Results of respiratory mechanics analysis in the critically ill depend on the method employed.
OBJECTIVE
To compare the measurements of total resistance and dynamic elastance determined by different techniques of respiratory mechanics analysis based on the time or frequency domains.


METHODS
Prospective study.


METHODS
A 12-bed medical and surgical intensive care unit in a 700-bed university hospital.


METHODS
Eighteen sedoparalyzed patients who needed controlled mechanical ventilation for acute or chronic acute respiratory failure.


METHODS
The total resistance and dynamic elastance in the time domain were determined by the occlusion technique and by multiple linear regression. The Fourier analysis was used to study the impedance of the respiratory system for elastance and resistance values in the frequency domain.


RESULTS
The ANOVA analysis of the elastance variable showed no statistical differences (Ef: 41.4+/-19.0 cmH(2)O/l, Emlr: 40.8+/-17.2 cmH(2)O/l Edyn,occ: 39.5+/-14.0 cmH(2)O/l; ns) and the correlation was very good (r=0.8-0.9). The total resistances were less with multiple linear regression (13.5+/-9.3 cmH(2)O/l per s, p<0.05) than Rmax (17.0+/-11.9 cmH(2)O/l per s) or Rf (17.6+/-10.2 cmH(2)O/l per s). There were no differences between Rmax and Rf (p=0.7) and the correlation between resistances was 0.7-0.9. The agreement analysis for variables without statistical differences showed the following limits: Edyn,occ-f: -17 to 13 cmH(2)O/l; Edyn,occ-mlr: -12 to 9 cmH(2)O/l; Emlr-f: -6 to 8 cmH(2)O/l; Rmax-f: -18 to 19 cmH(2)O/l per s. This last range was related to the autoPEEP level (r=0.9).


CONCLUSIONS
The wide agreement limits show that respiratory mechanics analysis is very dependent on the measurement technique used, particularly for resistance, perhaps due to the higher dependence on frequency.
Ruiz-Ferrón
F
F
Intensive Care Unit, University Hospital Ciudad de Jaén, Avenida del Ejercito Español 10, 23007 Jaén, Spain. FR271061@terra.es
Rucabado Aguilar
L
L
Ruiz Navarro
S
S
Ramirez Puerta
R
R
Parra Alonso
S
S
Muñoz Muñoz
J L
JL
D000208:Acute Disease; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D015982:Bias; D002908:Chronic Disease; D016638:Critical Illness; D003627:Data Interpretation, Statistical; D005583:Fourier Analysis; D006801:Humans; D016014:Linear Models; D008170:Lung Compliance; D008875:Middle Aged; D009716:Numerical Analysis, Computer-Assisted; D018467:Positive-Pressure Respiration, Intrinsic / Q000209:etiology; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000009:adverse effects; D012131:Respiratory Insufficiency / Q000175:diagnosis* / Q000503:physiopathology* / Q000628:therapy; D015656:Respiratory Mechanics; D012720:Severity of Illness Index; D012815:Signal Processing, Computer-Assisted