Time constant/volume relationship of passive expiration in mechanically ventilated ARDS patients.

Since the adult respiratory distress syndrome (ARDS) lung is known to be inhomogeneous, one could expect an uneven distribution of expiratory time constant during uninterrupted mechanical ventilation. We investigated the time constant/volume relationship of passive expiration, and their modification by external resistive elements. In 12 paralysed intubated ARDS patients, we determined the expiratory time constant (tau E) as a function of the expired volume (VE) during uninterrupted mechanical ventilation. Mean expiratory time was 2.9 +/- 0.3 s (+/- SD). VE was divided into five equal volume slices (portions) and a mean tau E calculated from the expiratory tidal volume/flow curve for each slice. The mean values of tau E for each volume slice did not differ significantly throughout expiration, averaging 690 +/- 218 ms (mean +/- SD of five slices and 12 patients). We show that the flow-dependent resistance of the endotracheal tube (RETT) is mainly responsible for the observed time constant homogeneity. We conclude that in ARDS patients during uninterrupted mechanical ventilation the time constants of passive expiration are markedly modified by the flow-dependent resistance of the endotracheal tube (RETT), and also by the external resistance of tubing and ventilator (REX). RETT and REX render tau E about three times larger than the time constant of the patient's respiratory system alone.

The Omnicarbon tilting-disc heart valve prosthesis. A clinical and Doppler echocardiographic follow-up.

From 1986 to 1990, 172 patients with a median age of 60.5 years (range 20 to 79 years) received 187 Omnicarbon valves (109 aortic valve replacements, 48 mitral valve replacements, and 15 double valve replacements). Patients were followed-up for a median observation period of 2.5 years (range 4 months to 5.2 years) by clinical and Doppler echocardiographic examination. Follow-up was complete in 98%. Operative mortality (death within 30 days) was 1.7%, and linearized late mortality was 2.6% per patient-year, corresponding to an actuarial survival rate for operative survivors of 89% after 4 years. The overall 4-year postoperative survival was 87% (93% for aortic valve replacement, 77% for mitral valve replacement). Compared with age- and sex-adjusted Swiss death rates, there was an excess mortality of 5% after 4 years. Percentages for freedom from valve-related complications at 4 years are as follows: thromboembolism, 98% (aortic valve replacement, 98%, and mitral valve replacement, 96%); anticoagulant-related hemorrhage, 95%; valve endocarditis, 96%; reoperation, 96%; and permanent valve-related impairment, 99%. The overall 4-year event-free survival was 76% (80% for aortic valve replacement and 69% for mitral valve replacement). New York Heart Association class improved in 88% of the patients by 1 to 3 grades, and only 3% remained in class III after operation. For the most commonly used aortic valve (23 mm), Doppler echocardiography revealed a peak pressure gradient of 29 +/- 10 mm Hg, a fractional shortening/peak pressure gradient ratio of 1.34 +/- 0.61, and a performance index of 0.35 +/- 0.08. In the most commonly used mitral valve (27 mm), the mean pressure gradient was 4.0 +/- 2.1 mm Hg. We conclude that excellent clinical and hemodynamic results can be obtained with the Omnicarbon prosthesis, in both the aortic and mitral positions.

Continuous calculation of intratracheal pressure in tracheally intubated patients.

BACKGROUND: Intratracheal pressure (Ptrach) should be the basis for analysis of lung mechanics. If measured at all, Ptrach is usually assessed by introducing a catheter into the trachea via the lumen of the endotracheal tube (ETT). The authors propose a computer-assisted method for calculating Ptrach on a point-by-point basis by subtracting the flow-dependent pressure drop delta PETT(V) across the ETT from the airway pressure (P(aw)), continuously measured at the proximal end of the ETT. METHODS: The authors measured the pressure-flow relationship of adult endotracheal tubes with different diameters (ID, 7-9 mm) at different lengths and of tracheostomy tubes (ID, 8-10 mm) in the laboratory. The coefficients of an approximation equation were fitted to the measured pressure-flow curves separately for inspiration and expiration. In 15 tracheally intubated patients under volume-controlled ventilation and spontaneous breathing, the calculated Ptrach was compared with the measured Ptrach. RESULTS: The authors present the coefficients of the "nonlinear approximation": delta PETT = K1.VK2, with delta PETT being the pressure drop across the ETT and K1 and K2 being the coefficients relating V to delta PETT. An important result was an inspiration/expiration asymmetry: the pressure drop caused by the inspiratory flow exceeds that of the expiratory flow. A complete description of the pressure-flow relationship of an ETT, therefore, requires a set of four coefficients: K1I, K2I, K1E, and K2E. The reason for this asymmetry is the abrupt sectional change between ETT and trachea and the asymmetric shape of the swivel connector. Comparison of calculated and measured Ptrach in patients gives a correspondence within +/- 1 cmH2O (mean limits of agreement). The mean root-mean-square (rms) deviation is 0.55 cmH2O. CONCLUSIONS: Ptrach can be monitored by combining our ETT coefficients and the flow and airway pressure continuously measured at the proximal end of the ETT.

Maneuver-free determination of compliance and resistance in ventilated ARDS patients.

At present, most methods of lung mechanics analysis do not take nonlinearities of compliance and resistance into account. Nevertheless, nonlinearity of compliance is an inherent property of the respiratory system in ARDS and nonlinearity of resistance is an inherent property of the endotracheal tube. Herein we describe a computer-assisted multipoint method (LOOP) for breath-by-breath calculation of total respiratory system compliance (Ctrs) and total respiratory system resistance (Rtrs). Unlike our previously published method, LOOP excludes nonlinearities of compliance and resistance by confining the data used from the P/V/V loop to sequences with constant flow in inspiration and with steadily decreasing flow in expiration. LOOP was applied to five patients ventilated after open heart surgery (HEART group) and 12 patients ventilated for ARDS (ARDS group). The compliance results from LOOP were compared with the semistatic reference values corrected for intrinsic PEEP (CsST,IP). In the ARDS patients the compliance values from LOOP (46 ml/mbar) corresponded well with the semistatic compliance (CsST,IP = 42 ml/mbar). Despite the fact that there is no reference method for resistance known to date, we also determined the semistatic resistance (RsST) at end-inspiratory pause. The resistance values determined with LOOP were 8.5 mbar/L/s (RsST = 7.3 mbar/L/s) in the HEART group and 11.1 mbar/L/s (RsST = 8.6 mbar/L/s) in the ARDS group. LOOP gives a good correspondence between the linear RC model and the measured data in ARDS patients. In conclusion, LOOP requires neither an end-inspiratory pause (EIP) nor additional determination of intrinsic PEEP and gives Ctrs, automatically corrected for IPEEP, as well as Rtrs breath by breath at the bedside.

Intrinsic PEEP monitored in the ventilated ARDS patient with a mathematical method.

Under mechanical volume-controlled ventilation, the intensive care patient can develop intrinsic positive end-expiratory pressure (iPEEP); that is, the passive expiration is terminated by the following inspiration before the alveolar pressure comes to its physical equilibrium value. We present a mathematical method to estimate this alveolar dynamic iPEEP breath by breath, without the need of a maneuver. We tested it in paralyzed patients ventilated for adult respiratory distress syndrome after multiple trauma and/or sepsis, and we compared the results obtained with the new mathematical method with those from the occlusion method introduced by Pepe and Marini. The results agreed well (median difference of 0.8 mbar in 201 investigations in 12 patients). However, the mathematically determined values, representing dynamic iPEEP, are systematically slightly smaller than those measured by the occlusion maneuver. A variation of expiratory time suggests that this difference might be due to mechanical time-constant inhomogeneity, viscoelastic processes, or other mechanisms showing time dependence.

[Traumatic aortic rupture--an emergency indication?]. / Traumatische Aortenruptur--Notfallindikation?

On the basis of a retrospective analysis that included 22 patients with traumatic rupture of the thoracic aorta, the appropriate time for surgical intervention will be evaluated. The patients were divided into two groups according to their clinical status at the time of surgery. Seven patients with unstable vital systems underwent immediate surgery; 5 out of 7 died intraoperatively. Because of either the surgeons decision or delayed diagnosis, 15 patients underwent surgical repair of the aorta after various time intervals; 3 of these expired late after the operation. These results indicate that the timing of surgical intervention in the stable covered aortic rupture with serious associated injuries should preferably be deferred until after the patients condition has stabilized.

[Arterial switch operation in transposition of great arteries and double-outlet right ventricle. Experience at the Brompton Hospital, London]. / Arterielle Switch-Operation bei TGA und DORV. Erfahrung des Brompton-Hospital, London.

Between 1981 and 1989 89 patients underwent anatomic correction of transposition of the great arteries with intact ventricular septum (n = 32), transposition with ventricular septum defect (n = 37) and double outlet right ventricle with subpulmonary ventricular septal defect (n = 20). The perioperative mortality was 17% (n = 15). The causes of death are discussed. The most common postoperative complication is right ventricular outflow tract-obstruction (RVOTO), accounting for two late deaths and necessitating reoperations in many patients. Besides RVOTO the mid-term results in arterial switch-operation are encouraging. Especially satisfactory are the absence of any problems with growth of the transferred coronary arteries, the function of the new aortic valve as well as the performance of the left ventricle. Of course, long-term experience is not yet available.

Decision-making aspects in the timing of surgical intervention in aortic rupture.

Twenty-one consecutive patients with traumatic rupture of the thoracic aorta were treated at the University Hospital of Basel, Switzerland. The patients were divided into two groups according to their clinical status at the time of surgery. Six patients with unstable vital functions underwent immediate surgery (group 1), while 15 patients were operated upon semi-urgently because of delayed diagnosis or electively (group 2). Five of 6 patients undergoing immediate repair in group 1 died intraoperatively, 3 of 15 patients with deferred surgery expired postoperatively after a period of 6 weeks to 3 months. All 13 survivors underwent follow-up for 10 months to 20 years. NMR imaging of the aorta in 12 patients revealed neither pseudoaneurysms nor stenosis at the anastomoses. The results indicate that the timing of the surgical intervention in stable contained aortic rupture with serious associated injuries should preferably be deferred until after stabilization of the clinical status.

Heart valve replacement with the Björk-Shiley and St Jude Medical prostheses: a randomized comparison in 178 patients.

In 178 patients, a randomized prospective comparison between the 60 degrees spherical disc Björk-Shiley (BS) and the St Jude Medical (SJM) heart valve prostheses was performed. Four-week perioperative mortality was zero in the BS (n = 84) and 4.3% in the SJM group (n = 94). During a mean (+/- SD) follow-up of 52 +/- 20 months or 778 patient-years, late cardiac mortality per year was 2.4% in the BS and 2.2% in the SJM group. The yearly thromboembolic rates were 1.4% in the BS and 2.0% in the SJM group. There was no mechanical valve failure or haemolytic anaemia. Paravalvular leaks and major bleeding complications occurred at low rates in both groups (1.1% and 2.2% per year in BS; 0.7% and 1.7% per year in SJM). Functional results were similarly good with 96% of patients with BS valves and 95% of patients with SJM prostheses being in NYHA classes I and II, respectively. We conclude that heart valve replacement with mechanical prostheses can be performed with equally good results using either the Björk-Shiley spherical disc valve or the St Jude Medical bileaflet prosthesis.

[Postoperative mortality in surgery of cholelithiasis: a retrospective analysis from the years 1972-1980]. / Postoperative Letalität in der Chirurgie der Cholelithiasis: eine retrospektive Analyse aus den Jahren 1972 bis 1980.

In a retrospective study (1972-1980) we analyzed the postoperative mortality of 2916 consecutive cholecystectomies or interventions on the common bile ducts respectively. The mean age of the patients was 54 years (17-92 years), 63% were older than 60 years; 74% were women. We show that age, histology, intervention, stone localization, sex and concomitant internal diseases influenced the early postoperative mortality. The overall mortality was 0.7% (21 patients), 0.7% in the under 60 years old patients, 1.8% in the older aged group. The mortality in chronic cholecystitis was 0.5%, in acute cholecystitis 2.6%. After simple cholecystectomy we observed a mortality of 0.3%, after cholecystectomy and common bile duct intervention 2.5% (p less than 0.001), and after intervention on the common bile ducts 7.3%. Stones only in the gallbladder were associated with a mortality of 0.3%, cholecysto- and choledocholithiasis with 2.8% and choledocholithiasis alone with 7.3%. The mortality in men was significantly (p less than 0.001) higher as in women (1.2 against 0.6%). In 76% of the deceased we diagnosed preoperatively a concomitant internal disease.

[Wound infection following appendectomy. Metronidazole vs ornidazole as single-dose prophylaxis in non-perforated appendix]. / Wundinfekte nach Appendektomie. Metronidazol vs Ornidazol als Einmalprophylaxe bei nicht-perforierter Appendix.

In an open prospective randomized study, the postoperative wound infection rate following removal of an unperforated appendix was evaluated in 187 patients who received either metronidazole (1 g suppositories) or ornidazole (500 mg iv or 500 mg suppositories) in a single dose preoperatively. The overall postoperative infection rate was 2.1%. Metronidazole and ornidazole suppositories are a cheap method of preventing postoperative infection in cases of unperforated appendix.