Lung Ultrasound: A Promising Tool to Monitor Ventilator-Associated Pneumonia in Critically Ill Patients

Guyi Wang; Xiaoying Ji; Yongshan Xu; Xudong Xiang

Crit Care. 2016;20(320)

Abstract and Introduction

Abstract

Ventilator-associated pneumonia (VAP) is the most frequent intensive care unit (ICU)-acquired infection that is independently associated with mortality. Accurate diagnosis and timely treatment have been shown to improve the prognosis of VAP. Chest X-ray or computed tomography imaging are used for conventional assessment of VAP, but these methods are impractical for real-time measurement in critical patients. Therefore, lung ultrasound (LUS) has been increasingly used for the assessment of VAP in the ICU. Traditionally, LUS has seemed unsuitable for the detection of lung parenchyma owing to the high acoustic impedance of air; however, the fact that the reflection and reverberation in the detection region of the ultrasound reflect the underlying pathology of lung diseases has led to the increased use of ultrasound imaging as a standard of care supported by evidence-based and expert consensus in the ICU. Considering that any type of pneumonia causes air volume changes in the lungs, accumulating evidence has shown that LUS effectively measures the presence of VAP as well as dynamic changes in VAP. This review offers evidence for ultrasound as a noninvasive, easily repeatable, and bedside means to assess VAP; in addition, it establishes a protocol for qualitative and quantitative monitoring of VAP.

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Abstract and Introduction
Background
Conclusions
References

Table 1. Published diagnostic criteria for VAP
VAP criteria	Inflammatory marks	Sputum	Chest radiography/LUS	Microbiologic or histopathology marks	PEEP/FiO₂
CDC criteria [11]	Temperature >38 °C, or >36 °C, or WBC ≥12,000 or ≤4000 cells/mm³ and new antimicrobial agent is started for ≥4 days	Purulent respiratory secretions		Microbiologic quantitative-positive Endotracheal aspirate ≥10⁵ CFU/mL Broncho-alveolar lavage ≥10⁴ CFU/mL Protected specimen brush ≥10³ CFU/mL or histological-positive Lung tissue ≥10⁴ CFU/g or positive for Legionella, influenza virus, RSV, adenovirus, or parainfluenza	After a period of stability or improvement on the ventilator, Minimum daily FiO₂ increase to 0.20 remain for 2 d or daily PEEP values increase to 3 cm H₂O
CPIS (a score of 6 is suggestive of VAP) [12]	Temperature 38.5–38.9 °C = 1 point; ≥39 or <36.5 °C = 2 points WBC <4000 or >11,000/mm³ = 1 point	Non-purulent respiratory secretions = 1 point; purulent respiratory secretions = 2 points	Chest radiography Diffuse infiltrate = 1 point Localized infiltrate = 2 points Progressive infiltrate (without cardiac disease or ARDS) = 2 points	Moderate or heavy microbiologic quantitative or heavy microbiologic quantitative-positive = 1 point Microbiologic quantitative-positive and same pathogenic bacteria seen on Gram stain = 2 points	PaO₂/FiO₂ ≤ 240 without ARDS = 2 points
CEPPIS (a score of 5 is suggestive of VAP) [12]	Temperature 38.5–38.9 °C = 1 point; ≥39 or <36.5 °C = 2 points Procalcitonin (ng/mL) ≥0.5 and <1 = 1 point; ≥1 = 2 points	Non-purulent respiratory secretions = 1 point; purulent respiratory secretions = 2 points	LUS-positive (sub-pleural echo-poor region or more with tissue-like echo texture) = 2 points	Microbiologic culture-positive = 2 points	PaO₂/FiO₂ ≤ 240 without ARDS = 2 points
CHEST [13]	Temperature >38 °C WBC <4000/mc³ or >12,000/mm³	Purulent respiratory secretions	Chest radiography New or progressive consolidation
Johanson criteria [14]	Temperature >38 °C WBC <12,000/mc³	Purulent respiratory secretions	Chest radiography New or progressive radiographic infiltrate

ARDS acute respiratory distress syndrome, CDC Centers for Disease Control and Prevention, CEPPIS Chest Echography and Procalcitonin Pulmonary Infection Score, CHEST American College of Chest Physicians, CPIS Clinical Pulmonary Infection Score, FiO ₂ fraction of inspired oxygen, PaO₂, PEEP positive end expiratory pressure, RSV respiratory syncytial virus, WBC white blood cell

Table 2. Spectral waveform analysis of pulmonary arterial flow patterns in different etiologies
	Pneumonia	Lung atelectasis	Tumor consolidation	Pulmonary embolism
Presence of flow signal	Detected	Detected	Detected	None detected
Flow signal density	High	Low	Low	None
PI ([Peak systolic velocity – End diastolic velocity]/Mean velocity)	Median	High	Low	None
RI ([Peak systolic velocity – End diastolic velocity]/Peak systolic velocity)	Median	High	Low	None
AT (duration from the beginning to the peak systolic velocity)	Median	Low	High	None
The feature of blood flow	Moderate-impedance flow	High-impedance flow	Low-impedance flow	No flow

Table 3. Comparison among different lung aeration scores
	Lung aeration score		Lung aeration change score (re-aeration/loss of aeration)
Application object	Lung aeration evaluation to predict post extubation distress [60] Lung aeration evaluation to patients with ARDS [55]		PEEP-induced lung aeration changes in patients with ARDS [61] Antibiotic-induced lung aeration changes in patients with VAP [28]
Value	N B1 B2 C	0 point 1 point 2 points 3 points	N ↔ B1; B1 ↔ B2; B2 ↔ C N ↔ B2; B2 ↔ C B2 ↔ C	1 point 3 points 5 points