Tag Archives: @ccmtutorials

Bilevel Pressure Control, BiLevel, BiVent, BiPAP, DuoPAP – a modern mode of ventilation

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The introduction of the active expiratory valve was a disruptive technology in critical care mechanical ventilation. This valve flutters when the airway pressure rises above the targeted level – to vent off surplus gas, but maintain airway pressure. It led to the development of newer modes of ventilation (and adjustments to older modes) that allowed the patient to breathe spontaneously independent of the ventilator. As such this was a development of intermittent mandatory ventilation (IMV) – without the risk of breath stacking and expiratory dys-synchrony.

The major mode of ventilation that evolved from the active expiratory valve has several different aliases – BiLevel, BIPAP, BIVENT, DuoPAP etc. but they are all, essentially, pressure controlled intermittent mandatory ventilation modes – that allow the patient to breathe supported or unsupported at a high (Phigh) or low (Plow) airway pressure.

I have chosen the term “Bilevel Pressure Control (BL-PC)” to describe this mode. This tutorial introduces BL-PC, from the perspective of IMV, explains the technology and then discusses the setup and use of the mode. It is a mode of ventilation that is used widely as the “default mode” in many ICUs and can be used in any patient at any time. @ccmtutorials http://www.ccmtutorials.org

Breathe Easy – Automatic Tube Compensation

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This tutorial is about Automatic Tube Compensation (ATC). ATC is a setting that has been included in most modern ventilators. Its aim is to reduce the work of breathing associated with the drop in pressure across the endotracheal tube. The ventilator senses pressure, flow and resistance and changes the pressure during the breath to ensure that the patient has the sensation that they are breathing through their own airway. There are two configurations of ATC – one is as an alternative to pressure support in patients who are essentially weaned from mechanical ventilation: essentially a spontaneous breathing trial. The second configuration is as an accessory to all pressure limited modes – such that the pressure waveform is crafted in inspiration and expiration to reduce the workload of breathing during both phases of respiration. @ccmtutorials http://www.ccmtutorials.org

Pressure Assist Control (Part 1)

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Virtually all “modern” modes of mechanical ventilation are built on a pressure controlled platform – the original of the species is Pressure Assist Control (PAC). This tutorial introduces PAC as it would be used on a patient admitted, for example, to ICU, with relatively normal lungs.
The tutorial commences with a clinical scenario followed by a guide to the settings on both Puritan Bennett and Drager ventilators. At this point in the course I am going to start spending more time on Drager devices as these ventilators were built from the ground up to be used as pressure controlled machines. There are nuances to the Drager ventilator that may be slightly counter-intuitive to clinicians who are familiar to other brands: in particular the use of a pressure limit (Pinsp) rather than a driving pressure above PEEP. I explain this with examples. I then explain how pressure control works and remind you of flow and time triggering.
All pressure controlled modes are time cycled with decelerating flow patterns. Care must be taken to ensure that inspiratory time is sufficiently long so as to ensure that the airway is adequately pressurized but not to long as will cause Auto-PEEP.
If you want to understand mechanical ventilation you absolutely must be able to interpret and craft ventilator waveforms – and this tutorial focuses on identifying abnormal waveforms in pressure control and correcting them. Hence there is a section on “Crafting the Pressure Waveform” and a section on “Crafting the Flow Waveform.”
Finally I discuss inspiratory time and tidal volumes

Pressure Controlled Ventilation – The Fundamentals Part 1

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It is time to discuss Pressure Controlled Ventilation. In general if a patient has normal lungs or minimal disease, it really does not matter what mode of ventilation you use, pressure or volume controlled. However, there are some major advantages to using Pressure Control – principally in Acute Hypoxic Respiratory Failure. There are also many disadvantages. This is the first of two tutorials that cover the fundamentals of Pressure Control. I start with a discussion of the terminology that I will be using – the Pressure Limit (PL), the Inspiratory Pressure (IP), the Driving Pressure (DP)/Inspiratory Ramp, the Inspiratory Time (Ti) and the Expiratory Time (Texp). Pressure Controlled Ventilation (PCV) is pressure targeted/limited and volume variable. Breaths are time cycled – in inspiration, expiration or both. The flow pattern is always decelerating.

Following the introduction of a clinical scenario – a patient who is developing ARDS, I describe the process of PCV. I explain that tidal volumes are variable in all settings and all modes of PCV and later describe how changing patient position, chest wall elastance and airway resistance can all impact the tidal volume. I discuss why pressure control is the best option for mechanically ventilating children (particularly where there is no endotracheal tube cuff and a significant air leak) and why you need to pay attention to the rise time and respiratory rate. Finally I discuss the major disadvantages of using PCV. I guarantee you’ll learn something!
@ccmtutorials

Positive End Expiratory Pressure – Phasic Shunting, Auto-PEEP & ARDS

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In the previous tutorials I explained how hypoxemia results from low lung volumes, resulting in low functional residual capacity, airway closure and atelectasis. We looked at the mechanisms by which CPAP reduces the work of breathing in obstructed airways and how, following lung recruitment, PEEP maintains FRC.

In this tutorial I elaborate on these themes. I look at the problem of phasic V/Q mismatch (shunt) during expiration and how it may cause dis-correlation between pulse oximeters and blood gasses. PEEP prevents this at the expense of increasing dead space and negatively impacting ventilation. Optimal PEEP should restore lung compliance – compliance is low with low and high lung volumes. Compliance may also appear poor in pressure control when there is clinically significant auto-PEEP: the ventilator cannot distinguish auto-PEEP from driving pressure and lower than expected tidal volumes may result.

I explain the concept of the “Waterfall” effect to overcome Auto-PEEP. Finally, in our first visit to ARDS, I introduce the problem of deciding on optimal PEEP in that setting. I guarantee that you will learn something. @ccmtutorials http://www.ccmtutorials.org

@ccmtutorials

Identifying and Quantifying Hypoxemia

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The next part of the course is all about hypoxic respiratory failure. To treat hypoxemia you must understand it. The purpose of this sequence of tutorials is to lead up to discussions on CPAP and PEEP and provide a platform for understanding Pressure Controlled Modes of Ventilation. The first tutorial looks at oxyhemoglobin saturation, why the oxyhemoglobin dissociation curve is essential knowledge for the practicing clinician, how pulse oximeters work and how to quantify hypoxemia (A-aO2 gradient and PaO2/FiO2 ratio).