Continuous Pressure Monitoring Research Articles

Intraluminal measurement probe increases resistance of pediatric endotracheal tubes

During mechanical ventilation the resistance of the endotracheal tube (ETT) causes a noticeable pressure drop between the airway pressure and the tracheal pressure. Analysis of lung mechanics requires knowledge of the tracheal pressure. Besides methods for calculation of the tracheal pressure [1,2], direct measurement of the tracheal pressure was suggested [3]. We hypothesized that the measure probe significantly increases the ETT's resistance and therefore is inappropriate for continuous monitoring of the intratracheal pressure in the presence of pediatric ETTs. In a laboratory study we investigated the pressure drop across pediatric ETTs with and without an intraluminal sensor probe.

Pheochromocytoma: cyclic attacks of hypertension alternating with hypotension

A 52-year-old woman was admitted to hospital with recurrent episodes of chest and abdominal pain, dyspnea, palpitations and diaphoresis. Continuous blood pressure recordings revealed rhythmic alternation between episodes of severe hypertension and episodes of hypotension. This cyclic hemodynamic crisis continued for 2 hours, with each cycle lasting around 15 min. Physical examination, electrocardiography, chest radiography, continuous intra-arterial pressure monitoring, blood and urine analysis, echocardiography, abdominal CT and 131I miodobenzylguanidine scanning. Pheochromocytoma--a catecholamine secreting tumor. Intravenous phentolamine and fluids, oral doxazosin and surgical removal of the tumor.

Multiplex Assessment of Cytokine and Chemokine Levels in Cerebrospinal Fluid following Severe Pediatric Traumatic Brain Injury: Effects of Moderate Hypothermia

This study performed a comprehensive analysis of cerebrospinal fluid (CSF) cytokine levels after severe traumatic brain injury (TBI) in children using a multiplex bead array assay and to evaluate the effects of moderate hypothermia on cytokine levels. To this end, samples were collected during two prospective randomized controlled trials of therapeutic moderate hypothermia in pediatric TBI. Thirty-six children with severe TBI (Glasgow Coma Scale [GCS] score of <or=8) and 10 children with negative diagnostic lumbar punctures. All children with TBI had continuous monitoring of intracranial pressure and CSF drainage via an intraventricular catheter. Moderate hypothermia (32-33 degrees C) was maintained for 48 h in 17 patients, and they were slowly re-warmed at 48-72 h. A multiplex bead array assay was used to analyze serial CSF samples (<18 h, 24 +/- 6 h, 48 +/- 6 h, and 72 +/- 6 h) for 21 pro-and anti-inflammatory cytokines and chemokines. Interleukin (IL)-8 and transforming growth factor beta were measured by enzyme-linked immunosorbant assay (ELISA). There was a strong correlation (Spearman correlation coefficient = 0.92, p < 0.001) between multiplex assay and ELISA for IL-8. Pro-inflammatory IL-1beta, -6 and -12p70, anti-inflammatory IL-10 and chemokines IL-8 and MIP-1alpha were increased after TBI compared to controls, p < 0.05; however, there was no association between cytokines and age, gender, initial GCS, or outcome. Hypothermia did not attenuate the increases in CSF cytokine levels after TBI versus normothermia. This investigation confirmed that the multiplex bead array assay is a useful method to measure CSF cytokine levels. Severe TBI in infants and children induces increases in pro- and anti-inflammatory cytokines and chemokines. It is the first clinical report of increased levels of MIP-1alpha after TBI in any patient population and the most comprehensive assessment of cytokines after TBI to date. Moderate therapeutic hypothermia did not attenuate the increase in CSF cytokine levels in children after TBI.

A Continuous and Non-Invasive Arterial Pressure Monitoring System in Dialysis Patients

Background: As symptomatic intradialytic hypotension in the hemodialysis (HD) patient is often a sudden event whose onset cannot be predicted by means of extemporary measures, continuous blood pressure (BP) measurement would be far more useful. We tested a new continuous noninvasive BP monitoring system, Harmonized Alert Sensing Technology (HASTE), which, by means of the analysis of the finger pulse wave, obtained from an O₂ sensor, estimates a beat-to-beat systolic pressure value (Esys) and supplies a continuous read-out. The study aim sought to verify the reliability of this non-invasive instrument in continuously providing systolic pressure values during HD. Methods: We studied 18 patients during HD treatment, initially comparing the Esys with the invasive blood pressure measurement (SYS). Subsequently, the Esys derived from the O₂ sensor in the arm with the shunt (S) and the arm without (N), respectively, were both compared with the cuff measurement. Results: The mean difference between SYS and Esys was 0.7 ± 13.3 mm Hg (p < 0.01; r = 0.80). There was a mean difference of 0.2 ± 21.9 mm Hg (p = NS; r = 0.67) between Esys(N) and Esys(S). The correlation was not statistically significant even between Esys(N) or Esys(S) versus the cuff measurement, respectively. Patient movement compromised the accuracy of the estimations made using the O₂ sensor in the non-fistula arm. Conclusions: A good correlation between the data estimated by HASTE compared with invasive BP suggests that the instrument may prove useful for continuously monitoring the blood pressure trends during the dynamic hemodialysis situation. However, its sensibility needs to be improved in order to be used indifferently in both arms with a view to achieving real intradialytic hypotension prevention.

Test on Soft Sedimentary Rock Under Different Loading Paths and its Interpretation

Tests on soft sedimentary rock under conventional triaxial and plane-strain compression and/or creep have been conducted. The purpose of the tests is to investigate the influence of intermediate principal stress that may affect the strength and dilatancy of the soft sedimentary rock under different loading paths. Meanwhile, theoretical simulations by an elasto-viscoplastic constitutive model were also conducted. Influence of membrane and filter paper was investigated using finite element analysis based on the elasto-viscoplastic model. Furthermore, particular attention was paid to the migration of excessive pore water pressure within a specimen, by continuous monitoring of the inner excessive pore water pressure of specimens and calculation with soil-water coupled finite element-finite difference (FE-FD) method. The shear strength, inherent dilatancy and creep behavior of soft rock were explained experimentally and numerically in detail.

Continuous intraventricular pressure monitoring for diagnosis of normal-pressure hydrocephalus

Normal-pressure hydrocephalus (NPH) syndrome is treatable by implantation of a cerebrospinal fluid (CSF) shunt. However, diagnosis of NPH by clinical and radiological findings alone is unreliable, and co-existing structural dementia can contribute to low success rates after shunt implantation. The aim of our study was to investigate whether long-term results after shunt implantation in NPH improve when surgical candidates are selected by continuous intraventricular pressure monitoring (CIPM). Ninety-two consecutive patients who were admitted with suspected NPH received CIPM for 48 h including an intraventricular steady-state infusion test to determine the resistance outflow. With positive CIPM, shunt implantation was performed and the patients were prospectively followed up for 1 to 10 years (median 6.5 years). CIPM was negative in 37 patients. Fifty-five patients had a positive CIPM and received CSF shunt. 96.1% of them improved from gait disturbance, 77.1% from cognitive impairment and 75.7% from urinary dysfunction. Clinical improvement remained during long-term follow-up in all but 3 patients who showed a decline at 4, 5 and 7 years, respectively. CIPM-related complications (ventriculitis) occurred in only one patient. CIPM is a safe and valuable tool to establish a reliable diagnosis of NPH and to identify promising surgical candidates.

Retroperitoneal Compartment Pressure Elevation Impairs Pancreatic Tissue Blood Flow

To investigate whether the increase of the retroperitoneal compartment pressure, as in the case of peripancreatic fluid accumulation in severe acute pancreatitis, simulated by infusing a colloid fluid into the retroperitoneum, has any effect on pancreatic tissue blood flow. Six male anesthetized swine were subjected to a transcutaneous placement of catheters into the retroperitoneal space. Through these catheters, a colloid solution was infused, under continuous retroperitoneal pressure monitoring, to achieve a pressure up to 20 mm Hg. Pancreatic tissue blood flow was assessed by colored microsphere injection technique, and pancreatic interstitial pressure was measured by means of a commercially available pressure monitor system before and after the distension of the retroperitoneal space, allowing the appropriate time for the animals to be stabilized from any intervention. The increase in the retroperitoneal compartment pressure was found to significantly increase pancreatic interstitial pressure (from 8 +/- 1 to 20 +/- 2.4 mm Hg, P = 0.001) as well as reduce pancreatic tissue blood flow (from 1.75 +/- 0.4 to 0.56 +/- 0.12 mL . min . g, P = 0.002). The increase of retroperitoneal pressure leads to an impairment of pancreatic tissue blood flow in the healthy pancreas. Although these findings support the hypothesis that peripancreatic fluid collection during the course of acute pancreatitis could contribute or augment pancreatic tissue ischemia, further assessment is necessary.

Asistencia al paciente politraumatizado. Realidad actual desde la perspectiva de las unidades de cuidados intensivos

To study the epidemiology and management of pediatric trauma patients as well as the organizational, human and technical resources dedicated to these children from the perspective of the pediatric intensive care unit (PICU).A standardized data collection form was sent to 43 PICUs in Spain. Items inquired about the existence of training courses, trauma clinical practice guidelines and trauma registers, and which physician was in charge of trauma patients. Data on casuistics, the age of trauma patients, and the availability of human and technical resources, were also recorded.Twenty-four PICUs completed the questionnaire. The PICU physician was responsible for trauma patient care in 66% of the hospitals. No training courses were available in 59% of the hospitals. No trauma register was available in 62% of the hospitals. Trauma patients represented 11% of PICU admissions, and most patients were aged up to 14 years old. An anesthetist was always at the hospital in 100% of the hospitals. A radiologist and traumatologist were always at the hospital in 91%, a neurosurgeon in 66% and a pediatric surgeon in 50%. The remaining surgical and medical specialties were on call. Continuous intracranial pressure monitoring was available in 87% of the PICUs, jugular venous saturation monitoring in 54% and continuous electroencephalogram and transcranial Doppler ultrasound in 50%. Computed tomography and ultrasound were available at all times in all hospitals. Magnetic nuclear resonance and echocardiography were available at all times in 44% of the hospitals, and arteriography in 42%.In Spain, the organization of pediatric trauma management is based on pediatric teams under the supervision of a PICU physician. Some hospitals show a lack of technical and human resources. Therefore, the minimum criteria required to consider a hospital as a pediatric trauma center should be established. Trauma training courses are required.

Haemodynamic changes during lung recruitment. A systematic review

The fundamental role of the cardio-respiratory system is to supply the tissues with adequate amount of oxygen to cover their metabolic need. Acute lung injury and acute respiratory distress syndrome are characterized by atelectasis of the alveoli, causing inadequate gas exchange in the lung and lack of oxygen supply to the body. Under these circumstances by increasing the FiO2 only may not be enough to improve oxygenation. One of the possible alternatives is the lung recruitment manoeuvre, during which the alveoli are opened up with high inflation pressure and to keep them open by maintaining appropriate positive end expiratory pressure. However, high intrathoracic pressures may cause haemodynamic instability by affecting the work of the heart and compressing the mediastinal veins. It is uncertain, how haemodynamics are best monitored during lung recruitment. Is continuous monitoring of the mean arterial pressure and the central venous pressure enough, or do we need to measure invasive haemodynamic parameters such as cardiac output and intrathoracic blood volume during such an aggressive intervention?. The aim of this article is to give a review of the possible answers for these questions based on the results of physiological and recently published clinical and experimental research. Key words: lung recruitment, acute respiratory distress syndrome, positive end expiratory pressure, extravascular lung water, oxygenation, hemodynamic monitoring.

Evaluation of landslide reactivation: A modified rainfall threshold model based on historical records of rainfall and landslides

This study proposes a modification of the conventional threshold model for assessing the probability of rainfall-induced landslide reactivation. The modification is based on the consideration that exceedance of a pre-determined rainfall threshold is a necessary but not sufficient condition to reactivate a landslide. The proposed method calculates the probability of reactivation as a function of the probability of exceedance of a pre-determined rainfall threshold, as well as the probability of occurrence of a landslide after such exceedance. The data for the calculation were obtained from historical records of landslides and rainfall. The method was applied to two complex landslides (“San Donato” and “La Salsa”) involving fine-grained debris in the southern section of the Apennine foredeep. The minimum rainfall threshold triggering landslide reactivation on the two slopes was determined by examining rainfall patterns during the 180 days preceding the slide events. For the San Donato and La Salsa landslides, the minimum triggering threshold consists of rainfall events lasting 15 days, with cumulated rainfall exceeding 150 and 180 mm, respectively. Based on hydrological and statistical analyses, the annual probabilities of exceeding the thresholds were estimated to be 0.38 and 0.25, respectively. During the period from 1950 to 1987, the minimum threshold was exceeded 14 times, and four reactivations occurred at San Donato; whereas, the threshold was exceeded 10 times and three reactivations occurred at La Salsa. Hence, the probabilities of landsliding after exceedance of the minimum rainfall threshold are 4/14 and 3/10, respectively. Finally, annual reactivation probabilities were calculated to be 0.11 and 0.08, respectively. The reliability of the minimum rainfall threshold was tested by: i) simulating variations in the stress–strain behavior of the slopes as a result of fluctuations in the water table from normal to extreme values; and ii) analyzing the results of continuous multi-year monitoring of pore pressure and rainfall variations on a slope composed of dominantly fine-grained debris.

Continuous intracranial pressure monitoring via the shunt reservoir to assess suspected shunt malfunction in adults with hydrocephalus

The authors attempted to determine whether continuous intracranial pressure monitoring via the shunt reservoir identifies ventriculoperitoneal (VP) shunt malfunctions that are not identified by radionuclide shunt patency study or shunt tap in adults with hydrocephalus. During a 2-year period, 26 adults underwent 32 in-hospital continuous intracranial pressure (ICP) monitoring evaluations via needle access of a shunt reservoir. Monitoring was performed for 26.8 +/- 13.8 hours (mean +/- standard deviation). No ICP waveform abnormality was detected in 31% of the evaluations (10 of 32). In contrast, abnormalities were detected in 69% (22 of 32 evaluations), including B waves (nine of 22 evaluations), siphoning (nine of 22 evaluations), and variable ICP (two of 22 evaluations). In 20 (91%) of these 22 evaluations, the ICP abnormality was detected only after continuous ICP monitoring; in the other two evaluations, ICP became abnormal immediately on accessing the shunt reservoir. On the basis of the ICP monitoring results, shunt revision was performed in 66% (21 of 32 evaluations) and medical therapy was administered in 34% (11 of 32 evaluations). Shunt revision led to symptom improvement in 82% (18 of 22 patients) and no change in 18% (four of 22 patients); medical therapy led to improvement in 18% (two of 11 patients), worsening in 18% (two of 11 patients), and no change in 64% (seven of 11 patients; p < 0.05). Continuous ICP monitoring via the shunt reservoir provides a more accurate assessment of shunt malfunction than transient ICP monitoring with a shunt tap or a radionuclide shunt patency study. It is a safe method for evaluating patients with suspected VP shunt malfunction, provides in vivo assessment of the effect of the shunt system on a patient's ICP, and can lead to more effective shunt revision.

Effects of interleukin‐6 (IL‐6) deletion in a murine model of ventilator‐associated lung injury (VALI)

Rationale: IL-6 is increased in both lung and plasma in animal models of VALI. Ventilation of ARDS patients with a low tidal volume (VT) improved mortality, and decreased circulating levels of IL-6. We thus hypothesized that IL-6 might contribute to the development of VALI. Methods: To test this hypothesis, 6-8 wk old mice deficient for IL-6 (IL6−/−; n=4) or wild-type controls (WT; n=5) were subjected to 4 hr mechanical ventilation (MV; VT 17ml/kg) following HCl aspiration. A femoral arterial catheter was placed for continuous monitoring of mean arterial pressure (MAP). After 4 hr, arterial blood gas analysis was performed, and lung injury was assessed by measurement of left lung wet/dry (W/D) weight. Results: W/D lung weight was significantly lower in IL-6−/− mice following MV+HCl, as compared with WT (5.3 ± 0.2 vs 6.8 ± 0.8 respectively; p<0.05). In addition, IL-6−/− mice were significantly protected from the development of shock as compared with WT animals (MAP 64 ± 16 vs. 18 ± 4 mmHg during last hr of MV and HCO3 12.2 ± 2.4 vs. 5.8 ± 1.6 mmol/L respectively; p < 0.05). Conclusions: These data support an important role for IL-6 in the pathogenesis of lung injury and circulatory collapse in this non-septic model of VALI. Strategies to interfere with IL-6 expression or signaling may therefore represent important therapeutic targets to limit local and systemic effects of injurious mechanical ventilation. Funded by NIH HL 073994

Endoscopic Ultrasound (EUS)-Guided Portal Vein Catheterization: A Novel Promising Approach for Portal Angiography and Portal Vein Pressure Measurements

Background: Portal vein (PV) pressure measurements can provide valuable clinical information for management of patients with liver disease and portal hypertension. Aim: To assess the feasibility of EUS-guided PV catheterization and pressure measurements in a porcine model. Methods: We performed acute and survival experiments on 50-kg pigs under general anesthesia. Intrahepatic branch of PV, was identified with linear array endoscopic ultrasound (EUS). PV puncture was performed using a 19 gauge fine needle aspiration (FNA) needle. A 0.035 inch guide wire was advanced through the needle into the PV under fluoroscopic and EUS guidance. The FNA needle was withdrawn over the wire and exchanged to a modified 5.5 Fr ERCP catheter. The catheter was advanced into the PV and.connected to a continuous pressure monitor. Iodinated contrast was injected through the catheter to confirm catheter position and to study PV anatomy. Continuous PV pressure measurements were obtained for a duration of 1 hour. Afterwards the catheter was removed, the animals were observed for 30 minutes and 3 animals were sacrificed for necropsy. The other 2 animals were survived for 2 weeks and then sacrificed. Results: We completed 5 animal experiments. PV catheterization, angiography and pressure measurement were performed in all animals without any problems or complications. Angiography through the catheter demonstrated good opacification of PV and its branches. The measurements demonstrated consistent results with minimal variability. There was no change in vital signs or hemodynamic parameters during PV catheterizations, angiography, pressure measurements and catheter removal in all animals. Survival experiments did not reveal any changes in animal condition, vital signs, behavior and eating habits post procedure. Postmortem examination in all animals revealed no active bleeding, or damage to the liver, other intraabdominal organs or blood vessels. Conclusions: EUS-guided PV catheterization is feasible, safe and can be used for portal anigiography and pressure measurements.

The effect of fibrinogen concentrate on thrombocytopenia.

The hypothesis that the administration of fibrinogen concentrate enables restoration of impaired clot formation and increased bleeding in severe thrombocytopenia was tested. Thirty pigs were anesthetized, instrumented for blood sampling (routine coagulation tests, modified thrombelastography ROTEM, hemodynamic monitoring and platelet apheresis to a target below 30 x 10(9) L(-1) after splenectomy. Thereafter 10 each of the animals randomly received two apheresis platelet concentrates, 250 mg kg(-1) fibrinogen concentrate or normal saline solution. A standardized liver injury was subsequently inflicted to induce uncontrolled hemorrhage. Median (Q1, Q3) clot firmness increased significantly more in thrombocytopenic pigs after fibrinogen administration (42 mm (41, 43) to 60 mm (57, 63)) than following platelet transfusion (40 mm (37, 45) to 52 mm (48, 55), P = 0.0004) or placebo (45 mm (41, 48) to 45 mm (43, 46), P = 0.0002). Median blood loss velocity after liver injury was significantly less with fibrinogen (33 mL min(-1), P = 0.005) than with platelets (62 mL min(-1), P = 0.037) or saline (84 mL min(-1), P = 0.005), and median survival time after liver injury was 55 min in the fibrinogen, 26 min in the platelet (P = 0.035) and 19 min in the saline group (P = < 0.0001). These data show for the first time that impaired clot formation during thrombocytopenia improves with administration of fibrinogen concentrate, which results in a slowdown of blood loss and prolonged survival.

Haemodynamic patterns in children with posttraumatic diffuse brain swelling. A preliminary study in 6 cases with neuroradiological features consistent with diffuse axonal injury

In the present report we describe the cerebral haemodynamics and the neuroradiological findings observed in six consecutive children, three males and three females aged 4-15.6 yrs (mean age 8.95) displaying a neuroradiological pattern consistent with diffuse axonal injury (DAI) along with slit ventricles. All the patients were admitted to the Paediatric Intensive Care Unit with GCS scores less than 8 after a severe brain injury. Serial head computed to mography (CT) and magnetic resonance (MR) scans demonstrated a radiological pattern of DAI. Transcranial Doppler Sonography (TCD) of the middle cerebral arteries was performed through the temporal bone window in all the patients. All patients but one underwent a continuous monitoring of intracranial pressure (ICP) and cerebral extraction of O(2) (CEO(2)). Treatment with barbiturates and hyperventilation was necessary in all the cases. In one patient, a bilateral decompressive cran iectomy was performed in order to decrease severe in tracranial hypertension. Hyperflow along with intracranial hyper tension, variably responsive to barbiturate medication, was observed in all the patients by means of TCD and CEO(2). Intracranial hypertension can be elevated in pediatric posttraumatic hyperflow syndromes associated with DAI. The observation of the time course of the parameters studied allowed us to modify the pharmacological treatment and/or perform surgical decompression (external cerebrospinal fluid (CSF) drainage in five cases; decompressive craniectomy in one case). Compartmental hyperflow TCD pattern was evident in only one patient. Although the limited number of pa tients in our series does not allow definite conclusions, we strongly believe that TCD, with ICP and CEO(2) monitoring, are useful tools in planning surgical strategy in children with neuroradiological signs of DAI.

A reliable method for monitoring intraabdominal pressure during natural orifice translumenal endoscopic surgery

Natural orifice translumenal endoscopic surgery (NOTES) provides surgical access to the peritoneal cavity without skin incisions. The NOTES procedure requires pneumoperitoneum for visualization and manipulation of abdominal organs, similar to laparoscopy. Accurate measurement of the pneumoperitoneum pressure is essential to avoid potentially deleterious effects of intraabdominal compartment syndrome. A reliable method for monitoring pneumoperitoneum pressures during NOTES has not been identified. This study evaluated several methods of monitoring intraabdominal pressures with a standard gastroscope during NOTES. Four female pigs (25 kg) were sedated, and a single-channel gastroscope was passed transgastrically into the peritoneal cavity. Pneumoperitoneum was achieved via a pressure insufflator through a percutaneous, intraperitoneal 14-gauge catheter. Three other pressures were recorded via separate catheters. First, a 14-gauge percutaneous catheter passed intraperitoneally measured true intraabdominal pressure. Second, a 14-gauge tube attached to the endoscope was used to measure endoscope tip pressure. The third pressure transducer was connected directly to the accessory channel of the endoscope. The abdomen was insufflated to a range of pressures (10-30 mmHg), and simultaneous pressures were recorded from all three pressure sensors. Pressure correlation curves were developed for all animals across all intraperitoneal pressures (mean error, -4.25 to -1 mmHg). Endoscope tip pressures correlated with biopsy channel pressures (R2 = 0.99). Biopsy channel and endoscope tip pressures fit a least-squares linear model to predict actual intraabdominal pressure (R = 0.99 for both). Both scope tip and biopsy channel port pressures were strongly correlative with true intraabdominal pressures (R2 = 0.98 and R2 = 0.99, respectively). This study demonstrates that monitoring pressure through an endoscope is reliable and predictive of true intraabdominal pressure. Gastroscope pressure monitoring is a useful adjunct to NOTES. Future NOTES procedures should incorporate continuous intraabdominal pressure monitoring to avoid the potentially deleterious effects of pneumoperitoneum during NOTES. This can be achieved by the integration of pressure-monitoring capabilities into gastroscopes.

Continuous Monitoring of Cerebrovascular Autoregulation After Subarachnoid Hemorrhage by Brain Tissue Oxygen Pressure Reactivity and Its Relation to Delayed Cerebral Infarction

Disturbances of cerebrovascular autoregulation are thought to be involved in delayed cerebral ischemia and infarction after aneurysmal subarachnoid hemorrhage (SAH). We hypothesized that the continuous monitoring of brain tissue oxygen (PtiO(2)) pressure reactivity enables the detection of impaired autoregulation after SAH and that impaired autoregulation is associated with delayed infarction. In 67 patients after severe SAH, continuous monitoring of cerebral perfusion pressure (CPP) and PtiO(2) was performed for an average of 7.4 days. For assessment of autoregulation, the index of PtiO(2) pressure reactivity (ORx) was calculated as a moving correlation coefficient between values of CPP and PtiO(2). Higher ORx values indicate disturbed autoregulation, whereas lower ORx values signify intact autoregulation. Twenty patients developed delayed cerebral infarction, and 47 did not. Mean ORx was significantly higher in the infarction group compared with the noninfarction group (0.43+/-0.09 vs 0.23+/-0.14, respectively; P<0.0001). In a day-by-day analysis, ORx did not differ between groups from days 1 to 4 after SAH but was significantly higher from day 5 onward in the infarction group, indicating a deficit of autoregulatory capacity. In a logistic-regression model, ORx values from days 5 and 6 after SAH carried predictive value for the occurrence of delayed infarction but before this event ultimately occurred (P=0.003). ORx indicates impaired autoregulation in patients who develop delayed infarction after SAH. Furthermore, this index may distinguish between patients who finally develop delayed infarction and those who do not.

Indomethacin and cerebral autoregulation in severe head injured patients: a transcranial Doppler study

To assess the effect of indomethacin on cerebral autoregulation, systemic and cerebral haemodynamics, in severe head trauma patients. Prospective, controlled clinical trial, with repeated measurements. A 12-bed adult general intensive care unit in a third level referral university hospital. 16 severely head injured patients, 14 males, age range 17-60. Indomethacin was administrated as a load plus continuous infusion. Indomethacin reactivity was assessed as the estimated cerebral blood flow change elicited by the load. Dynamic and static cerebral autoregulation tests were performed before indomethacin administration, and during its infusion. Systemic and cerebral haemodynamic changes were assessed through continuous monitoring of mean arterial pressure, transcranial Doppler cerebral blood flow velocity, intracranial pressure, cerebral perfusion pressure, and jugular venous oxygen saturation. Indomethacin loading dose was immediately followed by a cerebral blood flow median decrease of 36 or 29% (p = ns) evaluated by two different methods, by an ICP decrease and by an AVDO(2) increase from 3.52 to 6.15 mL/dL (p = 0.002). Dynamic autoregulation increased from a median of 28 to 57% (p<0.05) during indomethacin infusion; static autoregulation also increased, from a median of 72 to 89% (p = ns). Indomethacin decreased intracranial pressure and cerebral blood flow, and increased cerebral perfusion pressure, while maintaining tissue properties of further extracting O(2). The increase in both autoregulatory values reveals an enhancement of cerebral microvasculature reactivity under indomethacin, during hypertensive and--especially--during hypotensive situations.

Diagnosis, Treatment, and Analysis of Long-term Outcomes in Idiopathic Normal-Pressure Hydrocephalus

To the Editor: We read with interest the article by McGirt et al. (9) entitled “Diagnosis, Treatment, and Analysis of Long-term Outcomes in Idiopathic Normal Pressure Hydrocephalus.” The authors conclude that gait impairment is the primary symptom that independently predicted improvement after shunting. The study included 132 patients, 129 (98%) of whom had gait impairment as a feature. We would like to comment on this particular selection criterion, as well as improvements in the Mini Mental State Examination (MMSE) as the sole measure of postoperative cognitive improvement. One of the inclusion criteria for this study was presentation with two or more features of the classic triad. Thus, the analysis inevitably includes patients presenting with dementia and urinary incontinence symptoms but not gait ataxia. Although dementia was originally thought to be the main feature of this syndrome, we have now come to understand that gait disturbance is an essential selection feature for any study with normal pressure hydrocephalus (NPH) patients (4, 6). In a prospective study of 151 patients, Marmarou et al. (8) recently advised that gait improvement immediately after external lumbar drainage is the best prognostic indicator of a positive shunt outcome with greater than 90% accuracy for prediction. Although the two extra inclusion criteria, namely either A- or B-waves, present during continuous pressure monitoring and clinical improvement in symptoms during a 3-day trial of controlled cerebrospinal fluid (CSF) drainage should safeguard against any false positive cases, we still think that the presence of gait ataxia should have been an essential inclusion criterion in the above study. Recent guidelines published in Neurosurgery and studies by other authors suggest that currently there is no evidence to support the prognostic value of A- or-B waves in patients with idiopathic NPH (7, 11, 14). Furthermore, in the same review, we saw that the positive predictive value of the external lumbar drainage averages 85% (7). In the case of McGirt et al. (9), only three patients did not have gait ataxia. Because the level of significance was set at less than 0.05, this small number does not produce a Type I error. The MMSE (5) is a general screening tool for cognitive impairment, dementia, and delirium consisting of five areas of assessment: orientation, registration, attention and calculation, recall, and language. The procedure takes little more than 10 minutes to conduct which, combined with its simplicity in terms of the minimal training required to administer the test, make it one of the most widely used research tools for the screening of cognitive impairment (13). However, there are numerous weaknesses associated with this method which become particularly pertinent when the MMSE is used as the sole measure of cognitive capacity, as was the case in McGirt et al.'s article. Problems associated with the use of MMSE are the lack of a published scoring manual, leading to differences in scoring and interpretation between users (1), variations in the use of cut-off scores as an indication of impairment, and the need to incorporate the educational level of the patients in analyses (12). The type of cognitive decline experienced in NPH varies widely; thus, it is essential that measures used to assess dementia-related aspects of the disorder are sensitive to the range of difficulties with which patients present. Such symptoms may include dyscalculia, acalculia (4), depression, and anxiety (10). Furthermore, the importance of matching all neuropsychological test scores with premorbid intelligence quotient levels and age-matched control data to obtain an accurate perception of any cognitive decline is highlighted by Devito et al. (2). The MMSE does not cover the above aspects of performance, and its ability to assess deficits in hydrocephalus is further reduced by the study's failure to match the data according to the criteria outlined. The MMSE was developed as a screening tool for cognitive decline and should only be used as such (3). As a screening tool, it has its merits; however, it should always be used in conjunction with, and not replace, a comprehensive neuropsychological assessment. Although its brevity makes it speedy and efficient as a screen, it consequently lacks depth and insight into the nature of the cognitive components that may be impaired. It is understood that McGirt et al. began recruiting patients in 1993 when our understanding of NPH was still evolving; thus, the results of the study are noteworthy, particularly as the authors report their results in a large sample size. However, with respect to the inclusion criteria, we emphasize gait as an essential selection criterion. Furthermore, we do not recommend the use of MMSE to provide an accurate account of the cognitive difficulties associated with NPH but rather suggest the use of a formal neuropsychology assessment. Andrew Tarnaris Rebecca F. Stephenson Lisa Cipolotti London, England

Towards automating the pulmonary artery catheter: a canine validation study

We aimed to develop and conduct animal testing of a unique technique for continuous and automatic monitoring of both cardiac output (CO) and left atrial pressure (LAP) by mathematical analysis of a pulmonary artery pressure (PAP) waveform. Our technique specifically analyzes the PAP waveform over long time scales in which the confounding wave and inertial effects are attenuated so as to simultaneously estimate average proportional CO and absolute LAP based on a lumped parameter model. The proportional CO estimates may then be conveniently calibrated with a single thermodilution measurement. To evaluate the technique, we performed an experiment in a closed-chest dog in which the PAP waveform and highly invasive, gold standard aortic flow probe CO and LAP catheter measurements were simultaneously recorded during various pharmacological interventions. We report that the technique achieved an overall CO error of 15.1% after a single calibration and an overall LAP error of 14.4%. For comparison, the LAP error via conventional end-diastolic PAP estimates was over twice as high. With further successful testing, the technique may ultimately be employed so as to effectively automate the pulmonary artery catheter. This work was supported by the NHLBI Grant HL-080568 and an award from the American Heart Association.