With increasing utilization of mechanical ventilation during the past decade or so, complications related to its use have also increased. Ventilators are primarily indicated when acceptable safe levels of oxygenation and ventilation cannot be maintained by other means

Muren, Orhan

VCU Scholars Compass

Complications of Mechanical Ventilation* ORHAN MUREN, M.D. Associate Professor of Medicine and Anesthesiology, Medical College of Virginia, Health Sciences Division of Virginia Commonwealth University, Richmond, Virginia With increasing utilization of mechanical ven-tilation during the past decade or so, complica-tions related to its use have also increased. Ven-tilators are primarily indicated when acceptable safe levels of oxygenation and ventilation cannot be maintained by other means. The goal of assisted mechanical ventilation should be to improve arterial oxygen, C02 ten-sions, and pH to acceptable safe levels compatible with life or normal functioning. The following are the complications which may occur during assisted mechanical ventilation : 1 ) Reduced venous return and cardiac out-put. 2) Complications related to endotracheal tubes and tracheostomies. 3) Atelectasis. 4) Infection. 5) Oxygen toxicity. 6) Acid-base, fluid, and electrolyte disturb-ances. 7) Gastrointestinal problems. 8) Technical and mechanical problems. 9) Emotional stress. 10) Miscellaneous: cardiac arrhythmias, pul-monary emboli, pneumothorax, and so forth. Reduced venous return and cardiac output are commonly observed in patients with signifi-cant volume depletion. It is important that blood pressure and urine output should be checked at regular intervals. A central venous pressure cath-eter may need to be inserted for proper fluid replacements. The two other common causes of de-creased venous return are prolonged severe hy-* Presented by Dr. Muren at the Symposium on Respi-ratory Failure, May 26, 1972, at Richmond, Virginia. 154 poxemia and impaired sympathetic nervous sys-tem activity. Normal people can compensate for the de-creased venous return by a reflex increase in ven-ous tone and pressure provided: 1) mean airway pressure does not go above approximately 15 mm Hg, 2) effective blood volume is adequate, 3) sympathetic nervous system function is unim-paired. If any one or a combination of any of the above factors is not met, mechanical ventilation results in decreased cardiac output and lowering of arterial blood pressure. Proper adjustments in ventilators to reduce the mean intrathoracic pressure may need to be performed to improve decreased venous return. In this respect, volume cycled respirators are prob-ably advantageous over pressure cycled respira-tors. Negative pressure during exhalation may occasionally be used to improve venous return to the heart. However, this is somewhat contra-indicated in patients with chronic obstructive pul-monary disease. It may cause closure of airways leading to clinical or subclinical atelectasis. The following complications are related to endotracheal intubation and tracheostomies: 1 ) Tube in right main bronchus which causes massive atelectasis of the left lung. If not recognized this usually causes rapid de-terioration of pulmonary function. 2) Dislodgement, kinking of the tube, obstruc-tion by secretions, laryngeal edema and damage, herniation of cuff over end of the tube. 3) Complications related to tracheostomy: bleeding, infection, necrosis, tracheal stenosis, erosion of vessels, obstruction, and tracheoesophageal fistula. MCV QUARTERLY 9(2): 154-156, 1973 MUREN: COMPLICATIONS OF MECHANICAL VENTILATION 155 The incidence of atelectasis is increased especially in patients requiring prolonged assisted mechanical ventilation. The administration of high concentrations of 0 2 in inspired air causes further increase in the incidence of atelectasis. Adequate humidification of the inspired gas, chest physiotherapy, proper suction, and hydra-tion are essential in prevention and treatment of atelectasis. Bronchoscopy should be performed if atelectasis does not improve with conservative measures. Atelectasis may be first manifested by de-creasing compliance and increased alveolar-ar-terial 0 2 pressure gradient. To prevent atelectasis, a proper breathing pat-tern to obtain optimum ventilation should be main-tained. Intermittent sighing is also an important therapeutic measure to prevent atelectasis . Infla-tion hold and continuous position pressure ven-tilation are additional steps that may be used in prevention and treatment of this problem. As to 0 2 toxicity, two factors are primarily responsible for 0 2 toxicity in the lungs: l) high 0 2 tension in inspired air, 2) prolonged exposure to high inspired 0 2 tension. Patients may be at risk of develop-ing 0 2 toxicity if they are given inspired air containing 50% or greater 0 2 concentration for prolonged time. There seems to be an individual susceptibility. As a general rule, just enough 0 2 concentration in the inspired air should be given to maintain a safe and adequate level of oxygen tension in the arterial blood for a given patient. It should be noted that most pressure cycled ventilators administer higher 0 2 concentrations than one may think. On the air dilute setting, these ventilators usually deliver somewhere be-tween 60 to 95% 0 2 in inspired air. This is prevented by running the ventilator with compressed air and bleeding 1 to 3 L of 0 2 into the system. By measuring inspired 0 2 con-centration, proper adjustments should be made to administer the desired 0 2 concentrations in the inspired air. Infection, especially with gram negative or-ganisms, may be a dangerous problem. Nebulizers, humidifiers, and tubes with warm, humid inspired gases may be a source of a good culture media for many gram negative organisms. The respiratory tubing should be changed at least once daily and sterilized before it is used again. No respirator should be used for another patient unless proper sterilization techniques have been utilized. Acid-base, fluid, and electrolyte disturbances: one of the common iatrogenic complications of assisted mechanical ventilation is post-hypercapnic metabolic alkalosis. This is observed in patients with chronic respiratory acidosis. As a result of rapid lowering of P co,, pH may become alkalotic, since HC03 cannot be lowered significantly under these circumstances. Severe alkalosis can cause confusion, convulsions, coma, and even death. To prevent this, arterial pH should be monitored, and increased Pco, should be reduced gradually in chronic hypercapnia. Marked hyperventilation with severe respir-atory alkalosis alone can cause tetani with symp-toms and signs related to it. And again, arterial gas tensions and pH need to be monitored to prevent this problem. Some patients on prolonged assisted mechan-ical ventilation may develop fluid retention and even pulmonary congestion and edema, primarily interstitial type. Another complication of mechanical venti-lation is the development of inappropriate ADH-like electrolyte abnormality in some patients. This appears to be related to stimulation of ADH through thoracic volume chemoreceptors by posi-tive pressure breathing. Therefore, patients should be weighed and electrolytes should be checked repeatedly. Gastrointestinal complications consist of acute gastrointestinal bleeding, acute gastric dila-tion, ileus, and chronic aspiration during assisted ventilation. The physician should always consider these problems, and if they occur, proper steps must be taken. Technical and mechanical problems arise quite often. A physician or inhalation therapist should be prepared to cope with a respirator in case it becomes disconnected from the patient or mal-functions or in case the tube becomes obstructed. These complications can be disastrous for the patient within a few minutes. The ventilatory and 02 requirements of these patients change quite of-ten, so necessary adjustments must be made ac-cordingly. Emotional problems quite often arise from the inability to talk and communicate properly with people. Sincere understanding of the patient's problem and taking time to explain to the patient 156 MUREN: COMPLICATIONS OF MECHANICAL VENTILATION what is being done is extremely important in sta-bilizing the patient's emotional status. In general, patients receiving intensive respiratory care have a tendency to develop many cardiopulmonary prob-lems such as pulmonary emboli, cardiac arrhyth-mias, digitalis intoxication, and so forth . Other com-plications of assisted ventilation are pneumothorax and mediastinal emphysema, which may cause fur-ther deterioration of the pulmonary function; these must always be considered whenever pulmonary function of the patient becomes worse. Lastly, weaning the patient from ventilation may be a problem. The following guidelines are somewhat useful in deciding when to start wean-ing a patient: 1) Tidal volume should approach 5 to 6 ml/kg and vital capacity exceeds 10 ml/kg. 2) Alveolar-arterial 02 pressure gradient should be less than 300 mm Hg on 100% breathing. 3) The ratio between dead space and tidal vol-ume (VD/VT) should be less than 50%. 4) Inspiratory negative pressure should be more than 20 cm H20 negative pressure. Weaning is in general complete when vital capacity reaches 20 ml/kg. It should be noted that many patients may require additional 02 for some days or for weeks after weaning. Proper humidification must be provided when the patient is off the ventilator. Frequent short periods of spontaneous ventilation, that is, five to ten minutes per hour, should be attempted. As the patient's tolerance increases, time off the res-pirator is frequently increased. Vital signs, gen-eral appearance of the patient, and arterial gas studies are examined during these periods. The patient should not be allowed to sleep without assisted ventilation until he has tolerated three to four hour periods of spontaneous breathing dur-ing the day. During the weaning period, emotional support is extremely important. A patient who can commun-icate can get better emotional support. We insert a plastic tracheostomy tube which can be plugged to permit the patient to talk during the period of weaning. This has been very useful during this critical period. In conclusion, it must be recognized that properly trained physicians, nurses, and inhalation therapists are necessary for the care of acutely and critically ill patients with major pulmonary problems, to prevent and treat complications. Team work is essential for the proper management of those patients who require assisted mechanical ventilation. BIBLIOGRAPHY BAKER, J. P. Proper use of mechanical ventilators. Med. Coll. Va. Quart. 8:2, 1972. BENDIXEN, H . H., et al. Respiratory Care. St. Louis, C. V. Mosby Co., 1965. CHERNIACK, CHERNIACK, AND NAIMARK. Respiration in Health and Disease. Philadelphia, W. B. Saunders Co., 1972. Committee o~ Public Health. A report: Effective admin-istration of inhalational therapy with special reference to ambµlatory and emergency oxygen treatment. Bull. New York Acad. Med., 38:135, 1962. COMROE, J. H., JR. Physiology of Respiration. Chicago, Yearbook Medical Publishers, Inc., 1966. EGAN, D. F. Fundamentals of Inhalation Therapy . St. Louis, C. V. Mosby Co., 1969. SHELDON, G. P. Pressure breathing in chronic obstructible lung disease. Medicine 42 : 197, 1963. 

Complications of Mechanical Ventilation

http://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=1734&context=mcvq

Complications of Mechanical Ventilation

Abstract

Similar works

Full text

Available Versions

VCU Scholars Compass