Optimum levels of CPAP for tracheal extubation of newborn infants

July 1976 The Journal o f P E D I A T R I C S

109

Optimum levels of CPAP for tracheal extubation of newborn infants Arterial oxygen tension and func!ional residual capacity were studied in 16 intubated, spontaneously breathing newborn infants recovering from respiratory disease:" Studies were made at 2 cm H~O continuous positive airway pressure, af, zero end expiratory pressure, and following extubation. The study showed that Pao2 and FRC at 2 em H,~O CPAP were the same as observed following extubation, but that both values were significantly lower at ZEEP.

L a w r e n c e S. B e r m a n , M . D . , W i l l i a m W. Fox, M.D.,* Russell C. Raphaely, M.D.,

and John J. Dowries, Jr., M.D., Philadelphia, Pa.

CONTINUOUS POSITIVE AIRWAY PRESSURE is a form of therapy used in spontaneously breathing infants with the respiratory distress syndrome. When CPAP is applied via an endotracheal tube, guidelines for weaning and extubating the patient are required. However, RDS patients at zero end expiratory presstlre have been noted to have lower Pao~ values prior to tracheal extubation than following extubation? This study was undertaken to provide guidelines for m i n i m u m levels of CPAP to apply before extubating patients and to determine the effects of extubation on Pao._, at a constant inspired oxygen concentration.

METHODS Infants who were intubated and recovering from pulmonary disease were studied. They were breathing spontaneously and could maintain a Paco., of 50 torr or less and a Pao~ of 50 torr or more in 50% oxygen at 2 cm H~O CPAP. The 16 patients studied (Table I) had indwelling arterial catheters. Inspired oxygen concentrations (FIo.,) were regulated to achieve a P a Q of 50 to 90 From the Departments o f Anesthesia and Pediatrics, The Children's Hospital of Philadelphia and The University o f Pennsylvania School o f Medicine. Supported in part by United States Public Health Service Grant 5 2 1 GN-OO215-16 from the National Institutes o f Health. *Reprint address: The Children ~' Hospital of Philadelphia, No. 1 Children's Center, 34th & Civic Center Blvd., Philadelphia, Pa. 19104.

torr at 2 cm CPAP, and were maintained at a constant level throughout the study for each patient. The Pao2 and functional residual capacity were determined at 2 cm H~O CPAP, after two hours of ZEEP, and two hours following extubation. Arterial pH and blood gas tensions were analyzed with conventional electrodes (Instrumentation Laboratory Model 113 S). Abbreviations used arterial oxygen tension Pao[ FRC: functional residual capacity CPAP: continuous positive airway pressure ZEEP: zero end expiratory pressure RDS: respiratory distress syndrome PEcQ: expired carbon dioxide tension FIo2 : inspired oxygen concentrations To determine FRC, the helium rebreathing method' modified to maintain CPAP during measurement ~ was used (Fig. 1). Precisely 100 ml of a helium-oxygen-air mixture were placed into the reservoir bag. Helium concentration was measured by a catharometer (Warren E. Collins Company) using an internal electrical standard, calibrated with 3 and 13% helium. The Fio~ of the test gas was the same as the patient was breathing prior to the study; measurements were with a Beckman paramagnetic oxygen analyzer (Beckman Instruments, Inc.). The catharometer was standardized with the patient's inspired gas after absorption of water. The patient breathed the test gas for 30 seconds. The mean expired carbon dioxide tension was analyzed with a COs electrode (Instrumenta-

Vol. 89, No. 1, pp 109-112

110

Berman et al.

The Journal of Pediatrics July 1976

Gas So~lrce

Patient's Trachea

Fig. 1. System for maintaining CPAP during FRC determination. The entire system was pressurized to 2 cm H._,OCPAP at all times during the rebreathing of the test gas.

tion Laboratory Model 113 S) calibrated wifla 1.3 and 3.0% CO~. The final helium concentration was measured after absorption of water. The following formula was used to calculate FRC: ViCi Pb FRC= __ x - ( V i + Vd) Cf Pb-Pw-Pl~co~ where Vi -- initial helium volume; Ci = initial helium concentration; Cf --- final helium concentration; Vd = apparatus dead space; Pb = barometric pressure; and Pw = water vapor pressure at body temperature. Results were compared using the student "t" test for matched pairs. RESULTS The individual responses of the patients with a diagnosis of RDS are presented in Table II, and those of the patients with diseases other than RDS in Table III. Of the nine patients with RDS, seven demonstrated a decrease in Pao~ when CPAP was eliminated. All seven patients with diseases other than RDS also showed a decrease in Pao. ' with the elimination of CPAP. The mean Pao=' of all patients fell from 74 tO 60 torr with this change (p < 0.01). Following extubation there was an increase in Pao~ in seven of the RDS patients and in five of the other patients. The mean rise in Pao~ of all patients was 20 torr (p < 0.01) from a value of 60 torr on ZEEP to 80 torr extubated (Fig. 2).

Functional residual capacity also decreased in seven of the RDS patients and in all of the n o n - R D S patients with the elimination of CPAP. The mean decrease of the group was 9 ml/kg (p < 0.01) from 32 to 23 ml/kg. Following extubation, F R C returned to the previous m e a n level of 31 m l / k g (p < 0.01) (Fig. 3). The F R C increased in seven of the RDS p~t@nts and in five of the n o n - R D S patients. There was no significant change in P a c Q or arterial pH when CPAP was discontinued or following extubation. DISCUSSION Continuous positive airway pressure has been shown to be an effective means of treating hypoxemia of a variety of causes in newborn infantsr -~ The criteria for discontinuation of CPAP and extubation vary with the infant's disease, maturity, and other factors. In general, the Pao~ should be 50 torr or higher at an FIo2 of 0.50; the Paco ~ less than 50 torr with no apneic episodes; and roentgenograms of the chest should be showing improvement. W h e n the infant satisfies these criteria, a trial of breathing at ZEEP usually has been employed before extubation. ~, '~ The data presented, however, indicate such a trial may cause hypoxemia and delay the discontinuation of CPAP and extubation. Furthermore, most clinicians have advocated temporarily increasing the FIo~ following extubation. This study shows that an increase in FIo~ after extubation from ZEEP might result in hyperoxia. This study also shows that, in infants, the presence or

Volume 89 Number 1

Optimum levels of CPAP for tracheal extubation

Table I. Clinical characteristics of patients studied

PaO 2

111

( '1"_S. E.)

TORR

Duration Patient Weight No. (gin)

8O

Age (days)

int;fa tion (days)

FIo2

Diagnosis RDS RDS RDS RDS RDS RDS RDS RDS RDS Meconium aspiration Milk aspiration Diaphragmatic hernia Imperforate anus, sepsis Bowel obstruction, sepsis Gastroschisis Meconium aspiration

1 2 3 4 5 6 7 8 9 10

3,000 2,430 1,360 2,700 2,300 1,250 2,350 1,980 1,360 3,100

9 8 14 9 8 5 7 19 9 5

8 7 I4 8 5 4 6 17 8 5

0.48 0.35 0.41 0.32 0.35 0.30 0.40 0.38 0.40 0.50

11

12

1,820 3,700

42 4

3 4

0.40 0.36

13

1,710

11

4

0.28

14

1,600

12

2

0.30

15 16

3,100 3,480

3 4

1 4

0.36 0.36

absence of an endotracheal tube makes a significant difference in the FRC. In infants the F R C is a d y n a m i c r a t h e r than static balance of forces `~ a n d a difference in control of u p p e r airway resistance in i n t u b a t e d versus e x t u b a t e d patients is the most likely e x p l a n a t i o n for the observed changes in FRC. It has b e e n d e m o n s t r a t e d that patients with an audible grunt have an altered curve of expiratory resistance 1 a n d the study suggests that the expiratory resistance even in the n o n g r u n t i n g p a t i e n t m a y be altered by the dynamics of the u p p e r airway. F u n c t i o n a l residual capacity values in n o r m a l n e w b o r n infants h a v e b e e n f o u n d to be 30 to 32 m l / k g , ~ ll similar to the values at 2 cm H 2 0 C P A P a n d after e x t u b a t i o n f o u n d in this study. A l t h o u g h o u r patients h a d n o r m a l F R C values at the time of extubation, a b n o r m a l F R C values have b e e n reported at ages as late as one m o n t h in patients with R D S treated with m e c h a n i c a l ventilation without CPAP. 1~ C P A P p e r h a p s helps r e t u r n the F R C to a n o r m a l physiologic state more quickly by p r e v e n t i n g the onset o f intractable atelectasis. T r a c h e a l i n t u b a t i o n can cause a variety o f complications.':' M a n y of these, such as blockage o f the tube by secretions or accidental bronchial intubation, occur only while the patient is intubated. E x t u b a t i o n eliminates these hazards. O t h e r complications, such as subglottic stenosis,

70

60

2 cm CPAP

ZEEP

EXTUB

Fig. 2. Mean Pao.., values of all patients at 2 cm H.,O CPAP, at ZEEP and after extubation.

FRC

(• S.E.)

ml/k(

30

25

20

2 em CPAP

ZEEP

EXTUB

Fig. 3. Mean FRC of all patients at 2 cm H_,O CPAP, at ZEEP and after extubation.

g r a n u l o m a formation, a n d infection, are related to the total time of intubation, relative size relationship of the e n d o t r a c h e a l tube and the trachea, tube materials, and nursing care. Obviously patients should be e x t u b a t e d as soon as they can m a n a g e with a natural airway in order to avoid these complications. This study shows that i n t u b a t e d patients at Z E E P have a lower F R C a n d Paoz t h a n w h e n 2 cm H20 are applied or after extubation. It also demonstrates that F R C a n d Pao~ values at 2 cm H~O C P A P are similar to those same values after extubation. We r e c o m m e n d , therefore, that: (1) a n e w b o r n i n f a n t be e x t u b a t e d as soon as he is able to m a i n t a i n a satisfactory Pao~ with 2 cm H~O CPAP; a n d (2) inspired oxygen

1 12

Berman el al.

The Journal of Pediatrics .lu@ 1976

Table II. I n d i v i d u a l r e s p o n s e s o f the R D S p a t i e n t s to d i s c o n t i n u a t i o n o f C P A P to e x t u b a t i o n

2 cm H~O CPAP

ZEEP

Patient No.

Pao2 (tort)

FRC (ml/kg)

Paco 2 (torr)

A rte~ ial pH

1 2 3 4 5 6 7 8 9 Mean SD

85 55 65 68 86 62 55 74 79 70 12

28 26 20 24 37 34 27 22 48 30 9

38 37 42 49 40 47 43 52 35 43 6

7.38 W.36 7.29 7.35 7.36 7.27 7.30 7.35 7.29 7.33 604

Pao2 (tor 0

FRC (ml/kg)

45 54 50 59 87 50 83 41 75 60 17

19 23 21 19 18 18 23 21 36 22 6

After extubation

Paco.~ (torr)

A rterial pH

Pao2 (torr)

FRC (ml/kg)

Paco ~ (torO

A rte~ ial pH

47 40 43 54 37 40 47 34 36 42 6

7.28 7.38 7.28 7.30 7.36 7.30 7.33 7.37 7.32 7.32 0.04

81 62 64 63 101 76 82 73 72 75 12

29 28 19 21 35 20 38 16 44 28 10

42 40 41 45 35 43 50 46 39 42 4

7.32 7.33 7.28 7.33 7.32 7.28 7.28 7.35 7.33 7.31 0.03

T a b l e IlL I n d i v i d u a l r e s p o n s e s o f the n o n - R D S p a t i e n t s to d i s c o n t i n u a t i o n o f C P A P a n d to e x t u b a t i o n

2 cm H~O CPAP

ZEEP

Patient No.

PaQ (tot*)

FRC (ml/kg)

Paco ~ (torr)

Arterial pH

10 11 12 13 14 15 16 Mean SD

51 94 83 115 74 70 84 82 20

24 27 24 50 35 47 33 34 11

43 37 41 42 30 24 35 36 7

7.42 7.35 7.35 7.41 7.34 7.35 7.45 7.38 0.04

Pa% (torO

FRC (ml/kg)

49 56 45 96 47 60 61 59 17

19 25 22 36 28 23 22 25 6

c o n c e n t r a t i o n s s h o u l d n o t be i n c r e a s e d f o l l o w i n g e x t u b a tion o f a p a t i e n t o n 2 c m H~O C P A P unless d e m o n s t r a b l e h y p o x e m i a occurs. REFERENCES 1.

2. 3. 4.

5.

6.

Harrison VC, Heese deV, and Klein M: The significance of grunting in hyaline membrane disease, Pediatrics 41:549, 1968. Gregory GA: Newborn housestaff manual, University of California at San Francisco, 1971. Bancalari E: Personal communication. Krauss AN, and Auld PAM: Measurement of functional residual capacity in distressed neonates, J PEDIATR 77:228, 1970. Gregory GA, Kitterman JA, and Tooley WH: Lung volume in newborn infants after cardiovascular surgery, presented at the 1971 ASA meeting, Atlanta, Georgia, October 18, 1971. Gregory GA, Kinerman JA, Phibbs RH, Tooley WH, and Hamilton WK: Treatment of the idiopathic respiratory distress syndrome with continuous positive airway pressure, N Engl J Med 284:1333, 1971.

7.

After extubation

paco = (tor0

A rterial flH

37 37 43 28 27 24 40 34 7

7.45 7.38 7.34 7.42 7.31 7.28 7.39 7.38 0.06

(tort)

FRC (mt/kg)

Paco 2 (torr)

A rterial pg

43 120 90 87 86 98 127 93 27

47 41 21 34 31 42 32 35 9

44 43 39 35 37 14 33 35 10

7.45 7.38 7.34 7.39 7.27 7.34 7.42 7.37 0.06

Pao 2

Berman I~S~ Fox WW, Peckham GJ, and Downes J J: The effect of positive end-expiratory pressure on oxygenation in neonatal diseases associated with hypoxemia, Crit Care Med 2:45, 1974 (abstr.). 8. Holler JA, White JJ, Moynihan PC, and Galvias AG: Use of continuous positive airway pressure breathing in the improved management of neonatal emergencies, J Pediatr Surg 8:669, 1973. 9. Tori CA, Krauss AN, and Auld PAM: Serial studies of lung volume and Va/Q in hyaline membrane disease, Pediatr Res 7:82, 1973. 10. Olinsky A, Bryan MH, and Bryan AC: Influence of lung inflation on respiratory control in neonates, J Appl Physical 36:426, 1974. I I. Lacourt G, and Polgar G: Development of pulmonary function in late gestation, Acta Paediatr Scand 63:81, 1974. 12. Bryan MH, Hardin MJ, Reilly BJ, and Swyer PR: Pulmonary function studies during the first year of life in infants recovering from the respiratory distress syndrome, Pediatrics 52:169, 1973. 13. Reiler JP: Mechanical complications of artificial ventilation in the newborn, Biol Neonate 16:122, 1970.