Background
Mid-Frequency Ventilation was first described in the medical literature by Mireles-Cabodevila & Chatburn in 2008 [1]. The authors describe Mid-Frequency Ventilation (MFV) as setting ventilator frequencies greater than 35 cycles per minute, during Pressure Control-Continuous Mandatory Ventilation (PC-CMV) to provide increased minute ventilation support in patients with severe Acute Respiratory Distress Syndrome (ARDS). In this initial article the authors tested their theory on both a computer simulation model and bench study using newer generation conventional intensive care unit ventilators. Both test simulations where successful.
In 2010 Mireles-Cabodevila & al. applied the theory in a live neonatal & pediatric animal model; the results reinforced the previous hypothesis showing the potential benefits of MFV [2].
As of to date there have been no cases reported in the medical literature of MFV being applied in humans. I previously presented a case where MFV was applied for a patient with serve hypercapnia; however this was never submitted for publication [3].
The following case involves using MFV on a sophisticated transport ventilator, thus reinforcing the versatility of MFV. The operator does not need a special ventilator (e.g. oscillator) or mode (e.g. APRV). Even though one does not need a specific ventilator the device still needs to safely and effectively ventilate injured lungs. The transport ventilator used during this case is considered a “sophisticated” transport ventilator, one that can effectively ventilate injured lungs [4].
Case Summary
A 69 year old male patient was found by emergency medical services (EMS) in full cardiac arrest, with an initial rhythm of ventricular fibrillation. The patient was defibrillated and went into Pulses Electrical Activity. The patient received CPR, manual ventilation via resuscitation bag, fluid boluses and was administered a total of 4 epinephrine, 1 atropine, & 1 sodium bicarbonate before arriving to the emergency room (ER). Upon ER arrival the patient had a blood pressure of 134/73, pulse rate of 72, and was still manually ventilated. EMS had difficulty intubating the patient and it was approximately 30 minutes before the airway could be secured. After intubation ~ 20-30 ml of vomitus was suctioned from the endotracheal tube.
Initial ABG was: pH 7.08, paCO2 62, paO2 76 (on 100% FiO2)
Mechanical ventilation was initiated via a transport ventilator after intubation, with target tidal volumes of 8cc/kg/IDBW, resulting in extremely high peak airway pressures and plateau pressures.
The patient was switched to PC-CMV with a set pressure of 30 cmH20 (which obtained an exhaled Vt of ~ 4.5 ml/kg/IDBW, PEEP + 8, FiO2 70%. Calculated minute ventilation (VE) requirements where 200% of predicted, by IDBW (Radfords nanogram). The respiratory rate was set at a frequency of 40 breaths per minute & the I-time was adjusted for a 50% duty cycle. This obtained a minute ventilation of ~ 13 lpm, and the patient still triggered additional breaths resulting in a total VE of ~ 16 lpm.
The patient went immediately to the catherization lab for intervention and underwent cardiac catherization with 2 stent placements.
ABG on MFV: pH 7.23, paCO2 59, PaO2 68, HCO3 24.6, BD -3
The procedure was successful however the patient’s prognosis was still grim due to the initial cardiac arrest with resultant acute respiratory failure, both hypoxemic as well as hypercapnic, requiring high ventilatory support. The patient also aspirated gastric contents. The patient was transferred to the intensive care unit for further monitoring.
In the ICU the patient was switched to a conventional ICU ventilator and the respiratory rate was decreased within an hour.
The patient recovered from the cardiac catherization and from the initial lung insult; conversely the patient experienced an anoxic brain injury from the cardiac arrest. The patient experienced a lengthy ICU stay and was eventually trached and weaned off mechanical ventilation. After the ICU stay the patient was transferred to a long term care facility.
Discussion
Even though the patient did not experience an ideal recovery, the lung protective strategies implemented prevented further lung injury. Utilizing MFV provided sufficient ventilation in helping correct a severe acidosis, while maintaining lung protective goals (Vt target 4-6 ml/kg/IDBW & plateau pressures < 30 cmH2O). As demonstrated MFV can be applied using a sophisticated transport ventilator, giving the practitioner an additional option in regards to ventilating the patient with acute lung injury.
[1]. Mireles-Cabodevila, E. & Chatburn, R. (2008). Mid-Frequency Ventilation: Unconventional use of Conventional Mechanical Ventilation as a Lung Protection Strategy. Respiratory Care. 53 (12): 1669-1676.
[2]. Mireles-Cabodevila, E. & al. (2010). Proof of Concept: Mid-Frequency Ventilation in a neonatal & Pediatric Live Animal Model. American Journal of Thoracic Surgery.
[3]. Richey, S. (2010). Application of Mid-Frequency Ventilation.
http://kscottrichey.blogspot.com/2010/09/application-of-mid-frequency.html
[4]. Chipman, D. et. Al. (2007). Performance Comparison of 15 transport Ventilators. Respiratory Care. 52(6): 740-751.
