Evaluation of an automatic oscillometric method and of various cuffs for the measurement of arterial pressure in the neonate

Agreement of invasive versus non-invasive blood pressure in preterm neonates is not dependent on birth weight or gestational age

PURPOSE

Blood pressure constitutes an important parameter in the assessment of the cardiovascular status in preterm infants. Invasive arterial blood pressure (IBP) is considered the 'gold-standard', but non-invasive blood pressure (NIBP) is used frequently in preterm infants. The aim of this prospective study was to compare mean IBP and mean NIBP arterial blood pressure measurements in three subsets of preterm infants (>1500 g; 1000-1500 g, and <1000 g, and >31 weeks, 28-31 weeks, and <28 weeks of gestation).

METHODS

Prospective, simultaneous assessment of both IBP and NIBP measurements in 50 preterm neonates at 6, 12, 18, 24 h after birth in a tertiary University centre.

RESULTS

Mean gestational age was 26.7 +/- 2.2 (24-32) in group I (n= 18), 29.6 +/- 2.0 (27-34) in group II (n= 19) and 32.2 +/- 1.9(30-36) weeks in group III (n= 13), respectively; mean birth weight was 777 +/- 161 (495-995), 1251 +/- 154 (1010-1490) and 2010 +/- 332 (1590-2550) g. Mean IBP and mean NIBP increased significantly during the first 24 h of life in all three sub-groups (P < 0.01); IBP and NIBP measurements were significantly correlated, and showed good agreement, irrespective of birth weight and gestational age.

CONCLUSIONS

Although IBP monitoring is considered the 'gold standard', NIBP values showed good agreement with those obtained invasively irrespective of gestational age and birth weight. We conclude that NIBP monitoring constitutes an important parameter in the assessment of the cardiovascular status even in extremely low birth weight infants.

Comparison of noninvasive and central arterial blood pressure measurements in ELBW infants

OBJECTIVE

The objective of this study was to evaluate the difference between noninvasive and central arterial blood pressure measurements in extremely low-birth-weight (ELBW) infants.

STUDY DESIGN

We conducted a retrospective cohort study of infants with birth weight <or=1000 g and who were admitted to a single center in 2005. Paired noninvasive and umbilical arterial blood pressure measurements obtained in the first 72 h were compared. The primary outcome was the differential between the paired measurements. Noninvasive blood pressure (NBP) measurements were defined as clinically acceptable if the differential between the pairs was 15% or lower.

RESULT

We obtained 146 pairs of measurements from 38 infants. The median absolute differences between noninvasive and arterial systolic, mean and diastolic blood pressure measurements were +18.5, +12 and +10 mm Hg, respectively (percentage differential of 43, 39 and 41%, respectively). In total 75% of the noninvasive measurements of mean blood pressure were clinically unacceptable. No patient or measurement characteristic was significantly associated with clinically unacceptable noninvasive measurements.

CONCLUSION

In ELBW infants, NBP measurements substantially overestimate systolic, mean and diastolic blood pressures compared with central arterial measurements.

An optical oscillometric method for neonatal and premature infant blood pressure monitoring

PURPOSE

A preliminary study of a new optical oscillometric method to noninvasively measure systolic, mean, and diastolic blood pressures, in addition to heart and respiratory rates in very small extremities, is described. It employs transillumination of an extremity and measures the optical oscillation amplitude during cuff deflation from suprasystolic to zero pressure. The amplitude of the optical pulsatile oscillations is similar to that produced with the conventional pneumatic oscillometric method; however, the pulsatile optical signal is much larger and is present at all times when the cuff is deflated.

METHODS AND DESIGN

Two types of blood pressure verification studies were performed: (1) a weanling piglet study using a weanling piglet tail and (2) a human study using the little fingers of adult participants. For the weanling piglet study, direct femoral artery pressure, tail-cuff pressure, and optical oscillations were recorded in 5 anesthetized weanling piglets ranging in weight from 2 to 4 kg. Ten measurements were made in the pressure range of 30 to 175 mm Hg. For human study, data were obtained from 23 adult participants of both sexes with a little finger circumference of 4 cm or less. Radial artery pressure, measured with the conventional pneumatic oscillometric method, was used as the standard and was compared with the simultaneous optical oscillometric pressure in the little finger of the opposite arm.

MAIN OUTCOME MEASURES

This is an initial study demonstrating the optical oscillometric technique as a viable alternative for noninvasive blood pressure measurement in low birth-weight infants.

PRINCIPAL RESULTS

The weanling piglet data show a high correlation between direct arterial pressure and this new optical oscillometric method over a pressure range of approximately 30 to 175 mm Hg. The correlation coefficients of linear regression were 0.93, 0.93, and 0.91, respectively. The human little finger data show a high correlation between the pneumatic oscillometric mean arterial pressure and this new optical oscillometric method over a pressure range of approximately 40 to 140 mm Hg. The correlation coefficient of linear regression was 0.87.

CONCLUSIONS

This new optical oscillometric technique simplifies noninvasive blood pressure measurement because it was designed specifically for small-diameter extremities such as those found in low birth-weight infants. This new optical oscillometric device has the added benefit of continually monitoring pulse and respiration rates.

Blood pressure in the neonate: three non-invasive oscillometric pressure monitors compared with invasively measured blood pressure

AIM

To compare blood pressure in neonates obtained from three different oscillometer blood pressure monitors (Dinamap, Criticare, Hewlett-Packard) with arterial blood pressure (Hewlett-Packard' invasive unit).

STUDY DESIGN

A total of 32 randomized, non-invasive blood pressure series, each consisting of three measurements from each monitor, were obtained from 20 neonates (birthweight 531-4660 g). Each measurement was compared with the invasive pressure.

RESULTS

Two factors appear to have a systematic effect on the difference between oscillometric and invasive pressure (the measurement deviance): the size of the infant, e.g., the arm circumference, and the monitor system. For small infants, the non-invasively measured value tends to be too high. The deviance is partly reversed for larger infants (dependency on size significant for mean and diastolic pressure, p < 0.001). The difference between monitor systems is clearly significant (p < 0.001). Hewlett-Packard gives the lowest pressure values for all pressures. Thus, Criticare and Dinamap tended to show values too high in the smallest infants, while Hewlett-Packard tended to give values too low in larger infants. Birthweight, present weight and arm circumference affected measurement deviance approximately equally strongly, while factors such as the infant's sex, need of breath support and umbilical or radial arterial line were non-significant.

CONCLUSIONS

Blood pressure should preferably be measured invasively in severely ill neonates and preterm infants, being aware of pitfalls with measurements using different oscillometer monitors and the size/arm circumference of the infant.

Systolic blood pressure in babies of less than 32 weeks gestation in the first year of life. Northern Neonatal Nursing Initiative

AIM

To define the normal range of systolic blood pressure in a non-selective population based sample of babies of low gestation throughout early infancy.

METHODS

Daily measurements of systolic blood pressure were made in all the babies of less than 32 weeks gestation born in the North of England in 1990 and 1991 during the first 10 days of life. Additional measurements were obtained from 135 of these babies throughout the first year of life. Systolic pressure was measured by sensing arterial flow with a Doppler ultrasound probe. It was assumed that blood pressure had never been pathologically abnormal in the neonatal period if the child was alive and free from severe disability two years later. Data of adequate quality were available from 398 such children. Additional data wer collected, for comparative purposes, from 123 babies of 32, 36, or 40 weeks of gestation.

RESULTS

Systolic pressure correlated with weight and gestation at birth, and rose progressively during the first 10 days of life. The coefficient of variation did not vary with gestational or postnatal age (mean value 17%), the relation with gestation being closer than with birthweight. Systolic pressure rose 20% during the first 10 days from an initial mean of 42 mm Hg in babies of 24 weeks gestation, and by 42% from an initial mean of 48 mm Hg in babies of 31 weeks gestation. These findings were not altered by the exclusion of data from 14 babies who had inotropic support during this time. Simultaneous measurements in three centres using an oscillometric technique revealed that this technique tended to overestimate systolic pressure when this was below average. Systolic pressure finally stabilised at a mean of 92 (95% CI 72-112) mm Hg at a postconceptional age of 44-48 weeks irrespective of gestation at birth.

CONCLUSION

Systolic blood pressure 4-24 hours after birth was less than gestational age (in weeks) in only 3% of non-disabled long term survivors. Systolic pressure rose with increasing gestation and increasing postnatal age, but stabilised some six weeks after term, regardless of gestation at birth.

Use of pulse oximetry for blood pressure measurement after cardiac surgery

Blood pressure measurement using pulse oximeter waveform change was compared with an oscillometric measurement and the gold standard, intra-arterial measurement, in children after cardiac surgery. Forty six patients were enrolled and divided into groups according to weight. Simultaneous blood pressure measurements were obtained from the arterial catheter, the oscillometric device, and the pulse oximeter. Pulse oximeter measurements were obtained with a blood pressure cuff proximal to the oximeter probe. The blood pressure measurements from the pulse oximeter method correlated better with intra-arterial measurements than those from the oscillometric device (0.77-0.96 v 0.42-0.83). The absolute differences between the pulse oximeter and intra-arterial measurements were significantly smaller than between the oscillometric and intra-arterial measurements in children less than 15.0 kg. The pulse oximeter waveform change is an accurate and reliable way to measure blood pressure in children non-invasively, and is superior to the oscillometric method for small patients.

Accuracy of oscillometric blood pressure measurement in critically ill neonates with reference to the arterial pressure wave shape

OBJECTIVE

To perform further evaluation of the oscillometric device for neonatal arterial blood pressure (ABP) measurement, using a catheter-manometer system (CMS) for accurate intraarterial measurement. We aimed to describe the influence of the radial artery wave shape on oscillometric ABP determination, as pressure wave-shape influences the relationships between systolic arterial pressure (SAP), diastolic arterial pressure (DAP) and mean arterial pressure (MAP) in the wave. These relationships are part of the algorithms contributing to the final ABP determination in the oscillometric device.

DESIGN

Intra-patient comparison of two blood pressure measurement systems.

SETTING

Neonatal intensive care unit.

PATIENTS

In 51 critically ill newborn infants, ABP was determined oscillometrically in the brachial artery and, simultaneously, invasively in the radial artery using a high-fidelity CMS. Clinical data of the infants were: gestational age: 29 (25-41) weeks; birthweight: 1200 (500-3675) g, postnatal age: 6 (2-46) h.

METHODS

Statistical analysis was performed with the paired Student's t-test. Multiple regression analysis was used to determine the influence of birthweight and height of the blood pressure on the results.

MEASUREMENTS AND MAIN RESULTS

In 51 infants, 255 paired values of SAP, DAP and MAP were recorded. In all recordings, we determined the relationship between SAP, DAP and MAP, using the equation: MAP = alpha%(SAP - DAP) + DAP. For SAP, DAP, MAP and alpha, we computed mean differences (bias) and the limits of agreement (precision). Biases for SAP, DAP, MAP and alpha were significantly different from zero (P < 0.001) and the limits of agreement for SAP, DAP and MAP were wide: 18.8 mmHg, 17.2 mmHg and 15.2 mmHg respectively. The relationship between invasive and noninvasive values is only partly (7-19%) influenced by the height of the blood pressure; low values of SAP, DAP and MAP tend to give overestimated oscillometric values. In the relationship between SAP, DAP and MAP, alpha was found to be 47% invasively (as generally found in the radial artery in newborns) and 34% noninvasively (as generally found in the brachial/radial artery in adults).

CONCLUSIONS

Inaccuracy of the oscillometric device may be partly explained by the incorporation of an inappropriately fixed algorithm for final ABP determination in newborns. Care should be taken when interpreting the oscillometrically derived values in critically ill newborn infants.

A practical and reliable method of measuring blood pressure in the neonate by pulse oximetry

OBJECTIVE

We investigated the reliability of the plethysmographic waveform of the pulse oximeter to measure systolic blood pressure in sick neonates.

METHODS

Fifty infants admitted to the neonatal intensive care unit, with indwelling arterial catheters placed for their ongoing care, were enrolled. Median gestational age was 31 weeks (range, 24 to 40 weeks), and the mean birth weight was 1711 gm (range, 546 to 3856 gm). Blood pressure was recorded by an oscillometric method as well as from a transducer connected to an arterial catheter. Additionally, pulse oximeter blood pressures were obtained by gradually inflating an appropriately sized blood pressure cuff in increments of 2 to 5 mm Hg, on the same extremity as the oximeter probe, until the waveform just disappeared. The cuff was then rapidly inflated another 20 mm Hg and then gradually deflated in increments of 2 to 5 mm Hg until the waveform reappeared on the oximeter screen display. The pulse oximeter blood pressures were calculated both as the blood pressure noted at disappearance of the pulse oximeter waveform and as the blood pressure noted by the average pulse oximeter blood pressure at the disappearance and reappearance of the waveform. The mean intraarterial systolic blood pressure was 54 mm Hg (range, 36 to 82 mm Hg).

RESULTS

Blood pressures obtained by pulse oximetry showed a significantly better correlation with intraarterial measurements in comparison with those obtained by oscillometric instruments. Additionally, the limits of agreement (mean difference +/- 2 SD) between blood pressures obtained by intraarterial measurements and those obtained by pulse oximetry were within a clinically acceptable range as opposed to those obtained by the comparison of intraarterial and oscillometric methods.

CONCLUSION

Measurements of blood pressure in the neonate by means of pulse oximetry waveform analysis are easily obtainable and more accurate than those obtained by the oscillometric method.

The Dinamap 1846SX automated blood pressure recorder: comparison with the Hawksley random zero sphygmomanometer under field conditions

STUDY OBJECTIVE

The aim was to compare the performance of the Dinamap 1846SX automated oscillometric blood pressure recorder with that of the Hawksley random zero sphygmomanometer during use under field study conditions.

DESIGN

Two independent within subject measurement comparisons were made, one in adults and one in children, each conducted in three stages over several months while the Dinamap instruments were being used in epidemiological field surveys.

SETTING

The studies were done in outpatients clinics (adults) and primary schools (children).

PARTICIPANTS

141 adults (20-85 years) and 152 children (5-7 years) took part.

MEASUREMENTS AND MAIN RESULTS

In adults a pair of measurements was made with each instrument, the order alternating for consecutive subjects. In children one measurements was made with each instrument, in random order. Measurements with the Dinamap 1846SX were higher than those with the random zero sphygmomanometer both in adults (mean difference 8.1 mm Hg; 95% CI 6.5 to 9.7 mm Hg) and in children (mean difference 8.3 mm Hg; 95% CI 6.9 to 9.7 mm Hg). Diastolic measurements were on average very similar both in adults and in children. The results were consistent at all three stages of both studies. The differences in systolic measurement were independent of blood pressure level. However, the extent of agreement in diastolic pressure depended on the diastolic blood pressure level; in both studies Dinamap diastolic measurements were higher at low diastolic pressures while random zero diastolic measurements were higher at high diastolic pressures.

CONCLUSIONS

Systolic measurements made with the Dinamap 1846SX instrument are not directly comparable with those of the Hawksley random zero sphygmomanometer and are unlikely to be comparable with those of earlier Dinamap models. These differences have important implications for clinical practice and for comparisons of blood pressure measurement between epidemiological studies. However, the consistency of measurement by the Dinamap 1846SX over time suggests that the instrument may have a place in standardised blood pressure measurement in the research setting.

Arterial blood pressure in the very low birthweight neonate. Evaluation of an automatic oscillometric technique

The noninvasive oscillometric technique of arterial blood pressure determination was evaluated in fifteen very low birth weight neonates (less than 1,400 g). Measurement of invasive umbilical artery catheter pressure was used as a reference standard. By using a cuff width to arm circumference ratio of 0.33-0.42, mean blood pressure was overestimated by 6.2 (7.2) mmHg (mean and 1 SD), p less than 0.001. More accurate mean blood pressure measurements were recorded with a cuff width to arm circumference ratio of 0.44-0.55. Measurements of systolic and diastolic blood pressure showed similar results.

Dinamap fails to detect hypotension in very low birthweight infants

The accuracy of blood pressure measurements obtained from very low birthweight (less than 1500 g) neonates using the Dinamap oscillometric monitor was investigated. Comparisons using umbilical artery measurements showed that the monitor is less reliable in the lower pressure range and specifically that it tends to overestimate pressure in hypotensive infants.

Non-invasive oscillometric measurement of systolic, mean and diastolic blood pressure in infants with congenital heart defects after operation. A comparison with direct blood pressure measurements

The accuracy of indirect oscillometric blood pressure measurements has been evaluated in 32 infants up to 11 months of age undergoing heart surgery. In a number of 1029 simultaneous measurements the indirect blood pressure was compared with the direct value obtained from a radial artery catheter. Cuffs of different sizes were applied. The main results were as follows: Regarding the ratio of cuff width to arm circumference, the best correlation between oscillometric and direct blood pressure measurements was obtained with a ratio of 0.38-0.41. The value of indirect blood pressure measurements depends on the absolute height of the blood pressure. In low blood pressure there is a tendency to underestimate and in high blood pressure there is a tendency to overestimate by the oscillometric blood pressure measurement. By applying an appropriate cuff size and by using our diagrams it should be possible to derive a direct value for the blood pressure on the basis of indirect oscillometric blood pressure measurements.

A review of current methods of monitoring in neonatal intensive care

Neonatal intensive care requires continuous close monitoring of several physiological parameters. The machinery involved is complex but has to be understood by medical staff with the minimum of training in its use. Failure of correct application and interpretation of results can be dangerous for the sick or preterm infant.