Anaesthetic management of a parturient patient with a malignant hyperthermia partner

Abstract

Malignant hyperthermia (MH) is a rare but deleterious anaesthetic emergency that has an autosomal dominant inheritance. Successful management of the MH-susceptible fetus hinges on early suspicion and preparation. This case highlights the importance of knowing paternal anaesthetic risk as well as maternal in the parturient population. Paternal anaesthetic history is paramount in this situation, especially with a normal maternal risk, and preparation of the patient, staff and equipment is at the centre of the peripartum management of these patients.

Background

Malignant hyperthermia (MH) is an uncommon pharmacogenetic disorder of the muscle induced by exposure to certain anaesthetic agents characterised by hypermetabolism, muscle rigidity and muscle injury.¹ Presentation within the child population is similar to adults, with muscle rigidity, hypermetabolism and arrhythmias, and neonatal presentation is likely to fall under the same umbrella. Estimated incidence in the general surgical population is between 1:3000 to 1:100 000 and 1:125 000 in the US obstetric population.^{2 3}

Genetically, its pattern of inheritance is autosomal dominant with variable penetrance,⁴ related to mutations of the genes for the ryanodine receptor (RYR1) or calcium channels located within the sarcoplasmic reticulum. These mutations lead to rapid and uncontrolled release of calcium within the skeletal muscle cells and a hypermetabolic crisis.⁵

As an autosomal dominant inheritance exists, it would be reasonable to assess fetal risk of inheritance as 50%. Currently, no confirmed cases of fetal MH crisis have been reported, and rare literature exists on the anaesthetic considerations for the parturient patient with an MH-susceptible fetus.⁶

Management of MH crisis is well outlined by the Association of Anaesthetists of Great Britain and Ireland (AAGBI) and involves early recognition, immediate management, monitoring and treatment and follow-up.⁷ The use of dantrolene is advocated at an initial bolus dose of 2.5 mg/kg up to 10 mg/kg, alongside active cooling and measures to support against the sequelae of hypermetabolism.

In the paediatric population, management follows the same pathway of avoiding/removing precipitants, giving dantrolene and managing the consequences of hypermetabolism. Exposure to precipitants such as inhalational anaesthetics may be avoided through the use of intravenous anaesthetics. Recently, target-controlled infusion models have become available for propofol in children over 1 year of age (approximately 5 kg) and for remifentanil in children over 12 years of age (approximately 30 kg). The dosing of dantrolene is recommended at an initial bolus dose of 2–3 mg/kg, with subsequent doses at 1 mg/kg until treatment goals are achieved (temperature is less than 38.5 ºC or CO₂ less than 6 kPa with normal ventilation).

Case presentation

A woman in her 30s (Gravida 2 Parity 1) was admitted to hospital at 36+6 weeks with newly diagnosed pre-eclampsia (PET) and significant intrauterine growth restriction. She was booked for lower segment caesarean section (LSCS) the following morning to allow for effective management of her PET.

Following establishment on oral labetalol and normalisation of blood pressure, she was reviewed by a consultant anaesthetist who performed a preoperative assessment. The patient reported no significant medical history and had undergone a general anaesthetic previously without incident. No further sequelae of PET were reported or identified.

During the anaesthetic assessment, the patient’s partner joked that it was ‘lucky it was not him having an anaesthetic’ as he had confirmed MH with genetic correlation in his family. He was uncertain regarding his familial genotype but had undergone genetic testing due to a phenotypical presentation of high temperature, muscle rigidity and arrhythmia. This resulted in a discussion between the anaesthetic team and the family with regards to the potential risk to the fetus should a general anaesthetic be required given the dominant inheritance pattern.

The anaesthetic preference would be a spinal anaesthetic; however, a contingency plan was made should a general anaesthetic be required based on the management of malignant hyperpyrexia guidelines. The emergency theatre, obstetric and anaesthetic teams were informed about the patient should she deteriorate overnight and require a time pressured emergency caesarean out of hours. A vapour-free machine was sourced and set up in obstetric recovery. Total intravenous anaesthesia (TIVA) was agreed as the planned induction and maintenance anaesthetic and suggested protocol documented. Dantrolene availability was confirmed, and common triggering agents were highlighted for removal from theatre.

At 01:00 she developed acute hypertension and was therefore transferred to maternal high dependency unit (MHDU) and an arterial line inserted. Her blood pressure was managed with intravenous labetalol, hydralazine and magnesium sulfate. Due to the rapid deterioration in her condition, repeat bloods were taken to check platelet and clotting function.

Once blood pressure control had been established back to baseline, she was transferred to theatre to undergo an emergency LSCS category 2 under spinal anaesthesia at 02:52 hours. A live girl was delivered at 03:02 hours without ensuing incident, and she was transferred back to MHDU for ongoing blood pressure support and monitoring.

Outcome and follow-up

Following her procedure, she had a postpartum haemorrhage that required a return to theatre for insertion of Bakri balloon, exploration of incision and B-lynch suture. This was initially performed under spinal anaesthesia but converted to a general anaesthetic when the procedure persisted. She was induced with thiopentone and suxamethonium and maintained on isoflurane and awoken without incident.

Discussion

Currently, no UK guidelines exist for the management of the parturient patient with an MH-positive partner or MH-suspected partner, and this case highlights a potential need. Recommendations exist from the European Malignant Hyperthermia Group (EMHG)⁸ and Malignant Hyperthermia Association of the United States (MHAUS).⁹ The cornerstone of both these recommendations is suspicion and preparation. A proposed flowsheet of anaesthetic management throughout pregnancy is demonstrated in figure 1.

Figure 1.

A proposed flowsheet summary of the suggested management of the parturient patient with a malignant hyperthermia (MH) partner. IV GA, intravenous general anaesthesia; TIVA, total intravenous anaesthesia.

The current suggested dataset for an obstetric anaesthetic history from the Obstetrics Anaesthetists' Association (OAA) includes the patient (maternal) history of general anaesthesia and the maternal family history, but there is no recommendation to obtain the paternal history or paternal family history.¹⁰ Given the mode of inheritance for MH, it would seem pertinent to obtain paternal anaesthetic history alongside maternal as a matter of routine. Ideally, all autosomal dominant conditions such as MH should be documented from maternal and paternal families within the obstetric notes and a referral made to the anaesthetic department as soon as able to facilitate preparations.

Antenatal management

Anaesthetic input antenatally would be indicated:

• To adequately assess the patient with regards to MH risk and anaesthetic risks. Anaesthetic assessment should be undertaken as per the OAA guidance, with particular attention to general and regional anaesthetic risks.

• To form a shared decision with the patient, obstetricians and midwives regarding the birth plan, contingencies and to manage expectations.

• To inform the MH centre and/or tertiary delivery unit if applicable.

• To communicate with the staff undertaking the procedure and ensure adequate senior anaesthetic, obstetrician and midwifery presence.

If the paternal family is known to exhibit a causative mutation or known to the MH centre, fetal genetic testing may be undertaken; however, this is currently not recommended unless the procedure (chorionic villus sampling or amniocentesis) is being undertaken for another reason. Liaison with the MH centre would need to be undertaken if, for instance, a maternal condition precluded against regional anaesthesia.

Labour and delivery

The parturient patient with a fetal risk of MH may labour naturally or in midwifery led units as guided by the obstetric and maternal risks. The susceptibility to MH does not impede normal labour, nor does it seem to pose an increased risk to patients when isolated from the triggering agents; thus, if a vaginal delivery is desired, it can be safely undertaken.

Early regional anaesthesia would be recommended in the labour process as a well-functioning epidural may provide a means for regional anaesthesia in an emergency situation. Should a theatre admission become necessary, regional anaesthesia is the recommended anaesthetic for these patients, as it does not increase fetal MH risk compared with general anaesthesia. Optimisation for regional anaesthesia should be undertaken during the labour process (eg, ensure bloods are taken and up to date, intrauterine resuscitation to allow for regional anaesthetic time) to prevent general anaesthesia as possible.

If the patient is unsuitable for regional anaesthesia, or there are other constraints, and a general anaesthetic must be undertaken, the case should be treated as a suspected MH case:

• Ensure a vapour-free machine is available in theatre.

• Ensure a vapour-free circuit is available in theatre/MH filters.

• Ensure equipment to provide TIVA is available in theatre.

• Ensure triggering agents are avoided (inhalational agents/suxamethonium).

• Ensure dantrolene is READILY available.

• Ensure theatre team are aware of the anaesthetic risks and have roles assigned in case of emergency.

Postnatal

Following delivery of the MH-susceptible fetus, the MH risk returns to the population baseline for the mother. General anaesthesia can be undertaken in the mother with the usual adherence to national and local standards without increased risk of MH. Crossover of inhalational agents and suxamethonium into breast milk following general anaesthetic is negligible due to the rapid metabolism these agents undergo in the maternal circulation, and therefore, risk is not increased postnatally.

Learning points.

• Although incidence of malignant hyperthermia (MH) is rare, it is a potentially life-threatening diagnosis.

• Inheritance is autosomal dominant, and thus, there is a theoretical risk of an MH-negative parturient patient with an MH-positive fetus.

• History taking is the most vital step in managing this situation, as paternal history is rarely sought during obstetric anaesthesia.

• Management of the suspected MH fetus should be as per Association of Anaesthetists of Great Britain and Ireland (AAGBI) guidelines for MH cases.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).