Field Medicine

FIELD NEUROLOGY FOR DIVERS

Shortly after surfacing from the dive, your buddy experiences numbness and tingling in his limbs – a classic neurological symptom of decompression sickness. What you do next could make the difference between a close call and permanent injury.

Diving injuries involving the nervous system, including decompression sickness (DCS), arterial gas embolism (AGE) and ear barotrauma (EBT), are blessedly rare, but when they do happen, these conditions require prompt diagnosis and treatment to prevent serious and lasting injury. While care of an injured diver should be passed to trained diving and medical professionals as soon as possible, recreational divers can prepare themselves to handle emergencies and assist the professionals with DAN’s training programmes.

In this special report, former Director of

DAN Training Eric Douglas provides an overview of the On-Site Neurological Assessment for Divers, the first step in the process of seeking treatment for all forms of decompression illness (DCI), and DAN Member Dr. Herbert Newton explains the finer points of the nervous system and how physicians make a clinical diagnosis of DCI symptoms.

PERFORMING THE DAN ON-SITE NEUROLOGICAL ASSESSMENT FOR DIVERS

DAN’s On-Site Neurological Assessment for Divers is one of the most important classes we offer for the simple reason that it’s the first step in determining and documenting what’s wrong with a diver who surfaces with symptoms of DCI. In approximately 80 percent of dive accidents, injured divers exhibit numbness and tingling or weakness throughout the body. Often, though, an injured diver may not recognise these symptoms for what they are. In these cases, the neurological assessment can be an invaluable tool to determine the scope of the injuries and convince the diver that he or she really does need professional care.

CONDUCTING AN EXAM

A neurological examination begins as a conversation and progresses to a series of tests for physical ability and mental clarity. Only a medical doctor can make a diagnosis of DCI, but our course trains divers to methodically gather detailed information in a useful form. The on-site assessment slate (see image overleaf) is provided to divers as part of the class, and serves as both a guide for the process and a convenient way to record the information emergency responders, DAN medical personnel and other medical professionals will need to manage the case.

The first step is to collect basic data on the diver and a history of the event, recent dives and any obvious symptoms, as well as any symptoms the diver may not have considered. In our training, we teach divers to ask questions like:

• When did the symptom(s) begin?

• What are you feeling? (Go through a list of

potential problems.)

• What was the profile of your last dive, and how many dives have you made in the last 48 hours?

Collect maximum depth and bottomtime profiles, including safety stops, as well as breathing gas mixtures. Were there any instances of problems or unusual features such as equipment failure?

If pain is a symptom, ask the diver to rate the pain on a scale of 0 to 10. Ask if any of these symptoms could be explained by conditions the diver already knows about, like previous injuries or medical history.

Most of the questions are self-explanatory. By collecting this data, you are creating a clear record of the preceding events that can save time when medical professionals arrive.

ASSESSING MENTAL AWARENESS

After you gather the history, you will begin the actual assessment steps by collecting basic vital signs, including breathing and pulse rates and (if equipped and trained to do so) blood pressure data.

The next step is to assess the diver’s level of consciousness – whether he is alert, responds only to verbal stimuli, painful stimuli or is unconscious. Most often, injured divers will be alert and oriented, exhibiting other symptoms such as numbness or tingling. However, if you determine some impaired level of consciousness, your priority of care shifts to basic life support, monitoring the airway and supporting breathing and circulation

as necessary. When you determine that he is conscious, you will want to gauge his awareness, or orientation to person, time and place.You do this by asking questions about who the diver is and where he is. These questions give you a clearer understanding of the diver’s state of mind. With some neurological conditions, it’s possible for a person to seem perfectly lucid and coherent until you ask for a name or location.

Other assessments of mental function include the ability to follow commands, to express phrases, to name three objects and to interpret a sentence. You’ll also assess judgment, memory and calculations along with abstract reasoning. Each of these exams tests a different part of the brain, checking for injuries. With calculations, for example, you will ask the diver to perform a test called Serial Sevens.

That is, you will ask the diver to count backward from 100 by sevens. This requires the diver to calculate numbers, which is handled differently in the brain than is speech. Another way to perform this specific test is to ask the diver to repeat his phone number backward.

ASSESSING PHYSICAL CONDITION

The first step in evaluating a diver’s physical condition is to test his cranial nerves to see if they are compromised. This portion of the onsite exam involves a series of motor strength evaluations to assess for signs of asymmetry or weakness. There are 12 different cranial nerves that control sensation and muscular function on the face. These tests will identify insults to several of those key nerves. Aspects of this exam also include assessments of eye movements. The next step is to test strength and motor function by providing resistance to a series of muscle groups. You don’t need to know how strong the diver was in the first place; just be aware if one side of the body is weaker than the other, which would be a strong indication of

neurological deficit. In the course, you are taught (and have ample opportunity to practise) the test procedures for different muscle groups.

For example: To test grip strength, have the diver squeeze your fingers with both hands at the same time. This will let you detect if one hand is noticeably stronger than the other. Assess the shoulders, arms, hands, hip flexor muscles, legs and feet in much the same way, attempting to detect weaknesses. It is critically important to have a valid medical history at this point. It has happened more than once that an examiner has noted a weakness in a shoulder or a leg only to find out later that the diver had a pre-existing injury that led to that weakness and had nothing to do with the dive.

Just as you did with the face earlier, touch the body in several key spots to see if there is any change in sensation. Do this with both a soft touch and a sharp touch, altering stimulus perception. Do this with the diver’s eyes shut, asking him to identify the area being touched. Using a dermatomal map, a physician can correlate areas of reduced sensitivity with injuries to specific nerves. A dermatomal map shows the relationship between an area of skin and sensory fibres from a single spinal nerve. During treatment, the physician will then record changes to these areas and note responses to treatment.

Finally, assess the diver’s balance and coordination. A moving boat may preclude an assessment of balance. This test is performed by asking the diver to walk about 3 metres

(10 feet) and watching his feet. You should record any unusual gait, such as foot drags or stumbles that were not present before.

This could indicate a serious problem.

A thorough DAN On-Site Neurological Assessment for Divers takes about 10 minutes, perhaps a bit longer the first time through with the history portion of the exam. If you have a long transport time before you turn the diver over to advanced care, conduct this exam once an hour to check for any changes in the diver’s condition. Report the information you gathered to the emergency medical personnel or DAN medical staff. This will help them determine the best treatment for the diver.

THE NERVOUS SYSTEM

The nervous system consists of the brain and spinal cord (called the central nervous system, or CNS) and the cranial and peripheral nerves (referred to as the peripheral nervous system, or PNS). The cranial and peripheral nerves are extensions of the CNS that allow for motor and sensory information to travel to and from the brain.

Motor nerves connect the CNS with muscles in the face and extremities to coordinate movements directed by the brain. Sensory nerves send information from receptors in the tissues to the brain for processing; for example, the sensations of cold or touch.

The brain is divided into the cerebrum, cerebellum and the brainstem.

The cerebrum is further separated into the major lobes (frontal, parietal, temporal, occipital) as well as deeper white matter pathways and various motor and sensory nuclei. It controls and integrates motor, sensory and higher mental functions, such as thought, reason, emotion and memory. These functions are also called cortical functions, and their loss or deterioration is called cortical symptoms. The major descending motor pathways cross over from one side to the other (e.g., right to left) as they pass from the brain into the brainstem and spinal cord.

The cerebellum is a smaller structure behind and below the cerebrum. It is involved with the fine control of complex motor activity as well as maintenance of posture and balance. Injury to the cerebellum can cause walking difficulties (ataxia), incoordination and loss of balance. These symptoms are called cerebellar symptoms and signs.

The brainstem is a major conduit for all neural fibres to and from the brain. At this point, the 12 cranial nerves separate and follow their own paths, while motor and sensory fibres from peripheral nerves continue for a while as a bundle through the spinal cord. Injury to the brainstem may affect both cranial nerves and descending motor pathways, manifesting sometimes as “crossed deficits,” with a cranial nerve deficit on one side and a motor deficit on the other (e.g., left-sided eye movement palsy and right-arm and right-leg motor weakness). The spinal cord is composed of nerve bundles; some exit as the dorsal roots (sensory fibres) and ventral roots (motor fibres) through the space between the vertebrae and combine into a peripheral nerve. There are eight cervical

(C1 to C8), 12 thoracic (T1 to T12), five lumbar (L1 to L5) and five sacral (S1 to S5) pairs of nerves corresponding each to one spinal segment. The spinal cord parenchyma itself ends at the beginning of the lumbar region but the cauda equina, the descending lumbar and sacral nerve roots, continue through the canal and leave it through openings in the sacral bone.

NEXT STEPS

Once you have determined that a dive injury exists, the primary first aid care for an injured diver is still oxygen first aid, using high flow oxygen with as close to 100-percent inspired oxygen as possible. You can learn more about the indications and techniques for delivering oxygen first aid in a dive-related emergency in the DAN Oxygen First Aid for Scuba Diving Injuries course.