caused by anatomic and physiologic factors in overweight patients when using Goldmann applanation tonometry.

DESIGN

A prospective cohort study.

PARTICIPANTS

Seventy average-weight individuals who had no difficulties with IOP measurements at the slit lamp and 12 obese patients with suspected glaucoma who could position the head at the slit lamp only with great effort participated.

INTERVENTION

The authors compared IOP values between slit-lamp-mounted Goldmann applanation tonometry and Perkins hand-held tonometry.

MAIN OUTCOME MEASURE

The difference in Goldmann and Perkins IOP measurements was examined.

RESULTS

In the group of obese patients, the mean IOP was 20.9+/-2.28 mmHg (mean +/- standard deviation; range, 18-26 mmHg) for the right eye and 21.4+/-3.16 mmHg (range, 16-28 mmHg) for the left eye when determined by Goldmann tonometry and 16.3+/-2.39 mmHg (range, 13-20 mmHg) for the right eye and 16.3+/-2.42 (range, 11-19 mmHg) for the left eye when determined by Perkins tonometry. The mean decrease was 4.5+/-1.3 mmHg (range, 3-7 mmHg) for the right eye and 4.9+/-1.9 mmHg (range, 2-9 mmHg) for the left eye. In the control group, the mean difference between the two types of tonometers for the right eye was 0.34+/-0.69 mmHg and for the left eye was 0.33+/-0.82 mmHg. Patients who had a falsely elevated IOP on Goldmann tonometry had an average body mass index of 34+/-3.82 (range, 28.5-41.9); most were female (5:1 ratio).

CONCLUSION

The authors believe simultaneous breath-holding and thorax compression, with subsequent increase in venous pressure, may be a causative factor for transitory elevations of IOP. Perkins tonometry in obese patients may help avoid a false diagnosis of glaucoma caused by transitory elevations in IOP.

Comparison of intrathoracic and intra-abdominal measurements of central venous pressure

BACKGROUND

Complications can arise from standard intrathoracic central venous pressure (CVP) measurements in critically ill, mechanically ventilated patients. We have assessed the feasibility of catheterisation by the femoral route to measure CVP in the abdomen (ACVP). We compared measurements by the standard jugular or subclavian route (TCVP) with simultaneous ACVP measurements by the femoral route.

METHODS

Between June, 1994 and May, 1995, we recruited 20 critically ill adult patients with various disorders; all patients already had a TCVP line in situ. We placed a femoral catheter in the inferior vena cava close to the right atrium under electrocardiographic guidance. The catheter position was confirmed (and corrected if necessary) by chest radiography. CVP was measured from both sites hourly for 6 h. Positive end-expiratory pressure, mean airway pressure, and intra-abdominal pressure were recorded simultaneously.

FINDINGS

One patient was excluded because radiography showed that the catheter position was incorrect. For 133 paired measurements of ACVP and TCVP in the remaining 19 patients, the mean difference was 0.45 mm Hg (SD 0.89: 95% Cl 0.30-0.60); the limits of agreement were -1.33 to 2.23 mm Hg (-1.63 to 2.53). We found a small tendency for the difference between ACVP and TCVP to increase as positive end-expiratory pressure and mean airway pressure increased; the difference was statistically, but not clinically, significant.

INTERPRETATION

Our study showed that for clinical purposes CVP can be measured by a femoral catheter placed in the abdominal inferior vena cava near the right atrium. This approach can replace standard TCVP measurements in critically ill, mechanically ventilated patients.

Cardiovascular responses in paraplegic subjects during arm exercise

The purpose of this study was to examine cardiovascular responses during arm exercise in paraplegics compared to a well-matched control group. A group of 11 male paraplegics (P) with complete spinal cord-lesions between T6 and T12 and 11 male control subjects (C), matched for physical activity, sport participation and age performed maximal arm-cranking exercise and submaximal exercise at 20%, 40% and 60% of the maximal load for each individual. Cardiac output (Qc) was determined by the CO2 rebreathing method. Maximal oxygen uptake was significantly lower and maximal heart rate (fc) was significantly higher in P compared to C. At the same oxygen uptakes no significant differences were observed in Qc between P and C; however, stroke volume (SV) was significantly lower and fc significantly higher in P than in C. The lower SV in P could be explained by an impaired redistribution of blood and, therefore, a reduced ventricular filling pressure, due to pooling of venous blood caused by inactivity of the skeletal muscle pump in the legs and lack of sympathetic vasoconstriction below the lesion. In conclusion, in P maximal performance appears to have been limited by a smaller active muscle mass and a lower SV despite the higher fc,max. During submaximal exercise, however, this lower SV was compensated for by a higher fc and, thus at the same submaximal oxygen uptake, Qc was similar to that in the control group.

Positioning central venous catheters--a prospective survey

This paper reports the results of a prospective survey of 266 attempted central venous catheterisations by various routes, evaluating their success rate and incidence of immediate complications and attempts to demonstrate a relationship between patient height in centimetres (H) and ideal catheter length. The overall rate of intrathoracic placement was 230 from 239 catheterisations (96%) after 266 attempts (86%). Of these 230 catheters, 54 terminated in the right atrium (24%). To avoid right atrial placement with its well documented risk of cardiac tamponade, it is recommended that right infraclavicular subclavian catheters are inserted to H/10-2 cm, right internal or external jugular catheters to H/10 cm and left external jugular catheters to H/10 + 4 cm.

Hemodynamic monitoring in childhood

Hemodynamic monitoring is indicated in children with impending or manifest cardiocirculatory failure. Since cardiocirculatory failure is characterized by an imbalance between oxygen delivery and oxygen demand due to perfusion failure, the parameters monitored should aid in the assessment of these oxygen variables. Oxygen delivery depends on oxygen content and cardiac output. Cardiac output is determined by heart rate and stroke volume; stroke volume by preload, afterload and contractility. Since the direct measurement of oxygen consumption routinely is almost impossible, global oxygen utilization represented by mixed venous oxygen saturation may be used to quantify the relationship between oxygen delivery and oxygen consumption. Justification of invasive hemodynamic monitoring depends among other things on an optimal balance between usefulness of information and complications associated with the techniques used. In future, the development of further noninvasive techniques and the scientific evaluation of recommended monitoring techniques are prospects in cardiovascular monitoring in childhood.

Right Ventricular function in aortic and mitral valve disease

Radionuclide ventriculography of the right heart was performed in 56 patients within two weeks of cardiac catheterization using a gated first-pass technique. Thirteen patient served as normal controls, and 43 patients had severe aortic or mitral valve disease or both, 35 of whom subsequently underwent valve surgery. Right ventricular ejection fraction (RVEF) and the presence of central venous reflux was determined and related to catheterization findings. In normal patients, RVEF was 60 plus or minus 7 percent (mean plus or minus 1 SD). In patients with valvular disease, the RVEF was below the normal range in only 2/14 (14 per cent) when right ventricular peak systolic pressures were less than 50 mm Hg, compared with 16/29 (55 percent) with an RVEF below normal when right ventricular peak systolic pressures greater than 50 mm Hg (P less than .05). In contrast, there was no relation of right ventricular ejection fraction to ventricular filling pressure in valvular heart disease patients. There was no difference in early postoperative course in patients with normal or reduced ejection fraction. Central venous systolic reflux was not presented in normal patients, but was present in 3/12 (25 percent) and 22/25 (88 percent); P less than 0.1) of patients with right ventricular systolic pressures below and above 55 mm Hg, respectively, including all ten patients with documented tricuspid regurgitation. Radionuclide assessment of right ventricular function in patients with aortic or mitral valve disease or both provides information that cannot be inferred from right-sided pressure measurements.

Central venous cannulation and pressure monitoring

Central venous pressure (CVP) varies directly with circulating blood volume and vascular tone and inversely with right heart competency. Indications for central cannulation include cardiorespiratory arrest. The two general approaches to cannulation of central veins are peripheral and central. The physician's skill, patient's body habitus, clinical circumstances, age and thoracic deformity all influence the choice of technique. Three of the possible complications discussed are pneumothorax, arterial puncture and air embolus. Accurate measurement of CVP depends on the patient being supine, a patent and accurately located catheter and the establishment of a baseline external zero point.

Fatal cardiac tamponade and other mechanical complications of central venous catheters

A fatal cardiac tamponade caused by an intact polyethylene central venous catheter perforating the wall of the right ventricle is reported. A retrospective review of 105 central venous catheters used in an intensive care unit revealed a high incidence of catheter malposition and a 20 per cent mechanical complication rate. The possible causes of these malpositions and complications are discussed. Guidelines for the safer use of central venous catheters are presented.