Effect of Nitric Oxide Delivery Device on Tidal Volume Accuracy During Mechanical Ventilation at Small Tidal Volumes.

BACKGROUND: Inhaled nitric oxide (INO) is used in infants as a therapy for elevated pulmonary vascular resistance. When INO is delivered at low tidal volumes, displayed inspiratory and expiratory volumes vary widely. We hypothesize that volume is removed by the sampling line during the ventilation cycle, and this results in a net volume loss at low tidal volumes. This study aimed to measure the volumes delivered and to assess the accuracy of displayed ventilator values using a test lung. METHODS: A test lung was connected to a ventilator and an INO delivery system. All tests were performed with stable mode settings across volumes of 18, 30, 42, and 60 mL. Flow measured with a pneumotachometer attached between the test lung and the circuit assessed the percent error between inspiratory and expiratory volumes measured by the pneumotachometer measured and displayed on the ventilator under various INO/sample line conditions to determine where and how much volume was being displaced. RESULTS: Displayed and measured inspiratory volumes had small variations between the INO/sample line conditions and baseline. However, expiratory volumes, with the sample line connected, exhibited large percent error values that increased (-14, -20, -27, and -34) as tidal volume decreased (60, 42, 30, and 18 mL) and error was significantly larger compared to baseline in all tidal volumes (P < .01) with and without INO delivery. CONCLUSIONS: We concluded that inspiratory volumes were not affected by INO delivery, but additional removal of volume in the expiratory phase of the breath cycle by the sampling line results in a large error in the displayed expiratory volume.

Comparison of Work of Breathing Between Noninvasive Ventilation and Neurally Adjusted Ventilatory Assist in a Healthy and a Lung-Injured Piglet Model.

BACKGROUND: Noninvasive ventilation (NIV) is commonly used in neonates. A mode of NIV called neurally adjusted ventilatory assist (NAVA) offers patient-ventilator interactions by using electrical activity of the diaphragm to control mechanical breaths. We hypothesized that the work of breathing (WOB) would decrease with NIV-NAVA. Secondary objectives evaluated the impact of NIV-NAVA on arterial blood gases and respiratory parameters. METHODS: We compared WOB between synchronized breaths in NIV-NAVA and NIV in piglets with healthy lungs and then with surfactant-depleted lungs. Neonatal pigs (median, 2.0 [range, 1.8-2.4] kg) with healthy and then surfactant depleted lungs were sedated and ventilated with NIV-NAVA and NIV in random order. Airway flow and pressure waveforms were acquired. Waveforms were analyzed for the pressure-time product that reflected WOB. The primary outcome between modes was assessed with repeated measurement analysis of variance. RESULTS: The pressure-time product was significantly decreased for NIV-NAVA in both healthy and injured lungs (P < .001). PaO2 , PaCO2 , inspiratory tidal volume, and peak inspiratory flow were not different in either model. CONCLUSIONS: Synchronized breaths during NIV-NAVA resulted in decreased WOB compared with synchronized breaths during NIV.

Effect of ventilator mode on patient-ventilator synchrony and work of breathing in neonatal pigs.

BACKGROUND: Patient-ventilator asynchrony can result in increased work of breathing (WOB) and need for increased sedation, as well as respiratory muscle fatigue and prolonged mechanical ventilation. Different ventilator modes may result in varying degrees of asynchrony and WOB. OBJECTIVE: The objectives of this study were to assess the incidence of asynchrony and the effect of asynchrony on WOB in three modes of ventilation: pressure regulated volume control (PRVC), synchronized intermittent mandatory ventilation/volume control plus pressure support (SIMV/VC plus PS), and SIMV/PRVC plus PS. METHODS: Ten piglets (2.1 ± 0.3 kg) were studied, each in the healthy and surfactant-depleted, lung-injured state. Piglets were sedated, intubated, and ventilated with the three modes of ventilation randomly applied. Piglets then underwent surfactant washout, after which the lungs were re-recruited, and the modes of ventilation were repeated. Airway flow and pressure waveforms were acquired via pneumotachograph. Waveforms were analyzed for patient-ventilator asynchrony and pressure time product (PTP) as an estimate of patient WOB. RESULTS SIMV/VC plus PS had the highest incidence of asynchrony. The incidence of asynchrony was less in the injured lung. PTP (cm H2 O*S) was increased for SIMV/VC plus PS (healthy 0.10 ± 0.12; injured 0.15 ± 0.13) compared to PRVC (healthy 0.05 ± 0.05; injured 0.06 ± 0.03), (P < 0.03) in both the healthy and injured lung models. CONCLUSIONS: Asynchrony and WOB are highest with SIMV/VC plus PS. If SIMV is utilized, SIMV/PRVC plus a PS that optimizes tidal volume may be preferable. PRVC has the least asynchrony and WOB in the injured lung.

Reliability of Displayed Tidal Volume in Healthy and Surfactant-Depleted Piglets.

BACKGROUND: Volutrauma has been established as the key factor in ventilator-induced lung injury and can only be avoided if tidal volume (VT) is accurately displayed and delivered. The purpose of this study was to investigate the accuracy of displayed exhaled VT in a ventilator commonly used in small infants with or without a proximal flow sensor and using 3 methods to achieve a target VT in both a healthy and lung-injured neonatal pig model. METHODS: This was a prospective animal study utilizing 8 male pigs, approximately 2.0 kg (range 1.8-2.2 kg). Intubated, sedated, neonatal pigs were studied with both healthy and injured lungs using the Servo-i ventilator. In pressure-regulated volume control, both with and without a proximal flow sensor, we used 3 methods to set VT: (1) circuit compliance compensation (CCC) on, set VT 6-8 mL/kg; (2) CCC off, calculated VT using the manufacturer's circuit compliance factor; and (3) CCC off, set VT 10-12 mL/kg to approximate a target VT of 6-8 mL/kg. Ventilator-displayed exhaled VT measurements were compared with exhaled VT measured at the airway opening by a calibrated pneumotachograph. Bland-Altman plots were constructed to show the level of agreement between the two. RESULTS: CCC improved accuracy and precision of displayed exhaled VT when the sensor was not used, more markedly in the lung-injured model. Without CCC, the sensor improved accuracy and precision of displayed exhaled VT, again more markedly in the lung-injured model. CONCLUSIONS: When the Servo-i ventilator is used in neonates, CCC or the in-line sensor should be employed due to the large positive bias and imprecision seen with CCC off and no sensor in-line.

Application of mid-frequency ventilation in an animal model of lung injury: a pilot study.

BACKGROUND: Mid-frequency ventilation (MFV) is a mode of pressure control ventilation based on an optimal targeting scheme that maximizes alveolar ventilation and minimizes tidal volume (VT). This study was designed to compare the effects of conventional mechanical ventilation using a lung-protective strategy with MFV in a porcine model of lung injury. Our hypothesis was that MFV can maximize ventilation at higher frequencies without adverse consequences. We compared ventilation and hemodynamic outcomes between conventional ventilation and MFV. METHODS: This was a prospective study of 6 live Yorkshire pigs (10 ± 0.5 kg). The animals were subjected to lung injury induced by saline lavage and injurious conventional mechanical ventilation. Baseline conventional pressure control continuous mandatory ventilation was applied with V(T) = 6 mL/kg and PEEP determined using a decremental PEEP trial. A manual decision support algorithm was used to implement MFV using the same conventional ventilator. We measured P(aCO2), P(aO2), end-tidal carbon dioxide, cardiac output, arterial and venous blood oxygen saturation, pulmonary and systemic vascular pressures, and lactic acid. RESULTS: The MFV algorithm produced the same minute ventilation as conventional ventilation but with lower V(T) (-1 ± 0.7 mL/kg) and higher frequency (32.1 ± 6.8 vs 55.7 ± 15.8 breaths/min, P < .002). There were no differences between conventional ventilation and MFV for mean airway pressures (16.1 ± 1.3 vs 16.4 ± 2 cm H2O, P = .75) even when auto-PEEP was higher (0.6 ± 0.9 vs 2.4 ± 1.1 cm H2O, P = .02). There were no significant differences in any hemodynamic measurements, although heart rate was higher during MFV. CONCLUSIONS: In this pilot study, we demonstrate that MFV allows the use of higher breathing frequencies and lower V(T) than conventional ventilation to maximize alveolar ventilation. We describe the ventilatory or hemodynamic effects of MFV. We also demonstrate that the application of a decision support algorithm to manage MFV is feasible.

Validation of the accuracy of a transport ventilator utilizing a pediatric animal model.

OBJECTIVE: The objective of this study was to evaluate 2 transport ventilators utilizing both a test lung and a pediatric animal model. METHODS: Two transport ventilators were utilized for evaluations. A test lung or intubated, sedated pigs (n = 9) with healthy and injured lungs were ventilated using control and support modes. A test lung was used to evaluate alarm responsiveness, FIO2 accuracy, oxygen consumption, and duration of battery power. Pigs were utilized to evaluate the exhalation valve, ventilator response, volume accuracy, and noninvasive functionality. Respiratory mechanics were determined using a forced oscillation technique, and airway flow and pressure waveforms were acquired utilizing a pneumotachograph. RESULTS: For both ventilators, FIO2 accuracy was within 10% error. On an E cylinder of oxygen, the EMV+ operated for 3 hours 48 minutes and the LTV 1200 for 1 hour 4 minutes. On battery power, the LTV 1200 ventilated for 6 hours 51 minutes and the EMV+ for 12 hours 8 minutes. Ventilator response time was less (36%), and delta pressure was greater (38%) for the EMV+ utilizing noninvasive ventilation. The percent error for displayed volume was less than 10% for the EMV+. CONCLUSIONS: In this study, we demonstrate that there are differences between the 2 ventilators in regard to oxygen consumption, duration of battery power, and volume accuracy. Clinicians should be aware of these differences to optimize the choice and use of both ventilators depending on clinical need/setting.

Accuracy of displayed volume with three airway sensors in an animal model.

Optimal mechanical ventilation in infants and pediatrics depends on the reliability of flow sensors to correctly measure flow and integrate it into accurately displayed tidal volumes (V TE ). However, reliability of these devices has not been established. We hypothesize that reliability would be affected by both the type of flow sensors and ventilator controllers utilized. Intubated, sedated Sprague Dawley rats (n = 14) were ventilated (control and support modes) utilizing two different ventilators: 1) fixed orifice flow sensor (FOF) and 2) both a hot wire (HWF) and variable orifice flow sensor (VOF), independently. Accuracy of delivered tidal volume was obtained by comparing the displayed volume of the different sensors to breath waveforms acquired using a heated 0-5 L/min calibrated pneumotachograph. Analysis was performed utilizing ANOVA with P ≤ 0.05. Rats mean weight was 472 ± 46 g. For all modes, mean V TE % difference was demonstrated across all three measuring sensors. For volume control ventilation and pressure control ventilation or time cycled pressure limited assist control, there was a difference between all three sensors. For pressure support ventilation, there was a difference with the HWF only. R-square values were FOF 0.80, HWF 0.54, and VOF 0.16. The accuracy of delivered V TE is affected by both the flow sensor and ventilator controller to deliver the breath. We speculate that the flow sensor and the controller are associated with varying degrees of flow accuracy and control. We would expect volume accuracy for all modes to be equal if the flow accuracy were related to the inaccuracy of the flow sensors only.

Accuracy of small tidal volume measurement comparing two ventilator airway sensors.

Goals of modern mechanical ventilation in infants focus on preventing over-distention by limiting tidal volume. Accurate measurement of these volumes is essential. We hypothesized that tidal volume accuracy differs dependent upon the type of airway sensor utilized in tidal volumes less than 10 mL. Intubated, sedated Sprague Dawley rats (n = 40) were ventilated utilizing both control and support ventilator modes. Accuracy of volume delivery was compared between a fixed orifice flow sensor (FOF) and a hot wire anemometer (HWA) to a Hans Rudolph linear pneumotachograph positioned at the patient wye. Rats median weight was 476 grams (range 370-544), tidal volume (V T ) 3.5 mL (1.2-11.4), f 50 (18-102), and PIP 9.5 cm H 2 O (1-34). Across all modes, bias and precision were HWA -0.76, 1.09; FOF 0.22, 0.61. This study confirms that there are differences in the accuracy of small tidal volumes measured with a FOF as compared to a HWA. Utilizing a FOF, control modes exhibit improved precision and decreased bias as compared to support modes.

Validation of volume delivery with the use of heliox in mechanical ventilation.

Using a mixture of helium and oxygen (heliox) while mechanically ventilating patients to relieve lower airway obstruction is commonly practiced in intensive care units. The use of heliox with commercially available mechanical ventilators is usually accomplished by connecting the heliox mixture to the air inlet of the ventilator. Since most ventilators do not compensate for the difference in gas densities, particular attention to the delivered tidal volume (V T ) is required. We utilized a commercially available mechanical ventilator with an internal blending system that is capable of delivering heliox instead of medical air. It identifies and compensates for the gas mixture, theoretically enhancing stability in delivered and monitored parameters. Intubated, sedated male domestic pigs (n = 7) were ventilated with a mechanical ventilator equipped with an internal heliox blending system utilizing pressure assist control, pressure regulated volume control, and pressure support ventilation modes. Accuracy of volume delivery was assessed by comparing delivered V T measured at the patient wye using the variable orifice flow sensor connected to the ventilator and a heated 0-35 L/min pneumotachograph that was calibrated for flow, pressure, and volume, with a 0.80/0.20 heliox mix and 0.50 oxygen. A paired t-test was utilized with a P < 0.05. Pigs mean weight 9.0 ± 0.9 kg. Mean exhaled tidal volume for all modes and was 66 ± 16 mL. When comparing all modes for the 0.50 oxygen to the heliox mix, we found that exhaled tidal volume % difference increased when using heliox ( P ≤ 0.037). This study confirms that clinicians should be vigilant in monitoring delivered V T using a commercially available ventilator equipped with an internal heliox blending system. Accuracy of delivered V T can vary greatly with the use of heliox in this system, as well as other configurations.

Neurally triggered breaths have reduced response time, work of breathing, and asynchrony compared with pneumatically triggered breaths in a recovering animal model of lung injury.

OBJECTIVE: Our objective was to compare response time, pressure time product as a reflection of work of breathing, and incidence and type of asynchrony in neurally vs. pneumatically triggered breaths in a spontaneously breathing animal model with resolving lung injury. DESIGN: Prospective animal study. SETTING: Experimental laboratory. SUBJECTS: Male Yorkshire pigs. INTERVENTIONS: Intubated, sedated pigs were ventilated using neurally adjusted ventilatory assist and pressure support ventilation with healthy and sick/recruited lungs. After injury, the lung was recruited using a computer-driven protocol. Respiratory mechanics were determined using a forced oscillation technique, and airway flow and pressure waveforms were acquired using a pneumotachograph. MEASUREMENTS AND MAIN RESULTS: Waveforms were analyzed for trigger delay, pressure time product, and asynchrony. Trigger delay was defined as the time interval (ms) from initiation of a breath to the beginning of ventilator pressurization. Pressure time product was measured as the area of the pressure curve for animal effort (area A) and ventilator response (area B). Asynchrony was classified according to triggering problems, adequacy of flow delivery, and adequate breath termination. Mean values were compared using the Wilcoxon signed-ranks test (p < .05). Trigger delay (ms) was less in neurally triggered breaths (pressure support ventilation healthy 104 ± 27 vs. neurally adjusted ventilatory assist healthy 72 ± 30, pressure support ventilation sick/recruited 77 ± 18 vs. neurally adjusted ventilatory assist sick/recruited 38 ± 18, p < .01). Pressure time product areas A and B were decreased for neurally triggered breaths compared with pressure support ventilation in both healthy and recruited animals (p ≤ .02). Overall, the percentage of asynchrony was less for neurally adjusted ventilatory assist breaths in the recruited animals (pressure support ventilation 27% and neurally adjusted ventilatory assist 6%). CONCLUSIONS: Neurally triggered breaths have reduced asynchrony, trigger delay, and pressure time product, which may indicate reduced work of breathing associated with less effort to trigger the ventilator and faster response to effort. Further study is required to demonstrate if these differences will lead to decreased days of ventilation and less use of sedation in patients.

Neurally triggered breaths reduce trigger delay and improve ventilator response times in ventilated infants with bronchiolitis.

PURPOSE: Neurally adjusted ventilatory assist (NAVA) is a mode of ventilation designed to improve patient-ventilator interaction by interpreting a neural signal from the diaphragm to trigger a supported breath. We hypothesized that neurally triggered breaths would reduce trigger delay, ventilator response times, and work of breathing in pediatric patients with bronchiolitis. METHODS: Subjects with a clinical diagnosis of bronchiolitis were studied in volume support (pneumatic trigger) and NAVA (pneumatic and neural trigger) in a crossover design. Airway flow and pressure waveforms were obtained with a pneumotachograph and computerized digital recorder and were recorded for 120 s for each experiment. RESULTS: Neurally triggered breaths had less trigger delay (ms) (40 ± 27 vs. 98 ± 34; p < 0.001) and reduced ventilator response times (ms) (15 ± 7 vs. 36 ± 25; p < 0.001) compared with pneumatically triggered breaths. Neurally triggered breaths had reduced pressure-time product (PTP) area A (cmH(2)O * s), the area of the pressure curve from initiation of breath to start of ventilator pressurization (0.013 ± 0.010; p < 0.001), and reduced PTP area B (cmH(2)O * s), the area of the pressure curve from start of ventilator pressurization to return of baseline pressure (0.008 ± 0.006 vs. 0.023 ± 0.009; p = 0.003). Reduced PTP may indicate decreased work of breathing. CONCLUSION: Neurally triggered breaths reduce trigger delay, improve ventilator response times, and may decrease work of breathing in children with bronchiolitis. Further analysis is required to determine if neurally triggered breaths will improve patient-ventilator synchrony.

Reliability of displayed tidal volume in infants and children during dual-controlled ventilation.

OBJECTIVE: Previous studies have shown a significant difference between ventilator-measured tidal volume and actual-delivered tidal volume. However, these studies used external methods for measurement of compression volume. Our objective was to determine whether tidal volume could be accurately measured at the expiratory valve of a conventional ventilator using internal computer software to compensate for circuit compliance with a dual control mode of ventilation. DESIGN: Clinical study during an 8-month period. SETTING: Pediatric intensive care unit. PATIENTS: All patients admitted to the pediatric intensive care unit during the enrollment period who were mechanically ventilated using the Servo I (Maquet, Bridgewater, NJ) were eligible for this study. INTERVENTIONS: Patients were ventilated using a dual-control mode of ventilatory support and either an infant or adult circuit (with and without circuit compensation). MEASUREMENTS AND MAIN RESULTS: Tidal volume measured at the endotracheal tube using a pneumotachometer was compared with ventilator-displayed tidal volume. Sixty-eight patients were studied between September 2004 and April 2005. Age range was 2 days to 18 yrs (median, 23 mos) and weight range was 2.3 kg to 103 kg (median, 14.5 kg) with 41 male patients (60%). We found ventilator-displayed tidal volume, without circuit compensation, generally overestimates true-delivered tidal volume and, with circuit compensation, generally underestimates true-delivered tidal volume. However, agreement between tidal volume measured at the patient's airway and that measured with and without compensation for circuit compliance was good. The error in both cases, without and with circuit compensation, is relatively greater in infants and small children. CONCLUSIONS: There is an underestimation of delivered tidal volume when compensating for circuit volume loss measured at the ventilator. There is no improvement in measured tidal volume using circuit compensation in small infants and children.

WITHDRAWN: Reliability of displayed tidal volume in infants and children during dual controlled ventilation.

Ahead of Print article withdrawn by publisher: OBJECTIVE:: Previous studies have shown significant difference between ventilator-measured tidal volume and actual-delivered tidal volume. However, these studies utilized external methods for measurement of compression volume. Our objective was to determine whether tidal volume could be accurately measured at the expiratory valve of a conventional ventilator using internal computer software to compensate for circuit compliance, with a dual control mode of ventilation. DESIGN:: Clinical study during an 8-month period. SETTING:: Pediatric intensive care unit. PATIENTS:: All patients admitted to the pediatric intensive care unit during the enrollment period who were mechanically ventilated using the Servo i (Maquet, Bridgewater, NJ) were eligible for this study. INTERVENTIONS:: Patients were ventilated utilizing a dual control mode of ventilatory support and either an infant or adult circuit (with and without circuit compensation). MEASUREMENTS AND MAIN RESULTS:: Tidal volume measured at the endotracheal tube using a pneumotachometer was compared with ventilator-displayed tidal volume. Sixty-eight patients were studied between September 2004 and April 2005. Age range 2 days-18 yrs (median: 23 months), weight range 2.3-103 kg (median: 14.5 kg), with 41 (60%) male. We found ventilator-displayed tidal volume, without circuit compensation, generally overestimates true-delivered tidal volume, and with circuit compensation, generally underestimates true-delivered tidal volume. However, agreement between tidal volume measured at the patient's airway and that measured with and without compensation for circuit compliance was good. The error in both cases, without and with circuit compensation is relatively greater in infants and small children. CONCLUSION:: There is an underestimation of delivered tidal volume when compensating for circuit volume loss measured at the ventilator. There is no improvement in measured tidal volume utilizing circuit compensation in small infants and children.

Repeated measurements of respiratory mechanics in developing rats utilizing a forced oscillation technique.

The ability to successfully intubate the trachea of rats repeatedly over time, recover them, and perform repeated measures of changes in respiratory mechanics is important. The authors performed experiments utilizing 2 groups of rats at various ages in their development. Rats in the single-measurement group were studied at 1 age only. Rats in the repeated-measurement group were studied at each age point over time. Measurements of respiratory mechanics were made utilizing a forced-oscillation technique. We found no differences in respiratory mechanics between the 2 groups. Our results demonstrate that developing rats can be studied longitudinally to illustrate maturational changes in respiratory mechanics.

Reliability of measured tidal volume in mechanically ventilated young pigs with normal lungs.

OBJECTIVE: This study examined whether volumes can be accurately measured at the expiratory valve of a conventional ventilator using pressure support ventilation and positive end expiratory pressure with software compensation for circuit compliance available in the Servo iota ventilator. DESIGN AND SETTING: Comparison of two methods for measuring tidal volume in an animal laboratory. SUBJECTS: Twenty healthy, intubated, sedated, spontaneously breathing pigs. INTERVENTIONS: Volume was measured in ten neonatal-sized and ten pediatric-sized pigs ventilated with the Servo iota ventilator using pressure support ventilation and positive end expiratory pressure with and without circuit compliance compensation. We compared volume measured at the airway opening by pneumotachography to volume measured at the expiratory valve of a conventional ventilator. MEASUREMENTS AND RESULTS: The use of circuit compliance compensation significantly improved the agreement between the two volume methods in neonatal-sized piglets (concordance correlation coefficient: with circuit compliance compensation, 0.97; without, 0.87, p=0.002). In pediatric-sized pigs there was improvement in agreement between the two measurement methods due to circuit compliance compensation (concordance correlation coefficient with circuit compliance compensation, 0.97; without, 0.88, p=0.027). With circuit compliance compensation off there was positive bias: mean difference (bias) 2.97+/-0.12 in neonatal-sized and 3.75+/-0.38 in pediatric-sized pigs. CONCLUSIONS: Our results show that volume can be accurately measured at the expiratory valve of a conventional ventilator in neonatal- and pediatric-sized animals.

Validation of a noninvasive blood pressure monitoring device in normotensive and hypertensive pediatric intensive care patients.

OBJECTIVE: To evaluate the performance and to define limitations of a noninvasive blood pressure monitoring device in the critically ill pediatric population. METHOD: Patients were included in the study if they were admitted to the Pediatric Intensive Care Unit, were between the ages of 1 month and 18 years with wrist circumferences of > or =10 cm, and had an indwelling arterial line. Patients were excluded if their systolic blood pressure differed by > or =7.5% between their upper extremities. The measurements were collected simultaneously with those from an arterial line by a computer interfaced with the noninvasive blood pressure monitoring system and the patient's monitor. Heart rates were calculated from the recorded pulse waveforms of the arterial lines. Comparison analyses were performed via bias and precision plots of the blood pressure and heart rate data in addition to calculation of Pearson's correlation coefficients and concordance correlation coefficients. As a nonparametric method of comparison, the proportion of measurements that differed by greater than 10% was calculated. Results. Blood pressures and heart rates of 20 patients between the ages of 12 months and 17 years were monitored by a noninvasive blood pressure monitor for 30 min per patient. This data collection resulted in 2015 data points for each blood pressure and heart rate for comparison of methods. Concordance correlation coefficients were the following: systolic blood pressure, 0.93; diastolic blood pressure, 0.93; mean blood pressure, 0.94; and heart rate, 0.85. CONCLUSIONS: The noninvasive blood pressure monitor is capable of producing an accurate blood pressure measurement every 12-15 heartbeats in addition to providing a pulse waveform and digital display of the heart rate. Our study showed good agreement between the methods in the normotensive and hypertensive critically ill pediatric population with a wrist circumference limitation defined at > or =11 cm.