Patients

Twenty four patients (four women and 20 men), mean age 58.6 ±4.8 years (mean±SD), mean weight 72.3 ±10.2 kg, were investigated at least two hours after a classic intravenous anesthesia (midazolam 0.1 mg/kg/h, fentanyl 3.0 ±0.8 mg) for elective open- heart surgery. Patients presenting unstable angina, unilateral pul­monary pathology, chronic obstructive pulmonary disease, or asthma were excluded from the study. All patients gave their informed consent to the study which was accepted by the committee for ethics in human research of our institution.

Equipment

The HFJV was delivered with a respirator. Air and oxygen were supplied with a pressure of 4 atm, mixed with a blender and pulsed by an electronically controlled solenoid valve through a noncompli- ant 120 cm long and 0.7 cm inner diameter connecting tube. This tube was connected to an endotracheal jet-type tube with three separate lumens: the main lumen was used as conventional venti­lation, the first auxiliary lumen (1 mm diameter) as the tracheal airway pressure monitoring according to Brichant et al,® and the second auxiliary lumen as the “jet insufflation lumen” during HFJV (2 mm ID). Gas for entrainment by Venturi effect was provided by an anesthetic circuit connected to a respirator delivering a constant flow (30 L/min) of heated and humidified gas at the same FIo2 as jet ventilation. The expiration was allowed by an open T-shaped piece without a PEEP valve. The driving pressure of the ventilator, inspiratory/expiratory time ratio (I/E), and respiratory frequency were independently adjustable.
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The IPPV was administered using a volumetric respirator con­nected to the main lumen of the jet endotracheal tube. Gases were humidified and heated to 37°C using a cascade humidifier.

Respiratory and Hemodynamic Measurements

Airway pressure was measured using a 1 mm ID polyethylene catheter connected to a quartz pressure transducer and recorded on a chart recorder. The Paw was calculated electronically. Dynamic total respiratory compliance during IPPV was calculated by dividing peak airway pressure by inspiratory tidal volume.

Mean systemic arterial pressure, mean right atrial pressure, mean pulmonary arterial pressure, and pulmonary capillary wedge pressure were measured using a radial arterial cannula and a 7-F triple-lumen, Swan-Ganz catheter, respectively, connected to cali­brated quartz pressure transducers positioned at the midaxillary line. Gardiac output was measured in duplicate using thermodilu- tion technique and a bedside Edwards computer. Gardiac index, total systemic vascular resistance index, and total pulmonary vascular resistance index were calculated using standard equations.

Systemic arterial blood samples were drawn for the measurement of Pa02, PaC02 and pH with standard electrodes within one minute following the measurement of cardiac output. Oxygen saturation of hemoglobin (SaOJ was measured with a CO-oximeter.

The CBF was measured using a cerebrograph, according to a modified technique, after injection of 10 mCi of Xe diluted in a saline solution into the vena cava superior during end-expiration. The CBF was measured using three hemispheric detection probes placed on either side of the head at precisely identical anatomic localization. End-tidal 133Xe was monitored by constant aspiration of expired gas through a catheter placed in the main lumen of the endotracheal jet tube. An interval of 20 minutes was allowed between two measurements. Apcalis Oral Jelly

Based on the cerebral clearance of Xe, the following variables of cerebral hemodynamics were calculated (mean of six detectors): (1) F,: fast compartment flow which is accepted to be gray matter flow; (2) ISI: modified initial slope index according to Risberg et al representing the monoexponential slope of the early part of the Xe concentration curve between 0.5 and 1.5 minutes; this index reflects clearance from fast (2/3) and slow (1/3) compartments and represents the mean CBF; and (3) FF: fractional flow, ie, the ratio of gray matter flow over total CBF. The quality of CBF measure­ments was assessed by determination of the standard deviation between measured and theoretically expected curves. It was considered satisfactory when this standard deviation was below 1.5. In addition, individual variability of CBF determinations was documented by calculating the variation coefficient (SD/mean of the 24 patients) of CBF values during each of the experimental sessions.

Procedure

The effects of IPPV and HFJV were measured in the surgical intensive care unit two to four hours after the end of cardiac surgery. The study was started when the patient had reached a rectal temperature between 35.5 to 37.5°C, stable systemic hemodynam­ics with a mean systemic arterial pressure within ± 10 percent of preoperative value, and a stable sinus heart rate. Patients with postoperative cardiopulmonary instability were not included in the study. Prior to the beginning of the study, the patient received 5 mg morphine and 0.1 mg/kg pancuronium, intravenously.

Each patient was examined during three periods of 11 minutes separated by two intervals of 20 minutes: (1) first control period: IPPV1; (2) experimental period: HFJV; (3) second control period: IPPV2.

The FIo2 was maintained at 0.4. The inspiratory minute volume was ajusted to obtain a PaC02 between 4.5 to 5.5 kPa (IPPV: by changing tidal volume; HFJV: by changing driving pressure of the ventilator).

Statistical Analysis

The data (mean±SE) of the three experimental sessions were compared with an analysis of variance for repeated measurements followed by a modified Students f-test (Bonferroni method) when the F-ratio resulted in a p value <0.05.