Although shivering may occur in about 10% of normal labours and following general anaesthesia, it is particularly associated with regional (especially epidural) anaesthesia and analgesia, during which it has been reported to occur in up to two-thirds of cases. The cause is uncertain, but evidence suggests the tremor is at least partly thermoregulatory, accompanied by core-to-periphery heat redistribution due to sympathetic blockade. Centrally mediated shivering and vasoconstriction thresholds also appear to be lowered by neuraxial anaesthesia. Epidural blockade may inhibit the subjective feeling of being cold, even when the core temperature has fallen. Other postulated mechanisms include altered control of peripheral muscles and a central effect resulting from systemic absorption of local anaesthetic or its transport via the cerebrospinal fluid to the brain. In labour, the high levels of circulating catecholamines and general arousal may also be important. Finally, the tendency for maternal temperature to increase after prolonged epidural analgesia may contribute to shivering, although it has also been suggested that shivering may contribute to the increase in temperature. Shivering is also commonly seen after misoprostol, with reported incidences of 50-70%.
Problems and special considerations
In most cases, shivering is mild and benign, although if severe it may increase maternal catecholamine concentrations and metabolic rate, interfere with fetal and maternal monitoring and be alarming to the mother. It also increases maternal oxygen consumption and carbon dioxide production, although this is rarely a problem in practice. Rarely, the mother may be unable to cooperate with medical and midwifery staff during examinations, etc.
Anecdotally, epidural lidocaine (e.g. top-up for caesarean section) has been associated with an increased incidence of shivering compared with other local anaesthetics, but firm evidence is lacking, and this possibility must be weighed against any advantages of lidocaine (e.g. rapid speed of onset).
Management options
If shivering is mild, simple reassurance is often all that is required. Measures that have been studied include warming of epidural, intrathecal and intravenous solutions and administration of intravenous opioids (pethidine 10-30 mg has been shown to be especially effective in the non-pregnant population). Epidural opioids may also reduce the incidence and severity of shivering. Other drugs shown to be effective after general anaesthesia outside of obstetrics include clonidine and doxapram, although these are infrequently used in the maternity suite. Active warming appears to reduce the incidence of shivering during caesarean section under epidural anaesthesia if it commences preoperatively.
Key points
• Shivering is common during epidural analgesia and anaesthesia.
• Simple reassurance is adequate treatment in most cases.
Further reading
Crowley LJ, Buggy DJ. Shivering and neuraxial anesthesia. Reg Anesth Pain Med 2008; 33: 241-52.
Witte J, Sessler DI. Perioperative shivering: physiology and pharmacology. Anesthesiology 2002; 96: 467-84.