Robotic nephrectomy has become a common surgical procedure in recent years. Perioperatively, pneumothorax is a rare but well-documented complication, which can potentially be life threatening if not recognized and treated promptly. However, due to the mechanical ventilation and general anesthesia, patient may not show any signs and symptoms of respiratory distress or hemodynamic changes during surgery. Also, intraoperative changes of blood pressure and heart rate are often attributed to many other factors, such as dehydration, blood loss, surgical stimulation, inadequate anesthesia depth or side effects of anesthesia medications.
Postoperative chest pain and dyspnea. In our patient, the pneumothorax was not diagnosed until after the surgery when the patient complained of chest pain and dyspnea upon awakening. Given the recent history of NSTEMI, acute coronary syndrome was the first to be ruled out. Therefore, a 12-lead EKG was ordered, which did not show ST-T changes suggestive cardiac ischemia. Instead, it showed marked reduction in voltage amplitude on lead I, aVL, and V2 through V6, suggesting left-sided pneumothorax. Since only lead II was monitored intraoperatively and it showed only subtle increase in negative voltage, pneumothorax was never suspected during surgery.
EKG change and pneumothorax. EKG changes due to pneumothorax have been well documented in the literature [1, 2, 4]. Depressed amplitude of QRS and right axis deviation are due to 2 factors:
1. Increased distance between the heart and the electrodes. The heart is rotated and displaced to the right due to increased intrathoracic pressure.
2. The newly formed air cavity between the heart and the surface electrodes could reduce electrical conductance as air is a poor electrical conductor.
Voltage alternans are associated with respiration cycles. The heart is displaced more to the left with each inspiration as more air gets into the right lung, so V4-6 showed bigger R waves with inspiration and smaller ones with expiration as the heart is displaced more to the right.
In our patient, the voltages on lead I, aVL and V2 through V6 were markedly diminished due to the insulating effect of CO2 from pneumothorax on the left. Of note, the voltage on V1 was preserved, since V1 lead is placed to the right of the sternum. Our patient also presented with an extreme right superior EKG axis at 268 degree, which can be explained by the pre-existing left axis deviation and the newly diminished lateral lead amplitudes. After chest tube placement, the amplitude dramatically restored, and the EKG returned to near baseline.
Monitor other EKG leads. Retrospectively, the EKG changes could have been detected intraoperatively if lead I and lead V5 had been monitored. Routinely, anesthesiologists only monitor lead II due to the fact that lead II is the best lead for detecting rhythm abnormalities. Lead V5 is sometimes monitored to detect lateral wall ischemia. On the anesthesia monitor, lead I, II or III can be freely selected on the screen. We suggest that in a patient who is at risk of developing pneumothorax from a particular surgical procedure like robotic nephrectomy, the baseline voltages of lead I, II and III should be documented and compared periodically during surgery. In addition, lead V5 should be monitored continuously.
Right sided pneumothorax. In the case of right sided surgery, e.g., right nephrectomy, the EKG changes due to right-sided pneumothorax could be different from the left-sided pneumothorax. One case reported increased voltages on lead II and flipping of V5 from positive to negative . A second case reported amplitude diminution in lead I and aVR and flipping of V3 from negative to positive (poor progression). Also noted is q waves in lead II, III and aVF . Another right pneumothorax also reported amplitude diminution of lead I and rotation of the heart (mostly upright V4 to biphasic V4) . The carbon dioxide present in the right chest cavity might displace the heart towards left chest wall, causing the changes of voltage and axis. Rotation of the heart may affect the normal progression of QRS on precordial leads. One common finding in these case reports is diminished voltage in lead I.
Peak airway pressure. Although pneumothorax might cause an increase in peak airway pressure, however increased peak airway pressure can be attributed to many factors: Trendelenburg position, kinking of the anesthesia circuit, kinking of the endotracheal tube, right main stem intubation, and elevation of diaphragms due to insufflation of the abdominal cavity. Therefore, peak airway pressure increase alone is not diagnostic of pneumothorax.
Breath sound. Loss of breath sound on one side of the lung could be a sign of pneumothorax. However, due to the unique OR setting, the lungs could be difficult to auscultate due to the patient positioning, surgical draping, OR music or noise. In addition, right main stem intubation is a common cause of the loss of the breath sound on the left.
Positioning. Intraoperatively, the EKG monitoring is further complicated by the patient positioning. When the patient is placed in left lateral decubitus position (left side down), the position of the heart could be displaced or rotated. Therefore, the appearance of lead I, II, III, or V5 waveform could differ from that of the pre-operative twelve lead EKG . It is important to document the new baseline EKG appearance after the position change. Our patient was placed in the right lateral decubitus position (right side down). Because of the support of the mediastinum, the position of the heart and the appearance of EKG waveforms do not change much. Any deviation from the new baseline after the positioning, either right or left lateral decubitus, should trigger an investigation accordingly.
Point Of Care Ultrasound. Lastly, Point Of Care Ultrasound (POCUS) has become an invaluable tool for anesthesiologists. It is portable, non-invasive, and readily available in the operating room setting. Loss of lung sliding and pulsing is a sensitive indicator for pneumothorax.
In conclusion, for surgeries with high risk of developing pneumothorax, we suggest anesthesiologists monitor lead V5 continuously and/or check lead I and lead III periodically. Voltage diminution and polarity flipping in Lead I and precordial leads could be the first sign of pneumothorax.