Jukka Räsänen

Continuous positive airway pressure by face mask in acute cardiogenic pulmonary edema

The therapeutic efficacy of continuous positive airway pressure (CPAP) administered by face mask was studied in 40 patients with acute cardiogenic pulmonary edema and respiratory failure. Arterial blood gas values and pH, systemic arterial pressure, heart rate and respiratory rate were measured during administration of 30% oxygen with a high-flow face mask apparatus at ambient airway pressure. Twenty patients were then randomly chosen to continue ambient airway pressure breathing and 20 received 10 cm H2O of CPAP. The measurements were repeated 10, 60 and 180 minutes after therapy was initiated. During the first 10 minutes of CPAP treatment, arterial blood oxygen partial pressure increased 8 +/- 9 mm Hg (mean +/- 1 standard deviation), (p less than 0.01) and respiratory rate decreased 5 +/- 5 breaths/min (p less than 0.001). Systolic arterial pressure decreased 12 +/- 21 mm Hg (p less than 0.05), and heart rate by 10 +/- 11 beats/min (p less than 0.001). A decrease in respiratory rate by 2 +/- 5 breaths/min (p less than 0.05) was the only change that occurred in the control group. The improvement in arterial blood oxygenation persisted throughout the investigation period (p less than 0.05). Thirteen patients (65%) in the control group and 7 patients (35%) in the CPAP group met our criteria for treatment failure during the study (p = 0.068). Thus, CPAP administered by face mask improves gas exchange, decreases respiratory work, unloads circulatory stress, and may reduce the need for ventilator treatment in acute cardiogenic pulmonary edema.

Effect of Interfacing between Spontaneous Breathing and Mechanical Cycles on the Ventilation-Perfusion Distribution in Canine Lung Injury

BackgroundImproved matching between ventilation and perfusion (&OV0312;A/&OV0422;) has been proposed to be a major advantage of partial ventilatory support compared with controlled mechanical ventilation. This study was designed to determine whether a difference in gas exchange exists between partial ventilatory support techniques that allow unsupported spontaneous breathing to occur during any phase of the mechanical ventilatory cycle and those that provide mechanical support for each spontaneous inspiratory effort. MethodsTen anesthetized dogs with oleic acid-induced lung injury received, in random order, pressure-support ventilation (PSV) and airway pressure-release ventilation (APRV) with and without spontaneous breathing using equivalent airway pressure limits. Gas exchange was assessed by conventional blood gas analysis and by estimating the &OV0312;A/&OV0422; distributions using the multiple inert-gas elimination technique. ResultsDuring APRV, spontaneous breathing accounted for 10 ± 1% of the total expiratory minute ventilation. Breath-tobreath ventilatory support with PSV resulted in the highest total expiratory minute ventilation (P < 0.05). During spontaneous breathing with APRV, cardiac output increased from 3.9 ± 0.3 to 4.6 ± 0.41.min-1 (P< 0.05), arterial oxygen tension from 75 ± 3 to 107 ± 8 mmHg (P < 0.05), and oxygen delivery from 567 ± 47 to 719 ± 73 ml · kg min-1 (P < 0.05). PSV did not increase cardiac output, arterial oxygen tension, and oxygen delivery. Spontaneous breathing did not increase oxygen consumption. During APRV spontaneous breathing accounted for a 13 ± 2% decrease (P < 0.05) in blood flow to shunt units (&OV0312;A/&OV0422; < 0.005) and a 14 ± 2% increase (P < 0.05) in the perfusion of normal &OV0312;A/&OV0422; units (0.1 < &OV0312;A/&OV0422; < 10). Pulmonary blood flow distribution to shunt and normal &OV0312;A/&OV0422; units was similar during PSV and APRV without spontaneous breathing. Dead space (&OV0312;A/&OV0422; > 100) ventilation decreased by 6% during APRV with spontaneous breathing compared with PSV (P < 0.05). ConclusionsSpontaneous breathing superimposed on mechanical ventilation contributes to improved &OV0312;A/&OV0422; matching and increased systemic blood flow. Apparently, the spontaneous contribution to a mechanically assisted breath during PSV is not sufficient to counteract the &OV0312;A/&OV0422; maldistribution of positive pressure lung insufflation during acute lung injury.

Interfacing between Spontaneous Breathing and Mechanical Ventilation Affects Ventilation-Perfusion Distributions in Experimental Bronchoconstriction

The effect of interfacing between spontaneous and mechanical ventilation on ventilation-perfusion (VA/Q) distributions was determined during pressure-support ventilation (PSV) and in the presence and absence of spontaneous breathing during biphasic positive airway pressure (BIPAP) in 10 pigs with methacholine-induced bronchoconstriction. Whereas BIPAP without spontaneous breathing provides full and PSV breath-to-breath synchronized ventilatory support, BIPAP allows unrestricted spontaneous breathing throughout the mechanical cycle. Compared with BIPAP with and without spontaneous breathing, PSV effected an increase in ventilatory rate (p < 0.05) and a higher minute ventilation (VE) (p < 0.05). Spontaneous breathing during BIPAP accounted for 15 +/- 1% of the VE and increased cardiac output (CO) from 4.5 +/- 0.2 to 5.3 +/- 0.2 L/min (p < 0.05), Pao2 from 55 +/- 3 to 80 +/- 4 mm Hg (p < 0.05), and oxygen delivery (DO2) from 442 +/- 39 to 630 +/- 43 ml/min (p < 0.05). PSV did not increase CO, Pao2, and DO2. Spontaneous breathing did not affect oxygen consumption. During BIPAP spontaneous breathing accounted for a 15 +/- 2% decrease (p < 0.05) in blood flow to shunt units and a 16 +/- 2% increase (p < 0.05) in the perfusion of normal VA/Q units. Perfusion of shunt and normal VA/Q units was similar during PSV and BIPAP without spontaneous breathing. Dead space ventilation decreased with spontaneous breathing during BIPAP by 12% compared with PSV (p < 0.05). Dispersion of ventilation distribution was lowest during BIPAP. Uncoupling of spontaneous and mechanical ventilation during BIPAP improved gas exchange by allowing better VA/Q matching during experimental bronchoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxygen tensions and oxyhemoglobin saturations in the assessment of pulmonary gas exchange

We studied the theoretical basis for continuous monitoring of pulmonary gas exchange using arterial and mixed venous oximetry by examining the mathematical relationships between the calculated venous admixture (Qsp/Qt) and the ventilation-perfusion index, which is derived from oxyhemoglobin saturations. We compared this relationship with that between Qsp/Qt and its commonly used estimates: inspired oxygen concentration to arterial blood oxygen tension ratio, arterial to alveolar oxygen tension ratio, and alveolar-arterial oxygen tension difference. The relationship between Qsp/Qt and the oxygen tension-based indices is nonlinear and substantially influenced by changes in inspired oxygen concentration and arteriovenous oxygen content difference. Therefore, it is inaccurate within the clinically acceptable range of arterial blood oxygenation. In contrast, calculation of ventilation-perfusion index from arterial and mixed venous blood oxyhemoglobin saturations provides a linear estimate of Qsp/Qt that is minimally affected by alterations in inspired oxygen concentration or oxygen uptake and, therefore, will allow accurate continuous assessment of pulmonary gas exchange.

Neural network-based detection of esophageal intubation.

To improve the accuracy of early detection of inadvertent esophageal intubation, we designed, trained, and tested a neural network-based computer system to detect the mechanical differences between lung and esophagogastric ventilation. Ten 25 to 30-kg anesthetized swine were sequentially ventilated with tidal volumes of 9,12, and 15 mL/kg, using tubes placed in the trachea and in the esophagus, while flow and pressure waveforms were collected for 9–10 breaths. Gas remaining in the stomach was aspirated after each period of gastric ventilation. A computer program identified each mechanical inspiration, extracted the first 37 flow and pressure data points from each record, and normalized them to an equal amplitude. A back-propagation single-hidden-layer neural network was trained to identify the origin of flow and pressure waveforms as tracheal or esophageal. Ten different training and testing groups were assembled. In each group, data from nine subjects were used for training and data from the remaining subjects were used for testing. A total of 291 esophageal and 300 tracheal flow and pressure waveforms were analyzed by the network. The network identified esophageal intubation correctly during the first five breaths of all esophageal recordings. In one subject, the network identified the eighth esophageal breath as tracheal and could not identify three breaths. All tracheal intubations were identified correctly. Flow and pressure “signatures” of pulmonary and gastric ventilation are easily learned by a neural network. Therefore, neural-network recognition of esophageal intubation from flow and pressure signals is possible, and the development of an on-line detector for tracheal tube misplacement seems feasible. (Anesth Analg 1994;78:548–53)

Ventilatory pattern in respiratory failure arising from acute myocardial infarction. I. Respiratory and hemodynamic effects of IMV4 vs IPPV12 and PEEP0 vs PEEP10.

Positive end-expiratory pressure of 10 cm H2O (PEEP10) was compared with zero end-expiratory pressure (PEEP0), and intermittent mandatory ventilation (IMV), 4/min, with intermittent positive pressure ventilation (IPPV), 12/min, in 9 patients with pulmonary edema due to acute myocardial infarction (AMI). Systemic and pulmonary arterial pressures, pulmonary capillary wedge pressure (PCWP) and CVP, cardiac output (CO) and blood gases were measured during these four experimental interventions, and related parameters calculated. Paco2 was 39.3 ± 0.9 torr during IMV4 and 36.2 ± 1.3 torr during IPPV12, and PCWP remained between 20–30 mm Hg throughout the study. The ventilatory pattern was changed at random order with the patient serving as his own control. Both Pao2 and Pao2/Fio2 and Vo2 increased while venous admixture (Qsp/Qt) decreased with PEEP10. Cardiac and stroke indices (CI, SI) and oxygen delivery were lower with IPPV12 than they were with IMV4. Both left and right ventricular stroke work (LVSW, RVSW) were higher on IMV4. A moderate PEEP level (up to 10 cm H2O) seems beneficial in post-AMI pulmonary edema and has no significant hemodynamic side effects. The results indicate that of the four alternatives studied, IMV4 with PEEP10 is a ventilatory pattern of choice in the respiratory management of these patients, but each individual patient may require precise titration of each modality to achieve the optimal result.

Estimation of oxygen utilization by dual oximetry.

Total body oxygen utilization coefficient was estimated using continuous pulse and pulmonary artery oximetry (dual oximetry) in 17 patients with respiratory failure. Change in arterial and mixed venous oxygen saturations was induced by altering airway pressure. Continuous measurement of mixed venous oxygen saturation provided an accurate and linear estimate of oxygen utilization coefficient (r = -0.92), the true values being overestimated by 0.05 +/- 0.06 (mean +/- SD). Addition of pulse oximetry improved the correlation (r = 0.93) and decreased the difference between absolute values (0.02 +/- 0.06). Oxygen utilization coefficient can be estimated reliably in an online fashion using pulmonary artery oximetry. However, the use of dual oximetry will further improve the estimate.

Continuous breathing circuit flow and tracheal tube cuff leak: sources of error during pediatric indirect calorimetry.

ConclusionsAn indirect calorimeter in which measurement of Vo2 is based on internal constant flow rather than spirometry can be used to accurately measure Vo2 from a continuous-flow breathing circuit, if the total circuit flow is less than the internal flow. This limitation may restrict the use of continuous flow to a level below the subjects peak inspiratory flow. The accuracy of indirect calorimetry cannot be guaranteed for any amount of tracheal tube cuff leak. (Crit Care Med 1992; 20:1335–1340)

Ventilatory pattern in respiratory failure arising from acute myocardial infarction. II. PtcO2 and PtcCO2 compared to Pao2 and PaCO2 during IMV4 vs IPPV12 and PEEP0 vs PEEP10.

Transcutaneous oxygen and carbon dioxide tensions (PtcO2 and Ptcco2) were compared with Pao2 and Paco2 values in 9 patients with pulmonary edema due to acute myocardial infarction (AMI) measured during four experimental interventions: (a) intermittent mandatory ventilation (IMV) 4 /min + PEEP0 (cm H2O); (b) intermittent positive pressure ventilation (IPPV)12 + PEEP0; (c) IMV4 + PEEP10; and (d) IPPV12 + PEEP10. Ptco2 responded rapidly to the institution of PEEP, the rise correlating well with that in Pao2 both on IMV4 (r = 0.78) and IPPV12 (r = 0.87). On the other hand, correlations between Ptco2 vs CI and Pvo2 were poor (r being 0.45 and 0.24, respectively). Transcutaneous oxygen electrode is, thus, useful in monitoring patients with post-AMI pulmonary edema, as it rapidly reflects the effects of ventilatory therapy.A nonheated Ptcco2 sensor was used in 6 patients and a heated electrode in 3 patients. With the nonheated electrode, the correlation between Paco2 and Ptcco2 was good (r = 0.86) in 5 patients, while r in the 3 patients with the heated electrode was 0.73. One patient having a cardiac index of 1.6 L/min M2 showed a dissociation in Pco2 values. While Paco2 remained unchanged, Ptcco2 rose to 73 torr and within some minutes the patient had asystole. Ptcco2 tension generally shows good correlation with Paco2 and, thus, reflects ventilation. It may also prove to be useful in the early detection of critical low cardiac output states.

Changes in breath sound power spectra during experimental oleic acid-induced lung injury in pigs

To evaluate the effect of acute lung injury on the frequency spectra of breath sounds, we made serial acoustic recordings from nondependent, midlung and dependent regions of both lungs in ten 35- to 45-kg anesthetized, intubated, and mechanically ventilated pigs during development of acute lung injury induced with intravenous oleic acid in prone or supine position. Oleic acid injections rapidly produced severe derangements in the gas exchange and mechanical properties of the lung, with an average increase in venous admixture from 16 ± 12 to 62 ± 16% (P < 0.01), and a reduction in dynamic respiratory system compliance from 25 ± 4 to 14 ± 4 ml/cmH2O (P < 0.01). A concomitant increase in sound power was seen in all lung regions (P < 0.05), predominantly in frequencies 150-800 Hz. The deterioration in gas exchange and lung mechanics correlated best with concurrent spectral changes in the nondependent lung regions. Acute lung injury increases the power of breath sounds likely secondary to redistribution of ventilation from collapsed to aerated parts of the lung and improved sound transmission in dependent, consolidated areas.