Ring Blocks

A digital ring block (aka digital block) is the technique of blocking the nerves of the digits to achieve anesthesia of the finger(s). It is a useful procedure to facilitate minor surgery of the finger.

The nerves to be blocked are the palmar and dorsal digital nerves.

The two palmar nerves supply the anterior aspect of the fingers and are the terminal branches of the median nerve (lateral 3 1/2 fingers) and ulnar nerve (little finger and 1/2 ring finger).

The two dorsal nerves supply the posterior aspect of the fingers and arise from the radial nerve (lateral 2 1/2 to 3 1/2 fingers) and ulna nerve (medial 1 1/2 to 2 1/2 fingers).

If seen in cross section the nerves are at two, five, seven and ten o'clock positions

The procedure:

• The patient's hand and fingers are extended and fingers abducted from each other.
  
• The head of the metacarpal bone and base of the proximal phalanx is felt.
  
• The skin is cleaned.
• The needle is introduced between the fingers at the point of the interdigital fold and a skin wheal is raised. This is at the level of the head of the metacarpal bone.

• The needle is advanced along the axis of the fingers until the palmar aponeurosis is
  reached which is felt as a resistance.
  
• Before injection of local anaesthetic the needle must be aspirated to prevent intra-
  vascular injection.
  
• 1 to 2 mls of local anaesthetic is introduced as the needle is withdrawn.
  
• Subcutaneous injection around the base of the finger is then done through the same skin
  wheal to block the palmar and dorsal digital nerves.
• The procedure is repeated on the opposite side of the finger.
  
• Massaging the finger after infiltration facilitates spread and increases absorption of the
  local anaesthetic.
  

References:

• "Digital Ring Block", Dr. Mary Daniels, Department of Anaesthesia, The Chinese University of Hong Kong, http://sunzi1.lib.hku.hk/hkjo/view/23/2300620.pdf
• "Digital Nerve Block", Dr A Hazdic, New York School of Regional Anaesthesia, http://www.nysora.com/techniques/digital_block/
  

Marcain

Composition

Bupivacaine hydrochloride +/- Adrenaline

Actions

Bupivacaine is classed as a membrane stabilising agent and is a local anaesthetic of the amide type. Like all amines it causes a reversible blockade of impulse propagation along nerve fibres by preventing the inward movement of sodium ions through the nerve membrane.

Pharmacokinetics

Bupivacaine is a long acting, amide type local anaesthetic chemically related to lignocaine and mepivacaine. It is approximately four times as potent as lignocaine.

References:

• MIMS
  

Neostigmine methylsulfate

Actions

• An anticholinesterase agent which reversibly inhibits the hydrolysis of acetylcholine by competing with acetylcholine for attachment to acetylcholinesterase. As a result, acetylcholine accumulates at cholinergic synapses and its effects are prolonged and exaggerated.
  
• Produces a generalised cholinergic response, including miosis, increased tonus of intestinal and skeletal musculature, constriction of bronchi and ureters, bradycardia and stimulation of salivary and sweat glands.
  
• Used mainly for its direct cholinomimetic effect on skeletal muscle and to a lesser extent to increase the activity of smooth muscle.
• Because of its quaternary ammonium structure, neostigmine in moderate doses, does not cross the BBB to produce CNS effects. Extremely high doses, however, produce CNS stimulation followed by CNS depression.

Indications

• Reversal of the effects of neuromuscular blocking agents (e.g. tubocurarine, pancuronium).
  
• Prophylaxis and treatment of postoperative intestinal atony and urinary retention.
  
• Treatment of myasthenia gravis during acute exacerbations, when the condition is severe, or in neonates.

Pharmacokinetics

• For IV administration the elimination half-life is 47-60 minutes.
• For IM administration the elimination half-life is 50-91 minutes.
  
• Approximately 80% of a single IM dose of neostigmine is excreted in the urine in 24 hours, about 50% as unchanged drug and the remainder as metabolites.
  
• The major site of uptake is in the liver. It is metabolised partly by the hydrolysis of the ester linkage and partly by microsomal enzymes in the liver.

Common postoperative problems

Postoperative complications are common, despite good pre-op assessment, surgical technique and perioperative management.

Complications can be minimised by regular and close postoperative patient observation. Managing complications effectively requires quick diagnosis and treatment before the complication gets out of hand.

Postoperative pain

• Pain from surgical wounds should subside over the first few days, and should be controlled by planned analgesia. Some types of wounds (e.g. vertical abdominal incisions) are more painful than others.
• Postoperative pain can be reduced by:
  
  • Preoperative counselling - letting the patient know in advance what to expect after the operation in terms of wounds, IV lines, catheters, extent of pain, plans for pain relief and degree of mobility.
    
  • Peroperative measures - preemptive analgesia to ensure pain does not become established after operation e.g. long acting analgesics, local anaesthetic infiltration into the sound edges, regional nerve blocks, morphine epidurals etc.
    
  • Postoperative analgesia - better to prevent pain than to react to established pain!
    
  
  
• Patients vary in their tolerance for pain and need for analgesics. Anxiety, exhaustion and sleep deprivation all reduce pain tolerance.
  
• If the pain is not controlled by what seems to be a normal dose and frequency of analgesia, complications should be suspected.
  
  • Review dose in relation to expected severity of pain and the weight of the patient.
    
  • Consider local postoperative complications such as haematoma -> wound pain, bleeding into fascial compartment -> compartment syndrome, wound infection -> pain increasing after 48 hours.
    
  
  

Pyrexia

• Infection is not the only cause of postoperative pyrexia, however it should always be considered and investigated as a cause.
• Common postoperative infections include superficial and deep wound infections, chest infections (pneumonia), UTIs and IV cannula site infections.
• Infection is not likely to be a cause in fever developing within 2 hours of surgery - it normally takes longer to develop.
  
• Common non-infective causes of pyrexia include transfusion reactions, drug reactions, wound haematomas, DVT and pulmonary emboli.

Tachycardia

Tachycardia can be benign or malignant.
Benign causes of postoperative tachycardia:

• pain
• anxiety

Malignant causes of postoperative tachycardia:

• infection
• circulatory disturbances
• thyrotoxicosis
• Mild tachycardia can be a sign of incipient hypovolaemic shock resulting from haemorrgahe or dehgydration.
• Cardiac failure.
• AF or flutter.
• Anastomotic leakage - after bowel surgery.