• 11
    Apr
  • Are Low Tidal Volumes Safe? RESULTS

One hundred three patients were entered into the trial from October 1987 through February 1988. As shown in Table 1 and Figure 1, the groups were quite comparable in terms of age, sex, and severity of illness (as estimated by APACHE-II score). Age was bimo- dally distributed in both groups, the younger peak representing primarily patients admitted to the SICU after major trauma. The primary diagnoses necessi­tating admission to the SICU were similar in both groups (Table 1).

Table I—Demographic Data

Group 1 (12 mUcg)

Croup 2 (6 ml/kg)

Total patients

56

47

Male

39

31

Female

17

16

Mean age, у

58.6

59.6

Mean APACHE II score

13.3

13.3

Reasons for admission

to SICU

Multiple trauma

15

11

Celiotomy

20

24

Thoracotomy

1

1

Aortic procedure

13

7

Other

7

4

Total patients

56

47

Pulmonary function data are presented in Table 2. As expected, using lower Vt resulted in significantly (p<.001) lower peak airway pressures. Both average and maximum peak airway pressures were lower in the low Vt group. There were no differences between groups for either maximum or average PEEP used. Pa02 was significantly lower in the low Vt group, but the magnitude of the difference was small. Six patients in group 1 and eight patients in group 2 required FIo2 greater than 0.5 at some point during their SICU stay (p=.40). the number of patient days that FIo2 ex­ceeded 0.5 was seven and 11 in groups 1 and 2, respectively. The mean minimum PaO/FIOg ratio was similar in both groups.

Table 2—Pulmonary Function Data

Group 1 (12 ml/kg)

Group 2 (6 ml/kg)

Significance

Maximum peak airway

pressure, cm H20

Mean ± SD

38.8 ± 11.9

28.9 ±8.9

<.001

Median

36.0

28.0

Range

22.0-76.0

12.0-51.0

Average peak airway

pressure, cm H20

Mean ± SD

35.1 ±8.7

26.0 ±7.3

<.001

Median

34.0

25.7

Range

17.0-60.0

10.0-42.0

Maximum PEEP used,

cm H20

Mean ± SD

6.8±6.7

7.2±4.3

.18

Median

5.0

5.0

Range

5.0-20.0

5.0-20.0

Average PEEP used,

cm H20

Mean ± SD

5.4 ±2.3

6.0±2.5

.20

Median

5.0

5.0

Range

5.0-14.3

5.0-16.4

Maximum PaCVFlOa

Mean ± SD

328 ±86

284 ±75

.009

Median

326

255

Range

174-530

148-460

Average PaO/FIo2

Mean ± SD

294 ±86

260 ±78

.031

Median

278

240

Range

168-530

131-460

Minimum Pa(VFIo2

Mean ± SD

266 ±102

241 ±91

.191

Median

255

233

Range

70-530

105-460

The types of ventilators used are displayed in Table 3. A larger percentage of group 1 patients were managed on Puritan-Bennett 7200a ventilators; the difference between groups, however, was not signifi­cant (p =. 163).

Table 3—Ventilator Used

Group 1

Group 2

Puritan Bennett 7200a

28

24t

Puritan Bennett MA-1

5*

5

Puritan Bennett MA-2

0

1

Bear 1

13*

19$

Bear 2

1

4

Siemens Servo

0

1

Not documented

0

2

Total ventilators

47

56

Pulmonary infectious complications tended to occur with greater frequency among patients in group 1 (Vt=12 ml/kg); the difference between treatment arms approach statistical significance (p= .061; Table 4). Although more patients in group 1 had aortic vascular disease, this did not account for the trend toward a higher incidence of infection in this group, since only one patient recovering from an aortic procedure developed a pulmonary infection; this pa­tient was in group 1 (Table 5). The lone patient who developed pneumonia in the low Vt group was admit­ted to the SICU having aspirated a tooth following maxillofacial trauma. The organisms cultured from each pulmonary infection are tabulated in Table 5.

Table 4—Pulmonary Infectious Complications

Group 1

Group 2

Total patients

56

47

Pneumonia

6

1

Tracheobronchitis

4

1

Total infections

10

2

Incidence of infections

17.9%

4.3%*

The incidence of radiographically evident baro­trauma (eg, pneumothorax, pneumomediastinum, pneumopericardium, subcutaneous emphysema) was negligible. Only one patient from group 1 sustained a pneumothorax while on mechanical ventilation. This patient was admitted to the SICU with multiple trauma, including multiple rib fractures one day prior to development of the pneumothorax.

Table 5—Etiology of Pulmonary Infections

Group

Patient No.

Reason for Admission

Pneumonia (P) or Tracheobronchitis (ТВ)

Organism

2

Aortic procedure

P

Morganella
morganii

3

Celiotomy

ТВ

Aerococcus
viridans

14

Trauma

ТВ

Enterobacter
cloacae

20

Trauma

P

Streptococcus
pneumoniae

24

Trauma

ТВ

Neisseria
species

29

Trauma

ТВ

Branhamella
catarrhalis

31

Celiotomy

P

Staphylococcus
aureus

51

Trauma

P

Citwbacter
freundii

54

Trauma

P

Strep pneumoniae

56

Trauma

P

Staph aureus

2

8

Trauma

ТВ

Staph aureus

2

26

Trauma

P

Acinetobacter
calcoaceticus

The mean durations of intubation were 3.9 ±0.8 days and 2.3 ±0.5 days for patients in groups 1 and 2, respectively (p=.066). For duration of stay in the SICU, the means were 4.6 ±1.0 days (group 1) and 2.7 ± 0.5 days (group 2) (p = .064). On average, patients recovering from aortic surgery had a shorter duration of SICU stay than other patients (2.4 vs 4.1 days); thus, the trend toward shorter SICU stays in group 2 cannot be explained by the fewer patients recovering from aortic surgery in this group.

FIGURE 1. Age distribution for group 1 and group 2.

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