Acta anaesth. Scandinav. 1970, Supplementum XXXVII, 287-293.

CLINICAL E X P E R I E N C E S W I T H T H E TAKAOKA RESPIRATOR

J. STOFFREGEN, CH. MEYER-BURGDORFF and A. OPITZ, Gottingen, Germany

Since FRENCKNER’S Spiropulsator from 1934 (fig. 1)-you all know this picture drawn by TRIER-MOERCH and published in his Textbook of Anaes- thesia (Munksgaard, Copenhagen 1949)-respirators have to be connected as an extra part with the anaesthesia machine. This connection is rarely a mechanical one (for example, in Radcliffe’s positive-pressure respiration pump) ; mostly, however, pneumatic by means of a “bag in bag” (glas) system (like in the Bird Mark 4, Bird Mark 2, Engstrom ventilator, Drager Spiromat, Pulmomat, Bennett anaesthesia ventilator, Airshields Ventimeter ventilator, etc.). In these ventilators the rubber wall of a breathing or concertina bag separates both systems completely, the patient’s breathing circle and the gas which operates the machine, so that the respirator takes over the function of the anaesthetist squeezing the anaesthesia bag rhythmically. This basic concept, the combination of the anaesthesia machine and breathing bag and respirator generally used is big and expensive and requires permanent service.

The Brazilian engineer TAKAOKA solved this problem and developed a universal respirator (fig. 2), in which the anaesthetic gas mixture also operates the pressure-cycled respirator. This machine works on a low-flow basis. The cross-section shows-here during inspiration-the same main parts as the Spiro- pulsator :-

A diaphragm variably loaded by a spring is joined to the shaft of the valve, which swings between two magnetic rings. The adjustment range of the positive pressure is from 40 to 8 cm of water; the expiratory pressure is fixed at minus 5. The ratio between inspiration and expiration is 1 : 1 ; the expiratory pressure curve is concave. Respiratory minute volume is half of the minute flow rate set on the rotameter. Furthermore, the Takaoka respirator has a remarkable low respiratory rate, 6 to 8 cycles on an average, which can be reduced to 2 per minute. The hyperbolic function between inspiration time and rate (y is equal to x over minus one) results in an inspiration time lasting nearly 4 seconds at 8 breathing cycles, 5 seconds at 6 cycles, etc. Therefore surgery can be done almost without respiratory movements in the operating field, if the frequency is less than 8. This can be important for delicate and precise

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FIG. 1.-Principle of the Spiropulsator (TRIER-MOERCH, 1949; modified by STOFFREGEN).

FIG. 2.-Takaoka respirator (cross-section during inspiration),

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a b FIG. 3.-Arterial blood pressure and central venous pressure using the Takaoka respirator under extreme conditions (rate 2.8, tidal volume 2 litres). a, chest closed; b, chest opened.

work in surgery, for example, in small children undergoing a Blalock-Taussig or Cooley anastomosis.

If the frequency is lowered, the tidal volume has to be increased corre- spondingly in order to maintain the required minute volume, but the tidal volume can only be raised up to a certain limit. Large tidal volumes of more than 1.5 litres in adults with prolonged inspiration times should not be used. Otherwise, it will reduce venous return resulting in large respiratory waves in arterial blood pressure, actually a result of major changes in cardiac output.

Figure 3 shows the conditions in a 17-year-old male patient with aortic valve disease and aneurysm, ventilated by the Takaoka. In this study, we set for experimental purposes the tidal volume at 2 litres with a frequency of 2.8 per minute. The upper curve shows the arterial blood pressure and the lower one the central venous pressure. Under closed-chest conditions the arterial pressure varies, according to the respiratory phase, between 100 and 60 mm Hg and the diastolic between 65 and 40 mm Hg. The respiratory waves in the central venous pressure are-with a little difference in p h a s d r e c t e d opposite and range between 2 and 12 mm Hg. The figure on the right shows the same respiratory situation after the chest has been opened by vertical sternotomy ; because of the increased compliance the respiratory pressure waves are only half as high and running parallel.

In order to avoid major changes in cardiac output we do not use a rate of less than 6 cycles. Besides that, low rates of respiration and slowly increasing inflation pressures have advantages. To ventilate a patient’s lung artificially, unphysiological, transthoracic pressure gradients are necessary. This explains

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FIG. 4.-Garden’s Microvent.

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FIG. 5.-Type of surgery and age distribution of the pa- tients.

mmHg 160

mm Hg

97

mm Hg

mm Hg 40

20

rn Eq./L

22

FIG. 6.-Blood gases.

P 0 2

PH

P co2

1 4 4 No H C03 I St. Bic. I

h-4 I I I I

20 40 60 80 min otter Induction

292

FIG. 7.-Burn’s balance resuscitator (1946).

all differences (not only the haemodynamic changes) between spontaneous and artificial respiration. In case of spontaneous breathing the lungs passively fol- low the movements of the chest wall, increasing the chest diameter during inspiration. In artificial respiration, however, we push the lungs against the inside of the rigid muscle wall of the chest. Quite similar to a train, we have to overcome an initial resistance which increases with the speed of onset. It is at a minimum, if the inflation pressure increases very slowly and continuously due to the low flow rate. Especially the Takaoka respirator acts in this particu- lar way.

During the last 10 months we have used the Takaoka respirator in 284 patients and the Garden Microvent in another 150 (fig. 4). Of these patients, 28% (fig. 5) underwent surgery with the extracorporeal circulation, another 28% other types of intrathoracic operations, 31 yo major surgery on peripheral vessels and 13 yo neurosurgical procedures, half of them being intracranial.

The ages of the patients range from 6 weeks to 70 years, with a maximum in the first and second decades (the majority of these patients had congenital heart diseases) and another maximum between 40 and 60 years (mostly heart- valve diseases and peripheral vascular occlusions). We mention this to show that most of these patients were poor-risk cases.

Some examples of blood gases (fig. 6) demonstrate the efficiency of the Takaoka respirator: most of the data were within the desired slightly hyper- ventilated range (for instance, the average pH was 7.43, and pC0,28.4 Torr).

In view of our good experience with Mini-respirators we feel that these really are the respirators of a new generation-recently the Minivent 2 has been developed in England and the Mini-Bird in the United States-and this

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second generation of respirators will possibly, in the near future, displace most of our old-style respirators used in our operating theatres (including the ENG- STROM and DRLGER Spiromat). They are not only pocket-sized, robust, simple and inexpensive, but also nearly as good as, or probably better than, all the large machines we have been using up to now.

The Burn’s balance resuscitator (fig. 7) proves that this idea is not quite as new as most of you may expect. I t dates back to 1946.