PLANNING ANAESTHESIA
Final Objective: On completion of this module you will be able to formulate an appropriate anaesthesia for a given procedure, to organise the facilities available to you, and to plan for both expected and unexpected operative events.
Enabling Objective: To achieve this goal, you should understand:
Reference Reading:
PLANNING ANAESTHESIA OR SEDATION
There are many factors to consider when planning anaesthesia. Not all factors are directly related to the patient, but all factors relate to the safety of the patient. Our goals, as anaesthetists, should include:
1. Patient Factors.
Understanding the medical and physiological needs of our patients, so as to provide the best perioperative care.
2. Surgical Factors.
Understanding the requirements of the surgery and the surgeon, the anaesthetic requirements for safe conduct of surgery, and the subsequent physiological impact of surgery.
3. Environmental Factors
Assessing the environment in which we will be operating, so that we will have adequate equipment, supplies and staff, appropriately trained assistance, and a safe environment in which our patient can be managed for surgery, and discharged for continuing post-operative care.
4. Other Factors.
Anticipate problems that may arise during and after surgery, to consider possible preventive measures, to recognize signs that indicate the onset of problems, and to plan for solutions to those problems (plan A, plan B, etc)
Anaesthesia planning relies as much on communication as on preparation. Communication with all staff involved in the surgical procedure will enhance the experience for all the participants. Discussion with the surgeon will elucidate the surgical needs for anaesthesia, and may indicate the relative suitability of local, regional or general anaesthesia. Discussion with the patient pre-operatively will elucidate medical, physiological and psychological factors that may indicate the suitability or otherwise of various anaesthetic techniques and agents. Consideration should be given to general aspects of intra-operative care (positioning during the procedure, equipment requirements), allowing for a smoother flow of patient and staff movements, and to facilitate the surgical process. Discussion with nursing staff in relation to provision of appropriate nursing care, analgesia, fluids, haemodynamic monitoring or support, will enhance post-operative management of the patient.
The anaesthesia plan starts with a patient assessment and consideration of surgical requirements, and contains choices of anaesthetic agents and techniques, monitors, patient position, steps for induction and maintenance of anaesthesia, awakening from anaesthesia, and immediate post anaesthetic care.
CHOOSING & PLANNING AN ANAESTHETIC TECHNIQUE
However strong the indications may seem for using a particular technique,especially in an emergency, the best anaesthetic technique will be one with,which you are most experienced and confident.
An anaesthetic technique is selected based on:
1. Pre-operative examination and clinical evaluation
2. The type and extent of the surgical procedure
3. The ability to perform various anaesthetic techniques, based on experience and the availability of equipment and drugs.
Pre-operative examination and clinical evaluation
Routine history taking and examination of the patient will provide much information on the suitability of an anaesthetic technique for that particular patient. Important points in the preoperative interview are:
· Medical condition of the patient.
· Emergency or elective procedure
· Adequate fasting or risk of airway soiling
· Previous anaesthetic experience or problems related to anaesthesia
· Patient preference
Note that not all factors are of equal importance, but all should be considered, especially when the choice of anaesthetic technique is not obvious.
The type and extent of the surgical procedure
The type of surgical procedure may mandate the type of anaesthesia required. Many limb and superficial procedures are highly amenable to local or regional anaesthetic techniques. More invasive surgery, such as intra-abdominal or intra-thoracic procedures, requires the use of muscle relaxants to facilitate the surgery, and therefore require the use of general anaesthesia. Similarly, if the procedure planned is to be extensive, of long duration, or necessitates positioning of the patient that may be uncomfortable for the duration of the procedure, general anaesthesia may be the appropriate choice.
Major head and neck surgery
Upper abdominal or intra-abdominal
Intrathoracic
Intracranial & neurosurgery
Lower abdominal
Lower abdominal – extra-peritoneal
Groin, perineum
Lower limbs
Upper limbs
ANAESTHETIC TECHNIQUES
Local Anaesthesia (LA)
Highly suitable for superficial and peripheral operations, local anaesthesia is an excellent choice for skin and soft-tissue surgery of limited size, depth and duration.
Generally tolerated very well, but problems may arise with:
· Injection into areas of “tight” tissues
· Positioning of patient and duration of surgery (patient comfort)
· Use of tourniquets
· Toxicity of local anaesthetics and/or adjuvants (adrenaline, etc)
Regional Anaesthesia (RA)
Plexus Techniques
· Arm blocks via brachial plexus blockade
· Leg blocks via femoral and/or sciatic nerve blockade
Neuraxial Techniques
· Spinal anesthesia
· Epidural anaesthesia
Intravenous technique
· Bier’s block
Regional anaesthesia via neuraxial or plexus blockade has advantages of providing both analgesia as well as sympathetic nerve blockade, which may have a place in improving blood supply to the operative area, facilitating microvascular re-anastomotic techniques, and potentially reducing the incidence of postoperative chronic pain conditions.
Regional anaesthesia is often performed as a “single-shot” technique, using specific nerve block needles (either short-bevel needles to avoid cutting nerve fibres, or Tuohey-type needles. Insulated needles attached to a nerve stimulator are useful in identifying nerves for blockade) or catheters may be introduced to prolong the block, and provide continued analgesia. This is most commonly done with an epidural block to provide analgesia for women in labour.
Regional anaesthesia techniques may be contraindicated when patients have an abnormal clotting profile, or are treated with anticoagulant or anti-platelet agents. This is especially applicable to the neuraxial techniques, where the consequences of bleeding and haematoma formation in the confined space of the neural canal can result in permanent neurological injury e.g. paraplegia. Other contraindications include generalized sepsis, localised sepsis overlying the point of insertion, inability of the patient to co-operate or keep still and patient refusal.
Intravenous regional anaesthesia is an easy technique that requires minimal extra equipment. The importance of understanding the pharmacology of the local anaesthetic agent used intravenously cannot be overstated. The use of long-acting agents such as bupivacaine or ropivacaine is contraindicated because of the potential adverse effects of cardiotoxicity. Short-acting agents that are metabolized by plasma esterases are ideal. Double-cuff tourniquets are preferable because of the additional safety that is conferred. To reduce the effects of toxicity when the cuff is released the minimal cuff inflation times must be observed, ensuring that local anaesthetic agent metabolism and tissue binding is complete. Further caution must be exercised if performing a lower limb block, due to the amount of local anaesthetic agent that needs to be used.
General Anaesthesia (GA)
General anaesthesia is defined as a state characterized by unconsciousness, analgesia, muscle relaxation and depressed reflexes. It is a relatively simple task to achieve these conditions by administration of drugs with the necessary properties. The challenge is to produce the state of anaesthesia while preserving or improving patient health.
Thus, management of general anaesthesia consists of two separate but interrelated goals:
1. Reversible depression of nervous system functions
2. Maintenance, improvement or minimal disruption of organ function, in spite of pre-existing disease, surgical trauma, and effects of anaesthetic drugs and procedures.
The science, art, and craft of anaesthesia consist of understanding and achieving specific goals to accomplish the desired effects while minimizing the effects of the surgical stimulation and other functional abnormalities through the titration of drugs and ventilation, the management of fluids, the observation and protection of the patient’s body and the manipulation of temperature.
Of vital importance to our conduct of general anaesthesia is the provision and maintenance of a suitable airway, and the ability to provide for adequate gas exchange for the anaesthetized patient. Where a general anaesthetic technique is required, there are surgical and patient factors that influence the choice of airway and ventilation modes.
Our choices of airway management will include:
Ventilation
· Spontaneous (in the absence of a muscle relaxant)
· Intermittent Positive Pressure (when the patient is paralysed by muscle relaxants, or obtunded by other agents, such as opiates)
Airway
· Face mask ventilation
· Nasopharyngeal or Oropharyngeal airway – Guedel, etc
· Supraglottic airway device – LMA, ProSeal LMA, Cobra
· Endotracheal Tube (ETT)
· Subglottic tracheal device – tracheostomy, cricothyrotomy
Indicators for specific uses of ventilation and airway devices are as varied as the potential surgical procedures and patient co-morbidities. There are some broad indications to be considered.
Surgical Indications for ventilation via ETT:
Neurosurgery
· Muscle relaxation is required for most intracranial procedures
o absence of patient movement is paramount
o controlled ventilation allows CO2 manipulation, adding control to cerebral perfusion pressures and intracranial pressures
Intra-abdominal Procedures
· Muscle relaxation required to gain optimum surgical access
Intra-abdominal laparoscopic procedures
· Muscle relaxation required to allow adequate pneumoperitoneum
· Increased intra-abdominal pressure will reduce diaphragmatic excursion & ventilation, and is best managed with IPPV
· Pneumoperitoneum with CO2 will result in CO2 absorption & increased ventilatory requirements
Anaesthetic indications for ventilation via ETT
Airway protection
· Non-fasted emergency patient
· Gastro-intestinal obstruction or haemorrhage
· Acute abdomen
· Treatment with opiates or drugs that will cause gastric stasis, increasing risk of reflux & aspiration
· Hiatus hernia or symptomatic reflux
· Pregnancy > 14 weeks gestation, through to day 3 postpartum
· Upper airway haemorrhage
Facilitation of ventilation
· Restrictive lung disease
· Muscle dystrophy or weakness
· Prolonged operation or anaesthesia
o Prevention of hypoventilation and alveolar collapse
Respiratory correction of acid/base balance
Inability to access airway during procedure
· Prone position may prevent airway manipulation
· Sitting position may render head inaccessible beneath drapes or behind a support frame
· Patient position may be remote from anaesthetist
Choice of Airway Devices
Intubation with an endotracheal tube remains the gold standard for providing intermittent positive pressure ventilation and airway protection. The presence of an inflatable cuff allows isolation of the trachea from gastro-intestinal tract, protecting the airway from soiling, and giving the ability to provide positive pressure to the airways to achieve adequate ventilation.
Note that the introduction of an endotracheal tube is facilitated by a muscle relaxant, which also facilitates continuation of IPPV during a procedure. Not all cases require paralysis with a muscle relaxant, and in some cases (myasthenia gravis, muscular dystrophies) use of muscle relaxants is relatively contra-indicated. Pre-operative assessment will indicate those who require variations in technique. Useful alternatives such as potent opioids in higher doses (e.g. alfentanil) must be balanced against the possibility of cardiovascular depression and respiratory depression, leading to prolonged ventilation.
For surgical procedures that do not require paralysis for surgical or anaesthetic reasons, the choice of airway technique becomes much broader. Bag and mask ventilation may be ideal for short procedures, and may help avoid airway instrumentation. The use of an oral or nasal pharyngeal device will facilitate ventilation in some people. Supraglottic airway devices (e.g. LMA) generally provide a good airway seal, enable direct attachment of a ventilation circuit to the device, effectively isolate anaesthetic gases to the patient, and allow the anaesthetist to use their hands for other tasks. Intermittent positive pressure ventilation can be applied with all these techniques, but with varying degrees of safety and success. Always remember that a supraglottic airway is not isolated, that gastric insufflation can readily occur, and that reflux of gastric contents is possible.
Where a muscle relaxant is not to be used, the choice can be made to ventilate the patient (Intermittent Positive Pressure Ventilation – IPPV), or allow the patient to breathe (Spontaneous Ventilation – SV). Ventilating the patient will be necessary where respiratory drive has been obtunded by opiates, benzodiazepines or other depressant agents. This may be avoided by careful titration of drugs. A spontaneously ventilating patient may be allowed to breathe on either an endotracheal tube, a supraglottic airway or other airway device. An airway device will facilitate ventilation by improving the patency of the airway, avoiding obstruction by the tongue and other pharyngeal structures. However, the presence of an airway device will narrow the airway, increasing resistance to gas flow, and increasing the work of breathing. In combination with general anaesthesia, hypoventilation and hypercapnoea is commonly seen. This state is generally well tolerated in most patients for limited periods, but may be contraindicated in those with pre-existing respiratory disease (e.g. obstructive airways disease) or where surgery may be prolonged. Supraglottic airways generally provide a larger diameter airway when compared to endotracheal tubes, and are more suitable for the spontaneously breathing patient. Supraglottic tubes do not provide lung isolation or protection from contamination.
PAIN MANAGEMENT
Analgesia is an integral part of anaesthesia. Patient assessment and consideration of the surgical procedure will determine the analgesic requirements of the patient. Choices of analgesia can be varied, as are the methods for delivering that analgesia. Analgesia may range from the simple (paracetamol – simple to deliver, easy to manage) to the complex (epidural analgesia – requiring equipment and training for insertion and continued management). Pre-operative planning will allow assessment of the analgesic techniques available, the availability of equipment and staff to maintain analgesic regimens, and to discuss the appropriateness of possible regimens with all those involved – patient, surgeon, theatre staff and ward nurses. Where understanding and agreement is reached, better analgesia will result, improving surgical outcomes and patient satisfaction.
Intraoperative pain management may be achieved with:
Local anaesthesia
Local infiltration
Field blocks
Intra-articular
Regional anaesthesia techniques
Single shot techniques
Intermittent or continuous infusion via catheter
Parenteral analgesics
Opiates
Opiate-like agents (Tramadol, Ketamine)
Non-steroidal anti-inflammatories (NSAIDs)
Simple techniques for pain management, such as the use of parenteral opiates, are the backbone of many anaesthetic techniques. Planning for the appropriate use of parenteral agents in theatre involves an assessment of the patient, to avoid co-morbidities that may be impacted by or contra-indicate the use of certain parenteral agents.
Appropriate plans must be considered for the progression or discontinuation of analgesia. An analgesic plan will provide a framework in which staff can assess and monitor the patient and their analgesic requirements. Where the patient is not following that path, or analgesic requirements remain high or increased, thought must be given to surgical review of the patient. A plan can then be seen as a tool to initiate a response to the patient’s clinical condition.
INTRAOPERATIVE PLANNING ISSUES
Planning anaesthesia requires that many aspects of intra-operative care of the patient be considered prior to the commencement of the surgical procedure, to ensure the availability and delivery of appropriate and timely care to the patient. Of the many aspects of anaesthesia and surgery that should be considered, there are a few that should be given some attention.
Temperature
· Planning to avoid hypothermia
o Maintain patient clothing, coverage, etc, prior to theatre.
o Use of warmed fluids, warm blankets, active warming devices (forced air warmer, fluid warmers)
Fluids
· Consider replacement fluids to cover fasting and maintenance.
· Immediate resuscitation may also be required
· Use of crystalloids and/or colloids can often be planned
Blood
· There should be appropriate availability of safe blood for procedures where blood loss is expected.
· Consideration should be given to the immediate availability of O -ve type blood in obstetric units
· Consider the storage conditions of blood prior to use (the availability of controlled refrigeration), and the ability to warm blood during transfusion (to mitigate hypothermia)
Intravenous Access
· 16G or 18G cannulas are suitable for resuscitation, and procedures such as laparoscopy and laparotomy.
· Consider 2 cannulas for operations where blood loss may be significant.
· Smaller gauge cannulas (20 or 22) may be suitable for smaller procedures.
Urine Output
· Prolonged surgical procedures require a urinary catheter to monitor urine production and prevent bladder distention.
Emergency Response
· Regardless of how skilled we may be, there are times of crisis when extra help is necessary to adequately mange the patient.
· In preparation of the unexpected emergency, we should consider:
o Who will help you in an emergency?
§ Other anaesthetists in the building?
§ Medial or surgical staff, junior or senior?
§ Nursing staff, either from the theatre or elsewhere?
o How will people know you need help?
§ Is there an emergency call system or telephone?
§ Do you know how to use & operate the system, or who to dial?
o What will people do to help you?
§ Attempt to assign specific and suitable tasks to personnel as they approach to help.
§ When briefing those that come to help, be detailed but concise in description of the problem and the patient, as this will assist in delivery of appropriate care.
PLANNING FOR RECOVERY
Patients undergoing a surgical procedure with anaesthesia or sedation should be monitored for a period of time post-operatively to ensure that there are no early complications from either the surgery or anaesthetic that might require immediate intervention or return to theatre e.g. laryngospasm or bleeding.
Recovery planning is determined by the availability and level of:
· Staffing
· Equipment
· Skills
When these factors are known and considered, we can determine the type of patient that can or should be recovered by appropriate nursing staff with suitable monitoring. We should also be able to identify patients that require a higher degree of monitoring and post-operative care, such as the continued presence of the anaesthetist or another suitably trained medical officer.
Preparation of the patient for recovery should ensure that:
· The patient is awake or rousable.
· There is no residual paralysis.
· The patient is heamodynamically stable.
· The patient is comfortable with appropriate analgesia.
· There is an availability of suitable analgesics and anti-emetics for post-operative use.
SELF-ASSESSMENT QUESTIONS
1. For what type of surgery is it safe to use a supraglottic airway (e.g. laryngeal mask)? When should they not be used?
2. What medical conditions prevent the use of a laryngeal mask?
3. List the essential resources for a recovery unit.
ASSIGNMENT
Create an assessment form that can be used to determine when it is safe to discharge a patient from recovery to the ward.
Final Objective: On completion of this module you will be able to formulate an appropriate anaesthesia for a given procedure, to organise the facilities available to you, and to plan for both expected and unexpected operative events.
Enabling Objective: To achieve this goal, you should understand:
- The indications for anaesthesia and sedation, and the factors that will impact on those indications.
- The type of anaesthesia techniques available for given procedures
- The implications of the anaesthetic and its subsequent management
- The impact of anaesthesia and surgical procedures on the workload of personnel and the functioning of an operating theatre
- The importance of planning for expected and unexpected peri-operative events
Reference Reading:
- Developing Anaesthesia Textbook Chapters 1.
- Perioperative Medicine and Anaesthesia Seminar 2007
PLANNING ANAESTHESIA OR SEDATION
There are many factors to consider when planning anaesthesia. Not all factors are directly related to the patient, but all factors relate to the safety of the patient. Our goals, as anaesthetists, should include:
1. Patient Factors.
Understanding the medical and physiological needs of our patients, so as to provide the best perioperative care.
2. Surgical Factors.
Understanding the requirements of the surgery and the surgeon, the anaesthetic requirements for safe conduct of surgery, and the subsequent physiological impact of surgery.
3. Environmental Factors
Assessing the environment in which we will be operating, so that we will have adequate equipment, supplies and staff, appropriately trained assistance, and a safe environment in which our patient can be managed for surgery, and discharged for continuing post-operative care.
4. Other Factors.
Anticipate problems that may arise during and after surgery, to consider possible preventive measures, to recognize signs that indicate the onset of problems, and to plan for solutions to those problems (plan A, plan B, etc)
Anaesthesia planning relies as much on communication as on preparation. Communication with all staff involved in the surgical procedure will enhance the experience for all the participants. Discussion with the surgeon will elucidate the surgical needs for anaesthesia, and may indicate the relative suitability of local, regional or general anaesthesia. Discussion with the patient pre-operatively will elucidate medical, physiological and psychological factors that may indicate the suitability or otherwise of various anaesthetic techniques and agents. Consideration should be given to general aspects of intra-operative care (positioning during the procedure, equipment requirements), allowing for a smoother flow of patient and staff movements, and to facilitate the surgical process. Discussion with nursing staff in relation to provision of appropriate nursing care, analgesia, fluids, haemodynamic monitoring or support, will enhance post-operative management of the patient.
The anaesthesia plan starts with a patient assessment and consideration of surgical requirements, and contains choices of anaesthetic agents and techniques, monitors, patient position, steps for induction and maintenance of anaesthesia, awakening from anaesthesia, and immediate post anaesthetic care.
CHOOSING & PLANNING AN ANAESTHETIC TECHNIQUE
However strong the indications may seem for using a particular technique,especially in an emergency, the best anaesthetic technique will be one with,which you are most experienced and confident.
An anaesthetic technique is selected based on:
1. Pre-operative examination and clinical evaluation
2. The type and extent of the surgical procedure
3. The ability to perform various anaesthetic techniques, based on experience and the availability of equipment and drugs.
Pre-operative examination and clinical evaluation
Routine history taking and examination of the patient will provide much information on the suitability of an anaesthetic technique for that particular patient. Important points in the preoperative interview are:
· Medical condition of the patient.
· Emergency or elective procedure
· Adequate fasting or risk of airway soiling
· Previous anaesthetic experience or problems related to anaesthesia
· Patient preference
Note that not all factors are of equal importance, but all should be considered, especially when the choice of anaesthetic technique is not obvious.
The type and extent of the surgical procedure
The type of surgical procedure may mandate the type of anaesthesia required. Many limb and superficial procedures are highly amenable to local or regional anaesthetic techniques. More invasive surgery, such as intra-abdominal or intra-thoracic procedures, requires the use of muscle relaxants to facilitate the surgery, and therefore require the use of general anaesthesia. Similarly, if the procedure planned is to be extensive, of long duration, or necessitates positioning of the patient that may be uncomfortable for the duration of the procedure, general anaesthesia may be the appropriate choice.
Major head and neck surgery
Upper abdominal or intra-abdominal
Intrathoracic
Intracranial & neurosurgery
- Relaxant General Anaesthesia and Intermittent Positive Pressure Ventilation via an Endotracheal Tube
Lower abdominal
- General aneasthesia +/- relaxation +/- ETT
- Or Neuraxial RA
- Or combined GA/RA
Lower abdominal – extra-peritoneal
Groin, perineum
- General anaesthesia +/- relaxation +/- ETT
- Or Neuraxial RA
- Or nerve or field blocks
- Or combined GA/RA
Lower limbs
- General anaesthesia +/- relaxation +/- ETT
- Or Neuraxial/Plexus RA
- Or nerve or field blocks
- Or combined GA/RA
Upper limbs
- General anaesthesia +/- relaxation +/- ETT
- Or Plexus/Intravenous RA
- Or nerve or field blocks
ANAESTHETIC TECHNIQUES
Local Anaesthesia (LA)
Highly suitable for superficial and peripheral operations, local anaesthesia is an excellent choice for skin and soft-tissue surgery of limited size, depth and duration.
Generally tolerated very well, but problems may arise with:
· Injection into areas of “tight” tissues
· Positioning of patient and duration of surgery (patient comfort)
· Use of tourniquets
· Toxicity of local anaesthetics and/or adjuvants (adrenaline, etc)
Regional Anaesthesia (RA)
Plexus Techniques
· Arm blocks via brachial plexus blockade
· Leg blocks via femoral and/or sciatic nerve blockade
Neuraxial Techniques
· Spinal anesthesia
· Epidural anaesthesia
Intravenous technique
· Bier’s block
Regional anaesthesia via neuraxial or plexus blockade has advantages of providing both analgesia as well as sympathetic nerve blockade, which may have a place in improving blood supply to the operative area, facilitating microvascular re-anastomotic techniques, and potentially reducing the incidence of postoperative chronic pain conditions.
Regional anaesthesia is often performed as a “single-shot” technique, using specific nerve block needles (either short-bevel needles to avoid cutting nerve fibres, or Tuohey-type needles. Insulated needles attached to a nerve stimulator are useful in identifying nerves for blockade) or catheters may be introduced to prolong the block, and provide continued analgesia. This is most commonly done with an epidural block to provide analgesia for women in labour.
Regional anaesthesia techniques may be contraindicated when patients have an abnormal clotting profile, or are treated with anticoagulant or anti-platelet agents. This is especially applicable to the neuraxial techniques, where the consequences of bleeding and haematoma formation in the confined space of the neural canal can result in permanent neurological injury e.g. paraplegia. Other contraindications include generalized sepsis, localised sepsis overlying the point of insertion, inability of the patient to co-operate or keep still and patient refusal.
Intravenous regional anaesthesia is an easy technique that requires minimal extra equipment. The importance of understanding the pharmacology of the local anaesthetic agent used intravenously cannot be overstated. The use of long-acting agents such as bupivacaine or ropivacaine is contraindicated because of the potential adverse effects of cardiotoxicity. Short-acting agents that are metabolized by plasma esterases are ideal. Double-cuff tourniquets are preferable because of the additional safety that is conferred. To reduce the effects of toxicity when the cuff is released the minimal cuff inflation times must be observed, ensuring that local anaesthetic agent metabolism and tissue binding is complete. Further caution must be exercised if performing a lower limb block, due to the amount of local anaesthetic agent that needs to be used.
General Anaesthesia (GA)
General anaesthesia is defined as a state characterized by unconsciousness, analgesia, muscle relaxation and depressed reflexes. It is a relatively simple task to achieve these conditions by administration of drugs with the necessary properties. The challenge is to produce the state of anaesthesia while preserving or improving patient health.
Thus, management of general anaesthesia consists of two separate but interrelated goals:
1. Reversible depression of nervous system functions
2. Maintenance, improvement or minimal disruption of organ function, in spite of pre-existing disease, surgical trauma, and effects of anaesthetic drugs and procedures.
The science, art, and craft of anaesthesia consist of understanding and achieving specific goals to accomplish the desired effects while minimizing the effects of the surgical stimulation and other functional abnormalities through the titration of drugs and ventilation, the management of fluids, the observation and protection of the patient’s body and the manipulation of temperature.
Of vital importance to our conduct of general anaesthesia is the provision and maintenance of a suitable airway, and the ability to provide for adequate gas exchange for the anaesthetized patient. Where a general anaesthetic technique is required, there are surgical and patient factors that influence the choice of airway and ventilation modes.
Our choices of airway management will include:
Ventilation
· Spontaneous (in the absence of a muscle relaxant)
· Intermittent Positive Pressure (when the patient is paralysed by muscle relaxants, or obtunded by other agents, such as opiates)
Airway
· Face mask ventilation
· Nasopharyngeal or Oropharyngeal airway – Guedel, etc
· Supraglottic airway device – LMA, ProSeal LMA, Cobra
· Endotracheal Tube (ETT)
· Subglottic tracheal device – tracheostomy, cricothyrotomy
Indicators for specific uses of ventilation and airway devices are as varied as the potential surgical procedures and patient co-morbidities. There are some broad indications to be considered.
Surgical Indications for ventilation via ETT:
Neurosurgery
· Muscle relaxation is required for most intracranial procedures
o absence of patient movement is paramount
o controlled ventilation allows CO2 manipulation, adding control to cerebral perfusion pressures and intracranial pressures
Intra-abdominal Procedures
· Muscle relaxation required to gain optimum surgical access
Intra-abdominal laparoscopic procedures
· Muscle relaxation required to allow adequate pneumoperitoneum
· Increased intra-abdominal pressure will reduce diaphragmatic excursion & ventilation, and is best managed with IPPV
· Pneumoperitoneum with CO2 will result in CO2 absorption & increased ventilatory requirements
Anaesthetic indications for ventilation via ETT
Airway protection
· Non-fasted emergency patient
· Gastro-intestinal obstruction or haemorrhage
· Acute abdomen
· Treatment with opiates or drugs that will cause gastric stasis, increasing risk of reflux & aspiration
· Hiatus hernia or symptomatic reflux
· Pregnancy > 14 weeks gestation, through to day 3 postpartum
· Upper airway haemorrhage
Facilitation of ventilation
· Restrictive lung disease
· Muscle dystrophy or weakness
· Prolonged operation or anaesthesia
o Prevention of hypoventilation and alveolar collapse
Respiratory correction of acid/base balance
Inability to access airway during procedure
· Prone position may prevent airway manipulation
· Sitting position may render head inaccessible beneath drapes or behind a support frame
· Patient position may be remote from anaesthetist
Choice of Airway Devices
Intubation with an endotracheal tube remains the gold standard for providing intermittent positive pressure ventilation and airway protection. The presence of an inflatable cuff allows isolation of the trachea from gastro-intestinal tract, protecting the airway from soiling, and giving the ability to provide positive pressure to the airways to achieve adequate ventilation.
Note that the introduction of an endotracheal tube is facilitated by a muscle relaxant, which also facilitates continuation of IPPV during a procedure. Not all cases require paralysis with a muscle relaxant, and in some cases (myasthenia gravis, muscular dystrophies) use of muscle relaxants is relatively contra-indicated. Pre-operative assessment will indicate those who require variations in technique. Useful alternatives such as potent opioids in higher doses (e.g. alfentanil) must be balanced against the possibility of cardiovascular depression and respiratory depression, leading to prolonged ventilation.
For surgical procedures that do not require paralysis for surgical or anaesthetic reasons, the choice of airway technique becomes much broader. Bag and mask ventilation may be ideal for short procedures, and may help avoid airway instrumentation. The use of an oral or nasal pharyngeal device will facilitate ventilation in some people. Supraglottic airway devices (e.g. LMA) generally provide a good airway seal, enable direct attachment of a ventilation circuit to the device, effectively isolate anaesthetic gases to the patient, and allow the anaesthetist to use their hands for other tasks. Intermittent positive pressure ventilation can be applied with all these techniques, but with varying degrees of safety and success. Always remember that a supraglottic airway is not isolated, that gastric insufflation can readily occur, and that reflux of gastric contents is possible.
Where a muscle relaxant is not to be used, the choice can be made to ventilate the patient (Intermittent Positive Pressure Ventilation – IPPV), or allow the patient to breathe (Spontaneous Ventilation – SV). Ventilating the patient will be necessary where respiratory drive has been obtunded by opiates, benzodiazepines or other depressant agents. This may be avoided by careful titration of drugs. A spontaneously ventilating patient may be allowed to breathe on either an endotracheal tube, a supraglottic airway or other airway device. An airway device will facilitate ventilation by improving the patency of the airway, avoiding obstruction by the tongue and other pharyngeal structures. However, the presence of an airway device will narrow the airway, increasing resistance to gas flow, and increasing the work of breathing. In combination with general anaesthesia, hypoventilation and hypercapnoea is commonly seen. This state is generally well tolerated in most patients for limited periods, but may be contraindicated in those with pre-existing respiratory disease (e.g. obstructive airways disease) or where surgery may be prolonged. Supraglottic airways generally provide a larger diameter airway when compared to endotracheal tubes, and are more suitable for the spontaneously breathing patient. Supraglottic tubes do not provide lung isolation or protection from contamination.
PAIN MANAGEMENT
Analgesia is an integral part of anaesthesia. Patient assessment and consideration of the surgical procedure will determine the analgesic requirements of the patient. Choices of analgesia can be varied, as are the methods for delivering that analgesia. Analgesia may range from the simple (paracetamol – simple to deliver, easy to manage) to the complex (epidural analgesia – requiring equipment and training for insertion and continued management). Pre-operative planning will allow assessment of the analgesic techniques available, the availability of equipment and staff to maintain analgesic regimens, and to discuss the appropriateness of possible regimens with all those involved – patient, surgeon, theatre staff and ward nurses. Where understanding and agreement is reached, better analgesia will result, improving surgical outcomes and patient satisfaction.
Intraoperative pain management may be achieved with:
Local anaesthesia
Local infiltration
Field blocks
Intra-articular
Regional anaesthesia techniques
Single shot techniques
Intermittent or continuous infusion via catheter
Parenteral analgesics
Opiates
Opiate-like agents (Tramadol, Ketamine)
Non-steroidal anti-inflammatories (NSAIDs)
Simple techniques for pain management, such as the use of parenteral opiates, are the backbone of many anaesthetic techniques. Planning for the appropriate use of parenteral agents in theatre involves an assessment of the patient, to avoid co-morbidities that may be impacted by or contra-indicate the use of certain parenteral agents.
Appropriate plans must be considered for the progression or discontinuation of analgesia. An analgesic plan will provide a framework in which staff can assess and monitor the patient and their analgesic requirements. Where the patient is not following that path, or analgesic requirements remain high or increased, thought must be given to surgical review of the patient. A plan can then be seen as a tool to initiate a response to the patient’s clinical condition.
INTRAOPERATIVE PLANNING ISSUES
Planning anaesthesia requires that many aspects of intra-operative care of the patient be considered prior to the commencement of the surgical procedure, to ensure the availability and delivery of appropriate and timely care to the patient. Of the many aspects of anaesthesia and surgery that should be considered, there are a few that should be given some attention.
Temperature
· Planning to avoid hypothermia
o Maintain patient clothing, coverage, etc, prior to theatre.
o Use of warmed fluids, warm blankets, active warming devices (forced air warmer, fluid warmers)
Fluids
· Consider replacement fluids to cover fasting and maintenance.
· Immediate resuscitation may also be required
· Use of crystalloids and/or colloids can often be planned
Blood
· There should be appropriate availability of safe blood for procedures where blood loss is expected.
· Consideration should be given to the immediate availability of O -ve type blood in obstetric units
· Consider the storage conditions of blood prior to use (the availability of controlled refrigeration), and the ability to warm blood during transfusion (to mitigate hypothermia)
Intravenous Access
· 16G or 18G cannulas are suitable for resuscitation, and procedures such as laparoscopy and laparotomy.
· Consider 2 cannulas for operations where blood loss may be significant.
· Smaller gauge cannulas (20 or 22) may be suitable for smaller procedures.
Urine Output
· Prolonged surgical procedures require a urinary catheter to monitor urine production and prevent bladder distention.
Emergency Response
· Regardless of how skilled we may be, there are times of crisis when extra help is necessary to adequately mange the patient.
· In preparation of the unexpected emergency, we should consider:
o Who will help you in an emergency?
§ Other anaesthetists in the building?
§ Medial or surgical staff, junior or senior?
§ Nursing staff, either from the theatre or elsewhere?
o How will people know you need help?
§ Is there an emergency call system or telephone?
§ Do you know how to use & operate the system, or who to dial?
o What will people do to help you?
§ Attempt to assign specific and suitable tasks to personnel as they approach to help.
§ When briefing those that come to help, be detailed but concise in description of the problem and the patient, as this will assist in delivery of appropriate care.
PLANNING FOR RECOVERY
Patients undergoing a surgical procedure with anaesthesia or sedation should be monitored for a period of time post-operatively to ensure that there are no early complications from either the surgery or anaesthetic that might require immediate intervention or return to theatre e.g. laryngospasm or bleeding.
Recovery planning is determined by the availability and level of:
· Staffing
· Equipment
· Skills
When these factors are known and considered, we can determine the type of patient that can or should be recovered by appropriate nursing staff with suitable monitoring. We should also be able to identify patients that require a higher degree of monitoring and post-operative care, such as the continued presence of the anaesthetist or another suitably trained medical officer.
Preparation of the patient for recovery should ensure that:
· The patient is awake or rousable.
· There is no residual paralysis.
· The patient is heamodynamically stable.
· The patient is comfortable with appropriate analgesia.
· There is an availability of suitable analgesics and anti-emetics for post-operative use.
SELF-ASSESSMENT QUESTIONS
1. For what type of surgery is it safe to use a supraglottic airway (e.g. laryngeal mask)? When should they not be used?
2. What medical conditions prevent the use of a laryngeal mask?
3. List the essential resources for a recovery unit.
ASSIGNMENT
Create an assessment form that can be used to determine when it is safe to discharge a patient from recovery to the ward.
