Intracranial pressure changes during rapid sequence intubation: a swine model

Effects of intubation technique on intracranial pressure: a cadaveric study

Patients are at risk of increased intracranial pressure (ICP) during manipulation for endotracheal intubation. The aim of this cadaveric study was to quantify this relationship. Five fresh frozen adult cadaveric heads were used. The internal carotid artery (ICA) and internal jugular vein (IJV) were dissected bilaterally. All vessels were occluded on the right side. To mimic central venous pressures, the left IJV was cannulated and filled with water to maintain a pressure of approximately 7 cm H2O. The ICA cannula was attached to an oscillating water pump. Next, an ICP monitor was placed. Normophysiological volumes of water were infused to maintain normal ICP. Baseline ICP and IJV pressures were recorded. The heads were then placed in the sniffing position and in neutral position for nasal intubation, and finally an oral endotracheal tube was placed using standard head/neck maneuvers. The ICP was recorded. Mean baseline ICP was 13 mmHg (range 4-18 mmHg) and mean IJV pressure was 6 cm H2O. In the sniffing position, ICP increased in all specimens by a mean of 5 mmHg. In the neutral position, after intubation, the ICP increased in all specimens by a mean of 3 mmHg. Nasal intubation resulted in an increase in four of the five specimens. The mean increase in ICP with this maneuver was 2 mmHg. We present a cadaveric model of ICP measurement during neck manipulation using intracranial fluid dynamics. The ICP increased consistently. Following clinical studies, physicians involved in intubating patients with concern for raised ICP should change the technique to avoid complications.

Prevalence of significant traumatic brain injury among patients intubated in the field due to impaired level of consciousness

OBJECTIVE

Current guidelines advocate prehospital endotracheal intubation (ETI) in patients with suspected severe head injury and impaired level of consciousness. However, the ability to identify patients with traumatic brain injury (TBI) in the prehospital setting is limited and prehospital ETI carries a high complication rate. We investigated the prevalence of significant TBI among patients intubated in the field for that reason.

METHODS

Data were retrospectively collected from emergency medical services and hospital records of trauma patients for whom prehospital ETI was attempted and who were transferred to Rambam Health Care Campus, Israel. The indication for ETI was extracted. The primary outcome was significant TBI (clinical or radiographic) among patients intubated due to suspected severe head trauma.

RESULTS

In 57.3% (379/662) of the trauma patients, ETI was attempted due to impaired consciousness. 349 patients were included in the final analysis: 82.8% were male, the median age was 34 years (IQR 23.0-57.3), and 95.7% suffered blunt trauma. 253 patients (72.5%) had significant TBI. In a multivariable analysis, Glasgow Coma Scale>8 and alcohol intoxication were associated with a lower risk of TBI with OR of 0.26 (95% CI 0.13-0.51, p < 0.001) and 0.16 (95% CI 0.06-0.46, p < 0.001), respectively.

CONCLUSION

Altered mental status in the setting of trauma is a major reason for prehospital ETI. Although most of these patients had TBI, one in four of them did not suffer a significant TBI. Patients with a higher field GCS and those suffering from intoxication have a higher risk of misdiagnosis. Future studies should explore better tools for prehospital assessment of TBI and ways to better define and characterize patients who may benefit from early ETI.

High-Risk Airway Management in the Emergency Department: Diseases and Approaches, Part II

BACKGROUND

Successful airway management is critical to the practice of emergency medicine. Thus, emergency physicians must be ready to optimize and prepare for airway management in critically ill patients with a wide range of physiologic challenges. Challenges in airway management commonly encountered in the emergency department are discussed using a pearl and pitfall discussion in this second part of a 2-part series.

OBJECTIVE

This narrative review presents an evidence-based approach to airway and patient management during endotracheal intubation in challenging cases commonly encountered in the emergency department.

DISCUSSION

Adverse events during emergent airway management are common with postintubation cardiac arrest, reported in as many as 1 in 25 intubations. Many of these adverse events can be avoided by proper identification and understanding the underlying physiology, preparation, and postintubation management. Those with high-risk features including trauma, elevated intracranial pressure, upper gastrointestinal bleed, cardiac tamponade, aortic stenosis, morbid obesity, and pregnancy must be managed with airway expertise.

CONCLUSIONS

This narrative review discusses the pearls and pitfalls of commonly encountered physiologic high-risk intubations with a focus on the emergency clinician.

Henle fibre layer haemorrhage: clinical features and pathogenesis

BACKGROUND

To describe the clinical presentation and characteristic imaging features of deep retinal haemorrhages primarily located in the Henle fibre layer (HFL) of the macula. The spectrum of aetiologies and a comprehensive theory of pathogenesis are presented.

METHODS

This is a retrospective, multicentre case series evaluating eyes with retinal haemorrhage in HFL. Clinical features, underlying aetiology, systemic and ocular risk factors, visual acuity, and multimodal imaging including fundus photography and cross-sectional and en face optical coherence tomography (OCT) are presented.

RESULTS

Retinal haemorrhages localised to HFL in 33 eyes from 23 patients were secondary to acute blunt trauma to the head (n=2), eye (n=1) and trunk (n=1), ruptured intracranial aneurysm (Terson's syndrome, n=3), general anaesthesia (n=1), epidural anaesthesia (n=1), hypertension with anaemia (n=1), decompression retinopathy (n=1), postvitrectomy with intraocular gas (n=1), retinal vein occlusion (n=7), myopic degeneration (n=2), macular telangiectasia type 2 (n=1), and polypoidal choroidal vasculopathy (n=1). Defining clinical features included deep retinal haemorrhage with feathery margin and petaloid pattern radiating from the fovea. OCT demonstrated characteristic hyper-reflectivity from the haemorrhage delineated by obliquely oriented fibres in the Henle layer. Spontaneous resolution of HFL haemorrhage occurred after 3 months in 15 patients with follow-up.

CONCLUSION

The characteristic petaloid-shaped, deep intraretinal haemorrhage with a feathery margin localised to HFL is associated with various disorders. The terminology 'Henle fiber layer hemorrhage (HH)' is proposed to describe the clinical and OCT findings, which may result from abnormal retinal venous pressure from systemic or local retinovascular disorders affecting the deep capillary plexus or from choroidal vascular abnormalities.

Monro-Kellie 2.0: The dynamic vascular and venous pathophysiological components of intracranial pressure

For 200 years, the 'closed box' analogy of intracranial pressure (ICP) has underpinned neurosurgery and neuro-critical care. Cushing conceptualised the Monro-Kellie doctrine stating that a change in blood, brain or CSF volume resulted in reciprocal changes in one or both of the other two. When not possible, attempts to increase a volume further increase ICP. On this doctrine's "truth or relative untruth" depends many of the critical procedures in the surgery of the central nervous system. However, each volume component may not deserve the equal weighting this static concept implies. The slow production of CSF (0.35 ml/min) is dwarfed by the dynamic blood in and outflow (∼700 ml/min). Neuro-critical care practice focusing on arterial and ICP regulation has been questioned. Failure of venous efferent flow to precisely match arterial afferent flow will yield immediate and dramatic changes in intracranial blood volume and pressure. Interpreting ICP without interrogating its core drivers may be misleading. Multiple clinical conditions and the cerebral effects of altitude and microgravity relate to imbalances in this dynamic rather than ICP per se. This article reviews the Monro-Kellie doctrine, categorises venous outflow limitation conditions, relates physiological mechanisms to clinical conditions and suggests specific management options.

Anesthetic management of labor and delivery in patients with elevated intracranial pressure

The anesthetic management of labor and delivery in patients with elevated intracranial pressure is complex. This review discusses the etiologies of diffuse and focal pathologies which lead to elevated intracranial pressure in pregnancy. The role of neuraxial and general anesthesia in the management of labor and delivery is also examined. Finally, a comprehensive review of strategies to minimize increases in intracranial pressure during general anesthesia for cesarean delivery is presented.

Prehospital intubation in patients with isolated severe traumatic brain injury: a 4-year observational study

Objectives. To study the effect of prehospital intubation (PHI) on survival of patients with isolated severe traumatic brain injury (ISTBI). Method. Retrospective analyses of all intubated patients with ISTBI between 2008 and 2011 were studied. Comparison was made between those who were intubated in the PHI versus in the trauma resuscitation unit (TRU). Results. Among 1665 TBI patients, 160 met the inclusion criteria (105 underwent PHI, and 55 patients were intubated in TRU). PHI group was younger in age and had lower median scene motor GCS (P = 0.001). Ventilator days and hospital length of stay (P = 0.01 and 0.006, resp.) were higher in TRUI group. Mean ISS, length of stay, initial blood pressure, pneumonia, and ARDS were comparable among the two groups. Mortality rate was higher in the PHI group (54% versus 31%, P = 0.005). On multivariate regression analysis, scene motor GCS (OR 0.55; 95% CI 0.41-0.73) was an independent predictor for mortality. Conclusion. PHI did not offer survival benefit in our group of patients with ISTBI based on the head AIS and the scene motor GCS. However, more studies are warranted to prove this finding and identify patients who may benefit from this intervention.

Cerebrospinal Fluid Pressures Resulting From Experimental Traumatic Spinal Cord Injuries in a Pig Model

Despite considerable effort over the last four decades, research has failed to translate into consistently effective treatment options for spinal cord injury (SCI). This is partly attributed to differences between the injury response of humans and rodent models. Some of this difference could be because the cerebrospinal fluid (CSF) layer of the human spine is relatively large, while that of the rodents is extremely thin. We sought to characterize the fluid impulse induced in the CSF by experimental SCIs of moderate and high human-like severity, and to compare this with previous studies in which fluid impulse has been associated with neural tissue injury. We used a new in vivo pig model (n = 6 per injury group, mean age 124.5 days, 20.9 kg) incorporating four miniature pressure transducers that were implanted in pairs in the subarachnoid space, cranial, and caudal to the injury at 30 mm and 100 mm. Tissue sparing was assessed with Eriochrome Cyanine and Neutral Red staining. The median peak pressures near the injury were 522.5 and 868.8 mmHg (range 96.7–1430.0) and far from the injury were 7.6 and 36.3 mmHg (range 3.8–83.7), for the moderate and high injury severities, respectively. Pressure impulse (mmHg.ms), apparent wave speed, and apparent attenuation factor were also evaluated. The data indicates that the fluid pressure wave may be sufficient to affect the severity and extent of primary tissue damage close to the injury site. However, the CSF pressure was close to normal physiologic values at 100 mm from the injury. The high injury severity animals had less tissue sparing than the moderate injury severity animals; this difference was statistically significant only within 1.6 mm of the epicenter. These results indicate that future research seeking to elucidate the mechanical origins of primary tissue damage in SCI should consider the effects of CSF. This pig model provides advantages for basic and preclinical SCI research due to its similarities to human scale, including the existence of a human-like CSF fluid layer.

Prehospital non-drug assisted intubation for adult trauma patients with a Glasgow Coma Score less than 9

OBJECTIVES

Prehospital airway management for adult trauma patients remains controversial. We sought to review the frequency that paramedic non-drug assisted intubation or attempted intubation is performed for trauma patients in Ontario, Canada, and determine its association with mortality.

METHODS

We conducted a retrospective cohort study using the Ontario Trauma Registry's Comprehensive Data Set for 2002-2009. Eligible patients were greater than 16 years of age, had an initial Glasgow Coma Score of less than 9 and were cared for by ground-based non-critical care paramedics. The primary outcome was mortality. Outcomes were compared between patients undergoing prehospital intubation versus basic airway management. Logistic regression analyses were used to quantify the association between prehospital intubation and mortality.

RESULTS

Of the 2229 patients included in the analysis, 671 (30.1%) underwent prehospital intubation. Annual rates of prehospital intubation declined from 33.7% to 14.0% (ptrend<0.0001) over the study period. Unadjusted death rates were 66.0% versus 34.8% in the intubation and basic airway groups, respectively (p<0.0001). Intubation in the prehospital setting was associated with a heightened risk of mortality (adjusted OR 2.8, 95% CI 1.1 to 7.6).

CONCLUSIONS

Prehospital non-drug assisted intubation for trauma is being performed less frequently in Ontario, Canada. Within our study population, paramedic non-drug assisted intubation or attempted intubation was associated with a heightened risk of mortality.

The pressure distribution of cerebrospinal fluid responds to residual compression and decompression in an animal model of acute spinal cord injury

STUDY DESIGN

In vivo large animal (pig) model study of cerebrospinal fluid (CSF) pressures after acute experimental spinal cord injury (SCI).

OBJECTIVE

To determine how the CSF pressure (CSFP) and CSF pulse pressure amplitude (CSFPPA) cranial and caudal to the injury site change after an acute SCI with subsequent thecal occlusion and decompression.

SUMMARY OF BACKGROUND DATA

Lowering intrathecal pressure via CSF drainage is currently instituted to prevent ischemia-induced SCI during thoracoabdominal aortic aneurysm surgery and was recently investigated as a potential intervention for acute traumatic SCI. However, in SCI patients, persistent extradural compression commonly occludes the subarachnoid space. This may generate a CSFP differential across the injury site, which cannot be appreciated with lumbar catheter pressure measurements.

METHODS

Anesthetized pigs were subjected to an acute contusive SCI at T11 and 8 hours of sustained compression (n = 12), or sham surgery (n = 2). CSFP was measured cranial and caudal to the injury site, using miniature pressure transducers, during compression and for 6 hours after decompression.

RESULTS

The cranial-caudal CSFP differential increased (mean, 0.39 mm Hg/h), predominantly due to increased cranial pressure. On decompression, cranial CSFP decreased (mean, -1.16 mm Hg) and caudal CSFP increased (mean, 0.65 mm Hg). The CSFP differential did not change significantly after decompression. Cranial CSFPPA was greater than caudal CSFPPA, but this differential did not change during compression. On decompression, the caudal CSFPPA increased in some but not all animals.

CONCLUSION

Although extradural compression exists at the site of injury, lumbar CSFP may not accurately indicate CSFP cranial to the injury. Decompression may provide immediate, though perhaps partial, resolution of the pressure differential. CSFPPA was not a consistent indicator of decompression in this animal model. These findings may have implications for the design of future clinical protocols in which CSFP is monitored after acute SCI.

The relationship between out-of-hospital airway management and outcome among trauma patients with Glasgow Coma Scale Scores of 8 or less

BACKGROUND

Airway management remains a fundamental component of optimal care of the severely injured patient, with endotracheal intubation representing the definitive strategy for airway control. However, multiple studies document an association between out-of-hospital intubation and increased mortality for severe traumatic brain injury.

OBJECTIVES

To explore the relationship between out-of-hospital intubation attempts and outcome among trauma patients with Glasgow Coma Scale (GCS) scores ≤ 8 across sites participating in the Resuscitation Outcomes Consortium (ROC).

METHODS

The ROC Epistry-Trauma, an epidemiologic database of prehospital encounters with critically injured trauma victims, was used to identify emergency medical services (EMS)-treated patients with GCS scores ≤ 8. Multiple logistic regression was used to explore the association between intubation attempts and vital status at discharge, adjusting for the following covariates: age, gender, GCS score, hypotension, mechanism of injury, and ROC site. Sites were then stratified by frequency of intubation attempts and chi-square test for trend was used to associate the frequency of intubation attempts with outcome.

RESULTS

A total of 1,555 patients were included in this analysis; intubation was attempted in 758 of these. Patients in whom intubation was attempted had higher mortality (adjusted odds ratio [OR] 2.91, 95% confidence interval [CI] 2.13-3.98, p < 0.01). However, sites with higher rates of attempted intubation had lower mortality across all trauma victims with GCS scores ≤ 8 (OR 1.40, 95% CI 1.15-1.72, p < 0.01).

CONCLUSIONS

Patients in whom intubation is attempted have higher adjusted mortality. However, sites with a higher rate of attempted intubation have lower adjusted mortality across the entire cohort of trauma patients with GCS scores ≤ 8. Coma Scale score.

The need for standardized data reporting for prehospital airway management

Despite a widespread belief in the value of aggressive prehospital airway management, the therapeutic benefits of early tracheal intubation (TI) remain unclear. In fact, most attempts to elucidate the benefits of prehospital TI on outcome from traumatic brain injury and cardiopulmonary arrest have documented an increase in mortality associated with the procedure. While some degree of selection bias is likely present in these studies, the inherent adverse physiological effects of intubation and a high incidence of desaturation and subsequent hyperventilation may indicate a harmful effect of the procedure. This uncertainty regarding such a fundamental resuscitation procedure as TI underscores the need for standardized data reporting in prehospital airway management research. To this end, the Utstein prehospital airway conference proposed a set of variables that would move us in that direction. However, the present article by Lossius and colleagues documents how far we still have to travel before such standardization can be achieved. Only through these efforts can we elucidate the true benefits - or harm - of advanced airway management during critical resuscitation.