Intermittent mandatory ventilation

Synchronized intermittent mechanical ventilation (SIMV)

Synchronized Intermittent Mechanical Ventilation is a variation of IMV, in which the ventilator breaths are synchronized with the patient's inspiratory effort. SIMV, with and without pressure support, has not been shown to have any advantages over continuous mandatory ventilation (CMV) in terms of mortality or weaning success, and has been shown to result in longer weaning times when compared to t-piece trials or gradual reductions in pressure support. Some studies have shown an increase in patient work of breathing when switched from CMV to SIMV, and others have demonstrated potential detrimental effects of SIMV on respiratory muscles and respiratory drive.

Mandatory minute ventilation (MMV)

Mandatory minute ventilation is a mode which requires the operator to determine what the appropriate minute ventilation for the patient should be, and the ventilator then monitors the patient's ability to generate this volume every 7.5 seconds. If the calculation suggests the volume target will not be met, SIMV breaths are delivered at the targeted volume to achieve the desired minute ventilation. Allows spontaneous breathing with automatic adjustments of mandatory ventilation to the meet the patient’s preset minimum minute volume requirement. If the patient maintains the minute volume settings for VT x f, no mandatory breaths are delivered. If the patient's minute volume is insufficient, mandatory delivery of the preset tidal volume will occur until the minute volume is achieved. The method for monitoring whether or not the patient is meeting the required minute ventilation (VE) is different per ventilator brand and model, but generally there is a window of time being monitored and a smaller window being checked against that larger window (i.e., in the Dräger Evita® line of mechanical ventilators there is a moving 20-second window and every 7 seconds the current tidal volume and rate are measured against to decide for if a mechanical breath is needed to maintain the minute ventilation). MMV is the most optimal mode for weaning in neonatal and pediatric populations and has been shown to reduce long term complications related to mechanical ventilation.

Proportional assist ventilation (PAV)

Proportional assist ventilation is a mode in which the ventilator guarantees the percentage of work regardless of changes in pulmonary compliance and resistance.Younes M. Proportional assist ventilation, a new approach to ventilatory support. Theory. Am Rev Respir Dis 1992; 145(1):114-120. The ventilator varies the tidal volume and pressure based on the patients work of breathing, the amount it delivers is proportional to the percentage of assistance it is set to give.

Adaptive support ventilation (ASV)

Adaptive Support Ventilation is a positive pressure mode of mechanical ventilation that is closed-loop controlled. In this mode, the clinician enters patient ideal body weight and desired level of ventilation in percent of predicted alveolar ventilation and the ventilator then applies inspiratory pressures at a rate which leads to minimal work of breathing. The equation used to calculate this minimal work was derived from the work of Otis et.al. and published and discussed in Grodins and Yamashiro as early as 1977. In the ASV mode, every breath is synchronized with patient effort if such an effort exists, and otherwise, full mechanical ventilation is provided to the patient. Since the first implementation, ASV has undergone a number of refinements and is available on different ventilator brands under different names.

The invention of ASV is claimed by two competing groups, published as scientific article by one group and disclosed as one of the embodiments of US Patent No. 4986268. In this invention, the control algorithm computes the optimal rate of respiration to minimize the work rate of breathing. The rationale is to make the patient's breathing pattern comfortable and natural within safe limits, and thereby stimulate spontaneous breathing and reduce the weaning time.

References

References

1. Owens, William. (2012). "The Ventilator Book". First Draught Press.
2. Sassoon CS, Del Rosario N, Fei R, et al. Influence of pressure- and flow-triggered synchronous intermittent mandatory ventilation on inspiratory muscle work. Crit Care Med 1994; 22:1933.
3. Christopher KL, Neff TA, Bowman JL, et al. Demand and continuous flow intermittent mandatory ventilation systems" ''Chest'' 1985; 87:625.
4. Ortiz, G. (Jun 2010). "Outcomes of patients ventilated with synchronized intermittent mandatory ventilation with pressure support: a comparative propensity score study.". Chest.
5. Jounieaux, V. (Apr 1994). "Synchronized intermittent mandatory ventilation with and without pressure support ventilation in weaning patients with COPD from mechanical ventilation.". Chest.
6. Boles, JM. (May 2007). "Weaning from mechanical ventilation.". The European Respiratory Journal.
7. Brochard, L. (1 October 1994). "Comparison of three methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation". Am J Respir Crit Care Med.
8. Esteban, A. (Feb 9, 1995). "A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group.". The New England Journal of Medicine.
9. Marini, JJ. (Nov 1988). "External work output and force generation during synchronized intermittent mechanical ventilation. Effect of machine assistance on breathing effort.". The American Review of Respiratory Disease.
10. Imsand, C. (Jan 1994). "Regulation of inspiratory neuromuscular output during synchronized intermittent mechanical ventilation.". Anesthesiology.
11. Leung, P. (Jun 1997). "Comparison of assisted ventilator modes on triggering, patient effort, and dyspnea.". American Journal of Respiratory and Critical Care Medicine.
12. Scott O. Guthrie. (October 2005). "A crossover analysis of mandatory minute ventilation compared to synchronized intermittent mandatory ventilation in neonates". Journal of Perinatology.
13. (1950). "Mechanics of breathing in man". J Appl Physiol.
14. (1977). "Control of Ventilation". Marcel Dekker Inc..
15. (2008). "Computerized system for mechanical ventilation". J Clin Monit Comput.
16. (1994). "An adaptive lung ventilation controller". IEEE Trans Biomed Eng.
17. Tehrani, Fleur T., [http://www.freepatentsonline.com/4986268.html "Method and Apparatus for Controlling an Artificial Respirator"] US Patent No. 4986268, issued Jan. 22, 1991.