Journal of Clinical Medicine Research, ISSN 1918-3003 print, 1918-3011 online, Open Access
Article copyright, the authors; Journal compilation copyright, J Clin Med Res and Elmer Press Inc
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Original Article

Volume 9, Number 1, January 2017, pages 17-22

Use of a Respiratory Volume Monitor to Assess Respiratory Competence in Cardiac Surgery Patients After Extubation


Figure 1.
Figure 1. Measured MV, TV, and RR over a 30-min period using RVM (red) and the Puritan Bennett ventilator in SimV mode (black) for one example patient. Average errors between RVM and the ventilator for MV, TV, and RR are less than 10%.
Figure 2.
Figure 2. (a) MV, TV, and RR as percent of baseline before and after extubation. A nadir in ventilation occurs 30 min after extubation with MV significantly reduced to 77±9% of baseline (*P < 0.05) and TV significantly reduced to 71±9% of baseline (*P < 0.01), while RR is not significantly different at 113±8% of baseline. Sixty minutes after extubation, MV has returned to 118±16% of baseline and TV has returned to 105±16% of baseline. (b) Absolute values of MV, TV, and RR measured before and after extubation. MV falls significantly from 8.2 ± 0.4 L/min at baseline to 6.4 ± 0.9 L/min 30 min after extubation and TV was significantly reduced from 520 ± 40 mL at baseline to 370 ± 40 mL after extubation. (c) Average SpO2 values recorded before and after extubation. The minimum SpO2 value recorded at each time point among all subjects is shown as a “+”.
Figure 3.
Figure 3. Example respiratory traces from a representative patient (60-year-old male, BMI 29). Initial traces reflect ventilator breaths only with no spontaneous ventilation (a). As the patient awakes from anesthesia and progresses toward extubation, faster and shallower spontaneous breaths predominate with an occasional ventilator breath (b). Just after extubation, the patient’s breathing pattern is more irregular (c, d) and TVs and MVs decrease (d, e). TV and MV measurements increase over time after successful extubation (f, g, h).


Table 1. Subject Demographics
SexAge (years)BMI (kg/m2)Procedure
3Male6026.9CABG × 4
4Male8033.1CABG × 3
6Male5338.5Septal Myectomy
8Male8419.5CABG × 4
10Male8224.5CABG × 3
13Male6326.6CABG × 3
14Female6624.2Septal myectomy


Table 2. Respiratory Metrics Before and After Extubation (N = 14)
TV (mL)RR (breaths/min)MV (L/min)
Pre-extubation520 ± 4017.1 ± 1.58.2 ± 0.4
Post-extubation370 ± 4017.5 ± 1.06.4 ± 0.9
P< 0.010.4< 0.05


Table 3. Blood Gases Before and After Extubation
PCO2 (mm Hg)PaO2 (mm Hg)Bicarbonate (mEq/L)SpO2 (%)pHPCO2 (mm Hg)
Pre-extubation39.0 ± 1.8138 ± 1021.3 ± 0.599 ± 0.47.38 ± 0.02
Post-extubation41.8 ± 1.1136 ± 922.3 ± 0.498 ± 0.87.34 ± 0.01