James R Tomilson, MD F.C.C.P.;[unke...

James R Tomilson, MD F.C.C.P.;[unkeyable] K Scott Miller, MD FCCP; Daniel G Lorch, MD FCCP; Linda Smith, RRT; H David Reines, MD; and Steven A. Sahn, MD FCCP

pair hundred (200) consecutive medical and surgical patients requiring mechanical ventilation were come intoed into a prospective randomized trial of weaning according to either intermittent mandatory ventilation (IMV) or T-piece. Patients in these clusters were of similar age and sex and had the same total ventilation time (TVT) The research design provided equal time for each weaning fashion after specific criteria for oxygenation and ventilation were satisfied (Pa[O.sub.2] > 55 mm Hg in succession FL[o.sub.2] < 0.5; VE < 12 L/min and brace of the following four parameters: MVV > 2 VE VT > 5 ml/kg FVC > 10 ml/kg NIF [is les than or equal to] -20 cm [Hsub2]O) Of the original 200 patients 165 were enrolled into the weaning phase; 35 patients were withdrawn prior to weaning proper to the discretion of the attending physician or protocol error. Weaning time was not different between the IMV (53 [+ or -] 12 h mean [+ or -] SEM) and T-piece arranges (5.9[+ or -]1.4 h, p = NS) Of the 165 patients, 155 (93 percent) were weaned luckily by protocol, 79 in the IMV and 76 in the T-piece collection Of 155 patients, 136 (88 percent) were weaned onward the first attempt by protocol. Of the 19 who were not weaned, 11 third trial; three patients required three-day weans. We judge that clinically stable patients who require short-term mechanical ventilation and encounter standard bedside weaning criteria can be weaned efficiently from protocol using either IMV or T-piece techniques.

Since the advent of positive hurry ventilation, various methods for elective withdrawal of ventilatory support (weaning) have been proposed[1-3] The introduction of intermittent mandatory ventilation (IMV) as a [i]modus operandi[/i] of weaning has initiated a logomachy concerning the optimum weaning mode[4-7] Several studies have examined the attributes of T-piece and IMV weaning with inconclusive results[8-10] Criticism of these studies has included machine variability in relation to the work of breathing, improper application of the pair weaning methods, and the lack of a heterogeneous subject of attention population.[11-13]

We report the conclusions of a prospective, randomized trial of medical and surgical patients who were weaned from mechanical ventilation from either T-piece or IMV. To example the hypothesis that patients satisfying specific ventilatory and gas transfer criteria can wean rapidly according to either IMV or T-piece, a protocol was exhibited to ensure equal weaning time for all happy weaning attempts.

METHODS

Patient Population

through the whole extent of a 16-month period all adult patients requiring mechanical ventilation at the three hospitals in the Medical University of southern Carolina system (Medical University Hospital, Charleston Veterans Administration Medical Center and Charleston Memorial Hospital) were randomized into sum of two units groups following informed consent. All patients were ventilated with the same ventilator, a Bennett MA-1 (Puritan-Bennett Corp). IMV was administered with an H valve replacing the 9200 demand valve for the IMV circuit (Air Life-American Pharmaseal Co)

Experimental Design

To eliminate bias during the stabilization period of mechanical ventilation fit to possible differences in work of breathing using the sum of two units modes of ventilation, the brace groups were randomized according to months[14] During unmatched months (January, March, May, etc) patients were assigned to assisted mandatory ventilation (AMV) and during smooth months (February, April, June, etc) to the IMV way The stabilization period was defined as the time required for mechanical ventilation before the primary physician decided that the patient was "clinically stable." During the stabilization period, the primary physicians specified the rate, VT FI[o.sub.2], and even of PEEP. Only the ventilatory quality was predetermined by protocol; the patient remained onward the initial mode of ventilation until weaning was initiated. All patients had a [is greater than or equal to] 70 mm endotracheal tube in place before weaning was initiated. The weaning phase of the protocol was started when the patient was stable clinically and specific gas transfer and acid-base parameters were satisfied: (1) a Pa[O.sub.2] of > 55 mm Hg onward a FI[o.sub.2] of < 050; (2) a pH [is greater than or equal to ]730 and [is les than or equal to] 750; (3) pule [is less than or equal to] 5 cm [Hsub2] O; and (4) respiratory rate [is les than or equal to] 36/min.

Weaning parameters (spontaneous ventilatory measurements) were obtained according to the respiratory therapist at the beginning of each 8-h shift. Acceptable weaning parameters included: (1) minute ventilation (VE) < 12 L/min, and brace of the following four parameters: (2) maximum voluntary ventilation (MVV) > brace times VE; (3) tidal dimensions (VT) > 5 ml/kg carcass weight; (4) forced vital capacity (FVC) > 10 ml/kg carcass weight; and (5) negative inspiratory force (NIF) [is les than or equal to] -20 cm [Hsub2]O[15] When weaning parameters were satisfied, the patient was randomized immediately, according to hospital number, into either an IMV (even) or T-piece weaning custom (odd). The time from having acceptable weaning parameters to completion of a prosperous wean was recorded as weaning time (WT) Total ventilation time (TVT) was defined as the time from initiation of mechanical ventilation to completion of a prosperous wean. A successful wean was defined as discontinuation of mechanical ventilation for more than 48 h The decision to extubate the patient was made by way of the attending physicians.