The fast flush test measures the dynamic response of the entire blood pressure monitoring system

Blood pressure monitoring following kidney transplantation in children: a comparison of invasive and noninvasive measurements using Doppler as a benchmark technique

BACKGROUND

Blood pressure (BP) monitoring following pediatric kidney transplantation is essential for optimizing graft perfusion. Differences between invasive BP and noninvasive BP (NIBP) measurements are sometimes considerable. We aimed to assess agreement between invasive BP and NIBP in pediatric patients after kidney transplantation and compare with measurements obtained by systolic Doppler with manual sphygmomanometer as a reference technique.

METHODS

A prospective, observational cohort study, of children aged 18 years or younger, admitted immediately following kidney transplantation to the pediatric intensive care unit of a tertiary, university-affiliated medical center, between May 2019 and June 2021.

RESULTS

Eighty-two paired simultaneous measurements of invasive BP, NIBP, and Doppler BP in 18 patients were compared. Patients were significantly hypertensive, with mean systolic NIBP above the 95th percentile (96 ± 6%). Systolic invasive BP measurements were significantly higher than NIBP (149 ± 20 vs. 136 ± 15 mmHg, p < 0.001). Substantial differences (≥ 20 mmHg) were found in 23% (95% CI 15-34%). Similar disagreement was found between systolic invasive and Doppler BP (150 ± 23 and 137 ± 17 mmHg, respectively, p < 0.001). In contrast, systolic NIBP was in good agreement with Doppler BP (135 ± 17 and 138 ± 18, respectively, p = 0.27). A moderate to strong correlation was found between higher systolic invasive BP and the difference to systolic Doppler BP (Spearman's ρ = 0.63, p < 0.001).

CONCLUSIONS

In children immediately following kidney transplantation, clinically significant disagreement was found between invasive and noninvasive BP measurements. Invasive BP values were significantly higher than those obtained by Doppler. Better agreement was found between NIBP and Doppler. These issues should be considered when interpreting BP measurements in this sensitive patient population. A higher resolution version of the Graphical abstract is available as Supplementary information.

Effect of extension tube length on the damping coefficient and natural frequency in normotensive dogs

OBJECTIVE

To establish an acceptable extension tube length (ETL) to measure direct blood pressure (BP) in dogs.

DESIGN

Prospective, experimental study.

SETTING

University-based small animal research facility.

ANIMALS

Eight healthy Beagle dogs: 6 males and 2 females.

INTERVENTIONS

Each extension tube with lengths of 25, 50, 75, 115, 145, 205, and 275 cm were connected after the catheterization with a 22-Ga catheter in the dorsal pedal artery in sternal recumbency. A square wave from the fast-flush test was consecutively recorded 5 times to analyze the system's dynamic response characteristics according to the ETL. After recording the square wave, the ETL was converted to a Latin square. The dynamic response was analyzed using natural frequency (NF) and the damping coefficient (DC), both of which affect the damping factor. The average values of NF and DC were plotted against a graph showing the damping factor. Linear regression was used to evaluate the between-group changes in NF and DC.

MEASUREMENTS AND MAIN RESULTS

The DC gradually increased from 0.21 to 0.29 ξ, and the NF gradually decreased from 38 to 14 Hz according to the increase in ETL (P < 0.05). The dynamic response showed adequate damping with all ETLs.

CONCLUSION

With an increase in ETL, the NF decreased significantly, while the DC demonstrated a less significant change. Therefore, NF had a greater influence on the damping factor of arterial BP measurement. There was no difference between ETLs from 25 to 275 cm lines for measuring BP. An ETL of less than 275 cm is recommended as the damping amount is adequate. Moreover, an ETL less than 275 cm does not meaningfully affect BP measurement in dogs.

Performance of a machine-learning algorithm to predict hypotension in mechanically ventilated patients with COVID-19 admitted to the intensive care unit: a cohort study

The Hypotension Prediction Index (HPI) is a commercially available machine-learning algorithm that provides warnings for impending hypotension, based on real-time arterial waveform analysis. The HPI was developed with arterial waveform data of surgical and intensive care unit (ICU) patients, but has never been externally validated in the latter group. In this study, we evaluated diagnostic ability of the HPI with invasively collected arterial blood pressure data in 41 patients with COVID-19 admitted to the ICU for mechanical ventilation. Predictive ability was evaluated at HPI thresholds from 0 to 100, at incremental intervals of 5. After exceeding the studied threshold, the next 20 min were screened for positive (mean arterial pressure (MAP) < 65 mmHg for at least 1 min) or negative (absence of MAP < 65 mmHg for at least 1 min) events. Subsequently, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and time to event were determined for every threshold. Almost all patients (93%) experienced at least one hypotensive event. Median number of events was 21 [7–54] and time spent in hypotension was 114 min [20–303]. The optimal threshold was 90, with a sensitivity of 0.91 (95% confidence interval 0.81–0.98), specificity of 0.87 (0.81–0.92), PPV of 0.69 (0.61–0.77), NPV of 0.99 (0.97–1.00), and median time to event of 3.93 min (3.72–4.15). Discrimination ability of the HPI was excellent, with an area under the curve of 0.95 (0.93–0.97). This validation study shows that the HPI correctly predicts hypotension in mechanically ventilated COVID-19 patients in the ICU, and provides a basis for future studies to assess whether hypotension can be reduced in ICU patients using this algorithm.

Evaluation of the agreement of two oscillometric blood pressure devices with invasive blood pressure in anaesthetized chimpanzees (Pan troglodytes)

OBJECTIVE

To evaluate the agreement of two noninvasive blood pressure devices: a human device with the cuff placed on the wrist (Omron R1) and a veterinary device with the cuff placed on the upper brachium (Surgivet Advisor Vital Signs Monitor) with invasive blood pressure (IBP) measurement in anaesthetized chimpanzees.

STUDY DESIGN

Prospective clinical study.

ANIMALS

A convenience sample of 11 adult chimpanzees undergoing anaesthesia for translocation and routine health checks.

METHODS

Systolic (SAP) and diastolic arterial pressures (DAP) were continuously recorded via a transducer connected to a femoral artery cannula, and at 5 minute intervals from the two oscillometric devices. Agreement was explored using Bland-Altman analysis and bias defined as the mean difference between the two measurement methods. Spearman correlation coefficients were calculated. Significance was set at p < 0.05.

RESULTS

Bias and standard deviation for the Surgivet compared with IBP were 8.6 ± 18 for SAP and 8.4 ± 9.9 for DAP, showing a significant underestimation of both variables. Limits of agreement (LOA) were from -27 to 44 for SAP and from -11 to 28 for DAP. Correlation coefficients between the Surgivet and IBP values were 0.86 for SAP and 0.85 for DAP (p < 0.0001). Bias and standard deviation for the Omron compared with the IBP were -21 ± 25 for SAP and -18 ± 15 for DAP, showing a significant overestimation of both variables. LOA were from -70 to -28 for SAP and from -47 to 11 for DAP. Spearman correlation coefficients between the Omron and IBP values were 0.64 for SAP and 0.72 for DAP (p < 0.0001).

CONCLUSIONS AND CLINICAL RELEVANCE

Although neither device met all the criteria for device validation, the Surgivet presented better agreement with IBP values than the Omron in adult anaesthetized chimpanzees.

A DESCRIPTION OF ARTERIAL BLOOD PRESSURE MEASUREMENT IN TWO SPECIES OF FLYING FOXES (PTEROPUS VAMPYRUS AND PTEROPUS HYPOMELANUS)

Blood pressure assessment is valuable during management of chronic conditions with increased risk of developing hypertension and as a standard practice for anesthetic monitoring. Normal arterial blood pressure values have not been well described in megachiropteran species. Following anesthetic induction and maintenance with isoflurane in oxygen, arterial blood pressure was obtained from the posterior tibial artery of eight large flying foxes (Pteropus vampyrus) and six variable flying foxes (Pteropus hypomelanus), two with structural cardiac disease and four in good clinically health. Normal values reported as a median with interquartile range for systolic, diastolic, and mean (MAP) arterial pressures for P. vampyrus were 101 (94, 107), 69 (57, 80), and 86 (75, 93), respectively. Normal MAP for clinically healthy P. hypomelanus was 86 (67, 93). Placement of P. hypomelanus in a vertical head-down position did not alter blood pressure in clinically healthy bats, but significantly increased MAP in two bats with structural cardiac disease. Arterial catheterization of both the posterior tibial and median arteries in these species was easily performed without major complication.

The knowledge and practice of maintaining the patency of arterial catheters

BACKGROUND

Maintaining the patency of arterial catheters-routinely inserted in critically ill patients in intensive care units (ICUs)-is essential for obtaining physiological measurements and enabling blood sampling.

AIM

This study aims to evaluate current ICU nurse knowledge and practice of maintaining the patency of arterial catheters and explore the factors that influence nurses' knowledge level.

DESIGN

This was a cross-sectional survey conducted in China.

METHODS

This research was conducted in 20 tertiary hospitals in Beijing, China between March and June 2020. The data were collected by electronic questionnaire, which was designed in accordance with the literature and consisted of 28 questions. Descriptive and inferential statistics were used to analyse the data.

RESULTS

A total of 576 completed questionnaires were returned. The mean score of nurses' knowledges was 3.66 ± 1.35, which is a moderate level. There was a statistically significant difference between the mean scores of nurses with different professional titles and work experiences (mean 3.58 vs 4.04/7; mean 3.50 vs 3.58 vs 3.94/7). Considering ICU nurses' practice of maintaining the patency of arterial catheters, 376(65.3%)nurses replaced the pressure transducer as per the manual, and 347 (60.2%) nurses zeroed the pressure transducer once per shift. More than 90% ICU nurses aligned the transducer with the heart surface marker during zeroing procedures. Furthermore, 79.9% of nurses performed fast-flush tests routinely, 459 (85.9%) nurses flushed the arterial catheter routinely, and 80% of nurses evaluated the patency of the arterial catheter every shift.

CONCLUSIONS

This study found that the practices of ICU nurses varied, and their knowledge of how to maintain the patency of arterial catheters was moderate and could be improved. ICU nurses should be trained effectively to develop a unified standard of arterial catheter management.

RELEVANCE TO CLINICAL PRACTICE

Training programmes on arterial catheter management for ICU nurses are essential for improving knowledge and practice.

Intraarterial catheter diameter and dynamic response of arterial pressure monitoring system: a randomized controlled trial

The dynamic response (DR) of the arterial pressure monitoring system (APMS) may depend on the intraarterial catheter (IAC) diameter. We hypothesized that adequate DR would be more common when using a smaller IAC. We compared the DR of the AMPS (Auto Transducer™) between three IACs (BD Angiocath Plus™) with different diameters. 353 neurosurgical patients were randomized into three groups undergoing catheterization with a 20-, 22-, or 24-gauge IAC: 20G (n = 119), 22G (n = 117), and 24G (n = 117) groups, respectively. The DR, which depends on the natural frequency and damping coefficient, was divided into four types: adequate (primary outcome measure), underdamped, overdamped, and unacceptable. The frequency of intraoperative IAC malfunction was noted. Adequate DR was observed more frequently in the 22G and 24G groups than the 20G group (13.7% and 15.4% vs. 4.2%, P = 0.011 and 0.004, respectively). The frequency of underdamped DR was higher in the 20G group than the 24G group (86.6% vs. 69.2%, P = 0.001), whereas overdamped DR was more frequent in the 24G group than the 20G and 22G groups (6.0% vs. 0.0% and 0.0%, P = 0.007 and 0.014, respectively). IAC malfunctioned more frequently during surgery in the 24G group than the 20G and 22G groups (15.4% vs. 0.0% and 1.7%, P < 0.001 and P < 0.001, respectively). The frequency of adequate DR was low regardless of the IAC diameter. Nonetheless, in terms of DR and IAC malfunction, a 22-gauge BD Angiocath Plus™ was more suitable for invasive blood pressure monitoring with Auto Transducer™ than a 20- or 24-gauge BD Angiocath Plus™. Registration Registry: ClinicalTrials.gov. Registration number: NCT03642756. Date of Registration: July 27, 2018.

Heparinized Saline Solution vs. Saline Solution (0.9% Sodium Chloride) for the Maintenance of Dorsal Pedal Arterial Catheter Patency in Dogs Undergoing General Anesthesia: A Pilot Study

Heparin is widely used as an anticoagulant solution for maintaining arterial catheter patency. In humans, increasing evidence suggests that heparinized saline solution (HS) has no advantages over a saline (0.9% sodium chloride) solution (SS) in maintaining arterial catheter patency. To date, no studies have been conducted on the effectiveness of these solutions at maintaining arterial catheter patency in veterinary medicine. The objective of this pilot study was to determine the feasibility of a study and to report the treatment efficacy comparing HS and SS for the maintenance of the dorsal pedal arterial catheter patency during direct arterial blood pressure measurements in anesthetized dogs. Client-owned dogs undergoing abdominal surgery were allocated to two groups to receive either a continuous infusion of HS or SS through the dorsal pedal artery, and the arterial pressure waveform was monitored during general anesthesia. Our feasibility outcomes included the proportion of the screened veterinary patients that completed the study and the success rate of arterial catheter placement. The clinical outcomes were assessed by the number of catheter-flushing procedures, occlusion rate, the duration of the initial catheter-flushing procedures, and the duration of catheter occlusion. Of the 51 dogs screened, 41 (80.4%) completed the study. The success rate of arterial catheter placement in the HS and SS groups were 87.5 and 80.0%, respectively. There were no differences in the number of catheter-flushing procedures and occlusion rate between groups (28.6 vs. 20.0%, relative risk [RR]: 1.429, 95% confidence interval [CI]: 0.472–4.323, P = 0.719 and 14.3 vs. 15.0%, RR: 0.952, 95% CI: 0.217–4.179, P = 1.000, respectively). No differences were found in the probability of time to the initial catheter-flushing procedure and occlusion between groups assessed by the Kaplan-Meier method (P = 0.546 and P = 0.867, respectively). This study revealed the feasibility of a study comparing HS and SS for dorsal pedal arterial catheter patency during direct arterial blood pressure measurements in anesthetized dogs. Clinical outcome analyses were underpowered and thus, could not determine the meaningful differences in treatment efficacy between the groups. However, the information gained from this study provides insight for future study designs.

Assessment of a commercially available veterinary blood pressure device used on awake and anesthetized dogs

OBJECTIVE

To compare results of a commercially available device for oscillometrically measured blood pressure (OBP) with invasively measured blood pressure (IBP) in awake and anesthetized dogs.

ANIMALS

19 adult dogs (mean ± SD body weight, 17.8 ± 7.5 kg).

PROCEDURES

Blood pressures were measured in dogs while they were awake and anesthetized with isoflurane. The OBP was recorded on a thoracic limb, and IBP was simultaneously recorded from the median caudal artery. Agreement between OBP and IBP was evaluated with the Bland-Altman method. Guidelines of the American College of Veterinary Internal Medicine (ACVIM) were used for validation of the oscillometric device.

RESULTS

In awake dogs, mean bias of the oscillometric device was -11.12 mm Hg (95% limits of agreement [LOA], -61.14 to 38.90 mm Hg) for systolic arterial blood pressure (SAP), 9.39 mm Hg (LOA, -28.26 to 47.04 mm Hg) for diastolic arterial blood pressure (DAP), and -0.85 mm Hg (LOA, -40.54 to 38.84 mm Hg) for mean arterial blood pressure (MAP). In anesthetized dogs, mean bias was -12.27 mm Hg (LOA, -47.36 to 22.82 mm Hg) for SAP, -3.92 mm Hg (LOA, -25.28 to 17.44 mm Hg) for DAP, and -7.89 mm Hg (LOA, -32.31 to 16.53 mm Hg) for MAP. The oscillometric device did not fulfill ACVIM guidelines for the validation of such devices.

CONCLUSIONS AND CLINICAL RELEVANCE

Agreement between OBP and IBP results for awake and anesthetized dogs was poor. The oscillometric blood pressure device did not fulfill ACVIM guidelines for validation. Therefore, clinical use of this device cannot be recommended.

Estimation of central arterial pressure from the radial artery in patients undergoing invasive neuroradiological procedures

Backgrounds

Central arterial pressure can be derived from analysis of the peripheral artery waveform. The aim of this study was to compare central arterial pressures measured from an intra-aortic catheter with peripheral radial arterial pressures and with central arterial pressures estimated from the peripheral pressure wave using a pressure recording analytical method (PRAM).

Methods

We studied 21 patients undergoing digital subtraction cerebral angiography under local or general anesthesia and equipped with a radial arterial catheter. A second catheter was placed in the ascending aorta for central pressure wave acquisition. Central (AO) and peripheral (RA) arterial waveforms were recorded simultaneously by PRAM for 90–180 s. During an off-line analysis, AO pressures were reconstructed (AO_rec) from the RA trace using a mathematical model obtained by multi-linear regression analysis. The AO_rec values obtained by PRAM were compared with the true central pressure value obtained from the catheter placed in the ascending aorta.

Results

Systolic, diastolic and mean pressures ranged from 79 to 180 mmHg, 47 to 102 mmHg, and 58 to 128 mmHg, respectively, for AO, and 83 to 174 mmHg, 47 to 107 mmHg, and 60 to 129 mmHg, respectively, for RA. The correlation coefficients between AO and RA were 0.86 (p < 0.01), 0.83 (p < 0.01) and 0.86 (p < 0.01) for systolic, diastolic and mean pressures, respectively, and the mean differences − 0.3 mmHg, 2.4 mmHg and 1.5 mmHg. The correlation coefficients between AO and AO_rec were 0.92 (p < 0.001), 0.87 (p < 0.001) and 0.92 (p < 0.001), for systolic, diastolic and mean pressures, respectively, and the mean differences 0.01 mmHg, 1.8 mmHg and 1.2 mmHg.

Conclusions

PRAM can provide reliable estimates of central arterial pressure.

Electronic supplementary material

The online version of this article (10.1186/s12871-019-0844-1) contains supplementary material, which is available to authorized users.

Comparison of pulse pressure variation and pleth variability index in the prone position in pediatric patients under 2 years old

Background

The assessment of intravascular volume status is very important especially in children during anesthesia. Pulse pressure variation (PPV) and pleth variability index (PVI) are well known parameters for assessing intravascular volume status and fluid responsiveness. We compared PPV and PVI for children aged less than two years who underwent surgery in the prone position.

Methods

A total of 27 children were enrolled. We measured PPV and PVI at the same limb during surgery before and after changing the patients’ position from supine to prone. We then compared PPV and PVI at each period using Bland-Altman plot for bias between the two parameters and for any correlation. We also examined the difference between before and after the position change for each parameter, along with peak inspiratory pressure, heart rate and mean blood pressure.

Results

The bias between PPV and PVI was −2.2% with a 95% limits of agreement of −18.8% to 14.5%, not showing significant correlation at any period. Both PPV and PVI showed no significant difference before and after the position change.

Conclusions

No significant correlation between PVI and PPV was observed in children undergoing surgery in the prone position. Further studies relating PVI, PPV, and fluid responsiveness via adequate cardiac output estimation in children aged less than 2 years are required.

Noninvasive continuous arterial pressure monitoring with Clearsight during awake carotid endarterectomy: A prospective observational study

BACKGROUND

Continuous noninvasive blood pressure (CNBP) measurement using the volume-clamp method is a less invasive alternative compared with invasive intra-arterial monitoring for awake patients during carotid endarterectomy (CEA) under regional anaesthesia.

OBJECTIVE

We investigated the agreement of blood pressure (BP) recorded with invasive and CNBP methods during awake CEA.

DESIGN

A prospective observational study for assessing agreement with Bland-Altman plots, agreement-tolerability indices (ATI), concordance and interchangeability.

SETTING

Azienda Ospedaliera Universitaria G. Martino, Messina, a University tertiary referral centre in Italy.

PATIENTS

In 30 consecutive patients, we recorded continuously ipsilateral invasive and noninvasive BPs, from 3 min before carotid cross-clamping to 5 min after unclamping.

MAIN OUTCOME MEASURES

Primary outcome was bias, 95% limits of agreement, ATI, concordance and interchangeability for mean arterial pressure (MAP). Secondary outcomes were agreements for systolic arterial pressure and diastolic arterial pressure. Tracking of changes was assessed with four-quadrant polar plots and the trend interchangeability method. Optimal bias was defined as 5 mmHg or less.

RESULTS

A total of 2672 invasive and CNBP paired measurements (93% of overall data) were analysed, with a median of 92 readings per patient [IQR 76 to 100]. Mean (SD) bias for MAP, systolic arterial pressure and DAP were -6.8 (6.7), -3.0 (9.7) and -9.0 (5.4) mmHg, respectively. The ATIs were 0.88, 0.95 and 0.71, respectively, where ATI of 1.0 or less and at least 2.0 defined acceptable, marginal and unacceptable agreements. The four-quadrant plot analysis for beat-to-beat differences showed concordance rates of 97.3%, 99.98% and 96.4%, respectively. Polar plot analysis showed 95% limits of agreement of -3 to 3, -2 to 2 and -2 to 2 mmHg respectively. Trend interchangeability method showed an interchangeability rate of 95% for MAP.

CONCLUSION

During CEA performed under regional anaesthesia, CNBP offers a less invasive approach for BP monitoring. We found acceptable agreement for MAP defined by an ATI of 0.88 and an excellent 95% global interchangeability rate. A suboptimal bias of 7 mmHg was found with CNBP for MAP.

Impact of intravascular thrombosis on failure of radial arterial catheters in critically ill patients: a nested case-control study

PURPOSE

The patency of arterial catheters is essential for reliable invasive blood pressure monitoring. We sought to determine whether radial catheter failures were associated with intravascular thrombosis in critically ill adult patients.

METHODS

This unmatched case-control study was conducted within a prospective cohort of patients admitted to an intensive care unit. The arterial catheter failure was the main outcome, which identified cases. Controls were patients with patent catheter until removal or 28 days of follow-up. The prevalence of intravascular thrombosis in cases and controls was determined by ultrasonography of the cannulated radial artery. Assessors were blinded to clinical findings. Failing catheters were removed and examined microscopically.

RESULTS

Catheter failures occurred in 25.5% of 200 patients during 584 catheter-days (incidence rate, 87/1000 catheter-days). The median patency duration was 13.1 days. An intravascular thrombosis located in front of the catheter tip was diagnosed in 42 of 50 cases (84.0%) and 24 of 139 controls (17.3%). In multivariable logistic regression analysis, the probability of catheter failure was higher in patients with intravascular thrombosis [odds ratio (OR), 36.52; 95% confidence interval (CI), 12.86-103.74] and females (OR, 3.45; 95% CI 1.32-9.05), increased proportionally to arterial blood sampling frequency (OR, 1.20; 95% CI 1.04-1.38), and decreased in thrombocytopenia (OR, 0.28; 95% CI 0.10-0.78). After removal, 15.7% of failing catheters had some luminal fibrin deposits, but none were occluded.

CONCLUSIONS

Most failing radial arterial catheters had no luminal obstruction, but were associated with an intravascular thrombosis. Among predictive factors, arterial blood sampling frequency is the most susceptible to intervention.

Cardiac Output Monitoring by Pulse Contour Analysis, the Technical Basics of Less-Invasive Techniques

Routine use of cardiac output (CO) monitoring became available with the introduction of the pulmonary artery catheter into clinical practice. Since then, several systems have been developed that allow for a less-invasive CO monitoring. The so-called “non-calibrated pulse contour systems” (PCS) estimate CO based on pulse contour analysis of the arterial waveform, as determined by means of an arterial catheter without additional calibration. The transformation of the arterial waveform signal as a pressure measurement to a CO as a volume per time parameter requires a concise knowledge of the dynamic characteristics of the arterial vasculature. These characteristics cannot be measured non-invasively and must be estimated. Of the four commercially available systems, three use internal databases or nomograms based on patients’ demographic parameters and one uses a complex calculation to derive the necessary parameters from small oscillations of the arterial waveform that change with altered arterial dynamic characteristics. The operator must ensure that the arterial waveform is neither over- nor under-dampened. A fast-flush test of the catheter–transducer system allows for the evaluation of the dynamic response characteristics of the system and its dampening characteristics. Limitations to PCS must be acknowledged, i.e., in intra-aortic balloon-pump therapy or in states of low- or high-systemic vascular resistance where the accuracy is limited. Nevertheless, it has been shown that a perioperative algorithm-based use of PCS may reduce complications. When considering the method of operation and the limitations, the PCS are a helpful component in the armamentarium of the critical care physician.

Facile Fabrication of Binary Nanoscale Interface for No-Loss Microdroplet Transportation

Binary nanoscale interfacial materials are fundamental issues in many applications for smart surfaces. A binary nanoscale interface with binary surface morphology and binary wetting behaviors has been prepared by a facile wet-chemical method. The prepared surface presents superhydrophobicity and high adhesion with the droplet at the same time. The composition, surface morphology, and wetting behaviors of the prepared surface have been systematic studied. The special wetting behaviors can be contributed to the binary nanoscale effect. The stability of the prepared surface was also investigated. As a primary application, a facile device based on the prepared binary nanoscale interface with superhydrophobicity and high adhesion was constructed for microdroplet transportation.

Blood pressure monitoring during arrhythmia: agreement between automated brachial cuff and intra-arterial measurements

BACKGROUND

Since arrhythmia induces irregular pulse waves, it is widely considered to cause flawed oscillometric brachial cuff measurements of blood pressure (BP). However, strong data are lacking. We assessed whether the agreement of oscillometric measurements with intra-arterial measurements is worse during arrhythmia than during regular rhythm.

METHODS

Among patients of three intensive care units (ICUs), a prospective comparison of three pairs of intra-arterial and oscillometric BP readings was performed among patients with arrhythmia and an arterial line already present. After each inclusion in the arrhythmia group, one patient with regular rhythm was included as a control. International Organization for Standardization (ISO) standard validation required a mean bias <5 (sd 8) mm Hg.

RESULTS

In 135 patients with arrhythmia, the agreement between oscillometric and intra-arterial measurements of systolic, diastolic and mean BP was similar to that observed in 136 patients with regular rhythm: for mean BP, similar mean bias [-0.1 (sd 5.2) and 1.9 (sd 5.9) mm Hg]. In both groups, the ISO standard was satisfied for mean and diastolic BP, but not for systolic BP (sd >10 mm Hg) in our ICU population. The ability of oscillometry to detect hypotension (systolic BP <90 mm Hg or mean BP <65 mm Hg), response to therapy (>10% increase in mean BP after cardiovascular intervention) and hypertension (systolic BP >140 mm Hg) was good and similar during arrhythmia and regular rhythm (respective areas under the receiver operating characteristic curves ranging from 0.89 to 0.96, arrhythmia vs regular rhythm between-group comparisons all associated with P>0.3).

CONCLUSIONS

Contrary to widespread belief, arrhythmia did not cause flawed automated brachial cuff measurements.

Resonance artefacts in modern pressure monitoring systems

Resonance in pressure monitoring catheters is a well-known problem which was studied several years ago. Current piezoelectric devices have mechanical properties providing a resonance frequency and damping factor that theoretically assure resonance-free data. However, in particular cases, the coupling between the device, the catheter, and the vascular compliance of the patient could introduce artefacts in clinical settings leading to wrong pressure waveforms and values displayed in the monitor. In this research work we study a laboratory model of a clinical setting to evaluate in which cases the compound (catheter and device) could cause resonances in an unacceptable range. The classical pop-test is expanded for analysing the effect of the catheter. Results indicate that the presence of different catheters may alter significantly the acquired signal, up to an unacceptable level. Particular care should be used in the selection of the appropriate catheter. In particular, smaller diameters introduce higher damping coefficient that could help in avoiding undesired oscillations.

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

We know that a 10 cm departure from the reference level of pressure transducer position is equal to a 7.5 mmHg change of invasive hemodynamic pressure monitoring in a fluid-filled system. However, the relationship between the site level of a variable arterial pressure transducer and the pulse contour-derived parameters has yet to be established in critically ill patients. Moreover, the related quantitative analysis has never been investigated. Forty-two critically ill patients requiring PiCCO-Plus cardiac output monitoring were prospectively studied. The phlebostatic axis was defined as the zero reference level; the arterial pressure transducer was then vertically adjusted to different positions (+5, +10, +15, +20, -20, -15, -10, -5 cm) of departure from the zero reference site. The pulse contour waveform-derived parameters were recorded at each position. Elevation of the pressure transducer caused significantly positive changes in the continuous cardiac index (+CCI), stroke volume index (+SVI), and stroke volume variation (+SVV), and negative changes in the rate of left ventricular pressure rise during systole (-dP/dtmax), the systemic vascular resistance index (-SVRI), and vice versa. At the 5 cm position, the SVRI changes reached statistical significance with error. At the 10 cm position, the changes in CCI and dP/dtmax reached statistical significance with error, while the change in SVV reached statistical significance at 15 cm. The change rate of CCI was more than 5 % at the 15 cm position and approximately 10 % at the 20 cm position. On average, for every centimeter change of the transducer, there was a corresponding 0.014 L/min/m(2) CCI change and 0.36 % change rate, a 1.41 mmHg/s dP/dtmax change and 0.13 % change rate, and a 25 dyne/s/cm(5) SVRI change and 1.2 % change rate. The variation of arterial transducer position can result in inaccurate measurement of pulse contour waveform-derived parameters, especially when the transducer's vertical distance is more than 10 cm from the phlebostatic axis. These findings have clinical implications for continuous hemodynamic monitoring.

Comparison of directly measured arterial blood pressure at various anatomic locations in anesthetized dogs

OBJECTIVE

To determine whether directly measured arterial blood pressure differs among anatomic locations and whether arterial blood pressure is influenced by body position.

ANIMALS

33 client-owned dogs undergoing anesthesia.

PROCEDURES

Dogs undergoing anesthetic procedures had 20-gauge catheters placed in both the superficial palmar arch and the contralateral dorsal pedal artery (group 1 [n = 20]) or the superficial palmar arch and median sacral artery (group 2 [13]). Dogs were positioned in dorsal recumbency, and mean arterial blood pressure (MAP), systolic arterial blood pressure (SAP), and diastolic arterial blood pressure (DAP) were recorded for both arteries 4 times (2-minute interval between successive measurements). Dogs were positioned in right lateral recumbency, and blood pressure measurements were repeated.

RESULTS

Differences were detected between pressures measured at the 2 arterial sites in both groups. This was especially true for SAP measurements in group 1, in which hind limb measurements were a mean of 16.12 mm Hg higher than carpus measurements when dogs were in dorsal recumbency and 14.70 mm Hg higher than carpus measurements when dogs were in lateral recumbency. Also, there was significant dispersion about the mean for all SAP, DAP, and MAP measurements.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that arterial blood pressures may be dependent on anatomic location and body position. Because this may affect outcomes of studies conducted to validate indirect blood pressure measurement systems, care must be used when developing future studies or interpreting previous results.

Comparison of a continuous noninvasive arterial pressure device with invasive measurements in cardiovascular postsurgical intensive care patients: a prospective observational study

BACKGROUND

Arterial pressure monitoring using the a continuous noninvasive arterial pressure (CNAP) device during general anaesthesia is known to be interchangeable with continuous invasive arterial pressure (CIAP) monitoring. Agreement with invasive measurements in cardiovascular postsurgical intensive care patients has not been assessed.

OBJECTIVE

The objective of this study is to assess the agreement and interchangeability of CNAP with CIAP in cardiovascular postsurgical patients and to determine the effects of cardiac arrhythmia, catecholamine dosage, respiratory weaning and calibration intervals on agreement.

DESIGN

A prospective observational study.

SETTING

German university hospital cardiovascular ICU. Data were collected from April 2010 to December 2011.

PATIENTS

From 110 enrolled patients, 104 were included. Inclusion criteria were American Society of Anaesthesiologists (ASA) physical status III or IV patients undergoing controlled ventilation. Exclusion criteria included emergencies, complete heart block and marked arterial pressure differences greater than 10 mmHg in the two arms.

MAIN OUTCOME MEASURES

Bland-Altman plots, bias, precision, 95% limits of agreement, percentage error and agreement : tolerability indexes (ATIs) were estimated to determine clinical agreement.

RESULTS

From 11 222 arterial pressure readings, biases (SD) for CIAP-CNAP for systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and mean arterial pressure (MAP) for all patients were 4.3 (11.6), -9.4 (8) and -6 (7.6) mmHg, respectively. Cardiac arrhythmia (4.1 (13.1), -14.4 (8.3), -9.5 (8.9) mmHg) and long interval to last calibration [4.5 (15), -9.8 (9.5), -6.4 (9.1) mmHg] impaired the accuracy of CNAP with failed interchangeability criteria defined by the percentage error. In contrast, use of catecholamines (epinephrine or norepinephrine infusions >0.1 μg kg min), short calibration intervals and weaning conditions did not affect accuracy, interchangeability and agreement, especially of MAP. Agreement was defined as acceptable for MAP for all data and subgroups (ATI 0.8 to 1.0) and at worst, marginal for SAP and DAP (ATI 0.9 to 1.6).

CONCLUSION

CNAP showed acceptable agreement defined by the ATI with invasive measurements for MAP and partially for DAP, but there was considerable variability for SAP. MAP should be preferred for clinical decision making. Cardiac arrhythmia, in contrast to catecholamine dosage or weaning procedures, impaired the accuracy, agreement and interchangeability of CNAP.

TRIAL REGISTRATION

Clinical trials.gov identifier NCT01003665.

Facile fabrication of a flower-like CuO/Cu(OH)2 nanorod film with tunable wetting transition and excellent stability

The digital CA images and the SEM images of the prepared flower-like nanorods surface (A) before and (B) after modification by myristic acid, and (C) after annealing at 200 °C; (D) the schematic of the wetting behavior transition.

Effects of 8 hemodynamic conditions on direct blood pressure values obtained simultaneously from the carotid, femoral and dorsal pedal arteries in dogs

OBJECTIVES

This study aimed to evaluate the effect of 8 hemodynamic conditions on blood pressure measurements taken from the carotid, femoral and dorsal pedal arteries of dogs.

ANIMALS

Six healthy dogs.

METHODS

During isoflurane anesthesia, catheters were introduced into the carotid, femoral and dorsal pedal arteries of dogs to allow simultaneous monitoring of direct blood pressure in each artery. The dogs were submitted to 8 hemodynamic conditions induced by combining changes in heart rate (bradycardia, normocardia, tachycardia) with changes in blood pressure (hypotension, normotension, hypertension). Values obtained from each arterial catheter were compared and agreement between central (carotid) and peripheral (femoral and dorsal pedal) values were analyzed by the Bland-Altman method.

RESULTS

During hypotensive conditions, systolic arterial pressure (SAP) was lower in the femoral and dorsal pedal arteries compared to the carotid artery whereas during normotensive and hypertensive conditions, SAP was higher in peripheral arteries. During hypotensive states, increases in heart rate resulted in greater bias between central and peripheral SAP whereas during normotensive states, the bias decreased as heart rate increased. Mean and diastolic arterial pressures were lower in the femoral and dorsal pedal arteries than in the carotid artery during most hemodynamic conditions.

CONCLUSIONS

In healthy anesthetized dogs, invasive blood pressure measurements in peripheral arteries may differ significantly from measurements in a central artery. The greatest differences were observed in SAP and the magnitude of differences between central and peripheral blood pressure measurements varied according to the dog's hemodynamic condition.

Effect of systemic α1-adrenergic receptor blockade on central blood pressure response during exercise

The aortic pulse pressure (PP), which consists mainly of the incident wave and the reflected wave, has emerged as an important property of systemic blood vessels underlying the pathophysiology of cardiovascular disease. To determine the role of sympathetic nerve activity on the aortic PP response during dynamic exercise, we evaluated aortic hemodynamics during the right-leg knee-extension (40 and 60 % of maximal voluntary contraction) in six young adults with and without the systemic α1-adrenergic receptor blockade using prazosin (1 mg/20 kg body weight). The use of prazosin attenuated the exercise-induced increase in aortic PP (P < 0.05) but not in radial arterial PP. The amplitude of the reflected waves (via augmentation index) significantly decreased with the exercise and decreased more with the use of prazosin. These results suggest that during dynamic exercise the α1-adrenergic-mediated vasoconstrictor tone of the peripheral resistance vessels is manifestly involved in the magnitude of the reflected wave and the modulation of the aortic PP responses.

Measuring the level of agreement between directly measured blood pressure and pressure readings obtained with a veterinary-specific oscillometric unit in anesthetized dogs

OBJECTIVE

To determine if an oscillometric device optimized for use in dogs produces systolic, diastolic, and mean arterial pressures (MAPs) measurements that are in good agreement with directly obtained pressures

DESIGN

Prospective study.

SETTING

University teaching hospital.

ANIMALS

Twenty-one dogs under general anesthesia for surgical procedures.

INTERVENTIONS

A 20-Ga catheter was placed into the dorsal pedal artery and systolic, diastolic, and MAPs were directly measured using a validated blood pressure measurement system. Indirect blood pressure measurements were collected using a widely available veterinary oscillometric blood pressure unit. Results obtained by the 2 methods were then compared.

MEASUREMENTS AND MAIN RESULTS

Agreement between the directly and indirectly measured pressure demonstrated a bias of 9.9 mm Hg and limits of agreement (LOA) 73.7 to -53.9, a bias of -8.9 mm Hg and LOA 23.3 to -41.2, and a bias of -6.3 mm Hg and LOA 28.2 to -40.8 for systolic, diastolic, and MAP, respectively.

CONCLUSIONS

There was poor agreement between the direct and indirect measured blood pressure measurement systems. Therefore, use of the oscillometric blood pressure unit evaluated in this study for monitoring patients under anesthesia cannot be recommended at this time.

Agreement between directly measured blood pressure and pressures obtained with three veterinary-specific oscillometric units in cats

OBJECTIVE

To determine whether veterinary-specific oscillometric blood pressure units yield measurements that are in good agreement with directly measured blood pressures in cats.

DESIGN

Evaluation study.

ANIMALS

21 cats undergoing routine spaying or neutering.

PROCEDURES

A 24-gauge catheter was inserted in a dorsal pedal artery, and systolic, diastolic, and mean arterial pressures were directly measured with a validated pressure measurement system. Values were compared with indirect blood pressure measurements obtained with 3 veterinary-specific oscillometric blood pressure units.

RESULTS

There was poor agreement between indirectly and directly measured blood pressures. For unit 1, bias between indirectly and directly measured values was -14.9 mm Hg (95% limits of agreement [LOA], -52.2 to 22.4 mm Hg), 4.4 mm Hg (95% LOA, -26.0 to 34.8 mm Hg), and -1.3 mm Hg (95% LOA, -26.7 to 24.1 mm Hg) for systolic, diastolic, and mean arterial pressures, respectively. For unit 2, bias was -10.3 mm Hg (95% LOA, -52.9 to 32.2 mm Hg), 13.0 mm Hg (95% LOA, -32.1 to 58.0 mm Hg), and 9.1 mm Hg (95% LOA, -32.9 to 51.2 mm Hg) for systolic, diastolic, and mean arterial pressures, respectively. For unit 3, bias was -13.4 mm Hg (95% LOA, -51.8 to 25.1 mm Hg), 8.0 mm Hg (95% LOA, -25.5 to 41.6 mm Hg), and -3.6 mm Hg (95% LOA, -31.6 to 24.5 mm Hg) for systolic, diastolic, and mean arterial pressures, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that none of the 3 veterinary-specific oscillometric blood pressure units could be recommended for indirect measurement of blood pressure in cats.

The mean prehospital machine; accurate prehospital non-invasive blood pressure measurement in the critically ill patient

OBJECTIVE

Non-invasive blood pressure recordings may be inaccurate in the critically ill patient and measurement difficulties are intensified in the prehospital setting. This may adversely impact upon outcomes for many critically ill patients, particularly those with traumatic brain injury and/or lengthy prehospital times. This study aimed to validate a non-invasive, oscillometric, ambulatory blood pressure measuring device, the Oscar 2, Model 222 (SunTech Medical, Morrisville, USA) during the ambulance transport of critically ill patients.

METHODS

We have previously shown that mean arterial blood pressures observed by Intensive Care Unit nurses from a patient monitor can be considered interchangeable with reference intra-arterial integrated mean pressures. In the current study, we compared non-invasive device mean pressures to intra-arterial pressures observed by retrieval nurses from the patient monitor, during the ambulance transportation of critically ill patients. Device performance was required to fulfil the Association for the Advancement of Medical Instrumentation (AAMI) protocol requirements. Additionally, linear mixed effects analyses and Bland-Altman comparisons were undertaken.

RESULTS

For 157 measurements recorded from 23 patients, when the Oscar 2 did not indicate a measurement was associated with a fault, the device fulfilled the AAMI protocol requirements, with a mean error of -1.1 mmHg (standard deviation 7.8 mmHg), 95% confidence intervals (linear mixed effects analysis) -2.9, 0.8; P = 0.26. Bland-Altman plots indicated uniform agreement across a wide range of blood pressures. Sixteen percent of recordings were associated with a patient, environment, or device generated fault.

CONCLUSIONS

When the Oscar 2 does not indicate a fault has occurred, clinicians may be confident the mean pressure, within acceptable limits, is accurate, even during ambulance motion, administration of high doses of vasopressors and mechanical ventilation. The Oscar 2 appears to be an accurate and rugged out-of-hospital device.

Validation of arterial blood pressures observed from the patient monitor; a tool for prehospital research

OBJECTIVES

For some time, the inaccuracies of non-invasive blood pressure measurement in critically ill patients have been recognised. Measurement difficulties can occur even in optimal conditions, but in prehospital transportation vehicles, problems are exacerbated. Intra-arterial pressures must be used as the reference against which to compare the performance of non-invasive methods in the critically ill patient population. Intra-arterial manometer data observed from the patient monitor has frequently been used as the reference against which to assess the accuracy of noninvasive devices in the emergency setting. To test this method's validity, this study aimed to determine whether numerical monitor pressures can be considered interchangeable with independently sampled intra-arterial pressures.

METHODS

Intensive Care Unit nurses were asked to document arterial systolic, diastolic and mean pressures numerically displayed on the patient monitor. Observed pressures were compared to reference intra-arterial pressures independently recorded to a computer following analogue to digital conversion. Differences between observed and recorded pressures were evaluated using the Association for the Advancement of Medical Instrumentation (AAMI) protocol. Additionally, two-level linear mixed effects analyses and Bland-Altman comparisons were undertaken.

RESULTS

Systolic, diastolic and integrated mean pressures observed during 60 data collection sessions (n = 600) fulfilled AAMI protocol criteria. Integrated mean pressures were the most robust. For these pressures, mean error (reference minus observed) was 0.5 mm Hg (SD 1.4 mm Hg); 95% CI (two-level linear mixed effects analysis) 0.4-0.6 mm Hg; P < 0.001. Bland-Altman plots demonstrated tight 95% limits of agreement (-2.3 to 3.2 mm Hg), and uniform agreement across the range of mean blood pressures.

CONCLUSIONS

Integrated mean arterial pressures observed from a well maintained patient monitor can be considered interchangeable with independently sampled intra-arterial pressures and may be confidently used as the reference against which to test the accuracy of non-invasive blood pressure measuring methods in the prehospital or emergency setting.

Influence of hypercapnic vasodilation on cerebrovascular autoregulation and pial arteriolar bed resistance in piglets

Changes in both pial arteriolar resistance (PAR) and simulated arterial-arteriolar bed resistance (SimR) of a physiologically based biomechanical model of cerebrovascular pressure transmission, the dynamic relationship between arterial blood pressure and intracranial pressure, are used to test the hypothesis that hypercapnia disrupts autoregulatory reactivity. To evaluate pressure reactivity, vasopressin-induced acute hypertension was administered to normocapnic and hypercapnic (N = 12) piglets equipped with closed cranial windows. Pial arteriolar diameters were used to compute arteriolar resistance. Percent change of PAR (%DeltaPAR) and percent change of SimR (%DeltaSimR) in response to vasopressin-induced acute hypertension were computed and compared. Hypercapnia decreased cerebrovascular resistance. Indicative of active autoregulatory reactivity, vasopressin-induced hypertensive challenge resulted in an increase of both %DeltaPAR and %DeltaSimR for all normocapnic piglets. The hypercapnic piglets formed two statistically distinct populations. One-half of the hypercapnic piglets demonstrated a measured decrease of both %DeltaPAR and %DeltaSimR to pressure challenge, indicative of being pressure passive, whereas the other one-half demonstrated an increase in these percentages, indicative of active autoregulation. No other differences in measured variables were detectable between regulating and pressure-passive piglets. Changes in resistance calculated from using the model mirrored those calculated from arteriolar diameter measurements. In conclusion, vasodilation induced by hypercapnia has the potential to disrupt autoregulatory reactivity. Our physiologically based biomechanical model of cerebrovascular pressure transmission accurately estimates the changes in arteriolar resistance during conditions of active and passive cerebrovascular reactivity.

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.

[Reliability and survival of arterial catheters: optimal dynamic response]

OBJECTIVES

Blood pressure is one of the most critical haemodynamic parameter in the intensive care unit (ICU). The measurement relies mainly on invasive methods (arterial lines) but also on noninvasive methods (Oscillometric and Manual). It is crucial to be instantaneous and accurate to adapt any decision making plan. The aim of this study is to evaluate the reliability of this measure given by an arterial catheter over time. This can determine the maintenance of catheter patency before clinical total occlusion.

STUDY DESIGN

Observational prospective study.

PATIENTS AND METHODS

Damping coefficient (xi) and natural frequency (Fn) of the arterial catheter system are studied in vivo each 12 hours by a fast flush test (FFT) in 61 patients. The measurements of the arterial blood pressure invasively (arterial catheter method) and non invasively (oscillometric method) are compared each 12 hours until the catheter is removed.

RESULTS

All over the study period for each catheter (till 240 hours), the mean arterial blood pressure measurements given by either the catheter method or the oscillometric method were very concordant (coefficient > 0.7). Only 3.39% of the catheters had their physical characteristics (xi and Fn) in the optimal zone at T0; reaching 66.67% at T19. The maximal inserted time was highly correlated with a good operating catheter (R = 0.739; P < 10(-4)).

CONCLUSION

The measure of the arterial blood pressure invasively can still be reliable for a long period of time (10 days), as long as the catheter is inserted, especially when the mean arterial pressure is considered. Each time the distance of the catheter insertion site moves away 1 cm from the radiocarpal joint or the groin, the risk of troubleshooting is doubled; on each blood sample from the catheter, this risk is reduced by 20%.

The problem of artifacts in patient monitor data during surgery: a clinical and methodological review

Artifacts are a significant problem affecting the accurate display of information during surgery. They are also a source of false alarms. A secondary problem is the inadvertent recording of artifactual and inaccurate information in automated record keeping systems. Though most of the currently available patient monitors use techniques to minimize the effect of artifacts, their success is limited. We reviewed the problem of artifacts affecting patient monitor data during surgical cases. Methods adopted by currently marketed patient monitors to eliminate and minimize artifacts due to technical and environmental factors are reviewed and discussed. Also discussed are promising artifact detection and correction methods that are being investigated. These might be used to detect and eliminate artifacts with improved accuracy and specificity.

An Accuracy Evaluation of the T-Line® Tensymeter (Continuous Noninvasive Blood Pressure Management Device) versus Conventional Invasive Radial Artery Monitoring in Surgical Patients

Continuous beat-to-beat arterial blood pressure (BP) monitoring with a simultaneous arterial waveform display is typically achieved with an invasive arterial catheter. We evaluated a noninvasive device, the T-Line Tensymeter, that provides a calibrated arterial pressure waveform from which continuous BP measurements and heart rate may be computed by either a bedside host monitor or the tensymeter device itself. In 25 patients given general anesthesia, we measured systolic, mean, and diastolic BPs via the tensymeter and compared these measurements with those obtained from the contralateral radial artery catheter. Data were analyzed using the Bland Altman test to determine agreement between the two systems. The mean +/- sd bias and precision (mm Hg) were as follows: 1.7 +/- 7.0 and 5.7 +/- 4.4 for systolic BP; 2.3 +/- 6.9 and 5.7 +/- 4.5 for diastolic BP; and 1.7 +/- 5.3 and 4.0 +/- 4.8 for mean BP. Noninvasive pressures from the tensymeter-produced arterial waveform agreed with simultaneous contralateral BPs measured from arterial catheters within an acceptable clinical range for a limited population of surgical patients studied over a systolic arterial BP range from 41 to 189 mm Hg without significant temporal performance degradation. The tensymeter may enable physicians to circumvent arterial cannulation in certain circumstances (such as with low- or intermediate-risk procedures) on patients when beat-to-beat BP measurement is desirable.

Benefit of glyceryl trinitrate on arterial stiffness is directly due to effects on peripheral arteries

OBJECTIVE

To determine how the vasodilator glyceryl trinitrate (GTN) alters arterial stiffness and improves left ventricular afterload.

METHODS

Ascending aortic pressure waves were measured with fluid filled catheters of high fidelity in 50 patients undergoing cardiac surgery, before cardiopulmonary bypass, both before and after intravenous infusion of GTN. In all 50 patients, wave reflection was identifiable as a secondary boost to late systolic pressure, permitting the pressure wave to be separated into a primary component, attributable to left ventricular ejection and properties of the proximal aorta, and a secondary component, attributable to reflection of the primary wave from the peripheral vasculature.

RESULTS

GTN infusion caused no change in amplitude of the primary wave (mean (SD) 0.0 (1.4) mm Hg, not significant) but substantial reduction (14.6 (9.6) mm Hg, p < 0.0001) in amplitude of the secondary reflected wave. Fall in mean pressure was attributable to a mix of arteriolar and venous dilatation, with relative contributions unable to be separated.

CONCLUSION

Favourable effects of GTN on arterial stiffness can be attributed to effects on peripheral muscular arteries, causing reduction in wave reflection. Results conform with previous invasive studies on vasodilator agents and their known effects on calibre and compliance of muscular arteries.

Different techniques to measure intra-abdominal pressure (IAP): time for a critical re-appraisal

The diagnosis of intra-abdominal hypertension (IAH) or abdominal compartment syndrome (ACS) is heavily dependent on the reproducibility of the intra-abdominal pressure (IAP) measurement technique. Recent studies have shown that a clinical estimation of IAP by abdominal girth or by examiner's feel of the tenseness of the abdomen is far from accurate, with a sensitivity of around 40%. Consequently, the IAP needs to be measured with a more accurate, reproducible and reliable tool. The role of the intra-vesical pressure (IVP) as the gold standard for IAP has become a matter of debate. This review will focus on the previously described indirect IAP measurement techniques and will suggest new revised methods of IVP measurement less prone to error. Cost-effective manometry screening techniques will be discussed, as well as some options for the future with microchip transducers.