Electrographic lead I and V5 monitoring could have detected a missed left‐side pneumothorax intraoperatively

Abstract We present an EKG monitoring strategy to detect pneumothorax during high‐risk surgery. In the literature, EKG changes and pneumothorax are well‐described. However, anesthesiologists only monitor lead II on a three‐lead EKG system in the operating room. In our case, there was only a subtle change in lead II for a left‐sided pneumothorax, which could have been easily missed. On the contrary, there was a marked QRS amplitude reduction and T wave flattening/inversion in lead I and V5. We recommend lead V5 be added to the continuous monitoring and lead I be periodically checked for surgeries known to potentially cause pneumothorax.

The patient remained paralyzed with rocuronium during surgery.
Blood pressure, heart rate, oxygen saturation, end-tidal CO 2 , and peak airway pressure throughout surgery were all unremarkable.
However, upon awakening and extubating the endotracheal tube, the patient became combative and complained of chest pain and shortness of breath. At that time, the patient was breathing 6 L of oxygen via a simple facial mask. Oxygen saturation was 96%. Respiratory rate was 22. Blood pressure was 147/89. Slight tachycardia at 97 was noted. Hydromorphone was initially given for agitation and pain. The patient felt comfortable and fell asleep.
Due to the history of NSTEMI, the acute coronary syndrome was the first to rule out in the recovery room. Postoperative EKG showed a new right superior axis at 268 degrees and markedly reduced R wave amplitude in lateral leads, I and aVL, and precordial leads, V 2 through V 6 ( Figure 2). Also noted were T wave flattening/inversion in lead I, lead II, and precordial leads. Electrical alternans was most visible in V 6 . These EKG findings were consistent with left-sided pneumothorax (Kenzaka & Yamazaki, 2016). Stat chest X-ray was ordered, which revealed a large left-sided pneumothorax and a nearly total collapsed left lung ( Figure 3). Troponin, complete blood count, and basic metabolic panel were normal.
Chest tube was then urgently inserted, and the left lung was reexpanded. Post chest-tube EKG (Figure 4) showed restored voltages on lead I, aVL, and V 2 to V 6 , left anterior fascicular block, and left axis deviation, all of which were similar to the preoperative EKG findings ( Figure 1). Repeat chest X-ray is shown in Figure 5.

| DISCUSS ION
Robotic nephrectomy has become a common surgical procedure in recent years. Perioperatively, pneumothorax is a rare but well-documented complication, which can potentially be lifethreatening if not recognized and treated promptly. However, due to mechanical ventilation and general anesthesia, the patient may not show any signs and symptoms of respiratory distress or hemodynamic changes during surgery. Also, intraoperative changes in 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, the acute coronary syndrome was the first to be ruled out. Therefore, a 12lead EKG was ordered, which did not show ST-T changes suggestive of cardiac ischemia. Instead, it showed a marked reduction in voltage amplitude on lead I, aVL, and V 2 through V 6 , suggesting left-sided pneumothorax ( Figure 2). Since only lead II was monitored intraoperatively and it showed only a subtle increase in negative voltage, pneumothorax was never suspected during surgery.

| EKG changes and pneumothorax
EKG changes due to pneumothorax have been well-documented in the literature (Kleine & Roorda, 1976;Klin et al., 2021 et al. et al., 2008). Depressed amplitudes of QRS complexes and right axis deviation are due to two 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.
Electrical alternans are QRS amplitude changes associated with respiratory cycles. The heart is displaced more to the left with each inspiration as more air gets into the right lung. V 6 shows bigger R waves during inspiration and smaller ones during expiration.
In our patient, the voltages on lead I, aVL, and V 2 through V 6 were markedly diminished due to the insulating effect of CO 2 pneumothorax on the left. Of note, the voltage on V 1 was preserved, since V 1 lead was placed to the right of the sternum. Our patient also presented with an extreme right superior EKG axis at 268 degrees, which can be explained by the pre-existing left axis deviation and the newly diminished lateral lead amplitudes. After chest-tube placement, the amplitudes were dramatically restored, and the EKG returned close to the baseline.

| Monitoring other EKG leads
Retrospectively, the EKG changes could have been detected intraoperatively if lead I and lead V 5 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 V 5 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 V 5 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 report described increased voltages on lead II and flipping of V 5 polarity from positive to negative (Glenn et al., 1996). A second case reported amplitude diminution in lead I and aVR and flipping of V 3 polarity from negative to positive (poor progression). Also noted were q waves in lead II, III, and aVF (Tsilakis et al., 2007). Another right pneumothorax also reported amplitude diminution of lead I, and rotation of the heart (namely, upright V 4 to biphasic V 4 ) (Yamamoto et al., 2021). The CO 2 present in the right chest cavity might displace the heart towards the left chest wall, causing changes in voltage and axis. Rotation of the heart may affect the normal progression of QRS complexes on precordial leads. One common finding in these case reports is diminished voltage in lead I.

F I G U R E 5
Post chest-tube CXR | 5 of 5 LEE et al.

| Peak airway pressure
Although pneumothorax usually causes an increase in peak airway pressure, change of 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 CO 2 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 operating-room setting, the lungs could be difficult to auscultate due to the patient positioning, surgical draping, operating-room 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 the 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 V 5 waveforms could differ from that of the preoperative 12 lead EKG (Adams & Drew, 1997). 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 did 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, noninvasive, and readily available in the operating-room setting. Loss of lung sliding and pulsing is a sensitive indicator for pneumothorax; the presence of lung point confirms the diagnosis.
In conclusion, for surgeries with a high risk of developing pneumothorax, we suggest anesthesiologists monitor lead V 5 continuously and/or check lead I and lead III periodically. Voltage diminution in Lead I, and polarity flipping in precordial leads could be the first sign of pneumothorax.

AUTH O R CO NTR I B UTI O N S
Chihjen Lee contributed to conceptualization, data acquisition and analysis, literature search, manuscript preparation, editing, revision and proofreading. Roya Yumul contributed to conceptualization and manuscript preparation. Colby Vongchaichinsri contributed to manuscript preparation, editing and revision. Kevin Tsai contributed to data acquisition and analysis. Lena Wang contributed to conceptualization, data acquisition and analysis, literature search, manuscript preparation, editing, revision and proofreading.

CO N FLI C T O F I NTE R E S T
No conflict of interest.

DATA AVA I L A B I L I T Y S TAT E M E N T
No data available.

E TH I C A L A PPROVA L
Not applicable.

PATI E NT CO N S E NT S TATE M E NT
A written consent for publication was obtained from the patient.