Clinical stages in Removable partial denture construction

This guide will assist you in clinical stages of removable partial denture construction. You will, benefit by following the approaches suggested in this document.   It must be  understood  however,  that  there  may  be  necessary  modification  required  through  situations which  are  without  your  control.   Such  modification  should  always  be  discussed  with  and  agreed by your clinical teacher.

1^st visit

Preliminary Impressions 

   Selection of stock tray. Modification  of  the  tray  with  impression  compound  or autopolymerising  acrylic  as appropriate.

     Normally a high  viscosity alginate should be used as this will compensate for  the lack of  fit  of  the  stock  tray.   A  thin  layer  of  adhesive  should  be  applied  to  the  tray  before starting to mix the alginate. 

Prescription

It  is  essential  at  this  and  subsequent  stages  to  indicate  precisely  what  is  required  for  the  next  appointment. The prescription on the laboratory card must be clear and comprehensive. If there is

any  possibility  of  confusion  it  is    essential  to  discuss  the  case  personally  with  the  technician  involved.   All  casts  at  this  stage  should  be  poured  in  dental  stone and the type and material of  individual trays indicated.

If the laboratory card is not completed and dated, work will not be available for the next  appointment.

Design

The  design  of  a  partial  denture  should  be  determined  before  master  impressions are recorded.In this respect casts where there are opposing natural teeth in contact, casts must be mounted on

an  articulator  and  surveyed  to  produce  the  desired  design.      In  many  cases  where  there  are  sufficient teeth, casts can be placed in occlusion by hand prior to mounting.In other situations it  will be unnecessary to construct occlusal rims to register the jaw relationship of the patient. 

The sequence therefore is as follows:-

•     Pour preliminary casts.

•     Survey initially to vertical path of insertion.

•     In very few cases a second survey will be necessary to a modified path of insertion.

•     Mount casts on articulator.

•     Produce design for removable partial denture.

The  provisional  design  produced  should  be  discussed  with  your  clinical  teacher  before  the patient's  next  appointment.   At  this  stage  a  decision  should  be  made on  the  need  for  possible  tooth preparation or modification.  This may indicate that the following may be necessary:-

•     Rest  seat  preparation    to  provide  sufficient  space  and  a  horizontal  surface  for  any  support component.

•     Modification of tooth contour, by grinding or the addition of light-cured composite resin, to improve the action of clasp arms or the occlusal relationship.

The  proposed  design  should   be  drawn  on  the  laboratory  card  and also transferred to the study cast which should be retained for reference until the trial stage has been completed.   The design prescription must be clear and comprehensive.

If  surgical,  conservative  or  periodontal    treatment  is  indicated  this  must  be  completed    before recording  master  impressions   This  is  because  the  type  of  denture  required  may  influence  the overall  treatment  plan,  e.g.  rest  seats  incorporated  into  Class  II  restorations,  full  veneer  crowns contoured to provide undercut areas for retention, or tooth extraction as a result of over eruption.

2^nd Visit

Normally the second visit will be for master impressions if the preliminary casts have already been mounted and a design determined.   In cases where the preliminary casts could not be mounted however,  the  second  visit  will  be  devoted  to  recording the jaw relationship of the patient prior to mounting casts on the articulator and developing a design.

Recording Jaw Relationships

If an occlusal stop is present in the mouth you must determine whether the associated intercuspal position is acceptable.   If there is horizontal (antero-posterior or lateral) deviation of the mandible after the initial occlusal contact, it may be necessary to correct the deflective occlusal contact by tooth   modification,   extraction   or   (rarely)   orthodontic   treatment.     If   there   is   loss   of   vertical dimension of   occlusion (OVD) the appropriate increase will have to be determined by adjusting

occlusal rims in relation to the rest  vertical dimension (RVD).

For the purpose of jaw relationships and their registration partially dentate patients can be divided into two categories:-

·         Patients without an occlusal stop to indicate the correct intercuspal position or vertical dimension of occlusion.

·         Patients with occlusal contact in the intercuspal position. 

First Category

In the first category the OVD is determined by establishing   the RVD and modifying the occlusal rims  until  the  OVD  is    some  2-4mm  short  of  the  RVD,  this  distance  indicating  the  amount  of interocclusal clearance.   The horizontal jaw relationship recorded should be the retruded contact position.

• Occlusal rims (and wax trial dentures) should only be placed in the mouth long enough to carry out a particular clinical procedure.    On removal they should be chilled in a bowl of cold water to avoid distortion 
• In  the  mouth  the  fit  and  extension  of  the  rim  should  be  checked  and  modified  if necessary to produce acceptable stability. 
• The  upper  occlusal  rim  should  be  adjusted    so  that  the  occlusal  plane  is  correct  in relation to the remaining upper natural teeth. If there is an anterior saddle the rim must indicate  the  correct  incisal  level  and  degree  of  lip  support.  Removal  of  wax  from  the palatal  aspect  of  this  rim  might  be  necessary  in  order  to  allow  closure  of  the  mandible into the tooth position whilst retaining the incisal level. 
• Any occlusal contact (e.g. with an opposing tooth) should be checked when the patient closes with the upper rim in place.   If the occlusion   shows a premature contact between a  tooth  and  the  opposing  occlusal  rim,  the  rim  should  be  adjusted  accordingly  until  the occlusal contact is re-established.
• The lower rim should then be adjusted to produce even contact. 
• The  lower  rim   should  then  be  modified  so  that  there  is  a  small  space  (about  2-3mm) between the occlusal surface of the rim and the opposing teeth or rim with the mandible in the rest position. 
• The  retruded  contact  position  should  be  recorded  using  wax  or  an  occlusal  registration material  such  as  Bite  Registration  Paste.   Petroleum  jelly  should  be  spread  thinly  over the opposing wax rim to act as a separating medium. 
• The  casts  should  be  placed  in  occlusion  using  the  occlusal  rims  and     checked  to determine that the tooth relationship on the casts is the same as in the mouth.  If there is a  premature  contact  between  the  heels  of  a  cast  and  the  opposing  block  or  cast,  this should be eliminated prior to mounting.Correct if necessary.

Second Category

• The rims should be trimmed  until the natural occlusal contact is observed.  
• The occlusal contact should be checked with the natural teeth when the patient occludes with the upper rim in place.   If the vertical dimension of occlusion has been increased as a  result  of  a  premature  contact  between  a  lower  tooth  and  the  occlusal  rim,  the  rim should be reduced until the occlusal contact is re-established.
• The   lower   rim     should   be   adjusted   until   there   is   an   even   occlusion   at   the   OVD determined by the intercuspal position. 
• Locating notches should be cut in the upper rim, petroleum jelly applied as a separating medium  and  the  intercuspal  position  recorded  with  the  rims  in  place  using    wax  or registration paste. 
• The  casts  are  placed  in  occlusion  using  the  occlusal  rims  and  checked  to  ensure  that there is no premature contact between the heels of a cast and the opposing rim or cast.

Laboratory Prescription

• Shade, material and mould of artificial teeth should be specified.
• If  the  next  stage  is  the  try-in of a metal framework, the design should be drawn on the laboratory  card  and  full  instructions  given.     This  should  be  signed  by  your  clinical teacher.  The study casts should be retained as a guide for the technician.
• If the metal denture is restoring lower free-end saddles consider the need for the altered cast technique. If the technique is to be employed request the addition of acrylic trays to the framework in the saddle areas.
• If the anterior teeth require metal backings, a wax trial denture should be requested for the next stage so that the appearance and position of the teeth can be approved  before the metal framework is constructed.

Master Impressions

·         Wax stops should be placed on the fitting surface of the individual trays before modifying the peripheral extension if necessary.

·         Any over-extension of the tray should be corrected using a blue stone.

·         Any  under-extension   should  be  corrected  with  the  addition  of  self  curing  acrylic  resin (Total).    When  mandibular  free-end  saddle  areas  are  present,  border  moulding  of  the tray in the retro-mylohyoid areas should be undertaken routinely. 

Recording the Impression

·         The tray is dried and a thin layer of adhesive is applied to the whole of the inner surfaces of the tray and to an area extending 3mm beyond the periphery of the tray.

·         A low viscosity alginate is used to record the impression.   In some cases silicone based or rubber based materials may be used.

·         If the impression is satisfactory a cast should be poured in  either dental stone (for acrylic dentures) or improved dental stone (for cobalt chromium chromium dentures) as soon as possible.

·         All individual trays must be retained until treatment is completed. 

Laboratory Prescription

The  laboratory  prescription  should  indicate  the  material  to  be  used  for  cast  pouring. Bearing  in mind  that  the  occlusion  has  already  been  determined  naturally  or  by  occlusal  rims  prior  to establishing a design, the subsequent stage should be either trial dentures or the production of a metal casting.  In the former situation a shade and mould of teeth must be selected.

3^rd visit

In cases where registration was undertaken at the SECOND VISIT, this attendance will be for master impressions.

The Metal Framework

·         The framework must conform to the original design.

·         The framework must fit the master cast. If the fit is unsatisfactory on the cast it will also be unsatisfactory in the mouth.

·         All  components  which  are  designed  to  be  clear  of  the  gingival  margin  area  should  be checked to ensure that the clearance is adequate.

·         In the mouth, these aspects should be checked again,   remembering that the likelihood of  some  instability in free end saddle cases   may be due to spacing beneath the mesh retention.

·         The  occlusion  is  examined  to  ensure  that  there  are  no  premature  contacts  caused  by support units.  This should be done by visual examination, from comments by the patient and with the use of articulating paper or disclosing wax.   Any premature contact should normally be removed at this stage.

Accordingly  the  casts  must  be  remounted  to  this  relationship  and  the  teeth  set  for  asecond trial.

The Trial Denture

(This may be at the third visit or the fourth visit according to clinical requirements).

This is the last stage at which modifications can be made before the wax is replaced by acrylic.  A careful  routine  must  be  followed  to  prevent  any  mistakes  continuing  through  to  the  finished dentures.

The dentures should firstly be examined on the mounted casts in respect of :-

•   Adaptation of dentures on the casts.

•   Occlusion

•   Position of artificial teeth with regard to adjacent natural ones.

•   The arrangement of anterior teeth.

•   Extension and contouring of wax flanges.

In the mouth the trial dentures should be examined in respect of:-

• Adaptation of the dentures.
• Occlusion including the vertical dimension of occlusion.

·       Contouring  of  wax  flanges  with  regard  to  peripheral  extension,  shaping  of  polished surfaces, coverage of gingival margins. Appearance.   Modify  positions  of  teeth  and  incisal  edges  of  anterior  teeth  to  achieve  a pleasing result. Ask  for  patient's  comments on appearance. Show the patient the dentures in the mirror and ensure that they are satisfied.

·         If,  at  this  stage,  the  occlusion  is  incorrect,  modifications  must  be  carried  out  before continuing  with  the  next  stages.    An  increase  in  occlusal  height  may  be  achieved  by adding  pink  wax  to  the  occlusal  surfaces  of  posterior  teeth  on  one  of  the  dentures.  A reduction in occlusal height is achieved by replacing the posterior teeth on one denture with  wax  rims  and  adjusting  these  to  occlude  evenly  at  the  correct  vertical  dimension. Wax or bite registration paste may be used for the final recording.

 If  the  occlusion  has  been  re-recorded this will indicate a change in the jaw relationship. Accordingly  the  casts  must  be  remounted  to  this  relationship  and  the  teeth  set  for  asecond trial.

Laboratory Prescription

Carefully list and describe any modifications you wish the technician to carry out before finishing

the dentures.

To  ensure  that  interference  with  insertion  of  the  finished  denture  will  not  occur  as  a  result  of

inadequately  blocked  out  tooth  undercuts  the  following  instructions  and  procedure  must  be

followed:-

•   Undercuts  are  blocked  out  in  wax  on  the  master  cast,  in  respect  of  vertical  path  of

insertion.

•   The master cast  should be duplicated.

•   The denture should be processed on the duplicate cast.

•   The processed denture should be fitted back on master cast.

Final visit

Denture Insertion

•   Examine  the  dentures  and  check  there  are  no  sharp  edges  or  acrylic  'pearls'  on  the fitting  surface of the saddle areas.

•   Insert  denture  into  the  mouth.    Occasionally  the  denture  cannot  be  seated  because acrylic has been processed into an undercut area on the cast;   this is due to inadequate blocking  out  of  the  undercuts.  If  the  area  of  acrylic  to  be  removed  is  not  immediately apparent, use pressure relief cream.   Always remove the acrylic by approaching with the bur from the fitting surface.  

 The seal between denture and tooth in the non-undercut area should never be touched. 

•   In the mouth, check:-

• Adaptation of components
• Retention and stability
• Occlusion

•   Occlusal  contact  is  checked  by  asking  for  the  patient's  comments,  by  visual  inspection, and by the use of articulating paper.  Articulating paper should be inserted bilaterally and not unilaterally.  In the latter instance, the patient may tend to deviate the mandible to the side on which the paper is placed.

•   Occlusal  adjustment  should  be  continued  until  both  the  patient's  comments  and  visual inspection  confirm  that  even  contact  has  been  achieved  in  the  chosen  jaw  position. Attention should be given to occlusal contacts in lateral and protrusive positions. In many cases  the  dentures  will  be  adjusted  so  that  they  conform  to  the  occlusal  guidance provided by the remaining natural teeth.

Advice to the Patient

•   Insertion and removal of denture.   The patient must be taught the correct way to handle the denture. Vulnerable components must be pointed out.

•   A  printed  sheet  of  instructions  is  provided  for  the  patient.  This  will  mention  in particular aspects  such  as  cleaning/eating/wearing  at  night/pain/need  for  regular  recall  - including recall with the hygienist.

•   It is important to  discuss these points verbally with the patient first of all.  The purpose of the sheet is simply to act as an aide-memoir.

•   Finally you should ensure that  the patient knows who to contact (i.e. you) in the event of problems arising with the denture.   You are responsible for the prosthetic care of the patient  which  does  not  end  with  the  insertion  of  a  denture.   Where problems arise, an appointment MUST be made to see the patient at your next available opportunity.

Review appointment

The patient should be asked for comments on the first week or fortnight of wearing the dentures.

A   history   must   be   taken   of   any   complaint.     Subsequent  examination  must  be  directed  to diagnosing the cause of the complaint before making any adjustments.   Whether or not there are any  problems  reported  by  the  patient,  the  denture-bearing  tissues  must  be  examined  and  the occlusion must be checked.  At times a patient may claim to be perfectly comfortable even though extensive ulceration is present.

Any  inflammation  of  the  denture-bearing  tissues,  which  is  not  related  to  the  peripheral  area,  is most  likely  due  to  occlusal  causes.    Therefore  a  careful  inspection  must  be  made  of  occlusal contact in tooth position and excursive movements, and the necessary adjustments made.   The impression  surface  of  the  denture  must  not  be  'eased'  empirically.    Should  attention  of  the

impression surface be required, a disclosing material such as pressure indicator paste should be used.

A  check  must  be  made  on  the  patient's  oral  and  denture  hygiene  with  the  use  of  disclosing Solution. Steps to reinforce plaque control must taken if appropriate

Regional Anesthesia Manual—upper extremity blocks

Introduction

Peripheral nerve blocks are gaining widespread popularity for perioperative pain management because of their specific advantages over general anesthesia and central neuraxial anesthesia.

Pain relief with PNB avoids side effects such as somnolence, nausea and vomiting, hemodynamic instability and voiding difficulty inherent to general and central neuraxial anesthesia.

Patients who undergo surgery under PNB can bypass phase I recovery room and frequently be discharged expeditiously following ambulatory surgery.

Patients with unstable cardiovascular disease can undergo surgery under PNB without significant hemodynamic changes.

Patients who have abnormalities in hemostasis or infection which contraindicate use of central neuraxial block can be candidates for surgery under PNB.

A substantial savings in operating room turnover time can occur if PNB is done outside the operating room. If the patient has a functioning block preoperatively there is no induction or emergence time. Patients with a PNB can frequently position themselves.

When used as part of a combined general regional technique, PNB facilitates lighter planes of anesthesia, avoiding the use of opioids and allowing a quick emergence and recovery.

In order to carry out a regional block safely and effectively, the anesthesiologist must be proficient in the following:

Anatomy

                Have knowledge of the neural elements to be blocked, their relationship to muscular, vascular and other anatomic structures and their ultimate motor and sensory innervation. Knowledge of the innervation will provide guidance to select the most suitable technique for a particular surgical procedure. The bony, vascular, muscular and fascial relationships will serve as landmarks to guide the needle to the appropriate site, thus improving the success of the block and minimizing side effects and complications.

Pharmacology

                Knowledge of local anesthetic pharmacology will assist in the selection of the most appropriate local anesthetic drug and dosage. The anesthesiologist must also be familiar with the clinical pharmacokinetics i.e. pattern of onset of and recovery of the nerve block. This allows an assessment of the clinical efficacy of the block with respect to operative anesthesia and approximate duration of postoperative analgesia after a particular local anesthetic drug has been injected.

Complications and side effects

                Knowledge of the possible complications and the errors in the technique will help in preventing the complication and also in managing them effectively in case they do occur. Knowledge of the possible side effect which could occur from blockade of the other neural elements in the vicinity such as phrenic nerve, recurrent laryngeal nerve and the sympathetic nerves will help in patient education as well as in assessing the contraindication to the technique.

               

Local anesthetics: Clinical pharmacology, drug selection and toxicity

                To select an appropriate local anesthetic drug for a specific clinical situation, one should be familiar with the clinical pharmacology of the local anesthetic drugs and adjuvants.

                Local anesthetics exert their effect either by inhibiting the excitatory process in the nerve endings or in the nerve fibers. The following sequence of events is generally accepted as the mechanism of action of local anesthetic agents:

• Binding of the local anesthetic moiety to the receptor sites in the nerve membrane.
• Reduction in sodium permeability
• Decrease in the rate of depolarization
• Failure to achieve threshold potential
• Lack of development of propagated action potential
• Conduction blockade

The pharmacological activity of local anesthetic agents is influenced by their chemical structure, lipid solubility, protein binding, pKa.

Chemical Structure

               

                Based on their chemical structure local anesthetics can be grouped into:

• Aminoesters – Procaine, cocaine, tetracaine, choroprocaine. Aminoesters have an ester     linkage between the benzene ring and the intermediate chain.  These are hydrolyzed in the plasma by pseudocholinesterase.  One of the primary metabolites of ester compounds is paraminobenzoic acid.  Paba has known allergic potential.

• Aminoamides – Lidocaine, mepivacaine, bupivacaine, ropivacaine. Aminoamides have an amide link between the benzene ring and intermediate chain.  These are degraded in the liver by microsomal enzymes.  The amide drugs are not metabolized to paraaminobenzoic acid and rarely produce allergic reactions. Multidose vials of amide local anesthetic may contain methylparaben (MPF should always be used for regional anesthesia) which is a paraaminobenzoic acid derivative with allergic potential.

Lipid Solubility

                Lipid solubility is the primary determinant of intrinsic anesthetic potency. Potency increases as a function of lipid solubility until a blood/lipid partition coefficient of 4 is reached. Further increases in lipid solubility do not cause a further increase in the local anesthetic potency. Based on the lipid solubility and potency, local anesthetic drugs can be divided into 3 groups:

Low lipid solubility/potency:  Lipid partition coefficient < 1. These drugs must be administered in high concentrations (2 to 3 %) to achieve effective neural blockade. Local anesthetic drugs in this category include procaine and chloroprocaine.

Intermediate lipid solubility/potency:  Lipid partition coefficient 1-3. These drugs may be in concentrations of 1 to 2%. Local anesthetic drugs in this category include lidocaine, mepivacaine, and prilocaine.

High lipid solubility/potency:  Lipid partition coefficient >4. These drugs are clinically effective at low concentrations <1%. Local anesthetic drugs in this category include tetracaine, bupivacaine, and ropivacaine.

Protein Binding

Addition of larger chemical radicals to the amine or aromatic end of a local anesthetic compound increases its binding to protein, which is a determinant of local anesthetic duration.  Protein binding of commonly used local anesthetics is:

                                Bupivacaine-------------------------95%

                                Tetracaine---------------------------95%

                                Ropivacaine-------------------------94%

                                Mepivacaine------------------------74%

                                Lidocaine----------------------------65%

                                Procaine-------------------------------6%

PKa

Pka is the pH at which ionized and unionized fractions of a substance are present in an equal amount. The onset of local anesthetic effect will be determined by the total amount of unionized fraction of the local anesthetic agent because the unionized fraction primarily diffuses across the nerve membrane. The percentage of local anesthetic, which is present in the unionized form (cation or base) when injected into the tissue at (pH 7.4) is inversely proportional to the pKa of the agent. As the pH of the local anesthetic solution goes down, the unionized fraction will decrease when the pH increases the unionized fraction increases. There is a correlation between the onset of the block and the pKa of local anesthetic drug. The drugs with pKa of 7.6-7.8 ( lidocaine, mepivacaine, prilocaine) have a more rapid onset of action than do bupivacaine and tetracaine which have a pKa of  8.1 and 8.6 respectively. At the body pH  (7.4), 35 % of lidocaine exists in unionized base form and only 5 % of bupivacaine exists in unionized base form.

Adjuvant Drugs

These drugs can reduce the onset time, prolong the duration, increase the density and reduce dosages of the commonly used local anesthetics.

•                 Epinephrine-      Prolongs duration by vasoconstriction and slowed absorption.   Duration can be increased by 30-50%.  Peak plasma concentrations can also be reduced by 50%.  Can also be a marker for intravascular injection—tachycardia.
•                 Clonidine-           Prolongs duration of local anesthetics by synergistic alpha-2 effects.  Lesser or no prolongation with Bupivacaine and Ropicacaine but can prolong Mepivacaine-Lidocaine by 40-400% with 100 micrograms.  Larger doses are not additive and cause more side effects.

Upper Extremity Blocks

The plexus of nerves innervating the upper extremity is contained in a fascial sheath, which is surrounded by reliable anatomic landmarks. This allows an injection of local anesthetic to reliably block the sensory and motor innervation to the upper extremity with two exceptions—

Areas of the upper extremity with cervical plexus innervation. The sensation of the skin overlying the shoulder is supplied by the nerve roots C3 and C4 of the cervical plexus. These nerve roots lie superior to the most cephalad aspect of the brachial plexus. Interscalene blocks done with large volume of local anesthetic (35-40ml) may block these nerve roots as well in the vast majority of cases. The surgical procedures where C3 and C4 blocks are beneficial usually involve the clavicle.

Area of the upper extremity with intercosto-brachial (T2) innervation. The sensory innervation of the axilla and anterior shoulder is T2, which is also derived from outside the brachial plexus. A T2 block is required for shoulder surgery with anterior incisions (anterior stabilization for shoulder dislocation) and surgery involving the elbow and upper arm.

 

Innervation of the upper extremity

For convenience the branches of the brachial plexus which innervate the upper extremity can be divided into supraclavicular (branches from roots and trunks) and infraclavicular branches from the divisions, cords  and nerves.

All the supraclavicular branches are motor with the exception of the suprascapular nerve, which provides sensation to the shoulder joint. Suprascapular branches supply the scalene muscles, serratus anterior via the long thoracic nerve, muscles of the upper back and contribute to the phrenic nerve.

                The infraclavicular branches comprise all of the sensory and motor innervations to the upper extremity and are important to the anesthesiologist both from the point of view of technique (distribution of parasthesia, motor response if nerve stimulator is being used to locate the plexus) and extent of the block and identification of missed nerves.

Anatomic relations of the Brachial plexus

                Knowledge of the anatomic structures, which surround the brachial plexus, will help in the location of the plexus as well as in the prevention of complications.

Perivascular compartment

                This concept has promoted the single injection technique of the brachial plexus block. Clinically, proximal blocks behave as if there were a sheath surrounding the plexus. A single injection technique lends itself to a short onset and high success rate.  However with a more distally placed block like an axillary block, a single injection technique is less reliable because of the individual peripheral nerves begin to diverge. To improve the success of an axillary block several strategies are used to improve proximal spread of local anesthetic- such as injecting high in the axilla, adduction of the arm and application of pressure distal to the injection.

Vascular relationship

                There are no major vessels at the level of the roots except for vertebral vessels, which lie far medially and anterior to the plexus. A long needle directed horizontally in the interscalene space may get into the vertebral artery or vein. The needle can also get into the subarachnoid or epidural space via the intervetebral foramen. The trunks of the plexus also lie in close proximity to the subclavian artery, which separates them from the anterior scalene muscle. . This relationship must be born in mind when doing a subclavian perivascular approach is being used. Another anatomic fact is the significance that the inferior aspect of the trunk of the plexus may be trapped behind and under the artery. In this situation, there is probably a mechanical barrier to the spread of local anesthetic if it is placed high in the interscalene groove. So the most common elements of the brachial plexus missed with an interscalene approach are C8 and T1.

Blocks above the clavicle

Level of the roots – Interscalene brachial plexus block

Trunks – Subclavian perivascular brachial plexus block/ classical supraclavicular brachial plexus block

                  Blocks below the clavicle

Division/Cords – Infraclavicular brachial plexus block

Cords/Terminal nerves – Axillary brachial plexus block

Axillary Approach of the Brachial Plexus

                The axillary block is the most commonly used approach to the brachial plexus since this approach is free of the risk of pneumothorax.

Position:  The patient is placed supine with the arm abducted 90 degrees and flexion of the forearm with external rotation so that the forearm lies parallel to the long axis of the body. Hyperabduction will obliterate the axillary artery pulse in 80% of individuals because the artery is compressed between the head of the humerus and the pectoralis minor muscle.

Needle placement: The arterial pulse should be identified and followed as proximal as possible, ideally to the point where the pulse disappears beneath the pectoralis major. The artery is located between the index and middle fingers of the non-dominant hand. With light digital pressure the artery is fixed against the humeral head high in the axilla. A #22 gauge 1.5 cm B bevel needle is introduced slightly superior to the finger tip and advanced at about a 30 degree angle to the skin, tangential and parallel to the neurovascular bundle until one of the following 3 endpoints are met.

Slow needle placement until a parasthesia is obtained (Success rate 85-90%).

The transarterial approach: The needle is slowly advanced until bright red blood is obtained during continuous advancement. Once blood return is obtained, the needle should be advanced through the wall of the axillary artery until no additional blood can be aspirated. Once it has been verified by the aspiration that the needle tip lies posterior to the arterial wall (just 1-mm), the total anesthetic volume (40-50 ml) is injected in 5-ml increments posterior to the artery. Splitting the local anesthetic volume to deposit posterior and anterior reduces rather than increases the success rate of the block. The success of the block is related to the close proximity of the needle tip to the posterior wall of the artery (clinical sign to ensure this is aspiration of slight blood stained fluid during intermittent aspiration and injection). After approximately 20 ml of local anesthetic injection the needle can be withdrawn back though the artery and advances again through the posterior wall. This reconfirms that the needle tip is in close proximity to the posterior wall of the artery. Appropriately performed, the transarterial approach has nearly 100% success rate.  A sharp needle (not a blunt tipped nerve stimulator needle) should be used for the transarterial technique.

Axillary block using a nerve stimulator – Using an insulated needle, connect the negative lead to the needle. Use low output current (.3-.5ma) at l sec twitch rate. Look for an appropriate motor response in the hand in the distribution of the ulnar, radial, or median nerves. Please note that motor response at the elbow (biceps twitch) indicates that stimulation of the musculocutaneous nerve, which is outside the sheath. The injection at the endpoint will result in the block of the musculocutaneous only.

Epinephrine 1:200,000 (5 mcg/ml) should be used in all perivascular blocks. Direct close attention to the ECG or pulse oximeter pulse tone to effectively identify intravascular injection. After injecting 40-45cc, a small volume of local anesthetic should be injected subcutaneously over the axillary artery to block the branches of the intercostobrachial and medial brachial cutaneous nerve.

Assessing the Success of the Axillary Block

                If the onset of proximal motor block (loss of forearm extension; i.e. inability to point to the ceiling – radial nerve block) occurs within minutes of the injection, you can expect good surgical anesthesia in 20 minutes. Check the sensory distribution of the individual nerves to identify the unblocked nerves.

(Push, Pull, Pinch, Pinch)

 

Interscalene approach to the brachial plexus

This technique for brachial plexus anesthesia is used for surgical procedures of the upper arm and shoulder. This approach is specifically suited for shoulder surgery since it blocks the suprascapular nerve which supplies sensation to the shoulder joint.

Technique:  The key to success is correct identification of the interscalene groove. The patient should be supine and asked to elevate the head, bringing the sternocleidomastoid muscle into prominence. The index and middle fingers are places behind the clavicular head of the sternocleidomastoid muscle and the patient is asked to relax and turn the head and onto the opposite side with the chin in the midclavicular line. Turning the neck too far laterally will make the scalene muscles difficult to palpate. The palpating fingers are moved medially behind the sternocleidomastoid to lie on the anterior scalene muscle. The palpating fingers are then rolled laterally until the groove between the anterior and middle scalene muscles is identified. Please note that the groove is wider distally, so keep the distal palpating finger in the groove just above the clavicle. Keep the middle finger firmly in the distal part of the groove and the palpating index finger at the level of C6 anterior to the external jugular vein. If there is difficulty in identifying the anterior scalene muscle, ask the patient to maximally inhale. This makes the anterior scalene muscle more prominent and its palpation easier. The needle is inserted in the into the interscalene groove at the level of C6 which can be identified by drawing a line from the crycoid cartilage to the interscalene groove. An additional landmark is the external jugular vein when visible crosses the interscalene groove at the level of C6. With both the index and middle fingers in the groove, a #22 gauge B-bevel needle is inserted at the level of C6 perpendicular to all planes mostly mesiad, but slightly caudad and posterior. . The appropriate needle placement should be 60 degrees from the sagittal plane. The needle is advanced until a parasthesia is elicited in the shoulder or there is a motor evoked response in the forearm at <0.5 mA or the transverse process is contacted. If bone is contacted then the needle tip should be withdrawn and redirected caudad until the appropriate motor response or parasthesia is obtained.

        Please note that when a large volume of local anesthetic (35-40 ml) is injected especially in a thin patient, a visible swelling will appear above the clavicle defining the inferior portion of the supraclavicular brachial plexus. Due to the distance of the C8 and T1 nerve roots from the sight of injection, the ulnar nerve is frequently missed with the interscalene approach. Also, the intercostobrachial and brachial cutaneous nerves, which supply the axilla and medial aspect of the upper arm, will be missed.

Assessing the success of the Interscalene Block

                Motor block precedes sensory block. Innervation to the shoulder flexors are the first blocked. If the patient cannot lift the shoulder of the table within 2-3 minutes of local anesthesia (even with 0.5% Bupivacaine) expect good surgical anesthesia for shoulder surgery within 20 minutes.

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Infraclavicular brachial plexus block

Anatomy:  The boundaries of the infraclavicular fossa are pectoralis major and minor muscles anteriorly, ribs medially, clavicle and coracoid process superiorly and humerus laterally. The plexus is approached in close proximity to the coracoid process.

Technique:  the patient is supine, the ipsilateral arm is abducted to a 90-degree angle and the patient’s head is turned to the opposite side.

                

The following landmarks are identified and marked –

Medial head of the clavicle

Acromion process – The most prominent structure on the superior aspect of the shoulder. Axillary artery – at the highest point in the axilla place a mark on the pectoralis major, Doppler can be used to mark the axillary artery along the infraclavicular area

Mark the midpoint of the clavicle between the Acromion and the sternal head of the clavicle.

Needle entry site is – 2.5 cm below the midpoint of the clavicle along the axillary artery.

The anesthesiologist stands at the patient’s side opposite to the one being blocked. The needle entry site is infiltrated with local anesthesia. A 10 cm insulated block needle is inserted at a 60 degree angle to the sagittal plane directed away from the rib cage towards the axilla.   Pectoralis major contractions are observed at a depth of 1 – 3 cm. The plexus lies 3 – 7 cm deep. Since musculocutaneous and axillary nerves are outside the sheath, motor response of those two nerves (i.e. deltoid and biceps contractions) should not be accepted. If these two motor responses are obtained redirect the needle injection toward the apex of the axilla. The ideal motor evoked response is hand movement at (.3-.4)mA. Once ideal motor evoked response is obtained inject 40 – 50 ml of local anesthesia incrementally. If no motor response is encountered, progressive needle redirection to 80 degrees will yield an appropriate response.

Suprascapular Nerve Block

                The suprascapular nerve provides sensory innervation to 70% of the shoulder joint. The suprascapular nerve supplies Superior and posteriosuperior regions of the shoulder joint capsule and variable portions of the overlying skin. Anteriorly and inferiorly the skin and joint capsule are supplied by the axillary nerve, upper and lower subscapular nerves. Suprascapular nerve blocks can be used for postop analgesia but not for operative anesthesia.

Technique:  The patient should sit up and lean forward with the arms hanging loosely at the side. Draw a line along the length of the spine of the scapula. Palpate the acromion process at the edge of the spine of the scapula. At the point where the thicker acromion process fuses with the thinner spine of the scapula is marked. The skin is prepped. A 25 or 27 gauge needle is used to anesthetize the needle entry site at the marked point. An insulated block needle – (Stimuplex) 22g 2 inch (<70 kg) or 4 inch (>70 kg) is introduced through the marked point. The needle should contact bone at a depth of one inch. The needle is walked superiorly and medially until it slides off into the suprascapular notch. The needle should be advanced no more than 1 cm from the suprascapular notch because of the risk of pneumothorax. Stimulation of the suprascapular nerve causes contraction of the supraspinous and infraspinous muscles with abduction and external rotation of the arm. With the appropriate motor evoked response, inject 10 – 15 ml of local anesthesia.

Intravenous Regional Anesthesia  (IVRA, Bier Block)

IVRA can be used for short surgical procedures on the extremities. IVRA involves an IV injection of local anesthetic mixture into an exsanguinated extremity that is vascularly isolated by a tourniquet. It is technically simple. High reliability (97-100%), ease of administration and safety are major advantages of this technique. IVRA is suitable for surgical procedures below the elbow in the upper extremity and below the knee in the lower extremity of less than 1-hour duration. The only drug specifically approved by the FDA for IVRA is Lidocaine 0.5% preservative-free. For upper extremity blocks, a volume of 40-50 ml is used and for the lower extremity blocks, a concentration of 0.25% with a volume of 100-125 ml is used. The purpose of using a high volume is to assure an adequate distribution of local anesthetic in the entire venous system of the exsanguinated extremity.

Technique of IVRA

Start an IV infusion in the uninvolved extremity for drug administration and hydration.

Apply the appropriate monitors; give supplemental oxygen and adequate sedation to make the patient comfortable.  Check baseline SBP so that the appropriate tourniquet inflation pressure can be used (100 mm Hg higher than SBP).

Place a 20 or 22 G angiocath near the surgical site preferably in the dorsum of the hand. Do not place the angiocath near the site of the surgical incision.

Apply Webril gauze to the upper arm from armpit to elbow. This protects the skin and the ulnar nerve in the cubital tunnel.

Apply two separate tourniquets of the Webril. Place a 24-cm tourniquet proximally and 18-cm tourniquet distally on the upper arm. In obese patients with conical shaped upper arm, use a single large 30-cm tourniquet.

Elevate the extremity and exsanguinate with an Esmarch bandage from hand to distal tourniquet. While wrapping the arm be careful not to wrap the area over the angiocath. Compression of the angiocath hub beneath the Esmarch bandage can cause ulceration of the underlying skin.

Inflate the distal tourniquet to 250-mm Hg and then inflate the proximal tourniquet. Once the proximal tourniquet is inflated, deflate the distal tourniquet. Ensure that the inflation pressure is at least 100 mm Hg above the systolic pressure. In a hypertensive patient  > 250 mm Hg may be needed. This is very important for maintaining a bloodless surgical field.

Remove the Esmarch bandage and check for presence of a radial pulse.

Place a tourniquet proximal to the angiocath on the forearm and inject the local anesthetic solution into the angiocath slowly.

Remove the angiocath and compress site for 2 – 3 minutes.

Tourniquet Pain

                Tourniquet pain manifests itself in many forms: e.g. patient getting restless, vague complaints of aches and pains and pressure in the arm, tourniquet site, or in the shoulder. This may occur 20-30 minutes after the inflation of the proximal tourniquet. If you suspect that the patient is having tourniquet pain, inflate the distal cuff then deflate the proximal cuff. Always inform the surgeons before switching the tourniquets as they may be in the middle of a crucial maneuver and any tourniquet mishap may complicate their procedure. Supplemental analgesics and sedatives are also used to prevent and manage tourniquet pain.