Clinical review: Respiratory monitoring in the ICU - a consensus of 16

ABSTRACT: Monitoring plays an important role in the current management of patients with acute respiratory failure but sometimes lacks definition regarding which 'signals' and 'derived variables' should be prioritized as well as specifics related to timing (continuous versus intermittent) and modality (static versus dynamic). Many new techniques of respiratory monitoring have been made available for clinical use recently, but their place is not always well defined. Appropriate use of available monitoring techniques and correct interpretation of the data provided can help improve our understanding of the disease processes involved and the effects of clinical interventions. In this consensus paper, we provide an overview of the important parameters that can and should be monitored in the critically ill patient with respiratory failure and discuss how the data provided can impact on clinical management.     

Influence of pulmonary surfactant on in vitro bactericidal activities of amoxicillin, ceftazidime, and tobramycin.

The influence of a natural pulmonary surfactant on antibiotic activity was investigated to assess the possible use of exogenous surfactant as a vehicle for antibiotic delivery to the lung. The influence of surfactant on the bactericidal activity of amoxicillin was tested against Staphylococcus aureus and Streptococcus pneumoniae, and the influence of surfactant on the activities of ceftazidime and tobramycin was tested against Klebsiella pneumoniae, Pseudomonas aeruginosa, S. aureus, and S. pneumoniae. In vitro antibiotic activity was determined by killing curve studies in media with and without surfactant. Amoxicillin and ceftazidime activities were not changed in the presence of surfactant, except for a decreased killing rate of S. pneumoniae by ceftazidime in medium with additional rabbit serum. In contrast, killing curves with low concentrations of tobramycin (0.25x and 1x the MIC) showed a decreased level of activity of tobramycin against all pathogens tested in the presence of surfactant. With higher tobramycin concentrations (4x the MIC) killing rates were decreased less or were unchanged in the presence of surfactant. Concluding from the results of the study, both amoxicillin and ceftazidime can be combined with surfactant without the loss of activity. For mixing surfactant with tobramycin, dosages should be adjusted to overcome the partial inactivation of tobramycin by surfactant.     

Intraoperative evaluation of micromultiplane transesophageal echocardiographic probe in surgery for congenital heart disease.

INTRODUCTION: In the last years, transesophageal transducers for multiplane Doppler echocardiography have demonstrated their superior imaging performance in pediatric patients undergoing cardiac surgery. To date, the size of these probes has limited their use in neonates and small children. New technologies allowing performing TEE in smaller patients are therefore promising. METHODS: We report our clinical experience with the Oldelft micromultiplane TEE probe (8.2-7mm diameter tip with a 5.2mm diameter shaft) specifically meant for use in neonates. RESULTS: Forty-two patients were examined intra-operatively using the micromulti TEE harmonic transducer. Patients examined ranged in age from 4days to 6years and ranged in weight from 2.5 to 23.8kg. In two patients we had to adapt ventilatory settings because of increased airway resistance after probe insertion. In 3 patients surgical re-intervention was performed due to TEE assessment immediately after weaning from bypass. In two patients significant obstruction of the right ventricular outflow tract was still present after Fallot correction, and one patient had an additional muscular ventricular septal defect still present after VSD closure. CONCLUSIONS: The micromulti TEE harmonic transducer provided excellent diagnostic intra-operative TEE in neonates and small children without major complications, special attention should be taken for ventilatory parameters in neonates less than 3kg.     

In vitro effect of thyroid hormones on lipolysis of rat fat cells during aging

The in vitro effect of triiodothyronine (T3) 10(-5) M upon lipolysis was studied on white fat cells isolated from 1.5-6- and 30-month-old rats. We couldn't see any consistent effect of this hormone upon the basal lipolysis. We observed a T3 effect on epinephrine-stimulated lipolysis on the three groups of animals. After 1 h of incubation the increase of glycerol release varies with the dose of epinephrine; after 3 h the T3 effect persisted only in the 6-month and 30-month groups.     

Experimental case report: development of a pneumothorax monitored by electrical impedance tomography

Electrical impedance tomography (EIT) is a non‐invasive, radiation‐free functional imaging technique, which allows continuous bedside measurement of regional lung ventilation. Pneumothorax is an uncommon but nevertheless potentially dangerous incident that may arise unexpectedly. We report an incident of an accidental tension pneumothorax during an experimental ventilation study in a pig that was continuously monitored by EIT. The early sign of the occurring pneumothorax, prior to all clinical signs, was a fast increase of end‐expiratory impedance in the ventral part of the right lung indicating that non‐ventilated air entered this part, followed by a disappearance of ventilation in this region. At the same time the ventilation‐related impedance changes of the left lung remained almost unchanged. The pneumothorax onset was localized using a newly introduced pneumothorax dynamics map directly derived from dynamic EIT data. We conclude that non‐invasive EIT may be helpful as a tool to detect the development of a pneumothorax, which could be of particular interest during invasive procedures such as insertion of a central venous catheter.     

Changes in lipolytic activity of isolated adipocytes from rats throughout life span

The lipolytic response of isolated adipocytes from 1 1/2-, 6-, 24- and 32-month-old rats to various doses of epinephrine was studied. Both the basal and the maximal stimulated glycerol release were largest in the mature rats (6 months old) which had the largest adipocytes. Expressing glycerol release per unit cell surface area (which was drastically reduced with age) eliminated the difference between mature and senescent rats both in absence of epinephrine and at high doses of the hormone. However, at low epinephrine doses the adipocytes of the very young and the very old rats showed an enhanced response per unit surface area. A simple pharmacodynamic analysis based on the occupancy theory of drug-receptor interaction suggests that the sensitivity of rat adipocyte receptors is increased during senescence; this increase may be related to the decreased surface of old adipocytes. On the other hand, the decreased maximal lipolytic response during senescence may be due in part to a reduced number of receptors and to a reduced sensitivity of the cellular enzymatic system underlying lipolysis.     

A note on 'aging-pharmacodynamics' with application to the analysis of the age-dynamics of adipocyte response to epinephrine and insulin

This note aims at clearing some semantic problems in the literature concerning the analysis of the effect of age on dose-response curves as well as standardize the way such data should be presented. In particular it is shown how to assess the age-dynamics (i.e. the pattern of change as a mathematical function of age) of the sensitivity of a receptor system to a given agent, of the quantitative overall changes of the cellular response apparatus which affect response capacity, and of the interaction between different simultaneously acting agents. The concepts and theory are illustrated using as an example the in vitro isolated rat fat cell (or adipocyte) which we have recently studied extensively with regards to the age-dynamics of its lipolytic response to epinephrine and insulin. This 'aging-pharmacodynamics' analysis has led to the surprising conclusion of a rebound effect of age (decrease at maturity followed by increase at old age) on the sensitivity of the fat cell to epinephrine and to its antagonist (with respect to lipolysis) insulin, as well as a negative correlation of these sensitivities with fat cell size.     

Partial liquid ventilation improves lung function in ventilation-induced lung injury.

Disturbances in lung function and lung mechanics are present after ventilation with high peak inspiratory pressures (PIP) and low levels of positive end-expiratory pressure (PEEP). Therefore, the authors investigated whether partial liquid ventilation can re-establish lung function after ventilation-induced lung injury. Adult rats were exposed to high PIP without PEEP for 20 min. Thereafter, the animals were randomly divided into five groups. The first group was killed immediately after randomization and used as an untreated control. The second group received only sham treatment and ventilation, and three groups received treatment with perfluorocarbon (10 mL x kg(-1), 20 mL x kg(-1), and 20 ml x kg(-1) plus an additional 5 mL x kg(-1) after 1 h). The four groups were maintained on mechanical ventilation for a further 2-h observation period. Blood gases, lung mechanics, total protein concentration, minimal surface tension, and small/large surfactant aggregates ratio were determined. The results show that in ventilation-induced lung injury, partial liquid ventilation with different amounts of perflubron improves gas exchange and pulmonary function, when compared to a group of animals treated with standard respiratory care. These effects have been observed despite the presence of a high intra-alveolar protein concentration, especially in those groups treated with 10 and 20 mL of perflubron. The data suggest that replacement of perfluorocarbon, lost over time, is crucial to maintain the constant effects of partial liquid ventilation.