The effects of inverse ratio ventilation on intracranial pressure: a preliminary report.
OBJECTIVE
To determine the effects of pressure control inverse ratio ventilation [PC-IRV], as compared with volume controlled normal ratio ventilation [VC], on the intracranial pressure [ICP] of patients with severe head injury.


METHODS
A prospective study with unblinded intervention.


METHODS
The Intensive Therapy Unit of a base hospital.


METHODS
Nine cases of head injury requiring mechanical ventilation and intracranial pressure monitoring were studied.


METHODS
Patients were twice transferred from VC (1:E ratio 1:2) to PC-IRV (1:E ratio 2:1). Firstly, tidal volume was maintained at an equal value. Secondly, end tidal CO2 was maintained at an equal value. No other changes were made to ventilation, vasopressor therapy or ICP control.


RESULTS
Measurements were taken of ICP, mean arterial pressure (MAP) end tidal CO2 and respiratory parameters. In the first observation, there were significant changes in peak inspiratory pressure (PIP), mean airway pressure (Paw) and intrinsic positive end expiratory pressure (PEEP) but not for ICP, end tidal CO2, MAP and cerebral perfusion pressure (CPP). The correlation between change in ICP and change in end tidal CO2 was r = -0.74. In the second observation there were significant changes in tidal volume, PIP, Paw and intrinsic PEEP but not for ICP, MAP and CPP. The correlation between the change in ICP and the change in Paw was insignificant.


CONCLUSIONS
PC-IRV has a minimal net effect on ICP. Changes in ICP correlate more strongly with changes in CO2 than changes in Paw.
Clarke
J P
JP
Department of Anaesthesia, Royal Adelaide Hospital, South Australia.
D000293:Adolescent; D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology; D006259:Craniocerebral Trauma / Q000150:complications / Q000503:physiopathology / Q000628:therapy*; D005260:Female; D006801:Humans; D007427:Intracranial Pressure; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D017063:Outcome Assessment, Health Care; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000379:methods*; D013990:Tidal Volume