Inadvertent Subdural Injection

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Unusual response to epidural bolus : 

Unusual response to epidural bolus Craigavon Area Hospital Anaesthetic Case-Based Teaching Wednesday August 12th 2009 Facilitator: Dr. Andrew Ferguson

Slide 2: 

A 56 year old woman was admitted to hospital for a scheduled left hemicolectomy for tumour. Her medical history included COPD with exercise tolerance of 50-100 yards on the flat. She stopped smoking 5 years ago. She is moderately obese with BMI 31. Given the medical history the decision was made in conjunction with the patient to insert an epidural catheter for post-operative analgesia. She had a previous uneventful epidural for right knee replacement 2 years previously. Her only medications were ipratropium, budesonide and salbutamol inhalers and multivitamins. She had no known drug allergies. On the day of surgery the epidural catheter was sited uneventfully at the T10/11 space on the first attempt. Aspiration of the epidural catheter was negative for blood, as was placing the catheter tip dependent. A 3 ml test dose of 2.5 mg/ml levobupivaine was negative for adverse effect. Over the next 20 minutes an additional 20 ml of the levobupivacaine solution was administered.15 minutes later there was no evidence of block on testing to ice or pinprick. After a further 5 minutes the patient complained of numbness in her arms and hands. On clinical examination, the anesthetist confirmed the presence of sensory block in the upper extremities although no motor block was found in either the upper or lower limbs. Within 5 minutes of this the patient became unresponsive to voice or painful stimulus, although pulse rate was maintained at 67/minute and BP was 90-110 systolic. She was rapidly intubated and ventilated. The systolic blood pressure decreased to 90 systolic and was treated with a single dose of 5 mg of ephedrine. The patient was started on a propofol infusion and transferred to the Intensive Care Unit. She remained haemo-dynamically stable and when sedation was lightened 2 hours later had full motor function and was successfully extubated. What is the differential diagnosis? What do you think was the cause here? Would you have done anything differently? What is the relevant pathophysiology and anatomy? What other causes are there for failure to achieve adequate block after epidural? Is this likely to happen again if the patient has a epidural in the future? What other comments have you on this case?

Discussion : 

Discussion

Inadvertent Subdural Injection : 

Inadvertent Subdural Injection Anatomy, pathophysiology & outcomes

The Subdural Space : 

The Subdural Space Classic view Potential space between dura and arachnoid Contains small amount of serous fluid Modern view Traumatic dissection between layers of the meninges There is no potential space Either way… Runs from lower border of S2 to reach intracranially As high as floor of third ventricle Wider in cervical region Extends laterally over nerve roots Space may persist once formed, making spinal difficult

Subdural Space Anatomy : 

Subdural Space Anatomy Amorphous substance and neurothelial cells - NOT a potential space until traumatically disrupted

Clinical Features : 

Clinical Features Setting Anaesthetists after straightforward epidural catheter insertion Radiologists attempting myelography Estimated anaesthetic incidence 0.8% but who knows? Risk - Previous back surgery, recent LP, difficult block? Characteristics - less dense than spinal block Unexpectedly high block 20-35 minutes after epidural (74%) Patchy or failed block (restricted spread) (17%) Block out of proportion to volume (spread against gravity) Numb hands Swallowing difficulty Upper thoracic block + dyspnoea Variable sympathetic block/hypotension Intracranial extension => brainstem block/LOC/apnoea

Prevalence of case characteristics : 

Prevalence of case characteristics CSF aspirated freely in 11%! - likely mechanism of “failed spinal”

Prevalence of case characteristics : 

Prevalence of case characteristics

Prevalence of case characteristics : 

Prevalence of case characteristics

Prevalence of case characteristics : 

Prevalence of case characteristics

Prevalence of case characteristics : 

Prevalence of case characteristics

Prevalence of case characteristics : 

Prevalence of case characteristics

Radiographic imaging : 

Radiographic imaging Classic findings: extensive narrow lateral columns of contrast extend high into thoracic spine “railroad track” appearance May also have posterior pools of local in T-L spine Combined subdural and epidural pooling

Radiographic imaging : 

Radiographic imaging

Diagnosis & detection : 

Diagnosis & detection

Management : 

Management If failed spinal - success with repeat may be difficult => GA If epidural - success with repeat has been described so ? If high block => supportive management May require intubation/ventilation/sedation

Why epidurals fail… : 

Why epidurals fail… Transforaminal escape…way too much catheter! Often L1-L3 Lower abdominal analgesia…often mistaken for unilateral block Midline anatomical barrier Blombergs dorsomedian connective tissue band Savolaine’s dorsal midline septum (plica mediana dorsalis) Hogan’s distended midline pedicle (epidural fat) Spinal deformity Mmild scolioisis - spread is mainly to concave side of spine Catheter blockage End-hole catheters especially…blockage with tissue/clot/damage Catheter position in posterior compartment of epidural space ? higher incidence if low if low insertion (e.g. L4/5)

Radiology of epidural failure : 

Radiology of epidural failure

Literature : 

Literature

Literature : 

Literature

Literature : 

Literature

Literature : 

Literature

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