The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

Total minute ventilation is not an accurate representation of Alveolar Ventilation

Donna Hamel, RRT, RCP; Ira Cheifetz, MD, FAARC; Duke Children's Hospital; Durham NC, USA


Background:  
During positive pressure ventilation carbon dioxide elimination is routinely controlled by adjusting the tidal volume and/or respiratory rate (i.e., total minute ventilation). The minute ventilation displayed on mechanical ventilators represents the quantity of gas moving in and out of the lungs; however, it does not provide information as to the amount of the total ventilation that actually participates in gas exchange. To determine the quantity of gas that reaches the alveoli and participates in gas exchange, it is important to determine the alveolar minute ventilation (MVALV). Thus, we hypothesized that total minute ventilation is not an accurate representation of alveolar ventilation. 

Methods: 
Twenty mechanically ventilated PICU patients (0 -18 yrs) receiving continuous advanced respiratory mechanics monitoring (NICO2 Respiratory Profile Monitor; Respironics, Inc.) were included in this study. Data were electronically collected over a twenty-four hour period. Data analysis was performed using linear regression analysis. 


RESULTS: 


pt #

r2

data points
 
pt #

r2

data points

1

0.96

1470
 
11

0.49

1442

2

0.81

1245
 
12

0.37

1298

3

0.89

1115
 
13

0.88

1467

4

0.42

1290
 
14

0.89

1462

5

0.93

1452
 
15

0.78

1443

6

0.91

1470
 
16

0.54

1461

7

0.31

1460
 
17

0.54

1463

8

0.69

1475
 
18

0.03

1463

9

0.80

1410
 
19

0.92

1443

10

0.58

1359
 
20

0.91

1432


 
Conclusions:
In a heterogeneous population of pediatric patients, nine of the twenty patients (45%) studied demonstrated a poor correlation between total minute ventilation and alveolar minute ventilation (r2 > 0.7). These data suggest that monitoring alveolar minute volume provides clinicians with a more accurate assessment of ventilator management strategies. 

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