Usage of muscle relaxants -- a necessary part of anaesthesia during certain major operations -- may increase the risk of respiratory complications after surgery, a new study has found.

The findings suggest that most common complications involving the respiratory system were a reduced capacity of the lung transiently to absorb oxygen (5.2 per cent), and infections of the lung and respiratory tract (2.5 per cent). Anaesthetics make patients unconscious during an operation and prevent them from feeling pain. Muscles, however, are not paralysed by these drugs and may still move, suggests the paper published in The Lancet Respiratory Medicine journal.

"To prevent this, we also use muscle relaxants or, more precisely, neuromuscular blocking agents," said co-author Manfred Blobner, Professor at the Technical University of Munich (TUM) in Germany. "These drugs are particularly needed when operating on a patient's chest or abdomen. They are also used to protect the vocal chords from injury when a tube is placed in the airway to allow artificial ventilation," Blobner added.

The researchers also found that roughly three quarters of all patients (17,150 people) were treated with neuromuscular blocking agents. They were shown to have a significantly higher risk (+4.4 per cent) of developing any type of respiratory complication. The researchers did not look into how the use of muscle relaxants might cause the negative effects. Earlier studies have shown that even small amounts of muscle relaxants remaining in the bodies of patients could be responsible for some of the complications.

The team is planning to implement more targeted studies to identify the underlying mechanisms behind their findings. "Based on our results, we believe that patients undergoing minor surgical procedures, that does not necessarily require neuromuscular blocking drugs, might benefit from avoiding them," Blobner noted. For the study, the team involved 22,803 patients of 211 hospitals in 28 European countries.