Jun 16, 2017
In a very simplified approach to ventilation we can separate our vent strategies into either an obstructive or injury patient. Obstructive patients are known to have an increased amount of effort on the exhalation phase of the respiratory cycle. Exhalation is a passive phase of breathing and when a reduction in airway caliber occurs, there is little recruitment of muscle to assist in the process. A putative practice is to reasonably reduce the minute volume and increase the exhalation time. With the obstructive patient already having an underlying pathology that causes carbon dioxide (c02) retention, the reduction in minute volume is usually well tolerated. The injury patient is essentially for everyone else. In an attempt to reduce the frequency of barotrauma and acute lung injury, evidence suggests the routine use of lower tidal volumes (Vt). A standard practice is to start off around 6-8cc/kg of IBW. This strategy is the go-to method for patients presenting with decrease lung compliance due to infiltrates and in the worst case scenario Acute Respiratory Distress Syndrome (ARDS). The clinician usually battles the task of adequate oxygenation in this subset. Recruitment maneuvers are performed in an attempt to increase the surface area for gas exchange. These techniques are performed with inspiratory maneuvers, and maintained with PEEP. I believe we have seen vast improvement in the way we care for each of these disease processes. I don’t think we have opened up enough dialogue as to how to approach when these two pathologies collide. Before You Touch The Ventilator: There are a series of thought processes one must intuitively execute before we initiate a ventilator strategy. The first is recognizing that the sicker the patient is, the wide the pulse ox latency will be. A healthy individual will have an approx. 30 second lag from central to peripheral circulation. This increases as hemodynamics deteriorate. It is not uncommon for a septic patient to have over a 2 minute lag time. What does this mean for you? Don’t expect abrupt changes in oxygenation after each turn of the dial. A good practice is to allow two minutes between an adjustment and a response. For example, if I set my positive end expiratory pressure (PEEP) to 10, I shouldn’t briskly crank it to 15 without allowing an appropriate amount of time. Get in the habit of figuring out your PaC02/ETc02 gradient. Unless you are able to analyze blood gas values on transport, this is your time to figure out what your Knowing that the COPD patient lives off of a hypoxic drive, we can reasonably conclude that a saturation of 90% is a good goal for oxygenation. With an assumed right shift on the oxyhemoglobin disassociation curve, this would require a Pa02 of approx. 90-100 mmhg. The Strategy: To initiate this strategy we are assuming the patient is hypoxic and hypercapneic. Step 1. Start with 6cc’s /kg of IBW & Frequency of 12 bpm. Fi02 should be set at 1.0. Step 2. Auto Peep and Pplat should be assessed. Step 3. Set extrinsic PEEP to 75% of Auto Peep. This will aid in stenting open the terminal bronchiole and make up for diseased elastin. Preventing cyclic opening is a secondary benefit of this approach. Step 4. If VTE is < 50% of desired VT increase I time to 2 seconds for 2 minutes and watch for VTE to increase. This is a 5 second total cycle time and at a respiratory rate of 12 will give you a 2:3 ratio. Step 5. If after two minutes your VTE is at least 75% of your target Vt, dial the I time back to 1 second and maintain recruitment with PEEP.