New concept for the pressure setting of a programmable pressure valve and measurement of in vivo shunt flow performed using a microflowmeter. Technical note

The aim of this study was to establish a standard method for determining the pressure setting of the Codman Hakim valve (CHV) in patients with hydrocephalus. The authors' investigation was twofold. It focused on: 1) the relationships among CHV setting, intracranial pressure (ICP), intraabdominal pressure (IAP), hydrostatic pressure (HP), and perfusion pressure (PP); and 2) the shunt flow in 18 patients with normal-pressure hydrocephalus. With the patient in a sitting position, the pressure environment around the ventriculoperitoneal shunt stabilized when PP became equal to the CHV setting. The lower the CHV setting, the lower the ICP obtained in patients in a sitting position (ICPsit) settled. This indicated the possibility of calculating the CHV setting by the equation CHV setting = HP + ideal ICPsit - IAP, where the ideal ICPsit was estimated to be between -70 and -140 mm H2O. The CHV setting was individually determined for 18 patients by using this method. The ICPsit, was controlled at a level equal to the estimated ICPsit in most cases, which supported the rationality of our concept. Shunt flow was intermittent or very low when the patient assumed a supine position and between 200 and 600 microl/minute when the patient was seated. Determining the CHV setting by using the equation CHV setting = HP + ideal ICPsit - IAP was found to be useful when directly measuring HP and IAP in patients and estimating the ideal ICPsit to be between -70 and -140 mm H2O. Postoperative shunt control performed using this method was satisfactory, and shunt complications and the number of CHV resettings were lower than in those published in previous reports. Shunt-flow measurement performed in vivo and in real time by using a microflowmeter should be useful not only in testing the functioning of shunt systems, but also in clarifying the pathophysiology of hydrocephalus.     

Effects of ventriculoperitoneal shunt removal on cerebral oxygenation and brain compliance in chronic obstructive hydrocephalus

OBJECT: The pathophysiology of shunt malfunction has not been fully examined, probably because of the paucity of appropriate animal models. Using a canine model of chronic obstructive hydrocephalus, the effects of shunt placement and removal on physiological parameters were evaluated. METHODS: Fifteen dogs, nine in which chronic hydrocephalus was induced and six controls, were used in the experiment. Thirteen weeks after the induction of hydrocephalus, intracranial pressure (ICP), tissue and cerebrospinal fluid O2 saturation, response to hyperventilation, and brain compliance at low (5-15 mm Hg) and high (15-25 mm Hg) pressures were measured (untreated stage). Following this procedure, ventriculoperitoneal shunts were implanted in the dogs suffering from hydrocephalus. Two weeks later, the same series of measurements were repeated (shunted stage), following which the shunt systems were removed. One week after shunt removal, the last measurements were obtained (shunt-removed stage). All dogs underwent magnetic resonance imaging four times: before induction of hydrocephalus and before each measurement. All dogs with hydrocephalus also had ventriculomegaly (1.42 +/- 0.89 ml before induction of hydrocephalus compared with 3.4 +/- 1.64 ml 13 weeks after induction, p = 0.0064). In dogs in the untreated hydrocephalus stage, ICP remained within the normal range (8.33 +/- 2.60 mm Hg)--although it was significantly higher than that in the control group (5 +/- 1.41 mm Hg, p = 0.014). Tissue O2 saturation in the dogs in the hydrocephalus group (26.1 +/- 5.33 mm Hg) was lower than that in the dogs in the control group (48.7 +/- 4.27 mm Hg, p < 0.0001). After the dogs underwent shunt placement, significant improvement was observed in their ICP (5.22 +/- 2.17 mm Hg, p = 0.012) and tissue O2 saturation (35.2 +/- 6.80 mm Hg, p = 0.0084). However, removal of the shunt reversed these improvements back to the preshunt status. Hyperventilation induced significant decreases in ICP and O2 saturation at every measurement time and induced a significant decrease in tissue O2 saturation during the shunted stage, but not during the untreated and shunt-removed stages. Brain compliance measured at high pressure demonstrated a significant gradual decrease at every measurement. CONCLUSIONS: In chronic obstructive hydrocephalus, shunt placement improves ICP and cerebral oxygenation as well as the response to hyperventilation in the tissue. Shunt removal reverses these improvements back to levels present during the untreated stage. The decrease in brain compliance may be one of the factors responsible for symptoms in shunt malfunction.     

Treatment of intracranial hypertension using nonsurgical abdominal decompression

BACKGROUND: Elevated intra-abdominal pressure (IAP) increases intracranial pressure (ICP) and reduces cerebral perfusion pressure (CPP). We evaluated a nonsurgical means of reducing IAP to reverse this process. METHODS: Swine with a baseline ICP of 25 mm Hg produced by an intracranial balloon catheter were studied. In group 1 (n = 5), IAP was increased by 25 mm Hg. Continuous negative abdominal pressure (CNAP) was then applied. Group 2 (n = 4) had neither IAP elevation nor CNAP. Group 3 (n = 4) had CNAP without IAP elevation. RESULTS: Elevation of IAP by 25 mm Hg above baseline led to deleterious changes in ICP (25.8+/-0.8 to 39.0+/-2.8; p < 0.05) and CPP (85.2+/-2.0 to 64.8+/-2.6; p < 0.05). CNAP led to a reduction in IAP (30.2+/-1.2 to 20.4+/-1.3; p < 0.05) and improvements in cerebral perfusion (ICP, 33+/-2.7; CPP, 74.4+/-1.2; both p < 0.05). Group 2 had stable ICP (25.8+/-0.25 to 28.7+/-1.7; p > 0.05) and CPP (80.8+/-1.4 to 80.5+/-1.8; p > 0.05). In group 3, CNAP decreased cardiac index (2.9+/-0.2 to 1.1+/-0.4; p < 0.05), mean arterial pressure (105.2+/-4.0 to 38.2+/-12.0; p < 0.05), and CPP (74.2+/-4.7 to 14.5+/-12.2; p < 0.05). CONCLUSION: Elevations in IAP led to increased ICP and decreased CPP. CNAP ameliorated these intracranial disturbances. With normal IAP, CNAP impaired cerebral perfusion.     

Adverse impact of a calcium entry-blocker (verapamil) on intracranial pressure in patients with brain tumors

In order to examine the effects of verapamil on intracranial pressure (ICP) in patients with compromised intracranial compliance, five hypertensive patients with supratentorial tumors were given verapamil, 5 mg intravenously, at the time of anesthesia induction. Within 4 minutes, ICP increased 67% from 18 +/- 4 mm Hg (standard error) to 27 +/- 5 mm Hg (p less than 0.05), whereas mean arterial pressure decreased 20% from 111 +/- 7 mm Hg to 89 +/- 4 mm Hg (p less than 0.05), and cerebral perfusion pressure (CPP) decreased 33% from 93 +/- 11 mm Hg to 62 +/- 6 mm Hg (p less than 0.05). The increases in ICP responded promptly to hyperventilation and intravenous lidocaine (1.5 mg/kg). A control group of five hypertensive patients with supratentorial tumors received the same anesthetic agents without verapamil. In this group, ICP and CPP were unchanged. The authors conclude that calcium entry-blockers, such as verapamil, should be avoided in patients with compromised intracranial compliance unless ICP is being monitored and proper therapy for intracranial hypertension can be rapidly instituted.     

Optimum position for an anti-siphon device in a cerebrospinal fluid shunt system.

The effects on shunt flow from the position of an antisiphon device (ASD) and from changes in posture in hydrocephalic patients were examined. Fifty patients with hydrocephalus (including 36 with normal pressure hydrocephalus) were investigated, using quantitative radionuclide shuntography (99mtechnetium-pertechnetate) in the supine, sitting, and standing positions. The types of shunt valve used were as follows: Mishler dual chamber low pressure without ASD (16 cases), with ASD 40 cm below the level of the foramen of Monro (three cases), and with ASD 10 cm below the level of the foramen of Monro (12 cases); low pressure with integral ASD (14 cases); and medium pressure with integral ASD (five cases). In patients with a low pressure valve without ASD, shunt flow was least in the supine position (0.0011 ml/min) but increased significantly in the sitting position (0.4381 ml/min, P less than 0.001) because of the siphon effect. Conversely, in patients with a low pressure valve with integral ASD, shunt flow was maximal in the supine position (0.1056 ml/min) and decreased significantly in the sitting position (0.0017 ml/min, P less than 0.001), indicating overfunction of the ASD. Intracranial pressure (ICP) in the supine position increased significantly compared with patients with a low pressure valve without ASD (93.6 and 20.7 mm H2O, respectively, P less than 0.01). Intermediate values for shunt flow in the supine and sitting positions (0.0279 and 0.0896 ml/min, respectively) and for ICP (55.8 mm H2O) were obtained with patients with a low pressure valve with the ASD 10 cm below the level of the foramen of Monro (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Overdrainage after ventriculoperitoneal shunting in a patient with a wide depressed skull bone defect: The effect of atmospheric pressure gradient

IntroductionIn patients with traumatic brain injury, an effective approach for managing refractory intracranial hypertension is wide decompressive craniectomy. Postoperative hydrocephalus is a frequent complication requiring cerebrospinal fluid (CSF) diversion.Presentation of caseA 50-year-old male who underwent decompressive craniectomy after traumatic brain injury. He developed hydrocephalus postoperatively, and accordingly we placed a ventriculoperitoneal shunt. However, an imbalance between the intra- and extra-cranial atmospheric pressures led to overdrainage, and he suffered cognitive disorders and extremity weakness. He remained supine for 5 days to avoid the effect of gravity on CSF diversion. After 20 days, we performed a cranioplasty using a titanium plate. The postoperative course was uneventful, and the patient achieved satisfactory recovery.DisccusionThe gravitational effect and the atmospheric pressure gradient effect are two factors associated in the ventriculoperitoneal (VP) shunt treatment of hydrocephalus for the patient who had decompressive craniectomy. These effects can be eliminated by supine bed rest and cranioplasty.ConclusionWe herein emphasize the efficacy of VP shunt, supine bed rest and cranioplasty in treating hydrocephalus patients who have undergone craniectomy. A flexible application of these procedures to change the gravitational effect and the atmospheric pressure gradient effect should promote a favorable outcome.     

Treatment of hydrocephalus in adults by placement of an open ventricular shunt.

OBJECT: Ventricular shunt placement is the neurosurgical procedure most frequently associated with complications. Over the years, it has been a growing concern that the performance of most shunting devices does not conform to physiological parameters. An open ventriculoperitoneal (VP) bypass with a peritoneal catheter for which the cross-sectional internal diameter was 0.51 mm as a distinctive element for flow resistance was evaluated for use in the treatment of adult patients with hydrocephalus. METHODS: During a 2-year period, open shunts were surgically implanted in 54 adults with hydrocephalus; conventional shunts were implanted in 80 matched controls. Periodic evaluations were performed using neuroimaging studies and measures of clinical status. All patients were followed from 12 to 36 months. 18.5 +/- 4 months for patients with the open shunt and 19.1 +/- 8.1 months for controls (mean +/- standard deviation). The device continued to function in 50 patients with the open shunt (93%) and in 49 controls (61%: p < 0.001). The Evans index in patients with the open shunt was 0.33 +/- 0.09 throughout the follow up. No cases of infection, overdrainage, or slit ventricles were observed: the index in controls was 0.28 +/- 0.08; 60% of them developed slit ventricles. During the follow-up period occlusion occurred in four patients with the open shunt (7%) and in 31 controls (39%: p < 0.001). CONCLUSIONS: The daily cerebrospinal fluid (CSF) drainage through the open VP shunt is close to 500 ml of uninterrupted flow propelled by the hydrokinetic force generated by the combination of ventricular pressure and siphoning effect. It complies with hydrokinetic parameters imposed by a bypass connection between the ventricular and peritoneal cavities as well as with the physiological archetype of continuous flow and drainage according to CSF production. The open shunt is simple, inexpensive, and an effective treatment for hydrocephalus in adults.     

Effects of PEEP on the intracranial system of patients with head injury and subarachnoid hemorrhage: the role of respiratory system compliance

BACKGROUND: Positive end-expiratory pressure (PEEP) can be effective in improving oxygenation, but it may worsen or induce intracranial hypertension. The authors hypothesized that the intracranial effects of PEEP could be related to the changes in respiratory system compliance (Crs). METHODS: A prospective study investigated 21 comatose patients with severe head injury or subarachnoid hemorrhage receiving intracranial pressure (ICP) monitoring who required mechanical ventilation and PEEP. The 13 patients with normal Crs were analyzed as group A and the 8 patients with low Crs as group B. During the study, 0, 5, 8, and 12 cm H2O of PEEP were applied in a random sequence. Jugular pressure, central venous pressure (CVP), cerebral perfusion pressure (CPP), intracranial pressure (ICP), cerebral compliance, mean velocity of the middle cerebral arteries, and jugular oxygen saturation were evaluated simultaneously. RESULTS: In the group A patients, the PEEP increase from 0 to 12 cm H2O significantly increased CVP (from 10.6 +/- 3.3 to 13.8 +/- 3.3 mm Hg; p < 0.001) and jugular pressure (from 16.6 +/- 3.1 to 18.8 +/- 3.2 mm Hg; p < 0.001), but reduced mean arterial pressure (from 96.3 +/- 6.7 to 91.3 +/- 6.5 mm Hg; p < 0.01), CPP (from 82.2 +/- 6.9 to 77.0 +/- 6.2 mm Hg; p < 0.01), and mean velocity of the middle cerebral arteries (from 73.1 +/- 27.9 to 67.4 +/- 27.1 cm/sec; F = 7.15; p < 0.001). No significant variation in these parameters was observed in group B patients. After the PEEP increase, ICP and cerebral compliance did not change in either group. Although jugular oxygen saturation decreased slightly, it in no case dropped below 50%. CONCLUSIONS: In patients with low Crs, PEEP has no significant effect on cerebral and systemic hemodynamics. Monitoring of Crs may be useful for avoiding deleterious effects of PEEP on the intracranial system of patients with normal Crs.     

Changes in intracranial pressure (ICP) pulse wave following hydrocephalus

Summary The pulse pressure (PP) of the intracranial pressure pulse wave (ICPPW) was measured in experimental and clinical hydrocephalus: namely, obstructive and kaolin-induced hydrocephalus as an experimental study, and noncommunicating and communicating hydrocephalus as a clinical study.At approximately the same ICP level, the PP was much higher in the obstructive hydrocephalus group and slightly higher in the kaolin-induced hydrocephalus group than in the controls. Also the PP level in noncommunicating hydrocephalus patients [3.19mm Hg (SD: 1.04)] was significantly (P<0.05) higher than that in the communicating hydrocephalus patients [1.88 mm Hg (SD: 0.60)].The results of our research suggest that the stronger the disturbance of the communication of the CSF between cranial cavity and spinal cavity the higher the PP of ICPPW. This results from the distensibility of the spinal dural sac and exerts a great influence on the elasticity and the PP of the cranial system. It is reasonable, therefore, to suggest that a marked increase in the ratio of the PP to the ICP in the normal or slightly high ICP hydrocephalus may indicate disturbance of the CSF flow, especially loss of CSF communication between the cranial and spinal compartments.     

Experimental feline hydrocephalus. The role of biomechanical changes in ventricular enlargement in cats

In a craniectomy-durectomy model of kaolin-induced feline hydrocephalus, the pressure-volume index (PVI) technique of bolus manipulations of cerebrospinal fluid (CSF) was used to study the biomechanical changes associated with hydrocephalus. Steady-state intracranial pressure (ICP), PVI, and the resistance to the absorption of CSF were determined acutely and 3 to 5 weeks later in hydrocephalic cats and time-matched control cats. Steady-state ICP was 11.0 +/- 2.1 mm Hg (+/- standard deviation) in the hydrocephalic cats, compared to 10.8 +/- 2.2 mm Hg in the chronic control group (p greater than 0.1). The ICP in both the chronic hydrocephalic and chronic control groups was significantly higher (p less than 0.001) than after acute durectomy (mean ICP 8.5 +/- 1.2 mm Hg). Immediately after dural opening, the mean PVI was 3.6 +/- 0.2 ml (+/- standard error of the mean); over time, it decreased to 1.3 +/- 0.1 ml in the chronic control group (p less than 0.001), but remained elevated in the hydrocephalic group at 3.5 +/- 0.4 ml (p less than 0.001). Resistance to CSF absorption was 9.1 +/- 1.4 mm Hg/ml/min immediately after dural opening and increased to 28.8 +/- 4.5 mm Hg/ml/min (p less than 0.001) in the hydrocephalic cats; it increased even further in the chronic measurements in control cats, to 82.3 +/- 9.2 mm Hg/ml/min (p less than 0.001). Ventricular size was moderate to severely enlarged in all hydrocephalic cats, and normal in the control group. These results indicate that the biomechanical profile of the altered brain container model of kaolin-induced feline hydrocephalus resembles that described in hydrocephalic infants. As shown in the control subjects, an absorptive defect alone is not sufficient to cause progressive ventricular enlargement. Increased volume-buffering capacity coupled with a moderate increase of CSF absorption resistance facilitates volume storage in the ventricles.     

Development of a quick reference table for setting programmable pressure valves in patients with idiopathic normal pressure hydrocephalus

Quick and reliable setting of programmable pressure valves (PPVs) is important in the treatment of idiopathic normal pressure hydrocephalus (iNPH), especially for reducing overdrainage complications and related medical costs. A new quick reference table (QRT) was developed for improved PPV control and outcome. Shunt control can be based on the pressure environment in the sitting condition, given as hydrostatic pressure (HP) = intracranial pressure + PPV setting + intraabdominal pressure (IAP). Using this relationship, and estimating HP and IAP from the patient's height and body mass index, respectively, a QRT was designed, consisting of a matrix of the patient's height and weight. The QRT was used to make initial PPV settings in 25 patients with iNPH and the clinical outcomes were evaluated. Postoperative readjustments of the PPV were not necessary in 15 of the 25 patients. At 1 month after operation, the PPV setting was decreased once in 5 patients and increased once in 2 patients. Four of these 7 patients improved after a single readjustment. Three patients required further readjustments. At 3 months after operation, another 3 patients required a single readjustment and all improved after this readjustment. The readjustment rate was 40% and readjustment number was 0.68 times/patient. The mean PPV setting at 1 year after operation was 15.5 +/- 3.9 cmH(2)O. Use of the QRT in non-bedridden iNPH patients results in a low incidence of PPV readjustment.     

A laboratory model of shunt-dependent hydrocephalus. Development and biomechanical characterization

This study was designed to determine whether implanting shunts in hydrocephalic cats produced the same biomechanical changes as have previously been found in children with shunts. Neuraxis volume-buffering capacity (pressure-volume index: PVI) and the resistance to the absorption of cerebrospinal fluid (CSF) were determined before and 3 weeks after placing shunts in 16 hydrocephalic cats. Intracranial pressure (ICP) was monitored for at least 6 hours after the shunts were occluded. The brains were perfused in vivo and removed to assess the size of the ventricles. The mean PVI of the hydrocephalic cats was 3.6 +/- 0.2 ml (+/- standard error of the mean) before the shunts were placed. Three weeks after adequate shunt function was first established, the mean PVI decreased to 1.1 +/- 0.1 ml and was similar to values determined in control animals. Prior to shunt placement, the resistance to the absorption of CSF was 28.4 +/- 4.5 mm Hg/ml/min and did not vary with ICP. This parameter changed after shunting and increased as a function of ICP (r = 0.87, p less than 0.001). At ICP's below 20 mm Hg, the resistance to the absorption of CSF was 65.0 +/- 18.0 mm Hg/ml/min but increased to 220.0 +/- 40.5 mm Hg/ml/min when determined at ICP's above 20 mm Hg. Corroborating evidence for this linkage of resistance to the absorption of CSF to ICP was found in the inexorable rise of ICP during the 6 hours of monitoring after the shunts were occluded. After shunt placement, the ventricles were normal in size in 12 cats and slightly enlarged in four. The biomechanical profile and pressure response to shunt occlusion in this laboratory model resembles that previously described in shunt-dependent children. As in humans, shunt placement in hydrocephalic cats results in normalization of the PVI and a linkage of the resistance to the absorption of CSF to ICP. The significance of these changes as they relate to shunt dependency is discussed.     

Ventriculoperitoneal shunt of continuous flow vs valvular shunt for treatment of hydrocephalus in adults

BACKGROUND: Shunting for hydrocephalus is the neurosurgical procedure most frequently associated with long-term complications. We developed an alternative to valvular shunts based on a simple shunt procedure whose functioning depends on a peritoneal catheter with a highly precise cross-sectional internal diameter of 0.51 mm. Preliminary studies have shown that the shunt of continuous flow (SCF) is superior to valvular shunts for the treatment of hydrocephalus in adults. Here, we show the long-term performance of the SCF in adult patients with hydrocephalus secondary to a comprehensive variety of neurological disorders. METHODS: In a 5-year period, ventriculoperitoneal shunting was performed on 307 patients with hydrocephalus; 114 of them were treated with the SCF and 193 controls were treated with a conventional valvular shunt. Patients were followed from 1 to 5 years after surgery; endpoint observation was considered at surgical reintervention because of shunt failure. RESULTS: At the end of the observation period (44 +/- 17 months), the failure rate of the shunting device was 14% for the SCF and 46% for controls (P < .0002). Shunt endurance was 88% in patients with SCF and 60% in controls. Along the study, signs of overdrainage developed in 40% of patients treated with valvular shunt, but they were not observed in patients with SCF. CONCLUSIONS: The design of the SCF was calculated according to the mean rates of cerebrospinal fluid production; it takes simultaneous advantage of the intraventricular pressure and the siphon effect and complies with the principle of uninterrupted flow, maintaining a fair equilibrium that prevents under- and overdrainage. The SCF is a simple, inexpensive, and effective treatment for hydrocephalus in adults.     

Cerebral and cardiovascular responses to changes in head elevation in patients with intracranial hypertension

To establish if an optimum level of head elevation exists in patients with intracranial hypertension, the authors examined changes in intracranial pressure (ICP), systemic and pulmonary pressures, systemic flows, and intrapulmonary shunt fraction with the patient lying flat, and then with the head elevated at 15 degrees, 30 degrees, and 60 degrees. Cerebral perfusion pressure (CPP) was calculated. The lowest mean ICP was found with elevation of the head to 15 degrees (a fall of -4.5 +/- 1.6 mm Hg, p less than 0.001) and 30 degrees (a fall of -6.1 +/- 3.5 mm Hg, p less than 0.001); the CPP and cardiac output were maintained. With elevation of the head to 60 degrees, the mean ICP increased to -3.8 +/- 9.3 mm Hg of baseline, while the CPP decreased -7.9 +/- 9.3 mm Hg (p less than 0.02), and the cardiac index also fell -0.25 +/- 0.28 liters/min/sq m (p less than 0.01). No significant change in filling pressures, arterial oxygen content, or heart rate was encountered at any level of head elevation. Therefore, a moderate degree (15 degrees or 30 degrees) of head elevation provides a consistent reduction of ICP without concomitant compromise of cardiac function. Lower (0 degrees) or higher (60 degrees) degrees of head elevation may be detrimental to the patient because of changes in the ICP, CPP, and cardiac output.     

Estimation of intra-abdominal pressure by bladder pressure measurement: validity and methodology

BACKGROUND: Increased intra-abdominal pressure (IAP) is an adverse complication seen in critically ill, injured, and postoperative patients. IAP is estimated via the measurement of bladder pressure. Few studies have been performed to establish the actual relationship between IAP and bladder pressure. The purpose of this study was to confirm the association between intravesicular pressure and IAP and to determine the bladder volume that best approximates IAP. METHODS: Thirty-seven patients undergoing laparoscopy had intravesicular pressures measured with bladder volumes of 0, 50, 100, 150, and 200 mL at directly measured intra-abdominal pressures of 0, 5, 10, 15, 20, and 25 mm Hg. Correlation coefficients and differences were then determined. RESULTS: Across the IAP range of 0 to 25 mm Hg using all of the tested bladder volumes, the difference between IAP and intravesicular pressures (bias) was -3.8 +/- 0.29 mm Hg (95% confidence interval) and measurements were well correlated (R2 = 0.68). Assessing all IAPs tested, a bladder volume of 0 mL demonstrated the lowest bias (-0.79 +/- 0.73 mm Hg). When considering only elevated IAPs (25 mm Hg), a bladder volume of 50 mL revealed the lowest bias (-1.5 +/- 1.36 mm Hg). A bladder volume of 50 mL in patients with elevated IAP resulted in an intravesicular pressure 1 to 3 mm Hg higher than IAP (95% confidence interval). CONCLUSION: Intravesicular pressure closely approximates IAP. Instillation of 50 mL of liquid into the bladder improves the accuracy of the intravesicular pressure in measuring elevated IAPs.     

Subtle deterioration in shunted childhood hydrocephalus. A biomechanical and clinical profile

Eighteen hydrocephalic children who presented with subtle deterioration when their shunts malfunctioned were studied during shunt revision by means of the pressure-volume index (PVI) technique. Bolus manipulation of cerebrospinal fluid (CSF) was used to determine the PVI and the resistance to the absorption of CSF (Ro). Ventricular size was moderately to severely enlarged in all the children. Steady-state intracranial pressure (ICP) at the time of shunt revision was 17.5 +/- 7.3 mm Hg (range 8 to 35 mm Hg). Pressure waves could not be induced by bolus injections in the 8- to 35-mm Hg range of ICP tested. The mean +/- standard deviation (SD) of the predicted normal PVI for this group was 18.5 +/- 2.7 ml. The mean +/- standard error of the mean of the measured PVI was 35.5 +/- 2.1 ml, which represented a 187% +/- 33% (+/- SD) increase in volume-buffering capacity (p less than 0.001). The ICP did not fall after bolus injections in three children, so that the Ro could not be measured. In the remaining 15 patients, Ro increased linearly as a function of ICP (r = 0.74, p less than 0.001). At ICP's below 20 mm Hg, Ro ranged from 2.0 to 5.0 mm Hg/ml/min, but increased to as high as 21 mm Hg/ml/min when ICP was above 20 mm Hg. This study documents that subtle deterioration in shunted hydrocephalic children is accompanied by abnormally compliant pressure-volume curves. These children develop ventricular enlargement and neurological deterioration without acute episodic pressure waves. The biomechanical profile of this group differs from other children with CSF shunts.     

Experiences with the anti-siphon device (ASD) in shunt therapy of pediatric hydrocephalus

A follow-up study was performed on 41 hydrocephalic children with primary (10 patients) or secondary (31 patients) placement of an anti-siphon device (ASD) connected to their shunt. The clinical course before and after ASD implantation was compared in these two groups, including studies of the head circumference, the radiological ventricular size, cerebrospinal fluid pressure studies on the supine and upright patient, and the history of shunt-induced complaints and complications leading to hospitalization. The authors discuss the pathophysiological concept of the "chronic overdrainage " or slit-ventricle syndrome based on ventricular collapse due to chronic suction-induced overdrainage by the vertical shunt system in the upright patient. The use of an ASD in connection with the regular shunt system of children with hydrocephalus is proposed. This ASD-shunt combination successfully reduced the number of complaints and shunt dysfunctions over a period of more than 6 years.     

Prospective study of methodological issues in intracranial pressure monitoring in patients with hydrocephalus

OBJECT: Continuous intracranial pressure (ICP) monitoring is performed in selected patients with hydrocephalus to determine whether shunt placement is required. The mean ICP is usually calculated from end-hour readings manually recorded by nurses. The aim of this study was to evaluate the accuracy of manual recordings by comparing nurses' end-hour ICP readings with those of an online computerized ICP monitoring system that records one ICP value per second. METHODS: Continuous ICP monitoring was performed using a fiberoptic extradural sensor in 115 patients with hydrocephalus of different origins. A notebook computer was connected to an ICP monitor and was programmed to register one ICP value per second. In all patients, mean ICP values were calculated from data recorded manually by nurses at the end of every hour and from data recorded by the computer within the preselected time period. The two methods were compared using correlation analysis and the Bland and Altman method. The median number of ICP values noted manually by the nurses in each patient was 17 (interquartile range 15-18 readings), and that recorded by the software was 61,200 (interquartile range 54,000-64,800 readings). The correlation coefficient of the mean ICP values recorded by both methods was r = 0.99 (p < 0.001). The Bland and Altman analysis revealed a mean difference of 0.3 +/- 1.26 mm Hg between the two methods and that they were equally valid with all mean ICP values. CONCLUSIONS: The recording of end-hour ICP values by nurses is an accurate method of calculating the mean ICP after prolonged ICP monitoring in patients with hydrocephalus.     

Increased intra-abdominal, intrathoracic, and intracranial pressure after severe brain injury: multiple compartment syndrome

OBJECTIVES: Fluid therapy and/or acute lung injury may increase intra-abdominal pressure (IAP) and intrathoracic pressure, thereby increasing intracranial pressure (ICP) after traumatic brain injury (TBI). Further fluid administration to support cerebral perfusion or increasing ventilatory support to treat acute lung injury further increases ICP. This can create a cycle that ultimately produces multiple compartment syndrome (MCS). Both decompressive craniectomy (DC) and decompressive laparotomy (DL) decrease ICP. DL can also decrease IAP and ICP. We evaluated the serial application of DC and DL to treat MCS. METHODS: Data were analyzed for 102 consecutive patients with severe TBI who underwent DC alone to decrease ICP or in combination with DL to treat MCS. RESULTS: All 102 patients sustained blunt injury. Seventy percent were men with a mean age of 29.5 years, an Injury Severity Score of 34.4, and admission Glasgow Coma Scale score of 7.1. Fifty-one patients had diffuse brain injury and 51 had mass lesions. Seventy-eight patients (76%) underwent DC alone. Twenty-four (22%) had both therapies for MCS. Fifteen patients had DC before DL and nine had DL before DC. Mean time between DC and DL was 3.4 +/- 6 days. The mean IAP before DL was 28 +/- 5 mm Hg. Twenty-four-hour cumulative mean intrathoracic pressure decreased significantly after DL in the MCS group (p = 0.01). Mean ICP decreased significantly after both DC and DL (p < 0.05). CONCLUSION: Increased ICP may be from primary TBI or MCS. Patients with MCS have a higher Injury Severity Score, ICP, and fluid requirements, but no increase in mortality. Both DC and DL reduce ICP and can be used in sequence. MCS should be considered in multiply injured patients with increased ICP that does not respond to therapy.     

The effects of prone positioning on intraabdominal pressure and cardiovascular and renal function in patients with acute lung injury

To detect any harmful effects of prone positioning on intraabdominal pressure (IAP) and cardiovascular and renal function, we studied 16 mechanically ventilated patients with acute lung injury randomly in prone and supine positions, without minimizing the restriction of the abdomen. Effective renal blood flow index and glomerular filtration rate index were determined by the paraaminohippurate and inulin clearance techniques. Prone positioning resulted in an increase in IAP from 12 +/- 4 to 14 +/- 5 mm Hg (P < 0.05), PaO(2)/fraction of inspired oxygen from 220 +/- 91 to 267 +/- 82 mm Hg (P < 0.05), cardiac index from 4.1 +/- 1.1 to 4.4 +/- 0.7 L/min (P < 0.05), mean arterial pressure from 77 +/- 10 to 82 +/- 11 mm Hg (P < 0.01), and oxygen delivery index from 600 +/- 156 to 648 +/- 95 mL. min(-)(1). m(-)(2) (P < 0.05). Renal fraction of cardiac output decreased from 19.1% +/- 12.5% to 15.5% +/- 8.8% (P < 0.05), and renal vascular resistance index increased from 11762 +/- 6554 dynes. s. cm(-)(5). m(2) to 15078 +/- 10594 dynes. s. cm(-)(5). m(2) (P < 0.05), whereas effective renal blood flow index, glomerular filtration rate index, filtration fraction, urine volume, fractional sodium excretion, and osmolar and free water clearances remained constant during prone positioning. Prone positioning, when used in patients with acute lung injury, although it is associated with a small increase in IAP, contributes to improved arterial oxygenation and systemic blood flow without affecting renal perfusion and function. Apparently, special support to allow free chest and abdominal movement seems unnecessary when mechanically ventilated, hemodynamically stable patients without abdominal hypertension are proned to improve gas exchange. IMPLICATIONS: Prone positioning is increasingly used to improve gas exchange in patients with acute lung injury. However, during prone positioning an increase in intraabdominal pressure in these critically ill patients may promote dysfunction of other organs. Therefore, we performed a randomized study in mechanically ventilated patients with acute lung injury to investigate the cardiovascular and renal effects of prone positioning.