1.2: PREOPERATIVE INVESTIGATIONS
- Page ID
- 56783
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)As the prevalence of unrecognized disease in healthy individuals is low, routine investigations are not warranted. Additionally, in determining reference ranges for diagnostic tests, values that are outside the 95% confidence range for normal individuals are considered abnormal. Therefore, up to 5% of normal individuals can have “abnormal”results. Preoperative investigations should be safe, cost effective and likely to change perioperative management. Anaesthesia providers should practice selective preoperative testing based on the patient’s history and examination, the invasiveness of the anaesthetic technique and surgery, and knowledge of local high prevalence diseases.
Haemoglobin:
Indicated for patients older than 65 years of age having major surgery, all surgery withexpected significant blood loss or patients with suspected anaemia.
Platelets
Indicated for patients with haematological or liver disease, known or suspected plateletdysfunction or planned neuraxial anaesthesia.
Renal function test :
Mild to moderate renal impairment is usually asymptomatic. Renal impairment increasesperioperative morbidity/mortality and may necessitate drug dosage adjustments.Indicated for patients older than 50 years of age with intermediate to high-risk surgery,known or suspected renal disease or medicaons that affect renal function.
Electrocardiogram:
Indicated for patients with known or suspected cardiovascular disease or in high-risk surgeryas a preoperative baseline.
Blood glucose:
Indicated for patients with diabetes, steroid treatment and glycosuria.
Chest X-ray:
Indicated for patients with known or suspected respiratory/cardiac disease, heavy smokingor TB exposure.
Liver function tests:
Indicated for patients with known or suspected 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 havesurgery.
APPT and INR.
Indicated for patients with known or suspected coagulation abnormalities or receiving anticoagulant therapy.
Blood type, screen and crossmatch
Preoperative anaemia is common and often previously undiagnosed. Common causes inolder patients include iron deficiency, Vitamin B12 or folate deficiency, anaemia of chronic disease and chronic kidney disease. Both preoperative anaemia and allogeneic bloodtransfusion are independent preventable risk factors for poor postoperative outcomes. Patient Blood Management (PMB) is a clinical concept that focuses on optimizing red cellmass and erythropoiesis preoperatively, minimizing intraoperative blood loss and improving patient’s tolerance of anaemia postoperatively. Ideally patients undergoing elective surgerywith a high risk of severe postoperative anaemia should have their haemoglobin concentration and iron status tested at least 30 days before surgery.
Patients with or at risk of iron defficiency anaemia or with suboptimal iron stores (as definedby a ferritin level < 100 μg/L) in whom substantial blood loss is anticipated should be treatedwith preoperative iron therapy. Blood transfusions should be reserved for patients at risk ofcardiovascular instability due to the degree of their anaemia. In patients with anaemia ofchronic disease erythropoiesis-stimulating agents may be indicated.
Patients managed with anticoagulants require a multi disciplinary approach to decidewhether to cease therapy, organise bridging anticoagulation or defer surgery. Specific evaluation is required for patients who have received a drug-eluting cardiac stent within thelast 12 months, or a bare metal stent within the last 6 weeks or who have had a recentstroke.
Recommended intraoperative blood conservation strategies include minimally invasivesurgical techniques, meticulous haemostasis, regional anaesthesia, prevention ofhypothermia and acidosis, appropriate patient positioning, acute normovolaemichaemodilution, and intraoperative cell salvage and haemostasis analysis. Tranexamic acid isrecommended for patients undergoing surgery where anticipated blood loss is great enoughto cause anaemia that would require treatment.T
he decision to transfuse red blood cells should be based on both the haemoglobin level and the patient’s clinical status. Patients should not receive a transfusion if theirhaemoglobin level is > 100 g/L. Postoperative transfusion may be inappropriate for patientswith a haemoglobin level > 80 g/L, in the absence of acute myocardial or cerebral ischaemiaFor postoperative patients with acute myocardial or cerebral ischaemia and a haemoglobinlevel between 70-100 g/L, transfusion of a single unit of red blood cells, followed byreassessment of the patient’s status, is appropriate.