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High Thoracic Epidural for Cardiac and Thoracic Surgery
Guidelines (HTEA)
The epidural is used throughout the procedure and will be fully working upon return to the ward. In general, a lighter general anaesthetic is required during surgery and so the patients may awaken rapidly.
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Aim
To provide complete analgesia. Cardiac surgery – 2 days. Thoracic surgery – 3 days.
The prescription
Ropivacaine 0.2% with Morphine 4mg in a 200 ml polybag. Please ensure that you have enough available to last the night as a 200-ml bag may not last the night.
Epidural block adjustment
The typical block is from T1-7. The amount of anaesthetic ranges considerably between patients but as a general guide, elderly females need 3-7 ml/hr, elderly men need 5-8ml/hr and younger or large men require 7-10 ml/hr. The prescription will be 3-10 ml/hr for the morphine mix and 5-15 ml/hr with the Fentanyl mix, to allow for adequate adjustment. If higher rates are required then there may be a leak in the catheter system or the epidural is not working properly.
It is often difficult to differentiate a block when using ice as the sensory discrimination to cold with low dose Ropivacaine is often poor. Also, do not forget that the area above the clavicle may be innervated from cervical segments. In general, I find the “ice” test to be very unreliable above T2, perhaps because the neck and shoulder is a lower sensory area. Reliable signs for the upper end of the block include tingling of the fingers and hand weakness. The nature of the block however, allows for simplified adjustment.
If the block is too high, the fingers will tingle or the hand will become weak. If the block is inadequate then the patient will be in pain.
ADJUSTMENTS
- If hand is numb - turn infusion down by 2 ml/hr
- If mild pain and hands normal – increase infusion by 2 ml/hr
- If marked pain – will require bolus of 5-10 ml and rate increased by 2 ml/hr
- If still in marked pain despite bolus then epidural is not working – change to IV
If there is no pain and the hands are normal (accept tingling of the little finger) then you have got it just right!
Reportable observations
- Severe pain
- Extensive block where the entire arm is weak
- Respiratory depression (respiratory rate < 8 /min)
- Lower limb weakness
THE DO NOT’S
- Do not try to “wean” the epidural - it will only produce pain
- Do not turn down the epidural overnight - unless there is good reason to do so
- Do not turn down the epidural to treat hypotension - this will produce pain. Most episodes of hypotension in the patients are in the setting of the high cardiac output/ low SVR syndrome and responds to filling and/or Noradrenaline infusion. Of course, you may turn the infusion down if block is unnecessarily high
Hypotension and a High Thoracic Epidural
It is a very common misconception that a high thoracic epidural sited at T1-2 level, is the predominant cause of hypotension post cardiac surgery. This is not the case. The reason is that at this level only about half or two thirds of the sympathetic output (T1- 5/7) will be affected, leaving the lower sympathetic supply
(T7 – 10) relatively intact (approximately). Thus it is a contributor to systemic vasodilation, but the predominant cause is the systemic inflammatory response (SIRS) that results from cardiopulmonary bypass and from the surgery itself. This inflammatory response typically reaches a peak effect 6 – 8 hours postoperative, resulting in the greatest degree of vasodilation occurring during this time. [However, a classically sited mid thoracic epidural at T6 will certainly block all sympathetic output and definitely cause severe vasodilation].
One has to understand that the sole purpose of using an Epidural is to achieve pain relief, and so the dose should be adjusted only to optimise pain management. The epidural should never be adjusted to manage blood pressure. If the blood pressure is too low, vasoconstictors or inotropes should be used; and too high, vasodilators should be used.
Urinary catheters
Since the lower sympathetic supply to the bladder is not affected by a high thoracic epidural, it is not entirely necessary to keep a urinary catheter in situ. In practice most cardiac surgery patients are in ICU whilst the epidural is in place and so the urinary catheter remains. For younger patients and for thoracic patients (3 day epidural) removing the urinary catheter should be considered.
Serious complications
The most serious complication of epidural use is paraplegia from spinal compression, either from haematoma or infection. This is estimated to occur in 1: 20 000 cases. Although extremely rare, you should be aware of how it may present. Neurological signs may affect both sides and the legs will be affected. Paralysis or weakness of the legs is the sign to look out for, because the normally functioning T2/3 epidural does not affect the legs. If detected, it must be reported immediately, as the time from onset of signs to permanent damage is hours only! Other warning signs include severe tenderness over the insertion site or marked redness or pus discharge from the insertion site. Please check the insertion site through the hole cut in the dressing at least daily. If the catheter becomes disconnected from the bacterial filter it is not to be reconnected. The epidural is to be ceased and analgesia converted to IV opiate. Respiratory depression is possible because of fentanyl. This is treated by naloxone 0.1-0.4 mg IV or IM as required.
Mobilisation
The epidurals do not produce leg weakness and walking is allowed with appropriate assistance. It is prudent to allow the patient to sit before they first walk to ensure that postural hypotension does not occur.
Other considerations
IV access is to be maintained whilst the epidural is in situ.
In the event of haemodynamic catastrophe such as arrest, or shock or respiratory arrest, turn off the epidural. It can always be restarted at a later date, but the patient may benefit from restored sympathetic tone.
HTEA Catheter removal
Catheters are to remain in for 2-3 days postoperatively. There must be good reason to leave the catheter in beyond 72 hours!
Heparin
Patients may have the usual S/C heparin whilst the epidural is used.
Withhold the dose of heparin prior to epidural removal.
Heparin may be recommenced 2 hrs following catheter removal.
Warfarin
Warfarin may be commenced the evening prior to catheter removal, but the catheter must be removed by 0800 the morning after the first dose of Warfarin.
Contact Numbers
A/Prof Colin Royse 0408 467548 (mobile) or 9432 7000 (for home) or Pain Service
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