Lecture 14 - Anesthetic Risk Assessment Flashcards
American Society of Anesthesiologist (ASA)risk classification
I: NHP
Lee revised cardiac risk index
6 point score
- High risk surgical procedure
- History of IHD
- History of CCF
- History of cerebrovascular disease
- Insulin-dependent diabetes mellitus
- Chronic renal failure
Risk of major cardiac complication
- 0pt: 0.4%
- 1pt: 0.9%
- 2 pt: 7%
- 3+ pt: 11%
Surgical factors
- different operations have different mortality rates
- emergency operations have higher mortality rates
High risk surgical procedures : >5%
- major emergency procedures
- aortic/major vascular surgery
- prolonged surgery with large fluid shifts/blood loss
- peripheral vascular surgery
Intermediate risk
- intraperitoneal surgery
- intrathoracic surgery
- head and neck surgery
- major orthopedic surgery
- prostate surgery
Low risk surgical procedures
- endoscopic procedures
- superficial procedures
- cataract surgery
- breast surgery
Patient factors
- Age: higher number of concurrent disease, decline of physiological reserve, increased morbidity and mortality
- existing co-morbidity: cardiovascular, respiratory, neurological
- exercise tolerance
- medication
Patient factors: cardiovascular disease
- approximately 75% of patients who suffer perioperative death have cardiovascular disease
- conditions that are high odds ratio for cardiovascular death within 30 days of operation are: Previous MI, Angina, Hypertension, renal failure, cardiac failre
Myocardial injury after non-cardiac surgery
- myocardial ischeamia during or within 30 days after non-cardiac surgery
- incidence 8%
- 10% risk of death within 30 days
- 84% of patients with myocardial injury are asymptomatic - no chest pain or shortness of breath
How to assess cardiac risk
- static testing: electrocardiography, transthoracic echocardiography, transoesophageal echocardiography, cardiac catherisation
- Dynamic testing: exercise tolerance, exercise ECG, dobutamine stress echo, dipyridimole stress echo, cardiopulmonary exercise testing
Pre-operative functional assessment
- 1 MET = 3.5 ml O2/kg/min
- 1 MET - eating and dressing
- 4 MET = climbing 2 flights of stairs
- > 10 MET: able to participate in strenuous sport
Exercise tolerance and risk
- if
Cardiopulmonary exercise testing
- examines the ability of the CVS to deliver oxygen to tissues under stress
- if a patient is unable to elevate oxygen delivery to the required levels they are more likely to have a poor outcome
- myochardial ischeamia in absence of heart failure has little effect on outcome
- its an objective test to determine pre-operative fitness
- ## corelates well with post-operative survival
Parameters measured in cardiopulmonary exercise testing
- VO2 - volume of oxygen consumed
- METS - metabolic equivalents
- VCO2: volume of carbon dioxide produced in ml/min
- anaerobic threshold
Anaerobic threshold
- during exercise, when rise in VCO2 becomes disproportionate to rise in VO2
- indicates the level of exercise where body has reached maximal aerobic capacity
- if anerobic threshold >11 ml/min/kg, mortality rate is 0.8%
- if anerobic threshold is
BNP level
- marker of early distension of the right atrium - sign of cardiac failure
Which cardiac conditions worry most
- severe stenotic lesions: flow limitng
- coronary - disease severity and extent
- AS > MS
- severe pulmonary hypertension
Which cardiac conditions are not as worrisome
- regurgitant valvular lesions are rarely a problem perioperatively
- less concerned about CHF or arrythmia in the absence of ischemia
Preoperative non-invasive testing in known or suspected CAD
- rest echocardiography but little insight into CAD
- simple treadmill: exercise capacity
- stress or dobutamine echo
- myocardial perfusion imaging - exercise or dipyridamole
- exercise whenenver possible
Recommendations for coronary angiography in perioperative evaluation
- Class I: patients with suspected or known CAD
- evidence for high risk of adverse outcome based on non-invasive test results
- angina unresponsive to adequate medical therapy
- unstable angina particularly when facing intermediate risk or nigh risk noncardiac surgery
- equivocal non-invadive test results in patients at high clinical risk undergoing high-risk surgery
When is revascularization recommended
- fenerally only when justified by the usual clinical factors, apart from planned non-cardiac surgery
Preoperative therapy with b-blockers
- Class I: when b-blockers have been required in recent past for angina or hypertension. Also for patients undergoing vascular surgery with ischemia on preoperative testing
- Class IIa: when preoperative assessment identifies untreated hypertension, known CAD or major CAD risk factor
- Class IIIL contrainidication to b-blocade
- b-blockers reduce oxygen consumption of the hear
Administering b blockers
- start pre-op : titrate to HR 50-60bpm
- short acting b-blockers provide more flexible dosing
- Give orally if possible, with IV supplementation when patient is NPO
- b-blockers preopertively at least a week befor
Perioperative surveillance
- post operative myocardial ischemia is the strongest predictor of perioperative cardiac morbidity
- for patients with known or suspected CAD, undergoing high or intermiediate risk procedure: check ECG at baseline, immediately after procedure, and daily for 2 days. Also check cardiac troponin measurements 24 hours post op and on day 4, or hospital discharge