Lung-protective ventilation in neurosurgical patients

Focused Management of Patients With Severe Acute Brain Injury and ARDS

Considering the COVID-19 pandemic where concomitant occurrence of ARDS and severe acute brain injury (sABI) has increasingly coemerged, we synthesize existing data regarding the simultaneous management of both conditions. Our aim is to provide readers with fundamental principles and concepts for the management of sABI and ARDS, and highlight challenges and conflicts encountered while managing concurrent disease. Up to 40% of patients with sABI can develop ARDS. Although there are trials and guidelines to support the mainstays of treatment for ARDS and sABI independently, guidance on concomitant management is limited. Treatment strategies aimed at managing severe ARDS may at times conflict with the management of sABI. In this narrative review, we discuss the physiological basis and risks involved during simultaneous management of ARDS and sABI, summarize evidence for treatment decisions, and demonstrate these principles using hypothetical case scenarios. Use of invasive or noninvasive monitoring to assess brain and lung physiology may facilitate goal-directed treatment strategies with the potential to improve outcome. Understanding the pathophysiology and key treatment concepts for comanagement of these conditions is critical to optimizing care in this high-acuity patient population.

Lung-protective ventilation increases cerebral metabolism and non-inflammatory brain injury in porcine experimental sepsis

Background

Protective ventilation with lower tidal volumes reduces systemic and organ-specific inflammation. In sepsis-induced encephalopathy or acute brain injury the use of protective ventilation has not been widely investigated (experimentally or clinically). We hypothesized that protective ventilation would attenuate cerebral inflammation in a porcine endotoxemic sepsis model. The aim of the study was to study the effect of tidal volume on cerebral inflammatory response, cerebral metabolism and brain injury. Nine animals received protective mechanical ventilation with a tidal volume of 6 mL × kg⁻¹ and nine animals were ventilated with a tidal volume of 10 mL × kg⁻¹. During a 6-h experiment, the pigs received an endotoxin intravenous infusion of 0.25 µg × kg⁻¹ × h⁻¹. Systemic, superior sagittal sinus and jugular vein blood samples were analysed for inflammatory cytokines and S100B. Intracranial pressure, brain tissue oxygenation and brain microdialysis were sampled every hour.

Results

No differences in systemic or sagittal sinus levels of TNF-α or IL-6 were seen between the groups. The low tidal volume group had increased cerebral blood flow (p < 0.001) and cerebral oxygen delivery (p < 0.001), lower cerebral vascular resistance (p < 0.05), higher cerebral metabolic rate (p < 0.05) along with higher cerebral glucose consumption (p < 0.05) and lactate production (p < 0.05). Moreover, low tidal volume ventilation increased the levels of glutamate (p < 0.01), glycerol (p < 0.05) and showed a trend towards higher lactate to pyruvate ratio (p = 0.08) in cerebral microdialysate as well as higher levels of S-100B (p < 0.05) in jugular venous plasma compared with medium–high tidal volume ventilation.

Conclusions

Contrary to the hypothesis, protective ventilation did not affect inflammatory cytokines. The low tidal volume group had increased cerebral blood flow, cerebral oxygen delivery and cerebral metabolism together with increased levels of markers of brain injury compared with medium–high tidal volume ventilation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-021-00629-0.

Ischaemic stroke-induced distal organ damage: pathophysiology and new therapeutic strategies

Acute ischaemic stroke is associated with a high risk of non-neurological complications, which include respiratory failure, cardiovascular dysfunction, kidney and liver injury, and altered immune and endocrine function. The aim of this manuscript is to provide an overview of the main forms of stroke-induced distal organ damage, providing new pathophysiological insights and recommendations for clinical management.Non-neurological complications of stroke can affect outcomes, with potential for serious short-term and long-term consequences. Many of these complications can be prevented; when prevention is not feasible, early detection and proper management can still be effective in mitigating their adverse impact. The general care of stroke survivors entails not only treatment in the acute setting but also prevention of secondary complications that might hinder functional recovery. Acute ischaemic stroke triggers a cascade of events-including local and systemic activation of the immune system-which results in a number of systemic consequences and, ultimately, may cause organ failure. Understanding the pathophysiology and clinical relevance of non-neurological complications is a crucial component in the proper treatment of patients with acute stroke.Little evidence-based data is available to guide management of these complications. There is a clear need for improved surveillance and specific interventions for the prevention, early diagnosis, and proper management of non-neurological complications during the acute phase of ischaemic stroke, which should reduce morbidity and mortality.

Mechanical ventilation in patients with acute ischaemic stroke: from pathophysiology to clinical practice

Most patients with ischaemic stroke are managed on the ward or in specialty stroke units, but a significant number requires higher-acuity care and, consequently, admission to the intensive care unit. Mechanical ventilation is frequently performed in these patients due to swallowing dysfunction and airway or respiratory system compromise. Experimental studies have focused on stroke-induced immunosuppression and brain-lung crosstalk, leading to increased pulmonary damage and inflammation, as well as reduced alveolar macrophage phagocytic capability, which may increase the risk of infection. Pulmonary complications, such as respiratory failure, pneumonia, pleural effusions, acute respiratory distress syndrome, lung oedema, and pulmonary embolism from venous thromboembolism, are common and found to be among the major causes of death in this group of patients. Furthermore, over the past two decades, tracheostomy use has increased among stroke patients, who can have unique indications for this procedure—depending on the location and type of stroke—when compared to the general population. However, the optimal mechanical ventilator strategy remains unclear in this population. Although a high tidal volume (V_T) strategy has been used for many years, the latest evidence suggests that a protective ventilatory strategy (V_T = 6–8 mL/kg predicted body weight, positive end-expiratory pressure and rescue recruitment manoeuvres) may also have a role in brain-damaged patients, including those with stroke. The aim of this narrative review is to explore the pathophysiology of brain-lung interactions after acute ischaemic stroke and the management of mechanical ventilation in these patients.

Feasibility of Protective Ventilation During Elective Supratentorial Neurosurgery: A Randomized, Crossover, Clinical Trial

BACKGROUND

Traditional ventilation approaches, providing high tidal volumes (Vt), produce excessive alveolar distention and lung injury. Protective ventilation, employing lower Vt and positive end-expiratory pressure (PEEP), is an attractive alternative also for neuroanesthesia, when prolonged mechanical ventilation is needed. Nevertheless, protective ventilation during intracranial surgery may exert dangerous effects on intracranial pressure (ICP). We tested the feasibility of a protective ventilation strategy in neurosurgery.

MATERIALS AND METHODS

Our monocentric, double-blind, 1:1 randomized, 2×2 crossover study aimed at studying the effect size and variability of ICP in patients undergoing elective supratentorial brain tumor removal and alternatively ventilated with Vt 9 mL/kg-PEEP 0 mm Hg and Vt 7 mL/kg-PEEP 5 mm Hg. Respiratory rate was adjusted to maintain comparable end-tidal carbon dioxide between ventilation modes. ICP was measured through a subdural catheter inserted before dural opening.

RESULTS

Forty patients were enrolled; 8 (15%) were excluded after enrollment. ICP did not differ between traditional and protective ventilation (11.28±5.37, 11 [7 to 14.5] vs. 11.90±5.86, 11 [8 to 15] mm Hg; P=0.541). End-tidal carbon dioxide (28.91±2.28, 29 [28 to 30] vs. 28.00±2.17, 28 [27 to 29] mm Hg; P<0.001). Peak airway pressure (17.25±1.97, 17 [16 to 18.5] vs. 15.81±2.87, 15.5 [14 to 17] mm Hg; P<0.001) and plateau airway pressure (16.06±2.30, 16 [14.5 to 17] vs. 14.19±2.82, 14 [12.5 to 16] mm Hg; P<0.001) were higher during protective ventilation. Blood pressure, heart rate, and body temperature did not differ between ventilation modes. Dural tension was "acceptable for surgery" in all cases. ICP differences between ventilation modes were not affected by ICP values under traditional ventilation (coefficient=0.067; 95% confidence interval, -0.278 to 0.144; P=0.523).

CONCLUSIONS

Protective ventilation is a feasible alternative to traditional ventilation during elective neurosurgery.

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.

Lung-Protective Ventilation Strategies for Relief from Ventilator-Associated Lung Injury in Patients Undergoing Craniotomy: A Bicenter Randomized, Parallel, and Controlled Trial

Current evidence indicates that conventional mechanical ventilation often leads to lung inflammatory response and oxidative stress, while lung-protective ventilation (LPV) minimizes the risk of ventilator-associated lung injury (VALI). This study evaluated the effects of LPV on relief of pulmonary injury, inflammatory response, and oxidative stress among patients undergoing craniotomy. Sixty patients undergoing craniotomy received either conventional mechanical (12 mL/kg tidal volume [V_T] and 0 cm H₂O positive end-expiratory pressure [PEEP]; CV group) or protective lung (6 mL/kg V_T and 10 cm H₂O PEEP; PV group) ventilation. Hemodynamic variables, lung function indexes, and inflammatory and oxidative stress markers were assessed. The PV group exhibited greater dynamic lung compliance and lower respiratory index than the CV group during surgery (P < 0.05). The PV group exhibited higher plasma interleukin- (IL-) 10 levels and lower plasma malondialdehyde and nitric oxide and bronchoalveolar lavage fluid, IL-6, IL-8, tumor necrosis factor-α, IL-10, malondialdehyde, nitric oxide, and superoxide dismutase levels (P < 0.05) than the CV group. There were no significant differences in hemodynamic variables, blood loss, liquid input, urine output, or duration of mechanical ventilation between the two groups (P > 0.05). Patients receiving LPV during craniotomy exhibited low perioperative inflammatory response, oxidative stress, and VALI.

Neurocritical Care of Acute Subdural Hemorrhage

Although urgent surgical hematoma evacuation is necessary for most patients with subdural hematoma (SDH), well-orchestrated, evidenced-based, multidisciplinary, postoperative critical care is essential to achieve the best possible outcome. Acute SDH complicates approximately 11% of mild to moderate traumatic brain injuries (TBIs) that require hospitalization, and approximately 20% of severe TBIs. Acute SDH usually is related to a clear traumatic event, but in some cases can occur spontaneously. Management of SDH in the setting of TBI typically conforms to the Advanced Trauma Life Support protocol with airway taking priority, and management breathing and circulation occurring in parallel rather than sequence.

Changes in Therapeutic Intensity Level Following Airway Pressure Release Ventilation in Severe Traumatic Brain Injury

PURPOSE

Airway pressure release ventilation (APRV) utilizes high levels of airway pressure coupled with brief expiratory release to facilitate open lung ventilation. The aim of our study was to evaluate the effects of APRV-induced elevated airway pressure mean in patients with severe traumatic brain injury.

MATERIALS AND METHODS

This was a retrospective cohort study at a 424-bed Level I trauma center. Linear mixed effects models were developed to assess the difference in therapeutic intensity level (TIL), intracranial pressure (ICP), and cerebral perfusion pressure (CPP) over time following the application of APRV.

RESULTS

The study included 21 epochs of APRV in 21 patients. In the 6-hour epoch following the application of APRV, the TIL was significantly increased ( P = .002) and the ICP significantly decreased ( P = .041) compared to that before 6 hours. There was no significant change in CPP ( P = .42) over time. The baseline static compliance and time interaction was not significant for TIL (χ² = 0.2 [ df 1], P = .655), CPP (χ² = 0 [ df 1], P = 1), or ICP (χ² = 0.1 [ df 1], P = .752).

CONCLUSIONS

Application of APRV in patients with severe traumatic brain injury was associated with significantly, but not clinically meaningful, increased TIL and decreased ICP. No significant change in CPP was observed. No difference was observed based on the baseline pulmonary static compliance.

Intraoperative mechanical ventilation strategies to prevent postoperative pulmonary complications in patients with pulmonary and extrapulmonary comorbidities

A variety of patient characteristics and comorbidities have been identified, which increase the risk of postoperative pulmonary complications (PPCs), including smoking, age, chronic obstructive pulmonary disease, pulmonary hypertension, obstructive sleep apnea, cardiac and neurologic diseases as well as critical illness. In contrast to the variety of conditions, evidence for specific intraoperative ventilation strategies to reduce PPC is very limited for most comorbidities. Here, we provide an overview of and discuss possible implications for the intraoperative ventilatory management of patients with comorbidities.

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.

Critical care for patients with massive ischemic stroke

Malignant cerebral edema following ischemic stroke is life threatening, as it can cause inadequate blood flow and perfusion leading to irreversible tissue hypoxia and metabolic crisis. Increased intracranial pressure and brain shift can cause herniation syndrome and finally brain death. Multiple randomized clinical trials have shown that preemptive decompressive hemicraniectomy effectively reduces mortality and morbidity in patients with malignant middle cerebral artery infarction. Another life-saving decompressive surgery is suboccipital craniectomy for patients with brainstem compression by edematous cerebellar infarction. In addition to decompressive surgery, cerebrospinal fluid drainage by ventriculostomy should be considered for patients with acute hydrocephalus following stroke. Medical treatment begins with sedation, analgesia, and general measures including ventilatory support, head elevation, maintaining a neutral neck position, and avoiding conditions associated with intracranial hypertension. Optimization of cerebral perfusion pressure and reduction of intracranial pressure should always be pursued simultaneously. Osmotherapy with mannitol is the standard treatment for intracranial hypertension, but hypertonic saline is also an effective alternative. Therapeutic hypothermia may also be considered for treatment of brain edema and intracranial hypertension, but its neuroprotective effects have not been demonstrated in stroke. Barbiturate coma therapy has been used to reduce metabolic demand, but has become less popular because of its systemic adverse effects. Furthermore, general medical care is critical because of the complex interactions between the brain and other organ systems. Some challenging aspects of critical care, including ventilator support, sedation and analgesia, and performing neurological examinations in the setting of a minimal stimulation protocol, are addressed in this review.

Implementation of an evidence-based extubation readiness bundle in 499 brain-injured patients. a before-after evaluation of a quality improvement project

RATIONALE

Mechanical ventilation is associated with morbidity in patients with brain injury.

OBJECTIVES

This study aims to assess the effectiveness of an extubation readiness bundle to decrease ventilator time in patients with brain injury.

METHODS

Before-after design in two intensive care units (ICUs) in one university hospital. Brain-injured patients ventilated more than 24 hours were evaluated during two phases (a 3-yr control phase followed by a 22-mo intervention phase). Bundle components were protective ventilation, early enteral nutrition, standardization of antibiotherapy for hospital-acquired pneumonia, and systematic approach to extubation. The primary endpoint was the duration of mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

A total of 299 and 200 patients, respectively, were analyzed in the control and the intervention phases of this before-after study. The intervention phase was associated with lower tidal volume (P < 0.01), higher positive end-expiratory pressure (P < 0.01), and higher enteral intake in the first 7 days (P = 0.01). The duration of mechanical ventilation was 14.9 ± 11.7 days in the control phase and 12.6 ± 10.3 days in the intervention phase (P = 0.02). The hazard ratio for extubation was 1.28 (95% confidence interval [CI], 1.04-1.57; P = 0.02) in the intervention phase. Adjusted hazard ratio was 1.40 (95% CI, 1.12-1.76; P < 0.01) in multivariate analysis and 1.34 (95% CI, 1.03-1.74; P = 0.02) in propensity score-adjusted analysis. ICU-free days at Day 90 increased from 50 ± 33 in the control phase to 57 ± 29 in the intervention phase (P < 0.01). Mortality at Day 90 was 28.4% in the control phase and 23.5% in the intervention phase (P = 0.22).

CONCLUSIONS

The implementation of an evidence-based extubation readiness bundle was associated with a reduction in the duration of ventilation in patients with brain injury.

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.

Correlation between capnography and arterial carbon dioxide before, during, and after severe chest injury in swine

The relationship between end-tidal carbon dioxide (EtCO(2)) and arterial carbon dioxide (PaCO(2))-if better defined-could facilitate the difficult task of ventilation in prehospital trauma patients. We aimed to study the PaCO(2)-EtCO(2) relationship before, during, and after chest trauma, hemorrhage, and resuscitation in swine. Twenty-four swine were intubated, anesthetized, and monitored in an animal intensive care unit during three phases: phase 1 (day 1, healthy animals); phase 2 (day 2, injury), which consisted of blunt chest trauma, hemorrhage, and resuscitation; and phase 3 (day 2, after injury). "Respiratory maneuvers" (changes in respiratory rate and tidal volume [TV], intended to vary the PaCO(2) over a range of 25 to 85 mmHg, were performed during phases 1 and 3. End-tidal CO(2) and PaCO(2) were recorded after each respiratory maneuver and analyzed using linear regression. During phase 1, PaCO(2) and EtCO(2) were strongly correlated (r(2) = 0.97, P < 0.01). During phase 2, animals developed decreased oxygenation (PaO(2):FiO(2) [fraction of inspired oxygen] ratio <200) and hypotension (mean arterial pressure, 20-50 mmHg); the PaCO(2)-EtCO(2) relationship deteriorated (r(2) = 0.25, P < 0.0001). During phase 3, oxygenation, hemodynamics, and the PaCO(2)-EtCO(2) relationship recovered (r(2) = 0.92, P < 0.01). End-tidal CO(2) closely correlates to PaCO(2) in healthy animals and after injury/resuscitation across a wide range of respiratory rates and tidal volumes. Once oxygenation and hemodynamics are restored, EtCO(2) can be used to predict PaCO(2) following chest trauma/hemorrhage and should be considered for patient monitoring. This work demonstrated that EtCO(2) alone can reliably be used to estimate PaCO(2) in uninjured subjects and in those subjects who have been resuscitated from severe injury. Immediately after blunt chest injury, the correlation between EtCO(2) and PaCO(2) is temporarily unstable. Under these circumstances (with abnormal oxygenation and/or hemodynamics), greater caution and other monitoring tools may be required.

Pediatric traumatic brain injury: an update

PURPOSE OF REVIEW

The developing brain is particularly vulnerable to traumatic brain injury (TBI), leading to frequent disability or death. This article is an update of the pediatric specificities of TBI management.

RECENT FINDINGS

We review the evidences with regards to general management and therapeutic goals to prevent secondary injuries in pediatric TBI patients. Recent controversies in neurocritical care, such as multimodal neuromonitoring, hyperventilation, barbiturate coma, hypothermia, and decompressive surgery, are also highlighted.

SUMMARY

Many therapeutic modalities in pediatric TBI have a low level of evidence. Further research is needed to establish clear resuscitation goals. Universal objectives may not be suitable for all patients; intensive neuromonitoring may help in identifying individual therapeutic goals and guiding the selection of treatments.

Management and outcome of mechanically ventilated neurologic patients

OBJECTIVE

To describe and compare characteristics, ventilatory practices, and associated outcomes among mechanically ventilated patients with different types of brain injury and between neurologic and nonneurologic patients.

DESIGN

Secondary analysis of a prospective, observational, and multicenter study on mechanical ventilation.

SETTING

Three hundred forty-nine intensive care units from 23 countries.

PATIENTS

We included 552 mechanically ventilated neurologic patients (362 patients with stroke and 190 patients with brain trauma). For comparison we used a control group of 4,030 mixed patients who were ventilated for nonneurologic reasons.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We collected demographics, ventilatory settings, organ failures, and complications arising during ventilation and outcomes. Multivariate logistic regression analysis was performed with intensive care unit mortality as the dependent variable. At admission, a Glasgow Coma Scale score ≤8 was observed in 68% of the stroke, 77% of the brain trauma, and 29% of the nonneurologic patients. Modes of ventilation and use of a lung-protective strategy within the first week of mechanical ventilation were similar between groups. In comparison with nonneurologic patients, patients with neurologic disease developed fewer complications over the course of mechanical ventilation with the exception of a higher rate of ventilator-associated pneumonia in the brain trauma cohort. Neurologic patients showed higher rates of tracheotomy and longer duration of mechanical ventilation. Mortality in the intensive care unit was significantly (p < .001) higher in patients with stroke (45%) than in brain trauma (29%) and nonneurologic disease (30%). Factors associated with mortality were: stroke (in comparison to brain trauma), Glasgow Coma Scale score on day 1, and severity at admission in the intensive care unit.

CONCLUSIONS

In our study, one of every five mechanically ventilated patients received this therapy as a result of a neurologic disease. This cohort of patients showed a higher mortality rate than nonneurologic patients despite a lower incidence of extracerebral organ dysfunction.

Acute lung injury is an independent risk factor for brain hypoxia after severe traumatic brain injury

BACKGROUND

Pulmonary complications are frequently observed after severe traumatic brain injury (TBI), but little is known about the consequences of lung injury on brain tissue oxygenation and metabolism.

OBJECTIVE

We examined the association between lung function and brain tissue oxygen tension (PbtO2) in patients with severe TBI.

METHODS

We analyzed data from 78 patients with severe, nonpenetrating TBI who underwent continuous PbtO2 and intracranial pressure monitoring. Acute lung injury was defined by the presence of pulmonary infiltrates with a PaO2/FiO2 (PF) ratio less than 300 and the absence of left ventricular failure. A total of 587 simultaneous measurements of PbtO2 and PF ratio were examined using longitudinal data analysis.

RESULTS

PbtO2 correlated strongly with PaO2 and PF ratio (P < .05) independent of PaCO2, brain temperature, cerebral perfusion pressure, and hemoglobin. Acute lung injury was associated with lower PbtO2 (34.6 +/- 13.8 mm Hg at PF ratio >300 vs 30.2 +/- 10.8 mm Hg [PF ratio 200-300], 28.9 +/- 9.8 mm Hg [PF ratio 100-199], and 21.1 +/- 7.4 mm Hg [PF ratio <100], all P values <.01). After adjusting for intracranial pressure, Marshall computed tomography score, and APACHE II (Acute Physiology and Chronic Health Evaluation) score, acute lung injury was an independent risk factor for compromised PbtO2 (PbtO2 <20 mm Hg; adjusted odds ratio: 2.13, 95% confidence interval: 1.21-3.77; P < .01).

CONCLUSION

After severe TBI, PbtO2 correlates with PF ratio. Acute lung injury is associated with an increased risk of compromised PbtO2, independent from intracerebral and systemic injuries. Our findings support the use of lung-protective strategies to prevent brain hypoxia in TBI patients.

Use of invasive mechanical ventilation in Australian emergency departments

OBJECTIVE

There are few published reports describing the use of invasive mechanical ventilation in EDs. We explored the characteristics of patients receiving mechanical ventilation, the ventilator modes and parameters used as well as the duration of ventilation and the nature of ventilator decision-making in Australian ED.

METHODS

We conducted a 2 month prospective survey of adult patients who received invasive mechanical ventilation in 24 Australian ED. Data forms were completed by ED staff during the patient's ED presentation. We documented ventilator settings post intubation, after a 1 h stabilization period, and immediately before ED discharge or extubation. The person responsible for selection of ventilator settings was noted at each time point.

RESULTS

Data were recorded on 307 patients. Altered mental status (179/307 [58%, 95% CI 53-64]) was the most common indication for mechanical ventilation. Volume-controlled modes were most frequently used at all measured time points; with a median tidal volume of 8 mL/kg. Responsibility for initial selection of ventilator settings was shared between ED physicians (157/307 [51%, 95% CI 46-57]), ED nurses (111/307 [36%, 95% CI 31-42]) and ICU or paramedic staff (9/307 [3%, 95% CI 1-5]) (not recorded 30/307 [10%, 95% CI 6-13]). Ongoing responsibility for titration of ventilation was more commonly that of the ED nurse.

CONCLUSION

The application of mechanical ventilation was similar to descriptions reported in the critical care literature both in Australia and internationally. Decision-making responsibilities were shared by ED medical and nursing staff.

Impact of positive end-expiratory pressure on cerebral injury patients with hypoxemia

BACKGROUND

Traumatic brain injury or intracranial hemorrhage patients with acute lung injury/acute respiratory distress syndrome need mechanical ventilation. The use of positive end-expiratory pressure (PEEP) in this situation remains controversial. This study explored the impact of PEEP on intracranial pressure (ICP), cerebral perfusion pressure (CPP), central venous pressure (CVP), and mean arterial pressure (MAP) in cerebral injury patients.

METHODS

Nine cerebral injury patients with lung injury who needed mechanical ventilation and met the criteria for ICP monitoring were included in this study. Intraventricular catheters were positioned in 1 of the bilateral ventricles and connected to pressure transducers. Invasive arterial pressure and CVP were monitored continuously. Pressure control ventilation was applied during this clinical trial in a stepwise recruitment maneuver (RM) with 3 cm H₂O intermittent increments and decrements of PEEP.

RESULTS

A total of 28 RMs were completed in 9 patients. Mean values of MAP, CVP, ICP, and CPP 5 minutes after RMs showed no significant differences compared with baseline (P > 0.05). Correlation analysis of all the mean values of MAP, CVP, ICP, and CPP showed significant correlation between MAP and CPP, PEEP and CVP, PEEP and ICP, and PEEP and CPP with all P values less than 0.05.

CONCLUSION

The impact of PEEP on blood pressure, ICP, and CPP varies greatly in cerebral injury patients. Mean arterial pressure and ICP monitoring is of benefit when using PEEP in cerebral injury patients with hypoxemia.

Clinical review: Ventilatory strategies for obstetric, brain-injured and obese patients

The ventilatory management of patients with acute respiratory failure is supported by good evidence, aiming to reduce lung injury by pressure limitation and reducing the duration of ventilatory support by regular assessment for discontinuation. Certain patient groups, however, due to their altered physiology or disease-specific complications, may require some variation in usual ventilatory management. The present manuscript reviews the ventilatory management in three special populations, namely the patient with brain injury, the pregnant patient and the morbidly obese patient.

Neurologic injury and mechanical ventilation

Mechanical ventilation in neurologically injured patients presents a number of unique challenges. Patients who are intubated due to a primary neurologic injury often experience respiratory phenomena secondary to that injury, including elevation of intracranial pressure (ICP) in response to mechanical ventilation and variations in respiratory patterns. These problems often require unique ventilator strategies that are designed to minimize the impact of the ventilator on ICP and brain oxygenation. Balancing the need to maintain brain oxygenation and control of ICP can be complicated by the effects of ventilator management on ICP. We will examine the consequences of ventilator management as they relate to parameters that affect ICP and brain oxygenation in patients who have neurologic injury.

Respiratory care

PURPOSE OF THE REVIEW

Neurosurgical patients frequently develop respiratory complications, adversely affecting neurologic outcome and survival. The review summarizes current literature and management of respiratory complications associated with brain injury.

MAJOR FINDINGS

Respiratory complications are commonly associated with traumatic brain injury and subarachnoid haemorrhage. Lung-protective ventilation with reduced tidal volumes improves outcome in acute lung injury, and should be applied to neurosurgical patients in the absence of increased intracranial pressure. Weaning from the mechanical ventilation should be initiated as soon as possible, although the role of neurological status in the weaning process is not clear. Prevention of pneumonia and aspiration improves survival. In patients with difficult weaning, early bedside percutaneous tracheostomy should be considered.

FURTHER INVESTIGATIONS

Further studies are warranted to elucidate an optimal oxygenation and ventilation in brain-injured patients, weaning strategies, predictors of the failed weaning and extubation, respiratory support in patients with difficulties to wean, and early tracheostomy.

Special Cases: Mechanical Ventilation of Neurosurgical Patients

Mechanical ventilation has evolved greatly over the last half century, guided primarily by improved comprehension of the relevant pathology/physiology. Neurosurgical patients are a unique subgroup of patients who heavily use this technology for both support, and less commonly, as a therapy. Such patients demand special consideration with regard to mode of ventilation, use of positive end-expiratory pressure, and monitoring. In addition, meeting the ventilatory needs of neurosurgical patients while minimizing ventilatory-induced lung damage can be a challenging aspect of care.

A survey of static and dynamic work postures of operating room staff

Purpose

To determine reciprocal and synergistic effects of acute intracranial hypertension and ARDS on neuronal and pulmonary damage and to define possible mechanisms.

Methods

Twenty-eight mechanically ventilated pigs were randomized to four groups of seven each: control; acute intracranial hypertension (AICH); acute respiratory distress syndrome (ARDS); acute respiratory distress syndrome in combination with acute intracranial hypertension (ARDS + AICH). AICH was induced with an intracranial balloon catheter and the inflation volume was adjusted to keep intracranial pressure (ICP) at 30–40 cmH₂O. ARDS was induced by oleic acid infusion. Respiratory function, hemodynamics, extravascular lung water index (ELWI), lung and brain computed tomography (CT) scans, as well as inflammatory mediators, S100B, and neuronal serum enolase (NSE) were measured over a 4-h period. Lung and brain tissue were collected and examined at the end of the experiment.

Results

In both healthy and injured lungs, AICH caused increases in NSE and TNF-alpha plasma concentrations, extravascular lung water, and lung density in CT, the extent of poorly aerated (dystelectatic) and atelectatic lung regions, and an increase in the brain tissue water content. ARDS and AICH in combination induced damage in the hippocampus and decreased density in brain CT.

Conclusions

AICH induces lung injury and also exacerbates pre-existing damage. Increased extravascular lung water is an early marker. ARDS has a detrimental effect on the brain and acts synergistically with intracranial hypertension to cause histological hippocampal damage.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-011-2232-2) contains supplementary material, which is available to authorized users.