O. Stenqvist

Inhalation of nitric oxide in acute lung injury: results of a European multicentre study

Objective: To determine whether inhalation of nitric oxide (INO) can increase the frequency of reversal of acute lung injury (ALI) in nitric oxide (NO) responders. Design: Prospective, open, randomised, multicentre, parallel group phase III trial. Setting: General ICUs in 43 university and regional hospitals in Europe. Patients: Two hundred and sixty-eight adult patients with early ALI. Interventions: NO responders were patients whose PaO2 increased by more than 20 % when receiving 0, 2, 10 and 40 ppm of INO for 10 min within 96 h of study entry. Responders were randomly allocated to conventional treatment with or without INO. INO, 1–40 ppm, was given at the lowest effective dose for up to 30 days or until an end point was reached. The primary end point was reversal of ALI. Clinical outcome parameters and safety were assessed in all patients. Results: Two hundred and sixty-eight patients were recruited, of which 180 were randomised NO responders. Frequency of reversal of ALI was no different in INO patients (61 %) and controls (54 %; p > 0.2). Development of severe respiratory failure was lower in the INO (2.2 % ) than controls (10.3 %; p < 0.05). The mortality at 30 days was 44 % for INO patients, 40 % for control patients (p > 0.2 vs INO) and 45 % in non-responders. Conclusions: Improvement of oxygenation by INO did not increase the frequency of reversal of ALI. Use of inhaled NO in early ALI did not alter mortality although it did reduce the frequency of severe respiratory failure in patients developing severe hypoxaemia.

Positive end-expiratory pressure optimization using electric impedance tomography in morbidly obese patients during laparoscopic gastric bypass surgery.

Background:  Morbidly obese patients have an increased risk for peri‐operative lung complications and develop a decrease in functional residual capacity (FRC). Electric impedance tomography (EIT) can be used for continuous, fast‐response measurement of lung volume changes. This method was used to optimize positive end‐expiratory pressure (PEEP) to maintain FRC.

Estimation of functional residual capacity at the bedside using standard monitoring equipment: a modified nitrogen washout/washin technique requiring a small change of the inspired oxygen fraction.

We developed a modified nitrogen washin/washout technique based on standard monitors using inspiratory and end-tidal gas concentration values for functional residual capacity (FRC) measurements in patients with acute respiratory failure (ARF). For validation we used an oxygen-consuming lung model ventilated with an inspiratory oxygen fraction (Fio2) between 0.3 and 1.0. The respiratory quotient of the lung model was varied between 0.7 and 1.0. Measurements were performed changing Fio2 with fractions of 0.1, 0.2, and 0.3. In 28 patients with ARF, duplicate measurements were performed. In the lung model, an Fio2 change of 0.1 resulted in a value of 103 ± 5% of the reference FRC value of the lung model, and the precision was equally good up to an Fio2 of 1.0 with a value of 103 ± 7%. In the patients, duplicate measurements showed a bias of −5 mL with a 95% confidence interval [−38; 29 mL ]. A comparison of a change in Fio2 of 0.1 with 0.3 showed a bias of −9 mL and limits of agreement of [−365; 347 mL]. This study shows good precision of FRC measurements with standard monitors using a change in Fio2 of only 0.1. Measurements can be performed with equal precision up to an Fio2 of 1.0.

Conversion of inhaled nitric oxide to nitrate in man

1 Nitric oxide (NO) is potentially useful as a selective vasodilator drug in infants and adults with pulmonary hypertension. In vitro and in vivo observations demonstrate that NO may be converted to nitrate in the blood, to be further excreted into the urine. The aim of the present study was to assess quantitatively the importance of this pathway for inhaled NO in human subjects. 2 Healthy subjects inhaled 15NO (25 p.p.m.) for 1 h. The plasma and urine levels of 15NO3‐ were followed for 2 and 48 h, respectively. 3 The measured retention of 15NO in the lungs was 224 ± 13 μmol, corresponding to 90 ± 2% of the inhaled amount. Plasma 15NO3‐ increased during the inhalation of 15NO, to about 15μmoll_1, and fell when inhalation of 15NO was terminated. 4 Urinary excretion of 15NO3‐ during the first 24 h after inhalation was 154 ± 12μmol. During the following 24 h another 8 ± 2 μmol of 15NO3 appeared in the urine. 5 We conclude that conversion of inhaled NO to nitrate is a major metabolic pathway in man, covering more than 70% of its inactivation. The metabolic fate of the remaining NO inhaled requires further study.

Clinical evaluation of a partial CO2 rebreathing technique for cardiac output monitoring in critically ill patients

Background: Monitoring central hemodynamics is essential in critically ill patients and less invasive techniques are needed. In this study, the clinical and technical performance of a new non‐invasive cardiac output monitor (NICO) based on partial CO2 rebreathing technique and a modified Fick equation were evaluated. The various sources of possible errors in measurement of cardiac output (CO), carbon dioxide production (V˙CO2) and pulmonary shunt were also assessed.

Stiffness of Central Venous Catheters

Catheter stiffness has been suggested to be a principal factor in the thrombogenesis encountered after central venous cannulation. However, no data have been published to date about the stiffness of central venous catheters. A method for measuring catheter stiffness has been developed. The force needed to deflect a catheter tip 1.2 mm from a fastening point was measured with the help of a cantilever beam (Grass Model DA‐7). Six different sections of each catheter were measured, and the final results expressed as an average of these. Twenty‐seven central venous catheters made of silicone elastomer, polyurethane, polyvinylchloride, polyethylene and teflon were tested. The bending stiffness, EI (E=elastic modulus of the material, I = moment of inertia of catheter (a geometrical property)) was below 16×10‐6 Nm2 for all catheters made of silicone elastomer, polyvinylchloride and polyurethane. Polyethylene catheters were stiffer, but could be made softer by reduction of their diameters. Teflon catheters were up to 10 times stiffer than the catheters in the soft group. Heparinization and radioopacity of catheters do not significantly alter their bending stiffness. In a concomitant study the results indicate that there is a significantly lower incidence of thrombus formation in catheters with a bending stiffness below 16×10‐6 Nm2.

Chest electrical impedance tomography examination, data analysis, terminology, clinical use and recommendations: consensus statement of the TRanslational EIT developmeNt stuDy group

Electrical impedance tomography (EIT) has undergone 30 years of development. Functional chest examinations with this technology are considered clinically relevant, especially for monitoring regional lung ventilation in mechanically ventilated patients and for regional pulmonary function testing in patients with chronic lung diseases. As EIT becomes an established medical technology, it requires consensus examination, nomenclature, data analysis and interpretation schemes. Such consensus is needed to compare, understand and reproduce study findings from and among different research groups, to enable large clinical trials and, ultimately, routine clinical use. Recommendations of how EIT findings can be applied to generate diagnoses and impact clinical decision-making and therapy planning are required. This consensus paper was prepared by an international working group, collaborating on the clinical promotion of EIT called TRanslational EIT developmeNt stuDy group. It addresses the stated needs by providing (1) a new classification of core processes involved in chest EIT examinations and data analysis, (2) focus on clinical applications with structured reviews and outlooks (separately for adult and neonatal/paediatric patients), (3) a structured framework to categorise and understand the relationships among analysis approaches and their clinical roles, (4) consensus, unified terminology with clinical user-friendly definitions and explanations, (5) a review of all major work in thoracic EIT and (6) recommendations for future development (193 pages of online supplements systematically linked with the chief sections of the main document). We expect this information to be useful for clinicians and researchers working with EIT, as well as for industry producers of this technology.

Nitrous oxide: an ageing gentleman

IN 1994 Acta Anaesthesiologica Scandinavica celebrated the 150th anniversary for the clinical use of nitrous oxide with a series of articles covering all important aspects related to this anaesthetic agent (1, 2). These were the benefits and adverse effects of clinical use of nitrous oxide, as well as the possible harm of nitrous oxide for operating room staff, and last, but not least, the environmental aspects of medical use of nitrous oxide. Since then the use of the old-timer has come under attack again (3, 4). In this editorial we will discuss briefly the status of nitrous oxide, and then focus on any new information that requires that the clinical use of nitrous oxide should be altered.

Warning! Suctioning. A lung model evaluation of closed suctioning systems

Background: Closed system suctioning, CSS, has been advocated to avoid alveolar collapse. However, ventilator manufacturers indicate that extreme negative pressure levels can be obtained during closed system suctioning, impeding the performance of the ventilator.

Nitrous oxide kinetics

The first clinical trial with nitrous oxide performed by Horace Wells in Boston, USA, in the year of 1844 was a failure due to lack of knowledge on the kinetics of nitrous oxide. Shortly before, he had successfully tried the gas on himself. However, the academic and official trial was unsuccessful (l), because the gas bag was removed too soon as the time needed for induction was unknown to Mr. Wells. In fact, it would take more than one century before a deeper understanding of the kinetics of nitrous oxide emerged and some more decades before a scientific foundation was achieved. Thus, although the drug has been used for 150 years, only during the last 40 years have we moved from art to science and it is during the last decade that the introduction of fast response gas monitors have caused a revelation of the uptake and elimination of nitrous oxide to the anaesthesiologist working in clinics.