Flow Versus Pressure Triggering in Mechanically Ventilated Acute Respiratory Failure Patients Magdy M

198 Original article Flow versus pressure triggering in mechanically ventilated acute respiratory failure patients Magdy M. Khalila, Nevine M. Elfattaha, Mohsen M. El-Shafeyb, Nermine M. Riada, Raed A. Aidb, Alaa M. Ananyc Background The effects of fl ow triggering (FT) compared the PT group (P < 0.001). In patients with obstructive with pressure triggering (PT) on breathing effort have pulmonary disorders, combined pulmonary disorders, and been the focus of several studies, and discrepant results less severe disease (APACHE II <32.5), there was no have been reported; yet, it remains an area of confl ict that signifi cant difference between both PT and FT groups in warrants further studies. these parameters. Objective The aim of this work is to compare fl ow versus Conclusion FT may be considered to be better than PT in ventilating patients with acute respiratory failure. PT in ventilating acute respiratory failure patients with a restrictive pattern and those with higher severity scoring. In Patients and methods One hundred patients with acute obstructive and mixed ventilatory impairment, use of either respiratory failure of pulmonary origin were assigned of them does not make a difference. Egypt J Broncho 2015 randomly to two groups: 50 patients ventilated with PT 9:198–210 and 50 patients ventilated with FT. The primary end points © 2015 Egyptian Journal of Bronchology. were weaning duration, evaluation of patient/machine synchronization, total duration of ventilation and ICU stay as Egyptian Journal of Bronchology 2015 9:198–210 well time under sedation and occurrence of complications. Keywords: mechanical ventilation, respiratory failure, triggering Mortality was considered the secondary end point. Patients Key messages were categorized into those with obstructive, restrictive, and (1) Which is better: Flow or Pressure Triggering in Mechanically Ventilated combined pulmonary disease according to their medical Acute Respiratory Failure Patients? history, and clinical and radiological assessment, and also (2) Is there a difference in obstructive, restrictive or combined Respiratory Failure Patients? more and less severe disease according to the APACHE II (3) How do Flow or Pressure Triggering in Mechanically Ventilated Acute score level (cut-off point). Respiratory Failure Patients affect the outcome? a Results In all the patients studied, including those with D epartment of Chest Diseases, Ain Shams University, Cairo, bD epartment of Chest Disease, Mansoura University, Mansoura, restrictive pulmonary disorder and more severe disease cM inistry of Health, Cairo, Egypt (APACHE II score ≥32.5), there was a statistically Correspondence to Nevine M. Abd Elfattah, MD, PhD, 8 Ossman Abdel signifi cantly shorter duration of weaning, duration of Hafeez, Nasr City, Cairo 11371, Egypt ventilation, and duration of ICU stay in the FT group than Tel: +20 122 312 8770; fax: +224010321; the PT group. The pre-extubation oxygenation index was e-mail: [email protected] highly statistically signifi cantly better in the FT group than Received 22 April 2015 Accepted 26 April 2015 Introduction also be divided into those with normal versus abnormal Respiratory failure is a syndrome in which the chest radiography [2]. respiratory system fails in one or both of its gas- exchanging functions — that is, oxygenation of, Th ere are three locked steps to the diagnosis of ARF: and carbon dioxide elimination from, mixed venous (a) Th e clinical suspicion that ARF might be present, (pulmonary arterial) blood [1]. (b) Confi rmation by arterial blood gas analysis that ARF is present, and Acute respiratory failure is characterized by an (c) Further diagnostic steps that identify the specifi c inability to maintain adequate oxygenation (a PaO 2 etiology of the ARF [3]. of <50–55 mmHg or an arterial oxygen saturation by pulse oxymetry of <85% on room air), ventilation (a One of the most serious complications of ARF is PaCO2 >50 mmHg or increase of >10 mmHg over the nosocomial pneumonia, usually caused by virulent base line PaCO2), or both, which develops over a short organisms, frequently Gram-negative bacilli that period of time. For practical purposes, the onset usually cause necrotizing pneumonia, and may be resistant occurs over several hours or days [2]. to common antibiotics. Acute stress ulceration with resultant upper gastrointestinal bleeding is Acute respiratory failure can be classifi ed into a well-recognized complication in patients with hypercapnic or hypoxemic respiratory failure, and can respiratory failure [4]. 1687-8426 © 2015 Egyptian Journal of Bronchology DOI: 10.4103/1687-8426.158103 Effects of FT compared with PT Khalil et al. 199 Pulmonary embolism is a frequent fi nding in critically (3) Alter pressure–volume relationship: ill patients with ARF. When ARF and acute renal (a) Reverse or prevent atelectasis. failure occur concurrently in critically ill patients, each (b) Improve lung compliance. condition may worsen or precipitate the other [5]. (c) Prevent further lung injury. (4) Permit lung and airway healing. When correcting hypoxemia, the clinician must also address any coexisting hypercapnia and respiratory Selection of the initial ventilator setting is performed acidosis, and the immediacy of correction depends on the basis of the patient’s size and clinical condition. on the magnitude of the acidosis and its attendant Settings are entered and the proper function of the eff ects [1]. ventilator is verifi ed before connection to the patient. Ventilatory settings must be repeatedly reviewed When adequate oxygenation cannot be maintained by to optimize ventilatory support while minimizing noninvasive means or if progressive hypoventilation risks [10]. and hypercapnia with respiratory acidosis occurs, endotracheal intubation and mechanical ventilatory After initiating ventilatory support, the clinician should support should be initiated. Mechanical ventilation ‘fi ne-tune’ the trigger sensitivity setting. Fine-tuning is can produce positive pressure at the airway opening or necessary because too sensitive a setting can cause some create negative pressure around the chest wall. Use of ventilators to autotrigger whereas an unresponsive negative pressure ventilation is generally restricted to trigger level can add to the breathing work load and patients with chronic neuromuscular weakness or chest cause patient–ventilator asynchrony [11]. wall deformity [6]. Triggering refers to the mechanism through which For air to enter the lungs, a pressure gradient the ventilator senses inspiratory eff ort and delivers must exist between the airway and alveoli. This gas fl ow or a machine breath in concert with the can be accomplished either by increasing pressure patient’s inspiratory eff ort. In modern ventilators, the at the airway (positive-pressure ventilation) or demand valve is triggered by either a fall in pressure by lowering pressure at the level of the alveolus (pressure trigger) or a change in fl ow (fl ow trigger). (negative-pressure ventilation). Positive-pressure With pressure-triggered ventilation, a preset pressure ventilation can be achieved by an endotracheal or a sensitivity has to be achieved before the ventilator tracheostomy tube or noninvasively through a nasal delivers fresh gas into the inspiratory circuit; with mask or a facemask. In the past, this was invariably fl ow-triggered ventilation, a preset fl ow sensitivity is performed using an endotracheal or a tracheostomy used as the trigger mechanism [12]. tube, but in recent years, there has been an increasing trend toward the use of noninvasive ventilation, Th e most common trigger variables are time (the which can be accomplished using either a full face ventilator initiates a breath according to asset frequency, mask (covering both the nose and the mouth) or a independent of the patient’s spontaneous eff orts), nasal mask [7]. pressure (the ventilator senses the patient’s inspiratory eff ort in the form of a decrease in baseline pressure and In acute care settings, critical care ventilators or starts inspiration independent of the set frequency), portable positive-pressure devices are used in volume- and fl ow (the ventilator senses the patient’s inspiratory limited or pressure-limited modes. Although either eff ort as a decrease in the baseline fl ow through the mode can be used with the expectation of similar patient circuit or senses inspiratory fl ow directly with a rates of success, pressure-limited modes appear to sensor at the patient’s airway opening) [13]. be more readily accepted by patients. In the acute setting, nasal or oronasal masks are most commonly Pressure triggering (PT) is the oldest and simplest used [8]. technique for the detection of patient eff ort. Th e sensitivity or trigger threshold is set in centimeters of In 1994, Tobin [9] listed the objectives of mechanical H2O relative to the baseline pressure. ventilation as follows: As an example, if baseline pressure is 5 cmH2O and (1) Improve pulmonary gas exchange: the trigger threshold is 2 cmH2O, when patient eff ort (a) Reverse hypoxemia. causes pressure in the circuit to decrease to 3 cmH2O, (b) Relieve acute respiratory acidosis. the breath is triggered and if the baseline pressure is (2) Relieve respiratory distress: changed, for instance to 10 cmH2O and the trigger (a) Decrease oxygen cost of breathing. threshold remains the same (2 cmH2O), the ventilator (b) Reverse respiratory muscle fatigue. is triggered when circuit pressure decreases to less than 200 Egyptian Journal of Bronchology 8

Load more