PREOPERATIVE ASSESSMENT
Final Objective: On completion of this module you will recognize those aspects of a patient’s physical, physiological and mental status which influence the conduct of anaesthesia and you will be able to use this information to assess anaesthetic risk and create an appropriate anaesthetic plan with regard to the urgency of surgery and patient optimisation. You should also understand the importance of preoperative medications.
Enabling Objective: To achieve this goal, you should know how to:
Reference Reading:
PREOPERATIVE ASSESSMENT.
The preoperative visit of all patients by an anaesthetist is an essential requirement for the safe and successful conduct of anaesthesia.
All patients listed for surgery require full preoperative assessment. There are two essential aims of the preoperative assessment. Firstly, the anaesthetist must determine the most appropriate anaesthetic technique dependent on the patient’s medical condition, the planned surgery and their own individual preferences. Secondly the anaesthetist must determine the appropriate timing of the anaesthetic/surgery. Surgery may be considered elective, urgent and emergent. Where there is coexisting illness, every opportunity must be taken to improve the patient’s condition prior to surgery Elective should be delayed until the patient is fully optimised. The anaesthetist should not be intimidated into proceeding with anaesthesia if they have doubts. Urgent surgery can usually be delayed until the anaesthetist has had the opportunity to fully assess the patient and commenced optimisation. Urgent surgery does not dictate immediate surgery and anaesthesia. There is sufficient time to investigate and correct basic physiological derangements, in particular cardiovascular, respiratory and electrolyte abnormalities. For example, “emergency appendicectomy” should not proceed without assessment and rehydration. In certain life or limb threatening circumstances it may be necessary to anaesthetise and operate on acutely unwell patients or those with significant medical problems. This should only occur after discussion with the surgical team and the patient. These patients still require full assessment and attempted optimisation concurrent with anaesthesia and surgery.
In general the system of routine preoperative assessment follows reviewing the patient’s notes and past anaesthetic charts. Obtaining the patient’s medical history (especially respiratory and cardiovascular illnesses), fasting status, reflux risk, medications and allergies. The patient is examined with special attention to airway assessment. Investigations are reviewed and additional information is obtained if required. The patient is provided with an explanation of the anaesthetic and consent is obtained. Finally perioperative orders including premedication and documentation of the assessment and perioperative plan are made.
Some patients will have planned surgery and/or medical disorders that command extra consideration by the anaesthetist during the entire peri-operative period. Specific patient factors may require additional peri-operative investigations, intra-operative and post-operative monitoring, peri-operative medication and altered anaesthetic techniques.
The essential elements of peri-operative medicine are determining the true urgency of surgery with respect to patient optimisation and identifying specific patient problems that will necessitate additional peri-operative anaesthetic strategies beyond routine anaesthetic care
Medical History
The anaesthetist must take a medical history. This history includes why the patient is having the surgery and also any serious illness, in particular heart disease, respiratory disease (including asthma and smoking), diabetes, kidney disease and gastro-oesophageal reflux disorders.
Specific inquires must be made about angina (its incidence, precipitating factors, duration and use of anti-anginal medications), unstable coronary syndrome previous myocardial infarction and subsequent symptoms, symptoms of heart failure, symptoms of severe valvular heart disease, and significant arrhythmias. Patients should also be assessed for risk factors for coronary artery disease and evidence of associated diseases including diabetes, peripheral vascular disease, cerebrovascular disease and renal impairment.
Patients should have surgery delayed at least 6 weeks (with maximal medical assessment and treatment) and preferably 6 months after a myocardial infarction. Surgery should also be delayed if there is uncompensated heart failure or severe hypertension (systolic greater than 180 mmHg or diastolic greater than 110 mmHg). Patients with mild or moderate hypertension (systolic less than 180 mmHg, diastolic less than 110 mmHg) and no associated metabolic or cardiovascular disorder should proceed with surgery.
Active respiratory disease (asthma, infection) requires treatment prior to surgery. All patients should be encouraged to cease smoking.
Other conditions of importance include indigestion, heartburn and reflux that may indicate an increase risk of regurgitation and aspiration. Rheumatoid disease where patients may be anaemic and have limited movement of their joints which makes positioning for surgery and airway management difficult. Patients with diabetes have an increased incidence of ischaemic heart disease (often with silent ischaemia), renal dysfunction and autonomic and peripheral neuropathy. Chronic renal failure may cause anaemia, electrolyte abnormalities and altered drug excretion. Liver disease may also alter drug metabolism as well as delay coagulation.
The anaesthetist should also ask about medications, allergies and determine the patient’s exercise tolerance.
The patient’s exercise tolerance gives a good indication of the chance that the patient’s health will be poorly affected by surgery/anaesthesia. If the patient is unable to climb a flight of stairs or walk up a hill, then they are at increased perioperative risk.
Medications Drugs of special significance to anaesthesia include anticoagulants, steroids and diabetic treatment. As a general rule, with the exception of these drugs, it is best not to stop any drugs before surgery.
Allergy and Drug Reactions The anaesthetist must ask the patient about unusual, unexpected or unpleasant reactions to drugs. True allergic reactions are uncommon but any drug that has caused a skin reaction, facial or oral swelling, shortness of breath, choking, wheezing or hypotension should be considered to have caused an allergic response and must be avoided.
Anaesthetic History The anaesthetist should read any old anaesthetic notes. Good anaesthetic notes will include responses to drugs, ease of mask ventilation and endotracheal intubation and any anaesthetic complications. Patients should be asked about their prior anaesthetics.
Family History The anaesthetist should ask if anyone in the family has had a bad reaction to anaesthesia. Malignant hyperpyrexia and pseudocholinesterase deficiency are two inherited conditions of great concern to the anaesthetist.
Smoking and Alcohol Patients should be encouraged to stop smoking and alcohol before surgery.
Physical Examination The anaesthetist must perform a physical examination. This examination must pay special attention to the patient’s airway, cardiovascular and respiratory systems.
Every patient’s airway must be assessed to determine how difficult it will be to mask ventilate and intubate. This assessment includes measuring mouth opening, neck flexion and extension and the distance from the mandible to the thyroid cartilage and looking in the mouth.
Cardiovascular examination is particularly concerned with determining the hydration status of the patient (heart rate, blood pressure, postural drop, any signs of dehydration), signs of cardiac failure and cardiac valve abnormalities. Patients who have a low blood pressure and tachycardia must have intravenous fluid resuscitation before commencing surgery/anaesthesia.
Respiratory examination should look for signs of upper airway obstruction, bronchospasm or infection.
At this stage the anaesthetist may have diagnosed several problems that require further investigation and treatment before surgery.
Documentation The preoperative assessment should be documented, ideally on a preoperative assessment form.
PREOPERATIVE INVESTIGATIONS.
There is little evidence to support the performance of “routine “ investigations. An investigation should only be ordered if the results of it would affect the way in which the patient will be managed. The decision to order investigations will depend on the patient’s age, general health and proposed operation.
Healthy patients less than 40 years of age may require no investigations. Females less than 40 may require estimation of haemoglobin (Hb). Healthy patients between 40 and 60 may require no investigations or may need an electrocardiogram (ECG), full blood examination and renal function tests depending on the extent of surgery Women should have Hb estimated. All healthy patients greater than 60 years of age are more likely to need an ECG, full blood examination, renal function test and a chest X-ray.
For patients who are not healthy, preoperative investigations will depend on the patient’s history and examination:
Full blood examination (haemoglobin or haematocrit, white cell count, platelet count):
anaemia, pallor, jaundice, malignancy, blood loss, infection, cardiac/renal/hepatic disease and major surgery.
Renal function test (sodium, potassium, urea, creatinine): cardiac/renal/hepatic disease, diuretics, digoxin infection, diabetes, hypertension, vomiting and dehydration.
Electrocardiogram: cardiac/respiratory disease, hypertension, diabetes and atypical abdominal pain.
Blood glucose: diabetes, steroid treatment and glycosuria.
Chest X-ray: respiratory/cardiac disease, heavy smoking and TB exposure.
Cervical spine X-ray: severe rheumatoid arthritis, history of neck trauma
Liver function tests (bilirubin, ALT, AST): cardiac/hepatic disease, jaundice, severe infection, alcohol abuse and biliary surgery.
Thyroid function tests: check within 1 month of thyroid surgery. Patients with a very low TSH should not have surgery.
APPT: heparin, liver disease and major surgery.
INR: warfarin, liver disease, jaundice and major surgery.
INR & APPT: bleeding tendency, septicaemia and severe pre-eclampsia.
Blood group and cross match: major surgery with anticipated blood loss generation less than 15%.
RISK ASSESSMENT.
Having assessed the patient preoperatively, it is not surprising that the anaesthetists try to assess the risks of anaesthesia (and surgery). The leading cause of death after surgery is myocardial infarction and in addition there is significant morbidity from non-fatal infarction. Attempts have been made to identify factors that will predict those patients at risk.
A wide variety of other factors have been identified as contributing to the risk of mortality in the operative and postoperative period.
Increasing age:> 60 years
Worsening physical status
Increasing number of concurrent medical conditions, in particular
Emergency operations
The commonest method of categorizing patients is by using the ASA (American Society of Anesthesiologists) physical status classification.
ASA classification ASA 1: a normal healthy person
ASA 2: a patient a with mild systemic disease process which does not limit the patient’s activities in any way, e.g treated hypertension, stable diabetes.
ASA 3: a patient with moderate systemic disease limiting activity but not incapacitating
ASA 4: a patient with incapacitating systemic disease that is a constant threat to life e.g unstable angina
ASA 5: an extremely ill patient who is not expected to live 24 hours with or without an operation
Note: ‘E’ may be added to signify an emergency operation.
PREMEDICATION.
Premedication should be provided for a specific purpose. It may be used to relieve anxiety, provide analgesia, reduce airway secretions, reduce the risk of aspiration or prevent cardiovascular responses.
The most commonly prescribed anxiolytics are the benzodiazepines. They produce sedation and amnesia, are well absorbed from the gastrointestinal tract and are usually given orally 60 – 90 minutes preoperatively. Commonly used benzodiazepines include diazepam 5 – 10 mg and temazepam 10 – 20 mg. Lorazepam may cause prolonged postoperative sedation. The intravenous formulation of midazolam may be given orally (mixed with clear juice as it is bitter) 0.5 mg/kg.
Analgesics are now generally reserved for patients who are in pain preoperatively. It is also now not routine to prescribe drugs to reduce salivation preoperatively.
A variety of drug combinations are used to try and increase gastric pH and reduce gastric volume. Oral sodium citrate (30 ml) will increase gastric pH. H2 antagonists will reduce acid secretion and metoclopramide will increase gastric emptying.
The anticholinergic agents atropine and glycopyrrolate are used to protect against the occurrence of bradycardias and although they have been used preoperatively, they are more effective when administered intravenously at induction. Excessive vagal activity, causing profound bradycardias may occur with repeated doses of suxamethonium and during traction on the extraocular muscles.
There will be some patients that will require special premedication including diabetics, asthmatics, those patients taking steroid or anticoagulant treatment and patients with prosthetic or diseased heart valves.
PREOPERATIVE FASTING.
With the onset of anaesthesia, protective airway reflexes are diminished and patients are at risk of regurgitation and inhaling (aspirating) their stomach contents.
The aim of fasting is to minimize the risk of aspiration. However the anaesthetist should also consider patient comfort in the preoperative period and minimise any potential significant physiological changes that may occur from prolonged fasting.
As gastric secretion is continuous at 6 ml/kg/h and 1 ml/kg/h of saliva is swallowed, the stomach is never truly empty. Oral intake, gastric secretions and gastric emptying determine the residual gastric volume and pH. The residual gastric volume and speed at which the stomach empties will change with diseases, emotion, pain, hunger and gastric content.
The top 3 risk factors for aspiration are emergency surgery, light anaesthesia/unexpected response to stimulation and upper/lower gastrointestinal pathology.
Current generally accepted fasting intervals for elective uncomplicated cases are 2 hours for water and clear fluids, 4 hours for breast milk and 6 hours for solids (2, 4 and 6). “Nil by mouth” from midnight is not good anaesthetic practice.
SELF-ASSESSMENT QUESTIONS
ASSIGNMENT
Develop an algorithm for the management of a patient having major elective surgery.
{An algorithm is an effective method in which a definite list of well defined instructions for completing a task, when given an initial state, will proceed through a well defined series of successive states, eventually terminating in an end state. In a general sense, an algorithm is any set of instructions that result in a predictable result from a known beginning. Algorithms are only as good as the instructions given, however are an excellent way to process complex information.}
PREOPERATIVE ASSESSMENT CASE STUDIES.
Case 2.1
Tsahim is a 59-year-old male with poorly managed non-insulin dependent diabetes who presented with an infected lesion on his right foot. He has a fever, looks dehydrated and is quite confused. His blood pressure is 180/110. The surgeon insists on taking him straight to the operating theatre.
What further information would you be looking for in this man’s history?
What investigations would you request before agreeing to anaesthetise Tsahim?
Assign an ASA score to Tsahim.
Discuss the implications of delaying his surgery.
How would you assess his diabetic control and how would you manage his diabetes in the peri-operative period?
How will the physiological changes associated with diabetes affect anaesthesia?
What do you think about his blood pressure of 180/110?
Describe the options for premedication.
During the preoperative assessment Tsahim tells you that he has glaucoma and chronic kidney failure. He shows you his diuretic tablet and his eye drops.
Discuss the relevant pharmacology. What interactions between his own medication and anaesthetic agents might occur?
Tsahim’s serum potassium is 6 mEq/l. How will you manage this?
Case 2.2
You have been asked to see Ganbold who is a 56 year old man booked for an elective cholecystectomy. He has a history of rheumatic heart disease.
What further history do you require?
Discuss the relevance of the anticipated findings in your clinical examination.
What are the possible anaesthetic complications associated with his condition?
Describe the options for premedication.
What investigations would you order for this man?
His haemoglobin result is 70g/l. Discuss your proposed management.
Case 2.3
Badral is a 48-year-old man who is scheduled to have knee surgery. He is a heavy smoker with a history of hypertension. He was admitted to the hospital with a myocardial infarction 2 years ago and now reports occasional episodes of chest pain and shortness of breath associated with mild exertion and relieved by sublingual GTN. His exercise tolerance is limited due to his painful knee. His preoperative blood pressure is 160/105 and his heart rate is 98 beats/minute and there is an audible expiratory wheeze. Badral’s mother and father died in their 50’s. He doesn’t know what from. His brother had an anaesthetic and he took a long time to wake up.
Outline you main anaesthetic concerns.
Final Objective: On completion of this module you will recognize those aspects of a patient’s physical, physiological and mental status which influence the conduct of anaesthesia and you will be able to use this information to assess anaesthetic risk and create an appropriate anaesthetic plan with regard to the urgency of surgery and patient optimisation. You should also understand the importance of preoperative medications.
Enabling Objective: To achieve this goal, you should know how to:
- Evaluate significant aspects of the history and examination.
- Identify the perioperative effects of coexisting disease.
- Identify possible interactions between anaesthetic drugs and the patient’s own medication.
- Describe the basic pharmacology of drugs used for premedication and outline the objectives of premedication.
- Differentiate between appropriate and inappropriate preoperative investigations.
- Describe and apply systems of classifying patients with regard to anaesthetic risk.
Reference Reading:
- Developing Anaesthesia Textbook Chapters 1, 2, 3 & 4.
- Perioperative Medicine and Anaesthesia Seminar 2007 pages 6 – 161.
- Oxford Handbook of Anaesthesia. Chapters 1 – 13.
PREOPERATIVE ASSESSMENT.
The preoperative visit of all patients by an anaesthetist is an essential requirement for the safe and successful conduct of anaesthesia.
All patients listed for surgery require full preoperative assessment. There are two essential aims of the preoperative assessment. Firstly, the anaesthetist must determine the most appropriate anaesthetic technique dependent on the patient’s medical condition, the planned surgery and their own individual preferences. Secondly the anaesthetist must determine the appropriate timing of the anaesthetic/surgery. Surgery may be considered elective, urgent and emergent. Where there is coexisting illness, every opportunity must be taken to improve the patient’s condition prior to surgery Elective should be delayed until the patient is fully optimised. The anaesthetist should not be intimidated into proceeding with anaesthesia if they have doubts. Urgent surgery can usually be delayed until the anaesthetist has had the opportunity to fully assess the patient and commenced optimisation. Urgent surgery does not dictate immediate surgery and anaesthesia. There is sufficient time to investigate and correct basic physiological derangements, in particular cardiovascular, respiratory and electrolyte abnormalities. For example, “emergency appendicectomy” should not proceed without assessment and rehydration. In certain life or limb threatening circumstances it may be necessary to anaesthetise and operate on acutely unwell patients or those with significant medical problems. This should only occur after discussion with the surgical team and the patient. These patients still require full assessment and attempted optimisation concurrent with anaesthesia and surgery.
In general the system of routine preoperative assessment follows reviewing the patient’s notes and past anaesthetic charts. Obtaining the patient’s medical history (especially respiratory and cardiovascular illnesses), fasting status, reflux risk, medications and allergies. The patient is examined with special attention to airway assessment. Investigations are reviewed and additional information is obtained if required. The patient is provided with an explanation of the anaesthetic and consent is obtained. Finally perioperative orders including premedication and documentation of the assessment and perioperative plan are made.
Some patients will have planned surgery and/or medical disorders that command extra consideration by the anaesthetist during the entire peri-operative period. Specific patient factors may require additional peri-operative investigations, intra-operative and post-operative monitoring, peri-operative medication and altered anaesthetic techniques.
The essential elements of peri-operative medicine are determining the true urgency of surgery with respect to patient optimisation and identifying specific patient problems that will necessitate additional peri-operative anaesthetic strategies beyond routine anaesthetic care
Medical History
The anaesthetist must take a medical history. This history includes why the patient is having the surgery and also any serious illness, in particular heart disease, respiratory disease (including asthma and smoking), diabetes, kidney disease and gastro-oesophageal reflux disorders.
Specific inquires must be made about angina (its incidence, precipitating factors, duration and use of anti-anginal medications), unstable coronary syndrome previous myocardial infarction and subsequent symptoms, symptoms of heart failure, symptoms of severe valvular heart disease, and significant arrhythmias. Patients should also be assessed for risk factors for coronary artery disease and evidence of associated diseases including diabetes, peripheral vascular disease, cerebrovascular disease and renal impairment.
Patients should have surgery delayed at least 6 weeks (with maximal medical assessment and treatment) and preferably 6 months after a myocardial infarction. Surgery should also be delayed if there is uncompensated heart failure or severe hypertension (systolic greater than 180 mmHg or diastolic greater than 110 mmHg). Patients with mild or moderate hypertension (systolic less than 180 mmHg, diastolic less than 110 mmHg) and no associated metabolic or cardiovascular disorder should proceed with surgery.
Active respiratory disease (asthma, infection) requires treatment prior to surgery. All patients should be encouraged to cease smoking.
Other conditions of importance include indigestion, heartburn and reflux that may indicate an increase risk of regurgitation and aspiration. Rheumatoid disease where patients may be anaemic and have limited movement of their joints which makes positioning for surgery and airway management difficult. Patients with diabetes have an increased incidence of ischaemic heart disease (often with silent ischaemia), renal dysfunction and autonomic and peripheral neuropathy. Chronic renal failure may cause anaemia, electrolyte abnormalities and altered drug excretion. Liver disease may also alter drug metabolism as well as delay coagulation.
The anaesthetist should also ask about medications, allergies and determine the patient’s exercise tolerance.
The patient’s exercise tolerance gives a good indication of the chance that the patient’s health will be poorly affected by surgery/anaesthesia. If the patient is unable to climb a flight of stairs or walk up a hill, then they are at increased perioperative risk.
Medications Drugs of special significance to anaesthesia include anticoagulants, steroids and diabetic treatment. As a general rule, with the exception of these drugs, it is best not to stop any drugs before surgery.
Allergy and Drug Reactions The anaesthetist must ask the patient about unusual, unexpected or unpleasant reactions to drugs. True allergic reactions are uncommon but any drug that has caused a skin reaction, facial or oral swelling, shortness of breath, choking, wheezing or hypotension should be considered to have caused an allergic response and must be avoided.
Anaesthetic History The anaesthetist should read any old anaesthetic notes. Good anaesthetic notes will include responses to drugs, ease of mask ventilation and endotracheal intubation and any anaesthetic complications. Patients should be asked about their prior anaesthetics.
Family History The anaesthetist should ask if anyone in the family has had a bad reaction to anaesthesia. Malignant hyperpyrexia and pseudocholinesterase deficiency are two inherited conditions of great concern to the anaesthetist.
Smoking and Alcohol Patients should be encouraged to stop smoking and alcohol before surgery.
Physical Examination The anaesthetist must perform a physical examination. This examination must pay special attention to the patient’s airway, cardiovascular and respiratory systems.
Every patient’s airway must be assessed to determine how difficult it will be to mask ventilate and intubate. This assessment includes measuring mouth opening, neck flexion and extension and the distance from the mandible to the thyroid cartilage and looking in the mouth.
Cardiovascular examination is particularly concerned with determining the hydration status of the patient (heart rate, blood pressure, postural drop, any signs of dehydration), signs of cardiac failure and cardiac valve abnormalities. Patients who have a low blood pressure and tachycardia must have intravenous fluid resuscitation before commencing surgery/anaesthesia.
Respiratory examination should look for signs of upper airway obstruction, bronchospasm or infection.
At this stage the anaesthetist may have diagnosed several problems that require further investigation and treatment before surgery.
Documentation The preoperative assessment should be documented, ideally on a preoperative assessment form.
PREOPERATIVE INVESTIGATIONS.
There is little evidence to support the performance of “routine “ investigations. An investigation should only be ordered if the results of it would affect the way in which the patient will be managed. The decision to order investigations will depend on the patient’s age, general health and proposed operation.
Healthy patients less than 40 years of age may require no investigations. Females less than 40 may require estimation of haemoglobin (Hb). Healthy patients between 40 and 60 may require no investigations or may need an electrocardiogram (ECG), full blood examination and renal function tests depending on the extent of surgery Women should have Hb estimated. All healthy patients greater than 60 years of age are more likely to need an ECG, full blood examination, renal function test and a chest X-ray.
For patients who are not healthy, preoperative investigations will depend on the patient’s history and examination:
Full blood examination (haemoglobin or haematocrit, white cell count, platelet count):
anaemia, pallor, jaundice, malignancy, blood loss, infection, cardiac/renal/hepatic disease and major surgery.
Renal function test (sodium, potassium, urea, creatinine): cardiac/renal/hepatic disease, diuretics, digoxin infection, diabetes, hypertension, vomiting and dehydration.
Electrocardiogram: cardiac/respiratory disease, hypertension, diabetes and atypical abdominal pain.
Blood glucose: diabetes, steroid treatment and glycosuria.
Chest X-ray: respiratory/cardiac disease, heavy smoking and TB exposure.
Cervical spine X-ray: severe rheumatoid arthritis, history of neck trauma
Liver function tests (bilirubin, ALT, AST): cardiac/hepatic disease, jaundice, severe infection, alcohol abuse and biliary surgery.
Thyroid function tests: check within 1 month of thyroid surgery. Patients with a very low TSH should not have surgery.
APPT: heparin, liver disease and major surgery.
INR: warfarin, liver disease, jaundice and major surgery.
INR & APPT: bleeding tendency, septicaemia and severe pre-eclampsia.
Blood group and cross match: major surgery with anticipated blood loss generation less than 15%.
RISK ASSESSMENT.
Having assessed the patient preoperatively, it is not surprising that the anaesthetists try to assess the risks of anaesthesia (and surgery). The leading cause of death after surgery is myocardial infarction and in addition there is significant morbidity from non-fatal infarction. Attempts have been made to identify factors that will predict those patients at risk.
A wide variety of other factors have been identified as contributing to the risk of mortality in the operative and postoperative period.
Increasing age:> 60 years
Worsening physical status
Increasing number of concurrent medical conditions, in particular
- Myocardial infarction
- Diabetes mellitus
- Renal disease
- Intracranial
- Major vascular
- Intrathoracic
Emergency operations
The commonest method of categorizing patients is by using the ASA (American Society of Anesthesiologists) physical status classification.
ASA classification ASA 1: a normal healthy person
ASA 2: a patient a with mild systemic disease process which does not limit the patient’s activities in any way, e.g treated hypertension, stable diabetes.
ASA 3: a patient with moderate systemic disease limiting activity but not incapacitating
ASA 4: a patient with incapacitating systemic disease that is a constant threat to life e.g unstable angina
ASA 5: an extremely ill patient who is not expected to live 24 hours with or without an operation
Note: ‘E’ may be added to signify an emergency operation.
PREMEDICATION.
Premedication should be provided for a specific purpose. It may be used to relieve anxiety, provide analgesia, reduce airway secretions, reduce the risk of aspiration or prevent cardiovascular responses.
The most commonly prescribed anxiolytics are the benzodiazepines. They produce sedation and amnesia, are well absorbed from the gastrointestinal tract and are usually given orally 60 – 90 minutes preoperatively. Commonly used benzodiazepines include diazepam 5 – 10 mg and temazepam 10 – 20 mg. Lorazepam may cause prolonged postoperative sedation. The intravenous formulation of midazolam may be given orally (mixed with clear juice as it is bitter) 0.5 mg/kg.
Analgesics are now generally reserved for patients who are in pain preoperatively. It is also now not routine to prescribe drugs to reduce salivation preoperatively.
A variety of drug combinations are used to try and increase gastric pH and reduce gastric volume. Oral sodium citrate (30 ml) will increase gastric pH. H2 antagonists will reduce acid secretion and metoclopramide will increase gastric emptying.
The anticholinergic agents atropine and glycopyrrolate are used to protect against the occurrence of bradycardias and although they have been used preoperatively, they are more effective when administered intravenously at induction. Excessive vagal activity, causing profound bradycardias may occur with repeated doses of suxamethonium and during traction on the extraocular muscles.
There will be some patients that will require special premedication including diabetics, asthmatics, those patients taking steroid or anticoagulant treatment and patients with prosthetic or diseased heart valves.
PREOPERATIVE FASTING.
With the onset of anaesthesia, protective airway reflexes are diminished and patients are at risk of regurgitation and inhaling (aspirating) their stomach contents.
The aim of fasting is to minimize the risk of aspiration. However the anaesthetist should also consider patient comfort in the preoperative period and minimise any potential significant physiological changes that may occur from prolonged fasting.
As gastric secretion is continuous at 6 ml/kg/h and 1 ml/kg/h of saliva is swallowed, the stomach is never truly empty. Oral intake, gastric secretions and gastric emptying determine the residual gastric volume and pH. The residual gastric volume and speed at which the stomach empties will change with diseases, emotion, pain, hunger and gastric content.
The top 3 risk factors for aspiration are emergency surgery, light anaesthesia/unexpected response to stimulation and upper/lower gastrointestinal pathology.
Current generally accepted fasting intervals for elective uncomplicated cases are 2 hours for water and clear fluids, 4 hours for breast milk and 6 hours for solids (2, 4 and 6). “Nil by mouth” from midnight is not good anaesthetic practice.
SELF-ASSESSMENT QUESTIONS
- Outline the purpose of the preoperative visit.
- List important factors in predicting adverse postoperative morbidity and mortality.
- List in order of importance the essential information that should be found on patient’s old anaesthetic records.
- List drugs, their indications and dosages that may be useful for premedication.
- For which patients would the 2, 4 and 6 hours rules of fasting not apply?
- Which patient’s own medications may complicate anaesthesia?
ASSIGNMENT
Develop an algorithm for the management of a patient having major elective surgery.
{An algorithm is an effective method in which a definite list of well defined instructions for completing a task, when given an initial state, will proceed through a well defined series of successive states, eventually terminating in an end state. In a general sense, an algorithm is any set of instructions that result in a predictable result from a known beginning. Algorithms are only as good as the instructions given, however are an excellent way to process complex information.}
PREOPERATIVE ASSESSMENT CASE STUDIES.
Case 2.1
Tsahim is a 59-year-old male with poorly managed non-insulin dependent diabetes who presented with an infected lesion on his right foot. He has a fever, looks dehydrated and is quite confused. His blood pressure is 180/110. The surgeon insists on taking him straight to the operating theatre.
What further information would you be looking for in this man’s history?
What investigations would you request before agreeing to anaesthetise Tsahim?
Assign an ASA score to Tsahim.
Discuss the implications of delaying his surgery.
How would you assess his diabetic control and how would you manage his diabetes in the peri-operative period?
How will the physiological changes associated with diabetes affect anaesthesia?
What do you think about his blood pressure of 180/110?
Describe the options for premedication.
During the preoperative assessment Tsahim tells you that he has glaucoma and chronic kidney failure. He shows you his diuretic tablet and his eye drops.
Discuss the relevant pharmacology. What interactions between his own medication and anaesthetic agents might occur?
Tsahim’s serum potassium is 6 mEq/l. How will you manage this?
Case 2.2
You have been asked to see Ganbold who is a 56 year old man booked for an elective cholecystectomy. He has a history of rheumatic heart disease.
What further history do you require?
Discuss the relevance of the anticipated findings in your clinical examination.
What are the possible anaesthetic complications associated with his condition?
Describe the options for premedication.
What investigations would you order for this man?
His haemoglobin result is 70g/l. Discuss your proposed management.
Case 2.3
Badral is a 48-year-old man who is scheduled to have knee surgery. He is a heavy smoker with a history of hypertension. He was admitted to the hospital with a myocardial infarction 2 years ago and now reports occasional episodes of chest pain and shortness of breath associated with mild exertion and relieved by sublingual GTN. His exercise tolerance is limited due to his painful knee. His preoperative blood pressure is 160/105 and his heart rate is 98 beats/minute and there is an audible expiratory wheeze. Badral’s mother and father died in their 50’s. He doesn’t know what from. His brother had an anaesthetic and he took a long time to wake up.
Outline you main anaesthetic concerns.