An evidence-based approach to management of increased intracranial pressure

Fluid therapy and traumatic brain injury: A narrative review

Traumatic brain injury (TBI) is an important health and social problem. The mechanism of damage of this entity could be divided into two phases: (1) a primary acute injury because of the traumatic event; and (2) a secondary injury due to the hypotension and hypoxia generated by the previous lesion, which leads to ischemia and necrosis of neural cells. Cerebral edema is one of the most important prognosis markers observed in TBI. In the early stages of TBI, the cerebrospinal fluid compensates the cerebral edema. However, if edema increases, this mechanism fails, increasing intracranial pressure. To avoid this chain effect, several treatments are applied in the clinical practice, including elevation of the head of the bed, maintenance of normothermia, pain and sedation drugs, mechanical ventilation, neuromuscular blockade, controlled hyperventilation, and fluid therapy (FT). The goal of FT is to improve the circulatory system to avoid the lack of oxygen to organs. Therefore, rapid and early infusion of large volumes of crystalloids is performed in clinical practice to restore blood volume and blood pressure. Despite the relevance of FT in the early management of TBI, there are few clinical trials regarding which solution is better to apply. The aim of this study is to provide a narrative review about the role of the different types of FT used in the daily clinical practice on the management of TBI. To achieve this objective, a physiopathological approach to this entity will be also performed, summarizing why the different types of FT are used.

Effect of Hyperosmolar Therapy on Outcome Following Spontaneous Intracerebral Hemorrhage: Ethnic/Racial Variations of Intracerebral Hemorrhage (ERICH) Study

PURPOSE

We aimed to identify the effect of hyperosmolar therapy (mannitol and hypertonic saline) on outcomes after intracerebral hemorrhage (ICH) in the Ethnic/Racial Variations of Intracerebral Hemorrhage (ERICH) study.

METHODS

Comparison of ICH cases treated with hyperosmolar therapy versus untreated cases was performed using a propensity score based on age, initial Glasgow Coma Scale, location of ICH (lobar, deep, brainstem, and cerebellar), log-transformed initial ICH volume, presence of intraventricular hemorrhage, and surgical interventions. ERICH subjects with a pre-ICH modified Rankin Scale (mRS) score of 3 or lower were included. Treated cases were matched 1:1 to untreated cases by the closest propensity score (difference ≤.15), gender, and race and ethnicity (non-Hispanic white, non-Hispanic black, or Hispanic). The McNemar and the Wilcoxon signed-rank tests were used to compare 3-month mRS outcomes between the 2 groups. Good outcome was defined as a 3-month mRS score of 3 or lower.

RESULTS

As of December 31, 2013, the ERICH study enrolled 2279 cases, of which 304 hyperosmolar-treated cases were matched to 304 untreated cases. Treated cases had worse outcome at 3 months compared with untreated cases (McNemar, P = .0326), and the mean 3-month mRS score was lower in the untreated group (Wilcoxon, P = .0174). Post hoc analysis revealed more brain edema, herniation, and death at discharge for treated cases.

CONCLUSIONS

Hyperosmolar therapy was not associated with better 3-month mRS outcomes for ICH cases in the ERICH study. This finding likely resulted from greater hyperosmolar therapy use in patients with edema and herniation rather than those agents leading to worse outcomes. Further studies should be performed to determine if hyperosmolar agents are effective in preventing poor outcomes.

Management of Intracranial Pressure

PURPOSE OF REVIEW

Intracranial pressure (ICP) can be elevated in traumatic brain injury, large artery acute ischemic stroke, intracranial hemorrhage, intracranial neoplasms, and diffuse cerebral disorders such as meningitis, encephalitis, and acute hepatic failure. Raised ICP is also known as intracranial hypertension and is defined as a sustained ICP of greater than 20 mm Hg.

RECENT FINDINGS

ICP must be measured through an invasive brain catheter, typically an external ventricular catheter that can drain CSF and measure ICP, or through an intraparenchymal ICP probe. Proper recognition of the clinical signs of elevated ICP is essential for timely diagnosis and treatment to prevent cerebral hypoperfusion and possible brain death. Clinical signs of elevated ICP include headache, papilledema, nausea, and vomiting in the early phases, followed by stupor and coma, pupillary changes, hemiparesis or quadriparesis, posturing and respiratory abnormalities, and eventually cardiopulmonary arrest.

SUMMARY

Management of elevated ICP is, in part, dependent on the underlying cause. Medical options for treating elevated ICP include head of bed elevation, IV mannitol, hypertonic saline, transient hyperventilation, barbiturates, and, if ICP remains refractory, sedation, endotracheal intubation, mechanical ventilation, and neuromuscular paralysis. Surgical options include CSF drainage if hydrocephalus is present and decompression of a surgical lesion, such as an intracranial hematoma/large infarct or tumor, if the patient's condition is deemed salvageable. Future research should continue investigating medical and surgical options for the treatment of raised ICP, such as hypothermia, drugs that reduce cerebral edema, and operations aimed at reducing intracranial mass effect.

Management of raised intracranial pressure in children with traumatic brain injury

Increased intracranial pressure (ICP) is associated with worse outcome after traumatic brain injury (TBI). The current guidelines and management strategies are aimed at maintaining adequate cerebral perfusion pressure and treating elevated ICP. Despite controversies, ICP monitoring is important particularly after severe TBI to guide treatment and in developed countries is accepted as a standard of care. We provide a narrative review of the recent evidence for the use of ICP monitoring and management of ICP in pediatric TBI.

Demystifying process mapping: a key step in neurosurgical quality improvement initiatives

Reliable delivery of optimal care can be challenging for care providers. Health care leaders have integrated various business tools to assist them and their teams in ensuring consistent delivery of safe and top-quality care. The cornerstone to all quality improvement strategies is the detailed understanding of the current state of a process, captured by process mapping. Process mapping empowers caregivers to audit how they are currently delivering care to subsequently strategically plan improvement initiatives. As a community, neurosurgery has clearly shown dedication to enhancing patient safety and delivering quality care. A care redesign strategy named NERVS (Neurosurgery Enhanced Recovery after surgery, Value, and Safety) is currently being developed and piloted within our department. Through this initiative, a multidisciplinary team led by a clinician neurosurgeon has process mapped the way care is currently being delivered throughout the entire episode of care. Neurosurgeons are becoming leaders in quality programs, and their education on the quality improvement strategies and tools is essential. The authors present a comprehensive review of process mapping, demystifying its planning, its building, and its analysis. The particularities of using process maps, initially a business tool, in the health care arena are discussed, and their specific use in an academic neurosurgical department is presented.

Effect of osmotic agents on regional cerebral blood flow in traumatic brain injury

PURPOSE

Cerebral blood flow (CBF) is reduced after severe traumatic brain injury (TBI) with considerable regional variation. Osmotic agents are used to reduce elevated intracranial pressure (ICP), improve cerebral perfusion pressure, and presumably improve CBF. Yet, osmotic agents have other physiologic effects that can influence CBF. We sought to determine the regional effect of osmotic agents on CBF when administered to treat intracranial hypertension.

MATERIALS AND METHODS

In 8 patients with acute TBI, we measured regional CBF with positron emission tomography before and 1 hour after administration of equi-osmolar 20% mannitol (1 g/kg) or 23.4% hypertonic saline (0.686 mL/kg) in regions with focal injury and baseline hypoperfusion (CBF <25 mL per 100 g/min).

RESULTS

The ICP fell (22.4 ± 5.1 to 15.7 ± 7.2 mm Hg, P = .007), and cerebral perfusion pressure rose (75.7 ± 5.9 to 81.9 ± 10.3 mm Hg, P = .03). Global CBF tended to rise (30.9 ± 3.7 to 33.1 ± 4.2 mL per 100 g/min, P = .07). In regions with focal injury, baseline flow was 25.7 ± 9.1 mL per 100 g/min and was unchanged; in hypoperfused regions (15% of regions), flow rose from 18.6 ± 5.0 to 22.4 ± 6.4 mL per 100 g/min (P < .001). Osmotic therapy reduced the number of hypoperfused brain regions by 40% (P < .001).

CONCLUSION

Osmotic agents, in addition to lowering ICP, improve CBF to hypoperfused brain regions in patients with intracranial hypertension after TBI.

Effects of the neurological wake-up test on intracranial pressure and cerebral perfusion pressure in brain-injured patients

OBJECTIVE

To evaluate the effects of the neurological "wake-up test" (NWT), defined as interruption of continuous propofol sedation and evaluation of the patient's level of consciousness, on intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in patients with severe subarachnoid hemorrhage (SAH) or traumatic brain injury (TBI).

METHODS

A total of 127 NWT procedures in 21 severely brain-injured adult patients with either TBI (n = 12) or SAH (n = 9) were evaluated. ICP and CPP levels prior to, during and after the NWT procedure were recorded.

RESULTS

During the NWT, ICP increased from 13.4 +/- 6 mmHg at baseline to 22.7 +/- 12 (P < 0.05) and the CPP increased from 75.6 +/- 11 to 79.1 +/- 21 mmHg (P < 0.05) in TBI patients. Eight patients showed a reduced CPP during the NWT due to increased ICP. In SAH patients, ICP increased from 10.6 +/- 5 to 16.8 +/- 8 mmHg (P < 0.05) and the CPP increased from 76.9 +/- 13 to 84.6 +/- 15 mmHg (P < 0.05).

CONCLUSION

When continuous propofol sedation was interrupted and NWT was performed in severely brain-injured patients, the mean ICP and CPP levels were modestly increased. A subset of patients showed more pronounced changes. To date, the role of the NWT in the neurointensive care of TBI and SAH patients is unclear. Although the NWT is safe in the majority of patients and may provide useful clinical information about the patient's level of consciousness, alternate monitoring methods are suggested in patients showing marked ICP and/or CPP changes during NWT.

The role of animal models in evaluating reasonable safety and efficacy for human trials of cell-based interventions for neurologic conditions

Progress in regenerative medicine seems likely to produce new treatments for neurologic conditions that use human cells as therapeutic agents; at least one trial for such an intervention is already under way. The development of cell-based interventions for neurologic conditions (CBI-NCs) will likely include preclinical studies using animals as models for humans with conditions of interest. This paper explores predictive validity challenges and the proper role for animal models in developing CBI-NCs. In spite of limitations, animal models are and will remain an essential tool for gathering data in advance of first-in-human clinical trials. The goal of this paper is to provide a realistic lens for viewing the role of animal models in the context of CBI-NCs and to provide recommendations for moving forward through this challenging terrain.

Barbiturate infusion for intractable intracranial hypertension and its effect on brain oxygenation

OBJECTIVE

Barbiturate-induced coma can be used in patients to treat intractable intracranial hypertension when other therapies, such as osmotic therapy and sedation, have failed. Despite control of intracranial pressure, cerebral infarction may still occur in some patients, and the effect of barbiturates on outcome remains uncertain. In this study, we examined the relationship between barbiturate infusion and brain tissue oxygen (PbtO2).

METHODS

Ten volume-resuscitated brain-injured patients who were treated with pentobarbital infusion for intracranial hypertension and underwent PbtO2 monitoring were studied in a neurosurgical intensive care unit at a university-based Level I trauma center. PbtO2, intracranial pressure (ICP), mean arterial pressure, cerebral perfusion pressure (CPP), and brain temperature were continuously monitored and compared in settings in which barbiturates were or were not administered.

RESULTS

Data were available from 1595 hours of PbtO2 monitoring. When pentobarbital administration began, the mean ICP, CPP, and PbtO2 were 18 +/- 10, 72 +/- 18, and 28 +/- 12 mm Hg, respectively. During the 3 hours before barbiturate infusion, the maximum ICP was 24 +/- 13 mm Hg and the minimum CPP was 65 +/- 20 mm Hg. In the majority of patients (70%), we observed an increase in PbtO2 associated with pentobarbital infusion. Within this group, logistic regression analysis demonstrated that a higher likelihood of compromised brain oxygen (PbtO2 < 20 mm Hg) was associated with a decrease in pentobarbital dose after controlling for ICP and other physiological parameters (P < 0.001). In the remaining 3 patients, pentobarbital was associated with lower PbtO2 levels. These patients had higher ICP, lower CPP, and later initiation of barbiturates compared with patients whose PbtO2 increased.

CONCLUSION

Our preliminary findings suggest that pentobarbital administered for intractable intracranial hypertension is associated with a significant and independent increase in PbtO2 in the majority of patients. However, in some patients with more compromised brain physiology, pentobarbital may have a negative effect on PbtO2, particularly if administered late. Larger studies are needed to examine the relationship between barbiturates and cerebral oxygenation in brain-injured patients with refractory intracranial hypertension and to determine whether PbtO2 responses can help guide therapy.

Bispectral Index Monitoring Documents Burst Suppression During Pentobarbital Coma

During pentobarbital coma, electroencephalographic monitoring is used to document burst suppression (3-5 episodes of electrical activity/min). The current study evaluates the association of the bispectral index number and suppression ratio with a burst suppression pattern on electroencephalograph. The records of 7 patients (aged 2.9-14 years) who received pentobarbital for elevated intracranial pressure were retrospectively reviewed. The bispectral index number was 7 ± 5, 14 ± 3, and 37 ± 12, whereas the suppression ratio was 93 ± 7%, 75 ± 6%, and 29 ± 18% when the electroencephalograph showed ≤ 2, 3-5, and ≥ 6 bursts/min, respectively. The sensitivity and specificity of a bispectral index value of 10 to 20 were 96% and 92%, respectively, whereas the sensitivity and specificity of a suppression ratio of 65% to 85% were 89% and 88%, respectively, in demonstrating the presence of 3 to 5 bursts/min. Bispectral index monitoring may be easier to perform and may require less technical expertise to interpret.

Refractory increased intracranial pressure in severe traumatic brain injury: barbiturate coma and bispectral index monitoring

Patients with severe traumatic brain injury resulting in increased intracranial pressure refractory to first-tier interventions challenge the critical care team. After exhausting these initial interventions, critical care practitioners may utilize barbiturate-induced coma in an attempt to reduce the intracranial pressure. Titrating appropriate levels of barbiturate is imperative. Underdosing the drug may fail to control the intracranial pressure, whereas overdosing may lead to untoward effects such as hypotension and cardiac compromise. Monitoring for a therapeutic level of barbiturate coma includes targeting drug levels and using continuous electroencephalogram monitoring, considered the gold standard. New technology, the Bispectral Index monitor, utilizes electroencephalogram principles to monitor the level of sedation and hypnosis in the critical care environment. This technology is now being considered for targeting appropriate levels of barbiturate coma.

Osmotic therapy: fact and fiction

This review examines the available data on the use of osmotic agents in patients with head injury and ischemic stroke, summarizes the physiological effects of osmotic agents, and presents the leading hypotheses regarding the mechanism by which they reduce ICP. Finally, it addresses the validity of the following commonly held beliefs: mannitol accumulates in injured brain; mannitol shrinks only normal brain and can increase midline shift; osmolality can be used to monitor mannitol administration; mannitol should be not be administered if osmolality is >320 mOsm; and hypertonic saline is equally effective as mannitol.

Hyperosmolar therapy in the treatment of severe head injury in children: mannitol and hypertonic saline

Traumatic brain injury is the result of a primary, acute injury and is complicated by the development of secondary injury due to hypotension and hypoxia. Cerebral edema due to brain injury compromises the delivery of essential nutrients and alters normal intracranial pressure. The Monroe-Kellie Doctrine defines the principles of intracranial pressure homeostasis. Treatment for intracranial hypertension is aimed at reducing the volume of 1 of the 3 intracranial compartments, brain tissue, blood, and cerebrospinal fluid. Hyperosmolar therapy is one treatment intervention in the care of patients with severe head injury resulting in cerebral edema and intracranial hypertension. The effect of hyperosmolar solutions on brain tissue was first studied nearly 90 years ago. Since that time, mannitol has become the most widely used hyperosmolar solution to treat elevated intracranial pressure. Increasingly, hypertonic saline solutions are being used as an adjunct to mannitol in basic science research and clinical studies. Hyperosmolar solutions are effective in reducing elevated intracranial pressure through 2 distinct mechanisms: plasma expansion with a resultant decrease in blood hematocrit, reduced blood viscosity, and decreased cerebral blood volume; and the creation of an osmotic gradient that draws cerebral edema fluid from brain tissue into the circulation. The pediatric section of the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies adapted previously published guidelines for the treatment of adult brain injury into guidelines for the treatment of children with traumatic brain injury. These guidelines offer recommendations for the management of children with severe head injury, including the use of mannitol and hypertonic saline to treat intracranial hypertension. Acute and critical care pediatric advanced practice nurses caring for children with severe head injury should be familiar with management guidelines and the use of hyperosmolar solutions. The purpose of this article is to assist the advanced practice nurse in understanding the role of hyperosmolar therapy in the treatment of pediatric traumatic brain injury and review current guidelines for the use of mannitol and hypertonic saline.

Influence of moderate and profound hyperventilation on cerebral blood flow, oxygenation and metabolism

OBJECTIVE

The aim of the present study was to examine the impact of moderate and profound hyperventilation on regional cerebral blood flow (rCBF), oxygenation and metabolism.

MATERIALS AND METHODS

Twelve anesthetized pigs were subjected to moderate (mHV) and profound (pHV) hyperventilation (target arterial pO(2): 30 and 20 mmHg, respectively) for 30 min each, after baseline normoventilation (BL) for 1 h. Local cerebral extracellular fluid (ECF) concentrations of glucose, lactate, pyruvate and glutamate as well as brain tissue oxygenation (p(ti)O(2)) were monitored using microdialysis and a Licox oxygen sensor, respectively. In nine pigs, regional cerebral blood flow (rCBF) was also continuously measured via a thermal diffusion system.

RESULTS

Both moderate and profound hyperventilation resulted in a significant decrease in rCBF (BL: 37.9+/-4.3 ml/100 g/min; mHV: 29.4+/-3.6 ml/100 g/min; pHV: 23.6+/-4.7 ml/100 g/min; p<0.05) and p(ti)O(2) (BL: 22.7+/-4.1 mmHg; mHV: 18.9+/-4.9 mmHg; pHV: 13.0+/-2.2 mmHg; p<0.05). A p(ti)O(2) decrease below the critical threshold of 10 mmHg was induced in three animals by moderate hyperventilation and in five animals by profound hyperventilation. Furthermore, significant increases in lactate (BL: 1.06+/-0.18 mmol/l; mHV: 1.36+/-0.20 mmol/l; pHV: 1.67+/-0.17 mmol/l; p<0.005), pyruvate (BL: 46.4+/-7.8 micromol/l; mHV: 58.0+/-10.3 micromol/l; pHV: 66.1+/-12.7 micromol/l; p<0.05), and lactate/glucose ratio were observed during hyperventilation. (Data are presented as mean+/-S.E.M.)

CONCLUSIONS

Both moderate and profound hyperventilation may result in insufficient regional oxygen supply and anaerobic metabolism, even in the uninjured brain. Therefore, the use of hyperventilation cannot be considered as a safe procedure and should either be avoided or used with extreme caution.

Emergency department presentation of pediatric stroke

Pediatric stroke is not a common occurrence. When compared with adults, the pediatric population has a much more diverse group of risk factors, and while numerous rare congenital disorders are possible, most known etiologies are cardiac, vascular, or hematologic. The emergency department (ED) presentation of pediatric stroke does not differ greatly from that of adults, although posterior circulation ischemia is less common, and neurologic findings may be more difficult to recognize. ED treatment is also largely the same, with an attention to resuscitation and avoidance of hypoxia, hypotension, hyperthermia, and changes in blood sugar. Use of specialized agents such as aspirin and heparin should be considered in certain cases. It is important for the emergency physician to recognize acute neurologic events in pediatric patients to minimize complications.

Comparing the Bispectral Index and Suppression Ratio with Burst Suppression of the Electroencephalogram During Pentobarbital Infusions in Adult Intensive Care Patients

OBJECTIVE

The bispectral index (BIS), a processed variable derived from the raw electroencephalogram (EEG) used to guide sedation in the intensive care unit (ICU), has not been tested during barbiturate therapy for elevated intracranial pressure. We determined the BIS and suppression ratio (SR) values during traditional burst monitoring of the raw EEG during pentobarbital infusions.

DESIGN

Prospective, observational cohort study.

SETTING

A 42-bed multidisciplinary ICU in a tertiary care medical center.

PATIENTS

Twelve consecutive patients with elevated intracranial pressure treated with pentobarbital infusions.

INTERVENTION

All patients were monitored continuously with the Aspect Medical Systems A-1050 bedside EEG monitor using a bilateral referential montage. Pentobarbital doses were titrated based on the raw EEG to attain a burst-suppression pattern with a goal of 3-5 bursts/minute. Drug dosage, intracranial pressure, cerebral perfusion pressure values, EEG bursts/minute, BIS version 3.2, and SR were recorded daily.

MEASUREMENTS AND MAIN RESULTS

The 12 patients were monitored for 62 patient-days. Mean +/- SD age was 32 +/- 15 years, seven (58%) patients were male, mean Acute Physiology and Chronic Heath Evaluation II score was 17.0 +/- 5.0, and hospital mortality was 42%. The mean pentobarbital infusion rate was 124 +/- 49 mg/hour or 2.3 +/- 1.3 mg/kg/hour, and mean pentobarbital serum concentration was 29.7 +/- 13 microg/ml. The mean BIS value was 18 +/- 14, mean SR 56% +/- 36%; BIS correlated well with SR (r=-0.99, p<0.001). For patient-days with a burst-suppression pattern, BIS 3.2 (r=0.90, p<0.001) and SR (r=-0.89, p<0.001) strongly correlated with the number of bursts/minute. The mean BIS value corresponding to 3-5 bursts/minute was 15 (95% confidence interval [CI] 10-20); SR value was 71 (95% CI 61-80).

CONCLUSION

The Aspect A-1050 applied to patients and monitored by nurses and physicians works well as a bedside EEG monitor, providing a raw EEG signal to titrate barbiturate therapy. The continuous data trend and real-time digital output for the BIS and SR quantify the degree of EEG suppression well and may prove helpful in facilitating titration of barbiturate infusions.

Sensitive and specific photometric determination of mannitol in human serum

Mannitol is an osmotically active polyalcohol often present in fluids used for irrigation of exposed tissue during minimal invasive surgery. Since this polyol normally is not detected in human plasma to any significant extent, it may be used as a laboratory marker of absorption of mannitol-containing irrigative fluids during surgery. For this aim, we developed a photometric assay of mannitol in human blood or serum that may be performed in a near-patient setting. Following deproteinization of the sample with trichloroacetic acid, the supernatant is mixed with NAD+ and a commercially available preparation of mannitol 2-dehydrogenase and is incubated at pH 7.8 and at 37 degrees C for 30 to 60 minutes. At the end of the incubation period the solution is appropriately diluted and the concentration of NADH formed by oxidation of mannitol is determined photometrically at 340 nm. The limit of detection of serum mannitol with this assay is 0.05 mmol/l, the linear range of measurement extends to about 3 mmol/l. At analyte concentrations of 0.48, 1.38 and 3.48 mmol/l, coefficients of inter-assay variation of 12.1, 6.7 and 4.9%, respectively, were obtained. The analytical recovery of mannitol added to serum samples was close to 100%. Of 27 polyalcohols, monosaccharides and oligosaccharides tested, none exhibited a measurable substrate activity and only D-fructose significantly inhibited the oxidation of mannitol at sample concentrations above 10 mmol/l; the enzymatic reaction, however, was strongly affected by EDTA. The suitability of the assay as a routine diagnostic tool for detection and quantification of intraoperatively absorbed irrigation fluid was demonstrated by analyzing mannitol in serum samples obtained from 24 patients undergoing transurethral prostatectomy.

Nursing care of the acute head injury: a review of the evidence

This article aims to review the current evidence in relation to acute head injury care. Head injuries are a frequent cause of death and disability in western society with the first 72 h being an important period for prevention of further brain damage. The underlying physiology behind head injury and intracranial pressure will be discussed. The monitoring of intracranial pressure and implications for practice will be addressed. The specialized nursing care and drug therapy management that is necessary for acute head injury patients will be highlighted. Recommendations for practice will be given.

Use of an anesthesia cerebral monitor bispectral index to assess burst-suppression in pentobarbital coma

A seven-year-old child with generalized status epilepticus who was placed in a barbiturate coma was monitored with the bispectral index monitor in addition to the standard full channel electroencephalogram. This child had a low bispectral index number and high suppression ratio on the bispectral index monitor when the desired level of pentobarbital coma was induced. There was excellent correlation of the bispectral index monitor to the suppression ratio. The burst rate also correlated well to the bispectral index number and to the suppression ratio. Therefore the bispectral index monitor could allow the patient in barbiturate coma to leave the intensive care unit for diagnostic or therapeutic procedures and may one day replace the full-channel electroencephalogram in the management of patients in barbiturate coma.

The effects of sustained hyperventilation on regional cerebral blood volume in thiopental-anesthetized rats

Sustained hyperventilation has a time-limited effect on cerebrovascular dynamics. We investigated whether this effect was similar among brain regions by measuring regional cerebral blood volume (CBV) with steady-state susceptibility contrast magnetic resonance imaging during 3 h of hyperventilation. Regional CBV was determined in nine thiopental-anesthetized, mechanically-ventilated rats every 30 min in the dorsoparietal neocortex, the corpus striatum, and the cerebellum. The corpus striatum was the only brain region showing a stable reduction in CBV during the hypocapnic episode (PaCO(2), 24 +/- 3 mm Hg). In contrast, neocortex and, to a lesser extent, cerebellum exhibited a progressive return toward normal values despite continued hypocapnia. No evidence of a rebound in CBV was found on return to normal ventilation in the three brain regions. We conclude that sustained hyperventilation can lead to an uneven change in the reduction of CBV, possibly because of differences of brain vessels in their sensitivity to extracellular pH. Our results in neocortex confirm the transient effect of sustained hyperventilation on cerebral hemodynamics.

IMPLICATIONS

Sustained hyperventilation has a transient effect in decreasing cerebral blood volume (CBV). Using susceptibility contrast magnetic resonance imaging in thiopental-anesthetized rats, we found differences between brain regions in their transient CBV response to sustained hyperventilation.

Efficacy of hyperventilation, blood pressure elevation, and metabolic suppression therapy in controlling intracranial pressure after head injury

OBJECT

Hyperventilation therapy, blood pressure augmentation, and metabolic suppression therapy are often used to reduce intracranial pressure (ICP) and improve cerebral perfusion pressure (CPP) in intubated head-injured patients. In this study, as part of routine vasoreactivity testing, these three therapies were assessed in their effectiveness in reducing ICP.

METHODS

Thirty-three patients with a mean age of 33 +/- 13 years and a median Glasgow Coma Scale (GCS) score of 7 underwent a total of 70 vasoreactivity testing sessions from postinjury Days 0 to 13. After an initial 133Xe cerebral blood flow (CBF) assessment, transcranial Doppler ultrasonography recordings of the middle cerebral arteries were obtained to assess blood flow velocity changes resulting from transient hyperventilation (57 studies in 27 patients), phenylephrine-induced hypertension (55 studies in 26 patients), and propofol-induced metabolic suppression (43 studies in 21 patients). Changes in ICP, mean arterial blood pressure (MABP), CPP, PaCO2, and jugular venous oxygen saturation (SjvO2) were recorded. With hyperventilation therapy, patients experienced a mean decrease in PaCO2 from 35 +/- 5 to 27 +/- 5 mm Hg and in ICP from 20 +/- 11 to 13 +/- 8 mm Hg (p < 0.001). In no patient who underwent hyperventilation therapy did SjvO2 fall below 55%. With induced hypertension, MABP in patients increased by 14 +/- 5 mm Hg and ICP increased from 16 +/- 9 to 19 +/- 9 mm Hg (p = 0.001). With the aid of metabolic suppression, MABP remained stable and ICP decreased from 20 +/- 10 to 16 +/- 11 mm Hg (p < 0.001). A decrease in ICP of more than 20% below the baseline value was observed in 77.2, 5.5, and 48.8% of hyperventilation, induced-hypertension, and metabolic suppression tests, respectively (p < 0.001 for all comparisons). Predictors of an effective reduction in ICP included a high PaCO2 for hyperventilation, a high study GCS score for induced hypertension, and a high PaCO2 and a high CBF for metabolic suppression.

CONCLUSIONS

Of the three modalities tested to reduce ICP, hyperventilation therapy was the most consistently effective, metabolic suppression therapy was variably effective, and induced hypertension was generally ineffective and in some instances significantly raised ICP. The results of this study suggest that hyperventilation may be used more aggressively to control ICP in head-injured patients, provided it is performed in conjunction with monitoring of SjvO2.

Use of propofol and other nonbenzodiazepine sedatives in the intensive care unit

Sedatives continue to be used on a routine basis in critically ill patients. Although many agents are available and some approach an ideal, none are perfect. Patients require continuous reassessment of their pain and need for sedation. Pathophysiologic abnormalities that cause agitation, confusion, or delirium must be identified and treated before unilateral administration of potent sedative agents that may mask potentially lethal insufficiencies. The routine use of standardized and validated sedation scales and monitors is needed. It is hoped that reliable objective monitors of patients' level of consciousness and comfort will be forthcoming. Each sedative agent discussed in this article seems to have a place in the ICU pharmacologic armamentarium to ensure the safe and comfortable delivery of care. Etomidate is an attractive agent for short-term use to provide the rapid onset and offset of sedation in critically ill patients who are at risk for hemodynamic instability but seem to need sedation or anesthesia to perform a procedure or manipulate the airway. Ketamine administered through intramuscular injection or intravenous infusion provides quick, intense analgesia and anesthesia and allows patients to tolerate limited but painful procedures. The risk/benefit ratio associated with the use of this neuroleptic agent must be weighed carefully. Ketamine is contraindicated in patients who lack normal intracranial compliance or who have significant myocardial ischemia. Barbiturates are reserved mainly to induce coma in patients at risk for severe CNS ischemia, which frequently is associated with refractory intracranial hypertension, or in patients with status epilepticus. When administered in high doses, these drugs have prolonged sedative and depressant effects. Judicious hemodynamic monitoring is required when barbiturate coma is induced. Haloperidol is indicated in the treatment of delirium. Patients should be monitored for extrapyramidal side effects and, when they require higher doses, for potential electrocardiographic prolongation of the QT interval. Dexmedetomidine may evolve into an agent with qualities comparable with midazolam and propofol, and it may even become a drug of choice in select patients. Further study is required, however. Propofol has many of the qualities of an ideal sedative agent. Benzodiazepines and narcotics often are used in concert with propofol to provide reliable amnesia and to relieve pain, respectively. Propofol frequently causes hypotension when administered as a bolus or infusion, particularly in patients with limited cardiac reserve or hypovolemia. More data must be obtained to identify potential deleterious effects of hypertriglyceridemia, and further evaluation of the potential benefits in certain patient populations, such as neurosurgical patients, is needed.

What works in severe head injury?

Traumatic brain injury has an important socioeconomic impact in industrialized countries. However, well-conducted clinical trials are rare. Case-control studies have shown that prevention works. Pathophysiological understanding is becoming more complete as data on chemokines, local brain tissue oxygen tension and hypothermia accumulate. Multimodality monitoring will certainly assume greater importance in the future. Research with targeted therapeutic strategies indicates that secondary ischaemic insults can be prevented. Specific subgroups of patients with traumatic brain injury who will benefit from the use of hypothermia and barbiturates have been identified. Enteral feeding is the preferred nutritional strategy, and the follow-up period should be extended beyond the traditional 1 year.

Intracranial pressure and surgical decompression for traumatic brain injury: biological rationale and protocol for a randomized clinical trial

Commonly, severe traumatic brain injury (TBI) patients undergo amputation of contused brain; the rationale being that edema in presumed unsalvageable cerebrum increases intracranial pressure (ICP). Neuro-critical care expends great effort to control ICP and prevent secondary injury. Non-randomized investigations have employed hemicraniectomy with duraplasty after developing refractory ICP. We undertook a randomized pilot of hemicraniectomy with duraplasty as the initial surgery for severe TBI patients. Goals included reduced ICP therapeutic intensity and return to the operating room, and improved neurological outcome. Upon hospital presentation, the study was to randomize 92 patients with midline shift greater than the size of a surgically removable hematoma. One group was to receive standardized hemicraniectomy and duraplasty; the other would undergo 'traditional' craniotomy (with brain amputation at the neurosurgeon's discretion). A standardized medical protocol followed. The six-month Glasgow Outcome Scale was the primary outcome, with secondary measures including quality of life one year after TBI, duration and frequency of elevated ICP, intensive care unit (ICU) therapeutic intensity, operating room return, and ICU and hospital lengths-of-stay. This article presents the biological rationale and the evidence-based standardized protocols of the study and its outcome measures. The study has stopped and a phase III outcome trial is being organized.

Acute care management of severe traumatic brain injuries

Preservation or restoration of optimal neurologic function following traumatic brain injury (TBI) requires timely and aggressive therapeutic interventions. Effective diagnostic tools, together with an armamentarium of treatment modalities, have augmented the treatment strategies utilized today. In addition, the Guidelinesfor the Management of Severe Head Injury have established a standardized approach for the TBI patient. This article will provide current information regarding the resuscitation priorities, appropriate interventions, and pharmacological agents used in the treatment required by the complex nature of TBI. Also, a review of the occurrences associated with TBI will be discussed.

Management of raised intracranial pressure in children

Children suffer a significant number of head injuries as a result of their high activity levels, immature developmental skills and increased head-to-body mass ratio. Primary brain injury is irreversible, but secondary insults can be limited. Central to this is the management of raised intracranial pressure (ICP). The pathophysiology of head injury can explain some of the causes of raised ICP. Monitoring of ICP is important and this is closely linked to the maintenance of an adequate cerebral perfusion pressure and the importance of normovolaemia. Other interventions that have been shown to limit rises in ICP are appropriate use of positioning, mechanical ventilation and drug therapy. Less common therapies include jugular venous bulb oxygen saturation monitoring and the use of trometamol (THAM). Most nursing interventions do not actively reduce ICP, but they are central to its management. Reducing stimuli, avoiding cluster care, manual hyperinflation and limiting routine endotracheal suction may prevent an accumulative rise in ICP. Based on this literature review, it is possible to divide these interventions into first and second tier treatments, as shown in the protocol. Much of the suggested management will occur simultaneously, but it is important to assess the child's own response to each intervention and thus tailor treatment to minimize secondary brain injury.

Emergency management of the head trauma patient. Principles and practice

Management of the severely brain-injured dog or cat can be frustrating, especially considering the lack of proven effective therapies for head trauma patients. A working knowledge of the basic pathophysiology of head trauma and intracranial pressure (ICP) dynamics is essential to the logical treatment of head traumatized patients. Prevention and correction of hypotension and hypoxemia are necessary for preventing progressive increases in ICP. Mannitol is recommended in most cases of severe head trauma, but there is little evidence to support the use of glucocorticoids in acutely brain-injured dogs and cats. The role of surgical intervention for head-traumatized dogs and cats is still uncertain, but may be beneficial in some cases. Aggressive, expedient treatment and attentive patient monitoring are key aspects of successfully managing canine and feline head trauma patients.

Osmotherapy for elevated intracranial pressure: a critical reappraisal

The administration of osmotic agents is one of the principal strategies to lower elevated intracranial pressure (ICP) and to increase cerebral perfusion pressure. Of the 3 osmotic agents frequently used (mannitol, glycerol and sorbitol), each has characteristic advantages and disadvantages. In addition to renal filtration, sorbitol [elimination half-life (t1/2beta) approximately 1h] and glycerol (t1/2beta 0.2 to 1h) are metabolised, mainly by the liver. The risk of these compounds accumulating in patients with renal insufficiency is low. However, both compounds frequently affect glucose metabolism, leading to an increase in the serum glucose concentration. Mannitol is almost exclusively renally filtered and possesses the slowest elimination from serum (t1/2beta 2 to 4h). The t1/2beta of mannitol is markedly increased in patients with renal insufficiency, but it does not interfere with glucose metabolism. Entry into the cerebrospinal fluid (CSF) is highest with glycerol [CSF: serum ratio of the areas under the concentration-time curves (AUC(CSF): AUCs) approximately 0.25], intermediate with mannitol (AUC(CSF): AUCs approximately 0.15) and lowest with sorbitol (AUC(CSF): AUCs approximately 0.10). The elimination of all osmotic agents from the CSF compartment is substantially slower than from serum. During the elimination phase, the CSF-to-serum osmotic gradient is temporarily reversed. This is one cause of the paradoxical rise of ICP above the pretreatment level sometimes observed with osmotherapeutics. The ability of mannitol, glycerol and sorbitol to lower elevated ICP has been extensively documented. However, whether the use of osmotic agents, particularly with repeated application, improves outcome remains unproven. Therefore, these agents should only be used to treat manifest elevations of ICP, not for prophylaxis of brain oedema.

Subarachnoid hemorrhage following permissive hypercapnia in a patient with severe acute asthma

In this article, we describe a case of a subarachnoid hemorrhage (SAH) in an acute severe asthma patient following mechanical hypoventilation. A 49-year-old man was admitted to an Intensive Care Unit with an acute exacerbation of asthma. After 3 days of mechanical ventilation (hypercapnia and normoxaemia), it was noted that his right pupil was fixed, dilated, and unreactive to light. Computed tomography (CT) scan showed localized SAH within the basilar cisterns and diffuse cerebral swelling. On the fourth day, a new CT scan showed hemorrhage resorption and a cerebral swelling decrease. In the following days, the patient's condition continued improving with no detectable neurological deficits. A review of similar published reports showed that all patients performed respiratory acidosis, normoxaemia, and hypercapnia. The most frequent neurological sign was mydriasis, and all subjects showed cerebral edema. Since normoxaemic hypercapnia has been associated with absence, or less cerebral edema, we considered additional factors to explain cerebral edema and intracranial hypertension causes. Thus, intrathoracic pressures due to patient's efforts by forcibly exhaling, or during mechanical ventilation, would further increase intracranial pressure by limiting cerebral venous drainage. This case emphasizes the fact that patients with acute severe asthma who have developed profoundly hypercarbic without hypoxia before or during mechanical ventilation, may have raised critical intracranial pressure.

ICP measurement control: laboratory test of 7 types of intracranial pressure transducers

Intracranial pressure (ICP) monitoring has become an important parameter in the assessment of comatose patients, with raised intracranial pressure. The transducers in use have to fulfill the criteria of measurement accuracy, practicability and cost-effectiveness. However, these requirements are not always met in clinical practice. The need for ongoing quality control through independent laboratories remains. We have developed a laboratory set-up for the evaluation of intracranial pressure probes. Seven different types of currently used transducers have been tested for measurement accuracy. Under in vitro conditions 3 parameters were assessed: measurement accuracy, a 24 h drift and 10 day drifts. Tests for measurement accuracy were performed at increasing pressure levels of up to 80 mmHg. They were repeated 10 times per probe. This test allowed the simultaneous assessment of 5 different ICP probes. Drift was evaluated for 24 h and 10 days, at 6 pressure levels between 0 and 50 mmHg. Seven different types of ICP probes were tested (HanniSet, Camino, Codman, Spiegelberg, Medex, Epidyn and Gaeltec). Measurement accuracy was best with HanniSet probes. The maximum errors with this transducer were 3 mmHg. Camino and Codman showed similar results. Spiegelberg had slightly larger deviations. With Epidyn and Gaeltec the highest error were noted, up to 10 mmHg in the high pressure range. The 24 h drift was lowest with HanniSet (0.2 mmHg) and Camino (0.8 mmHg). The largest drifts were seen with Medex, Spiegelberg and Gaeltec (1.8 mmHg). Ten day drift was lowest with HanniSet (0.1 mmHg/day) and Codman (0.2 mmHg/day). The highest long-term drifts were found with Epidyn and Gaeltec (1.5 mmHg/day). Drift did not exhibit a linear pattern. After an initial rise in drift during the first 24-72 h, it decreased slowly during the next 7 days. Most ICP probes revealed measurement inaccuracy and drift. These results emphasize the necessity for ongoing evaluations of ICP probes. Therefore, tests for quality assurance are essential to establish a consistent standard of proficiency of ICP transducers.