Arterial and central venous pressure monitoring

A multimodal deep learning tool for detection of junctional ectopic tachycardia in children with congenital heart disease

Background

Junctional ectopic tachycardia (JET) is a prevalent life-threatening arrhythmia in children with congenital heart disease. It has a marked resemblance to normal sinus rhythm, often leading to delay in diagnosis and management.

Objective

The study sought to develop a novel multimodal automated arrhythmia detection tool that outperforms existing JET detection tools.

Methods

This is a cohort study performed on 40 patients with congenital heart disease at Texas Children's Hospital. Electrocardiogram and central venous pressure waveform data produced by bedside monitors are captured by the Sickbay platform. Convolutional neural networks (CNNs) were trained to classify each heartbeat as either normal sinus rhythm or JET based only on raw electrocardiogram signals.

Results

Our best model improved the area under the curve from 0.948 to 0.952 and the true positive rate at 5% false positive rate from 71.8% to 80.6%. Using a 3-model ensemble further improved the area under the curve to 0.953 and the true positive rate at 5% false positive rate to 85.2%. Results on a subset of data show that adding central venous pressure can significantly improve area under the receiver-operating characteristic curve from 0.646 to 0.825.

Conclusion

This study validates the efficacy of deep neural networks to notably improve JET detection accuracy. We have built a performant and reliable model that can be used to create a bedside alarm that diagnoses JET, allowing for precise diagnosis of this life-threatening postoperative arrhythmia and prompt intervention. Future validation of the model in a larger cohort is needed.

A comparison of different methods to maximise signal extraction when using central venous pressure to optimise atrioventricular delay after cardiac surgery

Objective

Our group has shown that central venous pressure (CVP) can optimise atrioventricular (AV) delay in temporary pacing (TP) after cardiac surgery. However, the signal-to-noise ratio (SNR) is influenced both by the methods used to mitigate the pressure effects of respiration and the number of heartbeats analysed. This paper systematically studies the effect of different analysis methods on SNR to maximise the accuracy of this technique.

Methods

We optimised AV delay in 16 patients with TP after cardiac surgery. Transitioning rapidly and repeatedly from a reference AV delay to different tested AV delays, we measured pressure differences before and after each transition. We analysed the resultant signals in different ways with the aim of maximising the SNR: (1) adjusting averaging window location (around versus after transition), (2) modifying window length (heartbeats analysed), and (3) applying different signal filtering methods to correct respiratory artefact.

Results

(1) The SNR was 27 % higher for averaging windows around the transition versus post-transition windows. (2) The optimal window length for CVP analysis was two respiratory cycle lengths versus one respiratory cycle length for optimising SNR for arterial blood pressure (ABP) signals. (3) Filtering with discrete wavelet transform improved SNR by 62 % for CVP measurements. When applying the optimal window length and filtering techniques, the correlation between ABP and CVP peak optima exceeded that of a single cycle length (R = 0.71 vs. R = 0.50, p < 0.001).

Conclusion

We demonstrated that utilising a specific set of techniques maximises the signal-to-noise ratio and hence the utility of this technique.

Systolic blood pressure measurements are unreliable for the management of acute spontaneous intracerebral hemorrhage

PURPOSE

Whether systolic blood pressure (SBP) is reliable in acute spontaneous intracerebral (sICH) by assessing agreement between simultaneous BP measurements obtained from cuff non-invasive blood pressure (NIBP) and radial arterial invasive blood pressure (AIBP) devices.

MATERIAL AND METHODS

Among 766 prospectively screened sICH subjects, 303 (39.5%) had NIBP and AIBP measurements. During the first 24 h, 2157 simultaneous paired measurement readings were abstracted. Paired NIBP/AIBP measurements were included in a Bland-Altman technique with 95% agreement limits and coefficients from regression analysis derived from a bootstrap procedure.

RESULTS

Variance for SBP was 66.1 mmHg, which was larger than the 44.3 mg Hg for diastolic blood pressure (DBP) or the 46.1 mmHg for mean arterial pressure (MAP). Pairwise comparison of mean biases showed a significant difference between SBP when compared to DBP (p < 0.0001) or MAP (p < 0.0001). The mean bias between DBP and MAP was not different (p = 0.68). Regression-based Bland Altman analysis found significant bias (slope -0.16, 95% CI -0.23, -0.09, p < 0.05) over the range of mean SBP. Bias over the range of mean DBP or MAP was not significant.

CONCLUSIONS

We concluded that SBP is an unreliable blood pressure measurement in patients with sICH.

Detection of Junctional Ectopic Tachycardia by Central Venous Pressure

Central venous pressure (CVP) is the blood pressure in the venae cavae, near the right atrium of the heart. This signal waveform is commonly collected in clinical settings, and yet there has been limited discussion of using this data for detecting arrhythmia and other cardiac events. In this paper, we develop a signal processing and feature engineering pipeline for CVP waveform analysis. Through a case study on pediatric junctional ectopic tachycardia (JET), we show that our extracted CVP features reliably detect JET with comparable results to the more commonly used electrocardiogram (ECG) features. This machine learning pipeline can thus improve the clinical diagnosis and ICU monitoring of arrhythmia. It also corroborates and complements the ECG-based diagnosis, especially when the ECG measurements are unavailable or corrupted.

Blood Pressure measurements are site dependent in a cohort of patients with neurological illness

Blood pressure (BP) management is a crucial part of critical care that directly affects morbidity and mortality. While BP has become a mainstay in patient care, the accuracy and precision of BP measures across commonly used sites (left upper arm, right upper arm, etc.) and methods have not been established. This study begins to fill this gap in literature by testing the null hypothesis that BP measurement does not vary according to site. This is a prospective, non-randomized, cross-sectional study of 80 neurocritical care unit patients. Near simultaneous non-invasive blood pressure (NIBP) readings from 4 different locations (bilateral upper arm, bilateral wrist) and, when available, intra-arterial blood pressure readings (IABP) were included. Pearson correlation coefficients and one-way repeated measures ANOVA were used to observe the systolic, diastolic, and mean arterial pressure (MAP) correlations. The BP measured at the four most common sites (left upper arm, left wrist, right upper arm, right wrist) had adequate correlation coefficients but were statistically significantly different and highly unpredictable. The median inter-site systolic variability was 10 mmHg (IQR 2 to 10 mmHg). The median inter-site MAP variability was 6mmHg with an interquartile range (IQR) of 3 to 9 mmHg. As expected, the values correlated to show that patients with high BP in one site tended to have high BP in another site. However, the unpredictable inter-site variability is concerning within the clinical setting where oftentimes BP measurement site is not standardized but resulting values are nevertheless used for treatment. There is prominent inter-site variability of BP measured across the 4 most common measurement sites. The variability persists across non-invasive (NIBP) and invasive (IABP) methods of assessment.

Rectal, central venous, gastric and bladder pressures versus esophageal pressure for the measurement of cough strength: a prospective clinical comparison

BACKGROUND

Cough pressure, an expression of expiratory muscle strength, is usually measured with esophageal or gastric balloons, but these invasive catheters can be uncomfortable for the patient or their placement impractical. Because pressure in the thorax and abdomen are expected to be similar during a cough, we hypothesized that measurement at other thoracic or abdominal locations might also be similar as well as useful in clinical scenarios. This study aimed to compare cough pressures measured at thoracic and abdominal sites that could serve as alternatives to esophageal pressures (P_es).

METHODS

Nine patients scheduled for laparotomy were asked to cough as forcefully as possible from total lung capacity in supine position. Three cough maneuvers were performed while P_es (the gold standard) as well as gastric, central venous, bladder and rectal pressures (P_ga, P_cv, P_bl, and P_rec, respectively) were measured simultaneously. The intraclass correlation coefficient (ICC) was used to evaluate the repeatability of the measurements in each patient at each site and evaluate agreement between alternative sites (P_ga, P_cv, P_bl, and P_rec) and P_es. Bland-Altman plots were used to compare P_es and the measurements at the other sites.

RESULTS

Median (first quartile, third quartile) maximum pressures were as follows: P_es 112 (89,148), P_ga 105 (92,156), P_cv 102 (91,149), P_bl 118 (93,157), and P_rec 103 (88,150) cmH₂O. The ICCs showed excellent within-site repeatability of the measurements (p < 0.001) and excellent agreement between alternative sites and P_es (p < 0.004). The Bland-Altman plots showed minimal differences between P_es, P_ga, P_cv, and P_rec. However, P_bl was higher than the other pressures in most patients, and the difference between P_es and P_bl was slightly larger.

CONCLUSIONS

Cough pressure can be measured in the esophagus, stomach, superior vena cava or rectum, since their values are similar. It can also be measured in the bladder, although the value will be slightly higher. These results potentially facilitate the assessment of dynamic expiratory muscle strength with fewer invasive catheter placements in most hospitalized patients, thus providing an option that will be particularly useful in those undergoing thoracic or abdominal surgery.

TRIAL REGISTRATION

NCT02957045 registered at November 7, 2016. Retrospectively registered.

The Correlation Between Inferior Vena Cava Diameter Measured by Ultrasonography and Central Venous Pressure

OBJECTIVE

To find a correlation between inferior vena cava (IVC) diameters, IVC compressibility index (CI) and central venous pressure (CVP).

METHODS

Prospective observational study was done at pediatric intensive care unit (PICU) of Kalawati Saran Children's Hospital (KSCH). Fifty children aged 5-18 y, presenting with shock were enrolled for the study. IVC diameters, CI and relevant clinical data were noted at enrollment, 30 min, 1 h, 6 h, and 12 h. Central line was placed at the time of admission.

RESULTS

Of 50 children enrolled, 28 were boys, with a mean age of 11 y. More than 80% of cases were diagnosed as septic shock. Mean maximum and minimum IVC diameter of 8.3 ± 2 mm and 3.7 ± 1.7 mm, respectively CI 58.2 ± 7% and CVP of 5.4 ± 1.5 cm of H₂O was observed at admission. CVP and IVC diameters showed a serial improvement with treatment; CI showed a serial decrease with treatment. Heart rate (HR) and systolic blood pressure (SBP) also showed a serial improvement at 12 h (p < 0.05). CVP showed a positive correlation with IVC diameter (r +0.312; p < 0.05), and a negative correlation with CI (r -0.343; p < 0.05).

CONCLUSIONS

Effective fluid resuscitation improves IVC diameters with a decrease in CI. IVC diameter has a positive correlation to CVP and CI has a negative correlation to CVP.

Use of the Kalman Filter for Aortic Pressure Waveform Noise Reduction

Clinical applications that require extraction and interpretation of physiological signals or waveforms are susceptible to corruption by noise or artifacts. Real-time hemodynamic monitoring systems are important for clinicians to assess the hemodynamic stability of surgical or intensive care patients by interpreting hemodynamic parameters generated by an analysis of aortic blood pressure (ABP) waveform measurements. Since hemodynamic parameter estimation algorithms often detect events and features from measured ABP waveforms to generate hemodynamic parameters, noise and artifacts integrated into ABP waveforms can severely distort the interpretation of hemodynamic parameters by hemodynamic algorithms. In this article, we propose the use of the Kalman filter and the 4-element Windkessel model with static parameters, arterial compliance C, peripheral resistance R, aortic impedance r, and the inertia of blood L, to represent aortic circulation for generating accurate estimations of ABP waveforms through noise and artifact reduction. Results show the Kalman filter could very effectively eliminate noise and generate a good estimation from the noisy ABP waveform based on the past state history. The power spectrum of the measured ABP waveform and the synthesized ABP waveform shows two similar harmonic frequencies.

Optimal Transducer Level for Atrial and Pulmonary Arterial Pressure Measurement in Patients with Functional Single Ventricle

This study aimed to investigate the optimal transducer level for accurate measurement of atrial and pulmonary arterial pressures in the supine position for patients with functional single ventricle. Contrast-enhanced chest computed tomographic images of 108 patients who underwent either the bidirectional cavopulmonary shunt (BCPS) placement or the Fontan procedure were reviewed. Vertical distances from the skin of the back to the uppermost levels of fluid in the single atrium or the pulmonary artery confluence and their ratios to the greatest anteroposterior (AP) diameter of the thoracic cage were determined. In patients who underwent BCPS, the ratios of the uppermost levels of blood in the atrium and pulmonary artery confluence to the greatest AP diameter of the thorax were 76.0 ± 8.1 and 56.3 ± 5.5 %, respectively. The distance (mm) between these two levels was calculated as 24.2 + 0.31 × age (years) (r ² = 0.08, P < 0.03). In patients who underwent the Fontan procedure, the ratios were 79.3 ± 10.0 and 58.3 ± 5.8 %, respectively. The distance (mm) between these two levels was calculated as 31.1 + 0.44 × age (years) (r ² = 0.05, P < 0.11). The optimal transducer levels for measuring atrial and pulmonary arterial pressures in the supine position are 75-80 and 55-60 % of the AP diameter of the thorax, respectively, in patients with functional single ventricle. We should consider the difference of the pressure when atrial and pulmonary arterial pressures were measured with the same level of transducers.

Primary study for detection of arterial blood pressure waveform components

The paper presents a technique to detect significant systolic peaks, the percussion (P) and tidal peak (T) and diastolic peak (D) from the arterial blood pressure (ABP) waveform. The technique is aimed at robust detection even in presence of significant noise. Singular Value Decomposition (SVD) based dominant period extraction of the ABP waveform followed by wavelet transform and local peak detection is applied to detect the points of interest. MIMIC-II ABP databse serves as a training dataset to select SVD and wavelet transform parameters and CSL Benchmark database is used to analyze the technique. Salient systolic peak detection for the CSL dataset was performed with positive predictive value and sensitivity figures of 98.48% and 99.24% respectively.

A Review of Central Venous Pressure and Its Reliability as a Hemodynamic Monitoring Tool in Veterinary Medicine

OBJECTIVE

To review the current literature regarding central venous pressure (CVP) in veterinary patients pertaining to placement (of central line), measurement, interpretation, use in veterinary medicine, limitations, and controversies in human medicine.

ETIOLOGY

CVP use in human medicine is a widely debated topic, as numerous sources have shown poor correlation of CVP measurements to the volume status of a patient. Owing to the ease of placement and monitoring in veterinary medicine, CVP remains a widely used modality for evaluating the hemodynamic status of a patient. A thorough evaluation of the veterinary and human literature should be performed to evaluate the role of CVP measurements in assessing volume status in veterinary patients.

DIAGNOSIS

Veterinary patients that benefit from accurate CVP readings include those suffering from hypovolemic or septic shock, heart disease, or renal disease or all of these. Other patients that may benefit from CVP monitoring include high-risk anesthetic patients undergoing major surgery, trending of fluid volume status in critically ill patients, patients with continued shock, and patients that require rapid or large amounts of fluids.

THERAPY

The goal of CVP use is to better understand a patient's intravascular volume status, which would allow early goal-directed therapy.

PROGNOSIS

CVP would most likely continue to play an important role in the hemodynamic monitoring of the critically ill veterinary patient; however, when available, cardiac output methods should be considered the first choice for hemodynamic monitoring.

Optimal level of the reference transducer for central venous pressure and pulmonary artery occlusion pressure monitoring in supine, prone, and sitting position

To guarantee accurate measurement of central venous pressure (CVP) or pulmonary artery occlusion pressure (PAOP), proper positioning of a reference transducer is a prerequisite. We investigated ideal transducer levels in supine, prone, and sitting position in adults. Chest computed tomography images of 113 patients, taken in supine or prone position were reviewed. For supine position, distances between the back and the uppermost blood level of both atria and their ratios to the largest anteroposterior (AP) diameter of thorax were calculated. For prone position, same distances and ratios were calculated from the anterior chest. For sitting position, distances between the mid-sternoclavicular joint and the most cephalad blood level of both atria and their ratios to the sternal length were calculated. The ratio of the uppermost blood level of right atrium (RA) and left atrium (LA) to the largest AP diameter of thorax was 0.81 ± 0.04 and 0.59 ± 0.03 from the back in supine position. That calculated from the anterior chest in prone position was 0.54 ± 0.03 and 0.46 ± 0.03. The ratio of the most cephalad blood level of RA and LA to the sternal length was 0.70 ± 0.10 and 0.68 ± 0.09 from the mid-sternoclavicular joint in sitting position, which corresponded to the upper border of 4th rib. Optimal CVP transducer levels are at four-fifths of the AP diameter of thorax in supine position, at a half of that in prone position, and at upper border of the 4th sternochondral joint in sitting position. PAOP transducer levels are similar in prone and sitting position, except for supine position which is at three-fifths of the AP diameter of thorax.

Highly skin-conformal microhairy sensor for pulse signal amplification

A bioinspired microhairy sensor is developed to enable ultraconformability on nonflat surfaces and significant enhancement in the signal-to-noise ratio of the retrieved signals. The device shows ≈12 times increase in the signal-to-noise ratio in the generated capacitive signals, allowing the ultraconformal microhair pressure sensors to be capable of measuring weak pulsations of internal jugular venous pulses stemming from a human neck.

The relationship between inferior vena cava diameter measured by bedside ultrasonography and central venous pressure value

Objective: We aimed to present inferior vena cava (IVC) diameter as a guiding method for detection of relationship between IVC diameter measured noninvasively with the help of ultrasonography (USG) and central venous pressure (CVP) and evaluation of patient's intravascular volume status.

Methods: Patients over the age of 18, to whom a central venous catheter was inserted to their subclavian vein or internal jugular vein were included in our study. IVC diameter measurements were recorded in millimeters following measurement by the same clinician with the help of USG both at the end-inspiratory and end-expiratory phase. CVP measurements were viewed on the monitor by means of piezoelectric transducer and recorded in mmHg. SPSS 18.0 package program was used for statistical analysis of data.

Results: Forty five patients were included in the study. The patients had the diagnosis of malignancy (35.6%), sepsis (13.3%), pneumonia, asthma, chronic obstructive pulmonary disease (11.1%). 11 patients (24.4%) required mechanical ventilation while 34 (75.6%) patients had spontaneous respiration. In patients with spontaneous respiration, a significant relationship was found between IVC diameters measured by ultrasonography at the end of expiratory and inspiratory phases and measured CVP values at the same phases (for expiratory p = 0.002, for inspiratory p= 0.001). There was no statistically significant association between IVC diameters measured by ultrasonography at the end of expiration and inspiration and measured CVP values at the same phases in mechanically ventilated patients.

Conclusions: IVC diameter measured by bedside ultrasonography can be used for determination of the intravascular volume status of the patients with spontaneous respiration.

Atrial stretch delays gastric emptying of liquids in awake rats

AIMS

We previously reported that mechanical atrial stretch (AS) by balloon distention increased gastric tonus in anesthetized rats. The present study evaluated the effect of AS on the gastric emptying of a liquid test meal in awake rats and its underlying neural mechanisms.

MAIN METHODS

Anesthetized male rats received a balloon catheter into the right atrium and a gastrostomy cannula. The next day, mean arterial pressure (MAP), heart rate (HR), central venous pressure (CVP), and cardiac output (CO) were continuously monitored. After the first 20min of monitoring (basal interval), the balloon was either distended or not (control) with 30, 50, or 70μl saline for 5min. Fifteen minutes later, the rats received the test meal (glucose solution with phenol red), and fractional gastric dye retention was determined 10, 20, or 30min later.

KEY FINDINGS

Heart rate and CVP values were transiently increased by 50 or 70μl AS but not 30μl AS, whereas gastric emptying was slower after 30, 50, or 70μl AS than after sham distention. Subdiaphragmatic vagotomy or splanchnicotomy+celiac ganglionectomy and capsaicin, ondansetron, hexamethonium, L-NAME, and glibenclamide treatment prevented the AS-induced delay in gastric emptying, whereas atropine and guanethidine treatment failed to prevent it.

SIGNIFICANCE

Atrial stretch inhibited the gastric emptying of liquid via non-adrenergic and non-cholinergic pathways that activate nitric oxide-K(+)ATP channels.

Vasodilation increases pulse pressure variation, mimicking hypovolemic status in rabbits

OBJECTIVE

To test the hypothesis that pulse pressure respiratory variation (PPV) amplification, observed in hypovolemia, can also be observed during sodium nitroprusside (SNP)-induced vasodilation.

INTRODUCTION

PPV is largely used for early identification of cardiac responsiveness, especially when hypovolemia is suspected. PPV results from respiratory variation in transpulmonary blood flow and reflects the left ventricular preload variations during respiratory cycles. Any factor that decreases left ventricular preload can be associated with PPV amplification, as seen in hypovolemia.

METHODS

Ten anesthetized and mechanically ventilated rabbits underwent progressive hypotension by either controlled hemorrhage (Group 1) or intravenous SNP infusion (Group 2). Animals in Group 1 (n = 5) had graded hemorrhage induced at 10% steps until 50% of the total volume was bled. Mean arterial pressure (MAP) steps were registered and assumed as pressure targets to be reached in Group 2. Group 2 (n = 5) was subjected to a progressive SNP infusion to reach similar pressure targets as those defined in Group 1. Heart rate (HR), systolic pressure variation (SPV) and PPV were measured at each MAP step, and the values were compared between the groups.

RESULTS

SPV and PPV were similar between the experimental models in all steps (p > 0.16). SPV increased earlier in Group 2.

CONCLUSION

Both pharmacologic vasodilation and graded hemorrhage induced PPV amplification similar to that observed in hypovolemia, reinforcing the idea that amplified arterial pressure variation does not necessarily represent hypovolemic status but rather potential cardiovascular responsiveness to fluid infusion.

Automated pre-ejection period variation indexed to tidal volume predicts fluid responsiveness after cardiac surgery

BACKGROUND

Reliable continuous monitoring of fluid responsiveness is an unsolved issue in patients ventilated with low tidal volume. We hypothesised that variations in the pre-ejection period (PEP) defined as the time interval between electrocardiogram (ECG) R-wave and onset of systolic upstroke in arterial blood pressure could reliably predict fluid responsiveness in patients ventilated with moderately low tidal volume. Furthermore, we hypothesised that indexing dynamic parameters to tidal volume would improve their prediction. The aim was to refine and automate a previously suggested algorithm for PEP variation (DeltaPEP) and to test this new parameter indexed to tidal volume (PEPV), as a marker of fluid responsiveness along with central venous pressure (CVP), pulse pressure variation (PPV) and DeltaPEP. Additionally, the aim was to evaluate the concept of indexing dynamic parameters to tidal volume.

METHODS

Arterial pressure, CVP, ECG and cardiac index (CI) were acquired from 23 mechanically ventilated post-cardiac surgery patients scheduled for volume expansion. PEPV, PPV and DeltaPEP were extracted.

RESULTS

Using responder/non-responder classification (response=change in CI>+15%), sensitivity and specificity were 100% and 83%, respectively, for PEPV, 94% and 83% for DeltaPEP, and 94% and 83% for PPV. CVP offered no relevant information. Tidal volume indexing improved sensitivity for DeltaPEP to 100%.

CONCLUSION

In this study in post-cardiac surgery patients, a refined parameter, PEPV, predicted fluid responsiveness better than PPV and DeltaPEP. Our results suggest that dynamic parameters using variations in PEP should be indexed to tidal volume.

High Definition Oscillometry: a novel technique for non-invasive blood pressure monitoring in the cynomolgus monkey (Macaca fascicularis)

BACKGROUND

Current approaches for accurate blood pressure determination rely predominantly on invasive techniques. High Definition Oscillometry (HDO) was evaluated as a potential non-invasive approach for accurate blood pressure recordings in cynomolgus monkeys.

METHODS

In conscious animals, systolic, diastolic, mean arterial blood pressure (MAP) and pulse/minute were determined 15 times within approx. 9 minutes per individual. This session was performed during 3 consecutive days. Anaesthesia induced hypotension was controlled simultaneously with HDO and telemetry as reference.

RESULTS

Repeated measurements were highly reproducible. After procedural habituation, mean MAP was 96.2 +/- 13.7 mmHg in males and 86.9 +/- 4.3 mmHg in females. Mean intraindividual coefficients of variation ranged between 10.8% and 2.4% depending on the session and parameter. Values determined by HDO corresponded to those reported for invasive techniques.

CONCLUSION

Our results demonstrate, using telemetry as reference, the accuracy of HDO-based non-invasive blood pressure measurements in macaques to detect drug-related cardiovascular changes.

Evaluation and treatment of hypotension in the preterm infant

A large proportion of very preterm infants receive treatment for hypotension. The definition of hypotension is unclear, and, currently, there is no evidence that treating it improves outcomes or, indeed, which treatment to choose among the available alternatives. Assessment of circulatory adequacy of the preterm infant requires a careful clinical assessment and may also require ancillary investigations. The most commonly used interventions, fluid boluses and dopamine, are problematic: fluid boluses are statistically associated with worse clinical outcomes and may not even increase blood pressure, whereas dopamine increases blood pressure mostly by causing vasoconstriction and may decrease perfusion. For neither intervention is there any reliable data showing clinical benefit. Prospective trials of intervention for hypotension and circulatory compromise are urgently required.

Establishing normal values of central venous pressure in very low birth weight infants

The objective of this paper is to establish a reference range of central venous pressure (CVP) values during the first 4 days of life in very low birth weight (VLBW) infants. A prospective observational study with continuous monitoring of CVP in VLBW newborns who had an umbilical venous catheter (UVC) positioned in or near the right atrium is conducted. All UVCs were inserted as part of normal care of the infants. The mean CVP (mCVP) was monitored for 72 h from recruitment, or until the UVC was removed. The mean mCVP was calculated for each infant. The median of the mean mCVPs was then calculated. Data were analysed in 17 infants. The median gestational age was 27 weeks and median birth weight was 940 g. Sixteen were mechanically ventilated and of these, six also received continuous positive airway pressure (CPAP) during the study period. One infant received no respiratory support. One infant died during the study period. The lowest mean mCVP was 2.8 mmHg and the highest was 13.9 mmHg. The median mean mCVP was 4.9 mmHg (interquartile range 4.4-6.1). The normal range of CVP in VLBW infants during the first 4 days of life is wider than previously suggested.

Arterial and central venous pressure monitoring

Pressure monitoring systems influence the contour of the displayed wave-forms and, on occasion, can introduce significant artifact in the pressure traces. It is important to understand the technical details of invasive pressure monitoring to interpret better the information presented. Careful observation of the arterial pressure waveform can provide information about ventricular function, the arterial system, and ventricular preload. In particular, systolic pressure variation during the respiratory cycle in mechanically ventilated patients is a clinically useful indicator of volume status. CVP monitoring is also used to assess intravascular volume, but this measurement is significantly influenced by ventricular compliance and intrathoracic pressure. Under most clinical circumstances, a trend in CVP values or its change with therapeutic maneuvers is more reliable than a single measurement. Like arterial pressure waveforms, CVP waveform morphology can provide important information about clinical pathophysiology.

Central venous pulse pressure analysis using an R-synchronized pressure measurement system

OBJECTIVE

The information derived from central venous catheters is underused. We developed an EKG-R synchronization and averaging system to obtained distinct CVP waveforms and analyzed components of these.

METHODS

Twenty-five paralyzed surgical patients undergoing CVP monitoring under mechanical ventilation were studied. CVP and EKG signals were analyzed employing our system, the mean CVP and CVP at end-diastole during expiration were compared, and CVP waveform components were measured using this system.

RESULTS

CVP waveforms were clearly visualized in all patients. They showed the a peak to be 1.8+/- 0.7 mmHg, which was the highest of three peaks, and the x trough to be lower than the y trough (-1.6+/- 0.7 mmHg and -0.9+/- 0.5 mmHg, respectively), with a mean pulse pressure of 3.4 mmHg. The difference between the mean CVP and CVP at end-diastole during expiration was 0.58+/- 0.81 mmHg.

CONCLUSIONS

The mean CVP can be used as an index of right ventricular preload in patients under mechanical ventilation with regular sinus rhythm. Our newly developed system is useful for clinical monitoring and for education in circulatory physiology.

Reduction of pulmonary edema after SAH with a pulmonary artery catheter-guided hemodynamic management protocol

INTRODUCTION

The frequency of pulmonary edema, which occurs with high frequency following subarachnoid hemorrhage (SAH), can be worsened by hypervolemic, hypertensive, hemodilution therapy for vasospasm. This study compares the complication rates for patients with SAH before and after institution of a pulmonary artery catheter-guided hemodynamic management protocol.

METHODS

Complication and outcome data were prospectively collected on 453 patients with spontaneous SAH. The patients were divided into groups treated from July 1998 through January 2000 (n = 174) and from February 2002 through June 2002 (n = 279). In group I, treatment consisted of hypervolemia (central venous pressures: >8 mmHg) and hypertension (mean arterial pressure: 110-130 mmHg). In group II, normovolemia was the goal, defined using a pulmonary artery catheter (wedge pressure: 10-14 mmHg). Cardiac output was enhanced (index: >4.5 L/minute/m2), and blood pressure elevations were moderated (mean pressure: >100 mmHg).

RESULTS

The average age, comorbidity, hemorrhage severity, and incidence of vasospasm were almost identical between the two groups. Statistically significant reductions were noted in patients in group II for two types of complications as well as for mortality. The rate of pulmonary edema (from 14 to 6%) and the rate of sepsis (from 14 to 6%) were both decreased (p <or= 0.03). Mortality decreased from 34 to 29% (p = 0.04). Other complications, such as myocardial infarction, were not affected.

CONCLUSIONS

These data show that a significant reduction in the frequency of pulmonary edema after SAH can be attained using a pulmonary artery catheter-guided hemodynamic management protocol.