Bronchodilator delivery by metered-dose inhaler in mechanically ventilated COPD patients: influence of tidal volume.

OBJECTIVE: The delivery of bronchodilator drugs with metered-dose inhaler (MDI) and a spacer in mechanically ventilated patients has become a widespread practice. However, the various ventilator settings that influence the efficacy of MDI are not well established. The tidal volume (VT) during drug delivery has been suggested as one of the factors that might increase the effectiveness of this therapy. To test this, the effect of two different VT on the bronchodilation induced by beta 2-agonists administered with MDI and a spacer in a group of mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) was examined. METHODS: Nine patients with COPD, mechanically ventilated on volume-controlled mode, were prospectively randomised to receive six puffs of salbutamol (S, 100 micrograms/puff) either with a VT of 8 ml/kg (normal VT, 582 +/- 85) or with a VT of 12 ml/kg (high VT, 912 +/- 137). With both modes inspiratory flow was identical. S was administered with an MDI adapted to the inspiratory limb of the ventilator circuit using an aerosol cloud enhancer spacer. After a 6-h washout, patients were crossed-over to receive S by the alternative mode of administration. Static and dynamic airway pressures, minimum (Rint) and maximum (Rrs) inspiratory resistance, the difference between Rrs and Rint (delta R), static end-inspiratory respiratory system compliance (Cst,rs), intrinsic positive end-expiratory pressure (PEEPi) and heart rate (HR) were measured before and at 15, 30 and 60 min after S. RESULTS: S caused a significant decrease in dynamic and static airway pressures, PEEPi, Rint and Rrs. These changes were not influenced by VT and were evident at 15, 30 and 60 min after S. With normal and high VT, Cst,rs, delta R and HR did not change after S. CONCLUSIONS: We conclude that S delivered with an MDI and a spacer device induces significant bronchodilation in mechanically ventilated patients with COPD, the magnitude of which is not affected by at least a 50% increase in VT. These results do not support the VT manipulations when bronchodilators are administered in adequate doses during controlled mechanical ventilation.

Undiagnosed central anticholinergic syndrome may lead to dangerous complications.

This report describes two cases of central anticholinergic syndrome, the first after general anaesthesia and the other during a prolonged stay in the intensive care unit. The symptoms in both patients resolved soon after physostigmine administration. There was a delay in the diagnosis of central anticholinergic syndrome, which resulted in acute lung injury and unanticipated intensive care unit admission. It is suggested that in cases of abnormal mental recovery after anaesthesia or sedation, the diagnosis of central anticholinergic syndrome should be considered.

Clinical and toxicological data in fenthion and omethoate acute poisoning.

This study paper reports on two cases of poisoning with the organophosphorus insecticides, fenthion and omethoate. The two victims were admitted in the Intensive Care Unit (ICU) a few hours after ingestion of the two insecticides. They received appropriate treatment for organophosphorous poisoning (gastric lavage, activated charcoal, atropine and pralidoxime) and supportive care. Both patients survived. Organophosphate blood levels were determined on admission (fenthion 2.9 micrograms/ml, omethoate 1.6 micrograms/ml) and during the hospitalisation and proved to be considerably high. Slow elimination rate of the poison already distributed in the body was indicated for both pesticides. The patient with omethoate poisoning remained clinically well (Glasgow Coma Scale: 15) and was discharged three days later. The patient with fenthion poisoning, who had also ingested 30 mg of bromazepam and 720 mg of oxetoron, developed cholinergic crisis six hours after admission and was intubated for 24 days, with concomitant complications.

Bronchodilator delivery by metered-dose inhaler in mechanically ventilated COPD patients: influence of end-inspiratory pause.

The delivery of bronchodilators with a metered-dose inhaler (MDI) and a spacer in mechanically ventilated patients has become widespread practice. However, the various ventilator settings that influence the efficacy of MDI are not well established. Application of an end-inspiratory pause (EIP) during drug delivery has been suggested as one of the factors that might increase the effectiveness of this therapy. To test this, the effect of EIP on the bronchodilation induced by beta2-agonists administered with MDI and a spacer in a group of mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) was examined. Twelve patients with COPD, mechanically ventilated on volume-controlled mode, were prospectively randomized to receive six puffs of salbutamol (100 microg x puff(-1)) either with or without EIP of 5 s duration. Salbutamol was administered with an MDI adapted to the inspiratory limb of the ventilator circuit using an aerosol cloud-enhancer spacer. After a 6 h wash-out, patients were crossed over to receive salbutamol by the alternative mode of administration. Static and dynamic airway pressures, minimum (Rmin) and maximum (Rmax) airflow resistance, the difference between Rmax and Rmin (deltaR), static end-inspiratory respiratory system compliance (Cst,rs) and cardiac frequency (fc) were measured before and at 15, 30 and 60 min after salbutamol administration. Salbutamol caused a significant decrease in dynamic and static airway pressures, Rmin and Rmax. These changes were not influenced by application of EIP and were evident at 15, 30 and 60 min after salbutamol. With and without EIP, Cst,rs,deltaR and fc did not change after salbutamol. In conclusion, salbutamol delivered with a metered-dose inhaler and a spacer device induced significant bronchodilation in mechanically ventilated patients with chronic obstructive pulmonary disease, the magnitude of which was not affected by an end-expiratory pause of 5 s. These results do not support the use of end-inspiratory pause when bronchodilators are administered in adequate doses during controlled mechanical ventilation.

Effects of mechanical ventilation on control of breathing.

During spontaneous breathing, respiratory muscle pressure (Pmus) waveform is determined by a complex system consisting of a motor arm, a control centre and various feedback mechanisms that convey information to the control centre. In mechanically ventilated patients, the pressure delivered by the ventilator (Paw) is incorporated into the system that controls breathing and may alter Pmus, which in turn modifies the Paw waveform. Thus, the response of the patient's respiratory effort to Paw and the response of Paw to patient effort constitute the two components of the control of breathing during mechanical ventilation. The response of Paw to patient effort depends on: 1) the mode of ventilatory support; 2) the mechanics of the respiratory system; and 3) the characteristics of the patient's respiratory effort. On the other hand, the response of patient effort to Paw is mediated through four feedback systems: 1) mechanical; 2) chemical; 3) reflex; and 4) behavioural. It follows that in mechanically ventilated patients the ventilatory output is determined by the interaction between the function of the ventilator and the patient's breathing control system. This interaction should be taken into account in the management of mechanically ventilated patients.