The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

OPTIMIZATION OF HIGH-FREQUENCY OSCILLATORY VENTILATION DURING THERAPEUTIC HYPOTHERMIA: A CASE STUDY

Carmen M. Drye1, Jaspal Singh2



Introduction: Therapeutic hypothermia is being increasingly used in the setting of post-cardiac arrest for cardiovascular and neurological protection. Meanwhile, high-frequency oscillatory ventilation (HFOV) is increasingly being used as a lung-protective strategy in the treatment of Acute Respiratory Distress Syndrome (ARDS) in adults. The effects of cooling of core body temperature upon settings used for high frequency oscillation have not been previously well-described. Here we describe a case in which therapeutic hypothermia and HFOV were employed simultaneously in a post-cardiac arrest patient who developed ARDS; moreover we describe our strategy to optimize usage of HFOV in such patients.

Case Summary:
A 53-year old male smoker with mild COPD experienced a witnessed ventricular fibrillation arrest for which he received 10 minutes of CPR and defibrillation with successful return of spontaneous circulation. He had been intubated and placed upon conventional mechanical ventilation upon arrival to our hospital. After prompt revascularization of his left anterior descending coronary artery, therapeutic hypothermia was induced through body surface cooling to a core temperature of 33C. Shortly afterwards, the patient developed severe hypoxic respiratory failure and worsening lung compliance; this was due to aspiration in the setting of cardiac arrest now progressing to ARDS. HFOV was employed, but interestingly the patient was easily able to achieve high frequencies of 8 Hz with low amplitudes; low arterial pCO2 levels were consistently obtained on this ventilation strategy employed during the cooling period. After the patient's body temperature was allowed to re-warm, pCO2 levels climbed and traditional HFOV settings were again utilized. Eventually the patient had an excellent recovery and was discharged to home.

Discussion:
The management of HFOV settings in patients undergoing therapeutic hypothermia can be altered to accommodate a lower metabolic rate with less carbon dioxide production. Importantly, we feel that higher frequencies and lower amplitude settings are optimal for such patients as they result in less tidal stretch and can be further lung-protective than most adult HFOV protocols encompass. Such a strategy seems optimal at least until more research is available to understand the complex interactions of hypothermia and treatment of ARDS.