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The purpose of this study was to evaluate the correlations of ultrasonographically estimated volumes of pleural fluid with the actual effusion volume in order to determine the most reliable formula.

In 32 consecutive patients with clinically diagnosed pleural effusion, an ultrasound estimation was made of the volume of effusion using four different formulae, including two in the erect position and two in the supine position. Closed-tube thoracostomy drainage using a 28-Fr chest tube was performed. The total drainage was calculated after confirmation of full lung re-expansion and complete drainage by plain chest radiographs and ultrasound. The ultrasonographically estimated volume was compared to the actual total volume drained as the gold standard.

There were 14 female and 18 male subjects. The mean age of all subjects was 41.56±18.34 years. Fifty percent of the effusions were in the left hemithorax. Metastatic disease accounted for the plurality of effusions (31.2%). The mean total volume drained for all the subjects was 2,770±1,841 mL. The ultrasonographically estimated volumes for the erect 1, erect 2, supine 1, and supine 2 formulae were 1,816±753 mL, 1,520±690 mL, 2,491±1,855 mL, and 1,393±787 mL, respectively. The Pearson correlation coefficients (r) for the estimate of each formula were 0.75, 0.81, 0.62, and 0.63, respectively.

Although both erect formulae showed similar correlations, the erect 2 formula (Goecke 2) was most closely correlated with the actual volume drained.

Pleural effusion is an excessive accumulation of fluid in the pleural space resulting from excess fluid production, decreased absorption, or both [

Ultrasonographically, pleural effusion volume can be estimated quantitatively or qualitatively. Qualitative estimations classify effusion as minimal, moderate, or massive [

Compared to radiography, ultrasonography has the advantage of being non-invasive, cost-effective, readily available, and repeatable. It is also radiation-free. Furthermore, chest ultrasonography shows better sensitivity and reliability than radiography [

Pleural effusion is frequently managed by thoracocentesis. Sometimes, the actual amount of effusion is at variance with the clinical presentation, and it is doubtful whether to drain. The ideal ultrasonographic formula for pleural effusion volume estimation should be simple, accurate, and rapidly/easily performed. This study was carried out to compare four quantitative ultrasonographic formulae to determine which best predicted the actual volume. Our results should be helpful in clinical decision-making regarding which patients require chest intubation and in assessing the completeness of effusion drainage before extubation.

This was a prospective cross-sectional study. In 32 consecutive patients with a clinical and radiologic diagnosis of pleural effusion, an estimation of the pleural effusion volume was made using a Mindray real-time ultrasound machine model DC-6 or DC-7 (Shenzhen Mindray Biomedical Electronics, Shenzhen, China) with a convex transducer (frequency of 3.8-5.0 MHz). Four different sonographic formulae were used for volume estimation.

Patients aged between 10 and 80 years, with a clinical and radiological diagnosis of effusion (>10 mm of pleural separation by fluid on ultrasonography, with the fluid layer changing with respiration and with different body positions [

A total of 52 subjects were recruited initially but 20 subjects were excluded. The exclusion criteria were loculated/encysted effusions, empyema, and patients at the extreme points of life who could not sit erect and/or obey breathing instructions. Those with thoracic deformities, diaphragmatic pathology, previous chest surgery, and incomplete fluid drainage on post-intubation ultrasonography (>5 mm of separation of the pleural layers) [

The ultrasonographic examination was first done with the patient flatly supine (no pillow or head rest) to obtain values (in millimeters) for the supine formulae. The chest was insonated at the laterodorsal/posterolateral part of the chest wall through the intercostal spaces (as an acoustic window), with the transducer perpendicular to the chest wall (transverse scan with no angling or tilting of the transducer) [

Thereafter, patients sat in a fully erect position (no slouching or reclining), and measurements (in centimeters) were taken for the erect formulae. The dorsolateral/posterolateral aspect of the chest wall was insonated through the intercostal spaces with the transducer oriented longitudinally along the long axis of the chest (

Erect 1 (Goecke 1): EV=X×90,

where EV=estimated effusion volume (mL); X=craniocaudal extent (cm) of the effusion at the dorsolateral chest wall measured in erect/sitting position with the probe oriented longitudinally; 90=empirical factor/constant [

Erect 2 (Goecke 2): EV=(X+LDD)×70,

where EV=estimated effusion volume (mL); X=craniocaudal extent of the effusion at the dorsolateral chest wall measured in the erect/sitting position with the probe oriented longitudinally; LDD=lung base to mid-diaphragm distance/subpulmonary height of the effusion (cm); 70=empirical factor/constant [

Supine 1 (Eibenberger): EV=47.6X-837,

where EV=estimated effusion volume (mL); X=maximum perpendicular distance between the pulmonary surface and the chest wall at maximal inspiration (mm) with the probe in the transverse position, perpendicular to the chest wall [

Supine 2 (Balik): EV=20X,

where EV=estimated effusion volume (mL); X=maximum perpendicular distance between the pulmonary surface and chest wall at maximal inspiration (mm) with the probe in transverse position, perpendicular to the chest wall [

Thoracocentesis was then performed under ultrasound guidance. A 28-Fr chest tube (Tyco Healthcare Kendall, Argyle, NY, USA) was inserted in the mid-axillary line through the fifth intercostal space and connected to an underwater seal drainage. Complete lung expansion on radiography and <5 mm separation of the pleural layers on ultrasonography were taken as evidence of total drainage of the effusion. The drained volume was then recorded as the total effusion volume.

The data were analyzed using SPSS ver. 20 for Windows (IBM Corp., Armonk, NY, USA). Pearson correlation analysis was performed to determine the extent of correlation between ultrasonographically estimated effusion volumes and the actual volume drained.

The study population was further subdivided based on age into two categories: >20 years old and <20 years old [

The degrees of correlation were classified as follows: r=0-0.20, very low and probably meaningless correlation; r=0.21-0.40, low correlation that might warrant further investigation; r=0.41-0.60, reasonable correlation; r=0.61-0.80, high correlation; and r=0.81 -1.0, excellent/very high correlation [

A total of 32 patients were analyzed in this study. They were aged 10-80 years, with a mean age of 42±18 years. There were 14 females (43.8%) and 18 males (56.3%). Half of the effusions were right-sided and the other half were on the left; there were no bilateral effusions.

The etiological causes of the pleural effusion are shown in

The mean total volume of actual pleural fluid drained for all the subjects was 2,770±1,841 mL. The ultrasonographically estimated mean effusion volumes obtained using the various formulae are displayed in

When all the subjects were analyzed together (uncategorized), the erect 2 (Goecke 2) formula showed the strongest (excellent/very high) correlation with the actual volume drained (r=0.81, P<0.001) followed by the erect 1 (Goecke 1) formula, which had a high correlation (r=0.75, P<0.001). The supine 1 (Eibenberger) and supine 2 (Balik) formulae yielded statistically significant results, but much lower correlation coefficients (

In patients aged <20 years old, only the volume estimate of the erect 2 (Goecke 2) formula showed a statistically significant correlation (r=0.97, P=0.03). The correlation coefficients obtained from the other formulae in this category of subjects were not statistically significant.

In patients >20 years old, both the erect 1 (Goecke 1) and erect 2 (Goecke 2) formulae yielded statistically significant high correlations, while both supine formulae yielded statistically significant but only moderate/reasonable correlations.

The sonographic estimates of the left-sided effusions correlated excellently and significantly with the actual drainage volume for all four formulae. For right-sided effusions, the erect 1 and erect 2 formulae yielded significant and high correlations (with correlation coefficients that were much lower than those obtained for the left side), while both supine formulae yielded only moderate/reasonable and weakly significant correlations.

The effective management of pleural effusion requires early recognition, some form of volume estimation, and identification of the underlying etiology [

These 4 formulae were evaluated because they can be performed easily and quickly, making them useful for routine clinical applications [

A previous study [

The supine formulae were developed to reflect the position-dependent distribution of fluid within the pleural cavity [

The supine 2 formula of Balik et al. [

Previous studies have reported a significant side difference (right hemithorax versus left hemithorax) in the level of correlation between sonographic estimates and actual pleural fluid volume drained [

In conclusion, it is important to quantify pleural effusion in order to ensure prompt and effective management; in particular, when deciding whether a chest tube should be inserted, especially when the clinical presentation and clinically suspected effusion volume are discordant, and also in ascertaining the completion of pleural fluid drainage before extubation. Ultrasonography is safe, cheap, and convenient route, and is easy to use in most patients, except in very young children. It is also convenient to use in patients who are in the intensive care unit. For daily clinical applications, a simple single measurement of the volume of pleural effusion is preferable to a formula requiring multiple measurements [

No potential conflict of interest relevant to this article was reported.

We thank Dr. Onigbinde and Stephen Olaoluwa for helping with the statistical analysis.

A. This image shows the patient and probe positions for obtaining measurements for the supine 1 and 2 formulae. B. The resultant chest ultrasonography shows the maximum perpendicular distance between the pulmonary surface and the chest wall at maximal inspiration (cursors).

A. This image depicts the patient and probe positions for obtaining measurements for the erect formulae. B, C. Corresponding chest sonography shows the craniocaudal extent (cursors) of the effusion (B) at the dorsolateral chest wall (erect 1 formula), as well as the lung base to mid-diaphragm distance/subpulmonary height (C) of the effusion (erect 2 formula).

Etiologies of pleural effusion in the subjects

Etiology | No. (%) |
---|---|

Pulmonary tuberculosis | 9 (28.1) |

Community-acquired pneumonia | 5 (15.6) |

Malignancy (including metastases) | 11 (34.4) |

Hemothorax | 2 (6.3) |

Chronic renal failure (with heart failure) | 1 (3.1) |

Corrosive esophagitis | 1 (3.1) |

Unknown | 3 (9.4) |

Actual volume drained and corresponding ultrasonographic estimates in various subsets of participants

Category | Volume drained (mL) | Erect 1 (mL) | Erect 2 (mL) | Supine 1 (mL) | Supine 2 (mL) |
---|---|---|---|---|---|

All subjects (n=32) | 2,769±1,841 | 1,816±753 | 1,520±690 | 2,491±1,855 | 1,393±787 |

Right-sided effusion (n=16) | 3,215±2,019 | 1,955±710 | 1,756±731 | 2,739±2,113 | 1,491±903 |

Left-sided effusion (n=16) | 2,324±1,584 | 1,677±1,677 | 1,358±1,358 | 2,242±2,242 | 1,294±1,294 |

Age <20 yr (n=5) | 1,327±900 | 1,037±556 | 1,027±467 | 1,046±979 | 792±412 |

Age >20 yr (n=27) | 3,037±1,855 | 1,960±700 | 1,631±692 | 2,758±1,865 | 1,504±794 |

Values are presented as meanĀ±SD.

Correlation between sonographic estimates and actual drainage volume in various subsets of participants

Parameter | Erect 1 |
Erect 2 |
Supine 1 |
Supine 2 |
||||
---|---|---|---|---|---|---|---|---|

r-value | P-value | r-value | P-value | r-value | P-value | r-value | P-value | |

All subjects | 0.75 | 0.001 | 0.81 | 0.000 | 0.62 | 0.000 | 0.63 | 0.000 |

Age (yr) | ||||||||

<20 | 0.76 | 0.124 | 0.97 | 0.034 | 0.80 | 0.108 | 0.80 | 0.107 |

>20 | 0.71 | 0.000 | 0.77 | 0.000 | 0.57 | 0.002 | 0.57 | 0.002 |

Side of effusion | ||||||||

Right-sided | 0.68 | 0.004 | 0.76 | 0.019 | 0.49 | 0.053 | 0.50 | 0.049 |

Left-sided | 0.84 | 0.000 | 0.83 | 0.000 | 0.82 | 0.000 | 0.82 | 0.000 |

r, Pearson correlation coefficient.