Ep 17 - Diffuse Axonal Injury with John Hell

 

Understanding and Managing Diffuse Axonal Injury in Neurointensive Care

Welcome to the St Emlyn’s blog. I’m Iain Beardsell, and today we delve into the complex and crucial topic of diffuse axonal injury (DAI) with insights from John Hell, a consultant in Neurointensive Care at the University Hospital of Southampton and former director of the Wessex Neuroscience’s Intensive Care Unit. With his extensive experience and co-authorship of the Neurointensive Care guidelines, John provides a comprehensive overview of DAI, its pathophysiology, management, and prognosis.

What is Diffuse Axonal Injury?

Diffuse axonal injury is a type of traumatic brain injury where the brain’s axons are sheared due to rapid acceleration or deceleration forces. This can occur in various scenarios, from minor to severe head injuries. The axons, which connect the grey matter (cell bodies) on the brain's surface to the white matter (nerve fibers) inside, are particularly susceptible to damage when subjected to such forces.

Pathophysiology of Diffuse Axonal Injury

The pathophysiology of DAI involves axonal shearing due to differing densities and connections between grey and white matter. When the brain moves at different rates within the skull during an injury, this shearing occurs. Initially, this stretching does not necessarily rupture the axons but causes them to swell and release mediators. These mediators lead to further axonal breakdown and secondary brain injury characterized by cerebral edema, increased intracranial pressure (ICP), and restricted diffusion of glucose and oxygen.

Clinical Presentation and Diagnosis

DAI can be challenging to diagnose initially, as early imaging might show minimal changes. However, small petechial hemorrhages at the grey-white matter interface can be indicative. These are more evident on MRI scans or repeat CT scans after 6 to 24 hours. Clinicians should be vigilant about mechanisms of injury, Glasgow Coma Scale (GCS) scores, and clinical presentation to suspect DAI.

Management Strategies in Neurointensive Care

The management of patients with DAI involves a multi-faceted approach focused on stabilizing and maintaining normal physiological parameters. Key steps include:

1. Initial Stabilization: Ensure normal blood pressure, oxygenation (PACO2 and PIO2), and venous drainage from the head by positioning the patient appropriately and avoiding obstructions like tight cervical collars.

2. Monitoring and Imaging: Initial imaging may show little, but repeat CT or MRI scans can reveal the extent of the injury. Placing an ICP monitor helps in maintaining adequate cerebral perfusion pressure (CPP) as ICP rises over 72 to 96 hours.

3. Intravenous Fluids: Use of normal saline is recommended due to its osmolality. Other fluids like Hartmann's, which are hypo-osmolar, can exacerbate cerebral edema by diluting plasma.

4. Anticoagulation Management: Reversal of anticoagulation and ensuring normal platelet function is crucial. Patients on anticoagulants should have these reversed immediately, and those on antiplatelet agents should receive platelet transfusions if still bleeding.

Prognosis and Outcomes

Prognosis in DAI is variable and often unpredictable based on initial presentation. While patients with poor GCS scores tend to do worse on average, individual outcomes can vary widely. Aggressive monitoring and management in neurointensive care units have shown that many patients can recover to independence and good quality of life, challenging the previous perception of uniformly poor outcomes.

Practical Insights for Emergency and Pre-Hospital Care

In emergency and pre-hospital settings, early interventions can significantly impact outcomes. Prioritizing normal physiological parameters, using appropriate induction agents, and ensuring timely referral to neurointensive care are essential steps. For instance, thiopental is recommended for induction in hemodynamically stable patients with isolated head injuries due to its efficacy in minimizing cerebral metabolic rate for oxygen (CMRO2). For unstable patients, ketamine remains a safe alternative despite old concerns about its use in head injuries.

Case Study and Practical Application

Consider a hypothetical case of a 45-year-old cyclist involved in a high-speed accident, resulting in severe head injury without intracranial bleed but with suspected DAI. The patient is intubated and ventilated by the pre-hospital team and transferred to a major trauma center. Initial CT shows minimal injury, but due to the mechanism and presentation, DAI is suspected.

In neurointensive care, management focuses on:

• Stabilization: Ensuring normal blood pressure, oxygenation, and venous drainage.
• Monitoring: Placing an ICP monitor and repeating imaging at 6, 12, or 24-hour intervals.
• Fluid Management: Using normal saline to maintain plasma osmolality.
• Anticoagulation Reversal: Reversing any anticoagulation and ensuring normal platelet function.

Over the next 72 to 96 hours, the patient’s condition is closely monitored, with adjustments made based on ICP readings and repeat imaging. The interdisciplinary team works together to minimize secondary brain injury and support recovery.

The Role of Education and Ongoing Research

Continuous education and staying updated with the latest guidelines and research are crucial for healthcare professionals managing traumatic brain injuries. The Neurointensive Care guidelines co-authored by John Hell and his team are a valuable resource available online, providing evidence-based practices for managing these complex cases.

Conclusion

Diffuse axonal injury remains a significant challenge in neurointensive care, requiring a comprehensive and multidisciplinary approach for optimal outcomes. Early recognition, aggressive management, and ongoing research are key to improving the prognosis for patients with DAI. By maintaining normal physiological parameters, utilizing appropriate fluids, and implementing timely interventions, healthcare professionals can make a substantial difference in the recovery and quality of life for these patients.

Thank you for joining us on the St Emlyn’s blog. We hope this detailed exploration of DAI provides valuable insights for your practice. Stay tuned for more discussions on critical topics in emergency and intensive care medicine.