The effects of 10 degrees reverse trendelenburg position on ICP and CPP in prone positioned patients subjected to craniotomy for occipital or cerebellar tumours

Anesthesia for Patients with Traumatic Brain Injuries

Traumatic brain injury (TBI) represents a wide spectrum of disease and disease severity. Because the primary brain injury occurs before the patient enters the health care system, medical interventions seek principally to prevent secondary injury. Anesthesia teams that provide care for patients with TBI both in and out of the operating room should be aware of the specific therapies and needs of this unique and complex patient population.

Definition, evaluation, and management of brain relaxation during craniotomy

The term 'brain relaxation' is routinely used to describe the size and firmness of the brain tissue during craniotomy. The status of brain relaxation is an important aspect of neuroanaesthesia practice and is relevant to the operating conditions, retraction injury, and likely patient outcomes. Brain relaxation is determined by the relationship between the volume of the intracranial contents and the capacity of the intracranial space (i.e. a content-space relationship). It is a concept related to, but distinct from, intracranial pressure. The evaluation of brain relaxation should be standardized to facilitate clinical communication and research collaboration. Both advantageous and disadvantageous effects of the various interventions for brain relaxation should be taken into account in patient care. The outcomes that matter the most to patients should be emphasized in defining, evaluating, and managing brain relaxation. To date, brain relaxation has not been reviewed specifically, and the aim of this manuscript is to discuss the current approaches to the definition, evaluation, and management of brain relaxation, knowledge gaps, and targets for future research.

Potential involvement of the extracranial venous system in central nervous system disorders and aging

BACKGROUND

The role of the extracranial venous system in the pathology of central nervous system (CNS) disorders and aging is largely unknown. It is acknowledged that the development of the venous system is subject to many variations and that these variations do not necessarily represent pathological findings. The idea has been changing with regards to the extracranial venous system.

DISCUSSION

A range of extracranial venous abnormalities have recently been reported, which could be classified as structural/morphological, hemodynamic/functional and those determined only by the composite criteria and use of multimodal imaging. The presence of these abnormalities usually disrupts normal blood flow and is associated with the development of prominent collateral circulation. The etiology of these abnormalities may be related to embryologic developmental arrest, aging or other comorbidities. Several CNS disorders have been linked to the presence and severity of jugular venous reflux. Another composite criteria-based vascular condition named chronic cerebrospinal venous insufficiency (CCSVI) was recently introduced. CCSVI is characterized by abnormalities of the main extracranial cerebrospinal venous outflow routes that may interfere with normal venous outflow.

SUMMARY

Additional research is needed to better define the role of the extracranial venous system in relation to CNS disorders and aging. The use of endovascular treatment for the correction of these extracranial venous abnormalities should be discouraged, until potential benefit is demonstrated in properly-designed, blinded, randomized and controlled clinical trials.

The relationship between intracranial pressure and the degree of brain swelling in patients subjected to infratentorial surgery

BACKGROUND

In patients with supratentorial tumours, intracranial pressure is a strong predictor of intra-operative brain swelling and thresholds for ICP associated with brain swelling have been defined. Whether these ICP thresholds can be applied during infratentorial surgery is uncertain. We studied the relationship between subdural ICP and the degree of brain swelling after opening of the dura mater in patients subjected to infratentorial surgery. Thresholds for ICP associated with brain swelling were defined.

METHODS

One hundred and nine adult patients subjected to infratentorial surgery were studied. Subdural ICP was measured immediately before opening of the dura and the degree of brain swelling was estimated by the neurosurgeon according to a four-point scale.

FINDINGS

At ICP less than 7 mmHg brain swelling did not occur. In the range from 7 to 13 mmHg 21 of 39 patients (54%) had moderate swelling, but not pronounced swelling. At ICP greater than 13 mmHg some degree of swelling occurred in all patients, and at ICP exceeding 24 mmHg pronounced cerebral swelling was found in all patients. Using logistic regression analysis specific thresholds for ICP associated with brain swelling were defined as follows: at an ICP equal to or greater than 13 mmHg, brain swelling occurred with 95% probability; and at an ICP less than 6 mmHg brain swelling occurred with 5% probability.

CONCLUSIONS

Subdural ICP measured before opening of the dura mater can predict the risk of brain swelling during infratentorial surgery. Thresholds for ICP associated with brain swelling are close to thresholds defined in patients undergoing supratentorial surgery.

Optimal reverse Trendelenburg position in patients undergoing craniotomy for cerebral tumors

Object

To the authors’ knowledge, repeated measurements of intracranial pressure (ICP), cerebral perfusion pressure (CPP), and the degree of dural tension during different positions on the operating table (reverse Trendelenburg position [rTp]) have not been studied in patients undergoing craniotomy.

Methods

In the present study 53 patients with supratentorial cerebral tumors who underwent craniotomy in the supine position were included. Subdural ICP, mean arterial blood pressure (MABP), CPP, and jugular bulb (JB) pressure were recorded, and the degree of dural tension was analyzed while patients were in the neutral operating position and at 5, 10, and 15° rTp. The optimal operating position was defined as the one at which subdural ICP was as low as possible, and CPP was greater than or equal to 60 mm Hg or as high as possible.

Subdural ICP, MABP, and JB pressure decreased significantly after each 5° change in rTp compared with the preceding position. Dural tension decreased significantly up to 10° rTp, but was unchanged at 15° rTp. At 5° rTp CPP remained unchanged, but it decreased significantly during 10 and 15° rTp. The optimal position in the majority of patients was determined to be 15° rTp.

Conclusions

Before opening the dura mater for craniotomy, repeated measurements of ICP and CPP, in the neutral position and at 5, 10, and 15° rTp, provide valuable information regarding the optimal level of ICP and CPP.

The Effects of Indomethacin on Intracranial Pressure and Cerebral Hemodynamics During Isoflurane or Propofol Anesthesia in Sheep with Intracranial Hypertension

The effect of indomethacin in reducing intracranial pressure (ICP) may be dependent on the choice of anesthetic regimen. We studied the effects of indomethacin on ICP and cerebral blood flow (CBF) during isoflurane or propofol anesthesia in a sheep model of intracranial hypertension. A crossover design was applied in which six sheep were anesthetized with isoflurane and propofol in a random order. Anesthetic depth was measured with response and state entropy. Changes in CBF, ICP, mean arterial blood pressure, arterio-venous oxygen difference, and Paco2 were measured at specific times before and after an IV indomethacin bolus (0.2 mg/kg). Response and state entropy values during anesthesia were similar in both groups. Isoflurane and propofol reduced CBF by 11% and 34%, respectively. Indomethacin caused a reduction in ICP within 15 s during both anesthetic regimens, with the decrease in ICP being significantly more pronounced during isoflurane (P = 0.009). In both anesthetic groups, indomethacin caused a simultaneous increase in mean arterial blood pressure and a further 17% versus 14% decrease in CBF from predrug values for isoflurane and propofol, respectively. The reduction in CBF was significantly more pronounced for propofol (P = 0.02). The effect on ICP, however, was most pronounced during isoflurane anesthesia. We suggest that the effect of indomethacin is partly mediated by an autoregulatory response.

Different compartments of intracranial pressure and its relationship to cerebral blood flow

BACKGROUND

The classical "Kellie-Monroe" doctrine considering the intracranial volume to be a closed system that is confined within the nearly rigid skull, conserves different mass, and has equal vascular inflow and outflow. Several experimental and clinical studies have given evidence that this is not entirely true from the (patho)physiologic point of view, even so our understanding of this phenomenon is incomplete.

METHODS

Review from the literature.

RESULTS

The present literature review revokes this classical doctrine and suggests a more differentiated description for the dynamic of intracranial pressure (ICP): instead of the previously suggested lumped-parameter models, the authors describe different intracranial compartments that are related to different brain regions.

CONCLUSION

This has the advantage of great practical use on the one hand and allows the demonstration of relevant intercompartimental intracranial pressure differences. In addition, these ICP differences can be revealed to different ICP compartments and to its relationship to CBF. Special reference is given to determine appropriate forms for the nonconstant resistance and compliance parameters.

The Effects of 10?? Reverse Trendelenburg Position on Subdural Intracranial Pressure and Cerebral Perfusion Pressure in Patients Subjected to Craniotomy for Cerebral Aneurysm

The aim of the current study was to examine the effects of 10 degrees reverse Trendelenburg position (rTp) on subdural intracranial pressure (ICP), cerebral perfusion pressure (CPP), and dural tension. Additionally, the relationship between preoperative Hunt and Hess (H and H) grade and the subdural ICP in patients scheduled for cerebral aneurysm surgery was investigated. Twenty-eight consecutive patients with a cerebral aneurysm were subjected to craniotomy in propofol/fentanyl or propofol/remifentanil anesthesia. Subdural ICP was measured after opening of the bone flap and exposure of dura. After reference measurements of subdural ICP and mean arterial blood pressure (MABP), the measurements were repeated during 10 degrees rTp. No significant differences between the anesthetic groups were disclosed. During 10 degrees rTp, a significant decrease in MABP, ICP, and jugular bulb pressure was observed whereas CPP remained unchanged. In H and H 0 patients (unruptured aneurysm), the ICP decreased from 2.9 +/- 2.6 mmHg to 0.4 +/- 2.2 mmHg at 10 degrees rTp. In H and H I to II patients, the ICP decreased from 9.3 +/- 3.8 mmHg to 4.6 +/- 3.3 mmHg at 10 degrees rTp. A significant difference in the mean baseline subdural ICP and DeltaICP (change in ICP) was found between patients with unruptured aneurysm and patients with subarachnoid hemorrhage (H&H I and II). Furthermore, the relationship between the subdural ICP at neutral position and DeltaICP was significant. In patients without intracranial hypertension, 10 degrees rTp decreases subdural ICP and dural tension in patients with ruptured as well as patients with unruptured cerebral aneurysm; CPP is unchanged.

Treatment of elevated intracranial pressure with indomethacin: friend or foe?

Indomethacin has been suggested as a therapeutic tool to manage elevated intracranial pressure in patients with severe head injury and patients undergoing craniotomy for brain tumors. Indomethacin is a non-selective cyclooxygenase inhibitor. Compared to other cyclooxygenase inhibitors indomethacin has unique effects on cerebral blood flow. Administration of indomethacin causes cerebral vasoconstriction and decreases cerebral blood flow, which elicits a decrease in intracranial pressure. The mechanism of indomethacin-induced cerebral vasoconstriction is not completely understood and controversies exist whether indomethacin causes cerebral ischemia. The primary aims of this article were to review the existing knowledge of indomethacin's influence upon cerebral hemodynamics and elevated ICP in patients with brain pathology. Furthermore, indomethacin's mechanism of action and whether it causes cerebral ischemia are discussed.

Subdural intracranial pressure, cerebral perfusion pressure, and degree of cerebral swelling in supra- and infratentorial space-occupying lesions in children

To our knowledge comparative studies of intracranial pressure (ICP) and degree of cerebral swelling during craniotomy for supratentorial or infratentorial space occupying lesion in children are not available. In this prospective study subdural ICP, cerebral perfusion pressure (CPP), dural tension, and the degree of cerebral swelling were analysed in supine and prone positioned children subjected to craniotomy for space occupying lesions.

MATERIAL AND METHOD

48 children with space occupying tumours were subjected to either isoflurane/nitrous oxide 50%/fentanyl (n = 22) or propofol/fentanyl/air/oxygen (n = 26). 25 children were operated supratentorially in supine position, while 23 patients were operated infratentorially in the prone position. Subdural ICP, mean arterial blood pressure (MABP), and CPP were measured just before opening of the dura. Dural tension was estimated before opening of dura, and the degree of cerebral swelling was estimated after opening of dura.

RESULTS

The age and weight of children anaesthetised with isoflurane in the prone position were significantly lower than the propofol anaesthetised groups. No significant inter-group differences as regards tumour size, midline shift, rectal temperature, MABP or PaCO2 were found. ICP in prone positioned children averaged 16.9 mm Hg against 9.0 mm Hg in supine positioned children (p < 0.001). In prone positioned children the dura was significantly tenser, and the degree of brain swelling after opening of dura was significantly more pronounced. No significant difference as regard ICP was disclosed when isoflurane/nitrous oxide/fentanyl and propofol/ fentanyl anaesthetized children were compared, but MABP and CPP were significantly lower in isoflurane anaesthetised children.

CONCLUSION

In children with cerebral tumours ICP is higher, and the degree of cerebral swelling more pronounced in the prone-compared with supine positioned children. Choice of anaesthesia did not influence ICP, but CPP was significantly lower during isoflurane anaesthesia.

Managing elevated intracranial pressure

PURPOSE OF REVIEW

Elevated intracranial pressure is one of the major deteriorating factors in patients with intracerebral lesions. Therefore, every year many experimental and clinical studies are performed to identify the best method for managing elevated intracranial pressure in head-injured patients. The current review summarizes the most important recent findings for the treatment of increased intracranial pressure.

RECENT FINDINGS

The currently most discussed treatments of elevated intracranial pressure are the use of hypertonic saline, which seems to be equal to mannitol, the use of hypothermia, and the performance of decompressive craniectomy.

SUMMARY

The treatment strategy to manage increased intracranial pressure includes decisions about anaesthetics, ventilation, head and body position, hypothermia, the use of osmotic drugs and surgical procedures. Propofol seems to be suitable for the sedation of patients with elevated intracranial pressure. Sudden increases in intracranial pressure can be treated using hyperosmotic agents, high-dose thiopental, or short episodes of mild hyperventilation. Surgical decompression of the cranium seems to improve the outcome in patients below the age of 50 years, especially children.

The effects of indomethacin on intracranial pressure and cerebral haemodynamics in patients undergoing craniotomy: A randomised prospective study

We compared the effects of indomethacin (bolus of 0.2 mg.kg-1 followed by an infusion of 0.2 mg.kg-1.h-1) and placebo on intracranial pressure and cerebral haemodynamics in 30 patients undergoing craniotomy for supratentorial brain tumours under propofol and fentanyl anaesthesia. Indomethacin was given before induction of anaesthesia and the infusion was terminated after opening of the dura. Subdural intracranial pressure was measured through the first burr hole and before opening the dura. Cerebral blood flow velocity, cerebral perfusion pressure, jugular bulb oxygen saturation, arterio-venous oxygen difference and carbon dioxide reactivity were measured; dural tension and the degree of brain swelling were estimated. Before induction of anaesthesia, indomethacin administration was associated with a significant decrease in cerebral blood flow velocity compared with placebo. After induction of anaesthesia, cerebral blood flow velocity and mean arterial blood pressure decreased significantly in both groups. Indomethacin was not associated with a decrease in intracranial pressure. There were no differences in cerebral perfusion pressure, dural tension or degree of brain swelling between the two groups. Carbon dioxide reactivity measured after induction of anaesthesia was significantly lower in the indomethacin group (p < 0.05). After removal of the bone flap, no significant difference in carbon dioxide reactivity was observed. We suggest that these findings are explained by propofol-induced cerebral vasoconstriction.

Baroreflex-induced sympathetic activation does not alter cerebrovascular CO2 responsiveness in humans

We investigated the effect of baroreflex-induced sympathetic activation, produced by lower body negative pressure (LBNP) at -40 mmHg, on cerebrovascular responsiveness to hyper- and hypocapnia in healthy humans. Transcranial Doppler ultrasound was used to measure blood flow velocity (CFV) in the middle cerebral artery during variations in end-tidal carbon dioxide pressure (PET,CO2) of +10, +5, 0, -5, and -10 mmHg relative to eupnoea. The slopes of the linear relationships between PET,CO2 and CFV were computed separately for hyper- and hypocapnia during the LBNP and no-LBNP conditions. LBNP decreased pulse pressure, but did not change mean arterial pressure. LBNP evoked an increase in ventilation that resulted in a 9 +/- 2 mmHg decrease in PET,CO2, which was corrected by CO2 supplementation of the inspired air. LBNP did not affect cerebrovascular CO2 response slopes during steady-state hypercapnia (3.14 +/- 0.24 vs. 2.96 +/- 0.26 cm s-1 mmHg-1) or hypocapnia (1.31 +/- 0.18 vs. 1.32 +/- 0.19 cm s-1 mmHg-1), or the CFV responses to voluntary apnoea (+51 +/- 19 vs. +50 +/- 18 %). Thus, cerebrovascular CO2 responsiveness was not altered by baroreflex-induced sympathetic activation. Our data challenge the concept that sympathetic activation restrains cerebrovascular responses to alterations in CO2 pressure.