α7 nicotinic acetylcholine receptor agonist GTS-21 attenuates ventilator-induced tumour necrosis factor-α production and lung injury

BACKGROUND

Mechanical ventilation (MV) induces an inflammatory response that can lead to lung injury. The vagus nerve can limit the inflammatory response through the cholinergic anti-inflammatory pathway. We evaluated the effects of stimulation of the cholinergic anti-inflammatory pathway with the selective partial α7 nicotinic acetylcholine receptor (α7nAChR) agonist GTS-21 on inflammation and lung injury induced by MV using clinically relevant ventilator settings. Furthermore, we investigated whether altering endogenous cholinergic signalling, by administration of the non-specific nAChR antagonist mecamylamine and the peripherally acting acetylcholinesterase inhibitor neostigmine, modulates the MV-induced inflammatory response.

METHODS

C57BL6 mice were injected i.p. with either the selective α7nAChR agonist GTS-21 (8 mg kg(-1)), the acetylcholinesterase inhibitor neostigmine (80 μg kg(-1)), the nAChR antagonist mecamylamine (1 mg kg(-1)), or a placebo; followed by 4 h of MV (8 ml kg(-1), 1.5 cm H(2)O PEEP).

RESULTS

MV resulted in release of cytokines in plasma and lungs compared with unventilated mice. Lung and plasma levels of tumour necrosis factor (TNF)-α, but not of interleukin-10, were lower in GTS-21-treated animals compared with placebo (P<0.05). In addition, GTS-21 lowered the alveolar-arterial gradient, indicating improved lung function (P=0.04). Neither neostigmine nor mecamylamine had an effect on MV-induced inflammation or lung function.

CONCLUSIONS

MV with clinically relevant ventilator settings results in pulmonary and systemic inflammation. Stimulation of the cholinergic anti-inflammatory pathway with GTS-21 attenuates MV-induced release of TNF-α, which was associated with reduced lung injury. Modulation of endogenous cholinergic signalling did not affect the MV-induced inflammatory response. Selective stimulation of the cholinergic anti-inflammatory pathway may represent new treatment options for MV-induced lung injury.

‘Blind’ transfusion of blood products in exsanguinating trauma patients

BACKGROUND

In trauma, as interventions are carried out to stop bleeding, ongoing resuscitation with blood products is of vital importance. As transfusion policy in exsanguinating patients cannot be based on laboratory tests, transfusion of blood products is performed empirically or 'blindly'. The aim of this study was to delineate 'blind' transfusion practice in the hectic clinical situation of exsanguination.

METHODS

Seventeen trauma patients were selected who died due to uncontrolled bleeding despite haemostatic interventions within 24h after admission and who received more than 12 U of RBC. Transfusion data were compared with a theoretically optimal transfusion model with a fixed ratio between units of RBC, FFP, and platelets. The difference between the observed and expected amounts of blood products was calculated.

RESULTS

The patients (82%) received insufficient amounts of FFP and platelets when compared to the calculated amounts. The total numbers of transfused FFP and platelets were on average 50% lower than the calculated amounts. Regression models showed an increase of FFP and platelets with increasing amounts of RBC but not in sufficient quantities.

CONCLUSION

Exsanguinating trauma patients receiving massive transfusions are subject to 'blind' transfusion. This is associated with insufficient transfusion of both FFP and platelets, which may aggravate bleeding. A 'blind' transfusion strategy consisting of a validated guideline with a predefined ratio of the different blood products, timing of laboratory tests as well as a sound logistic protocol facilitating this procedure, involving the blood bank and treating physicians, is needed urgently.

A fast, digitally controlled flow proportional gas injection system for studies in lung function

The aim of this paper is to describe a device for flow proportional injection of tracer gas in the lungs of mechanically ventilated patients. This device may then be used for the study of the multiple breath indicator gas washout technique to determine the end-expiratory lung volume. Such a tracer gas injection device may also be used in the study of other techniques that rely on uptake and elimination of tracer gas by the lungs. In this paper, an injector is described which enables injection of indicator gas at a predetermined concentration in a breathing circuit independent of the type of breathing. The presented setup uses a control computer to produce steering signals to a multivalve array in proportion to the input breathing signals. The multivalve array consists of ten circular valves, each with a different diameter, which can be opened or closed individually according to the input signal of the array. By opening of a certain combination of valves an amount of sulphur hexafluoride gas proportional to the inspiratory breathing signal is released. The rate of transmission between the components of the injection system was 80 Hz. The injector has a full flow range between 0-10 L/min. The delay time between the breathing signal and the flow response was 70 ms. The aimed washin gas concentration of 1% SF6 was achieved after 0.5 s. The study describes the results of tests to determine valve-flow ratios, step response and dynamic response of the injector. The flow output response of the injector system was shown to increase in input frequencies above 3 Hz. The valve flow ratios showed the largest relative deviation in the two smallest valves of the 10 valve array, respectively 0.005 L/min (25%) and 0.002 L/min (20%). We conclude that the injector can achieve a stable concentration of indicator gas in a breathing system with an accuracy of 0.005 L/min to execute the multiple breath indicator washout test in human subjects. The results of the study indicate that the injector may be of use in other application fields in respiratory physiology in which breathing circuit injection of indicator gas is required.

Noninvasive monitoring of nonshunted pulmonary capillary blood flow in the acute respiratory distress syndrome

OBJECTIVE

Noninvasive monitoring of nonshunted pulmonary capillary blood flow, using the alveolar amplitude response technique (AART) in a porcine model of the acute respiratory distress syndrome.

DESIGN

Experimental animal study.

SETTING

University center for animal experiments.

INTERVENTIONS

In 12 mechanically ventilated pigs, the nonshunted pulmonary capillary blood flow was varied by means of lung lavages and the application of positive end-expiratory pressure.

MEASUREMENTS AND MAIN RESULTS

Nonshunted pulmonary capillary blood flow was determined by AART. Cardiac output (determined by the thermodilution method) corrected for venous admixture was used for comparison (r2 varied between .58 and .94; p < .01). The trend in the development of nonshunted pulmonary capillary blood flow as measured with AART was in agreement with the trend detected by cardiac output corrected for venous admixture in 92% of all events.

CONCLUSIONS

We conclude that AART can be used to monitor changes in nonshunted pulmonary capillary blood flow in cases of acute respiratory distress syndrome noninvasively and continuously.

A novel method of evaluation of three heat-moisture exchangers in six different ventilator settings

OBJECTIVE

The purpose of this study was to assess and compare the humidification, heating, and resistance properties of three commercially available heat-moisture exchangers (HMEs). To mimic clinical conditions, a previously validated, new, realistic experimental set-up and measurement protocol was used.

DESIGN

Prospective, comparative experimental study.

SETTING

Surgical Intensive Care Unit, University Hospital of Rotterdam.

MATERIALS

An experimental set-up consisting of a patient model, measurement systems, and ventilator and three different HME types.

INTERVENTIONS

The air flow, pressure in the ventilation circuit, pressure difference over the HME, and partial water vapour pressure and temperature at each side of the HMEs were measured. Measurements were repeated every 30 min during the first 2 h and every hour up to 24 h for each HME at six different ventilator settings. The mean inspiratory and maximum expiratory resistance, flow-weighted mean absolute humidity and temperature outputs, and humidification and heating efficiencies of HMEs were calculated.

MEASUREMENTS AND RESULTS

The Dar Hygroster had the highest humidity output, temperature output, humidification efficiency, and heating efficiency values throughout the study (32.8 +/- 21. mg/l, 32.2 +/- 0.8 degrees C, 86.3 +/- 2.3%, and 0.9 +/- 0.01%, respectively) in comparison to the Humid-Vent Filter (25.3 +/- 3.2 mg/l, 31.9 +/- 0.8 degrees C, 72.2 +/- 5.3%, 0.9 +/- 0.02%, respectively) and the Pall Ultipor BB100 breathing circuit filter (23.4 +/- 3 mg/l, 28.3 +/- 0.7 degrees C, 68.8 +/- 5.9%, 0.8 +/- 0.02%, respectively). The inspiratory and expiratory resistance of the HMEs remained below clinically acceptable maximum values (2.60 +/- 0.04 and 2.45 +/- 0.05 cmH2O/l per s, respectively).

CONCLUSION

The Dar Hygroster filter was found to have the highest humidity and temperature output of all three HMEs, the Humid-Vent filter had a satisfactory humidity output only at low tidal volume flow rate and minute volume settings, whereas the Pall Ultipore BB 100 never achieved a sufficient humidity and temperature output.

A silicon bidirectional flow sensor for measuring respiratory flow

We describe a solid-state, silicon integrated, bidirectional flow sensor for respiratory applications. The sensor is a thermal vector sensor. The electronic circuitry for obtaining bidirectional sensitivity is presented together with actual application to a healthy volunteer put on mechanical ventilation. The sensor's input flow range is from -60 to +60 L/min, and its rise-time is < or = 40 ms and fall-time is < or = 60 ms. The effect of changes in gas composition as used in mechanically ventilated patients on the sensor output signal are estimated to be less than 2%. The temperature sensitivity is about -1.5% per degree Celsius.

An experimental set-up to test heat-moisture exchangers

OBJECTIVES

The purpose of this study was to build an experimental set-up to assess continuously the humidification, heating and resistance properties of heat-moisture exchangers (HMEs) under clinical conditions.

DESIGN

The experimental set-up consists of a patient model, measurement systems and a ventilator.

SETTING

Surgical ICU, University Hospital of Rotterdam.

MATERIALS

A clinically used HME.

MEASUREMENTS AND RESULTS

The air flow, pressure in the ventilation circuit, pressure difference over the HME, and partial water vapour pressure and temperature at each side of the HME were measured. The resistance, absolute humidity, humidification efficiency and temperature difference at the patient side of the HME were calculated. Measurements were performed during 24 h. The temperature output, humidity output and lung mechanics of the patient model were similar to values found in mechanically ventilated patients. The measurement system was in agreement with the ISO draft standard and was capable of measuring dynamic variation of water and heat exchange over the range of a clinically used ventilator setting.

CONCLUSION

The experimental set-up described is reliable for evaluating HMEs and can also be used for future clinical evaluation of HMEs. The main advantages of this set-up over those described previously are: (i) measurements of dynamic variations of water and heat exchange; (ii) on-line measurements of expiratory, as well as inspiratory resistance.