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Dynamic preoperative assessment of cardiac reserve in elective aortic surgery
Insights
Predicting cardiac complications after abdominal aortic surgery is crucial. A myocardial performance curve using pulmonary artery wedge pressure (PAWP) effectively identifies high-risk patients, preventing complications like myocardial infarction and pulmonary edema.
Area of Science:
- Cardiovascular Surgery
- Critical Care Medicine
- Anesthesiology
Background:
- Myocardial infarction is a major cause of mortality after abdominal aortic surgery.
- Traditional predictors like ECGs and patient history are often unreliable in vascular patients.
- Claudication can mask underlying myocardial insufficiency during stress tests.
Purpose of the Study:
- To evaluate the utility of a myocardial performance curve in identifying patients at risk of cardiac complications.
- To establish safe intravenous fluid management limits during surgery.
Main Methods:
- Preoperative assessment of 29 patients undergoing elective aortic bifurcation grafting.
- Utilized a Swann-Ganz catheter to measure pulmonary artery wedge pressure (PAWP) during fluid infusion.
- Constructed Frank-Starling curves by plotting left ventricular stroke work index (LVSWI) against PAWP.
Main Results:
- 'Upslope' values significantly differed between patients with (1.568 ± 0.681) and without (7.094 ± 0.745) postoperative cardiac complications (P < 0.001).
- Pulmonary artery wedge pressure maximum (PAWPmax) identified the threshold beyond which cardiac work output decreased.
- All 6 patients experiencing pulmonary edema or myocardial infarction had PAWP exceeding their individual PAWPmax.
Conclusions:
- The myocardial performance curve is a reliable method for identifying high-risk patients undergoing aortic surgery.
- Individualized control of intravenous therapy based on PAWPmax can prevent adverse cardiac events and pulmonary edema.
- This approach enhances perioperative safety in patients with potential cardiac compromise.
Abstract:
Myocardial infarction accounts for over 50 per cent of mortality following elective abdominal aortic surgery. Previous history of ischaemic heart disease and abnormal ECGs, common in vascular patients, are unreliable parameters for predicting myocardial response to stress. Exercise ECGs are often valueless, as claudication may mask myocardial insufficiency. Myocardial performance was studied preoperatively in 29 consecutive patients undergoing elective aortic bifurcation grafting, using a Swann-Ganz catheter to measure the rise in pulmonary artery wedge pressure (PAWP) produced by rapid intravenous infusion of plasma (200-400 ml). A Frank-Starling Curve was obtained by plotting LVSWI against PAWP. Two important values were obtained: (a) 'Upslope' or gradient of the ascending portion of the curve. Low values identify patients most at risk from cardiac complications. Six patients who suffered from postoperative cardiac complications had a mean 'upslope' value of 1.568 +/- 0.681 (1 s.e.m.), whereas the 23 who did not, had a mean value of 7.094 +/- 0.745 (1 s.e.m.), a significant difference (P less than 0.001); (b) 'PAWPmax', the ventricular filling pressure above which work output dropped. Infusion beyond this may precipitate pulmonary oedema. PAWP was observed at levels greater than PAWPmax in all 6 patients who developed either pulmonary oedema or myocardial infarction. The myocardial performance curve can reliably identify high risk patients and permit control of intravenous therapy within individual safety limits, thereby preventing pulmonary oedema.