Effect of positive end-expiratory pressure on the incidence of venous air embolism and on the cardiovascular response to the sitting position during neurosurgery

We have studied prospectively the effect of 10 cm H2O of PEEP on the incidence of venous air embolism and on the cardiovascular response to change from the supine to the seated position in a large neurosurgical population. Patients were allocated randomly to receive either PEEP (10 cm H2O, n = 45) or conventional (control, n = 44) ventilation. Cardiovascular and respiratory variables were measured in the supine and sitting positions, and monitoring included precordial Doppler probe, pulmonary artery pressure and expiratory carbon dioxide concentration. Venous air embolism was assumed if changes in precordial Doppler sounds occurred, end-tidal carbon dioxide concentration decreased or air could be retrieved from a central venous multi-orifice catheter. The incidence of venous air embolism (26%) did not differ between patients undergoing conventional ventilation and those undergoing ventilation with 10 cm H2O of PEEP. Venous air embolism was always detected first by alterations in Doppler sounds. Cardiac output was significantly higher in patients undergoing conventional ventilation than in those undergoing ventilation with PEEP in the supine but not in the sitting position. Furthermore, pulmonary vascular resistance increased significantly only in the upright position in those undergoing ventilation with PEEP. The pulmonary artery wedge pressure to central venous pressure gradient did not attain negative values with PEEP or with upright positioning. We conclude that the use of PEEP during neurosurgical procedures performed in the sitting position should be abandoned as it does not decrease the incidence of venous air embolism but is associated with significant adverse cardiovascular effects.      

Venous air emboli occur during release of positive end-expiratory pressure and repositioning after sitting position surgery.

We studied the effect of positive end-expiratory pressure (PEEP) release and positioning on the occurrence of venous air embolism (VAE). Eighteen consecutive patients (8 women, 10 men; ASA grade I-III) undergoing neurosurgery in the sitting position were studied. After induction of anesthesia ventilation was controlled with a PEEP of 5 cm H(2)O in an oxygen-air gas mixture. A transesophageal echocardiographic (TEE) probe was inserted. Preoperatively, a patent foramen ovale was excluded in all patients. TEE monitoring was performed during surgery, during PEEP release at the end of surgery with the patient still in the sitting position, and during change of the patient position into the supine position. The severity of VAE was differentiated as follows: grade 1 = only microbubbles; grade 2 = microbubbles and decrease of end-tidal carbon dioxide partial pressure (PETCO(2)) by more than 1.5 mm Hg; grade 3 = microbubbles combined with a decrease of PETCO(2) by more than 1.5 mm Hg, and a decrease of mean arterial blood pressure by at least 20 mm Hg. During surgery, VAE with a grade of 1, 2 or 3 occurred in 7, 4, and 2 patients, respectively. After PEEP release, VAE of grades 1, 2, and 3 were observed in 7, 2, and 1 patients, respectively. During repositioning from sitting to supine position, VAE of grades 1, 2, and 3 was observed in 6, 1, and 1 patients, respectively. The patient with VAE grade 3 needed inotropic support until 2 h after surgery to maintain sufficient blood pressure. No patient showed any sign of paradoxical arterial embolism or cardiac dysfunction. We conclude that VAE occurs not only during surgery in the sitting position, but also with release of PEEP and during repositioning to the supine position. IMPLICATIONS: This study shows that venous air embolism (VAE) occurs not only during surgery in the sitting position but also during positive end-expiratory pressure release and repositioning of the patient into the supine position. Continuous monitoring for VAE should be performed until the patient is returned to the supine position.     

Effects of positive end-expiratory pressure on intracranial pressure and compliance in brain-injured patients.

Hypoxic pulmonary disorders and head injuries associated with increased intracranial pressure (ICP) frequently co-exist. Positive end-expiratory pressure (PEEP) improves hypoxemia but has been reported to impede cerebral venous return, potentially causing a further increase in ICP. This study examined the effects of PEEP on ICP at different levels of brain compliance. continuous ICP recordings were obtained after insertion of Scott cannulas to the lateral ventricles of seven comatose patients. Brain compliance was assessed by calculation of the pressure volume index. Patients were maintained in a 30 degrees head-up position. Maintenance of PEEP to levels of 40 cm H2O pressure for as long as 18 hours did not increase ICP in patients with either normal or low intracranial compliance, and did not increase ICP in the absence of pulmonary disease. Central venous pressure and pulmonary artery wedge pressure increased proportionately as PEEP was increased. No consistent changes were found in blood pressure recordings, nor were there any reductions in cardiac output found during the studies. Abrupt discontinuation of PEEP did not result in increased ICP except for a transient rise on two occasions when respiratory secretions became copious and the patients were inadequately ventilated. Improved oxygenation in two patients as a result of PEEP was concomitant with improved intracranial compliance and neurological status. In patients with brain injuries, PEEP improves arterial oxygenation without increasing ICP as previously supposed. Consequently, PEEP is a valuable form of therapy for the comatose patient with pulmonary disorders such as pneumonia or pulmonary edema.     

Intracranial and spinal cord hemodynamics in the sitting position in dogs in the presence and absence of increased intracranial pressure

The effect of the sitting position on cerebral blood flow (CBF), spinal cord blood flow (SCBF), and cerebral metabolic rate for oxygen (CMRo2) was studied in anesthetized dogs with and without increased intracranial pressure. Blood flow measurements were made at four time periods: (a) initial supine; (b) after 5 min in the sitting position; (c) after 60 min in the sitting position; and (d) 15 min after resuming the supine position. Six dogs (group 1) served as a control group with a normal intracranial pressure (ICP). In five dogs (group 2) ICP was elevated with a parietal epidural balloon 1 h before the first measurements of blood flows were made. Saline was injected incrementally into the balloon so as to reach a steady-state ICP of 30 mm Hg for 1 h. Elevation of ICP in group 2 resulted in significantly lower CBF, SCBF, and CMRo2 compared with group 1. Postural changes in group 1 did not result in any significant change in blood flow measurements whereas in group 2, after 1 h in the sitting position, there were significant decreases in CBF and SCBF compared with the initial supine measurements. There was, however, no corresponding decrease in CMRo2 in group 2 with change in position. These data suggest that both the brain and spinal cord may be at risk for ischemia during sitting position procedures under general anesthesia in the presence of elevated ICP.     

Changes in superior sagittal sinus pressure in children with head elevation, jugular venous compression, and PEEP

Air embolism is a potential hazard during craniotomy whenever intracranial venous pressure is subatmospheric. In order to better understand both the risk of air embolism and its treatment in neurosurgical patients, the authors have investigated the relationship of superior sagittal sinus pressure (SSP) to head position in 15 children and examined the effects of both jugular venous compression and positive end-expiratory airway pressure (PEEP) on SSP. Progressive head elevation significantly decreased mean SSP and, in five patients, SSP was less than 0 mm Hg at 90 degrees torso elevation. A PEEP of 10 cm H2O was ineffective in significantly increasing SSP at any degree of head elevation, whereas bilateral internal jugular compression always caused a significant increase in SSP. The authors conclude that children are at risk for venous air embolism when undergoing suboccipital craniectomy in the sitting position because intracranial venous pressure is often subatmospheric when the head is elevated. Furthermore, maintaining PEEP does not appear to be a reliable treatment for increasing SSP, whereas bilateral internal jugular compression is effective.     

Safe use of PEEP in patients with severe head injury

Thirty-three patients with severe head trauma were studied to determine whether the use of positive end-expiratory pressure (PEEP) would cause an increase in intracranial pressure (ICP). Changes in ICP induced by PEEP were then correlated with a panel of physiological variables to try to explain these changes. Mean ICP increased from 13.2 +/- 7.7 mm Hg (+/- standard deviation) to 14.5 +/- 7.5 mm Hg (p less than 0.005) due to 10 cm H2O PEEP, but the eight patients with elevated baseline ICP experienced no significant increase. Cardiac output and venous admixture (Qs/Qt) declined significantly, while central venous pressure, peak inspiratory pressure, functional residual capacity, and arterial pCO2 increased significantly due to PEEP. Blood pressure and cerebral perfusion pressure were unchanged. The change in ICP due to PEEP correlated significantly with a combination of cardiac output, peak inspiratory pressure, Qs/Qt, and changes in blood pressure and arterial pCO2 due to PEEP, indicating that the effect of PEEP on ICP could be largely explained by its effect on hemodynamic and respiratory variables. No patient deteriorated clinically due to PEEP. It is concluded that 10 cm H2O PEEP increases ICP slightly via its effect on other physiological variables, but that this small increase in ICP is clinically inconsequential.     

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.     

Oxygenation and cerebral perfusion pressure improved in the prone position

BACKGROUND: Treatment of patients in the prone position is a well-established method to improve oxygenation in general intensive care unit (ICU) practice. This method is rarely used in a neurosurgical ICU, considering the risk of intracranial hypertension. The aim of this study was to analyse the effect of prone position on intracranial pressure (ICP), cerebral perfusion pressure (CPP) and systemic oxygenation in patients with reduced intracranial compliance. We hypothesize that the beneficial effects of prone position can outweigh the hazardous effects on the intracranial pressure. METHODS: Eight patients with traumatic brain injury or subarachnoid hemorrhage (SAH) were studied in the supine and prone posture. Hemodynamics, arterial oxygenation, respiratory mechanics, ICP and CPP were continuously measured. RESULTS: A significant improvement in PaO(2) was observed in the prone position, from 12.6 +/- 1.4 kPa to 15.7 +/- 3.2 kPa (P= 0.02). Both intracranial pressure and mean arterial pressure increased in the prone position, from 12 +/- 6 to 15 +/- 4 mmHg (P= 0.03) and from 78 +/- 8 to 88 +/- 8 mmHg (P= 0.005), respectively. Arterial pressure increased to a greater extent than ICP, resulting in improved CPP, from 66 +/- 7 to 73 +/- 8 mmHg (P= 0.03) in the prone position. CONCLUSIONS: The prone position can be used to improve the oxygenation as well as CPP in patients with traumatic brain injury or SAH. However, this method results in raised ICP, and should be used cautiously in patients with reduced intracranial compliance.     

Change of intracranial pressure in neurosurgical patients by hyperventilation, positive negative pressure ventilation and PEEP (author's transl)]

The effects of a hyperventilation, positive negative pressure ventilation (PNPV) and ventilation using positive endexpiratory pressure (PEEP), on intracranial pressure (ICP) was measured in 24 patients suffering from different neurosurgical disorders. The patients were given a basic anaesthesia including muscle relaxation. The investigations showed, that hyperventilation, followed by a PCO2 of 26 and 30 torr, clearly lowered the intracranial pressure. The pressure drop was much more pronounced when the preexisting ICP was high than when it was low, due to the form of the compliance curve of the brain. PNPV also lowered intracranial pressure, but a harmful effect of this technique on lung function and structure is known. Its use is justified only for short periods and in addition to other measures for lowering ICP. The results also demonstrated that PNPV possesses limited beneficial properties with regard to the subject discussed here. Ventilation by PEEP significantly increased ICP. This technique is to be employed with caution in neurosurgery. Arterial pressure (radial artery) and central venous pressure (subclavian vein) were also recorded.     

Effect of positive end expiratory pressure ventilation on intracranial pressure in man.

THsi study was designed to define the effect of positive end expiratory pressure (PEEP) ventilation on intracranial pressure (ICP). In 25 patients with severe head trauma with and without associated pulmonary injury the following parameters were simultaneously monitored under mechanical ventilation with and without PEEP:ICP, arterial blood pressure, central venous pressure, arterial blood gases, and cardiac rate. In addition, the volume-pressure response (VPR) was evaluted in each patient to assess cerebral elastance. The results indicate a significant increase in ICP with the application of PEEP only in the 12 patients who manifested increased cerebral elastance by VPR. Half of this latter group manifested impairment of cerebral perfusion pressure to levels less than 60 mm Hg. Return to baseline CIP levels was observed with termination of PEEP. No significantly consistent changes in other parameters were noted.     

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)     

Effects on intracranial pressure of dural puncture in supine and head-elevated positions. A study on the cat

BACKGROUND: Lumbar dural puncture may reduce intracranial pressure (ICP) due to a hydrostatic pressure gradient created by distal opening of the spinal fluid column towards the atmosphere. The magnitude of the reduction in hydrostatic force on the brain should depend on the vertical distance between the brain and the dural opening, and thus will increase by head elevation. No studies have analyzed ICP after dural puncture in supine and upright positions. METHODS: This study on the cat records ICP, mean arterial pressure, and central venous pressure before and after dural puncture in supine and head-elevated positions. The dural puncture was performed at a level corresponding to the lumbar region. Results: Initially ICP was 10.9 +/- 1.9 mmHg (mean +/- SD), which decreased to 5.1 +/- 2.0 mmHg after 24.5 cm (18 mmHg) of head elevation (n = 7). Intracranial pressure decreased to 5.2 +/-3.5 mmHg following dural puncture in the supine position and to -11.3 +/- 4.2 mmHg after the head elevation (n = 7). Active drainage of CSF fluid in the supine position in a volume similar to that spontaneously drained after head elevation reduced ICP by 2.0 +/- 0.5 mmHg (n = 3). CONCLUSIONS: The results show that a significant ICP reduction may occur following opening of the spinal canal. The reduction can be explained more by hydrostatic forces than by loss of CSF; also explaining why it is more significant when upright than supine. The decrease in ICP increases transvascular pressure, which may induce the disappearance of the normally present subdural venous collapse with an increase in venous blood volume.     

Prevention of venous air embolism in paediatric neurosurgical procedures performed in the sitting position by combined use of MAST suit and PEEP

We studied 60 children undergoing neurosurgical procedures inthe sitting position. Routine monitoring included ECG, pulseoximetry, invasive arterial pressure, in particular mean arterialpressure (MAP), and right atrial pressure (RAP). Children wereallocated to two groups. In group B lower body positive pressureand positive end-expiratory pressure (PEEP) were used for preventingvenous air embolism (VAE). In this group, antishock trousers(MAST suit) were adjusted in supine children. After inductionof anaesthesia, different positions were studied: supine andsitting before MAST suit inflation, sitting with MAST suit inflatedup to a pressure of 40 mm Hg in the lower compartments and 30mm Hg in the abdominal compartment, and finally a combinationof lower body positive pressure and PEEP of 8–10cm H₂O.In group A no MAST suit or PEEP was used. Continuous monitoringof end-tidal carbon dioxide pressure throughout (PE'_co2 wasused to detect VAE. In order to evaluate the transmission ofpressures from the right atrium to the veins at the base ofthe skull, jugular bulb venous pressure (JBVP) was measuredin 20 patients by retrograde catheterization. The incidenceof VAE was compared in the two groups. On placing children intothe sitting position, a significant decrease in RAP and JBVPwas noted without significant changes in MAP in the two groups.Inflation of the MAST suit induced a dramatic increase in RAPand JBVP, reinforced by addition of PEEP. There was a strongpositive relationship between RAP and JBVP. There were no deleteriousside effects or differences between the two groups in peroperativeblood product requirements or surgical general conditions. VAEwas not noted in group B, compared with a 26% incidence of peroperativeVAE detected by a decrease in PE'_co2, of at least 0.4 kPa resultingin significant cardiovascular changes in group A. The combinationof PEEP and lower body positive pressure could be a satisfactorymethod of preventing VAE.     

Effet de la position sur la pression intracrânienne

The question as to whether the head and trunk of neurosurgery patients should be elevated remains controversial. This question is particularly important when intracranial hypertension is present. Head up position may have beneficial effects on intracranial pressure (ICP) via changes in mean arterial pressure (MAP), airway pressure, central venous pressure and cerebro spinal fluid displacement. However, in some circumstances, head up position may decrease MAP which in turn will result in a paradoxical rise in ICP through autoregulation mechanisms. Therefore, the degree of head elevation has to be titrated by evaluating the most adequate cerebral perfusion pressure (CPP) for each patient by means of transcranial Doppler or measurement of jugular venous blood oxygen saturation. Head elevation above 30° should be avoided in all cases. In most patients with intracranial hypertension, head and trunk elevation up to 30° is useful in helping to decrease ICP, providest that a safe CPP of at least 70 mmHg or even 80 mmHg is maintained. Patients in poor haemodynamic conditions are best nursed flat. CPP is thus the most important factor in assessment and monitoring when considering head elevation in patients with increased ICP.     

Prone position in mechanically ventilated patients with reduced intracranial compliance

BACKGROUND: Prone position has been used for several years to treat acute lung insufficiency, but in previous studies patients with unstable intracranial pressure (ICP) are mostly excluded. The aim of this study was to investigate if prone position is a safe and useful treatment in patients with reduced intracranial compliance. METHODS: A consecutive, prospective pilot study of 11 patients admitted to the neuro intensive care unit (NICU) due to traumatic brain injury or intracerebral haemorrhage. ICP, cerebral perfusion pressure (CPP), heart rate (HR), mean arterial blood pressure (MABP), arterial partial pressure of oxygen (PaO(2)), arterial partial pressure of carbon dioxide (PaCO(2)), arterial oxygen saturation (SaO(2)) and respiratory system compliance were measured before, three times during and two times after the patients were placed in the prone position. RESULTS: No significant changes were demonstrated in ICP, CPP or MABP. PaO(2) and SaO(2) were significantly increased in the prone position. HR was significantly increased in the prone position and after 10 min in the supine post-prone position and the respiratory system compliance was increased after 1 h in the supine post-prone position. CONCLUSION: Turning NICU patients from the supine to the prone position did not influence ICP, CPP or MABP, but significantly improved patient PaO(2), SaO(2) and respiratory system compliance.     

Positional hypoxaemia following post-traumatic pulmonary insufficiency.

The effect of body position on ventilatory function was evaluated in a patient with unilateral lung disease. The patient's pulmonary dynamics were examined in the supine, right, and left decubitus positions under conditions of positive pressure ventilation with zero end-expiratory pressure (ZEEP) and 5 cm H2O (0.9 KPa) positive end expiratory pressure (PEEP). When the patient was positioned so that the "diseased" lung was dependent, there was a marked decrease in PaO2 and increase in venous admixture when compared to the values in the supine position. These changes were relatively greater in the ZEEP, than the PEEP situation. When the "diseased* lung was not dependent, there was an increase in PaO2 and a decrease in venous admixture. This was most pronounced when PEEP was applied. Changes in body position may result in clinically significant alterations in pulmonary gas exchange, especially in patients with pre-existing pulmonary dysfunction.     

Positive end-expiratory pressure alters intracranial and cerebral perfusion pressure in severe traumatic brain injury

BACKGROUND: Optimizing intracranial pressure (ICP) and cerebral perfusion pressure (CPP) is important in the management of severe traumatic brain injury (TBI). In trauma patients with TBI and respiratory dysfunction, positive end-expiratory pressure (PEEP) is often required to support oxygenation. Increases in PEEP may lead to reduced CPP. We hypothesized that increases in PEEP are associated with compromised hemodynamics and altered cerebral perfusion. METHODS: Twenty patients (mean Injury Severity Score of 28) with TBI (Glasgow Coma Scale score < 8) were examined. All required simultaneous ICP and hemodynamic monitoring. Data were categorized on the basis of PEEP levels. Variables included central venous pressure, pulmonary artery occlusion pressure, cardiac index, oxygen delivery, and oxygen consumption indices. Differences were assessed using Kruskal-Wallis analysis of variance. RESULTS: Data were expressed as mean +/- SE. As PEEP increased from 0 to 5, to 6 to 10 and 11 to 15 cm H O, ICP decreased from 14.7 +/- 0.2 to 13.6 +/- 0.2 and 13.1 +/- 0.3 mm Hg, respectively. Concurrently, CPP improved from 77.5 +/- 0.3 to 80.1 +/- 0.5 and 78.9 +/- 0.7 mm Hg. As central venous pressure (5.9 +/- 0.1, 8.3 +/- 0.2, and 12.0 +/- 0.3 mm Hg) and pulmonary artery occlusion pressure (8.3 +/- 0.2, 11.6 +/- 0.4, and 15.6 +/- 0.4 mm Hg) increased with rising levels of PEEP, cardiac index, oxygen delivery, and oxygen consumption indices remained unaffected. Overall mortality was 30%. CONCLUSION: In trauma patients with severe TBI, the strategy of increasing PEEP to optimize oxygenation is not associated with reduced cerebral perfusion or compromised oxygen transport.     

Intracranial hypertension with polyradiculopathy--early CSF diversion to optimize neurological recovery

Cerebral venous sinus thrombosis (CVST) and idiopathic intracranial hypertension (IIH) are common considerations in young patients presenting with isolated intracranial hypertension. We report two patients with progressive visual failure and polyradiculopathy with areflexic quadriparesis, secondary to raised intracranial pressure (ICP). Both underwent cerebrospinal fluid diversion with complete recovery. Such a fulminant presentation of raised ICP with an excellent outcome has rarely been reported in the literature.     

Posture-related changes in the pressure environment of the ventriculoperitoneal shunt system

OBJECT: The purpose of this study is to clarify the whole pressure environment of the ventriculoperitoneal (VP) shunt system in patients with successfully treated hydrocephalus and to determine which factor of the pressure environment has a preventive effect on overdrainage. METHODS: Thirteen patients with hydrocephalus who had been treated with VP shunt therapy by using a Codman-Hakim programmable valve without incidence of overdrainage were examined. The authors evaluated intracranial pressure (ICP), intraabdominal pressure (IAP), hydrostatic pressure (HP), and the perfusion pressure (PP) of the shunt system with the patients both supine and sitting. With patients supine, ICP, IAP, and HP were 4.6 +/- 3 mm Hg, 5.7 +/- 3.3 mm Hg, and 3.3 +/- 1 mm Hg, respectively. As a result, the PP was only 2.2 +/- 4.9 mm Hg. When the patients sat up, the IAP increased to 14.7 +/- 4.8 mm Hg, and ICP decreased to-- 14.2 +/- 4.5 mm Hg. The increased IAP and decreased ICP offset 67% of the HP (42.9 +/- 3.5 mm Hg), and consequently the PP (14 +/- 6.3 mm Hg) corresponded to only 33% of HP. CONCLUSIONS: The results observed in patients indicated that IAP as well as ICP play an important role in VP shunt therapy and that the increased IAP and the decreased ICP in patients placed in the upright position allow them to adapt to the siphoning effect and for overdrainage thereby to be avoided.     

Head elevation reduces head-rotation associated increased ICP in patients with intracranial tumours

PURPOSE: To quantify the effects of graded head rotation and elevation on intracranial pressure (ICP) in neurosurgical patients, before and after induction of general anesthesia. METHODS: Patients with supratentorial tumours (n=12), scheduled for craniotomy with planned ICP monitoring, underwent baseline ICP measurements awake and supine (0 degrees rotation and elevation). Incremental degrees of head rotation (15 degrees) and of head elevation (10 degrees) were performed independently and in combination. Paired measurements of ICP at all levels of head rotation and elevation were also performed before and after induction of general anesthesia (n=6). RESULTS: The baseline ICP was 12.3 +/- 6.4 mmHg (n=12). Changes of ICP were proportional to the degree of head rotation or elevation. Head rotation of 60 degrees maximally increased ICP to 24.8 +/- 14.3 mmHg (P < 0.05). Head elevation above 20 degrees reduced ICP with a maximal reduction to -0.2 +/- 5.5 mmHg at 40 degrees elevation (P < 0.01). Head elevation to 30 degrees reduced the intracranial hypertension associated with head rotation. No differences were observed between ICP measurements made before or after induction of general anesthesia (n=6). Three patients experienced headache with extreme head rotation (<60 degrees) and intracranial hypertension (ICP > 20 mmHg). CONCLUSION: Head rotation of 60 degrees caused an increase in ICP. Concomitant head elevation to 30 degrees reduced the intracranial hypertension associated with head rotation. Headache with head rotation may provide a useful clinical warning of elevated ICP.