Ventilatory strategies for patients with acute brain injury

Recognizing Risks and Optimizing Perioperative Care to Reduce Respiratory Complications in the Pediatric Patient

There have been significant advancements in the safe delivery of anesthesia as well as improvements in surgical technique; however, the perioperative period can still be high risk for the pediatric patient. Perioperative respiratory complications (PRCs) are some of the most common critical events that can occur in pediatric surgical patients and they can lead to increased length of hospitalization, worsened patient outcomes, and higher hospital and postoperative costs. It is important to determine the various factors that put pediatric patients at increased risk of PRCs. This will allow for more detailed and accurate informed consent, optimized perioperative management strategy, improved allocation of clinical resources, and, hopefully, better patient experience. There are only a few risk prediction models/scoring tools developed for and validated in the pediatric patient population, but they have been useful in helping identify the key factors associated with a high likelihood of developing PRCs. Some of these factors are patient factors, while others are procedure-related factors. Some of these factors may be modified such that the patient’s clinical status is optimized preoperatively to decrease the risk of PRCs occurring perioperatively. Fore knowledge of the factors that are not able to be modified can help guide allocation of perioperative clinical resources such that the negative impact of these non-modifiable factors is buffered. Additional training in pediatric anesthesia or focused expertise in pediatric airway management, vascular access and management of massive hemorrhage should be considered for the perioperative management of the less than 3 age group. Intraoperative ventilation strategy plays a key role in determining respiratory outcomes for both adult and pediatric surgical patients. Key components of lung protective mechanical ventilation strategy such as low tidal volume and moderate PEEP used in the management of acute respiratory distress syndrome (ARDS) in pediatric intensive care units have been adopted in pediatric operating rooms. Adequate post-operative analgesia that balances pain control with appropriate mental status and respiratory drive is important in reducing PRCs.

Brain ultrasonography: methodology, basic and advanced principles and clinical applications. A narrative review

Brain ultrasonography can be used to evaluate cerebral anatomy and pathology, as well as cerebral circulation through analysis of blood flow velocities. Transcranial colour-coded duplex sonography is a generally safe, repeatable, non-invasive, bedside technique that has a strong potential in neurocritical care patients in many clinical scenarios, including traumatic brain injury, aneurysmal subarachnoid haemorrhage, hydrocephalus, and the diagnosis of cerebral circulatory arrest. Furthermore, the clinical applications of this technique may extend to different settings, including the general intensive care unit and the emergency department. Its increasing use reflects a growing interest in non-invasive cerebral and systemic assessment. The aim of this manuscript is to provide an overview of the basic and advanced principles underlying brain ultrasonography, and to review the different techniques and different clinical applications of this approach in the monitoring and treatment of critically ill patients.

Combined lung and brain ultrasonography for an individualized "brain-protective ventilation strategy" in neurocritical care patients with challenging ventilation needs

When intracranial hypertension and severe lung damage coexist in the same clinical scenario, their management poses a difficult challenge, especially as concerns mechanical ventilation management. The needs of combined lung and brain protection from secondary damage may conflict, as ventilation strategies commonly used in patients with ARDS are potentially associated with an increased risk of intracranial hypertension. In particular, the use of positive end-expiratory pressure, recruitment maneuvers, prone positioning, and protective lung ventilation can have undesirable effects on cerebral physiology: they may positively or negatively affect intracranial pressure, based on the final repercussions on PaO₂ and cerebral perfusion pressure (through changes in cardiac output, mean arterial pressure, venous return, PaO₂ and PaCO₂), also according to the baseline conditions of cerebral autoregulation. Lung ultrasound (LUS) and brain ultrasound (BUS, as a combination of optic nerve sheath diameter assessment and cerebrovascular Doppler ultrasound) have independently proven their potential in respectively monitoring lung aeration and brain physiology at the bedside. In this narrative review, we describe how the combined use of LUS and BUS on neurocritical patients with demanding mechanical ventilation needs can contribute to ventilation management, with the aim of a tailored "brain-protective ventilation strategy."

[Topical respiratory strategies in neurocritical care]

Management of the respiratory tract and maintenance of adequate gas exchange are the basic goals of critical care. Injury to the nervous system is often accompanied by development of respiratory disorders. On the other hand, changes in the gas composition of arterial blood can cause brain damage. In addition, approaches to the patient with respiratory failure, which are used in general critical care and neurocritical care, may differ. The presented literature review is devoted to modern respiratory strategies used in neurocritical care.

Effects of Prone Position and Positive End-Expiratory Pressure on Noninvasive Estimators of ICP: A Pilot Study

BACKGROUND

Prone positioning and positive end-expiratory pressure can improve pulmonary gas exchange and respiratory mechanics. However, they may be associated with the development of intracranial hypertension. Intracranial pressure (ICP) can be noninvasively estimated from the sonographic measurement of the optic nerve sheath diameter (ONSD) and from the transcranial Doppler analysis of the pulsatility (ICPPI) and the diastolic component (ICPFVd) of the velocity waveform.

METHODS

The effect of the prone positioning and positive end-expiratory pressure on ONSD, ICPFVd, and ICPPI was assessed in a prospective study of 30 patients undergoing spine surgery. One-way repeated measures analysis of variance, fixed-effect multivariate regression models, and receiver operating characteristic analyses were used to analyze numerical data.

RESULTS

The mean values of ONSD, ICPFVd, and ICPPI significantly increased after change from supine to prone position. Receiver operating characteristic analyses demonstrated that, among the noninvasive methods, the mean ONSD measure had the greatest area under the curve signifying it is the most effective in distinguishing a hypothetical change in ICP between supine and prone positioning (0.86±0.034 [0.79 to 0.92]). A cutoff of 0.43 cm was found to be a best separator of ONSD value between supine and prone with a specificity of 75.0 and a sensitivity of 86.7.

CONCLUSIONS

Noninvasive ICP estimation may be useful in patients at risk of developing intracranial hypertension who require prone positioning.

Intracranial Pressure During Pressure Control and Pressure-Regulated Volume Control Ventilation in Patients with Traumatic Brain Injury: A Randomized Crossover trial

INTRODUCTION

Mechanical ventilation with control of partial arterial CO2 pressures (PaCO2) is used to treat or stabilize intracranial pressure (ICP) in patients with traumatic brain injury (TBI). Pressure-regulated volume control (PRVC) is a ventilator mode where inspiratory pressures are automatically adjusted to deliver the patient a pre-set stable tidal volume (TV). This may result in a more stable PaCO2 and thus a more stable ICP compared with conventional pressure control (PC) ventilation. The aim of this study was to compare PC and PRVC ventilation in TBI patients with respect to ICP and PaCO2.

METHODS

This is a randomized crossover trial including eleven patients with a moderate or severe TBI who were mechanically ventilated and had ICP monitoring. Each patient was administered alternating 2-h periods of PC and PRVC ventilation. The outcome variables were ICP and PaCO2.

RESULTS

Fifty-two (26 PC, 26 PRVC) study periods were included. Mean ICP was 10.8 mmHg with PC and 10.3 mmHg with PRVC ventilation (p = 0.38). Mean PaCO2 was 36.5 mmHg (4.87 kPa) with PC and 36.1 mmHg (4.81 kPa) with PRVC (p = 0.38). There were less fluctuations in ICP (p = 0.02) and PaCO2 (p = 0.05) with PRVC ventilation.

CONCLUSIONS

Mean ICP and PaCO2 were similar for PC and PRVC ventilation in TBI patients, but PRVC ventilation resulted in less fluctuation in both ICP and PaCO2. We cannot exclude that the two ventilatory modes would have impact on ICP in patients with higher ICP values; however, the similar PaCO2 observations argue against this.

Righting Reflex Predicts Long-Term Histological and Behavioral Outcomes in a Closed Head Model of Traumatic Brain Injury

Blunt impact produces a heterogeneous brain injury in people and in animal models of traumatic brain injury. We report that a single closed head impact to adult C57/BL6 mice produced two injury syndromes (CHI-1 and CHI-2). CHI-1 mice spontaneously reinitiated breathing after injury while CHI-2 mice had prolonged apnea and regained breathing only after cardiopulmonary resuscitation and supplementation of 100% O₂. The CHI-1 group significantly regained righting reflex more rapidly than the CHI-2 group. At 7 days post-injury, CHI-1, but not CHI-2 mice, acquired but had no long-term retention of an active place avoidance task. The behavioral deficits of CHI-1 and CHI-2 mice were retained one-month after the injury. CHI-1 mice had loss of hippocampal neurons and localized white matter injury at one month after injury. CHI-2 had a larger loss of hippocampal neurons and more widespread loss of myelin and axons. High-speed videos made during the injury were followed by assessment of breathing and righting reflex. These videos show that CHI-2 mice experienced a larger vertical g-force than CHI-1 mice. Time to regain righting reflex in CHI-2 mice significantly correlated with vertical g-force. Thus, physiological responses occurring immediately after injury can be valuable surrogate markers of subsequent behavioral and histological deficits.

Lung protective ventilation (ARDSNet) versus airway pressure release ventilation: ventilatory management in a combined model of acute lung and brain injury

BACKGROUND

Concomitant lung/brain traumatic injury results in significant morbidity and mortality. Lung protective ventilation (Acute Respiratory Distress Syndrome Network [ARDSNet]) has become the standard for managing adult respiratory distress syndrome; however, the resulting permissive hypercapnea may compound traumatic brain injury. Airway pressure release ventilation (APRV) offers an alternative strategy for the management of this patient population. APRV was hypothesized to retard the progression of acute lung/brain injury to a degree greater than ARDSNet in a swine model.

METHODS

Yorkshire swine were randomized to ARDSNet, APRV, or sham. Ventilatory settings and pulmonary parameters, vitals, blood gases, quantitative histopathology, and cerebral microdialysis were compared between groups using χ2, Fisher's exact, Student's t test, Wilcoxon rank-sum, and mixed-effects repeated-measures modeling.

RESULTS

Twenty-two swine (17 male, 5 female), weighing a mean (SD) of 25 (6.0) kg, were randomized to APRV (n = 9), ARDSNet (n = 12), or sham (n = 1). PaO2/FIO2 ratio dropped significantly, while intracranial pressure increased significantly for all three groups immediately following lung and brain injury. Over time, peak inspiratory pressure, mean airway pressure, and PaO2/FIO2 ratio significantly increased, while total respiratory rate significantly decreased within the APRV group compared with the ARDSNet group. Histopathology did not show significant differences between groups in overall brain or lung tissue injury; however, cerebral microdialysis trends suggested increased ischemia within the APRV group compared with ARDSNet over time.

CONCLUSION

Previous studies have not evaluated the effects of APRV in this population. While our macroscopic parameters and histopathology did not observe a significant difference between groups, microdialysis data suggest a trend toward increased cerebral ischemia associated with APRV over time. Additional and future studies should focus on extending the time interval for observation to further delineate differences between groups.

PEEP role in ICU and operating room: from pathophysiology to clinical practice

Positive end expiratory pressure (PEEP) may prevent cyclic opening and collapsing alveoli in acute respiratory distress syndrome (ARDS) patients, but it may play a role also in general anesthesia. This review is organized in two sections. The first one reports the pathophysiological effect of PEEP on thoracic pressure and hemodynamic and cerebral perfusion pressure. The second section summarizes the knowledge and evidence of the use of PEEP in general anesthesia and intensive care. More specifically, for intensive care this review refers to ARDS and traumatic brain injured patients.

High-frequency oscillation and tracheal gas insufflation in patients with severe acute respiratory distress syndrome and traumatic brain injury: an interventional physiological study

Introduction

In acute respiratory distress syndrome (ARDS), combined high-frequency oscillation (HFO) and tracheal gas insufflation (TGI) improves gas exchange compared with conventional mechanical ventilation (CMV). We evaluated the effect of HFO-TGI on PaO₂/fractional inspired O₂ (FiO₂) and PaCO₂, systemic hemodynamics, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) in patients with traumatic brain injury (TBI) and concurrent severe ARDS.

Methods

We studied 13 TBI/ARDS patients requiring anesthesia, hyperosmolar therapy, and ventilation with moderate-to-high CMV-tidal volumes for ICP control. Patients had PaO₂/FiO₂ <100 mm Hg at end-expiratory pressure ≥10 cm H₂O. Patients received consecutive, daily, 12-hour rescue sessions of HFO-TGI interspersed with 12-hour periods of CMV. HFO-TGI was discontinued when the post-HFO-TGI PaO₂/FiO₂ exceeded 100 mm Hg for >12 hours. Arterial/central-venous blood gases, hemodynamics, and ICP were recorded before, during (every 4 hours), and after HFO-TGI, and were analyzed by using repeated measures analysis of variance. Respiratory mechanics were assessed before and after HFO-TGI.

Results

Each patient received three to four HFO-TGI sessions (total sessions, n = 43). Pre-HFO-TGI PaO₂/FiO₂ (mean ± standard deviation (SD): 83.2 ± 15.5 mm Hg) increased on average by approximately 130% to163% during HFO-TGI (P < 0.01) and remained improved by approximately 73% after HFO-TGI (P < 0.01). Pre-HFO-TGI CMV plateau pressure (30.4 ± 4.5 cm H₂O) and respiratory compliance (37.8 ± 9.2 ml/cm H₂O), respectively, improved on average by approximately 7.5% and 20% after HFO-TGI (P < 0.01 for both). During HFO-TGI, systemic hemodynamics remained unchanged. Transient improvements were observed after 4 hours of HFO-TGI versus pre-HFO-TGI CMV in PaCO₂ (37.7 ± 9.9 versus 41.2 ± 10.8 mm Hg; P < 0.01), ICP (17.2 ± 5.4 versus 19.7 ± 5.9 mm Hg; P < 0.05), and CPP (77.2 ± 14.6 versus 71.9 ± 14.8 mm Hg; P < 0.05).

Conclusions

In TBI/ARDS patients, HFO-TGI may improve oxygenation and respiratory mechanics, without adversely affecting PaCO₂, hemodynamics, or ICP. These findings support the use of HFO-TGI as a rescue ventilatory strategy in patients with severe TBI and imminent oxygenation failure due to severe ARDS.

Prehospital management of severe traumatic brain injury: concepts and ongoing controversies

PURPOSE OF REVIEW

Prehospital management affects long-term outcome of patients with severe traumatic brain injury (TBI). This article reviews the current concepts and ongoing controversies of prehospital treatment of severe TBI.

RECENT FINDINGS

Prehospital management focuses on the prevention of secondary brain injury and rapid transport to a neurotrauma center for definitive diagnosis and life- as well as brain-saving emergency treatment such as decompressive craniotomy. There is a broad consensus that adequate airway management, prevention of hypoxia, hypocapnia or hypercapnia, prevention of hypotension and control of hemorrhage represent preclinical therapeutic modalities that may contribute to improved survival in severe TBI. The precise role of prehospital endotracheal intubation, osmotic agents and early therapeutic hypothermia needs to be clarified in the context of time required for transportation, local infrastructure, geographical factors and availability of experienced emergency teams.

SUMMARY

Prehospital management of TBI remains challenging. There are no universal objectives suitable to all patients. Randomized, controlled clinical trials are necessary for developing optimal protocols for paramedic and physician emergency medical teams.

Intensive Care Management of Subarachnoid Haemorrhage

Aneurysmal subarachnoid haemorrhage (SAH) is a devastating disease associated with high mortality and poor outcome in many survivors. Aggressive treatment by a comprehensive multidisciplinary team is associated with improved outcome, but the intensive care management of SAH presents significant challenges. Multimodal neuromonitoring may detect secondary insults before irreversible neuronal damage has occurred, and is increasingly being used to guide treatment. This article reviews current trends in the intensive care management of SAH from aspects of initial resuscitation to recent developments in the prevention and management of complications, including delayed cerebral ischaemia. Evidence from clinical trials and recent consensus guidance is reviewed.

Clinical review: Respiratory monitoring in the ICU - a consensus of 16

Monitoring plays an important role in the current management of patients with acute respiratory failure but sometimes lacks definition regarding which 'signals' and 'derived variables' should be prioritized as well as specifics related to timing (continuous versus intermittent) and modality (static versus dynamic). Many new techniques of respiratory monitoring have been made available for clinical use recently, but their place is not always well defined. Appropriate use of available monitoring techniques and correct interpretation of the data provided can help improve our understanding of the disease processes involved and the effects of clinical interventions. In this consensus paper, we provide an overview of the important parameters that can and should be monitored in the critically ill patient with respiratory failure and discuss how the data provided can impact on clinical management.

Pulmonary complications in patients with severe brain injury

Pulmonary complications are prevalent in the critically ill neurological population. Respiratory failure, pneumonia, acute lung injury and the acute respiratory distress syndrome (ALI/ARDS), pulmonary edema, pulmonary contusions and pneumo/hemothorax, and pulmonary embolism are frequently encountered in the setting of severe brain injury. Direct brain injury, depressed level of consciousness and inability to protect the airway, disruption of natural defense barriers, decreased mobility, and secondary neurological insults inherent to severe brain injury are the main cause of pulmonary complications in critically ill neurological patients. Prevention strategies and current and future therapies need to be implemented to avoid and treat the development of these life-threatening medical complications.

Prolonged heparin-free extracorporeal membrane oxygenation in multiple injured acute respiratory distress syndrome patients with traumatic brain injury

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) can be used as an "ultima ratio" strategy in multiple injured patients with severe thoracic trauma. However, systemic anticoagulation during ECMO is recommended and thus traumatic brain injury (TBI) and intracranial bleeding are well-accepted contraindications for ECMO therapy.

METHODS

This report describes three cases of prolonged heparin-free venovenous ECMO in multiple injured acute respiratory distress syndrome patients with severe TBI failing conventional mechanical ventilation.

RESULTS

: Using this strategy, neither ECMO-associated bleeding nor clotting of the extracorporeal circuit occurred. All patients survived.

CONCLUSIONS

Based on our experience, we recommend the use of heparin-free ECMO in multiple injured patients with pulmonary failure that is not successfully controlled by lung-protective ventilation even if severe TBI is present.

LEVEL OF EVIDENCE

IV, therapeutic study.

High-frequency oscillation as a rescue strategy for brain-injured adult patients with acute lung injury and acute respiratory distress syndrome

Acute lung injury and acute respiratory distress syndrome (ARDS) occur frequently in brain-injured patients. Single organ dysfunction ventilator strategies result in a conflict between lung protective ventilation and the prevention of secondary neurological insult(s). The objectives of this study were to determine if clinical and physiological benefits of high-frequency oscillatory ventilation (HFOV) exist compared to conventional ventilation and to determine what data there are on the effects of HFOV on cerebral perfusion pressure and intracranial pressure. Systematic review was designed. An optimally sensitive search strategy was used that included; OVID MEDLINE, OVID EMBASE, Cochrane Clinical Trials Register, and hand searching of references of retrieved articles and proceedings of meetings. Study selection includes published randomized controlled trials comparing HFOV with conventional ventilation in adults with ARDS and observational studies of the use of HFOV in adults with ARDS and traumatic brain injury (TBI). Both authors reviewed all trials. A data extraction form was used. In adults with ARDS no mortality benefit has been shown with HFOV, oxygenation improves, arterial partial pressure of CO(2) may increase and there is no change in mean arterial blood pressure. There are few data describing HFOV in adults with TBI. In the small, low quality, studies that have been reported there have not been uncontrollable changes in intracranial pressure. HFOV has not been shown to have any mortality benefit in adults with ARDS. There are insufficient data to clarify the role, or safety, of HFOV in adults with TBI and concurrent ARDS.

[Detection of a cerebral ischaemia episode during surgery by monitoring the brain tissue oxygen pressure]

The detection and treatment of cerebral ischaemia and tissue hypoxia for the prevention of secondary injury are the basic objectives during anaesthesia for neurosurgical procedures. The monitoring of the tissue oxygen pressure is direct and can enable potentially harmful situations to be detected in real time. Although it was initially used in neurocritical patients, its use has extended to surgical patients. We present the case of a patient subjected to surgical resection of a dural arteriovenous fistula in which the brain tissue oxygen pressure around the area of the lesion was monitored. The finding of an episode of cerebral tissue hypoxia during closure of the craniotomy determined the treatment of the patient. We highlight the possible use of this neuromonitoring for the rapid detection of regional cerebral hypoxia events in the peri-operative period of vascular neurosurgery, procedures that have a significant risk of, mainly ischaemic, hypoxia episodes.

Pediatric acute respiratory failure: areas of debate in the pediatric critical care setting

Pediatric intensive care units across the world care for large numbers of mechanically ventilated infants and children on a daily basis, yet management of these patients is far from standardized. This lack of standardization may be a necessity in certain situations given variation between underlying disease processes, pathophysiology, response to therapy and available resources. However, there are many situations in which similar patients are managed differently across pediatric intensive care units simply because there are a shortage of available data to guide the management of these critically ill infants and children. Thus, a large fraction of pediatric critical care involves a combination of institutional preference, individual experience, opinion and extrapolation of adult data.