Archives of Anesthesiology and Critical Care 2015. 1(3):65-66.

Variable Ventilation Stochastic or Physiologic
Atabak Najafi

Abstract


Variability of tidal volume and respiratory rate in normally breathing man has long been demonstrated [1]. However because of lack of knowledge and technology primary ventilators could only deliver a fixed tidal volume in a fixed rate the so called volume controlled ventilation (VCV). VCV was volume preset time triggered and cycled and there was no synchronization with patient’s breaths. At that time ventiltory management was associated with serious lung damage caused by ventilator [2-3]. Today that is referred as ventilator induced lung injury.

Frequent complications of ventilatory support forced physicians and engineers to develop newer modes of mechanical ventilation. Advances in control mechanisms, servo valves, flow and pressure sensors led to introduction of synchronized modes of ventilation like synchronized intermittent mandatory ventilation (SIMV) and pressure support ventilation (PSV).

Synchronization of mechanical ventilation was a big step toward physiological ventilation and showed fewer complications compared with non synchronized ventilation [4]. Patient can interact with ventilator in initiation of inspiration and in PSV respiratory rate is controlled by the patient’s inspiratory effort so patient is not locked to a fixed respiratory rate delivered by the ventilator. PSV is more physiological form of mechanical ventilation in being patient triggering, pressure limited and flow cycled. Although PSV was introduced as a weaning mode of ventilation it showed it is effectiveness in ventilatory management of respiratory failure [5]. Even in severe cases of acute respiratory failure PSV provided better oxygenation with higher tidal volumes and lower peak inspiratory pressure compared with assist control ventilation [6]. So it is commonly used in critical care setting.

After releasing patients from fixed respiratory rate during mechanical ventilation, technological advances in field of mechanical ventilation released patients from fixed support pressure and tidal volume by introduction of proportional assist ventilation (PAV) and neurally adjusted ventilatory assist (NAVA) in both forms of ventilation level of support pressure is determined by patient’s inspiratory effort. For PAV negative pressure generated at the beginning of inspiration and for NAVA electrical activity of diaphragm controls the level of pressure support. Although tidal volume is variable during PSV but variability of tidal volume is more with PAV [7] and PAV is accompanied with lesser work of breathing and asynchrony than PSV [8] PAV and NAVA both prevent hyperinflation of lungs, decrease patient`s ventilator asynchrony and restore variability of tidal volume and breathing pattern compared with PSV [9].

Another form of ventilation recently introduced to clinical practice is noisy pressure support ventilation (noisy PSV).

In noisy PSV in contrast with PAV and NAVA there is no percent of support pressure setting and intensivist can set the level of support and percentage of variability in pressure support. Support pressure and tidal volume are randomly changing during ventilation so it is very similar to spontaneous breathing.

Suki B et al. showed the benefits of variability and noise in life support systems [10].

Variability of tidal volume is effective in recruiting atelectatic lung [11] also variable tidal volume improves lung mechanics and gas exchange in animal model of acute lung injury [12]. Noisy PSV is also superior to PSV and pressure controlled ventilation (PCV) in terms of oxygenation and lung protection [13]. Noisy ventilation improves lung function and reduces lung damage compared with standard lung protective strategies [14]. Noisy PSV in surfactant depleted pigs redistributes perfusion toward nondependent lung regions [15] variable tidal volumes enhances surfactant secretion in alveoli [16] in acute hypoxemic respiratory failure noisy PSV was associated with better synchrony than PSV [17].

Variable ventilation has many benefits in being similar to spontaneous physiological ventilation so patients with better respiratory condition have more variability of breathing and vice versa [18].

Variability of tidal volume generated by the computer is comparable with physiologically derived noise from the aspect of lung mechanics and gas exchange [19].

There have been tremendous advances in field of mechanical ventilation specially in assisted modes of ventilation but we do not see the same level of improvement in controlled modes of ventilation.

The question is: how can we help non spontaneously breathing patients? They have the same physiology and same lung so if spontaneously breathing patients benefit from variability of ventilation why should we fetter apneustic patients to a fixed rate and tidal volume.

Now it is time for ventilator producing companies to be more thoughtful of these patients and give them the chance to breathe more physiologically by adding stochastic noise or variability to their respiratory rate and tidal volume in conventional controlled modes of mechanical ventilation like pressure controlled or volume controlled ventilation

Keywords


Variable ; Ventilation

Full Text:

PDF

References


Kuratomi Y, Okazaki N, Ishihara T, Arai T, Kira S. Variability of breath-by-breath tidal volume and its characteristics in normal and diseased subjects. Ventilatory monitoring with electrical impedance pneumography. Jpn J Med. 1985; 24(2):141-9.

Avignon PD, Hedenstrom G, Hedman C. Pulmonary complications in respirator patients. Acta Med Scand Suppl. 1956; 316:86-90.

Nash G, Blennerhassett JB, Pontoppidan H. Pulmonary lesions associated with oxygen therapy and artifical ventilation. N Engl J Med. 1967; 276(7):368-74.

Ramanathan R. Synchronized intermittent mandatory ventilation and pressure support: to sync or not to sync? Pressure support or no pressure support? J Perinatol. 2005; 25 Suppl 2:S23-5; discussion S26-7.

Tejeda M, Boix JH, Alvarez F, Balanzá R, Morales M. Comparison of pressure support ventilation and assist-control ventilation in the treatment of respiratory failure. Chest. 1997; 111(5):1322-5.

Tokioka H, Saito S, Kosaka F. Comparison of pressure support ventilation and assist control ventilation in patients with acute respiratory failure. Intensive Care Med. 1989; 15(6):364-7.

Ranieri VM, Giuliani R, Mascia L, Grasso S, Petruzzelli V, Puntillo N, et al. Patient-ventilator interaction during acute hypercapnia: pressure-support vs. proportional-assist ventilation. J Appl Physiol (1985). 1996; 81(1):426-36.

Wrigge H, Golisch W, Zinserling J, Sydow M, Almeling G, Burchardi H. Proportional assist versus pressure support ventilation: effects on breathing pattern and respiratory work of patients with chronic obstructive pulmonary disease. Intensive Care Med. 1999; 25(8):790-8.

Schmidt M, Kindler F, Cecchini J, Poitou T, Morawiec E, Persichini R, et al. Neurally adjusted ventilatory assist and proportional assist ventilation both improve patient-ventilator interaction. Crit Care. 2015; 19:56.

Suki B, Alencar AM, Sujeer MK, Lutchen KR, Collins JJ, Andrade JS Jr, et al. Life-support system benefits from noise. Nature. 1998; 393(6681):127-8.

Mutch WA, Harms S, Ruth Graham M, Kowalski SE, Girling LG, Lefevre GR. Biologically variable or naturally noisy mechanical ventilation recruits atelectatic lung. Am J Respir Crit Care Med. 2000; 162(1):319-23.

Arold SP, Mora R, Lutchen KR, Ingenito EP, Suki B. Variable tidal volume ventilation improves lung mechanics and gas exchange in a rodent model of acute lung injury. Am J Respir Crit Care Med. 2002; 165(3):366-71.

Spieth PM, Carvalho AR, Güldner A, Kasper M, Schubert R, Carvalho NC, et al. Pressure support improves oxygenation and lung protection compared to pressure-controlled ventilation and is further improved by random variation of pressure support. Crit Care Med. 2011; 39(4):746-55.

Spieth PM, Carvalho AR, Pelosi P, Hoehn C, Meissner C, Kasper M, et al. Variable tidal volumes improve lung protective ventilation strategies in experimental lung injury. Am J Respir Crit Care Med. 2009; 179(8):684-93.

Gama de Abreu M, Spieth PM, Pelosi P, Carvalho AR, Walter C, Schreiber-Ferstl A, et al. Noisy pressure support ventilation: a pilot study on a new assisted ventilation mode in experimental lung injury. Crit Care Med. 2008; 36(3):818-27.

Arold SP, Bartolák-Suki E, Suki B. Variable stretch pattern enhances surfactant secretion in alveolar type II cells in culture. Am J Physiol Lung Cell Mol Physiol. 2009; 296(4):L574-81.

Spieth PM, Güldner A, Huhle R, Beda A, Bluth T, Schreiter D, et al. Short-term effects of noisy pressure support ventilation in patients with acute hypoxemic respiratory failure. Crit Care. 2013 ;17(5):R261.

Wysocki M, Cracco C, Teixeira A, Mercat A, Diehl JL, Lefort Y, et al. Reduced breathing variability as a predictor of unsuccessful patient separation from mechanical ventilation. Crit Care Med. 2006; 34(8):2076-83.

Froehlich KF, Graham MR, Buchman TG, Girling LG, Scafetta N, West BJ, et al. Physiological noise versus white noise to drive a variable ventilator in a porcine model of lung injury. Can J Anaesth. 2008; 55(9):577-86.


Refbacks

  • There are currently no refbacks.


Creative Commons Attribution-NonCommercial 3.0

This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License which allows users to read, copy, distribute and make derivative works for non-commercial purposes from the material, as long as the author of the original work is cited properly.