Cross reference, cross reference, cross reference! Inappropriate relative bradycardia is when the heart rate is slower than it should be given everything else that is going on. This is may occur because vagal tone is over-riding the sympathetic input to the heart. Peritonitis is a classic that can do this. Look at the other perfusion parameters and work out how fast the heart rate should be. If it’s lower than expected then go looking for an underlying reason. Upper airway obstruction and parenchymal lung disease (especially pneumonias) can also do it. It also occurs with pretty much all the things that were listed last week under vagal arrest so...