Spontaneous pneumomediastinum: A report of two cases at a district general hospital

Introduction

Spontaneous pneumomediastinum (Hamman’s syndrome) was first described during the 17th century by Louise Bourgeois and subsequently published by Lois Hamman in 1939. ¹ It is a rare complication of vaginal birth with an incidence of 1 in 100,000 deliveries. ² Described here are two cases that occurred at our hospital between 2017 and 2019.

Case 1

A 31-year-old woman in her first pregnancy attended the midwifery-led birthing unit at 41 weeks of gestation in spontaneous labour. She had no significant past medical history, was a non-smoker, and her pregnancy leading up to labour had been uncomplicated. On admission, she was in established labour and had artificial rupture of membranes following slow progress of her first stage; she subsequently progressed well. She managed the contractions with Entonox®. Whilst in the active second stage of labour, she reported sudden facial swelling but no dyspnoea, palpitation, or wheeze. The obstetric anaesthetist reviewed and initiated intravenous (IV) hydrocortisone and chlorphenamine although remained unconvinced the symptoms were due to an allergic reaction. The woman was transferred to the high-risk obstetric unit where she was reviewed by the obstetrician. She was advised to reduce the duration of the second stage, and a male infant was delivered by Neville-Barnes forceps in good condition, with Apgars of 9, 10, and 10 at 1, 5, and 10 min respectively.

A medical review was sought following the third stage and she was found to have surgical emphysema on the chest wall. Her observations remained normal, and the case was discussed with the cardiothoracic team who advised computerised tomography (CT) of the thorax without contrast. The imaging showed extensive surgical emphysema within the upper anterior chest wall, lower neck bilaterally, and post paraspinal soft tissue; there was extensive pneumomediastinum but no pneumothorax. A subsequent CT thorax with oral contrast showed no evidence of an oesophageal tear.

The woman was observed on the postnatal unit. She remained stable and was able to mobilise and care for her baby without restriction. She was discharged on day 3 following delivery. An outpatient chest radiograph (CXR) arranged two weeks after discharge showed complete resolution of the pneumomediastinum.

Case 2

A 34-year-old woman in her first pregnancy attended the midwifery-led birthing unit at 38 weeks of gestation in spontaneous labour. She had no significant past medical history but had previously smoked until the age of 20. Her antenatal care was unremarkable. She had a straightforward delivery in the birthing pool and had Entonox® during a short first stage of labour. A right labial hematoma was identified and required evacuation in the operating theatre under spinal anaesthesia, and she was commenced on prophylactic antibiotics.

The next day she reported bubbling under the skin around the chest, which was tracking up towards the ears with associated chest tightness and dyspnoea on exertion; her observations remained normal throughout. She was reviewed by the medical team and started on high flow oxygen. She was transferred back to the high-risk obstetric unit and reviewed by an ear, nose, and throat (ENT) specialist as recommended by the medical team. A CT of the neck and chest performed with IV contrast showed extensive soft tissue emphysema of chest and neck tracking down into the mediastinum, and a small right apical pneumothorax.

Oxygen therapy was stopped within 24 h of diagnosis as she was maintaining good oxygen saturation. She still had a mild degree of dyspnoea on exertion which improved during her time in hospital. CXR performed on day 3 showed resolution of the pneumothorax and she was discharged home. At the respiratory clinic two weeks later, she was asymptomatic and a repeat CXR showed complete resolution of surgical emphysema.

Discussion

Spontaneous pneumomediastinum is thought to be caused by prolonged excessive Valsalva manoeuvre during the second stage of labour. ³ Within the non-pregnant population, protracted vomiting and coughing are common symptoms preceding the condition.^3,4 This leads to rupturing of marginal alveoli and air leaking into the mediastinum. ⁵ Individuals with a history of smoking, illicit drug use, or asthma are at a higher risk of developing pneumomediastinum. ³ Neither woman described here had any predisposing factors which would have raised suspicion of pneumomediastinum during labour. Although most cases are identified postpartum, the first case described shows the onset of pneumomediastinum intrapartum. Common symptoms include chest pain or tightness, dyspnoea, dysphagia, dysphonia, palpitations, and a tearing sensation around the neck may also be experienced, as air leaks from the mediastinum and into the subcutaneous tissue.^6–8 The ensuing surgical emphysema presents with crepitus around the chest wall extending towards the neck and behind the ears as well as facial or neck swelling. Presence of surgical emphysema often correlates with a more favourable outcome as entrapped air can vacate the mediastinum. ⁶

A CXR is commonly performed early on in the investigation of women with respiratory symptoms in pregnancy as shown in Figure 1. Pneumomediastinum is classically identified by the lifting of the pleura from the heart borders and extension of air into the fascial planes of the neck.^6,9 A systematic review showed that CXR has a sensitivity of 83% in diagnosing pneumomediastinum. ¹⁰

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Figure 1.

Proposed algorithm for pneumomediastinum. CXR: Chest radiograph; MDT: multi-disciplinary team; CT: computerised tomography; IV: intravenous.

Although spontaneous pneumomediastinum is often benign, other emergency diagnoses need to be considered. These include pulmonary or air embolism, pneumothorax, oesophageal rupture, or aortic dissection.^1,6 An oesophageal tear (Boerhaave syndrome) has similar clinical features but is more commonly associated with severe hyperemesis; to date, no cases of oesophageal tear secondary to second stage labour have been reported in literature. Aortic dissection is rare within this population; however, a personal history of Marfan’s, Ehler-Danlos, or aortic valvular disease, or a family history of aortic aneurysm should raise suspicion of this pathology and the woman appropriately investigated.

When there is doubt about the diagnosis or suspicion of other differential diagnoses, a CT chest & neck with IV contrast is useful to aid management. CXR or CT thorax with oral contrast should be performed if clinical features suggest Boerhaave syndrome. ³

Once the diagnosis of pneumomediastinum is established, treatment protocol does not deviate from those diagnosed with pneumomediastinum outside of pregnancy. Anxiolytic, analgesia, and antitussives can be given, and the woman is advised against significant physical exertion. ¹¹ Although high flow oxygen has been utilised in treating spontaneous pneumomediastinum, there is lack of evidence to support its use would hasten recovery.^11–13 In cases when pneumomediastinum is suspected during the second stage of labour, minimising that period by trial of instrumental delivery is recommended. ¹⁴

A secondary pneumothorax can develop, which is identified through radiological imaging of the lungs. Rarely, air continues to build and is unable to escape the mediastinum causing significant compression of the great vessels and impendence of venous return, ultimately leading to cardiogenic shock.^6,15,16 This is termed malignant pneumomediastinum, which is a medical emergency and needs surgical intervention to relieve trapped air by splitting the sternum. ⁵ Therefore, women with confirmed pneumomediastinum should be monitored for 24 h with regular measurement of vital signs. After the initial 24 h, if the woman is not requiring oxygen therapy and the vital signs remain normal, complications are very unlikely and discharge can be considered.

Recovery of the condition takes 3 to 14 days. ¹⁷ A follow-up CXR can be performed two weeks following diagnosis to confirm resolution. If pneumomediastinum persists, the woman should be reviewed in a specialist setting and underlying conditions considered. A history of spontaneous pneumomediastinum at a previous delivery does not mandate caesarean section in a future pregnancy. The use of epidural anaesthesia has been suggested for women in labour with this history as it may reduce the likelihood of involuntary pushing and to facilitate operative vaginal delivery. ⁴ The flowchart in Figure 2 summarises a proposed management algorithm for women presenting with features of pneumomediastinum during the intrapartum and postpartum period.

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Figure 2.

Chest radiograph for case 2: (L) demonstrates air pockets infiltrating the mediastinum at point of diagnosis; (R) demonstrates complete resolution 17 days later. The yellow arrows show the lifting of the left heart border. The red arrows show the subcutaneous emphysema affecting the thorax and spreading towards the neck. The four radio-opaque circular spots are buttons of the woman’s gown.

Women can be reassured of the self-limiting disease course upon confirming pneumomediastinum and the favourable prognosis it carries. ¹³ Smokers should be advised and given provision for smoking cessation as it carries benefits in general health in the longer term.^18,19

Conclusion

The two cases described here demonstrate a variety of management approaches, and the importance of timely recognition of the clinical signs, appropriate investigations and multidisciplinary management in the acute setting, including obstetric and respiratory expertise. Reassuringly, treatment is usually conservative, and women can be reassured of the likely good prognosis.

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