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Anaesthesia

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Local Anesthesia & Central Neuraxial Blockade

Question
53 out of 132
 

True about spinal opioids are all except?



A Acts on dorsal horn substantia gelatinosa
B Can cause Itching
C Function of the intestines are not affected
D Can cause respiratory depression

Ans. C

Function of the intestines are not affected
Spinal opioids acts on dorsal horn cells of substantia gelatinosa whereas local anaesthetics on spinal nerve roots.

Intrathecal and epidural opioids have been used following a wide variety of surgical procedures and other acutely painful conditions.

Intrathecal opioids are easy to administer either to provide surgical anaesthesia or as an additional technique when general anaesthesia is given. Many patients will remain comfortable for 24 hours or more after a single injection of intrathecal morphine.

The epidural route has been used even more extensively although the reason for this is not clear. It may be that anaesthetists are more familiar with the epidural route for the delivery of long term analgesia and because of the potential advantages in terms of long term catheter use and freedom from post -spinal puncture headache.

Side effects are common using these routes of delivery. They include nausea, vomiting, itching (which is much more common with morphine than other drugs) and urinary retention and ileus.

Of most concern however, as with any opioid, is the possibility of respiratory depression. Early respiratory depression may be caused by systemic drug absorption.

Late respiratory depression is from rostral (towards the head) spread in the cerebrospinal fluid and the incidence is increased by factors such as dose, age, posture, aqueous solubility of the drug administered, positive pressure ventilation and increased intra-abdominal pressure

It should be assumed that all patients are at risk of this occasional complication and a high level of care and vigilance should be maintained. Many centres recommend that patients receiving analgesia by these methods should be in a high dependency or intensive therapy unit.

Trained personnel should be present at all times to check on the rate and depth of respiration and level of consciousness of the patient at regular intervals, protocols should be available for immediate treatment of complications and medical staff have received appropriate training.

Respiratory rate alone is insufficient to measure the status of respiration. A more global assessment is necessary particularly during the first 24 hours of treatment. Any patient receiving intrathecal or epidural opioids whose level of consciousness drops must be assumed to have respiratory depression until proved otherwise. Where available, the use of supple-mentary oxygen has been recommended.

It is particularly dangerous to prescribe other opioids to patients receiving intrathecal or epidural opioids as this increases the likelihood of clinically significant respiratory depression.

Opioid/local anaesthetic mixtures have been adopted in some centres in an attempt to reduce the frequency and severity of side effects seen with infusions of pure local anaesthetics.

Dilute concentrations of these agents have been combined with opioids and delivered by infusion through an epidural catheter.

These mixtures appear to produce a synergistic effect. Bupivacaine appears to be most suitable for this purpose as dilute solutions produce a very limited motor block.

A mixture of bupivacaine 0.1% and morphine 0.01% infused at 3/4ml/h gives good pain relief and permits the patient to walk without the risk of hypotension.

Local Anesthesia & Central Neuraxial Blockade Flashcard List

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