(1121) Ventilator Waveform Analysis: The Square Root Sign in a Patient With a Tracheal-Pleural Fistula

Sunday, January 21, 2024

9:45 AM – 10:45 AM MT

Location: Connections Central - RST 11

First Author(s)

Daniel Rozenbaum, MD

Stanford University Medical Center
Stanford, California

Co-Author(s)

MW

Matthew Wingo, MD

Cardiac Surgery Fellow
Stanford Health Care, United States
PP

Pranjal Patel, MD

Clinical Assistant Professor
Stanford University, United States
AN

Aussama Nassar, MD, MSc, , FACS

Associate Clinical Professor of Surgery, Program Director Surgical Critical Care
Stanford University
Stanford, California
HB

Harmeet Singh Bedi, MD

Director of Interventional Pulmonology & Bronchoscopy, Clinical Associate Professor
Stanford University School of Medicine, United States
NL

Natalie Shaubie Lui, MD

Assistant Professor of Cardiothoracic Surgery
Stanford Health Care, United States

Introduction: The analysis of ventilator waveforms provides important information at the bedside. We describe a case where the volume-over-time (Vxt) curve assisted in monitoring the degree of air leak through a tracheal-pleural fistula.

Description: A 72-year-old male with esophageal squamous cell carcinoma presented for three-field esophagectomy three months after finishing neoadjuvant chemotherapy. During the operation, the tumor was deemed unresectable after it was found to invade the trachea, which was unintentionally entered. Esophagectomy was aborted, and a right-sided chest tube was placed. Bronchoscopy evidenced a 1x1cm opening in the distal posterior trachea with visible tumor. The patient was extubated and brought to the intensive care unit.
Over the next few hours, the patient developed worsening hypoxia and hypercapnia requiring reintubation. On the ventilator, the Vxt curve indicated a worsening circuit leak, with an increasing height of the sharp reset on the expiratory limb of that curve. His chest tube had a larger air leak, and serial CXRs evidenced an enlarging pneumothorax. His endotracheal tube was advanced to the left mainstem bronchus with resolution of the air leak, and the patient was transported to the operating room for stenting of his tracheal defect. The patient was later extubated, but his course was complicated by difficulty handling secretions, mucous plugging and need for reintubation. The patient eventually transitioned to comfort care and died on postoperative day 8.

Discussion: The Vxt curve on ventilators provides a useful piece of information: a mismatch between delivered and retrieved tidal volumes. Before the beginning of a new breath, the expiratory limb of the curve will reset to zero, hence a sharp drop will appear whenever the retrieved volume is smaller than the delivered volume. Due to its appearance, this sharp drop has been named the “square root sign”, and its height provides a visual clue to the degree of mismatch. When encountered, this sign should prompt the clinician to systematically evaluate the ventilator circuit and patient anatomy for causes of a circuit leak, including a tracheal-pleural fistula in the appropriate setting.