The Treatment of Respiratory Failure with Continuous Ventilatory Support

The Treatment of Respiratory Failure with Continuous Ventilatory Support THOMAS F. NEALON, JR., M.D., F.A.C.S.* STEVEN CARL SANDLER, M.D.**

In present-day hospitals patients with respiratory failure are being seen with increasing frequency by both general and thoracic surgeons. Satisfactory care of these patients often involves numerous medical disciplines; close cooperation between the surgeon, anesthesiologist, internist, house staff and nursing staff is of paramount importance. These patients are often older individuals, have multiple systemic problems, and are undergoing operations of considerable magnitude. Despite this, since the care of patients with respiratory failure is much better understood today than it was ten years ago, it is possible to resuscitate many of these patients. We have been treating respiratory failure with continuous ventilatory support at Jefferson Medical College Hospital for the past several years; our experiences are described in this report. Respiratory failure can be defined as the inability of the lungs to maintain physiologic levels of oxygen and carbon dioxide in the blood. Various authors have specified levels they consider abnormal, saying for example, that a Pco2 of 50 mm. Hg or greater means pulmonary failure. This sort of labeling is actually a matter of convenience based primarily on statistics rather than on physiology. A Pco 2 greater than 50 mm. Hg may be present in a relatively well compensated individual. It is important to remember that levels of both oxygen and carbon dioxide are affected in pulmonary failure and changes in one usually are associated with changes in the other. From a pathophysiologic standpoint, there are four basic causes of respiratory failure: (1) increased metabolic rate, (2) increased physio-

This work was supported in part by U.S. Public Health Service Grants HE-03349-08, HE-04486-06, and FR-72, and a grant from the Heart Association of Northeastern Pennsylvania *Professor of Surgery, Jefferson Medical College, Philadelphia, Pennsylvania **Fellow of the Heart Association of Southeastern Pennsylvania

Surgical Clinics of North America- Vol. 47, No. 5, October, 1967

1207

1208

THOMAS

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NEALON, STEVEN CARL SANDLER

logic shunting of blood; (3) decreased oxygen transport in the blood, and (4) increased pulmonary dead space. 2 Elevated metabolic rate is seen in the classic picture of the patient with airway obstruction and decreased compliance who must work so much harder to breathe. Agitation is often a major component of the increased work of breathing. There are numerous pathologic states which cause perfusion of nonventilated areas of the lung and ventilation of nonperfused areas. Abnormalities in the relationship between ventilation and perfusion result in diminished oxygen transport in the blood, increased shunting, and increased dead space. Increase in physiological dead space is seen in patients with tachypnea owing to the uneven ventilation due to rapid respiratory rate. In caring for the patient with pulmonary failure it is important to delineate which of these states exists. From the standpoint of therapy, it is often useful to divide the causes of respiratory failure into two broad categories: intrapulmonary and extrapulmonary. The most common type seen on the surgical service is the intrapulmonary type in which pathological changes take place in the tracheobronchial tree and lung parenchyma. Common causes are pneumonia, atelectasis, chronic bronchitis, and emphysema and pulmonary fibrosis. With the changes in the tracheobronchial tree and pulmonary parenchyma, there is usually associated decrease in compliance with an increase in airway resistance. This is especially true in obstructive lung disease such as emphysema, bronchitis, and bronchial asthma. In restrictive lung disease such as pulmonary fibrosis, edema, and pneumonia there is also reduced compliance. Often, however, airway resistance is normal and presents no difficulty. The extrapulmonary type of pulmonary failure is the less common of the two types and usually the easier to treat. This is seen in the patient with a muscular, neurologic, or neuromuscular abnormality, but without any structural or functional pulmonary abnormality. Because compliance and airway resistance are usually normal in this group, it is easier to assist ventilation.

DIAGNOSIS In the patient with compromised pulmonary reserve, a surgical procedure is often the precipitating factor that causes respiratory failure. Anesthesia and pain superimposed on poor pulmonary function often result in pulmonary failure. This is especially true in patients undergoing cardiac or pulmonary operations but can be equally true with other types of surgery. The diagnosis of pulmonary failure in the surgical patient is usually not difficult. The cardinal findings are dyspnea, hypertension, hypoxia, and hypercapnea. 2 Associated findings which may be present include pallor, sweating, tachypnea, cyanosis, tachycardia, and clouded sensorium. The patient may have to work so hard to move enough air for

THE TREATMENT OF RESPIRATORY FAILURE WITH VENTILATORY SUPPORT

1209

adequate ventilation that if allowed to continue he will ultimately exhaust himself. The late manifestations include hypotension, tachycardia, anuria, and finally generalized collapse. It is often impossible to make an early diagnosis on clinical grounds alone. We have found arterial blood gas studies to be the best method of diagnosis and of monitoring function in patients with suspected pulmonary failure.

TREATMENT Bjork, in Sweden,3 first treated ventilatory insufficiency after pulmonary resection with tracheostomy and prolonged artificial ventilation. Dammann in this country 4 demonstrated the value of this technique in supporting patients after open cardiac procedures. Since that time, many others have used continuous mechanical support of the ventilation to treat patients in respiratory failure. 2 • 5 • 6 •8 - 14 The surgeon is often first confronted with the problem of pulmonary failure in the recovery room or several days following surgery. Blood gas studies should be obtained to substantiate the clinical diagnosis. Analysis of the arterial blood usually shows the pH to be in the range of 7.30 or below, the Pco 2 50 mm. Hg or greater, and the Po 2 75 mm. Hg or less. In our experience these values are highly variable and are related to pre-existing chronic lung disease, the type of care being given to the patient, and the degree of compensation. It must be established that the somnolent patient is not suffering from prolonged effects of anesthetic gases, narcotics, or curare-like drugs. Narcotic-induced depression of ventilation is common in postoperative patients. Unless this is recognized, unnecessarily radical therapy may be instituted. However, intensive therapy may be necessary in these patients to insure survival during the period of respiratory depression.

The First Concern- the Establishment of an Adequate Airway PASSAGE OF A NASOTRACHEAL TUBE. A large nasotracheal tube can be passed without undue difficulty. The universal fitting on the proximal end of the tracheal tube allows the attachment of a respirator. The nasotracheal tube assures adequate access to the tracheobronchial tree and permits one to begin immediate support of the ventilation. At the same time one can delay a decision as to whether prolonged ventilatory support and a tracheostomy are necessary. With a nasotracheal tube in place, many patients can be carried through the initial period of difficulty. In an occasional patient the irritation of the nasotracheal tube is sufficient stimulation to adequate breathing. The standard catheter available may be too short for adequate aspiration through such a tube. If an emergency situation arises, a sterile Levin nasogastric tube may be used. TRACHEOSTOMY. When it is anticipated that a patient will require continuous ventilatory support, the advisability of doing a tracheostomy must be considered. We have been generally reluctant to leave a naso-

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NEALON, STEVEN CARL SANDLER

Figure 1. Cuffed Jackson tracheostomy tube with Atkins-Cannard adaptor (A). An endotracheal tube balloon cuff has been attached to the metal tracheostomy tube (B). The adaptor at the proximal end of the tube allows ready attachment to a respirator.

tracheal tube in place for more than 36 hours in an adult. If the patient needs continuous support beyond that period, we remove the tube and perform a tracheostomy. We have had good results with cuffed Jackson tracheostomy tubes with 15-mm. Atkins-Cannard adaptors (Fig. 1). The adaptor can be attached to most modern respirators and the inner cannula can be removed and cleaned several times daily. The balloon must always be checked prior to the insertion of the tracheostomy tube. In patients who require prolonged continuous ventilatory assistance, the support is instituted wherever they are in the hospital before they

Figure 2. Ambu bag to manually support ventilation. The bag can be attached to the face mask shown or a tracheostomy or endotracheal tube. When desired, oxygen can be flowed into the bag.

THE TREATMENT OF RESPIRATORY FAILURE WITH VENTILATORY SUPPORT

1211

are moved to a unit for specialized care. In transit they are ventilated and given additional oxygen, usually manually by an Ambu bag (Fig. 2) into which additional oxygen is flowing.

Respirator Therapy As soon as the patient arrives in the special unit he is attached to an Engstrom ventilator. This is a volume-controlled respirator which must control the patient's respiration to be effective. The initial phase of respirator therapy is usually the most difficult. The patient is often restless, synchronization with the respirator is poor, and adequate ventilation may be difficult to establish. By ventilating the patient at a rapid rate with adequate tidal volumes, Pco2 will, in most cases, be lowered to apneic levels where the ventilation can be controlled. Hyperventilation is accomplished using either an Ambu bag or the ventilator itself. In those patients who cannot be hyperventilated to apnea careful drug administration is usually necessary. Narcotics, alphaprodine (Nisentil), hydromorphone (Dilaudid), morphine, or meperidine (Demerol) have been used effectively, in that order. We usually begin with small doses (10 to 20 mg.) of Nisentil intravenously. This drug is a strong respiratory depressant and in most instances this dose has been sufficient to suppress the respiratory drive for short periods. For a more prolonged effect twice the intravenous dose can be given intramuscularly. Once the patient has been controlled, drugs, such as phenobarbital or hydroxyzine (Vistaril) are used to maintain sedation. Patients who are restless due to postoperative wound pain usually respond to Demerol, Dilaudid or morphine. Hyperventilation has been credited with reducing the need for narcotics for pain. 8 Resynchronization of the patient's respirations with the ventilator may be a problem after the patient has been disconnected from it to be aspirated. The nurses can usually hyperventilate the patient to apnea manually, using an Ambu bag. If this is not possible, some suppression by drugs will be necessary. Proper management of continuous ventilatory support requires monitoring by means of blood gas analyses. 2 • 14 It is desirable to maintain the Pco 2 and the Po 2 of arterial blood near normal. These values can be individually influenced by adjusting the composition and volume of the ventilatory gas. Increasing the volume of ventilation will wash out additional carbon dioxide and lower the Pco 2 • The Po 2 of the blood varies directly with the concentration of oxygen in the inspired gas. In the machine we use, the volume of oxygen and of room air can be adjusted separately. This allows more complete control of the Po 2 • We attempt to produce normal gas tensions and pH in the arterial blood. A blood sample is analyzed for Pco 2 , Po 2 and pH as soon as the patient is stabilized on the machine. If gas values are not optimal, the ventilation is adjusted and the blood analyzed again after a period of 30 minutes. This routine is repeated until satisfactory values are obtained. The minute volumes of oxygen and room air used to maintain optimal values are kept constant until there is evidence for change on the basis of later blood gas analyses.

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NEALON, STEVEN CARL SANDLER

Once the patient's ventilation has been stabilized at the desired level, the normal range of gas tensions can be continued by maintaining the ventilation unchanged. We repeat the blood studies daily for the first two or three days. When the patient is kept on the machine longer and is remaining stable we have extended the interval to two or more days. Considerable nursing care is required for any patient receiving continuous ventilatory support. A specially trained nurse should be in attendance at all times. A cuffed endotracheal tube is used routinely. It must be remembered that with such a device there is no airway about the tube such as exists when a regular tracheostomy tube is in the trachea. If the tube blocks, the patient cannot breathe and it must be unblocked immediately or he will be asphyxiated. We have not had serious problems with pulmonary infections as a result of the tracheostomy. However, special precautions must be taken: 1. A sterilized catheter is used each time the trachea is aspirated. 2. The nurse aspirating the trachea wears a sterile rubber glove to handle the catheter. 3. The catheter is irrigated with sterile saline from a sterile cup which is changed for each aspiration. 4. Tracheal aspiration must be limited to 3 to 5 seconds at a time to avoid precipitating cardiac arrest. 7 On the other hand, the number of aspirations is not limited provided the patient is allowed to recover between aspirations. A special tracheostomy aspiration kit with sterile equipment is made up by the hospital (Fig. 3). On the first day of treatment the patient is fed intravenously. On

Figure 3. Tracheostomy aspiration equipment. Nurse uses sterile glove to handle the catheter which is cleared by aspiration of saline from the aluminum cup. Saline is instilled with the syringe. All equipment shown is sterile and used only once unless resterilized. Packets containing 10 of each item are supplied by the central sterile supply room.

THE TREATMENT OF RESPIRATORY FAILURE WITH VENTILATORY SUPPORT

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the following day he is started on oral fluids if his gastrointestinal tract is functioning; the diet is then gradually increased. Patients on continuous ventilatory support can eat a regular diet after a few days. They can even get out of bed to eat while the ventilatory support continues. At such times assisted ventilation is less troublesome. Weaning the Patient from the Ventilator A decision must be made as to when continuous ventilatory support should be discontinued. Continuous support not only provides more satisfactory gaseous exchange for the patient but also markedly reduces the amount of effort the patient must expend to breathe. Consequently, an additional period of ventilatory assistance beyond the time when the patient can adequately ventilate himself without support may be utilized to diminish the work of breathing. It is of interest that stabilization of the patient being artificially ventilated occurs at various C0 2 levels. The Pco 2 of a patient with chronic lung disease will often stabilize at a higher value than in one who has essentially normal lungs. Realization of this fact will often help avoid artificial ventilation for unnecessarily prolonged periods, because patients may be alert with relatively good Po 2 levels while the Pco 2 is elevated above 50 mm. Hg. After the patient has been well stabilized on the basis of both clinical appearance and blood gas analyses he can then be given a trial off the ventilator. Ventilation is discontinued and blood gases are analyzed 30 minutes, two and four hours later. A drop in the Po 2 does not necessarily signal the need for renewed ventilatory support. An oxygen collar can be put over the tracheostomy and oxygen flowed at a rate sufficient to maintain a normal Po2 • On the other hand, if the Pco2 rises or the patient is forced to labor to keep it within normal limits, the ventilatory support is resumed. If the patient holds a normal Pco 2 without effort the continuous support is permanently discontinued. An oxygen collar is put over the tracheostomy and intermittent positive pressure breathing (IPPB) is used as often as necessary to maintain a normal Pco 2 • The IPPB is best accomplished at intervals of two to four hours for periods of 20 minutes. It can be discontinued gradually as the patient progresses. The oxygen collar is usually necessary for a few days. The higher oxygen levels in the ventilating gases required during continuous support can be reduced after the ventilatory support is stopped. 14 We use an oxygen collar at flows of 4 to 7liters per minute of humidified oxygen. During the first few days of the weaning period we have returned some patients to continuous artificial ventilation during the night. This allows for better stabilization of the patient, reduces the work of breathing, and enables the patient to sleep well with sedation. The tracheostomy may be plugged during periods of breathing ambient air. With improved ventilation, smaller tracheostomy tubes without balloons are used until the point is reached where tracheostomy is no longer needed. At this time the patient is breathing well by the oronasal route and is able to expectorate tracheobronchial secretions.

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Table 1.

CASE

1.

c. K.

2. J,

3.

c.

c.w.

4. T.V.

DIAGNOSIS

Carcinoma right lung, advanced chronic obstructive pulmonary emphysema Recurrent Initral stenosis Ruptured abdominal aortic aneurysm, advanced chronic obstructive pulmonary emphysema Recurrent Initral stenosis

8. J.M.

Recurrent Initral stenosis

9. M.S.

Recurrent Initral stenosis

11. J, K. 12. W. F.

13.

w.w.

14. E. R.

NEALON, STEVEN CARL SANDLER

Pertinent Data in 20 Cases Given Continuous Ventilatory Support

5. W.W. Chronic bullous emphysema,recurrent pneumothorax 6. G. H. Chronic obstructive pulmonary emphysema with superimposed infection and CO, narcosis 7. T. F. Interventricular septal defect, congestive heart failure

10. H. G.

F.

Bronchiectasis, empyema left lung, leftsided bronchopleural fistula, previous left lower lobe and lingulectomy Carcinoma of right lung Carcinoma of the esophagus

Myasthenia gravis with thymoma Recurrent left pneumothorax,empyema left lung, malnutrition, drug addiction

TREATMENT

TYPE OF RESPIRATOR

RESULTS

Right radical pneumonectomy; tracheostomy

Bird, Recovered Engstrom but died at later date

Open cardiotomy with insertion of StarrEdwards valve; tracheostomy Aneurysmectomy and placement of dacron graft prosthesis; tracheostomy

Engstrom

Open cardiotomy with insertion of StarrEdwards valve; tracheostomy Right pneumonectomy; tracheostomy

Bird, Recovered Engstrom but died at later date

Alive

Bird, Alive Engstrom

Engstrom

Dead

Tracheostomy

Bird, Alive Engstrom

Pulmonary artery banding

NasotraDead cheal tube; Bird, Engstrom Bird, Alive Engstrom

Open cardiotomy with insertion of StarrEdwards valve; tracheostomy Open cardiotomy with insertion of StarrEdwards valve; tracheostomy Left pneumonectomy; tracheostomy

Right pneumonectomy; tracheostomy Radioactive cobalt therapy; esophagectomy and colonic bypass, 3-stage; tracheostomy Thymectomy; tracheostomy Drainage of empyema cavity; tracheostomy

Engstrom

Dead

Bennett, Bird

Alive

Bennett, Recovered Bird, but died at Engstrom later date Bird, Dead Bennett, Engstrom Bird, Alive Engstrom Bennett Dead

THE TREATMENT OF RESPIRATORY FAILURE WITH VENTILATORY SUPPORT

Table 1.

Pertinent Data in 20 Cases Given Continuous Ventilatory Support (Continued) DIAGNOSIS

CASE

15. P. G.

Nonresectable carcinoma of right lung

16. A.J.

Carcinoma of right lung

17.

v. s.

18. N. P.

TREATMENT

w.

TYPE OF RESPIRATOR

RESULTS

Right exploratory thoracotomy

NasotraAcute myocheal tube; cardia! Bird, infarction, Bennett dead Right pneumonectomy; Bird Dead tracheostomy Cholecystectomy; apNasotraRecovered pendectomy with cheal tube; but died at Bennett, later date drainage of appenBird diceal abscess; I & D of groin abscess; tracheostomy

Empyema of gallbladder, perforated appendix, groin abscess, chronic obstructive pulmonary emphysema with C0 2 narcosis Right pneumonectomy; Carcinoma right lung tracheostomy

Carcinoma of left lung Crainiotomy, vagotomy, pyloroplasty, hiatal with cerebral metasherniorrhaphy, tasis, bleeding tracheostomy duodenal ulcer, hiatal hernia R. Chronic bronchitis and Tracheostomy emphysema, recurrent pneumonitis, C0 2 narcosis, cerebrovascular accident

19. R. K.

20.

1215

Bennett, Bird, Engstrom Bird

Alive

Bennett, Engstrom

Dead

Dead

RESULTS Using the technique outlined we have used continuous ventilatory support in 20 patients. Table 1 lists the pertinent data conceming these patients. All of these patients were gravely ill when first treated. Eleven of the 20 were resuscitated from the respiratory failure but four of these ultimately died of their basic disease. Of the nine deaths which occurred during ventilatory support, five were due to progression of the basic disease and one to an acute myocardial infarction. The other three can be related to the management of the support although the basic disease probably contributed. Patient 5 probably succumbed as a result of an overzealous tracheal aspiration. This danger has been emphasized by other writers. 7 Individual periods of aspirations must be kept brief (3 to 5 seconds). They can be repeated as often as necessary provided the patient has been allowed to clear his dyspnea in the interim. Patient 16 also died as a result of a tracheal aspiration even though it was performed properly. He had an inordinate fear of the procedure and almost went berserk when aspirated. His profuse secretions dictated the need for aspiration which could be accomplished if he were heavily sedated. An aspiration at a time when his sedation had lightened put him into a severe state of agitation followed by cardiac arrest. Given a similar patient again we would carry him under very heavy sedation.

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Patient 7, a six-week-old infant with a ventricular septal defect and refractory cardiac failure, had undergone pulmonary banding four days earlier. Ventilation with a pressure-cycled respirator had become ineffective because of high airway pressures secondary to bronchospasm. At the time he was turned over to our care he had clinical and x-ray evidence of widespread bilateral pneumonitis. Initially 90 per cent oxygen was needed to satisfy the infant's respiratory needs. The bronchospasm disappeared and he became quiet, pink, and well ventilated. His arterial blood had a Po2 of 90 mm. Hg, and a Pco 2 of 24 mm. Hg. In the next two days his oxygen requirements decreased to 75 per cent. On the following day he became progressively more unresponsive and required increasing amounts of oxygen. He died on the eighth postoperative day due to our inability to clear secretions from the tracheobronchial tree and hepatization of his lungs. In this case the hepatization of the lung was probably caused by the high oxygen concentration in the inspired gas, in spite of the fact that the tension of oxygen in the arterial blood never rose above 90 mm. Hg. We think it advisable to restrict the oxygen in the ventilating gas to no more than 65 per cent when the support extends beyond 24 hours. Unfortunately one is limited in choice of gas concentrations in most ventilators because they allow only for room air, 40 per cent oxygen, or 100 per cent oxygen. We do not perform a tracheostomy on infants. We put in the largest endotracheal tube possible and leave it in place for several days without changing it.

CASE REPORTS CASE 6. A 62-year-old retired man was admitted to JMCH with respiratory difficulty. He had been bothered by dyspnea due to pulmonary emphysema for 6 years but it had become much more pronounced in the 3 days prior to his admission. A pulmonary infiltration was found and he was put in an oxygen tent, given IPPB and started on antibiotics. He was seen by us as an emergency on the following day. He was markedly cyanotic in the oxygen tent, comatose, and his respiratory efforts were ineffectual. He obviously had a very poor airway. An emergency tracheostomy was done in bed without anesthesia. A copious amount of viscid purulent material was aspirated from his trachea, and a cuffed tracheostomy tube was inserted and attached to a pressure controlled respirator. The patient's color changed noticeably. While the tracheostomy was being performed, an arterial blood sample was taken which showed a Po 2 of 54 and a Pco 2 of 64. After the ventilator had been attached a second sample was taken. The Po 2 had risen as expected, to 250 but the Pco 2 had risen to 84 (Fig. 4). A check with another sample showed a further rise in Po 2 to 325 and a Pco2 of 86. The patient was in severe bronchospasm and his respiratory exchange was very poor. Although the pressure on the ventilator was set at its maximum and the inspiratory flow rate lowered, a good exchange could not be effected with the machine. It became obvious that this type of ventilator would not work on this patient and it was decided to transfer him to our special unit where a volume-regulated ventilator could be used. In the meantime the pressure-controlled ventilator was detached and the patient was hyperventilated manually using an Ambu bag, whereupon the Po 2 fell to 120 (lower oxygen mixture) but the Pco 2 also fell to 58 (Fig. 4). When

THE TREATMENT OF RESPIRATORY FAILURE WITH VENTILATORY SUPPORT

p 02 Figure 4. Chart of blood gas values in Case 6. Tracheostomy and ventilation assistance with a pressure-controlled respirator improved the p0 2 but the pC0 2 also rose. Manual assistance lowered the pCO,. Owing to the lower concentration of oxygen being administered, the p(), also dropped but it remained in a normal range. A volume-controlled respirator maintained the improvement.

1217

200

(mm Hg) 100

pC0 2 (mm Hg) 0

I

I

f'l'

02 TENT

Pressure 1_ 1 Ventilation

Tracheostomy

ti

2

Volume

Controlled Ventilation

the patient was attached to the Engstrom ventilator it was possible to adjust the concentration and volume of the ventilating gas to effect a Po2 of 100 and a Pco 2 of 40. The patient was ventilated continuously for 5 days, then switched to an oxygen collar with periodic IPPB. The oxygen was stopped on the ninth day and the patient was discharged from the hospital after 45 days with instructions to use the IPPB four times daily. The tracheostomy was left in place and he was trained to aspirate his copious tracheobronchial secretions through the tracheostomy.

Comment. The limitation of clinical observation and the importance of blood gas analyses in assessing blood gas levels is well illustrated here. Although the patient's color improved remarkably on the first ventilator, and he appeared to be doing better, his Pco 2 was actually rising. The gas determinations immediately demonstrated this and pinpointed the need for different treatment. This patient could not be ventilated by a pressure controlled respirator. The resistance created by the severe bronchospasm caused the pressure to rise to the predetermined level when only a small amount of gas had entered the lungs. That the problem was due to inadequate ventilation is well demonstrated by the ready reduction of the Pco 2 with manual ventilation. CAsE 10. A 41-year-old woman was admitted to JMCH on May 8, 1966 with a history of pulmonary complaints extending over a 12-year period. She had severe basilar bronchiectasis and had had pulmonary resections of her left lower lobe and of part of her lingula 10 and 12 years earlier. An empyema that developed in January 1966 was treated by open drainage. She had a persistently draining cavity and a bronchopleural fistula since that time. She entered the hospital at this time for removal of the remaining left upper lobe, much of which appeared on x-ray to be destroyed (Fig. 5). The patient was prepared with postural drainage, IPPB, and antibiotics. On

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NEALON, STEVEN CARL SANDLER

Figure 5. Bronchogram in Case 10. Most of remaining left upper lobe appears to be destroyed.

P02 mmHg

pH

PC02 mmHg

Room Air

POST-OPERATIVE DAYS

Figure 6. Chart of blood gas values in Case 10. Use of a ventilator corrected the gas values in the recoverv room. When the ventilator was detached the following day the patient maintained good blood gas levels for awhile but they began to deteriorate, indicating the need for more prolonged ventilation. (From Pennsylvania Med. J. 69:49, 1966.)

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May 20, 1966 the remaining pulmonary tissue was excised from the left hemithorax. She tolerated the operation without difficulty. She left the operating room in good condition but in the recovery room she had persistent hypoventilation, made worse by an average dose of analgesic. She was treated by nasal oxygen and initial blood gas studies showed a Po 2 of 175, a Pco2 of 55 and a pH of 7.27. She became more stuporous and 4 hours after operation it became necessary to ventilate her lungs through a cuffed nasotracheal tube and a pressure regulated ventilator. With this apparatus the patient's condition stabilized (Po 2 , 126; Pco2 , 33; and pH, 7.51 (Fig. 6). The next morning the ventilator was discontinued. The nasotracheal tube was removed after repeated arterial blood gas studies done over a period of 4 hours were within normal limits. That evening the patient began again to accumulate carbon dioxide. Arterial blood studies demonstrated a Po 2 of 147, a Pco 2 of 61 and a pH of 7.27. It was evident that prolonged ventilatory support was necessary. Tracheostomy was performed and she was again attached to the ventilator with good results. Ventilatory support was continued for 4 days. For the next week she used an oxygen collar and periodic IPPB. Because of cachexia, her hospital stay was prolonged; she left on the 95th day after operation. At that time, while she was breathing room air, she had a Po2 of 53, a Pco2 of 56 and a pH of 7.36.

Comment. It was not anticipated that continuous ventilatory support for this patient would be required postoperatively. Because of the possibility that the narcotic was responsible for her depression immediately postoperatively, a nasotracheal tube was used. When the tube was removed it appeared that she might be able to get along without assisted ventilation. However, before the end of the day it was obvious that she would need further ventilatory support so a tracheostomy was performed. As can be seen from the values at the time of her discharge, this patient tolerated an elevated Pco2 without obvious effect on her sensorium.

CHOICE OF RESPIRATOR There are many types of ventilators available today. These can be divided into three main categories depending upon the principle controlling inspiration and expiration. In pressure-cycled respirators, the inspiratory phase ends when a preset pressure has been reached. In volume-cycled respirators, inspiration ends and expiration begins when a preset volume has been delivered. In time-cycled respirators, inspiration and expiration are controlled by a preset rate and preset duration. Time-cycled respirators are now less frequently used than the first two types. PRESSURE-CYCLED RESPIRATORS. Most of these respirators are activated by a small increment of negative pressure which occurs when the patient begins to inspire. The apparatus will then continue to deliver gas into the tracheobronchial tree until a preset pressure has been reached. Once this pressure has been reached the delivery of gas stops and is not resumed until it is triggered by another respiratory effort. Most of these machines function by assisting the ventilation of the patient. If there is concern that the patient may become apneic, the machine can be adjusted so that it will cycle automatically if no respiration occurs in a preset period of time. In this type of respirator, inspiration will continue until the preset pressure has been reached. There must be some resistance

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THOMAS

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NEALON, STEVEN CARL SANDLER

to generate the pressure necessary to cycle the machine. If this resistance is not present, the machine will become fixed in the inspiratory phase. Such a series of events occurs in the presence of a large air leak.'"· 12 On the other hand, if the resistance increases, the duration of inspiration is reduced markedly, and the machine cycles almost immediately after inspiration begins, thus delivering a very small volume. This situation is seen in the presence of increased endobronchial pressure due to mechanical obstruction, accumulation of secretions or bronchospasm. TIME-CYCLED REsPIRATORS. In this group of machines the duration of inspiration and expiration are determined basically by the speed of the driving mechanism and the reduction gearing which connect this to the chamber that delivers the output. 10• 12 Changes in the resistance to its action have no serious effect on either phase of ventilation. VoLUME-CYCLED RESPIRATORS. In a volume-cycled respirator, inspiration continues until the machine has delivered the predetermined volume. To prevent the danger of excessive pressure build-up, a safety valve allows the excess gas to be expelled to the atmosphere if the pressure rises above a preset level. Some of these machines can assist the ventilation while others function only by controlling it.

Proper use of any of the presently available ventilators will result in successful management of the great majority of patients in respiratory failure. Pressure-regulated respirators, which are usually patient triggered, are the type used in most hospitals today. The patient must begin to inhale to trip a valve in the machine which initiates inspiration. Inspiration then proceeds until a predetennined pressure has been reached within the lungs, at which time the flow to the patient is terminated and a passive expiratory phase occurs. This works well in most patients. However, in patients with bronchospasm, the increased intrabronchial pressure forces the machine to terminate the flow of gas prematurely, causing a decrease in tidal volume. As the tidal volume decreases, hypercapnea increases, the patient attempts to take more breaths thereby triggering the machine again and again, creating more bronchospasm, causing earlier terinination of inspiration, and faster breathing. In this way, a vicious cycle is formed. In most patients the use of bronchodilators locally or systeinically will help to avert bronchospasm and its associated effects. Persistent bronchospasm is most often seen in patients with chronic bronchitis and emphysema. During the past year, we have treated several such patients who were unresponsive to bronchodilators and to ventilation with pressure-cycled ventilators. In this situation we have found the Engstrom respirator very useful. The Engstrom respirator is a volume-regulated, pressure-liinited ventilator which will maintain sustained pressure at a selected level until a preset volume of gas has been delivered. The pressure of gas delivered by this apparatus to a patient in bronchospasm rises rapidly also. However, when the selected pressure is reached, the gas which would raise the pressure higher is blown off through a safety valve, but the inspiratory phase continues until the preset volume has been delivered. Additional portions of this gas insure that the alveoli behind the more stenosed bronchi get as large a share of the predeterinined volume as possible. As the ventilation increases, hypercapnea is reduced and bronchospasm eases-facilitating better ventilation.

THE TREATMENT OF RESPIRATORY FAILURE WITH VENTILATORY SUPPORT

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BLOOD GAS ANALYSIS There are various methods of obtaining arterial blood samples. In postoperative cardiac surgery patients, the arterial catheter which is used to monitor arterial pressure can be used to obtain arterial blood samples. In the majority of our patients, we use a Cournand needle of large bore placed in the bronchial artery. Placement of the needle is accomplished under local infiltration anesthesia using aseptic technique. We have found it advantageous to maintain the arm in a slightly hyperextended position using a small lightweight brace. Once the needle is in place, arterial blood samples can be obtained at frequent intervals with little discomfort to the patient. Blood samples are collected anaerobically using a well-sealed plastic disposable syringe in which the dead space has been filled with aqueous heparin solution. Samples are analyzed using the Astrup microanalyzer for pH and Pco 2 ; Po 2 is determined using the Clark electrode. With the Sigaard Anderson nomogram, base excess, standard and actual bicarbonate, and buffer base may be calculated. The Astrup analyzer can also be used in the microanalysis of capillary blood samples. This is accomplished using small amounts of blood obtained from the arterialized finger tip or ear lobe using heparinized capillary tubes. We insert a needle when a series of determinations are to be done. For isolated analyses we use the finger stick. The importance of determination of blood gas values cannot be overemphasized. It is often impossible to make the diagnosis of respiratory failure on clinical grounds alone. Blood gas studies are helpful in evaluating the patient before beginning treatment to determine the severity of his disability. They are mandatory for monitoring the patient during therapy on the ventilators and when he is being weaned from the apparatus once the acute phase of pulmonary failure has passed. It is well known that cyanosis may be clinically absent in a patient with severe hypoxia. On the other hand, normal mental status does not rule out hypercapnea. It is generally found that changes in Po2 occur much more rapidly than changes in Pco2 • 11 This is related to several factors including ventilation-perfusion ratio abnormalities and the presence of chronic lung disease. With decreased alveolar ventilation the Pco 2 in arterial blood increases. On the other hand, because of the shape of oxygen dissociation curve, Po 2 must fall markedly before a change in oxygen saturation takes place- demonstrating the poor correlation between Po 2 and arterial saturation with 0 2 • 6

SUMMARY Pulmonary failure in the surgical patient is being seen with increasing frequency in the modern general hospital. The various causes and types of respiratory failure are discussed and correct management is described. The importance of arterial blood gas studies in both the diagnosis and treatment of respiratory failure is emphasized. The type of venti-

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THOMAS

F.

NEALON, STEVEN CARL SANDLER

lators available, the principles of ventilator assistance, and the treatment of patients refractory to the common pressure-cycled respirators are discussed. Illustrative case histories of patients with respiratory failure are presented.

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