Measuring pressure under burns pressure garments using the Oxford Pressure Monitor

Pressure garments are used extensively in the treatment of hypertrophic scarring following burn injuries. The Oxford Pressure Monitor was used to measure garment-scar interface pressure (mmHg) using a number of fabric types over various body parts. The results indicate a wide range of pressure values between different garments and body parts with the greatest pressures found over the dorsum of hands and feet. The problems of achieving 'optimal pressure' over hypertrophic scarring are discussed with emphasis on the need for more accurate measuring equipment.     

Pressure by design: How to improve the consistency of pressure garments in the clinical environment and implement a simple method for gathering evidence to establish efficacy

Pressure garments are used to treat scars after major trauma including burns. However, the ideal pressure for treatment is not known. Pressures exerted are not routinely measured and garments exert a wide range of pressures. Therefore, current treatment and its efficacy are variable.Pressure Garment Design Tools were introduced in 2012 but their application in hospitals has not been reported. A Garment Dimension and Pressure Calculator was used to audit pressures delivered by 8 pressure garments made for children using the hospital department’s standard reduction factor. The tool was easy to use and showed that pressures exerted by standard garments ranged from 15 to 54 mmHg with highest pressures exerted on wrists.Results of our pilot study indicated that the Garment Dimension and Pressure Calculator was slightly quicker to use than our normal manual process for calculating garment dimensions and enabled easy auditing of past treatment. The Pressure Garment Design Tool was easy to use and calculated garments that exerted the mean target pressures of 15 mmHg and 25 mmHg, improving consistency.Pressures exerted by garments were difficult and time consuming to measure with the Picopress sensor. Pressure was not distributed evenly around the limbs and measurements were inaccurate on the smallest limbs.     

The assessment of erythema and thickness on burn related scars during pressure garment therapy as a preventive measure for hypertrophic scarring

The aim of this study was threefold: (1) Assess the pressure loss of two types of pressure garments that are used in the treatment of hypertrophic scars after burn injury, (2) investigate the influence of two different levels of compression on erythema and thickness of burn scars and (3) examine the association between erythema and thickness. The study was a prospective trial in which 76 burn scars in 60 patients were objectively assessed with the Minolta Chromameter CR-300 for erythema and with the Dermascan C for thickness of the scar over a period of 3 months. Each patient was randomly assigned to a "normal" or "lower" compression class treatment, with respectively mean values of 15 and 10 mmHg pressure after wearing the garment for 1 month. Measurements for both parameters were taken at 0, 1, 2 and 3 months of treatment. Pressure garments with "normal" compression did lose significantly more compression over 1 month (4.82 mmHg) than did the garments from the low compression class (2.57 mmHg). Scars that were treated with garments from a "normal" compression class did score significantly better for thickness compared to the "low" compression class. The difference in thickness was most evident at 1 month. Thereafter no further significant improvement between the two different treatments over time could be obtained. This difference was not found for erythema. Positive correlations could be found between erythema and thickness values at all of the three test points while changes in erythema and thickness only correlated significantly after the first month. The pattern of change of both parameters correlated at a high level of significance after 3 months of treatment. These data suggest that pressure garments that deliver a pressure of at least 15 mmHg pressure tend to accelerate scar maturation and that measurements of the pattern of change of the erythema can be used to predict changes in scar thickness and vice versa.     

Designing pressure garments capable of exerting specific pressures on limbs

Pressure garments have been used prophylactically and to treat hypertrophic scars, resulting from serious burns, since the early 1970s. They are custom-made from elastic fabrics by commercial producers and hospital staff. However, no clear scientifically established method has ever been published for their design and manufacture. Previous work [2] identified the most commonly used fabrics and construction methods for the production of pressure garments by hospital staff in UK burn units. These methods were evaluated by measuring pressures delivered to both cylinder models and to human limbs using I-scan pressure sensors. A new calibration method was developed for the I-scan system to enable measurement of low interface pressures to an accuracy of +/-2.5 mmHg. The effects of cylinder/limb circumference and pressure garment design on the pressures exerted were established. These measurements confirm the limitations of current pressure garment construction methods used in UK hospitals. A new method for designing pressure garments that will exert specific known pressures is proposed and evaluated for human thighs. Evaluation of the proposed design method is ongoing for other body parts.     

Pressure garment design tool to monitor exerted pressures

Pressure garments are used in the treatment of hypertrophic scarring following serious burns. The use of pressure garments is believed to hasten the maturation process, reduce pruritus associated with immature hypertrophic scars and prevent the formation of contractures over flexor joints. Pressure garments are normally made to measure for individual patients from elastic fabrics and are worn continuously for up to 2 years or until scar maturation. There are 2 methods of constructing pressure garments. The most common method, called the Reduction Factor method, involves reducing the patient's circumferential measurements by a certain percentage. The second method uses the Laplace Law to calculate the dimensions of pressure garments based on the circumferential measurements of the patient and the tension profile of the fabric. The Laplace Law method is complicated to utilise manually and no design tool is currently available to aid this process. This paper presents the development and suggested use of 2 new pressure garment design tools that will aid pressure garment design using the Reduction Factor and Laplace Law methods. Both tools calculate the pressure garment dimensions and the mean pressure that will be exerted around the body at each measurement point. Monitoring the pressures exerted by pressure garments and noting the clinical outcome would enable clinicians to build an understanding of the implications of particular pressures on scar outcome, maturation times and patient compliance rates. Once the optimum pressure for particular treatments is known, the Laplace Law method described in this paper can be used to deliver those average pressures to all patients. This paper also presents the results of a small scale audit of measurements taken for the fabrication of pressure garments in two UK hospitals. This audit highlights the wide range of pressures that are exerted using the Reduction Factor method and that manual pattern ‘smoothing’ can dramatically change the actual Reduction Factors used.     

The effect of changes of posture on the urethral closure pressure in healthy women

The effect of changes of posture on hydrodynamic parameters considered important for the maintenance of urinary continence was investigated in 14 healthy women. The subjects were investigated in the supine and erect positions using a previously described technique for simultaneous urethrocystometry, including recording of the urethral pressure profile. It was found that a change from the supine to the standing position increased the maximum intravesical pressure from a mean value of 13 mmHg to 22 mmHg. There was a simultaneous increase in the maximum intra-urethral pressure from a mean of 66 mmHg to 82 mmHg. As a consequence, the urethral closure pressure increased from a mean of 53 mmHg to 60 mmHg. The functional length of the urethra increased from 25 mm to 28 mm, and the absolute length from 28 mm to 36 mm. It is concluded that in healthy women, a change from the supine to the standing position causes a rise in the maximum intra-urethral pressure and an increase in the absolute and functional lengths of the urethra. These effects counteract the simultaneous increase in bladder pressure, and can be regarded as compensatory mechanisms for the maintenance of continence.     

Estimation of intraoperative aortocoronary bypass saphenous vein graft circumference from its preoperative compliance

The aim of this study was to determine if the intraoperative circumference of aortocoronary saphenous vein bypass grafts could be predicted from preoperative measurement with B-mode ultrasound sonography in 50 patients. The circumference of the saphenous vein was measured during stepwise increments of a thigh congestive cuff from 0 to 60 mmHg. The circumference of the corresponding segment of the coronary bypass vein graft was measured intraoperatively with callipers. The intraoperative circumference was higher (11.8+/-2.3 mm) than the preoperative circumference (10.2+/-2.4 mm, P=0.006) matched to its corresponding intraoperative mean arterial pressure (57+/-15 mmHg). The prediction of the intraoperative circumference by estimation from the preoperative pressure-circumference relationship fitted by a linear model (r = 0.412, P = 0.004) did not improve on the preoperative circumference matched by arterial pressure alone (r = 0.429, P = 0.003). The intraoperative circumference of the graft vein exceeded its preoperative circumference by 12%. Prediction of the intraoperative graft vein circumference is underestimated by a linear model of its preoperative compliance.     

Assessment of the arterial tonometer (N-CAT) for the continuous blood pressure measurement in rapid atrial fibrillation

The N-CAT is a newly developed arterial tonometer (TBP) able to determine systolic, diastolic and mean arterial blood pressures continuously and noninvasively. The aim of this study was to evaluate the accuracy and reliability of TBP relative to directly measured invasive blood pressure (IBP) in ten haemodynamically stable postoperative cardiac patients who were in rapid atrial fibrillation (HR ≥ 100 bpm). There were differences between TBP and IBP for systolic (?1.7 mmHg) and diastolic (+0.9 mmHg) values but not for the mean arterial blood pressures. The N-CAT was able to follow blood pressure changes closely and demonstrated an average systolic, diastolic and mean bias (±SD) of ?1.71 ± 4.6, 0.99 ± 4.6 and 0.33 ± 4.2 mmHg, respectively. Although these biases are within the required standards for equivalency for noninvasive blood pressure to invasively determined blood pressure, approximately 20% of the readings were > ±10 mmHg while only 5% were > ±20 mmHg. Moreover, there were occasional discrepancies of sufficient magnitude and duration which may limit the clinical usefulness of the N-CAT in patients in whom continuous and accurate blood pressure measurement is required.     

New calibration method for I-scan sensors to enable the precise measurement of pressures delivered by 'pressure garments'

Accurate measurement of the pressure delivered by medical compression products is highly desirable both in monitoring treatment and in developing new pressure inducing garments or products. There are several complications in measuring pressure at the garment/body interface and at present no ideal pressure measurement tool exists for this purpose. This paper summarises a thorough evaluation of the accuracy and reproducibility of measurements taken following both of Tekscan Inc.’s recommended calibration procedures for I-scan sensors; and presents an improved method for calibrating and using I-scan pressure sensors. The proposed calibration method enables accurate (±2.1 mmHg) measurement of pressures delivered by pressure garments to body parts with a circumference ≥30 cm. This method is too cumbersome for routine clinical use but is very useful, accurate and reproducible for product development or clinical evaluation purposes.     

Intraluminal pressure adjacent to left colonic anastomoses

A cumulative total of 89 h of pressure data was acquired from both sides of a left colonic anastomosis in 15 patients over a median period of 7 postoperative study days. Patients had a colonic ileus lasting 3-10 days and during this proximal and distal inactivity the intraluminal pressure remained within 6 mmHg of atmospheric pressure. After recovery of activity, pressures proximal to the anastomosis in excess of 10 mmHg occurred during less than 1 per cent of the recording time. Distal peak pressures were significantly elevated with respect to the proximal site (P less than 0.001). Two-thirds of the distal pressures recorded were between 10 and 20 mmHg and 98 per cent were less than 50 mmHg; the peak distal pressure was 90 mmHg. Four patients had distal repetitive tonic contractions creating a pressure difference across the anastomosis with a mean of 20 mmHg and a peak of 45 mmHg. Each contraction persisted for 15-20 min. Intraluminal pressures are unlikely to play a role in anastomotic dehiscence.     

External application of hypertonic salt solution for treatment of posttraumatic oedema

In 20 New Zealand rabbits (two groups of 10 rabbits each), hind limb circumference and anterior compartment pressure were measured following ketamin anaesthesia (time zero). During the same anaesthesia, closed transverse proximal tibial shaft fractures were created in both groups. Twenty-four hours after the fractures, during a second anaesthesia, limb circumference and compartment pressure were measured as before, and fractured limbs were fixed to the rabbits' bodies. At the same time, treatment was started: one group received external application of saturated salt solution and the other group received intermittent ice application. During 48 hours of treatment (from 24 to 72 hours) in the saturated salt solution group, the mean limb circumference decreased from 125.70 +/- 9.93 mm to 115.70 +/- 8.78 mm (p = 0.005) and the mean compartment pressure decreased from 18.30 +/- 1.70 mmHg to 12.40 +/- 1.77 mmHg (p = 0.005). In the control group, the mean limb circumference decreased from 127.85 +/- 7.47 mm to 122.00 +/- 6.83 mm (not significant) and the mean compartment pressure decreased from 19.57 +/- 1.27 mmHg to 17.85 +/- 2.67 mmHg (not significant). In short, differences in compartment pressure and limb circumference before and after treatment were statistically significant in the saturated salt solution group (p = 0.005) but not in the control group.     

Normative blood pressure data in the early neonatal period

There has been a temporal trend towards increased birth weight over the past three decades. This increase in birth weight may have resulted in an increase in neonatal blood pressure. Neonatal hypertension is becoming more common, especially in neonatal intensive care unit survivors. Current normative values are required to assist in diagnosis and appropriate management of neonatal hypotension and hypertension. The objective of this study was to determine normative blood pressure readings in healthy term neonates. Term neonates from the postnatal ward were enrolled from August 2003 to August 2005. Exclusion criteria included infants of mothers with preeclampsia, hypertension of any cause, gestational diabetes, type 1 diabetes mellitus and illicit substance use, infant congenital or chromosomal anomaly, admission to the neonatal intensive care unit or possible sepsis. Of the 406 infants enrolled, 218 were male. The median systolic, diastolic and mean blood pressures on day 1 of life were 65 mmHg, 45 mmHg, and 48 mmHg, respectively. On day 4, these values had increased to 70 mmHg, 46 mmHg and 54 mmHg. There was a significant elevation in blood pressure from day 1 to day 2 of life. There was no significant difference in blood pressure readings with respect to birth weight or length. The only significant difference between the sexes was a lower mean and diastolic pressure on day 2 in boys. This study has provided current normative blood pressure readings of healthy term neonates that can be used to assess both hypotension and hypertension in the term neonate. No increase in blood pressure was noted from previous studies.     

Effect of sufentanil on intracranial pressure in neurosurgical patients

The effects of sufentanil on intracranial pressure, mean arterial pressure, cerebral perfusion pressure and heart rate were studied in 20 neurosurgical intensive care unit patients. Epidural intracranial pressure probes were implanted in patients who suffered head injury, intracerebral haemorrhage or underwent tumour resection. Sufentanil was given intravenously in sequential doses of 0.5, 1.0 and 2.0 micrograms/kg. Fifteen minutes elapsed after each dose. The patients were allocated to either group 1 (baseline intracranial pressure less than 20 mmHg) or group 2 (baseline intracranial pressure greater than 20 mmHg). Intracranial pressure did not change significantly in either group. Therefore the falls in mean arterial pressure with the highest dose in both groups and with 1.0 micrograms/kg in group 2, closely reflect corresponding reductions in cerebral perfusion pressure. As sufentanil in itself exerts no effects on intracranial pressure, concomitant haemodynamic changes are the critical factor for an adequate cerebral perfusion pressure.     

Association between intracranial pulse pressure levels and brain energy metabolism in a patient with an aneurysmal subarachnoid haemorrhage

This report addresses whether intracranial pulse pressure amplitudes are associated with brain energy metabolism, examined by intracerebral microdialysis. We present a 65-year-old female with an aneurysmal subarachnoid haemorrhage (SAH) from a left posterior communicating artery (PCOM) aneurysm. She underwent simultaneous intracranial pressure (ICP) monitoring and microdialysis (MD) as part of a diagnostic workout because of a lack of clinical improvement after long-term intensive care management. Over a 4-day period, a total of 128 samples of metabolites (glutamate, glycerol, lactate and pyruvate) were gathered, allowing retrospective comparisons with the levels of intracranial pulse pressure amplitudes (the mean ICP wave amplitude). During this 4-day period, mean ICP was normal (<15 mmHg), while mean ICP wave amplitude was high (>/=5 mmHg) in 47% of the recording time. There was a highly significant relationship between the levels of the mean ICP wave amplitude and the levels of glutamate, glycerol and lactate/pyruvate ratio. The levels of metabolites were increased when the mean ICP wave amplitude was >/=5 mmHg as compared with mean ICP wave amplitude levels <5 mmHg. We tentatively suggest that increased mean ICP wave amplitudes indicative of reduced intracranial compliance can be associated with brain ischaemia.     

Evaluation of a new blood pressure cuff for patients with large and normal arm circumferences

A new multisize blood pressure cuff (TriCuff; Inmed) which automatically adjusts to fit any size arm was tested against the routinely used 12 x 23 cm cuff in patients with an arm circumference less than 33 cm (group A = 30) and against the 15 x 33 cm cuff as well as the 12 x 23 cm cuff in patients with arm circumference greater than 33 cm (group B = 26). Arm circumference in group A was 25 +/- 3 cm and in group B 38 +/- 3 cm (P less than 0.01). Systolic blood pressure (SBP) and diastolic blood pressure (DBP) in group A was 125 +/- 20 mmHg and 78 +/- 11 mmHg respectively with the TriCuff and 124 +/- 19 mmHg and 78 +/- 13 mmHg with the 12 x 23 cm cuff. In group B SBP and DBP with the TriCuff was 134.6 +/- 13.3 mmHg and 84 +/- 17 mmHg respectively compared with 132 +/- 15 mmHg and 83.8 +/- 16 mmHg measured by the 15 x 33 cm cuff. SBP and DBP with the 12 x 23 cm cuff was 139.8 +/- 16 mmHg and 90.8 +/- 14 mmHg respectively. Both these values are significantly higher (P less than 0.05) compared with the new cuff and the larger cuff. Using the 12 x 23 cm cuff in group B resulted in the false diagnosis of hypertension in 3 normotensive patients. The TriCuff gives accurate blood pressure measurements in patients with different arm circumferences and should prevent false-positive diagnoses of hypertension in obese patients.     

Effect of blood pressure instrument and cuff side on blood pressure reading in pregnant women in the lateral recumbent position

BACKGROUND: Hydrostatic forces affect non-invasive blood pressure measurement in the lateral position. This study assessed the extent of this effect with the mercury column sphygmomanometer and Dinamap oscillometric instrument as well as different recommendations for comparing supine and lateral blood pressure measurements. METHOD: Thirty-two term pregnant women were studied in the antenatal clinic. Blood pressure was recorded from both arms in the right lateral and supine recumbent positions, using the sphygmomanometer and Dinamap. RESULTS: Blood pressure in the uppermost arm while lateral was lower than supine by a mean 10 mmHg or more. Systolic, mean and diastolic pressures in the dependent arm while lateral were higher than supine by a mean (SD) 3.1 (6.8)mmHg, 5.6 (6.8)mmHg, and 6.9 (8.7)mmHg using the sphygmomanometer and 3.8 (8.1)mmHg, 3.2 (7.1)mmHg, and 1.9 (5.3)mmHg using the Dinamap. Systolic, mean and diastolic pressure values calculated as the average taken from both arms in the lateral position were lower than supine by a mean (SD) 3.5 (7.5)mmHg, 3.9 (4.7) mmHg, and 4.1 (5.8)mmHg using the sphygmomanometer and 4.6 (6.0)mmHg, 4.9 (4.4)mmHg, and 4.8 (4.4)mmHg using the Dinamap. Corresponding blood pressure readings were always higher using the Dinamap than the sphygmomanometer. CONCLUSIONS: In normotensive non-labouring term pregnant women, the use of the dependent arm or an average blood pressure from both arms while in the lateral position will give a closer reading to supine blood pressure than the use of the uppermost arm. However, use of the dependent arm is simpler.     

Monitoring of cerebrospinal dynamics using continuous analysis of intracranial pressure and cerebral perfusion pressure in head injury

Summary Cerebrospinal dynamics has been investigated by statistical analysis of results of computerised monitoring of 80 head injured patients admitted to the Intensive Care Unit at Pinderfields General Hospital. One minute average values of intracranial pressure (ICP), systemic arterial pressure (ABP), cerebral perfusion pressure (CPP), amplitude of the fundamental component of the intracranial pressure pulse wave and the short-term moving correlation coefficient between that amplitude and mean ICP (RAP) were recorded. It was found that reduction of CPP down to 40mmHg was more often caused by decrease in ABP than increase in ICP. Further falls in CPP below 40mmHg were caused by substantial increases in ICP above 25 mmHg. The relationship between the ICP pulse wave amplitude and CPP showed a significant gradual increase in amplitude with CPP decreasing from 75 to 30 mmHg. For CPP below 30 mmHg there is a sharp decrease in amplitude followed by a change in the coefficient RAP from positive to negative values. This was interpreted as a sign of critical disturbance in cerebral circulation.     

The effects of isoflurane and desflurane on intracranial pressure,cerebral perfusion pressure,and cerebral arteriovenous oxygen content difference in normocapnic patients with supratentorial brain tumors

BACKGROUND: Desflurane is a volatile anesthetic agent with low solubility whose use in neurosurgery has been debated because of its effect on intracranial pressure and cerebral blood flow. The purpose of this study was to determine the variations on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) as well as on cerebral arteriovenous oxygen content difference (AVDo(2)) in normocapnic patients scheduled to undergo removal of supratentorial brain tumors with no evidence of mass effect during anesthesia with isoflurane or desflurane. METHODS: In 60 patients scheduled to undergo craniotomy and removal of supratentorial brain tumors with no evidence of midline shift, anesthesia was induced with intravenous fentanyl, thiopental, and vecuronium and was maintained with 60% nitrous oxide in oxygen. Patients were assigned to two groups randomized to receive 1 minimum alveolar concentration isoflurane or desflurane for 30 min. Heart rate, mean arterial pressure, intraparenchymal ICP, and CPP were monitored continuously. Before and after 30 min of continuous administration of the inhaled agents, AVDo(2) was calculated. RESULTS: There were no significant differences between groups in heart rate, mean arterial pressure, ICP, and CPP. ICP measurements throughout the study did not change within each group compared to baseline values. Mean arterial pressure decreased significantly in all patients compared to baseline values, changing from 105 +/- 14 mmHg (mean +/- SD) to 85 +/- 10 mmHg in the isoflurane group and from 107 +/- 11 mmHg to 86 +/- 10 mmHg in the desflurane group (P < 0.05 in both groups). CPP also decreased within each group compared with baseline values, changing from 95 +/- 15 mmHg to 74 +/- 11 mmHg in the isoflurane group and from 95 +/- 16 mmHg to 74 +/- 10 mmHg in the desflurane group (P < 0.05 in both groups). Cerebral AVDo(2) decreased significantly in both groups throughout the study, changing from 2.35 +/- 0.77 mm to 1.82 +/- 0.61 mm (mmol/l) in the isoflurane group (P < 0.05) and from 2.23 +/- 0.72 mm to 1.94 +/- 0.76 mm in the desflurane group (P < 0.05), without differences between groups. CONCLUSIONS: The results of this study indicate that there are no variations on ICP in normocapnic patients undergoing removal of supratentorial brain tumors without midline shift, as they were anesthetized with isoflurane or desflurane. CPP and cerebral AVDo(2) decreased with both agents.     

Effects of alfentanil on intracranial pressure in children undergoing ventriculoperitoneal shunt revision.

The effects of alfentanil on intracranial pressure in patients with diminished intracranial compliance has not been established. Ten patients with hydrocephalus of varying etiologies, ages 16 months to 20 yr, presenting for ventriculoperitoneal shunt revision were studied. Following induction of anesthesia with thiopental, nitrous oxide/oxygen, and isoflurane, the trachea was intubated and anesthesia was maintained with isoflurane (0.5%), nitrous oxide (70%), and oxygen. After a minimum of 30 min and after the new shunt was placed, alfentanil was administered in increments of 10, 20, and 40 micrograms/kg at 3-min intervals, and intracranial pressure was measured over 12 min via the new shunt. In these unstimulated, normocapnic (PETCO2 32-38 mmHg) patients, heart rate, mean arterial pressure, and cerebral perfusion pressure declined from 110 +/- 26 beats/min, 90 +/- 11 mmHg, and 71 +/- 14 mmHg, to 84 +/- 25 beats/min, 66 +/- 11 mmHg, and 45 +/- 16 mmHg (mean +/- SD), respectively, by 3 min after the third dose (P less than 0.001). Intracranial pressure did not change from baseline (19 +/- 14 mmHg vs. 21 +/- 11) after any dose of alfentanil. Contrary to earlier studies in adult patients with brain tumors, the authors found that alfentanil, in pediatric patients with hydrocephalus anesthetized with oxygen, nitrous oxide, and isoflurane, did not increase intracranial pressure within a 9-min study period. The significant decreases in cerebral perfusion pressure observed merit concern and further study.     

Relationship between intracranial pressure and critical closing pressure in patients with neurotrauma

BACKGROUND: The driving pressure gradient for cerebral perfusion is the difference between mean arterial pressure (MAP) and critical closing pressure (CCP = zero flow pressure). Therefore, determination of the difference between MAP and CCP should provide an appropriate monitoring of the effective cerebral perfusion pressure (CPP(eff)). Based on this concept, the authors compared conventional measurements of cerebral perfusion pressure by MAP and intracranial pressure (CPP(ICP)) with CPP(eff). METHODS: Simultaneous synchronized recordings of pressure waveforms of the radial artery and blood flow velocities of the middle cerebral artery were performed in 70 head trauma patients. CCP was calculated from pressure-flow velocity plots by linear extrapolation to zero flow. RESULTS: Intracranial pressure measured by intraventricular probes and CCP ranged from 3 to 71 and 4 to 70 mmHg, respectively. Linear correlation between ICP and CCP was r = 0.91. CPP(ICP) was 77 +/- 20 mmHg and did not differ from CPP(eff); linear correlation was r = 0.92. However, limits of agreement were only +/- 16.2 mmHg. Therefore, in 51.4% of the patients, CPP(ICP) overestimated CPP(eff) by 19.8 mmHg at most. CONCLUSION: Assuming that CPP(eff) (MAP - CCP) takes into account more determinants of cerebral downstream pressure, in individual cases, the actual gold standard of CPP determination (MAP - ICP) might overestimate the CPP(eff) of therapeutic significance.