Patients of the ICU's often require bronchodilatory treatment due to bronchospasm caused by conditions like : acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD) or asthma. The β2 adrenergic drugs are one of the most commonly used for this purpose. However it is known that they may cause tachycardia and may have substantial proarrhythmic effect. The investigators' aim is to estimate the influence of nebulized bronchodilatory drugs on selected electrophysiological parameters, whose changes are generally recognized as potentially increasing the risk of ventricular and supraventricular arrhythmias. Two drugs will be compared - salbutamol given in two doses and ipratropium bromide

50 mechanically ventilated patients above 18 years of age and with presence of clinical features of bronchospasm requiring treatment with nebulised short-acting beta-2 mimetic.

Participants will be randomly allocated into two equal groups: a group that was to receive the dose of 2.5 mg and a group that was to receive the dose of 5 mg of nebulised salbutamol. The duration of nebulisation will be set for 20 minutes and Holter ECG data are to be recorded for 60 minutes from the initiation of the nebuliser. The acquired Holter ECG data will be analysed at 10 time points: before salbutamol administration and 5, 10, 15, 20, 25, 30, 40, 50, and 60 minutes following initiation of nebulisation. Changes in QT interval, corrected QT intervals calculated using Bazett's correction and the Framingham formula and transmural dispersion of repolarization TDR will be assessed.

Inclusion Criteria:

• the necessity of b2 adrenergics an m2 mimetics administration

Exclusion Criteria:

• patients with past medical history of ventricular arrhythmias ( ventricular tachycardia, ventricular fibril, Torsade de pointes)
• patients with persistent atrial fibrillation
• patients with abnormal plasma sodium, potassium, magnesium, and ionized calcium concentration