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Intrinsic positive end-expiratory pressure (PEEP) occurs when airway outflow is higher than zero at end-expiration. Differences in the time constant among alveolar units may result in an uneven distribution of intrinsic PEEP. The authors conducted a computer simulation of a 2-compartment respiratory system and calculated intrinsic PEEP for each alveolar unit and confirmed it with a test-lung experiment. Ventilator settings, including respiratory rate, inspiratory time, pause time, and external PEEP, were tested at various values in combination with various airway resistance and alveolar compliance values. The simulation was performed by calculating the flow, pressure, and volume every millisecond. The data demonstrated that the larger the difference of time constant between 2 respiratory units, the greater the difference in intrinsic PEEP between the units. A higher respiratory frequency and a larger percentage of inspiratory time resulted in an increase in the intrinsic PEEP at the central airway, as well as a wide difference in the intrinsic PEEP between airway units. These phenomena were confirmed by a 2-compartment test-lung study. The authors demonstrated and verified an uneven distribution of intrinsic PEEP in 2 different experiments, which raised a warning that some respiratory units might have much higher intrinsic PEEP than the intrinsic PEEP measured clinically. [ABSTRACT FROM AUTHOR]

The Airway Scope AWS-S100® (AWS, Pentax, Tokyo), a rigid video laryngoscope with integrated tube guidance that has recently become commercially available, helped the authors to establish airways in two patients with in-hospital cardiopulmonary arrest, after failed attempts to intubate the patients using the Macintosh laryngoscope (that only commanded the Cormack–Lehane grade 4 glottic views), the laryngeal mask airway, and even surgical cricothyroidotomy for the second case. This showed the utility of the AWS in the management of difficult airway cases even in emergency settings. [ABSTRACT FROM AUTHOR]

Restrictive ventilatory dysfunction is defined as a reduced vital capacity compared with the predicted value. The causes of such respiratory dysfunction include reduced muscle power, increased lung elastic- ity, and increased chest wall elasticity. During intraoperative mechanical ventilation, the patient's tidal volume is reduced to prevent increases in airway pressure. Due to the associated reduction in the ventilatory time constant, the patient's respiratory frequency can be easily increased to compensate for the reduction in their tidal volume, resulting in the maintenance of an adequate arterial partial pressure of carbon dioxide. As the resultant rise in intrathoracic pressure compresses the pulmonary vessels, pulmonary vascular resistance increases, and this can induce right ventricle failure and/or left ventricle collapse. Increased intrathoracic pressure also leads to reductions in venous return and cardiac output, especially in patients with increased chest wall elasticity. As fatigue and weakness of the ventilatory muscles can cause respiratory failure in such patients ; muscle relaxant should be reversed ; motor nerve blockade must be avoided; and pain management must be con- ducted carefully after surgery.

Background: Since the tidal flow-volume (V-V) curve obtained during mechanical ventilation is difficult to interpret, there have been few reports on how to interpret it., Methods: The tidal V-V curve during mechanical ventilation was analyzed using a computer simulation. Ventilatory modes, the time constant of a patient's respiratory system (TC), spontaneous breathing during mechanical ventilation, airway obstructions, and circuit leakage were simulated., Results: The inspiratory shape depended on ventilatory modes and was affected by TC only in pressure-regulated breathing. The expiratory shape was not dependent on ventilatory modes and was influenced by TC. Spontaneous breathing synchronized with the mandatory ventilatory phase increased the flow rate. Characteristic double expiratory flow pattern was observed in spontaneous expiration during the inspiratory phase of the ventilator. A dip in the expiratory tidal V-V curve was observed with a peripheral airway obstruction model. A central airway obstruction attenuated the slope of the expiratory phase. In circuit leakage, the tidal V-V curve did not return to the origin at the end of the expiration., Conclusions: New findings on the tidal V-V curve were observed and this systematic analysis will be helpful in clinical respiratory care.

A 63-year-old woman developed laryngopharyngeal edema after a cervical spinal tumor resection in prone position. The tracheal tube was removed after 11 hours of general anesthesia and nasal airway was inserted because stridor was audible. Blisters were found on the skin of the anterior neck of the patient. Examinations at 3 h after the extubation suggested upper airway stenosis including stridor, increased work of breathing, oxygenation impairment, and hypercapnia. The trachea of the patient was intubated and the examination of the upper airway by inserting a fiberoptic bronchoscope through the patient's mouth revealed laryngopharyngeal edema. It was considered that the disturbance of venous and/or lymphatic flow of anterior neck due to extensive neck anteflexion during the surgery in prone position had induced the laryngopharyngeal edema; however, we could not verify the cause of the edema. The edema persisted for weeks. We conclude that we should avoid extensive neck anteflexion during surgery in prone position and it is recommended to observe the upper airway for a few hours after extubation because there could be airway obstruction due to delayed and/ or progressive laryngopharyngeal edema.

We report a case of a 3-year-old boy who had undergone total cavopulmonary connection for repair of corrected transposition of the great arteries (cTGA), and developed intractable supraventricular tachyarrhythmia. The patient was in cardiogenic shock and did not respond to antiarrhythmic drugs and cardioversion, and we used extracorporeal life support (ECLS) to maintain hemodynamics. We used dexmedetomidine to block sympathetic activity. After administration of dexmedetomidine, tachycardia was improved, and the sinus rhythm returned. No recurrence was observed. In conclusion, dexmedetomidine might be useful for intractable supraventricular tachyarrhythmia after pediatric congenital heart surgery.

Background: Pressure support ventilation (PSV) usually provides good patient-ventilator synchrony, but asynchrony is sometimes encountered. Double breathing is one form of asynchrony in which the ventilator assists two or more times during a single inspiration of the patient., Methods: Double breathing was analyzed using a computer simulation., Results: In an obstructive lung model, inspiratory support was terminated just after the beginning of the inspiration lasting until inspiratory effort triggering the ventilator again. One of the causes of this premature termination was that the compressed and consumed volume in the circuit created a high peak inspiratory flow setting. The other cause was oscillation of the airway pressure. Reducing the circuit volume, slowing the inspiratory rise time, or decreasing the termination criteria could prevent this phenomenon. In a restrictive lung model, the time-constant of the lung was so short that the inspiratory flow finished early and double breathing occurred. It was difficult to prevent this phenomenon by adjusting the circuit assembly or respiratory parameters., Conclusions: Double breathing during PSV was considered to be closely associated with obstructive or restrictive lung. If the problem arises and cannot be resolved by adjusting ventilatory parameters, the ventilatory mode must be changed.

Diaphragmatic paralysis after cardiovascular surgery requires early diagnosis prior to extubation. The effectiveness of ultrasonography and a lung mechanics assessment was evaluated. Paralysis of the diaphragm was diagnosed when the diaphragm failed to move or moved in a cephalad direction during inspiration. It was diagnosed in 3 of 40 patients (7.5%) who underwent cardiovascular surgery from 1998 to 1999. Patients were extubated when all parameters met the extubation criteria, irrespective of the presence or absence of diaphragmatic paralysis. One patient required prolonged assisted ventilation and died from mediastinitis on the 35th postoperative day. The other 2 patients required assisted ventilation for an additional 1-3 days. Ultrasonography and a lung mechanics assessment are effective tools for the early diagnosis of diaphragmatic paralysis and assessment of respiratory function after cardiovascular surgery.