Respiratory Care

Complications from mechanical ventilation have been frequently reported. Some can be prevented by careful ventilatory monitoring and by the establishment of protocols, while others can be avoided by an understanding of mechanical ventilation's effects on cardiopulmonary physiology. The major cardiovascular complication of mechanical ventilation is depression of cardiac output, the magnitude of which is influenced by the mode of mechanical ventilation used. PEEP with controlled mechanical ventilation produces a greater cardiac output depression than does PEEP with intermittent mandatory ventilation (IMV), and PEEP with continuous positive airway pressure (CPAP) produces the least depression of the three. Because this depression of cardiac output during PEEP can be marked, oxygen delivery must be monitored after PEEP has been initiated. Recent studies have shown that the extent of oxygen delivery is not reliably reflected by the mixed venous oxygen tension measurement, so oxygen delivery to the tissues must be calculated. Another major cardiovascular complication of mechanical ventilation is pulmonary barotrauma, the risk of which can be minimized by the use of low tidal volumes with PEEP. High-frequency positive-pressure ventilation (HFPPV) may solve the problem of providing adequate alveolar ventilation at low mean airway pressures with little depression of cardiac output and low risk of pulmonary barotrauma; however, more research needs to be done on this ventilatory mode before it can be used routinely. The ideal ventilator circuit of the future will provide a constant tidal volume, a low compressible volume, and a low internal compliance.

Passage of air from the bronchi into the pleural space during mechanical ventilation results in pneumothorax, for which prompt chest-tube placement is necessary. Positive airway pressure and external chest-tube suction establish a pressure gradient that may allow air to escape continuously in a persistent bronchopleural air leak (PBL). Although its significance in the natural history and prognosis of severe acute respiratory failure (ARF) has not been established, the presence of a PBL can lead to persistent lung collapse, loss of effective tidal volume and positive end-expiratory pressure (PEEP), seeding of the pleural space with airway organisms, and intractable respiratory acidosis. Clinicians have tried several therapeutic approaches intended to minimize the bronchopleural pressure gradient, maintain gas exchange, and reinflate the affected lung. In addition to adjustments in ventilator settings and external suction, these include the application of PEEP to the chest tube, occlusion of the tube during part of the ventilator cycle, independent ventilation of the two lungs, and high-frequency ventilation. Direct closure or plugging of the leak site has also been attempted. So far there is no single best therapy, and patients with severe PBL continue to have a poor prognosis, perhaps owing to the severity of the underlying respiratory dysfunction as much as to the leak. Careful general respiratory care, early vigorous treatment of ARF, and ventilator management aimed at reducing the factors that predispose to pneumothorax and PBL may reduce the incidence of this often devastating complication.

Complications of tracheal tubes are common and occasionally severe. They may be classified according to their time of occurrence: during the intubation or tracheotomy, while the endotracheal or tracheostomy tube is in place, during extubation or decannulation, or after extubation or decannulation. Numerous factors, of which excessive cuff pressure is the best understood, contribute to the pathogenesis of these complica-tions. Each of the four varieties of tracheal intubation (nasotracheal intubation, orotracheal intubation, cricothyroidotomy, tracheostomy) has unique advantages and disadvantages. Although tracheostomy is the preferred method for long-term airway management, optimal timing of tracheotomy remains controversial. Tracheotomy should be performed only after consideration is given to many clinical factors relevant to each patient and should not be performed solely because an arbitrary number of days of intubation has elapsed. Following simple guidelines will allow respiratory care personnel to avoid many of the complications of artificial airways and to recognize early those that do occur.

Obtaining blood samples from arteries is important in the diagnosis and the monitor-ing of treatment in many medical situations. While arterial puncture by needle is indicated for one or a low number of intermittent samplings, arterial catheterization is indicated for multiple sampling. Both procedures are subject to complications; those associated with catheterization include embolic phenomena, thrombus formation, arterial occlusion, aneurysm formation, arteriovenous fistula, infection, sensory loss, hematoma formation, bleeding, pain, inadvertent injection of drugs, and collection of inaccurate data. These complications may be precipitated by certain catheter mate-rials, by vessel and catheter size, by duration of cannulation, by irrigation, by pre-existing arterial disease, and by low cardiac output. Measures to prevent com-plications include choosing the most distal sites, using Allen's test or a modification thereof, using small diameter, short, Teflon catheters, securing catheters properly, using a continuous, slow infusion of heparinized saline, and not injecting potentially toxic or irritating substances through arterial catheters.

Patients who require respiratory therapy are more likely than other patients to develop bacterial infections of the respiratory tract. These patients are more susceptible than healthy persons to colonization of the respiratory tract by pathogenic organisms from the environment and other persons. They also are likely to aspirate contaminated oropharyngeal secretions into the tracheobronchial tree; and they usually have impaired antibacterial defense mechanisms of the lower respiratory tract. While respiratory therapy cannot be held accountable for these abnormalities, respiratory therapy equipment and techniques play a dual role in the problem of respiratory infections, having both positive and negative effects. On the positive side, therapy aims to decrease sources of pathogens, to improve mucociliary clearance, and to enhance antibacterial defense mechanisms—by the use of humidification, aerosols, lung inflation, cough, suctioning, oxygen, and drugs that act on the airway. On the negative side, respiratory therapy equipment can act as reservoirs and agents of transmission of infectious bacteria, suctioning can compromise the mucociliary defense system, and alveolar hyperoxia can depress the antibacterial defense mecha-nisms of the lower respiratory tract. It is therefore important to adequately clean and decontaminate equipment, to schedule changes of equipment, to use certain dispos-able devices, to employ proper suctioning procedures, and to avoid alveolar hyperox-ia. Improved techniques are needed for preventing aspiration of oropharyngeal secretions and for stimulating mucociliary function and the antibacterial function of lung cells. But in the absence of such improved techniques, it is critically important that respiratory therapy equipment and techniques not actively promote the occur-rence of infections by serving as sources or vehicles of transmission of infectious organisms or by adversely affecting antibacterial defense mechanisms.

The complications that may occur as a result of endotracheal suctioning are generally avoidable or reversible. Tissue trauma can be prevented by the smooth introduction of the suction catheter along the proper course, by the use of regulated suction, and by the intermittent rather than continuous occlusion of the thumb port. Hypoxemia can be prevented by preoxygenation. The risk of cardiac arrhythmias can be minimized by preoxygenation and by the avoidance of repeated nasotracheal suctioning attempts. The practitioner can avoid precipitating subsegmental atelectasis by guarding against the application of active suction during endobronchial impaction of the catheter, and he can usually reverse any diffuse microatelectasis by hyperinflation after the suction-ing procedure. The repeated performance of nasotracheal suctioning predisposes a patient to pneumonia, as does insufficient attention to aseptic technique. Some degree of coughing by the patient being suctioned is often unavoidable, and the practitioner must be aware of possible complications of the cough itself. The bronchoconstriction that may occur secondary to the mechanical stimulus afforded by the catheter can be treated with bronchodilator drugs. Finally, the practitioner can facilitate entry of the catheter into the left mainstem bronchus by turning the patient's head to the right and/or by using angle-tipped catheters.

Chest physiotherapy (CPT) is administered to mobilize respiratory secretions and to increase the amount of tracheobronchial mucus cleared from the respiratory tree. CPT consists of one or more of the following: therapeutic positioning, percussion, vibration, and coughing. In therapeutic positioning, also called postural or bronchial drainage, the position of choice is “good”-lung-down,-“bad”-lung-up, and positioning is gaining in popularity as a means of enhancing air entry into alveoli that have collapsed as a result of localized conditions. Complications of CPT have been infrequently reported but are severe when they occur. Some of these are massive pulmonary hemorrhage, perhaps caused by clots dislodged during percussion, a decrease in PaO₂ from positioning the "bad" lung down, and rib fractures in a neonate with hyaline membrane disease. Percussion and vibration should not be done when bright red hemoptysis is present and recent, and head-down positioning should be used cautiously and only when the affected lung is uppermost. Adverse physiologic effects associated with CPT occur in a small proportion of the patients studied and generally are of modest clinical significance. Some that have been reported are an increase in intracranial pressure (ICP), a fall in PaO₂, a decrease in cardiac output, which may make CPT hazardous in the first 24 hours after a procedure like mitral valve replacement, a fall in FEV1, possibly caused by percussion without the prior administration of a bronchodilator, a fall in specific airways conductance, and a decrease in total lung/thorax compliance. Patients with increased ICP, hypoxemia, cardiovascular or hemodynamic instability, and marked bronchospasm should be treated with extreme caution and monitored carefully. Recognition of the nature of and potential for the complications and adverse effects of CPT allows the therapist to modify therapy so that it may be safely administered to both the critically and the chronically ill.

Mechanical aids to intermittent lung inflation (treatments of 30 minutes or less) include IPPB, incentive spirometry, blow bottles, and intermittent CPAP. We consider true complications of their use to be those complications documented by one or more studies or by several case reports. Besides documented complications there are theore-tic or suggested complications. For IPPB, we identified three documented complica-tions: increased airway resistance, barotrauma, and nosocomial infection. Six other, theoretic complications of IPPB are: excessive oxygenation, gastric distention, hyper-ventilation, impaction of secretions, psychological dependence, and impedance of venous return. We found no documented complications of incentive spirometry; two theoretic complications are hyperventilation and barotrauma. For blow bottles, no documented complications exist; theoretic complications are hyperventilation, in-creased atelectasis, and barotrauma. For intermittent CPAP, no complications exist. We believe that the lack of documented complications of the use of these mechanical aids to intermittent lung inflation may have encouraged their widespread use despite the relative absence of documentation of their efficacy. Because these therapies are costly and of questionable value, cost-effective and efficacious methods of intermittent lung inflation should be encouraged.