Inspiratory pressure-volume curves at different positive end-expiratory pressure levels in patients with ALI/ARDS.

BACKGROUND: In lung protective strategy, positive end-expiratory pressure (PEEP) slightly higher than the Pflex (the airway pressure corresponding to the lower inflection point (LIP) on the inspiratory pressure-volume (P-V) curve measured with ZEEP) is generally recommended. However, this method to determine optimal PEEP lacks a theoretical background and there is no clinical report that investigated how the P-V relationship would be with such PEEP. Therefore, we measured inspiratory P-V curves at different PEEP levels to increase our knowledge about the inspiratory P-V curve with PEEP. METHODS: In eight consecutive patients with ALI/ARDS, inspiratory P-V curves were repeatedly measured at different PEEP levels by low flow inflation technique and LIP was assessed in all inspiratory P-V curves. Afterwards, the minimum PEEP level at which LIP was not identifiable (PEEP(LIP)(-)) was determined and the relationship between Pflex and PEEP(LIP)(-) was investigated. RESULTS: Pflex and PEEP(LIP)(-) could be determined in all patients. Pflex was 9.4+/-2.0 cmH2O (range: 7 to 12 cmH2O) and PEEP(LIP)(-) was 7.9+/-1.6 cmH2O (range: 5 to 10 cmH2O) (mean+/-SD, P=0.0877). PEEP(LIP)(-) was lower than the Pflex in five patients, and significantly lower than the Pflex + 2 cmH2O (P=0.0024). CONCLUSION: From the analysis of inspiratory P-V curves at different PEEP levels, PEEP 2 cmH2O higher than the Pflex may not be necessary to prevent cyclic collapse and reopening of alveoli, at least in some ALI/ARDS patients. Further studies are needed to confirm this preliminary result.

The effect of breath termination criterion on breathing patterns and the work of breathing during pressure support ventilation.

UNLABELLED: With pressure support ventilation (PSV), each PSV breath is flow-cycled, and the breath termination criterion (TC) is usually nonadjustable. When TC does not match the interaction between the patient's inspiratory-expiratory efforts to the opening and closing of the inspiratory and expiratory valves, patient-ventilator asynchrony may occur, and the work of breathing (WOB) may increase. Therefore, we studied the effect of TC on breathing patterns and WOB during PSV in eight patients with acute respiratory distress syndrome or acute lung injury. We studied five levels of TC during PSV-1%, 5%, 20%, 35%, and 45% of the peak inspiratory flow. With increasing levels of TC, the tidal volume decreased and respiratory frequency increased, along with a decrease in duty cycle. WOB markedly increased with increasing levels of TC from 0.31 +/- 0.12 J/L with TC 1% to 0.51 +/- 0.11 J/L with TC 45%. Premature termination with double breathing occurred in one patient with TC 35% and four patients with TC 45%. Delayed termination with a duty cycle of >0.5 occurred in two patients with TC 1%. In conclusion, the proper adjustment of TC improves patient-ventilator synchrony and decreases WOB during PSV. IMPLICATIONS: Although termination criterion (TC) is usually nonadjustable, it influences the effectiveness of pressure support ventilation for mechanical ventilation. The proper adjustment of TC is crucial to improve patient-ventilator synchrony and decrease work of breathing. TC 5% of the peak inspiratory flow may be the optimal value for patients with acute respiratory distress syndrome or acute lung injury.

[A case of hypothyroidism found by delayed awakening after the operation].

We report a case of hypothyroidism found by delayed awakening after surgery. A 55-year-old male patient had been suffering from elevated creatine phosphokinase (CPK) and cartinoembryonic antigen (CEA) of unknown origin before the operation. Laparoscopic cholecystectomy was performed under general anesthesia combined with epidural block. Hypotension, low arterial oxygen saturation, hypothermia and metabolic acidosis developed and continued during the operation. Awakening was delayed for about two hours postoperatively. Specific examination resulted in a definitive diagnosis of hypothyoidism. We should pay careful attention to any patient with elevated CPK and CEA of unknown origin before surgery, continuous hypotension, respiratory and circulatory failure and metabolic disorder during surgery, and delayed awakening after surgery that may be the result of hypothyroidism.

[Unexpected difficult intubation caused by a laryngeal web].

We report a case of unexpected difficult intubation in an adult caused by a laryngeal web. A 43-year-old woman with uterine myoma was scheduled for abdominal hysterectomy. After induction of anesthesia, the vocal cords were seen clearly under laryngoscopy. Although intubation was attempted several times, a 6.5 mm internal diameter tracheal tube could not be passed below the level of the vocal cords because of resistance, and we used a laryngeal mask during anesthesia. Next morning after the operation, she developed dyspnea. Bronchoscopy revealed a very narrow airway below the level of vocal cords caused by a laryngeal web. Tracheostomy was performed. Two weeks later, tracheostomy was closed without any sequela.

[Recurrent nerve palsy after endotracheal intubation].

We encountered left recurrent nerve palsy in four patients who had undergone surgery unrelated to the course of the vagus nerve or recurrent nerve, during which they had received endotracheal anesthesia. They were intubated without difficulty and underwent surgery without trouble, but postoperatively they all complained of hoarseness. We used a disposable ENTRASOFT endotracheal tube with high volume, low-pressure cuff in three patients and a disposable PORTEX endotracheal tube with low volume, standard cuff in one patient. In three patients recurrent nerve palsy healed completely within two months after the operation, and one patient was recovering from the palsy on the twentieth day after the operation. We believe that the most plausible explanation of recurrent nerve palsy is the excessive pressure from the inflated endotracheal tube cuff on the intralaryngeal course of the anterior branch of the recurrent nerve. Monitoring cuff pressure is most important to prevent recurrent nerve palsy after endotracheal intubation.

[Perioperative management of two patients with severe dilated cardiomyopathy].

We report perioperative management of two patients with severe dilated cardiomyopathy belonging to the group IV of classification of Inoh (ejection fraction 18% and 30%). In the preoperative period, they developed severe congestive heart failure. Dopamine, dobutamine, and furosemide were given to improve cardiac function. Anesthesia was performed safely under continuous cardiac output and mixed venous saturation monitoring. We consider that preoperative evaluation and management are very important to prevent intraoperative and postoperative complications in patients with severe dilated cardiomyopathy.

[A case of severe bronchospasm under epidural anesthesia with fentanyl].

A case of severe bronchospasm under epidural anesthesia with fentanyl was described. The etiology of the bronchospasm may not have been related to sympathetic nervous blockade, histamine release, or anaphylaxis. In an asthmatic patient, it should be noted that epidural anesthesia with fentanyl could develop bronchospasm.

Pressure support ventilation augments spontaneous breathing with improved thoracoabdominal synchrony in neonates with congenital heart disease.

UNLABELLED: In neonates, during spontaneous breathing with demand-type continuous positive airway pressure (CPAP), high airway resistance caused by small endotracheal tubes, time delay for triggering, and rapid respiratory frequency may result in patient-ventilator asynchrony. Such asynchrony may alter normal breathing patterns and thoracoabdominal synchrony. We, therefore, studied whether pressure support ventilation (PSV) could augment spontaneous breathing and improve synchrony between the rib cage (RC) and the abdominal (AB) motions in nine postoperative neonates with congenital heart disease. Three successive levels of PSV (0, 5, and 10 cm H2O) were used randomly. With increasing levels of PSV, the tidal volume (VT) increased and the respiratory frequency decreased, associated with an increase in minute ventilation. To assess thoracoabdominal synchrony, maximum compartment amplitude (MCA)/VT (MCA = AB + RC) and the phase delay of the RC-to-AB motion during inspiration (the ratio of the time delay to the inspiratory time) were measured using respiratory inductive plethysmography. When the motions of the RC and AB were out of phase, MCA/VT exceeded 1.0. MCA/VT decreased significantly from 1.3 +/- 0.3 without PSV to 1.0 +/- 0.0 with PSV of 10 cm H2O. The phase delay and paradoxical motion of the RC observed in seven of the nine cases without PSV also disappeared with PSV of 10 cm H2O. In conclusion, PSV can effectively augment spontaneous breathing with better thoracoabdominal synchrony in neonates. IMPLICATIONS: Assisting spontaneous ventilation in a neonate is often difficult. Because pressure support ventilation facilitates coordination between the patient and ventilator in adults and children, we thought it might be effective in neonates. Our study supports this conclusion.

[A severe case of reexpansion pulmonary edema in an asthmatic patient].

A 60-year-old man with poorly controlled bronchial asthma was proposed for an emergency appendectomy. His preoperative chest X-P revealed that his left lung was completely collapsed with pneumothorax, but its onset was unclear. Following the left thoracocentesis, appendectomy was performed under general anesthesia (oxygen-halothane). About one hour after the thoracocentesis, pinkish foamy tracheal secretion was massively drained and its protein concentration was 3.8 g.dl-1.PaCO2 was 95 mmHg and PaO2 was 69 mmHg (FIO2 1.0). His chest X-P showed signs of pulmonary edema in his left lung and infiltrating shadow was observed in his right lung. IMV with PEEP, aminophylline and prednisolone improved his respiratory status and on the 11 th day he was weaned from the respirator. In a case of pneumothorax with unclear duration like ours, it is necessary to consider the possibility of the reexpansion pulmonary edema.

The effectiveness of pressure support ventilation for mechanical ventilatory support in children.

BACKGROUND: The rapid respiratory frequency of children may lead to patient-ventilator asynchrony and increase the work of breathing during mechanical ventilation, and the use of a small endotracheal tube and a demand valve can further increase this work of breathing. Although pressure support ventilation (PSV) is well known to reduce the work of breathing in adults, there are no reports regarding clinical studies of PSV in children. Therefore, the effect of PSV on breathing patterns and the work of breathing in children was studied. METHODS: Six children (3-5 yr of age) were studied in the immediate postoperative period. Three levels of PSV, 0, 5, and 10 cmH2O, were employed. Airway pressure, flow, tidal volume, minute ventilation, and respiratory frequency were measured. To assess the work of breathing, the negative deflection of esophageal pressure (delta Pes) caused by inspiratory effort was measured. The inspiratory work of breathing was also estimated directly by measuring the esophageal pressure-volume loop using the Campbell technique. RESULTS: Although minute ventilation did not change with PSV, tidal volume increased and respiratory frequency decreased with increasing levels of PSV. The delta Pes decreased markedly from 8.9 cmH2O with PSV of 0 cmH2O to 5.7 cmH2O with PSV of 5 cmH2O and 2.7 cmH2O with PSV of 10 cmH2O. The mechanical work of breathing also decreased from 0.743 Joules/l with PSV of 0 cmH2O to 0.463 Joules/l with PSV of 5 cmH2O and 0.196 Joules/l with PSV of 10 cmH2O. CONCLUSIONS: It was concluded that PSV can effectively augment spontaneous breathing and reduce the work of breathing in children.

[Retrospective analysis of 15 cases with severe pulmonary embolism].

We evaluated retrospectively the clinical indicators for the treatment of 15 patients with severe pulmonary embolism. All patients had moderate or severe pulmonary hypertension with deteriorated oxygenation. Thrombolytic agents and catecholamines were administered and mechanical ventilation was performed so as to treat right heart failure and improve oxygenation. In 14 patients, the pulmonary artery pressure decreased gradually and PaO2 increased in response to these therapies. The 14 patients were discharged from ICU without any symptoms. One patient died of cerebral hemorrhage due to the side effects of tissue plasminogen activator. We conclude that the pulmonary artery pressure and PaO2 are useful indicators for the treatment of the early phase of severe pulmonary embolism. Moreover, timely use of cetecholamine is very important for the maintenance of pulmonary circulation and acceleration of thrombolysis.

The effect of pressure support ventilation on auto-PEEP in a patient with asthma.

We report the effect of pressure support ventilation (PSV) on auto-PEEP in a patient with asthma. The patient showed a high level of auto-PEEP during spontaneous breathing through a T-piece. PSV effectively decreased auto-PEEP and inspiratory muscle effort with increasing levels of PSV.

Effectiveness of pressure support ventilation for mechanical ventilatory support in patients with status asthmaticus.

We compared the effects of pressure support ventilation (PSV) with those of assist control ventilation (ACV) on breathing patterns and blood gas exchange in six patients with status asthmaticus. Both PSV and ACV delivered adequate minute ventilation (PSV: 7.5 +/- 1.4 l/min/m2, ACV: 7.3 +/- 1.3 l/min/m2) to correct respiratory acidosis (pH = 7.33 +/- 0.12 during both PSV and ACV) and prevent hypoxia. Peak airway pressure during PSV was significantly lower with the same tidal volume than that during ACV (PSV: 30 +/- 10 cmH2O (2.9 +/- 1.0 kPa), ACV: 50 +/- 13 cmH2O (4.9 +/- 1.3 kPa)). The lower airway pressure during PSV was due to persistent inspiratory muscle activity. The oxygen cost of breathing estimated by oxygen consumption was equivalent in both modes. We conclude that PSV is effective in supplying tidal volumes adequate to improve hypercarbia at markedly lower airway pressures than ACV.

[Is airway occlusion pressure useful to predict successful weaning from mechanical ventilation in patients with acute respiratory failure?].

The purpose of this study was to evaluate whether airway occlusion pressure (P0.1) would be a useful predictor for successful weaning in mechanically ventilated patients with acute respiratory failure. We studied 23 marginal weaning candidates. Fourteen patients were able to be weaned from the ventilator, and 9 patients were not able to be weaned. P0.1 and other respiratory parameters were measured just prior to weaning and at the end of weaning or at the time of discontinuation of weaning. The mean value of P0.1 in the failed group was higher than that in the successful group both before and after weaning periods. However, P0.1 varied widely among patients and did not separate the failure group from the success group because of overlap between the two. There were significant differences between the two groups of the conventional weaning parameters, such as respiratory rate, minute ventilation, PaO2, and oxygen equivalent. We conclude that P0.1 is helpful to predict successful weaning. However, it can not be used as a single parameter for weaning because of the wide variations of absolute values among patients with acute respiratory failure.

Efficacy of flow-by during continuous positive airway pressure ventilation.

We investigated clinically the differences in respiratory work of patients imposed by three modes of one ventilator: the flow-by system, the demand valve system, and the pressure support system. Inspiratory work using flow-by and pressure support systems was reduced sufficiently when compared to the demand valve system. Moreover, fluctuation of the airway pressure was minimal with the flow-by mode. These results suggest that the flow-by mode is beneficial to patients breathing spontaneously with continuous positive airway pressure.