Coronary haemo-dynamics and myocardial metabolism during weaning from mechanical ventilation in cardiac surgical patients

Abstract

The present clinical study was undertaken to assess the alterations in myocardial metabolism and coronary" haemodynamics during weaning from mechanical ventilation in postop-cluded reduced preload to the right ventricle, increased right ventricular afterload with a consequent decrease in output to the left heart. 3 Other hypotheses have included a direct mechanical effect of lung inflation on the heart and reflex neural and humoral changes initiated by lung inflation. 4-7 In addition, transmural cardiac pressure changes during mechanical ventilation may influence ventricular volumes, distribution of myocardial blood flow and myocardial oxygen consumption. From the abundance of potential mechanisms it is evident that mechanical ventilation and positive end-expiratory pressure can affect the cardiovascular system in a multifactorial manner. 8 In addition, there have been preliminary animal studies indicating that mechanical ventilation may alter regional myocardial blood flow, and result in changes in ventricular function and haemodynamic performance. 9Patients with coronary artery disease are also at higher risk for myocardial ischaemia, much of which is silent. However, detection of this ischaemia may be clinically difficult. Recent work indicates that the ischaemia, whether silent or symptomatic, may have similar consequences, thus the detection of ischaemia assumes a high priority. ~~ Therefore, the present clinical study was undertaken to assess the alterations in myocardial metabolism, coronary and systemic haemodynamics occurring during weaning from mechanical ventilation in postoperative coronary artery bypass patients, and to determine whether silent ischaemia occurs and what its potential medium may be. Methods PatientsThe study population consisted of 17 patients with previously symptomatic but stable coronary artery disease scheduled to undergo coronary artery bypass surgery. Patients with valvular heart disease, congestive heart failure or unstable angina were excluded from participation in the study. The protocol had been approved by the subcommittee of human studies of the Massachusetts General Hospital and written informed consent was obtained from each patient. The patient data are summarized in Tables I and I1 fasting state and were maintained on their usual medications through to the morning of surgery. Catheterization protocol and coronary blood flow measurementsOn the morning of surgery the patients were taken to the cardiac catheterization laboratory after receiving premedication of morphine O. 1 mg. kg -I , scopolamine 0.3-0.4 mg.kg -~, and lorazepam 2-4 rag., iv. Routine monitors included a two-lead electrocardiogram (I1, Vs), radial arterial, and pulmonary arterial catheters. A precalibrated Baim dual port coronary thermodilution catheter was placed using local I% lidocaine anaesthesia via the right internal jugular vein into the great cardiac vein under fluoroscopic guidance. Angiography confirmed that the distal thermistor was positioned in the great cardiac vein with the proximal ther...

Proposed Entry Criteria for Postoperative Cardiac Extracorporeal Membrane Oxygenation After Pediatric Open Heart Surgery

“…This level of predicted mortality has been used in entry criteria for ECMO in neonates for years (6). The predictive value of lactate level for outcome after cardiac surgery has already been described by several authors (7,8). Central venous oxygen saturation used as an indicator of mixed venous saturation and of cardiac output has been discussed controversially in the literature (9)(10)(11).…”

Reverse iontophoresis: A non-invasive technique for measuring blood lactate level

“…Lactate monitoring has been suggested to be valuable for many patients in emergency medicine: for surgical patients [13][14][15][16], for trauma patients [17], for patients with head injury or cerebral ischemia [18][19][20][21][22], acute intestinal ischemia [23], liver ischemia [24], transplanted organ surveillance, e.g. myocutaneous flaps [25], intrapartum for the foetus [26,27], and patients with septic shock [10,28,29].…”

Simultaneous transdermal extraction of glucose and lactate from human subjects by reverse iontophoresis

“…Therefore, it is possible to predict organ failure from serial lactate measurements (Gersh and Anderson 1993). Lactate monitoring has been suggested as valuable for many patients in emergency medicine: for surgical patients (Elia et al 1991;Hildingsson et al 1996;Carrier et al 1998;Habicht et al 1998), for trauma patients (Slomovitz 1998), for patients with head injury or cerebral ischemia (Valadka 1998;Menzel et al 1999), acute intestinal ischemia (Murray et al 1994), liver ischemia (Rasmussen et al 1994), transplanted organ surveillance eg, myocutaneous fl aps (Rojdmark et al 1998), intrapartum for the fetus (Westgren et al 1999), and patients with septic shock (Boer et al 1994).…”