Nitrous oxide: use in cardiovascular risk patients

Nitrous oxide (N2O) has been used in clinical anaesthesia for more than 150 years. Its use is encouraged in combination with new anaesthetics to reduce the cost. Nevertheless there is some evidence to show that N2O impairs myocardial function: e.g. producing a decrease in myocardial contractility and abnormal coronary blood flow. Regional myocardial ischaemia occurs and the recovery after N2O withdrawal is delayed. These dose-dependent effects are enhanced by an increase in sympathetic tone and by a direct effect on the myocardium (inhibition of trans-sarcolemmal calcium ion entry). Haemodynamic parameters are affected; namely a decreased blood pressure and cardiac index and an increase in systemic vascular resistance. Pulmonary circulation is dramatically affected if the pulmonary artery pressure is increased prior to N2O administration. Regional circulation is also modified (decrease in splanchnic and renal blood flow). Therefore the use of N2O cannot be recommended in patients with cardiovascular risk factors who are undergoing cardiac and/or non-cardiac procedures.