ABSTRACT
HYPOTHESIS: Amplified spontaneous pattern (ASP) ventilation is a new method for giving partial support by reproducing, in an amplified manner, the patients' own spontaneous flow wave form, thereby optimizing patient adaptation to support. OBJECTIVES: To study clinical use of ASP ventilation for the first time in terms of flow wave form, patient synchronization, ventilation pattern, work of breathing (WOB), and inspiratory effort by transpulmonary pressure (TPP) and to compare ASP and pressure support ventilation applied in a similar clinical setting. PATIENTS AND METHOD: We studied 20 patients after heart surgery during weaning from controlled ventilation. Each patient was ventilated during 4 phases of 15 min each with two similar levels of support using ASP and PS applied successively and randomly. Maximum support (ASPmax and PSmax) was that which was set to give the same respiratory frequency (F) and tidal volume (VT) as that recorded during the earlier period of controlled ventilation. Half support (PEA1/2 and PS1/2) was set for half the aforementioned levels. At the end of each phase we obtained gas measurements and flow (V) curves and VT and pressure in airways and esophagus (Pes) to measure F, VT, the ratio of inspiratory to total time (TI/TTOT and TPP, as well as the VT/Pes loop with a mechanical ventilation monitor. The WOB was determined by measuring area under the curve (Campbell's method). RESULTS: We observed no significant differences between the two modes, with similar levels of support, with regard to ventilation (PaCO2) or ventilatory pattern (F, VT, TI/TTOT). De-adaptation occurred, however, eight times with PS (25%) but never with ASP. WOB and TPP decreased with PS when level of support increased, whereas with ASP these variables were constant regardless of level of amplification within the normal range. CONCLUSIONS: Adaptation to support is better with ASP than with PS during postoperative weaning and causes no significant respiratory work overload.
Subject(s)
Postoperative Care/methods , Respiratory Therapy/methods , Adaptation, Physiological , Carbon Dioxide/blood , Heart Valve Prosthesis Implantation , Hemodynamics , Humans , Myocardial Revascularization , Oxygen/blood , Partial Pressure , Postoperative Complications/physiopathology , Postoperative Complications/therapy , Prospective Studies , Pulmonary Gas Exchange , Pulmonary Ventilation , Respiration Disorders/physiopathology , Respiration Disorders/therapy , Respiratory Function Tests , Respiratory Muscles/physiopathology , Ventilator Weaning , Work of BreathingABSTRACT
Low molecular weight heparins are a group of drugs that have only recently been introduced in clinical practice. The are widely used for prophylaxis in thromboembolic disease and are being employed increasingly to treat established venous thrombosis. One way in which these drugs are often used is for prophylaxis in the perioperative period for patients at high risk of developing venous thromboembolism, and the anesthesiologist must therefore be familiar with the main aspects of this application. We review pharmacological characteristics of these drugs as well as the literature on low molecular weight heparins, stressing points of main interest to the anesthesiologist and intensive care recovery unit specialist, namely adverse effects (mainly bleeding) and the implications that use of low molecular weight heparin will have on choice of anesthetic (in particular the dilemma of whether to use local/regional anesthesia).
