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Risk assessment
PREOPERATIVE ASSESSMENT
Risk assessment
Cost versus benefit There are arguably only two indications for surgery—improvement of symptoms (quality of life) and improvement of prognosis (quantity of life). The likelihood of achieving a meaningful improvement in symptoms or prognosis (‘the benefit’) must be balanced against the risks of death or an outcome that results in a reduced quality of life (‘the cost’, Figure 1); this assessment must be made by the surgeon and the patient.
Joseph E Arrowsmith Iain Mackenzie
Is surgery indicated? Virtually every aspect of our lives is governed by the assessment of risk, from the premium we pay for motor insurance, to judging when it is safe to cross the road. Many decisions can be made purely on the basis of collective learning and personal experience, while others require an evidence base and risk assessment tools. Risk assessment forms an integral part of patient care in all branches of medicine. Clinicians must understand the risks and benefits of diagnostic tests, expectant management and therapeutic interventions and be able to convey them to patients in an understandable way. An appreciation of risk can guide many aspects of perioperative care, including choice of surgical procedure, physiological monitoring and the need for intensive care.
The assessment from the surgical perspective (if this occurs explicitly) is often made in consultation with a multidisciplinary team (particularly in cases involving malignancy or transplantation) and is usually based on issues of prognosis in relation to treatment method, but may occasionally consider issues related to symptom control (palliation). This exercise has been assisted by the analysis of objective outcomes (e.g. postoperative survival, complications) in the context of preoperative factors (Figure 2), and has allowed the development of a number of predictive tools (Figure 3) which are typically validated in prospective studies using new populations of patients. In clinical use, these tools have a significant potential for misinterpretation or misuse. • Having been calibrated against specific endpoints, they are valid only at estimating the risk of the same endpoints, rather than adverse outcomes in general. • These tools are valid in assessing only the outcome of groups of patients, not individual patients. • They cannot account for the influence of other significant factors present in individual patients that were not included in the original tool.
Joseph E Arrowsmith is a Consultant in Cardiothoracic Anaesthesia and Intensive Care at Papworth Hospital NHS Trust, Cambridge, UK. Iain Mackenzie is a Consultant in Intensive Care and Anaesthesia at Addenbrooke’s Hospital, Cambridge, UK.
Cost versus benefit
Reason for surgery (benefit)
Possible outcome (cost) Death
Increased quantity of life (longevity)
Cataract extraction in octogenarian Progressive deterioration in quality of life
Risk of death
All outcomes
Risk of death or no improvement in quality of life
Coronary artery bypass grafting in an 80-year-old
Current quality of life Increased quality of life
Quality of life improved Quality of life significantly improved
Appendicectomy in 24-year-old
Elective repair of abdominal aortic aneurysm
Emergency repair of abdominal aortic aneurysm
1
SURGERY 23:12
442
© 2005 The Medicine Publishing Company Ltd
PREOPERATIVE ASSESSMENT
their own inherent risks and few have 100% sensitivity and 100% specificity; what are the chances that a woman with a ‘positive’ mammogram has breast cancer?
Generic basis of risk assessment models Patient Disease Comorbidities
Surgery
Physiology
Age, sex, body mass index, functional status Severity, previous interventions, established complications Cardiac, respiratory, renal, hepatic, neurological, endocrine, metabolic, haematological, pregnancy, preterm birth Elective vs emergency, open vs closed, surface vs intracavitary, radical vs conservative, single-stage vs multi-stage Temperature, blood gases, haematocrit, leukocyte count, urine output, conscious level, blood pressure, coagulation status
Do I want surgery? The patient must decide if the intervention is worthwhile, and this decision is based on a separate cost/benefit analysis which considers objective (what is the risk that I will not survive the intervention?) and subjective (quality of life) information on outcome. There are three prerequisites for a clinician to successfully convey this information to a patient. The clinician must: • have accurate information about the risk of objective and subjective outcomes • understand the information • be able to convey the information in a way that can be understood and retained by the patient. This second analysis is often deeply flawed because the patient is presented with information relating only to objective outcomes, with little or no other information. Thus, the risk of death with an intervention may be acceptably low (or the risk of death without the intervention high), but the risk of an irreversibly worsened quality of life (e.g. loss of independence, mental faculties, continence, eyesight) may be unacceptable for a patient, and would lead him to decline surgery if he understood the risks. One of the most significant reasons for this bias in the information provided to patients is the paucity of quality-of-life outcome data. Another common problem for patients (and clinicians!) is the inappropriate use of statistical or conditional probabilities (Figure 4).1 Similarly, potentially ambiguous terms such as ‘common’ or ‘rare’ should not be used without explanation (Figure 5).
2
Risk assessment tools in common use Non-cardiac surgery
Goldman Cardiac Risk Index Detsky (Modified) Cardiac Risk Index Cardiac surgery Parsonnet Score EuroSCORE General surgery POSSUM Trauma Injury severity score (ISS) Revised trauma score (RTS) Postoperative intensive APACHE I, II, III care Multiorgan Dysfunction Score (MODS)
Understanding statistical data Conditional probabilities ‘The incidence of breast cancer in women is 0.8%. There is a 90% probability that a woman with breast cancer will have a positive mammogram. There is a 7% chance that a woman who does not have breast cancer will have a positive mammogram. What is the probability that a woman with a positive mammogram actually has breast cancer?’
EuroSCORE: European system for cardiac operative risk evaluation; POSSUM: Physiologic operative severity score for enumeration of mortality and morbidity; APACHE: Acute physiology and chronic health evaluation.
3
Whether implicit or explicit, a full assessment of the cost/benefit balance allows the surgeon to know whether a proposed intervention is indicated, and should be offered to the patient. In the UK, clinicians are not obliged to provide treatment that is deemed futile. In a small number of conditions (e.g. acute dissection of the ascending aorta, where the cumulative mortality rises by 1% for every hour of conservative management), the benefits of prompt surgery far outweigh the risks. Similarly, the risks associated with cataract extraction, even in the frailest octogenarian, are almost always outweighed by the benefits of sight restoration. Decision-making is rarely this straightforward in practice. Which type of surgery should a patient with symptomatic triple-vessel coronary disease and potentially curable bowel cancer have first —coronary bypass or colectomy? When should a young patient with asymptomatic aortic regurgitation undergo valve replacement, and which type of valve should be used? Furthermore, many investigations and diagnostic tests (e.g. coronary angiography) have
SURGERY 23:12
Natural frequency ‘Of a thousand women, eight have breast cancer. Of these eight women, seven will have a positive mammogram. Of the remaining 992 women who don’t have breast cancer, about 70 will still have a positive mammogram. Of all of the women who had a positive mammogram, how many actually have breast cancer?’ When presented with the same basic data about mammography, physicians given the information as natural frequencies were much more likely to arrive at the correct answer: 9%. A phenomenon termed ‘medical innumeracy’. Source: Gigerenzer (see REFERENCE). 4
443
© 2005 The Medicine Publishing Company Ltd
PREOPERATIVE ASSESSMENT
Preoperative assessment of the surgical patient
Correlation between terms often used to describe the chances of an event and incidence 1:10
Likelihood of nausea and vomiting after routine surgery
1:100
Risk of death following elective coronary artery surgery
1:1,400
Risk of dying in a house fire (in the UK)
1:10,000
Risk of gastric perforation during endoscopic biopsy
1:100,000
Risk of hepatitis C after blood transfusion
1:1,000,000
Additional lifetime risk of cancer per chest radiograph
1:6,500,000
Risk of dying from a lightning strike
1:10,068,347,520
Chances of winning UK lottery (choosing 6 numbers from 49)
Where 1:10 1:100 1:1000 1:10,000 1:100,000
Joseph E Arrowsmith Iain Mackenzie
Consecutive publications by the UK National Confidential Enquiry into Perioperative Deaths (NCEPOD) have cited inadequate preoperative preparation, inappropriate intraoperative monitoring and poor postoperative care as contributing to perioperative mortality. Preoperative assessment is used to decide if a patient can withstand the physiological stresses of anaesthesia and surgery. Furthermore, an evaluation of potential interactions between concurrent diseases, surgery and anaesthesia offers an opportunity to improve physical condition before surgery, select appropriate perioperative care, and modify outcome.
very common common uncommon rare very rare
Case note review Preoperative assessment involves taking a careful history, carrying out a thorough physical examination, ordering appropriate investigations and carefully documenting the findings. Part of this process may have been undertaken in the Outpatient or Preadmission Clinic, but the temptation to dispense with an unnecessarily repetitive assessment immediately before surgery must be resisted. Moreover, it should not be assumed that preoperative assessment is the sole responsibility of the anaesthetist. At the very least, the medical record should be reviewed (Figure 1) and a brief interview and physical examination done. Risk factors associated with increased perioperative mortality and morbidity should be sought (Figure 2). Records of previous surgery and anaesthesia should be scrutinized for evidence of adverse events or difficulties in airway management. In addition to anti-anginal, antihypertensive, diuretic and antiplatelet drugs, it is not unusual to find that patients are taking oral hypoglycaemics, histamine antagonists, proton pump inhibitors, bronchodilators, corticosteroids or psychotropic drugs. The use of these drugs may indicate other disease and must be considered when prescribing premedication. Discovering if the patient has recently been exposed to drugs that interfere with coagulation (e.g. aspirin, NSAIDs, clopidogrel, glycoprotein IIb/ IIIa antagonists, thrombolytics, heparin, warfarin), as well as the interval since cessation, is important.
5
In the wake of a number of high-profile cases where patients and relatives where given misleading information on which to base their decision to decline or undergo treatment, it is apparent that patients must be informed about the risk they actually face rather than being quoted results obtained at other centres (national or international). Similarly, surgeons should also quote their own results if a risk model is used. u
REFERENCE 1 Gigerenzer G. Reckoning with risk: learning to live with uncertainty. London: Penguin, 2002. CROSS REFERENCES Celinski M, Jonas M. Scoring systems in the ICU. Surgery 2004: 22(4): 94–7. Falter F, Martinelli G. Perioperative care of the patient with cardiovascular disease undergoing non-cardiac surgery Surgery 2005; 23(7): 246–50. Waller J R, Kendall S W H. Preoperative investigation in adult cardiac surgery. Surgery 2004: 22(6): 123–5.
SURGERY 23:12
Joseph E Arrowsmith is a Consultant in Cardiothoracic Anaesthesia and Intensive Care at Papworth Hospital NHS Trust, Cambridge, UK. Iain Mackenzie is a Consultant in Intensive Care and Anaesthesia at Addenbrooke’s Hospital, Cambridge, UK.
444
© 2005 The Medicine Publishing Company Ltd
Risk assessment
Cost versus benefit There are arguably only two indications for surgery—improvement of symptoms (quality of life) and improvement of prognosis (quantity of life). The likelihood of achieving a meaningful improvement in symptoms or prognosis (‘the benefit’) must be balanced against the risks of death or an outcome that results in a reduced quality of life (‘the cost’, Figure 1); this assessment must be made by the surgeon and the patient.
Joseph E Arrowsmith Iain Mackenzie
Is surgery indicated? Virtually every aspect of our lives is governed by the assessment of risk, from the premium we pay for motor insurance, to judging when it is safe to cross the road. Many decisions can be made purely on the basis of collective learning and personal experience, while others require an evidence base and risk assessment tools. Risk assessment forms an integral part of patient care in all branches of medicine. Clinicians must understand the risks and benefits of diagnostic tests, expectant management and therapeutic interventions and be able to convey them to patients in an understandable way. An appreciation of risk can guide many aspects of perioperative care, including choice of surgical procedure, physiological monitoring and the need for intensive care.
The assessment from the surgical perspective (if this occurs explicitly) is often made in consultation with a multidisciplinary team (particularly in cases involving malignancy or transplantation) and is usually based on issues of prognosis in relation to treatment method, but may occasionally consider issues related to symptom control (palliation). This exercise has been assisted by the analysis of objective outcomes (e.g. postoperative survival, complications) in the context of preoperative factors (Figure 2), and has allowed the development of a number of predictive tools (Figure 3) which are typically validated in prospective studies using new populations of patients. In clinical use, these tools have a significant potential for misinterpretation or misuse. • Having been calibrated against specific endpoints, they are valid only at estimating the risk of the same endpoints, rather than adverse outcomes in general. • These tools are valid in assessing only the outcome of groups of patients, not individual patients. • They cannot account for the influence of other significant factors present in individual patients that were not included in the original tool.
Joseph E Arrowsmith is a Consultant in Cardiothoracic Anaesthesia and Intensive Care at Papworth Hospital NHS Trust, Cambridge, UK. Iain Mackenzie is a Consultant in Intensive Care and Anaesthesia at Addenbrooke’s Hospital, Cambridge, UK.
Cost versus benefit
Reason for surgery (benefit)
Possible outcome (cost) Death
Increased quantity of life (longevity)
Cataract extraction in octogenarian Progressive deterioration in quality of life
Risk of death
All outcomes
Risk of death or no improvement in quality of life
Coronary artery bypass grafting in an 80-year-old
Current quality of life Increased quality of life
Quality of life improved Quality of life significantly improved
Appendicectomy in 24-year-old
Elective repair of abdominal aortic aneurysm
Emergency repair of abdominal aortic aneurysm
1
SURGERY 23:12
442
© 2005 The Medicine Publishing Company Ltd
PREOPERATIVE ASSESSMENT
their own inherent risks and few have 100% sensitivity and 100% specificity; what are the chances that a woman with a ‘positive’ mammogram has breast cancer?
Generic basis of risk assessment models Patient Disease Comorbidities
Surgery
Physiology
Age, sex, body mass index, functional status Severity, previous interventions, established complications Cardiac, respiratory, renal, hepatic, neurological, endocrine, metabolic, haematological, pregnancy, preterm birth Elective vs emergency, open vs closed, surface vs intracavitary, radical vs conservative, single-stage vs multi-stage Temperature, blood gases, haematocrit, leukocyte count, urine output, conscious level, blood pressure, coagulation status
Do I want surgery? The patient must decide if the intervention is worthwhile, and this decision is based on a separate cost/benefit analysis which considers objective (what is the risk that I will not survive the intervention?) and subjective (quality of life) information on outcome. There are three prerequisites for a clinician to successfully convey this information to a patient. The clinician must: • have accurate information about the risk of objective and subjective outcomes • understand the information • be able to convey the information in a way that can be understood and retained by the patient. This second analysis is often deeply flawed because the patient is presented with information relating only to objective outcomes, with little or no other information. Thus, the risk of death with an intervention may be acceptably low (or the risk of death without the intervention high), but the risk of an irreversibly worsened quality of life (e.g. loss of independence, mental faculties, continence, eyesight) may be unacceptable for a patient, and would lead him to decline surgery if he understood the risks. One of the most significant reasons for this bias in the information provided to patients is the paucity of quality-of-life outcome data. Another common problem for patients (and clinicians!) is the inappropriate use of statistical or conditional probabilities (Figure 4).1 Similarly, potentially ambiguous terms such as ‘common’ or ‘rare’ should not be used without explanation (Figure 5).
2
Risk assessment tools in common use Non-cardiac surgery
Goldman Cardiac Risk Index Detsky (Modified) Cardiac Risk Index Cardiac surgery Parsonnet Score EuroSCORE General surgery POSSUM Trauma Injury severity score (ISS) Revised trauma score (RTS) Postoperative intensive APACHE I, II, III care Multiorgan Dysfunction Score (MODS)
Understanding statistical data Conditional probabilities ‘The incidence of breast cancer in women is 0.8%. There is a 90% probability that a woman with breast cancer will have a positive mammogram. There is a 7% chance that a woman who does not have breast cancer will have a positive mammogram. What is the probability that a woman with a positive mammogram actually has breast cancer?’
EuroSCORE: European system for cardiac operative risk evaluation; POSSUM: Physiologic operative severity score for enumeration of mortality and morbidity; APACHE: Acute physiology and chronic health evaluation.
3
Whether implicit or explicit, a full assessment of the cost/benefit balance allows the surgeon to know whether a proposed intervention is indicated, and should be offered to the patient. In the UK, clinicians are not obliged to provide treatment that is deemed futile. In a small number of conditions (e.g. acute dissection of the ascending aorta, where the cumulative mortality rises by 1% for every hour of conservative management), the benefits of prompt surgery far outweigh the risks. Similarly, the risks associated with cataract extraction, even in the frailest octogenarian, are almost always outweighed by the benefits of sight restoration. Decision-making is rarely this straightforward in practice. Which type of surgery should a patient with symptomatic triple-vessel coronary disease and potentially curable bowel cancer have first —coronary bypass or colectomy? When should a young patient with asymptomatic aortic regurgitation undergo valve replacement, and which type of valve should be used? Furthermore, many investigations and diagnostic tests (e.g. coronary angiography) have
SURGERY 23:12
Natural frequency ‘Of a thousand women, eight have breast cancer. Of these eight women, seven will have a positive mammogram. Of the remaining 992 women who don’t have breast cancer, about 70 will still have a positive mammogram. Of all of the women who had a positive mammogram, how many actually have breast cancer?’ When presented with the same basic data about mammography, physicians given the information as natural frequencies were much more likely to arrive at the correct answer: 9%. A phenomenon termed ‘medical innumeracy’. Source: Gigerenzer (see REFERENCE). 4
443
© 2005 The Medicine Publishing Company Ltd
PREOPERATIVE ASSESSMENT
Preoperative assessment of the surgical patient
Correlation between terms often used to describe the chances of an event and incidence 1:10
Likelihood of nausea and vomiting after routine surgery
1:100
Risk of death following elective coronary artery surgery
1:1,400
Risk of dying in a house fire (in the UK)
1:10,000
Risk of gastric perforation during endoscopic biopsy
1:100,000
Risk of hepatitis C after blood transfusion
1:1,000,000
Additional lifetime risk of cancer per chest radiograph
1:6,500,000
Risk of dying from a lightning strike
1:10,068,347,520
Chances of winning UK lottery (choosing 6 numbers from 49)
Where 1:10 1:100 1:1000 1:10,000 1:100,000
Joseph E Arrowsmith Iain Mackenzie
Consecutive publications by the UK National Confidential Enquiry into Perioperative Deaths (NCEPOD) have cited inadequate preoperative preparation, inappropriate intraoperative monitoring and poor postoperative care as contributing to perioperative mortality. Preoperative assessment is used to decide if a patient can withstand the physiological stresses of anaesthesia and surgery. Furthermore, an evaluation of potential interactions between concurrent diseases, surgery and anaesthesia offers an opportunity to improve physical condition before surgery, select appropriate perioperative care, and modify outcome.
very common common uncommon rare very rare
Case note review Preoperative assessment involves taking a careful history, carrying out a thorough physical examination, ordering appropriate investigations and carefully documenting the findings. Part of this process may have been undertaken in the Outpatient or Preadmission Clinic, but the temptation to dispense with an unnecessarily repetitive assessment immediately before surgery must be resisted. Moreover, it should not be assumed that preoperative assessment is the sole responsibility of the anaesthetist. At the very least, the medical record should be reviewed (Figure 1) and a brief interview and physical examination done. Risk factors associated with increased perioperative mortality and morbidity should be sought (Figure 2). Records of previous surgery and anaesthesia should be scrutinized for evidence of adverse events or difficulties in airway management. In addition to anti-anginal, antihypertensive, diuretic and antiplatelet drugs, it is not unusual to find that patients are taking oral hypoglycaemics, histamine antagonists, proton pump inhibitors, bronchodilators, corticosteroids or psychotropic drugs. The use of these drugs may indicate other disease and must be considered when prescribing premedication. Discovering if the patient has recently been exposed to drugs that interfere with coagulation (e.g. aspirin, NSAIDs, clopidogrel, glycoprotein IIb/ IIIa antagonists, thrombolytics, heparin, warfarin), as well as the interval since cessation, is important.
5
In the wake of a number of high-profile cases where patients and relatives where given misleading information on which to base their decision to decline or undergo treatment, it is apparent that patients must be informed about the risk they actually face rather than being quoted results obtained at other centres (national or international). Similarly, surgeons should also quote their own results if a risk model is used. u
REFERENCE 1 Gigerenzer G. Reckoning with risk: learning to live with uncertainty. London: Penguin, 2002. CROSS REFERENCES Celinski M, Jonas M. Scoring systems in the ICU. Surgery 2004: 22(4): 94–7. Falter F, Martinelli G. Perioperative care of the patient with cardiovascular disease undergoing non-cardiac surgery Surgery 2005; 23(7): 246–50. Waller J R, Kendall S W H. Preoperative investigation in adult cardiac surgery. Surgery 2004: 22(6): 123–5.
SURGERY 23:12
Joseph E Arrowsmith is a Consultant in Cardiothoracic Anaesthesia and Intensive Care at Papworth Hospital NHS Trust, Cambridge, UK. Iain Mackenzie is a Consultant in Intensive Care and Anaesthesia at Addenbrooke’s Hospital, Cambridge, UK.
444
© 2005 The Medicine Publishing Company Ltd