Philip G. Boysen

Sleep apnea, hypopnea and oxygen desaturation in normal subjects. A strong male predominance.

Thirty asymptomatic men and 19 asymptomatic women were monitored during one nights sleep to determine the incidence of breathing abnormalities and oxygen desaturation in normal subjects. Twenty men accounted for 264 episodes of nocturnal oxygen desaturation or abnormal breathing. Women never experienced oxygen desaturation, and only three had a total of nine episodes of apnea. These sex differences were highly significant (P less than 0.003). In men, increasing age and obesity correlated positively with the incidence of nocturnal oxygen desaturation and abnormal breathing. Four asymptomatic men weighing more than 90 kg dropped their saturation to very low levels (68 to 72 per cent). Abnormal breathing and oxygen desaturation during sleep in subjects with chronic obstructive lung disease of the syndrome of hypersomnolence with periodic breathing may represent the superimposition of smoking or obesity on a normal tendency to snoring and oxygen desaturation in men.

Alcohol increases sleep apnea and oxygen desaturation in asymptomatic men

Using standard sleep techniques, we performed a placebo-controlled and randomized study to assess the effect of alcohol ingestion (2 ml/kg of body weight) on breathing and oxygen saturation during sleep. Twenty asymptomatic men volunteered for the two-night study: 11 were given a placebo on night 1, and alcohol on night 2 (group A); nine were given alcohol on night 1 and a placebo on night 2 (group B). We compared the incidence of sleep events (apnea, hypopnea and arterial oxygen disaturation) during the nights the subjects received alcohol and during the nights they received the placebo. Alcohol was associated with significant increases in the occurrence of the following: the number of sleep events (207 to 383,p less than 0.01), the events of arterial oxygen disaturation (118 to 226, p less than 0.01) and the number of apneic events (20 to 110, p less than 0.01). Alcohol had no significant effects on the number of times hypopnea occurred. Values obtained during sleep on the control night after alcohol ingestion also showed that the episodes of arterial oxygen desaturation remained statistically increased over control values before the ingestion of any alcohol (p = 0.01). These results show that in asymptomatic men alcohol ingestion increases the incidence of arterial oxygen desaturation and disordered breathing during sleep and that the increase in arterial oxygen desaturation persists for an additional night, even when no alcohol is consumed.

Sleep-disordered breathing and nocturnal oxygen desaturation in postmenopausal women.

Twenty postmenopausal women were monitored for disordered breathing (apnea and hypopnea) and oxygen desaturation during one nights sleep. These women were compared with 18 premenopausal women previously reported to have a low incidence of sleep-disordered breathing and nocturnal oxygen desaturation. Twelve of the 20 postmenopausal women had 102 episodes of sleep-disordered breathing and 118 episodes of oxygen desaturation, compared with only six episodes of apnea in two premenopausal women (P less than 0.01). Premenopausal women did not become desaturated. Of the postmenopausal women, 11 became desaturated; and in five of them saturation decreased to less than 85 per cent. Duration of sleep, and increased age and weight: height ratios, correlated significantly with the incidence of desaturation (P less than 0.01--P less than 0.05). Postmenopausal women resemble men with respect to disordered breathing during sleep and nocturnal oxygen desaturation. Protection from these sleep events in premenopausal women might be afforded by the respiratory stimulant effects of circulating progesterone.

Menopause, medroxyprogesterone and breathing during sleep

Twenty-one postmenopausal women were monitored for sleep-disordered breathing and nocturnal oxygen desaturation to evaluate the contribution of progestational hormones to the occurrence of these sleep events. For approximately one month 11 subjects received 30 mg of medroxyprogesterone (MPG) daily, and 10 received placebo tablets in a randomized, double-blind controlled study. Respiration, saturation and electroencephalography were monitored during one night of sleep before and one night after therapy. Contrasted with the low incidence of disordered breathing and desaturation in premenopausal women, 71 percent of the postmenopausal women had such events. In the placebo-treated group, all measured variables of sleep and breathing were identical on the two nights, which suggested that the findings of a single night of sleep monitoring may be representative of other nights of sleep. Although several subjects appeared to show improvement with MPG, only the maximum duration of apnea was significantly reduced the second night (p less than 0.03).

Lorazepam and midazolam in the intensive care unit: a randomized, prospective, multicenter study of hemodynamics, oxygen transport, efficacy, and cost.

OBJECTIVES To evaluate and compare the clinical efficacy, impact on hemodynamic and oxygen transport variables, safety profiles, and cost efficiency of sedation and anxiolysis with lorazepam vs. continuous infusion of midazolam in critically ill, intensive care unit patients. DESIGN Multicenter, prospective, randomized, open-label study. SETTING Teaching hospitals. PATIENTS Ninety-five critically ill, mechanically ventilated patients with fiberoptic pulmonary artery catheters in place were randomly assigned to receive short-term (8 hrs) sedation with either intermittent intravenous injection lorazepam (group A, n = 50) or continuous intravenous infusion midazolam (group B, n = 45) titrated to clinical response. MEASUREMENTS AND MAIN RESULTS The severity of illness, demographic characteristics, levels of anxiety and agitation, hemodynamic parameters, oxygen transport variables, quality of sedation, nursing acceptance, and laboratory chemistries reflecting drug safety were recorded. There were no significant differences with regard to demographic data, hemodynamic and oxygen transport variables, or levels of anxiety/agitation between the two groups at baseline, 5 mins, 30 mins, and 4 and 8 hrs after administration of sedation. There were no significant differences in the quality of sedation or anxiolysis. Midazolam-treated patients used significantly larger amounts of drug for similar levels of sedation and anxiolysis (14.4 +/- 1.2 mg/8 hrs vs. 1.6 +/- 0.1 mg/8 hrs, p = .001). Both drugs were safely administered and patient and nurse satisfaction was similar. CONCLUSIONS Sedation and anxiolysis with lorazepam and midazolam in critically ill patients is safe and clinically effective. Hemodynamic and oxygen transport variables are similarly affected by both drugs. The dose of midazolam required for sedation is much larger than the dose of lorazepam required for sedation, and midazolam is therefore less cost-efficient.

Accurate determination of end-tidal carbon dioxide during administration of oxygen by nasal cannulae

Measurement of end-tidal carbon dioxide tension (PetCO2) by mass spectrometry or infrared capnometry provides a clinically useful approximation of arterial carbon dioxide tension (PaCO2) in intubated patients. Although several devices have been proposed to samplePetCO2 during spontaneous breathing (i.e., unintubated patients receiving supplemental oxygen), thus far no reports have documented their efficacy. This article reports the use of an easily constructed modification of simple nasal cannulae that permits accurate sampling ofPetCO2 during oxygen administration to unintubated patients. After amputation of the closed tip, a cap from a syringe was inserted via a slit made at the base into one prong of a pair of nasal cannulae. A capnometer was connected to the syringe cap, andPetCO2 and PaCO2 were determined simultaneously during the administration of 3 L/min oxygen via nasal cannulae to 21 normocapnic patients. The PaCO2 —PetCO2 gradients were calculated and compared with values obtained in the same patients after intubation and mechanical ventilation. No significant difference was found between the calculated gradients with nasal cannulae (2.09±2.18 mm Hg) versus intubation (2.87±2.82 mm Hg). Simultaneous oxygen administration and accurate sampling ofPetCO2 may be achieved in unintubated patients by using this easily constructed modification of nasal cannulae.

High-frequency percussive ventilation compared with conventional mechanical ventilation

In seven patients with severe respiratory distress, conventional mechanical ventilation and PEEP were used initially for respiratory support, which was changed to high-frequency percussive ventilation (HFPV) at the same level of airway pressure and FIO2. During both modes of ventilation, patients could breathe spontaneously via a low-threshold demand valve. With HFPV, PaO2 improved significantly (p < .01) compared with PaO2 during conventional methods. Cardiac output was unaffected by the change to HFPV.

Graded exercise testing and postthoracotomy complications

A controversy exists over whether or not preoperative exercise testing can predict postthoracotomy complications. This study was designed to evaluate the usefulness of a presurgical exercise protocol in patients with lung disease, but no evidence of cardiac disease. Seventy patients underwent baseline pulmonary function testing and split function perfusion studies, when indicated, to calculate predicted postoperative pulmonary function. Noninvasive data were incrementally collected from 17 patients by using a treadmill exercise tolerance test that was designed to elicit maximal performance. Inhaled and exhaled gas flow and volume, the partial pressure of O2 and CO2, maximal O2 consumption (VO2max), and maximal minute ventilation (VE max) were measured. The breathing and heart rate reserves were calculated by standard formulae in an attempt to separate cardiac from pulmonary exercise limitation. Two patients had postoperative cardiopulmonary complications after thoracotomy and lung resection, and six patients had noncardiopulmonary complications. There was no significant prognostic relationship among VO2max, VE max, maximum O2 pulse, and the incidence of postoperative cardiopulmonary complications. The percentages of predicted VE max and predicted maximum heart rate were related to the occurrence of total complications, but not specifically to cardiopulmonary complications. The results emphasize the difficulty in attempting to exercise thoracotomy candidates with chronic lung disease to maximal performance. Excluding patients from further surgical consideration because of exercise limitation is not feasible based on these data.

Failure of high frequency jet ventilation to ventilate patients adequately during extracorporeal shock-wave lithotripsy

High frequency jet ventilation (HFJV) has been used successfully for extracorporeal shock-wave lithotripsy (ESWL) to diminish renal stone movement during general anesthesia and to decrease the number of shocks delivered inadvertently to healthy tissue (1). Although usually uneventful, we present here eight cases out of 407 in which HFJV failed to ventilate patients undergoing ESWL, which necessitated the use of conventional mechanical ventilation (CMV).

A mechanical model of spontaneous ventilation.

An Emerson 3-PV ventilator was modified to function as a model for spontaneous ventilation. Respiratory rates, tidal volumes, inspiratory/expiratory time ratios, and flow rates were adjusted to produce sinusoidal inspiratory and expiratory flow patterns that mimicked physiologic ventilation.