Abstract A forty two year old male, a chronic smoker, was posted for lumbar discectomy at L3-4 level. General anaesthesia was administered and was maintained with isoflurane and nitrous oxide with oxygen. On turning the patient to prone position, the patient developed hypoxaemia. Air entry was reduced on the left lung field along with a rise in peak inspiratory pressure. CT scan of the thorax showed left sided pneumothorax, pneumomediastinum and subcutaneous emphysema. A chest tube thoracostomy was done and the patient made an uneventful recovery. We recommend that pneumothorax should be considered a possibility in any patient who has unexplained hypoxaemia during general anaesthesia and exercise caution while using nitrous oxide in chronic smokers.
Pneumothorax, hypoxaemia, smoker.
Pneumothorax is an uncommon but potentially serious occurrence during anaesthesia. Initial clinical signs may be subtle but progression to tension pneumothorax can result in significant cardiorespiratory instability. We present a case of spontaneous pneumothorax in a chronic smoker following general anaesthesia.
A forty two year old male diagnosed with prolapsed intervertebral disc at L3-4 level, was posted for discectomy. Pre anaesthetic assessment revealed that the patient was a chronic smoker and alcohol consumer and was being treated for alcohol withdrawal symptoms with sertraline and clonazepam for the past one month. There were no other medical problems. The blood workup, electrocardiogram and chest radiograph were normal (Figure 1).
General anaesthesia was planned and induced with intravenous morphine 6mg, glycopyrrolate 0.2mg, midazolam 2mg, propofol 100mg and vecuronium 8mg. Trachea was intubated with 8.0 mm ID endotracheal (ET) tube which was fixed at 23 cm, after confirming bilateral equal air entry by auscultation. Anaesthesia was maintained with 66% nitrous oxide (N2O) + 33% oxygen (O2) and isoflurane. The haemodynamics were stable and the arterial oxygen saturation by pulse oximetry (SpO2) was 100%. The patient was then turned to prone position. Within five minutes, the SpO2 started falling and came down to 85%. The peak inspiratory pressure increased from 25 cm of water (H2O) to 35 cm H2O. On auscultation, it was found that there was no air entry on the left lung field. Endobronchial migration of the ET tube was suspected. The ET tube fixation was checked and its position was found to be unaltered (23cm). The tube was withdrawn by 2 cm but there was no improvement in air entry on the left side. N2O was discontinued and the patient was ventilated with 100% O2. SpO2 improved to 96%. During this period, there was no cardiovascular instability.
The patient was then turned to supine position. Air entry improved on the left side but it was still less compared to the right side. SpO2 came up to 98%. Pneumothorax was suspected considering the fall in SpO2, increase in airway pressure and decreased air entry on the left side. A bedside chest radiograph was taken but the image obtained was not clear. It was decided to postpone the surgery and the patient was shifted to the radiology department where a computerized tomographic (CT) scan of the thorax was done. The CT scan showed left sided pneumothorax, pneumomediastinum and subcutaneous emphysema along with a bulla on the left apicoposterior segment (Figures 2, 3, 4 & 5 respectively). The patient was then shifted to the intensive care unit (ICU) where a chest tube thoracostomy was done. Air entry improved subsequently and the patient was able to maintain a Spo2 of 98 to 99% with 35% FiO2 on T piece. The trachea was extubated after observing the patient for two hours in ICU. He was taken up for surgery three days later, with the chest tube in situ and this time, the perioperative period was uneventful and the chest tube was removed on the first postoperative day.
The development of a pneumothorax is a rare complication during general anaesthesia. It has been reported to occur during spontaneous as well as controlled ventilation. Our patient was receiving controlled ventilation in prone position when the desaturation episode started. Lee et al,reported a similar incident in which a patient undergoing cervical spine surgery in prone position developed pneumothorax. But here, the administration of an antibiotic led to bronchospasm followed by a rise in peak airway pressure causing tension pneumothorax. In our case, no antibiotic was administered.
Bansal et al, described a case of pneumothorax complicating pulmonary thromboembolism in a chronic smoker who was operated for femur fracture under combined spinal epidural anaesthesia. In this case, the authors attributed the pneumothorax to the severe bouts of coughing induced by pulmonary thromboembolism. Our patient was a chronic smoker. Smoking may lead to inflammation and obstruction of small airways, accounting for an increased risk of spontaneous pneumothorax. Chronic smokers are also known be at risk of developing spontaneous pneumothorax following episodes of exertion such as coughing.
According to Bense et al,the lifetime risk of developing a pneumothorax in healthy male smokers may be as much as 12% compared with 0.1% in non-smoker males. Rupture of subpleural blebs or bullae is associated with spontaneous pneumothorax. The etiology of such bullous changes in otherwise apparently healthy lungs is unclear. Undoubtedly smoking plays a role.[5,6 ] In our patient, CT scan showed a bulla in the left apico posterior segment. There could have been another bulla which could have ruptured and produced the pneumothorax.
Our patient received N2O as a part of general anaesthesia for around thirty minutes. N2O administration may have caused expansion of the preexisting bulla, causing a rupture leading to pneumothorax. The role of N2O in expanding existing pneumothoraces is well described.
The clinical presentation of pneumothorax is highly variable, ranging from no obvious clinical signs to tension pneumothorax with impending cardiorespiratory arrest. Anaesthetized patients are unable to complain of chest pain or dyspnoea, the two most common symptoms of pneumothorax. Hence, a high index of suspicion is required. High risk situations include surgical and anaesthetic procedures around the base of neck or the chest wall.[9 ] Classically, physical examination of the exposed chest may show tachypneoa, tachycardia, tracheal deviation, unilaterally decreased chest movement, diminished or absent breath sounds, hyper-resonance or subcutaneous emphysema. However, smaller pneumothoraces may not be detectable. Our patient had reduced air entry on the left side and increased PIP. Subcutaneous emphysema was later detected by CT scan.
The severity of the clinical presentation depends on the size of the pneumothorax, rapidity of accumulation, age of the patient, mobility of the mediastinum and the presence of any underlying lung disease. The diagnosis of pneumothorax during general anaesthesia is therefore difficult. The clinical presentation is variable because the signs and symptoms are not always correlated with the size of pneumothorax.[10,11] Even if there are changes in vital signs (pulse oximetry, blood pressure and pulse rate), they are usually non specific and there are more usual causes of such changes. As a result, a pneumothorax is often regarded as a diagnosis of exclusion.
This incident now brings us to the question whether all patients with history of chronic smoking should be screened by CT scan of the thorax to look for preexisting bullae or blebs. In a study conducted by Sihoe et al, the authors tested the hypothesis that CT scanning can help to predict the probability of the occurrence of primary spontaneous pneumothorax (PSP) by detecting lung bullae. They concluded that detection of lung bullae by CT scanning in the contralateral lung following unilateral PSP is associated with a higher rate of subsequent occurrence of pneumothorax in that lung. However, we feel that routine screening of all chronic smokers by CT scan of the thorax is not practically feasible considering the cost involved, the issue of radiation and the rarity of pneumothorax as a complication.
We therefore conclude that pneumothorax should be considered one of the differential diagnoses in any patient who has unexplained hypoxaemia during general anaesthesia and exercise caution while using nitrous oxide in chronic smokers.
Criteria for inclusion in the authors’ list
Dr. K. Sulfiqdeen- concept, design, definition of intellectual content, literature search and manuscript preparation.
Dr. K. Pradeep – literature search, manuscript preparation, manuscript editing and manuscript review.
Dr. S. Parthibhan- literature search and manuscript preparation
We thank Dr. Senthil M.D and Dr. Upasana M.D, associate professors in the department of radiology, Saveeetha Medical College Hospital, for their technical help.
The manuscript was not presented anywhere else and there are no conflicts of interest for either of the authors to declare.
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- Fig. 1- Preoperative chest radiograph.
- Fig. 2- CT scan showing left sided pneumothorax (marked with arrow).
- Fig.3- CT scan showing pneumomediastinum (marked with arrow).
- Fig. 4- CT scan showing subcutaneous emphysema (marked with arrow).
- Fig. 5- CT scan showing bulla on the left apicoposterior segment (marked with arrow).
Fig. 6- Chest radiograph showing intercostal drainage tube in
Running title- Pneumothorax during general anaesthesia.
First Author: Dr. Kaja Mohideen Sulfiqdeen DNB, Senior Resident, Department Of Anaesthesiology, Saveetha Medical College Hospital, Thandalam, Kanchipuram district, Tamilnadu.
Second Author: Dr. Karunagaran Pradeep MD, Assistant Professor, Department Of Anaesthesiology, Saveetha Medical College Hospital, Thandalam, Kanchipuram district, Tamilnadu. (Corresponding author)
Third Author: Dr. Shanmugam Parthibhan MD, Assistant Professor, Department Of Anaesthesiology, Saveetha Medical College Hospital, Thandalam, Kanchipuram district, Tamilnadu.
Dr. K. Pradeep
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