Core Topics in General & Emergency Surgery: Companion to Specialist Surgical Practice (75 page)
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Authors: Simon Paterson-Brown MBBS MPhil MS FRCS
There is emerging evidence that estimation of serum concentration of biomarkers in the preoperative period may assist risk stratification for patients undergoing surgery. Brain natriuretic peptide (BNP) and C-reactive protein (CRP) are the most promising biomarkers for risk assessment. BNP is released from cardiac ventricles in response to excessive stretching and elevated serum concentrations are correlated with prognosis in heart failure.
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Elevated preoperative serum concentration of BNP (> 40 pg/mL) was associated with an increased risk of death and perioperative cardiac events in a study of 204 patients undergoing non-cardiac surgery.
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A further study of 190 patients undergoing elective non-cardiac surgery also identified elevated serum NT-proBNP (a co-secretory product of BNP) as a predictor of postoperative cardiac complications, which was independently prognostic on multivariate analysis.
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A recent meta-analysis examined the predictive value of preoperative serum BNP concentrations for predicting postoperative mortality and cardiac complications following vascular surgery.
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The authors concluded that elevated BNP concentrations were predictive of adverse outcome, but there was wide variation in the serum concentration of BNP that was chosen as the threshold for discrimination (range 35–100 pg/mL). The optimal discriminatory concentration remains unknown and it is likely that threshold values may vary depending on the patient group under investigation.
CRP is a marker of systemic inflammation and serum concentrations are associated with atherosclerotic disease and adverse outcomes in cancer. A preoperative serum CRP concentration greater than 6.5 mg/L was associated with increased 30-day mortality and postoperative cardiac complication rates in a study involving 592 patients undergoing vascular surgery (odds ratio 2.5; 95% confidence interval 1.5–4.3).
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Moreover, this association was independent of serum BNP concentration and also established cardiac risk factors. The association between elevated CRP concentration and adverse perioperative outcome may be due, in part, to a correlation between markers of systemic inflammation and exercise capacity. Elevated serum CRP concentrations have been demonstrated to be inversely correlated with VO
2
max in male subjects without evidence of coronary heart disease.
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Further study is required to determine the true value of serum biomarkers in risk assessment for surgical patients.
Brain natriuretic peptide (BNP) and C-reactive protein (CRP) are the most promising biomarkers for risk assessment. Elevated preoperative serum concentrations have been associated with increased risk of mortality and cardiac complications in surgical patients; however, the optimal threshold cut-off value remains unknown. The real value of serum biomarkers may lie in the selection of patients into high- or low-risk groups and therefore help identify which patients merit further assessment.
The use of risk prediction models, scoring systems, exercise tests and serum biomarkers as adjuncts to decision-making is an increasingly important part of surgical practice. This information must then be communicated effectively to the patient to allow fully informed choice. GMC guidance on this issue states that:
Clear, accurate information about the risks of any proposed investigation or treatment, presented in a way patients can understand, can help them make informed decisions. The amount of information about risk that the clinician should share with patients will depend on the individual patient and what they want, or need, to know. Discussions with patients should therefore focus on their individual situation and the risk to them.
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In communicating risk there are several techniques to impart the concept of how likely it is that the patient will have a complication of the procedure, or die as a result of it. These broadly fall into using numerical data or descriptive details of risk. As always, this communication must be tailored to the needs and expectations of the individual patient and it is likely that a combination of these techniques will be most appropriate.
Percentages alone are often not well understood, and as they apply to a population rather than an individual patient, they may be misleading. Odds, relative risk and absolute risk may be too complex, but quoting for example ‘a 1 in 10 or 1 in 100 chance’ may be helpful. Using relativity (comparison with a concept the patient understands) or examples (‘of the last 50 patients this has happened to …’) may also clarify the concept of surgical risk to the patient.
Finally, it is worth remembering that the perceived surgical risk that concerns the surgeon is not necessarily what the patient is worried about. Assessing, discussing and communicating risk has the primary aim of allowing patients to understand what may happen to them, and to help them make an informed choice about investigation or therapeutic options. However, as a consequence of this, coupled with careful documentation, it affords the surgeon some protection against litigation.
Key points
Estimation of surgical risk is vital to enhance treatment decision-making and facilitate informed consent, anticipate potential complications and target aspects of care to optimise the patient, and allow meaningful comparison of clinical outcomes, audit and quality assurance.
Determination of surgical risk is complex, but may be more simply considered in terms of
patient-related
risks and
procedural-related
risks.
Patient-related risk factors will be influenced by patient age, comorbidity, the underlying disease process, nutritional status and the performance status of the patient.
Procedural-related risk factors include the grade of severity of the procedure planned, urgency of the procedure, volume of blood loss and other technical aspects.
Risk prediction models and scoring systems (such as POSSUM, ASA and the Revised Cardiac Risk Index) have been developed in an attempt to improve risk prediction. These tools work best for patient populations (groups) rather than individual patients, and therefore their main value is for audit purposes and comparing outcomes between different units and within the same units over time. There is no perfect risk prediction model.
Assessment of functional capacity may be easily undertaken through the use of simple screening questions. More objective measurements may be performed by using standardised walking tests or CPEX testing.
Serum biomarkers, such as BNP and CRP, may have a future role in identifying high-risk surgical patient groups, who may then benefit from more detailed assessment.
Estimation of surgical risk should include a thorough clinical assessment, an assessment of the functional capacity of the patient (through simple questions relating to METs) and should take into account the severity of the surgical procedure proposed. If this process identifies the patient to be at high risk, then further testing should be considered – for example, objective exercise testing (CPEX).
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