Complications in the Ventilated Patient

Angiotensin-converting enzyme inhibitor captopril attenuates ventilator-induced lung injury in rats

We hypothesized that lung inflammation and parenchymal apoptosis in ventilator-induced lung injury (VILI) are related to ANG II and assessed the ability of the angiotensin-converting enzyme inhibitor captopril to attenuate VILI in rats. Adult male Sprague-Dawley rats were randomized to receive two ventilation strategies for 2 h: 1) tidal volume of 40 ml/kg, respiratory rate of 25 breaths/min, and inspiratory O2 fraction of 0.21 [high-volume, 0 positive end-expiratory pressure (HVZP) group] and 2) injection of captopril (100 mg/kg ip) 30 min before HVZP ventilation (HVZP+CAP group). Another group, which did not receive ventilation, served as the control. Mean arterial pressure was significantly lower in the HVZP+CAP group than in the HVZP group at 2 h of ventilation. Total protein levels were significantly higher in bronchoalveolar lavage fluid (BALF) recovered from HVZP-ventilated rats than from controls. BALF macrophage inflammatory protein-2 and lung ANG II were significantly higher in the HVZP group than in the control and HVZP+CAP groups. Lung ANG II levels correlated positively with BALF protein and macrophage inflammatory protein-2. The number of apoptotic airway and alveolar wall cells was significantly higher in the HVZP and HVZP+CAP groups than in the control group and significantly lower in the HVZP+CAP group than in the HVZP group. These results suggest that the efficiency of captopril to attenuate VILI is related to reduction of inflammatory cytokines and inhibition of apoptosis and indicate that VILI is partly mediated by the local angiotensin system.

Late-Onset Occult Pneumothorax After Lung Volume-Reduction Surgery

BACKGROUND

Lung volume-reduction surgery has proved to be a reliable palliative surgical treatment for patients with severe emphysema. Nonetheless, late complications can arise after lung volume-reduction surgery although this matter has been poorly investigated by previous studies.

METHODS

We report a series of 6 patients undergoing unilateral lung volume-reduction surgery at our institution between October 1995 and December 2004, who were readmitted several months after discharge because of the occurrence of occult pneumothorax mimicking acute respiratory failure.

RESULTS

Occult pneumothorax occurred in 3.3% of the 182 patients treated with lung volume-reduction surgery at our institution. Patients were readmitted after a mean of 94 days (range, 20 to 700 days) from the discharge. Chest roentgenography was unable to detect the occurrence of pneumothorax, which was instead revealed by means of a computed tomographic scan in all patients. The interval between admission and correct diagnosis averaged 22.4 hours. The number of air collections ranged between two and four. Treatment entailed solely blind chest drainage placement in 2 patients and awake video-assisted thoracoscopic surgery in the others, including placement of chest tube under direct vision in 1 patient, repair of lung tears by means of cyanoacrylate glue in 2 and bovine pericardium patch plus cyanoacrylate glue apposition in 1 patient.

CONCLUSIONS

In conclusion, we believe that occult pneumothorax should be kept in mind as one of the possible late complications of lung volume-reduction surgery and should be suspected whenever sudden worsening of dyspnea is noticed even in the presence of an uneventful chest roentgenogram. Awake video-assisted thoracoscopic surgery management can represent an effective option in these instances.

Mechanical ventilatory support

This chapter reviews the most updated knowledge regarding mechanical ventilation, its' indications and its' features both diagnostic and therapeutic. Further, the various modes of mechanical ventilation are described. The reader will also gain insight into the pathophysiology of various disease processes and the mode of ventilation that may be the most helpful in their treatment. Weaning is also discussed as well as a relatively new type of ventilation, non-invasive.

Complications of mechanical ventilation. A bedside approach

Instead of cataloging complications reported to occur during mechanical ventilation, the authors have discussed the potential causes for several common scenarios in the management of ventilated patients. These include the new development of hypotension, acute respiratory distress (fighting the ventilator), repeated sounding of the ventilator's high-pressure alarm, hypoxemia, blood from the endotracheal tube, and the problem of diagnosing VAP. In the course of considering likely explanations for this group of circumstances for which the clinician is consulted or called to the bedside, virtually all reported ventilator-associated complications must be discussed. This new approach to an important aspect of ICU care may aid in clinical problem-solving and reduce the likelihood that a diagnosis will be missed or inappropriate measures taken in the absence of a systematic, pathophysiology-based approach.

High-inflation pressure and positive end-expiratory pressure. Injurious to the lung? No

Survival rates in ARDS with conventional ventilation using high oxygen fractions and low PEEP levels have been reported to be less than 10%. In three prospective evaluations of ARDS in the 1980s, mortality rates remained greater than 60%. Early studies using high-level PEEP therapy in severe ARDS by Douglas, Downs, Kirby, and Civetta showed improved survival rates with ranges between 60% and 80%. In 1979 Gallagher reviewed 59 patients with ARDS who were treated with PEEP greater than 15 cm H2O titrated to improve FRC by achieving an intrapulmonary shunt fraction of 15%. The overall survival was 65%, with only 5% of the patients dying secondary to respiratory failure. In the more recent study by Miller in trauma patients and later by DiRusso in a variety of surgical patients, the overall mortality rate for those patients receiving PEEP greater than 15 cm H2O was 20% to 30%. Of the 14 patients who died, only seven (10% of the total) succumbed to respiratory failure. The remaining patients died from the primary underlying disease with normal oxygenation or after significant weaning from high PEEP levels. By using a goal-oriented approach to the management of patients with severe ARDS, we have found that high-level PEEP therapy was effective in lowering the intrapulmonary shunt and improving the SaO2 at acceptable levels of inspired oxygen. All of these patients were ventilated with traditional high tidal volumes (10 to 15 mL/kg) and therefore exhibited high peak inspiratory airway pressures. This support method did not seem to cause lung injury or an excessive amount of barotrauma in these patients, but in fact, was associated with a lower mortality rate (30%) than reported in other studies of patients with lesser degrees of lung oxygenation dysfunction and extrapulmonary organ system dysfunction. Currently available information indicates that increases in mean airway pressure (induced with PEEP or other modes of ventilatory support to restore losses in FRC that occur during ARDS) and limiting exposure to toxic concentrations of oxygen minimize ventilator-induced secondary lung injury and maximize chances for survival. Arbitrary limitations of peak inspiratory or end-expiratory airway pressure or mandatory tidal volume in patients with severe ARDS seem to be unfounded. Failure to achieve adequate physiologic end-points in these patients may increase morbidity and mortality rates.

Doxapram reversal of respiratory failure in a patient refusing assisted ventilation

A 75-year-old man with severe chronic obstructive pulmonary disease and epistaxis experienced progressive respiratory failure after receiving an injection of meperidine and hydroxyzine in preparation for nasal packing. The patient and his family refused endotracheal intubation; despite aggressive medical care, he continued to deteriorate toward an expected fatal outcome. An i.v. infusion of doxapram hydrochloride at 2 mg/min rapidly reversed his downhill course and hypercarbic coma. This case illustrates the potential usefulness of doxapram in the emergency setting. The mechanism of action, indications, dosing methods, and potential side effects of this agent are discussed.

Portable chest radiographs identify mechanical ventilator-associated hyperinflation

OBJECTIVE

Portable chest radiographs (CRs) are obtained routinely in mechanically ventilated patients, but little is known about relationships between CR findings and ventilator parameters. It is unclear whether radiographically apparent hyperinflation correlates with tidal volume (VT), body weight (BW), VT/kg, or levels of peak airway pressure (PAP), positive end-expiratory pressure (PEEP), or pressure support (PS).

DESIGN

Prospective comparison of CR and ventilator parameters in 62 mechanically ventilated patients in surgical and medical intensive care units of a university hospital.

PATIENT SELECTION

All mechanically ventilated adults with portable CR on four separate dates.

METHODS

Chest radiographs were classified by subjective assessments as hyperinflated (H+) or nonhyperinflated (H-), independent of knowledge of patients or their mechanical ventilation. Chest radiographs were reclassified independently as H+, H-, or indeterminate by a radiologist using objective criteria. Ventilator parameters recorded at the time of the CR were obtained and compared.

RESULTS

Patients with CRs classified subjectively as H+ compared with patients with CRs classified as H- had a larger VT/kg (12.0 +/- 0.4 ml/kg [mean +/- SEM] vs 10.2 +/- 0.4; p = 0.004), lower BW (70.8 +/- 2.9 kg vs 81.5 +/- 3.8; p = 0.03), higher PEEP (6.5 +/- 0.5 cm H2O vs 5.0 +/- 0.4; p = 0.01), and higher PAP (38.2 +/- 2.1 cm H2O vs. 33.4 +/- 1.8; p = 0.06). Using objective CR classifications, patients with H+ CRs had a VT/kg of 12.6 +/- 0.4, larger than in the indeterminate (11.1 +/- 0.8) and H- (9.9 +/- 0.3) groups (p < 0.001). The BW differed among objectively classified groups (66.5 +/- 2.7 H+, 68.9 +/- 5.1 indeterminate, and 85.2 +/- 3.7 H-; p < 0.001), but other ventilator parameters did not correlate univariately with the degree of inflation on CR. Multivariate analysis showed that higher VT was predictive of H+ after adjusting for BW in subjective (p = 0.076) and objective (p = 0.017) classifications. PEEP (p = 0.004) and older age (p = 0.021) were also associated with H+ in multivariate analysis. Four of 25 (16 percent) patients with objectively H+ CRs developed barotrauma, while no patient with H- CR had this complication (p = 0.037).

CONCLUSIONS

In mechanically ventilated patients, hyperinflation seen on portable CR is associated with higher VT, VT/kg, and lower BW, and may help predict subsequent barotrauma.

Outcome of patients with systemic rheumatic disease admitted to medical intensive care units

The outcome of patients admitted to intensive care units is known to be influenced by such factors as age, previous health status, severity of disease, and diagnosis. To estimate the outcome of such patients with systemic rheumatic diseases and to determine if the severity of these diseases unfavourably influences the prognosis at the time of admission to a medical intensive care unit, the clinical courses of all patients with systemic rheumatic disease admitted to two medical intensive care units between January 1978 and December 1988 were studied retrospectively. Sixty nine patients with systemic lupus erythematosus (n = 16), necrotising vasculitis (n = 19), rheumatoid arthritis (n = 19), and other systemic rheumatic diseases (n = 15) were included. The mean (SD) age on admission into the medical intensive care unit was 53 (17) years and the mean simplified acute physiological score was 12 (5.5). The principal diagnoses on admission were infectious complications (29/69 patients) and acute exacerbation of the systemic rheumatic disease (19/69 patients). The death rate in the medical intensive care unit was 33% (23/69 patients) and was similar to that of a non-selected population with comparable simplified acute physiological score. The death rate in hospital was 42% (29/69 patients). Infection was the main cause of death in the medical intensive care unit (19/23 patients) and the infection was mainly acquired in the unit. Only the simplified acute physiological score on admission was a statistically significant prognostic factor: the simplified acute physiological score in patients who died was 15 (5.2) v 9.9 (4.7) for survivors. Long term outcome analysis showed that 83% (33/40 patients) of patients were still alive after admission to the medical intensive care unit with a follow up time between two months and nine years (mean 38 months). The death rate was relatively high and was mainly due to nosocomial infections. It was not different, however, from that of nonselected patients and the long term prognosis was highly favourable. This shows that the complications are often reversible, particularly infectious applications, and justifies admission to the medical intensive care unit of this group of patients.

Optimisation of respiratory function

OBJECTIVE

To apply pathophysiological principles in the management of patients with acute and chronic respiratory impairment.

CONCLUSIONS

Knowledge of the pathophysiology of respiratory disorders is a key element in treatment of patients with impending or established respiratory failure. Therapies to improve and support abnormal gas exchange will minimise the complications of hypoxia and interventions to optimise ventilation and work of breathing may obviate the need for mechanical ventilation.

Tracheal stenosis and failure to wean from mechanical ventilation due to herpetic tracheitis

A 64-year-old man with chronic obstructive pulmonary disease presented with pneumococcal pneumonia that progressed to respiratory failure within one week, requiring mechanical ventilation. Despite a low minute ventilation and clear chest roentgenogram, multiple weaning attempts failed. Bronchoscopy revealed significant narrowing of the distal trachea with erythema, edema, and ulceration of the mucosa. Cytology of tracheal washings was consistent with herpes simplex virus, and the patient was successfully extubated following treatment with intravenous acyclovir. Bronchoscopy following acyclovir therapy demonstrated resolution of the inflammation and narrowing. Herpetic tracheitis is a rarely recognized reversible cause of tracheal stenosis, especially in a nonimmunocompromised patient. It should be suspected in patients without an obvious cause of failure to wean from mechanical ventilation, and can be successfully treated with acyclovir.