Epidemiology, practice of ventilation and outcome for patients at increased risk of postoperative pulmonary complications

BACKGROUND Limited information exists about the epidemiology and outcome of surgical patients at increased risk of postoperative pulmonary complications (PPCs), and how intraoperative ventilation was managed in these patients. OBJECTIVES To determine the incidence of surgical patients at increased risk of PPCs, and to compare the intraoperative ventilation management and postoperative outcomes with patients at low risk of PPCs. DESIGN This was a prospective international 1-week observational study using the ‘Assess Respiratory Risk in Surgical Patients in Catalonia risk score’ (ARISCAT score) for PPC for risk stratification. PATIENTS AND SETTING Adult patients requiring intraoperative ventilation during general anaesthesia for surgery in 146 hospitals across 29 countries. MAIN OUTCOME MEASURES The primary outcome was the incidence of patients at increased risk of PPCs based on the ARISCAT score. Secondary outcomes included intraoperative ventilatory management and clinical outcomes. RESULTS A total of 9864 patients fulfilled the inclusion criteria. The incidence of patients at increased risk was 28.4%. The most frequently chosen tidal volume (VT) size was 500 ml, or 7 to 9 ml kg1 predicted body weight, slightly lower in patients at increased risk of PPCs. Levels of positive end-expiratory pressure (PEEP) were slightly higher in patients at increased risk of PPCs, with 14.3% receiving more than 5 cmH2O PEEP compared with 7.6% in patients at low risk of PPCs (P < 0.001). Patients with a predicted preoperative increased risk of PPCs developed PPCs more frequently: 19 versus 7%, relative risk (RR) 3.16 (95% confidence interval 2.76 to 3.61), P < 0.001) and had longer hospital stays. The only ventilatory factor associated with the occurrence of PPCs was the peak pressure. CONCLUSION The incidence of patients with a predicted increased risk of PPCs is high. A large proportion of patients receive high VT and low PEEP levels. PPCs occur frequently in patients at increased risk, with worse clinical outcome

Epidemiology, practice of ventilation and outcome for patients at increased risk of postoperative pulmonary complications: LAS VEGAS - An observational study in 29 countries

BACKGROUND Limited information exists about the epidemiology and outcome of surgical patients at increased risk of postoperative pulmonary complications (PPCs), and how intraoperative ventilation was managed in these patients. OBJECTIVES To determine the incidence of surgical patients at increased risk of PPCs, and to compare the intraoperative ventilation management and postoperative outcomes with patients at low risk of PPCs. DESIGN This was a prospective international 1-week observational study using the ‘Assess Respiratory Risk in Surgical Patients in Catalonia risk score’ (ARISCAT score) for PPC for risk stratification. PATIENTS AND SETTING Adult patients requiring intraoperative ventilation during general anaesthesia for surgery in 146 hospitals across 29 countries. MAIN OUTCOME MEASURES The primary outcome was the incidence of patients at increased risk of PPCs based on the ARISCAT score. Secondary outcomes included intraoperative ventilatory management and clinical outcomes. RESULTS A total of 9864 patients fulfilled the inclusion criteria. The incidence of patients at increased risk was 28.4%. The most frequently chosen tidal volume (V T) size was 500 ml, or 7 to 9 ml kg−1 predicted body weight, slightly lower in patients at increased risk of PPCs. Levels of positive end-expiratory pressure (PEEP) were slightly higher in patients at increased risk of PPCs, with 14.3% receiving more than 5 cmH2O PEEP compared with 7.6% in patients at low risk of PPCs (P ˂ 0.001). Patients with a predicted preoperative increased risk of PPCs developed PPCs more frequently: 19 versus 7%, relative risk (RR) 3.16 (95% confidence interval 2.76 to 3.61), P ˂ 0.001) and had longer hospital stays. The only ventilatory factor associated with the occurrence of PPCs was the peak pressure. CONCLUSION The incidence of patients with a predicted increased risk of PPCs is high. A large proportion of patients receive high V T and low PEEP levels. PPCs occur frequently in patients at increased risk, with worse clinical outcome.</p

HIGH-EFFICIENCY FRESNEL ACOUSTIC LENSES

ABSTRACT Acoustic Fresnel lenses have emerged in recent years as an alternative t o the conventional spherical lenses for focusing sound waves in appllcations such as acoustic microscopy. Fresnel lenses offer the advantage of near-planar geometry and, therefore, ease of fabrication compared t o spherical lenses. The Fresnel acoustic lenses reported so far, however, have the disadvantage of low efficiency; only about 40% o f the input signal is directed towards the focus. In this work the design and fabrication of &quot;binary&quot; acoustic Fresnel lenses that offer much higher efficiencies will be described. These lenses, while being still nearly planar, have multiple phase levels t o achieve phase shifts other than 0 and 180 degrees as used in conventional, two phase Fresnel lenses. Acoustic Fresnel lenses were fabricated at frequencies of about 1 MHz and 170 MHz. Measurements of the focusing efficiency and point spread function have been performed to characterize the operation o f these lenses. Focusing efficiencies in excess of 8096 have been achieved with these lenses The measurements compare well t o theoretical simulations. I NTRO D U CTI 0 N Scanning acoustic microscopy (SAM) has been shown to be a useful tool for imaging samples and characterizing mechanical properties of materials.1 The acoustic lens is perhaps the most important part o f a SAM because imaging with good resolution requires a diffraction limited focus. These lenses typically have diameters of a few hundred microns at UHF frequencies and mechanical grinding and polishing are the standard processes used in the fabrication of these lenses. These techniques are time consuming and expensive and alternative methods are desirable t o manufacture high quality lenses at low cost. One proposed scheme is t o use an isotropic etching technique in crystalline silicon for fabricating spherical lenses.2 Although this is a batch processing technique that has potential for low cost manufacturing, it requires precision process control which may be difficult t o achieve and which would increase the cost o f manufacturing. Another method for fabrication of lenses was demonstrated by Yamada, In this method near-planar Fresnel lenses were fabricated in quartz substrates using conventional microfabrication processes. where N is the number of phase levels. These lenses are fabricated using subsequent masking and etching steps. 2&quot; phase levels may be achieved for n masking steps. For example, only 3 masks are needed t o realize 8 phase levels with an efficiency o f 95% The radius o f the kth phase step is given by7 where zo is the focal length and h is the wavelength. The step size between subsequent phase levels is given by7 1993 ULTRASONICS SYMPOSIUM -57