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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.54 no.4 Campinas July/Aug. 2004
Silent myocardial ischemia and ventilation in the morbidity obese patient, currently interesting subjects
Two scientific articles studying aspects of anesthesia in these groups of patients are published in this edition.
The relationship between silent myocardial ischemia and anesthetic technique for non-cardiac surgeries in patients at risk and potential predictive markers are relevant issues in our daily practice.
In a study published in this edition, two neuraxial anesthetic techniques - epidural and spinal - have not shown differences in the incidence of silent myocardial ischemia in patients submitted to endoscopic prostate resection, evaluated by Holter 24 hours after surgery. A different result was found in a study monitoring patients submitted to upper abdominal surgeries under general anesthesia, associated or not to epidural anesthesia and postoperative systemic or epidural analgesia. In the group receiving epidural associated to general anesthesia, the incidence of silent myocardial ischemia, both in the intra and postoperative period, has been up to 4 times lower in the first 24 hours1.
Invasive diagnostic methods may be indicated for risk patients scheduled for vascular surgeries or for patients with more than one clinical risk factor. Special care is needed for diabetes mellitus patients due to their high prevalence of silent myocardial ischemia2.
Laito et al., in 2004, have observed that variations in preope- rative heart rate evaluated by Holter in elderly patients awaiting for surgical fractured hip surgery were prognostic for prolonged silent myocardial ischemia (longer than 10 minutes)3.
Silent myocardial ischemia is a relatively common clinical event, yet not totally explained. Evidences suggest that patients at high risk for myocardial ischemia, even in the absence of symptoms, benefit from accurate diagnostic, eventually invasive, investigation and prompt treatment4.
The impact of morbid obesity on respiratory mechanics has been observed in several studies. Primary means to decrease this undesirable change were studied during bariatric surgery and surgical treatment of other problems which may affect this group of patients. The effects of changes in tidal volume, respiratory rate, PEEP, head up position, pneumoperitoneum and abdominal wall opening were evaluated5-7.
In a study published in this edition, ventilation was performed with tidal volume of 8 ml per kg of ideal weight and monitored by SpO2 and PETCO2 with predetermined values, without PEEP during gastroplasty. Tidal volume and/or respiratory rate adjustments guided by PETCO2 and SpO2 have provided adequate results.
Sprung et al.6 have not observed the same results in a comparative study between two ventilation regimens for morbidly obese patients. The impact of PEEP and head up position on cardiac output, evaluated by Perilli et al.8, is partially opposed to the benefit of these ventilation strategies.
Notwithstanding the demonstration that tidal volume calculated as a function of patient's ideal weight is efficient, the discussion about PEEP use and ideal value still remains.
Judymara Lauzi Gozzani, TSA, M.D.
Editor in Chief, Brazilian Journal of Anesthesiology
01. Limberi S, Markou N, Sakayianni K et al - Coronary artery disease and upper abdominal surgery: impact of anesthesia on perioperative myocardial ischemia. Hepatogastroenterology, 2003;50:1814-1820.
02. Sprynger M - Evaluation, severity and prognostic significance of silent myocardial ischaemia in vascular patients. Acta Chir Belg, 2003;103:255-261.
03. Laitio TT, Huikuri HV, Makikallio TH et al - The breakdown of fractal heart rate dynamics predicts prolonged postoperative myocardial ischemia. Anesth Analg, 2004;98: 1239-1244.
04. Almeda FQ, Kason TT, Nathan S et al - Silent myocardial ischemia: concepts and controversies. Am J Med, 2004;116: 112-118.
05. Sprung J, Whalley DG, Falcone T et al - The impact of morbid obesity, pneumoperitoneum, and posture on respiratory system mechanics and oxygenation during laparoscopy. Anesth Analg, 2002;94:1345-1350.
06. Sprung J, Whalley DG, Falcone T et al - The effects of tidal volume and respiratory rate on oxygenation and respiratory mechanics during laparoscopy in morbidly obese patients. Anesth Analg, 2003;97:268-274.
07. Auler Jr JOC , Miyoshi E, Fernandes CR et al - The effects of abdominal opening on respiratory mechanics during general anesthesia in normal and morbidly obese patients: a comparative study. Anesth Analg, 2002;94:741-748.
08. Perilli V, Sollazzi L, Modesti C et al - Comparison of positive end-expiratory pressure with reverse Trendelenburg position in morbidly obese patients undergoing bariatric surgery: effects on hemodynamics and pulmonary gas exchange. Obes Surg, 2003;13:605-609.