Association between diaphragmatic dysfunction after adult cardiovascular surgery and prognosis of mechanical ventilation: a retrospective cohort study.

BACKGROUND: Diaphragmatic dysfunction often occurs after adult cardiovascular surgery. The prognostic effect of diaphragmatic dysfunction on ventilatory management in patients after cardiovascular surgery is unknown. This study aimed to investigate the association between diaphragmatic dysfunction and prognosis of ventilatory management in adult postoperative cardiovascular surgery patients. METHODS: This study was a single-center retrospective cohort study conducted at a tertiary care university hospital. This study included adult patients admitted to the intensive care unit under tracheal intubation after cardiovascular surgery. Spontaneous breathing trial was performed, and bilateral diaphragmatic motion was assessed using ultrasonography; diaphragmatic dysfunction was classified as normal, incomplete dysfunction, or complete dysfunction. The primary outcome was weaning off in mechanical ventilation. The duration of mechanical ventilation was defined as duration from the date of ICU admission to the date of weaning off in mechanical ventilation. The secondary outcomes were reintubation, death from all causes, improvement of diaphragm position assessed by chest radiographs. The subdistribution hazard ratio or hazard ratio (HR) with 95% confidence of intervals (CIs) were estimated by Fine-Gray models or Cox proportional hazard models adjusted for potential confounders. RESULTS: Of 153 patients analyzed, 49 patients (32.0%) had diaphragmatic dysfunction. Diaphragmatic dysfunction consisted of incomplete dysfunction in 38 patients and complete dysfunction in 11 patients. Diaphragmatic dysfunction groups had longer duration of mechanical ventilation (68 h [interquartile range (IQR) 39-114] vs 23 h [15-67], adjusted subdistribution HR 0.63, 95% CIs 0.43-0.92). There was a higher rate of reintubation (12.2% vs 2.9%, univariate logistic regression analysis p = 0.034, unadjusted odds ratio = 4.70, 95% CIs 1.12-19.65), and a tendency to have higher death from all causes in the diaphragmatic dysfunction group during follow-up period (maximum 6.5 years) (18.4% vs 9.6%, adjusted HR 1.64, 95% CIs 0.59-4.53). The time to improvement of diaphragm position on chest radiograph was significantly longer in the diaphragmatic dysfunction group (14 days [IQR 6-29] vs 5 days [IQR 2-10], adjusted subdistribution HR 0.54, 95% CIs 0.38-0.77). CONCLUSIONS: Diaphragmatic dysfunction after adult cardiovascular surgery was significantly associated with longer duration of mechanical ventilation and higher reintubation.

Simulation of pressure support for spontaneous breathing trials in neonates.

BACKGROUND: Endotracheal tubes used for neonates are not as resistant to breathing as originally anticipated; therefore, spontaneous breathing trials (SBTs) with continuous positive airway pressure (CPAP), without pressure support (PS), are recommended. However, PS extubation criteria have predetermined pressure values for each endotracheal tube diameter (PS 10 cmH2O with 3.0- and 3.5-mm tubes or PS 8 cmH2O with 4.0-mm tubes). This study aimed to assess the validity of these SBT criteria for neonates, using an artificial lung simulator, ASL 5000™ lung simulator, and a SERVO-i Universal™ ventilator (minute volume, 240-360 mL/kg/min; tidal volume, 30 mL; respiratory rate, 24-36/min; lung compliance, 0.5 mL/cmH2O/kg; resistance, 40 cmH2O/L/s) in an intensive care unit. We simulated a spontaneous breathing test in a 3-kg neonate after cardiac surgery with 3.0-3.5-mm endotracheal tubes. We measured the work of breathing (WOB), trigger work, and parameters of pressure support ventilation (PSV), T-piece breathing, or ASL 5000™ alone. RESULTS: WOB displayed respiratory rate dependency under intubation. PS compensating tube resistance fluctuated with respiratory rate. At a respiratory rate of 24/min, the endotracheal tube did not greatly influence WOB under PSV and the regression line of WOB converged with the WOB of ASL 5000™ alone under PS 1 cmH2O; however, at 36/min, endotracheal tube was resistant to breathing under PSV because trigger work increased exponentially with PS ≤ 9 cmH2O. The regression line of WOB under PSV converged with the WOB of T-piece breathing under PS 1 cmH2O. Furthermore, PS compensating endotracheal tube resistance was 6 cmH2O. The WOB of ASL 5000™ alone approached that of respiratory distress syndrome (RDS); however, the pressure of patient effort was normal physiological range at PS 10 cmH2O. PS equalizing WOB under PSV with that after extubation depended on the respiratory rate and upper airway resistance. If WOB after extubation equaled that of T-piece breathing, the PS was 0 cmH2O regardless of the respiratory rates. If WOB after extubation approximated  to that of ASL 5000™ alone, the PS depended on the respiratory rate. CONCLUSION: SBT strategies should be selected per neonatal respiratory rates and upper airway resistance.

Oxygen management in mechanically ventilated patients: A multicenter prospective observational study.

PURPOSE: To observe arterial oxygen in relation to fraction of inspired oxygen (FIO2) during mechanical ventilation (MV). MATERIALS AND METHODS: In this multicenter prospective observational study, we included adult patients required MV for >48h during the period from March to May 2015. We obtained FIO2, PaO2 and SaO2 from commencement of MV until the 7th day of MV in the ICU. RESULTS: We included 454 patients from 28 ICUs in this study. The median APACHE II score was 22. Median values of FIO2, PaO2 and SaO2 were 0.40, 96mmHg and 98%. After day two, patients spent most of their time with a FIO2 between 0.3 and 0.49 with median PaO2 of approximately 90mmHg and SaO2 of 97%. PaO2 was ≥100mmHg during 47.2% of the study period and was ≥130mmHg during 18.4% of the study period. FIO2 was more likely decreased when PaO2 was ≥130mmHg or SaO2 was ≥99% with a FIO2 of 0.5 or greater. When FIO2 was <0.5, however, FIO2 was less likely decreased regardless of the value of PaO2 and SaO2. CONCLUSIONS: In our multicenter prospective study, we found that hyperoxemia was common and that hyperoxemia was not corrected.

[Perioperative Management of Restrictive Pulmonary Disease].

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.

[Clinical application of the tidal flow-volume curve--a computer simulation].

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.

Clinical trial of a method for confirming the effects of spinal anesthesia in patients with spinal cord injury.

In this case series study, we prospectively examined whether it might be possible to check the effect of spinal anesthesia (SA), based on the disappearance of lower extremity reflexes and spasticity, in patients with spinal cord injury (SCI), in whom the effect cannot be confirmed by the pinprick test or by using the Bromage scale. In 40 patients with chronic, clinically complete cervical SCI who were scheduled to receive SA, pre-anesthetic examination revealed that the Babinski sign, patellar tendon reflex, and spasticity (assessed using the Ashworth scale) were all positive in 31 patients, while two of these three pre-anesthetic assessment parameters were positive in eight patients. The effect of SA in these 39 patients (97.5 %) was confirmed by demonstrating the absence of both the Babinski sign and patellar tendon reflex and loss of spasticity after SA. Our results suggested that the effect of SA can be confirmed by the disappearance of the Babinski sign and patellar tendon reflex and loss of spasticity in most patients with complete cervical SCI, although determination of the level of the block is difficult. In conclusion, loss of the Babinski sign, patellar tendon reflex, and spasticity might be useful for checking the effect of SA in cervical SCI patients.

[Case of laryngopharyngeal edema after a spinal tumor resection in prone position with extensive neck flexion].

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.

[The effect of dexmedetomidine in a child with intractable supraventricular tachyarrythmia after total cavopulmonary connection].

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.

Tracheal intubation using Airway Scope in two patients with difficult airway during cardiopulmonary resuscitation.

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.

Central airway occlusion underestimates intrinsic positive end-expiratory pressure: a numerical and physical simulation.

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.

[Analysis by computer simulation of double breathing during pressure support ventilation].

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.

Ultrasonography and lung mechanics can diagnose diaphragmatic paralysis quickly.

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.