Simultaneous monitoring of intratidal compliance and resistance in mechanically ventilated piglets: A feasibility study in two different study groups.

Compliance measures the force counteracting parenchymal lung distension. In mechanical ventilation, intratidal compliance-volume (C(V))-profiles therefore change depending on PEEP, tidal volume (VT), and underlying mechanical lung properties. Resistance counteracts gas flow through the airways. Due to anatomical linking between parenchyma and airways, intratidal resistance-volume (R(V))-profiles are hypothesised to change in a non-linear way as well. We analysed respiratory system mechanics in fifteen piglets with lavage-induced lung injury and nine healthy piglets ventilated at different PEEP/VT-settings. In healthy lungs, R(V)-profiles remained mostly constant and linear at all PEEP-settings whereas the shape of the C(V)-profiles showed an increase toward a maximum followed by a decrease (small PEEP) or volume-dependent decrease (large PEEP). In the lavage group, a large drop in resistance at small volumes and slow decrease toward larger volumes was found for small PEEP/VT-settings where C(V)-profiles revealed a volume-dependent increase (small PEEP) or a decrease (large PEEP and large VT). R(V)-profiles depend characteristically on PEEP, VT, and possibly whether lungs are healthy or not. Curved R(V)-profiles might indicate pathological changes in the underlying mechanical lung properties and/or might be a sign of derecruitment.

Pulmonary shunt is independent of decrease in cardiac output during unsupported spontaneous breathing in the pig.

BACKGROUND: During mechanical ventilation (MV), pulmonary shunt is cardiac output (CO) dependent; however, whether this relationship is valid during unsupported spontaneous breathing (SB) is unknown. The CO dependency of the calculated venous admixture was investigated, with both minor and major shunt, during unsupported SB, MV, and SB with continuous positive airway pressure (CPAP). METHODS: In seven anesthetized supine piglets breathing 100% oxygen, unsupported SB, MV (with tidal volume and respiratory rate corresponding to SB), and 8 cm H2O CPAP (airway pressure corresponding to MV) were applied at random. Venous return and CO were reduced by partial balloon occlusion of the inferior vena cava. Measurements were repeated with the left main bronchus blocked, creating a nonrecruitable pulmonary shunt. RESULTS: CO decreased from 4.2 l/min (95% CI, 3.9-4.5) to 2.5 l/min (95% CI, 2.2-2.7) with partially occluded venous return. Irrespective of whether shunt was minor or major, during unsupported SB, venous admixture was independent of CO (slope: minor shunt, 0.5; major shunt, 1.1% · min(-1) · l(-1)) and mixed venous oxygen tension. During both MV and CPAP, venous admixture was dependent on CO (slope MV: minor shunt, 1.9; major shunt, 3.5; CPAP: minor shunt, 1.3; major shunt, 2.9% · min(-1) · l(-1)) and mixed-venous oxygen tension (coefficient of determination 0.61-0.86 for all regressions). CONCLUSIONS: In contrast to MV and CPAP, venous admixture was independent of CO during unsupported SB, and was unaffected by mixed-venous oxygen tension, casting doubt on the role of hypoxic pulmonary vasoconstriction in pulmonary blood flow redistribution during unsupported SB.

Spontaneous breathing improves shunt fraction and oxygenation in comparison with controlled ventilation at a similar amount of lung collapse.

BACKGROUND: Spontaneous breathing (SB), when allowed during mechanical ventilation (MV), improves oxygenation in different models of acute lung injury. However, it is not known whether oxygenation is improved during mechanically unsupported SB. Therefore, we compared SB without any support with controlled MV at identical tidal volume (VT) and respiratory rate (RR) without positive end-expiratory pressure in a porcine lung collapse model. METHODS: In 25 anesthetized piglets, stable lung collapse was induced by application of negative pressure, and animals were randomized to either resume SB or to be kept on MV at identical VT (5 mL/kg; 95% confidence interval: 3.8 to 6.4) and RR (65 per minute [57 to 73]) as had been measured during an initial SB period. Oxygenation was assessed by blood gas analysis (n=15) completed by multiple inert gas elimination technique (n=8 of the 15) for shunt measurement. In addition, possible lung recruitment was studied with computed tomography of the chest (n=10). RESULTS: After induction of lung collapse, PaO2/FIO2 decreased to 90 mm Hg (76 to 103). With SB, PaO2/FIO2 increased to 235 mm Hg (177 to 293) within 15 minutes, whereas MV at identical Vt and RR did not cause any improvement in oxygenation. Intrapulmonary shunt by 45 minutes after induction of lung collapse was lower during SB (SB: 27% [24 to 30] versus MV: 41% [28 to 55]; P=0.017). Neither SB nor MV reduced collapsed lung areas on computed tomography. CONCLUSIONS: SB without any support improves oxygenation and reduces shunt in comparison with MV at identical settings. This seems to be achieved without any major signs of recruitment of collapsed lung regions.

Analysis of dynamic intratidal compliance in a lung collapse model.

BACKGROUND: For mechanical ventilation to be lung-protective, an accepted suggestion is to place the tidal volume (V(T)) between the lower and upper inflection point of the airway pressure-volume relation. The drawback of this approach is, however, that the pressure-volume relation is assessed under quasistatic, no-flow conditions, which the lungs never experience during ventilation. Intratidal nonlinearity must be assessed under real (i.e., dynamic) conditions. With the dynamic gliding-SLICE technique that generates a high-resolution description of intratidal mechanics, the current study analyzed the profile of the compliance of the respiratory system (C(RS)). METHODS: In 12 anesthetized piglets with lung collapse, the pressure-volume relation was acquired at different levels of positive end-expiratory pressure (PEEP: 0, 5, 10, and 15 cm H(2)O). Lung collapse was assessed by computed tomography and the intratidal course of C(RS) using the gliding-SLICE method. RESULTS: Depending on PEEP, C(RS) showed characteristic profiles. With low PEEP, C(RS) increased up to 20% above the compliance at early inspiration, suggesting intratidal recruitment; whereas a profile of decreasing C(RS), signaling overdistension, occurred with V(T) > 5 ml/kg and high PEEP levels. At the highest volume range, C(RS) was up to 60% less than the maximum. With PEEP 10 cm H(2)O, C(RS) was high and did not decrease before 5 ml/kg V(T) was delivered. CONCLUSIONS: The profile of dynamic C(RS) reflects nonlinear intratidal mechanics of the respiratory system. The SLICE analysis has the potential to detect intratidal recruitment and overdistension. This might help in finding a combination of PEEP and V(T) level that is protective from a lung-mechanics perspective.

Practical experiences and in vitro and in vivo validation studies with a new gastric tonometric probe in human adult patients.

PURPOSE: This study provides practical experiences with a new, simple, balloon-free gastric tonometric probe (probe) and reports the results of simultaneous in vitro and in vivo measurements with a conventional, ballooned gastric air tonometer (catheter) and the new device. MATERIALS AND METHODS: Ten healthy volunteers and 50 anesthetized surgical patients with different American Society of Anesthesiologists (ASA) scores, scheduled for neurologic, orthopedic, trauma, and cardiac operations, were enrolled in the study. The values of 60 in vitro and, in 12 surgical patients, 101 in vivo paired Pco(2) measurements--performed simultaneously with the new tonometric probe and the catheter that was connected to a Tonocap monitor--were compared. The tolerability of the measurement with the new probe was examined, and the results of gastric tonometry and, in surgical cases, the gastric tonometric, end-expiratory, and arterial Pco(2) values were registered. The results were evaluated by analysis of variance test. The data of the in vivo paired measurements were evaluated by Bland-Altman analysis. RESULTS: The use of the probe proved to be well tolerated and easily applicable in the studied cases. The results of 20 measurements obtained in healthy volunteers and those of 520 measurements in the surgical cases correspond to the data obtained with the classical methods published in the medical literature. During in vitro paired measurements, there was a good agreement between the data obtained with the 2 methods; however, in the in vivo studies, the results of measurements performed with the probe were mostly higher. CONCLUSIONS: The differences between the results obtained with the 2 methods might have been caused by the quicker equilibration property of the probe and by the fundamental differences between the 2 methods. The new probe seems to be applicable for routine human measurements.

Quality and safety guidelines of postanaesthesia care: Working Party on Post Anaesthesia Care (approved by the European Board and Section of Anaesthesiology, Union Européenne des Médecins Spécialistes).

Postanaesthesia care units are standard parts of hospital care in most European Union countries. Their main purpose is to identify and immediately treat early complications of surgery or anaesthesia, before they develop into deleterious problems. This review, prepared by the Working Party on Post Anaesthesia Care of the European Board of Anaesthesiology. European Union of Medical Specialists (Union Européenne des Médecins Spécialistes) and approved by the European Board and Section of Anaesthesiology, gives recommendations on relevant aspects of organization, responsibilities, methods, safety and quality control of postanaesthesia care.

Change in expiratory flow detects partial endotracheal tube obstruction in pressure-controlled ventilation.

Only extreme degrees of endotracheal tube (ETT) narrowing can be detected with monitoring of tidal volume (V(T)) during pressure-controlled ventilation (PCV). To assess the degree of ETT obstruction in PCV and to compare it to V(T) monitoring, we produced 3 levels of partial ETT obstruction in 11 healthy anesthetized piglets using ETTs of 4 different inner diameters (IDs 9.0, 8.0, 7.0, and 6.0 mm). An expiratory flow over volume ((e)-V) curve was plotted and the time constant (tau(e)) at 15% of expiration time (T(e)) was calculated. We also calculated the fractional volume expired during the first 15% of T(e) (V(ex fract,15)) and compared those variables to full expiratory V(T) for each of the 3 obstructions. V(T) monitoring failed to detect ETT narrowing. By contrast, V(ex fract,15) decreased and tau(e) increased significantly with increasing ETT narrowing (for IDs 9.0, 8.0, 7.0, and 6.0, mean V(ex fract,15) was 195, 180, 146, and 134 mL respectively and mean tau(e) was 380, 491, 635, 794 ms for IDs 9.0, 8.0, 7.0, and 6.0 respectively). We conclude that when the elastic recoil that drives (e) is appropriately considered, analysis of (e) and V(ex fract,15) detects partial ETT obstruction during PCV.

[Risk factors for fatal outcome in subdural hemorrhage]. / A subduralis vérzés miatt kezelt betegek halálozását befolyásoló tényezók.

BACKGROUND: Subdural haemorrhage (SDH) is of high public health importance because of its frequency, high case fatality ratio (CFR) and the young age of affected population. Despite the fact that the effectivity of guideline based treatment has been improved in the last decade, the Hungarian praxis shows variable compliance for recommendations. OBJECTIVES: The study aimed to describe the heterogeneity of the treatment effectivity (by geographically identifying the populations provided with appropriate or non-optimal level care), to determine the relationship between the institutional proxies quality and the results of treatment for SDH by linking the proxies properties to the patients' records. METHODS: The institutions' protocols were assessed by a self-completed questionnaire in 1997. The participating hospitals treated 79% of the Hungarian patients with SDH. The Hungarian hospital discharge data in 1997-1999 were the source of patient specific data. The risk factors of lethal outcome were investigated by logistic regression analysis. RESULTS: High proportion of patients had been treated in hospital with low compliance for guidelines. The non-permanent access to neurosurgical service and CT facility, the lack of intracranial pressure monitoring and the respiration support provided out of intensive care units worsened the survival of subjects. It was quantified that the full compliance could have diminished the case fatality ratio by 15-20%. The ratio of extreme county level CFRs exceeded 2.36 and extrapolating the effectivity observed in the county with lowest lethality, the Hungarian CFR would have been reduced by 21% among patients with SDH main diagnosis. (The interpretation of findings is limited by the lack of differentiation between acute and chronic cases and of direct categorisation of severity for subdural haemorrhage in the official hospital discharge records). DISCUSSION: The study results urge the increase of compliance for evidence based guidelines, since despite of some validity issues, it was demonstrated that the deviation from recommended practice is reflected in the disadvantageous outcome.

[Postoperative vomiting]. / A posztoperatív hányásról.

INTRODUCTION: Nausea and vomiting following general anaesthesia are among the most frequent adverse reactions causing complications, the relief of which is an absolute demand. 5-HT3 receptor antagonists, such as ondansetron, belonging to the latest class of antiemetics were launched more than a decade ago. PATIENTS/METHODS: Efficacy and tolerability of ondansetron injection in prevention of postoperative nausea and vomiting were investigated in a prospective, randomised, double-blind, placebo controlled, three-armed clinical study in 148 patients undergoing laparoscopic cholecystectomy. Moreover the authors also investigated the effect of timing of dosing, i.e. whether the administration of antiemetic drug before starting anaesthesia has any advantage comparing its use at the end of operation. RESULTS: While using a standard surgical and anaesthesia method vomiting after laparoscopic cholecystectomy occurred in a frequency of 44.7% of the patients in the placebo group, whereas the figures decreased significantly after administration of 4 mg ondansetron at the end (28.9%) or before (25.5%) anaesthesia. Inclusively the frequency of severe cases decreased from 19.2% of control group up to 8.9% and 4.3% in the active groups, respectively. CONCLUSIONS: Intravenous administration of 4 mg ondansetron effectively reduces vomiting occurring in more than 40% of patients after laparoscopic cholecystectomy, especially the frequency of severe cases, and mainly if administered before operation. The preparation is safe; no clinical or laboratory adverse reactions, complications have been observed in the studied patients.