Understanding the Pleurevac

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Understanding

the

Pleurevac

482 PEDIATRICS Vol. 67 No. 4 April 1981

Alan D. Rothberg, MB, BCh, FCP(SA), Keith H. Marks, MB, BCh,

FCP(SA), MRCP, and M. Jeffrey Maisels, MB, BCh

From the Department of Pediatrics, The Milton S. Hershey Medical Center, The Pennsylvania State University College of Medicine, Hershey

ABSTRACT. The infant nonmetered Pleurevac was stud-ied under laboratory conditions. Evacuation of a spirom-eter was measured at various negative pressures through the infant thoracostomy tubes routinely used in the din-ical setting. In addition, a tension pneumothorax model was designed, and factors affecting its evacuation rate were studied. In accordance with Poiseuille’s law, the evacuation rate was proportional to the negative pressure applied to the thoracostomy tube, and the radius of the tube. The airflow rate (bubble rate) through the Pleure-vac was found to be of minor importance in affecting evacuation. Pediatrics 67:482-484, 1981; pneumothorax, Pleurevac.

Tension pneumothorax is a common complica-tion of neonatal respiratory disease, particularly when intermittent positive pressure ventilation is necessary, and the infant nonmetered Pleurevac (Deknatel, Queens Vifiage, NY) is widely used in its management. The instructions for use include a suggested water level (ie, negative pressure) of 20 cm in the suction control chamber, and a warning against the use of high airflow rates when a negative pressure >20 cm H20 is required. Remarkably, no data are provided regarding the factors which may influence the rate of evacuation of a pneumothorax. Conflicting information is provided in the litera-ture,’3 and an informal review of neonatal units revealed wide variations in the negative pressure and flow rate settings of the Pleurevac; in addition some confusion exists as to the effect of “fast” and “slow” airflow rates (as judged by the frequency of bubbling) on the ability of the Pleurevac to drain a pneumothorax. Because we could find no data to

Received for publication June 9, 1980; accepted July 24, 1980. Reprint requests to (M.J.M.) Department of Pediatrics, The Milton S. Hershey Medical Center, Hershey, PA 17033. PEDIATRICS (ISSN 0031 4005). Copyright © 1981 by the American Academy of Pediatrics.

support the use of any particular group of settings for this instrument, a study was designed to evalu-ate the function of this system in the laboratory.

MATERIALS AND METHODS

The Pleurevac suction control chamber was con-nected to a vacuum source, and the water seal chamber was connected to a 7-liter spirometer (Warren E. Collins, Inc, Braintree, MA). Air was evacuated from the spirometer through single (No. 10 or No. 12 French) or double (No. 10 French)

thoracostomy tubes sealed into the spirometer out-let. Single tubes were connected directly to the Pleurevac tubing, and double tubes were connected via a Y-connector. The rate of evacuation of air was measured at low and high airflow rates through the suction control chamber. The low rate was defined as the lowest airflow rate required to produce con-tinuous bubbling in the suction control chamber. The high rate was the highest rate that could be achieved without producing overflow of water into the collecting system. Repeated measurements were made at low and high airflow rates with 5, 10, 15, 20, 25, and 30 cm H20 in the suction control

chamber.

To evaluate the Pleurevac under simulated con-ditions of constantly reaccumulating pneumo-thorax, air was added to a model (Fig 1) at a rate of 1.5 liters/mm. An intermediate airflow rate through the suction control chamber was selected, and the

air was evacuated through a single (No. 10 or 12

French) thoracostomy tube (TT). The pressure in the model was monitored with the Pleurevac dis-connected (ie, with air escaping through the TT under positive pressure), and with negative pres-sures of 5, 10, 15, and 20 cm H20 applied to the TT.

In this way we were able to measure the negative

pressure required to bring the pressure in the model to atmospheric and subatmosphenc levels.

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AIR

THORACOSTOMY

TUBE TO

PLEUREVAC

uJ z 0 -< C > u I-0 0 (1) 8 6 4 2

0

5

10

15

20

ARTICLES 483

MANOM

ETER

WATER

Fig 1. Tension pneumothorax model. Water is added to flask leaving 30-nil volume. Air is blown through model at 1.5 liters/mm.

RESULTS

As shown in Fig 2, the rate of evacuation of air from the spirometer was dependent largely on the negative pressure applied to the TT (ie, the water level in the suction control chamber) and the caliber or number of TTs. When two TTs were used, there

was

a

small increase in the evacuation rate when the airflow rate through the suction control cham-ber was increased. This effect was minimal to ab-sent when one size 12 or 10 TT was used.

The tension pneumothorax model demonstrated a significant pressure buildup when air was added to the bottle at a rate of 1.5 liters/mm and allowed to escape through the restrictive thoracostomy tubes usually used for small infants. The amount of

negative pressure required to restore atmospheric pressure in the model was dependent upon the caliber of the TT (Fig 3).

DISCUSSION

Poiseuille’s law states that flow is dependent upon the radius and length of a tube, and the pressure gradient across the tube. F = P ‘i r4/8 i1 where F = flow through the tube; &P = pressure gradient across the tube; r = radius, 1 = length, /L = viscosity.

Not surprisingly, our results are explained by this law. In the spirometer evacuation experiment (Fig 2), increasing the pressure gradient (P) by adding water to the Pleurevac, and/or increasing the cali-ber of the TT (r) resulted in a greater spirometer evacuation rate (F). In the tension pneumothorax

model (Figs 1 and 3), with a constant flow (F)

through the system, prior to application of the Pleurevac suction, the bottle pressure (and there-fore i.P) will be less when a larger TT (r) is used. Similarly, with the Pleurevac connected, evacuation of the constant flow (F) requires less pressure to restore the system to atmospheric pressure when a larger TT (r) is used.

Pneumothorax is a common occurrence in the neonatal intensive care setting, particularly in in-fants requiring positive pressure ventilation for hya-line membrane disease.4’5 With the use of constant flow respirators, the possibility exists that, in the

10

----.

-Two #10

Thoracostomy tubes

-- Single #12 Tube Single # 10 Tube

U 2 6 10 14 18 22 26 30

CONTROL CHAMBER WATER LEVEL (cmH2O)

Fig 2. Pleurevac evacuation of spirometer. Control chamber water level = negative pressure applied to tho-racostomy tubes. * HIGH and LOW represent high and low airflow rates through control chamber (see text).

PLEUREVAC

DISCONNECTED

PLEUREVAC

IN LINE

LU

I-0

WATER

LEVEL

IN SUCTION

CONTROL

CHAMBER

(cm)

Fig 3. Tension pneumothorax model. Note positive pressure in bottle prior to connection of Pleurevac, and effects of thoracostomy tube size on negative pressure required to return bottle pressure to atmospheric pres-sure.

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6.0

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1. Yu VYH, Liew SW, Roberton NRC: Pneumothorax in the newborn. Arch Dis Child 50:449, 1975

2. Monin P, Vert P: Pneumothorax. Clin Perinatol 5:335, 1978 3. Van Way CW: Chest tubes and pleural mechanics. Ohio

Medical Products-Items and Topics 22:4, 1976

4. Boyle lu, Oh W: Respiratory distress syndrome. Clin Pen-natol 5:283, 1978

5. Corbet A, Adams J: Current therapy in hyaline membrane

disease. Clin Peninatol 5:299, 1978

6. Plenat F, Vert P, Dither F, et a!: Pulmonary interstitial emphysema. Clin Peninatol 5:351, 1978

484 PLEUREVAC

presence of a large pulmonary air leak, a significant volume of air may continue to accumulate in the pleural space. Based on our data (Fig 2), with the application of negative pressure of 20 cm H20 (as suggested by the manufacturer), the Pleurevac has the capacity to evacuate more than 4 liters of air per minute, depending upon the size and number of

TTs. This evacuation rate is probably adequate under most conditions. However, in the event of a large air leak, such as a bronchopleural fistula, higher evacuation rates may be necessary. Under these circumstances, assuming that the TT is pat-ent’ and the accumulating air is in continuity with the TT and not loculated elsewhere (eg, in the subpleural space),6 our pneumothorax model dem-onstrates that the simplest maneuver is to add water to the suction control chamber to increase negative pressure and thus the evacuation rate. If

this does not produce the desired result, a larger

TT or a second tube should be placed. The small bore (No. 10 to 12 French) TT used in small infants imposes a significant resistance to airflow (Figs 2 and 3).

It should be noted that the negative pressure

applied to the TT may only affect intrapleural pressure in the immediate vicinity of the tip of the tube. Fig 4 is a representative recording of esopha-geal and pleural pressure from a premature infant with severe hyaline membrane disease who required

a peak inspiratory pressure of 40 cm H20 and end-expiratory pressure of6 cm H20. Two thoracostomy tubes and a negative pressure of 25 cm H20 were

Fig 4. Intrapleural (Ppl) and esophageal (Pes) pressure measurements in infant with hyaline membrane disease who required positive pressure ventilation. Note positive pleural pressure recorded from one thoracostomy tube while -25 cm H2O pressure was applied to second tube on same side of thorax.

necessary initially to evacuate a right-sided pneu-mothorax. Following stabilization of the patient’s

condition and evacuation of the pneumothorax, pleural pressure measured through one of the tho-racostomy tubes approximated esophageal pres-sure. The measured pleural pressure in this tube was positive although a negative pressure of 25 cm

H20 was being applied to the pleural space (through

the second TT). This suggests that the two tubes were in separate spaces and that one tube reflected

transmitted airway pressure while the other re-flected Pleurevac pressure.

Recommendations vary regarding the negative pressure necessary to evacuate a pneumothorax in infants with hyaline membrane disease requiring positive pressure ventilation. Suggested levels range from -5 to -20 cm H20.”2 Our data show that under laboratory conditions the Pleurevac is capa-ble of evacuating substantial volumes of air even at low negative pressure with a small caliber TT. For routine use in small infants, therefore, it appears to be unnecessary to initiate therapy with 20 cm H20 in the suction control chamber. In fact, in an infant requiring positive pressure ventilation, the addition of high negative pleural pressure will further in-crease the transpulmonary pressure in the region of the thoracostomy tube tip and could, conceivably, have deleterious effects on the underlying lung. Our

data also demonstrate that, under most conditions, little is to be gained from the use of a high airflow and bubble rate through the suction control cham-ber. Furthermore, such flow rates contribute, sig-nificantly, to the noise level in the neonatal inten-sive care unit and are disturbing to medical and nursing staff and, perhaps, the infants themselves. In a situation of constantly reaccumulating tension pneumothorax, evacuation may be achieved by in-creasing the negative pressure in the Pleurevac or by increasing the caliber or number of thoracos-tomy tubes.

REFERENCES

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1981;67;482

Pediatrics

Alan D. Rothberg, Keith H. Marks and M. Jeffrey Maisels