| More

Mechanical ventilation. Part II: Basic principles and function of ventilators.

Views: 125 Downloads: 52


Mechanical ventilation is the process of supporting respiration by manual or mechanical means. When normal breathing is inefficient or has stopped, mechanical ventilation is life-saving and should be applied at once. The ventilator increases the patient's ventilation by inflating the lungs with oxygen or a mixture of air and oxygen. Ventilators play an important role in the anaesthetic management of patients, as well as in the treatment of patients in the ICU. However, there are differences between the anaesthetic ventilators and the ventilators in ICU. The main indication for mechanical ventilation is difficulty in ventilation and/or oxygenation of the patient because of any respiratory or other disease. The aims of mechanical ventilation are to supply adequate oxygen to patients with a limited vital capacity, to treat ventilatory failure, to reduce dyspnoea and to facilitate rest of fatigued breathing muscles. Depression of the central nervous system function is a pre-requirement for mechanical ventilation. Some times, opioids or muscle relaxants can be used in order to depress patient's breathing. Mechanical ventilation can be applied using many different modes: assisted ventilation, controlled ventilation, continuous positive pressure ventilation, intermittent positive pressure ventilation and jet ventilation. Furthermore, there are different types of automatic ventilators built to provide positive pressure ventilation in anaesthetized or heavily sedated or comatose patients: manual ventilators (Ambu-bag), volumecontrolled ventilators with pressure cycling, volume-controlled ventilators with time cycling and pressure-controlled ventilators. In veterinary practice, the ventilator should be portable, compact and easy to operate. The controls on most anaesthetic ventilators include settings for tidal volume, inspiratory time, inspiratory pressure, respiratory rate and inspiration: expiration (I:E) ratio. The initial settings should be between 10-20 ml/kg for tidal volume, 12-30 cmH2 0 for the inspiratory pressure and 8-15 breaths/min for the respiratory rate. Mechanical ventilation is a very important part of treatment in the ICU, but many problems may arise during application of mechanical ventilation in critically ill patients. All connections should be checked in advance and periodically for mechanical problems like leaks. Moreover, complications like lung injury, pneumonia, pneumothorax, myopathy and respiratory failure can occur during the course of mechanical ventilation causing difficulty in weaning.


Function; principles; ventilators

Full Text:



Amato MB, Barbas CS, Medeiros DM et al. (1998) Effect of a protective-ventilation strategy on mortality in the acute respiratory distress syndrome. Ν Engl J Med, 338:347-354.

Battaglia AM, Shawver D (2007) Mechanical Ventilation. In: Small Animal Emergency and Critical Care. Elsevier, Misouri, pp. 116-123.

Branson RD (1994) Flow-triggering systems. Respir Care, 39:138-144.

Chatburn RL (1992) Classification of mechanical ventilators. Respir Care, 37:1009-1025.

Chatburn RL (2010) Understanding mechanical ventilators. Expert Rev Respir Med, 4:809-819.

Dorsch JA, Dorsch SE (2008) Anesthesia Ventilators. In: Anesthesia Equipment, fifth edn, Williams & Wilkins, Philadelphia, pp. 311-371.

Drellich S (2002) Principles of mechanical ventilation. Vet Clin Small Anim, 32:087-1100.

Goulet R, Hess D, Kacmarek RM (1997) Pressure vs flow triggering during pressure support ventilation. Chest, 111:1649-1653.

Grasso S. Measurement and interpretation of respirtaory system mechanics during controlled mechanical ventilation for general anesthesia. In: Proceedings AVA Spring Meeting, 2011 Bari, Italy. pp 21-34.

Gravenstein JS, Nederstigt JA (1990) Monitoring for disconnection: ventilators with bellows rising on expiration can deliver tidal volumes after disconnection. J Clin Monit, 6:207-210.

Gravenstein N, Banner MJ, McLaughlin G (1987) Tidal volume changes due to the interaction of anesthesia machine and anesthesia ventilator. J Clin Monit, 3:187-190.

Gurkan OU, O'Donnell C, Brower R et al. (2003) Differential effects of mechanical ventilatory strategy on lung injury and systemic organ inflammation in mice. Am J Physiol Lung Cell Mol Physiol, 285:L710-718.

Hammond R (2007) Automatic ventilators. In: Manual of Canine and Feline Anaesthesia and Analgesia. Second edn, BSAVA, Gloucecter, pp. 49-60.

Hartsfield SM (1999) Airway management and ventilation. In: Essentials of Small Animal Anesthesia and Analgesia. Lippincott, Philadelphia, pp. 292-325.

Hartsfield S (2007) Airway management and Ventilation. In: Lumb & Jones' Veterinary Anesthesia and Analgesia, fourth edn, Blackwell, Oxford, pp. 495-531

Haskins SC (2011a) Discontinuation of ventilator support. Modes of ventilation and an approach to a challenging situation. AVA Spring meeting,Vol., Bari, Italy, pp. 51-54.

Haskins SC (2011b) Long-term ventilation in an intensive care unit; an evaluation of techniques and results. AVA Spring meeting, Vol., Bari, Italy, pp. 38-41.

Hess DR(2010) Ventilator modes: where have we come from and where are we going? Chest, 137:1256-1258.

Hopper K, Haskins SC, Kass PH et al. (2007) Indications, management, and outcome of long-term positive-pressure ventilation in dogs and cats: 148 cases (1990-2001). J Am Vet Med Assoc, 230:64-75.

Lee JA, Drobatz KJ, Koch MW et al. (2005) Indications for and outcome of positive-pressure ventilation in cats: 53 cases (1993-2002). J Am Vet Med Assoc, 226:924-931.

Maclntyre NR (1986) Respiratory function during pressure support ventilation. Chest, 89:677-683.

Maclntyre NR (2004) Evidence-based ventilator weaning and discontinuation. Respir Care, 49:830-836.

Maclntyre Ν (2006) Discontinuing mechanical ventilatory support: removing positive pressure ventilation vs removing the artificial airway. Chest, 130:1635-1636.

Maclntyre Ν (2007) Discontinuing mechanical ventilatory support. Chest, 132:1049-1056.

Maclntyre NR, Cook DJ, Ely EW, Jr. et al. (2001) Evidence-based guidelines for weaning and discontinuing ventilatory support: a collective task force facilitated by the American College of Chest Physicians; the American Association for Respiratory Care; and the American College of Critical Care Medicine. Chest, 120:375S-395S.

Marino PL (1998) Modes of assisted ventilation. In: The ICU Book. Lippincott, Philadelphia, pp. 473-489.

McKelvey D, Hollingshead KW (2003) Special Techniques. In: Veterinary Anesthesia and Analgesia. Third edn, Elsevier, 286-314.

Mushin WW, Rendell-Baker L, Thompson PW et al. (1980) Physical Aspects of Automatic Ventilators:Basic Principles. In: Automatic Ventilation of the Lungs, third edn, Oxford, pp. 62-131.

Nunn J (2000) Artificial ventilation. In: Nunnass Applied Respiratory Physiology. 587-622.

Ranieri VM (2011) Ventilator Induced Lung Injury Mechanisms. AVA Spring Meeting,Vol., Bari, Italy, pp. 35-37.

Ranieri VM, Suter PM, Tortorella C et al. (1999) Effect of mechanical ventilation on inflammatory mediators in patients with acute respiratory distress syndrome: a randomized controlled trial. Jama,282:54-61.

Richard JC, Carlucci A, Breton L et al. (2002) Bench testing of pressure support ventilation with three different generations of ventilators. Intensive Care Med, 28:1049-1057.

Richard JC, Kacmarek RM (2009) ICU mechanical ventilators, technological advances vs. user friendliness: the right picture is worth a thousand numbers. Intensive Care Med, 35:1662-1663.

Sassoon CS, Gruer SE (1995) Characteristics of the ventilator pressure-and flow-trigger variables. Intensive Care Med, 21:159-168.

Schmidt GA, Hall GB (2005) Management of the ventilated patient. In: Principles of critical care, third edn, The McGraw-Hill Companies, 481-498.

Singer BD, Corbridge TC (2009) Basic invasive mechanical ventilation. South Med J, 102:1238-1245.

Sorrell-Raschi L (2009) Blood gas and oximetry monitoring. In: Small Animal Critical care Medicine. 1st ed, Elsevier press, Misouri: pp 878-886

Stefanopoulou Ρ (2009) Pressure-Volume Ventilators: Advantages, disadvantages and basic settings. Pneumon Supplement, 22:26-28.

Stewart TE, Meade MO, Cook DJ et al. (1998) Evaluation of a ventilation strategy to prevent barotrauma in patients at high risk for acute respiratory distress syndrome. Pressure- and Volume-

Limited Ventilation Strategy Group. Ν Engl J Med, 338:355-361.

Stewart, N. I., Jagelman, T. A. & Webster N. R. 2011. Emerging modes of ventilation in the intensive care unit. Br J Anaesth, 107, 74-82.

Sykes MK, McNicol MW, Campell EJM (1976) Physiological aspects of mechanical ventilation. In: Respiratory failure. Second edn.Szpisjak DF, Lamb CL, Klions KD (2005) Oxygen consumption with mechanical ventilation in a field anesthesia machine. Anesth Analg, 100:1713-1717.

Thille AW, Lyazidi A, Richard JC et al. (2009) A bench study of intensive-care-unit ventilators: new versus old and turbine-basedversus compressed gas-based ventilators. Intensive Care Med, 35:1368-1376.

Tobin MJ (2001) Advances in mechanical ventilation. Ν Engl J Med, 344:1986-1996.

Toi G, Palmer J (2010) Principles of mechanical ventilation. Anaesthesia and Intensive Care Medicine, 38:1145-1146.

Tung A, Drum ML, Morgan S (2005) Effect of inspiratory time on tidal volume delivery in anesthesia and intensive care unit ventilators operating in pressure control mode. J Clin Anesth, 17:8-15.

Ward CS (1975) Ventilators-Resuscitators, Respirtaors, Breathing Systems. In: Anaesthetic Equipment. Macmillan, England, pp. 117-145.


  • There are currently no refbacks.