[Minute of the 235th Meeting of the Thoracic Surgery Section, Surgical Society of Moscow and the Moscow region (December 10, 2002)].
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Brain Injuries↗
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Ventilator waveforms and the physiology of pressure support ventilation.
Pressure support ventilation (PSV) is a commonly used mode. It is patient-triggered, pressure-limited, and (normally) flow-cycled. Triggering difficulty occurring during PSV is usually due to intrinsic positive end-expiratory pressure. The airway pressure generated at the initiation of inhalation is determined by the pressure support setting and the pressure rise time (pressurization rate) settings on the ventilator. The rise-time setting is clinician-adjustable on many current-generation ventilators. Flow delivery during PSV is determined by the pressure support setting, the pressure generated by the respiratory muscles, and respiratory system mechanics. The delivered tidal volume is determined by the area under the flow-time curve. Patient-ventilator dyssynchrony may occur during PSV if the flow at which the ventilator cycles to exhalation does not coincide with the termination of neural inspiration. The newer generation ventilators offer clinician-adjustable flow-termination during PSV. Ventilator waveforms may be useful to appropriately adjust the ventilator during PSV.
Adult↗
The role of ventilator graphics when setting dual-control modes.
Dual-control ventilation modes were introduced with the goal of combining the advantages of volume-control ventilation (constant minute ventilation) and pressure-control ventilation (rapid, variable flow). Dual-control ventilation modes have gained popularity despite little evidence to support routine use. The individual operation and response of the dual-control modes must be understood by the clinician to allow safe and effective use. Graphic displays of pressure, volume, and flow can aid the clinician in detecting inappropriate use of dual-control modes and adjusting settings accordingly. Inspecting the waveforms will lead clinicians to the realization that dual-control does not guarantee a set tidal volume and that variability in delivered tidal volume is greater with dual-control than with pressure control. These realizations have important implications for low-tidal volume strategies.
Data Display↗
Using ventilator graphics to identify patient-ventilator asynchrony.
Patient-ventilator interaction can be described as the relationship between 2 respiratory pumps: (1) the patient's pulmonary system, which is controlled by the neuromuscular system and influenced by the mechanical characteristics of the lungs and thorax, and (2) the ventilator, which is controlled by the ventilator settings and the function of the flow valve. When the 2 pumps function in synchrony, every phase of the breath is perfectly matched. Anything that upsets the harmony between the 2 pumps results in asynchrony and causes patient discomfort and unnecessarily increases work of breathing. This article discusses asynchrony relative to the 4 phases of a breath and illustrates how asynchrony can be identified with the 3 standard ventilator waveforms: pressure, flow, and volume. The 4 phases of a breath are: (1) The trigger mechanism (ie, initiation of the inspiration), which is influenced by the trigger-sensitivity setting, patient effort, and valve responsiveness. (2) The inspiratory-flow phase. During both volume-controlled and pressure-controlled ventilation the patient's flow demand should be carefully evaluated, using the pressure and flow waveforms. (3) Breath termination (ie, the end of the inspiration). Ideally, the ventilator terminates inspiratory flow in synchrony with the patient's neural timing, but frequently the ventilator terminates inspiration either early or late, relative to the patient's neural timing. During volume-controlled ventilation we can adjust variables that affect inspiratory time (eg, peak flow, tidal volume). During pressure-controlled or pressure-support ventilation we can adjust variables that affect when the inspiration terminates (eg, inspiratory time, expiratory sensitivity). (4) Expiratory phase. Patients with obstructive lung disease are particularly prone to developing intrinsic positive end-expiratory pressure (auto-PEEP) and therefore have difficulty triggering the ventilator. Bedside evaluation for the presence of auto-PEEP should be routinely performed and corrective adjustments made when appropriate.
Data Display↗
Using ventilator and cardiovascular graphics in the patient who is hemodynamically unstable.
The interaction of a mechanical ventilator and the human cardiovascular system is complex. One of the most important effects of positive-pressure ventilation (PPV) is that it can decrease venous return. PPV also alters right- and left-ventricular ejection. Increased lung volume increases right-ventricular size by increasing pulmonary vascular resistance, causing intraventricular cardiac-septum shift, and decreasing left-ventricular filling. Increased intrathoracic pressure reduces afterload on the LV and increases ejection of blood from the LV. Understanding and managing these complex and often opposing interactions in critically ill patients is facilitated by analysis of hemodynamic and ventilator waveforms at the bedside. The relationship of PPV to changes in the arterial pressure waveform gives important information regarding appropriate fluid and vasopressor treatment. This article focuses on effects of respiratory pressures on hemodynamics and considers how cardiac pressures can be transmitted to the airway and cause ventilator malfunction.
Blood Pressure↗
Applied respiratory physiology: use of ventilator waveforms and mechanics in the management of critically ill patients.
Graphical waveforms have become ubiquitous in clinical care. Using and understanding pictures and symbols is a daily activity. Humans are neurologically equipped to understand symbolic information and have done so for millennia. Cave drawings are examples of using images to convey information. The same approach used in understanding "art" is needed to use ventilator waveforms effectively. Didactic study, frequent viewing, and understanding of the background of the artist (artistic context) are needed to fully appreciate art. Using waveforms to care for patients requires understanding of the clinical context under which they are obtained, factors that affect their creation, and artifacts that interfere with interpretation. This article summarizes the presentation and discussions at this Journal Conference on ventilator waveforms in relation to lung and chest wall compliance, resistance, carbon dioxide kinetics, hemodynamics, specific modes of ventilation, specific lung diseases, and ventilator-weaning.
Airway Resistance↗
[Anesthesia for scoliosis surgery: preoperative assessment and risk screening of patients undergoing surgery to correct spinal deformity].
Spinal column deformity is associated with potentially serious alterations of respiratory and cardiac function. Such alterations, in association with the underlying disease that caused the deformity--such as neuromuscular disease--are risk factors that affect the prognosis for scoliosis patients undergoing anesthesia and surgery. It is important for the anesthesiologist to carry out a detailed preoperative assessment to identify patients at risk with the aim of decreasing morbidity and mortality related to surgical correction of deformities. Of paramount importance is awareness of the risk of injury to the spinal cord that will affect function. Other issues are how to manage the patient in anomalous positions, the risk associated with hypothermia secondary to exposure of a large surgical field for a long period, and bleeding, which can sometimes exceed the patient's total volume. In the case of scoliosis surgery, all those situations may converge, obliging us to provide careful intraoperative monitoring, particularly of spinal function; to choose the appropriate anesthetic technique; and to maintain vigilance during the early postoperative period to foresee possible complications. Because scoliosis surgery is multidisciplinary, several teams must work together to assure success.
Anesthesia↗
[Surgical treatment of obstructive sleep apnea hypopnea syndrome after velopharyngeal ring ligation procedure].
PURPOSE: To evaluate the effect of removal of ligation thread combined adenoidectomy in the treatment of obstructive sleep apnea hypopnea syndrome (OSAHS) after velopharyngeal ring ligation procedure (VRLP). METHODS: The upper airway was examined with dynamic fiberoptic pharyngoscope in six patients with cleft palate who were diagnosed as OSAHS by polysomnography(PSG) after VRLP. All the patients underwent removal of ligation thread and adenoidectomy. Three months after operation, they were recalled back and were examined with polysomnography and dynamic fiberoptic pharyngoscope. The preoperative and postoperative PSG data were analysed with t test and chi-square test to determine the statistical differences. RESULTS: In patients with OSAHS after VRLP, a ring scar was observed on the upper airway at the soft palate level and a remarkable narrow nasopharyngeal meatus was found mainly because of adenoidal hypertrophy. After removal of ligation thread and adenoidectomy, no velopharyngeal incompetence was found, the upper airway morphology was smooth, respiration disorder during sleeping was completely disappeared and sleep architecture became normal. There were significant differences between preoperative and postoperative PSG data. CONCLUSION: Removal of ligation thread combined adenoidectomy was an effective treatment for OSAHS after VRLP.
Adenoidectomy↗
[Radiograph of a Bochdalek hernia].
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Female↗
[Relationships between spinal deformities and respiratory function in patients with severe motor and intellectual disabilities syndrome].
The term severe motor and intellectual disabilities syndrome (SMIDS) refers to describe a heterogeneous group of disorders with severe physical disabilities and profound mental retardation. Many patients with SMIDS have spinal deformities such as spinal rotation and scoliosis. On the other hand, they often have respiratory dysfunction, resulting in high mortality from respiratory failure. Therefore, we hypothesized that spinal abnormalities might affect respiratory dysfunction, and analyzed the correlation between spinal abnormalities (Cobb angles (CA) and spinal rotation scores (SRS)) and respiratory parameters (observed during tidal breathing at static supine posture) in 10 patients with SMIDS (M: F 2:8, age 29.0 +/- 7.3 years). The patients inability to make effort in spirometry prevented us from evaluating vital capacity and forced expiratory volume. We measured respiratory rate, tidal volume, and expiratory gas during tidal breathing for 10 minutes. There was no patient with the athethotic type of CP. CA and SRS were found to be correlated with each other (r = 0.81, p < 0.01). CA was inversely correlated with tidal volume (both Vt and Vt/Height;r = -0.69, p < 0.05). Both CA and SRS correlated with respiratory rate (r = 0.67 and 0.69, respectively). Moreover, the slope of the regression lines of the VO2-VCO2 plots (V-slope) was correlated with CA (r = 0.86, p < 0.01). Contrary to our expectation, none of the respiratory parameters showed significant correlations with BMI. Moreover, we found no relationship between the spinal deformity (CA or SRS) and BMI. These observations suggest that the spinal abnormalities affect respiratory patterns in a restrictive manner and increase the respiratory change rate during tidal breathing in patients with SMIDS.
Adult↗
Respiratory dysfunction and management in spinal cord injury.
Respiratory dysfunction is a major cause of morbidity and mortality in spinal cord injury (SCI), which causes impairment of respiratory muscles, reduced vital capacity, ineffective cough, reduction in lung and chest wall compliance, and excess oxygen cost of breathing due to distortion of the respiratory system. Severely affected individuals may require assisted ventilation, which can cause problems with speech production. Appropriate candidates can sometimes be liberated from mechanical ventilation by phrenic-nerve pacing and pacing of the external intercostal muscles. Partial recovery of respiratory-muscle performance occurs spontaneously. The eventual vital capacity depends on the extent of spontaneous recovery, years since injury, smoking, a history of chest injury or surgery, and maximum inspiratory pressure. Also, respiratory-muscle training and abdominal binders improve performance of the respiratory muscles. For patients on long-term ventilation, speech production is difficult. Often, practitioners are reluctant to deflate the tracheostomy tube cuff to allow speech production. Yet cuff-deflation can be done safely. Standard ventilator settings produce poor speech quality. Recent studies demonstrated vast improvement with long inspiratory time and positive end-expiratory pressure. Abdominal binders improve speech quality in patients with phrenic-nerve pacers. Recent data show that the level and completeness of injury and older age at the time of injury may not be related directly to mortality in SCI, which suggests that the care of SCI has improved. The data indicate that independent predictors of all-cause mortality include diabetes mellitus, heart disease, cigarette smoking, and percent-of-predicted forced expiratory volume in the first second. An important clinical problem in SCI is weak cough, which causes retention of secretions during infections. Methods for secretion clearance include chest physical therapy, spontaneous cough, suctioning, cough assistance by forced compression of the abdomen ("quad cough"), and mechanical insufflation-exsufflation. Recently described but not yet available for general use is activation of the abdominal muscles via an epidural electrode placed at spinal cord level T9-L1.
Breathing Exercises↗
[Pharmacokinetic simulation of high-dose administration of dexmedetomidine for decubitus treatment].
We used only dexmedetomidine to sedate a patient with Alzheimer disease, Parkinson's syndrome and emaciation for decubitus treatment in the prone position. The infusion rate of dexmedetomidine without a loading dose was increased until sufficient sedation was attained. The maximum plasma concentration and the plasma concentration in a stable state, which were calculated by pharmacokinetic simulation analysis, were 2.3 ng x ml(-1) and 1.5 ng x ml(-1), respectively. Respiration disorder did not occur and hemodynamic stability was preserved despite administration up to 11.5 mcg x kg(-1) x h(-1). An increase in the dose per weight was needed to increase the absolute dose because of emaciation. It was found by pharmacokinetic simulation analysis that the plasma concentration of dexmedetomidine required for decubitus treatment might be higher than the plasma concentration considered to be necessary for sedation in intensive care units. The simulation was conducted to administer dexmedetomidine, to estimate hemodynamic reaction, and to estimate the necessary plasma concentration. We conclude that dexmedetomidine is useful as an anesthetic agent for decubitus treatment in the prone position, although further investigations with regard to its safety are required.
Aged↗
Care of the chronic tracheostomy.
A minority of patients with neuromuscular disease require placement of a tracheostomy, usually for the purpose of providing mechanical ventilation. Often the tracheostomy is performed during a hospital admission for an acute illness. The debate about the appropriate timing of tracheostomy in critically ill patients has not been resolved; however, the weight of evidence now favors performing a tracheostomy early (within 7 d of translaryngeal intubation) if the period of mechanical ventilation is likely to be prolonged beyond 3 weeks. For patients with chronic progressive weakness who develop respiratory difficulty, the consensus of opinion is that tracheostomy should be performed in patients with severe bulbar involvement, inability to effectively cough up secretions despite mechanical aids for secretion clearance, or for those who are unable to tolerate or fail noninvasive ventilation. The decision to perform tracheostomy in patients with chronic neuromuscular weakness involves consideration of several factors, including complications, resources, quality of life, ethical issues, cosmetic issues, and cost. Complications from tracheostomy and physician-perceived poor quality of life often lead to a negative bias, such that some patients may be denied this life-saving procedure. Special training is needed to provide long-term tracheostomy care, and an organized approach should be followed to decannulate patients who recover from their acute illness. Appropriate and skilled care could significantly improve the longevity and quality of life of those patients with neuromuscular disease who have a tracheostomy for long-term ventilation.
Acute Disease↗
[From steel lung to modern techniques of resuscitation].
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France↗
Phrenic nerve pacing in quadriplegia.
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Adult↗
[Functional respiratory disorders].
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Arousal↗
[Joubert's syndrome].
We report a new case of pathologically documented Joubert syndrome. A review of 35 published cases showed that this syndrome, first described by Joubert and Eisenring in 1969, is well individualized and exhibits consistent features, including attacks of tachypnea alternating with respiratory pauses, abnormal ocular movements, severe psychomotor retardation, and ataxia. Anatomic anomalies include vermian agenesis with cystic dilatation of the fourth ventricle. Inheritance of this condition is autosomal and recessive. Onset is in the neonatal period and prognosis is severe. Significant anatomic resemblances with the Dandy-Walker syndrome exist, although genetic and clinical features are different. The origin of this syndrome is unknown, but a study of peroxisomes is required since three cases of Joubert syndrome with pipecolic acidemia have been reported and resemblances exist between some recognized peroxisomal diseases and Joubert syndrome.
Cerebral Ventricles↗
[Conduction disorders in Cheyne-Stokes respiration caused by cardiac insufficiency].
This report describes a case of Cheyne-Stokes respiration linked to heart failure, with periodic disturbances of atrioventricular conduction during the augmentation phase of the tidal volume. The circulatory retardation caused by heart failure induced a phase lag of the negative retroaction system and secondarily an oscillation in the respiratory command. The conduction disturbances resulted from vagal stimulation of multifactorial origin. The atrioventricular conduction disturbances were analogous to those seen in other periodic respiratory diseases.
Aged↗