Pre-op CT Findings Linked to Post-op Mechanical Ventilation

Certain factors observed on thoracic CT preoperatively are predictive of the need for postoperative mechanical ventilation, according to a study published in the American Journal of Roentgenology.

Those factors include bronchial wall thickening, pericardial effusion, shorter lung height, and greater anteroposterior chest diameter.

"We took a retrospective look at patients who had major abdominal or pelvic surgery and then also had thoracic CT within the last year before the surgery to investigate any CT imaging predictors to identify the patients who are likely to get postoperative mechanical ventilation," Arzu Canan, MD, the study's lead author and assistant professor, Cardiothoracic Imaging Division, Department of Radiology, University of Texas (UT) Southwestern Medical Center, Dallas, Texas, in an interview with Medscape Medical News.

Two radiologists reviewed preoperative thoracic CT examinations performed between January 2014 and December 2018 for a total of 165 patients. Case patients were those who required mechanical ventilation after surgery. They were matched in a 3:1 ratio with control patients on the basis of age, sex, body mass index, chronic obstructive pulmonary disease (COPD), smoking status, and type of surgery.

Figure 1. Sagittal chest CT image of a 62-year-old woman who underwent hysterectomy for uterine cancer demonstrates measurement of right lung height at the hilar level from apex to the diaphragmatic dome. Right lung height was 20.1 cm for reader 1 and 20.0 cm for reader 2. The patient did not require postoperative mechanical ventilation after the surgery.

Figure 2. Sagittal chest CT image of the same patient shown in Figure 1. The image demonstrates measurement of left lung height at the hilar level from apex to the diaphragmatic dome. Left lung height was 21.7 cm for reader 1 and 21.3 cm for reader 2.

Control patients were those who could be extubated in the operating room at the end of the procedure; who were breathing spontaneously when they left the operating room after surgery; and who did not require transfer from the operating room to the intensive care unit (ICU).

The study included 42 case patients and 123 matched control patients. On multivariable statistical analysis, the investigators found that bronchial wall thickening generated an odds ratio for mechanical ventilation of 4.6 (95% CI: 1.3, 16.5; P = .02); pericardial effusion generated an odds ratio of 5.1 (95% CI: 1.7, 15.5; P = .004); mean lung height generated an odds ratio of 0.8 (95% CI: 0.7, 1.001; P = .05); and anteroposterior chest diameter generated an odds ratio of 1.2 (95% CI: 1.1013; 1.4; P = .03).

"We found that having bronchial wall thickening, having pericardial effusion, having smaller lung heights, and increased anteroposterior chest dimensions were significantly higher amongst cases and predicted postoperative ventilation in these patients," said Canan.

The senior author of the article, Amanda Fox MD, MPH, professor of anesthesiology and pain management, UT Southwestern, told Medscape Medical News that there is a lack of knowledge of factors for predicting when to extubate and when not to extubate patients in the operating room who undergo noncardiac surgery. This led the investigators to consider whether information on CT could guide decisions as to who may need a ventilator after surgery.

"The next step would be to validate that these markers are associated with post-op mechanical ventilation at our center and other centers," said Fox. "If we do validate that these are robust markers, the next study after that would look at what can we do with that information in terms of patient management that can make a difference."

The findings could assist in planning use of the ICU, Fox explained. "It would be better to [be able to] plan for an ICU stay. You avoid a patient getting extubated and then needing to be reintubated.... You avoid a surprise need for an ICU bed after the surgery." Although the study was conducted before the COVID-19 pandemic, the pandemic has underlined the importance of ICU beds in healthcare facilities, she added.

Daria Manos, MD, FRCPC, who was not involved in the study, told Medscape that patient characteristics such as age, obesity, chronic lung disease, and smoking are predictive of the need for postoperative mechanical ventilation, but she noted that the study investigators dug deeper by assessing possible factors on imaging that may predict the need for postoperative ventilation. Manos is a professor of diagnostic radiology at Dalhousie University, in Halifax, Nova Scotia, Canada, and president of the Canadian Society of Thoracic Radiology, an affiliate of the Canadian Association of Radiologists,

"I think it is key to take from this paper that bronchial wall thickening is important to look at," said Manos. "We know that smoking and COPD are risk factors for mechanical ventilation after surgery. What is really interesting about this paper is it has started to unpack that, showing that bronchial wall thickening is an independent risk factor for postoperative mechanical ventilation."

Manos commended the collaboration between clinicians in anesthesiology and radiology in conducting the study. "We don't often see that [collaboration across medical specialties in research], so it is really great to see anesthesiology and radiology working together and finding common ground."

Canan, Fox, and Manos report no relevant financial relationships.

AJR Am J Roentgenol. Published online September 1, 2021. Abstract

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