Friday, March 25, 2011

SmartCare "Too Short for This Ride"

I remember when I was younger how upset I got over the fact that I was too short to ride a stand up roller coaster. It would have been not so traumatic; however my younger brother of two years was able to ride and antagonized me the rest of the day.
Yes, I was the Husky (short & chubby) kid and isolated from sports where height is an advantage.

Being too short for riding a roller coaster or playing basketball is a common occurrence, however what about being too short for a mode of mechanical ventilation?

Monday, March 21, 2011

Intrinsic PEEP (PEEP i)

Assessment of PEEPi based on a end-expiratory occlusion. Maneuver is high-lighted.

Intrinsic PEEP (PEEPi) is the difference between total PEEP and external PEEP, and provides information on the amount of dynamic hyper-inflation working on the respiratory system as well as the intra-thoracic organs. 

PEEPi has the same adverse effects of PEEP regarding both hemodynamics, barotrauma, and volutrauma.
PEEPi affects patient triggering by creating a inspiratory threshold load to be over come by the patient during spontaneous breathing.

Monday, March 14, 2011

Anesthesia Machines: Bellows vs. Piston

Correspondence 2008.

Attached are three documents:

1. Article on gas consumption in bellow driving anesthesia machines, comparing both Draeger & GE, this is one of the main reasons Draeger switched to a piston (to conserve on fresh gas, allowing for minimal flow anesthesia < or = 1/4 liter total fresh gas flow).

2. Abstract comparing the Apollo (piston) & Aisys (bellows) in regards to the accuracy of tidal volume delivery, with the new technology the Aisys can also accurately deliver both large & small tidal volumes. 

3. A letter I wrote to a customer on the limitations of the (Draeger's) Narkomed 2B (an older bellows machine) in regards to ventilating the morbidly obese patient. 

Wednesday, March 2, 2011

The Not So Smart, “SmartCare”

SmartCare/PS® or SmartCare Pressure support (™ Draeger Medical, Telford, PA) is the only automated weaning ventilator mode in the United States that relies entirely on a rule-based expert system[1]. Sales specialists are quick to insist that the software upgrade will pay for itself, and decease intensive care unit, ventilator days. 

Before considering such a large capital purchase expense, one should consider the following; "Is SmartCare quicker then in-place protocols?" PEEP restraints during spontaneous breathing trials, and high intrinsic diaphragmatic rates. 

Is it Quicker?

The term "automated" is a little misleading, since the practitioner first has to identify if the patient is even a candidate to perform spontaneous breathing trials.
After screening the patient the operator needs to change the mode to "Spontaneous", and make selections under the following categories; Body weight, Airway Type, Medical History, & Night Rest.

Entering patient data into these categories determine rules for the ventilator to follow, in regards to pressure support titration, respiratory rate limits, and end-tidal carbon dioxide limits (etCO2).
After initiating a SmartCare session (starting the mode), the ventilator adapts the level of pressure support[2] to maintain the patient in a "Zone of Respiratory Comfort"[3], slowly progressing to a spontaneous breathing trial (SBT) at the rule-based predetermined minimum pressure support[4].

The quickest a patient can transition and complete a spontaneous breathing trial from the initiation of SmartCare is one (1) hour and two (2) minutes. This is much slower then the many standard Respiratory Therapist Driven Weaning protocols I'm familiar with. The current SBT protocol at seven different hospitals I'm familiar with, the SBT trial time is thirty (30) minutes (this is for both surgical & medical patients).
So at these facilities with proactive weaning protocols, Smartcare would be unnecessary.

Positive Expiratory End-Pressure restraints

Another consideration with SmartCare is that it will not perform a SBT on PEEP settings ≥ 8 cmH2O. Some institutions will use higher PEEP during SBT's with the morbidly obese patients and patients that have trigger asynchronies, secondary to dynamic hyper-inflation.

 High diaphragmatic frequencies

Many patients receiving mechanical ventilation have high intrinsic diaphragm rates (≥ 30), even when very well assisted. This usually is unnoticed because the ventilator only measures machine or patient triggered breaths; however the patient's true rate may be higher. The practitioner may notice ventilator flow distortions, in which the patient is attempting to initiate a breath however the machine doesn't provide one (a.k.a ineffective efforts, or missed trigger attempts). 

Missed Trigger Attempts, notice the flow distortions (purple flow waveform) without associated breaths. Measured rate 12 bpm, however intrinsic rate 30 bpm.

This is a problem with the SmartCare classification models.

After pressure support is decreased and the patients true respiratory rate is unmasked (by the reduction in ineffective efforts)   a patient who has a rate of ≥ 30 bpm with no other manifestations of distress, will never be classified "Normal Ventilation", they will be classified as "Tachypnea" or "Severe Tachypnea".
 A seasoned Respiratory Therapist may notice that the patient is actually becoming more synchronous at the lower levels of support; the SmartCare model will fail the patient and increase the pressure support setting.

Dr. Magdy Younes stated in a lecture on ventilator synchrony[5], that in his sampled ventilator population that 50% of his ICU patients had a diaphragm rate > 30 bpm and 25% of these patients had a diaphragmatic rate > 35, even when very well assisted.
So, in this patient population SmartCare would be a poor choice for a weaning modality.

In my own ICU patients I sampled ~ 20 patients and I calculated that 7% had intrinsic diaphragmatic rates > 30, even in patients that the minute ventilation was 100% supported by the ventilator (e.g. 72kg IDW patient, preset minute ventilation of ≥ 7.2 liters).


SmartCare is an automated weaning platform which uses an intelligent control scheme to wean mechanically ventilated patients. Even though the system is automated the operator still needs to first determine if the patient is ready for SBT's and second select a few basic parameters before initiating the mode. In comparison to Respiratory Therapist Weaning protocols, SmartCare may be much slower in performing a SBT. In regards to higher PEEP levels and higher intrinsic diaphragmatic rates, SmartCare's models will not perform a spontaneous breathing trial in these patients.

[1] Chatburn, R. & Mireles, E. (2011). Closed-loop Control of Mechanical Ventilation: Description and Classification of Targeting Schemes. Respiratory Care. 1 (56).
[2] SmartCare continuously monitors EtCO2, Vt, & RR (measurements collected every 10 seconds). With these measurements the software classifies the patient status every 2-5 minutes. Based on the classification status the ventilator will ↑ or ↓ pressure support, or set-off an alarm condition.
[3] Zone of Respiratory Comfort is based on patients' weight selected & medical history.
[4] Minimum pressure support level is predetermined by Airway Type, active humidifier vs. heat moisture exchanger.
[5] Magdy Younes presented a lecture circa 2006, on ventilator asynchrony & PAV+ it was recorded for Covidien.

New auto-weaning ventilator might make pulmonologist obsolete