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PubMed1995

Large tidal volume ventilation does not improve oxygenation in morbidly obese patients during anesthesia.

Eight morbidly obese patients (body mass index [BMI] = 46) were studied during general anesthesia and controlled mechanical ventilation. To evaluate the effect of large tidal volume ventilation on oxygenation and ventilation, the baseline 13 mL/kg tidal volume (VT) (calculated by the ideal body weight) was increased in 3 mL/kg volume increments to 22 mL/kg, while ventilatory rate (RR) and inspiratory time (TI) were kept constant. Each volume increment was maintained for 15 min. Gas exchange was assessed by measuring the arterial blood oxygen tensions, and calculating the indices of alveolar-arterial oxygen tension difference [P(A-a)O2] and arterial/alveolar oxygen tension ratio (a/A). Peak inspiratory airway pressure (Ppeak), end-inspiratory airway pressure (Pplateau), and compliance of the respiratory system (CRS) were recorded using the Capnomac Ultima (Datex, Helsinki, Finland) on-line respiratory monitor. Increasing tidal volumes to 22 mL/kg increased the recorded Ppeak (26.3 +/- 4.1 vs 37.9 +/- 3.2 cm H2O, P < 0.008), Pplateau (21.5 +/- 3.6 vs 27.7 +/- 4.3 cm H2O, P < 0.01), and CRS (39.8 +/- 7.7 vs 48.5 +/- 8.3 mL/cm H2O) significantly without improving arterial oxygen tension and resulted in severe hypocapnia. Since changes in arterial oxygenation were small and not statistically significant, mechanical ventilation of morbidly obese patients with large VTS seems to offer no advantage to smaller (13 mL/kg ideal body weight) VTS.

Adult↗

PubMed1976

Sinus arrhythmia in man: influence of tidal volume and oesophageal pressure.

The effect of tidal volume (VT) and of the intrathoracic pressure (Poes) on the respiratory sinus arrhythmia (RSA) was studied in healthy subjects. They breathed into a spirometer with a VT of 1, 1.5, and 2 1, at a standardized, slow respiratory rate, 6-min-1 (A). Poes was varied by (B) adding a negative inspiratory pressure (NIP) of 5 cm of water and by (C) intermittent positive pressure ventilation (IPPV) at identical VT and respiratory frequency. In separate study (D), intermittent negative pressure ventilation (INPV) was induced by applying negative pressure on the thorax. In A, increasing VT provoked an augmented RSA by a more marked tachycardia as well as bradycardia. On increasing the amplitude of Poes in B, RSA was somewhat more marked due to a lower minimum heart rate. Whem comparing respiratory cycles that had similar Poes but a different VT, the larger VT caused a slight increase in the RSA amplitude due to a more marked deceleration of the heart rate. IPPV almost abolished RSA, whereas INPV did not reduce the arrhythmia. It is concluded that pulmonary stretch reflexes to a minor extent contribute to RSA, whereas the hypothesis of a central nervous origin does not gain support. Cardiovascular reflexes remain the main possible cause of RSA.

Adult↗

PubMed2003

Enhancement of the endotoxin recognition pathway by ventilation with a large tidal volume in rabbits.

Ventilation with a small tidal volume (V(t)) is associated with better clinical outcomes than with a large V(t), particularly in critical settings, including acute lung injury. To determine whether V(t) influences the lipopolysaccaharide (LPS) recognition pathway, we studied CD14 expression in rabbit lungs and the release of TNF-alpha by cultured alveolar macrophages after 240 min of ventilation with a large (20 ml/kg) vs. a small (5 ml/kg) V(t). We also applied small or large V(t) to lungs instilled with 50 microg/kg of LPS. The alveolar macrophages collected after large V(t) ventilation revealed a 20-fold increase in LPS-induced TNF-alpha release compared with those collected after small V(t) ventilation, whereas TNF-alpha was undetectable without LPS stimulation. In animals ventilated with a large V(t), the expression of CD14 mRNA in whole lung homogenates and the expression of CD14 protein on alveolar macrophages, assessed by immunohistochemistry, were both significantly increased in the absence of LPS stimulation. A large V(t) applied to LPS-instilled lungs increased the pulmonary albumin permeability and TNF-alpha release into the plasma. These results suggest that mechanical stress caused by a large V(t) sensitizes the lungs to endotoxin, a phenomenon that may occur partially via the upregulation of CD14.

Albumins↗

PubMed1998

[The application of low tidal volume pressure-controlled ventilation in patients with acute respiratory distress syndrome].

Low tidal volume pressure-controlled ventilation therapy was used in 32 patients with ARDS. There were resulted a lower peak inspiratory pressure (PIP) level than that of control group, thus a decline in incidence of overventilation and the overventilation induced mortality. The results suggest that low tidal volume pressure-controlled ventilation may consider as preferred ventilation mortality in management of ARDS.

Adolescent↗

PubMed1994

Effect of body position on spontaneous respiratory rate and tidal volume in patients with obesity, abdominal distension and ascites.

BACKGROUND: Nursing textbooks and tradition suggest that the high-Fowler's position is best to optimize diaphragmatic excursion and effective breathing pattern. The optimal position for intubated patients with obesity, ascites or abdominal distention has yet to be determined but is important because weaning trial outcomes may reflect the effect of position rather than weaning trial tolerance. OBJECTIVE: To determine the body position that optimizes breathing pattern (tidal volume and respiratory rate) in spontaneously breathing, intubated patients with a large abdomen. METHODS: Nineteen intubated patients with abdominal distention, ascites or obesity who were on continuous positive airway pressure or the pressure support ventilation mode were studied in the 0 degrees, 45 degrees, 90 degrees and reverse Trendelenburg's at 45 degrees positions for 5 minutes prior to data collection. RESULTS: The RT at 45 degrees position resulted in a significantly larger tidal volume and lower respiratory rate than the 90 degrees position in intubated, spontaneously breathing patients with a large abdomen. The 45 degrees position resulted in a significantly lower respiratory rate than at 90 degrees; however, no difference in tidal volume was demonstrated. DISCUSSION: A high respiratory rate and low tidal volume potentiates atelectasis and ultimately failure to wean. It is important that the effect of positioning on breathing pattern in intubated patients be determined so that care planning results in optimal outcomes. CONCLUSIONS: The results of this study have implications for the selection of chair and bed positioning during weaning trials.

Adult↗

PubMed1991

Large tidal volume ventilation improves pulmonary gas exchange during lower abdominal surgery in Trendelenburg's position.

Impaired pulmonary gas exchange is a common complication of general anaesthesia. Periodic hyperinflation of the lungs and large tidal volume ventilation were the first preventive measures to be widely embraced, but their effectiveness in clinical practice has never been clearly established by controlled clinical studies. To assess their effects in high-risk patients we studied 24 adults having lower abdominal gynaecological surgery in the Trendelenburg (head down) position. Pulmonary oxygen exchange was determined during four steady-states: awake control (AC), after 30 min of conventional tidal volume (CVT, 7.5 ml.kg-1) or high tidal volume (HVT, 12.7 ml.kg-1) ventilation, introduced in random order, and five minutes after manual hyperinflations (HI) of the lungs. The patients' lungs were ventilated with air/O2 by an Ohmeda volume-controlled ventilator via a circle system. The FIO2 was controlled at 0.5, and FETCO2 was controlled by adding dead space during HVT. Arterial blood gas analysis was used to calculate the oxygen tension-based indices of gas exchange. There was significant deterioration of (A-a)DO2 at 30 min in Group A, whose lungs were first ventilated with CVT (81.6 +/- 7.2 to 166.8 +/- 13.7 mmHg, P less than 0.001); but not in Group B, whose lungs were first ventilated with HVT (77.0 +/- 9.9 to 104.4 +/- 16.8 mmHg). When Group A and B data were pooled there was no difference between randomized CVT and HVT, but improvement occurred after HI. In this model of compromised O2 exchange large inflation volumes (HVT and HI) were of considerable clinical benefit, HVT prevented and HI reversed the gas exchange disorder.

Abdomen↗

PubMed2005

The influence of flow rate on breathing circuit compliance and tidal volume delivered to patients in mechanical ventilation.

Assessment of the gas volume that actually reaches the airways during mechanical ventilation appears to be a difficult task because of the presence of the breathing circuit. Most ventilators measure tidal volume at ventilator level making the determination of circuit compliance a critical factor in estimating the actual tidal volume. Tubing compliance can be measured in several ways and its value, being strongly dependent on the compressibility of the gas, may significantly differ depending on the measurement procedure. This paper addresses the dependence of the circuit compliance on the flow rate, and a theoretical hypothesis on the pneumatic behaviour of the breathing circuit is formulated and experimentally validated, with several tests conducted in vitro on an infant analogue. The dependence of the compliance on the inspiratory flow is experimentally assessed, and differences of about 20% on the measured value in the common flow range utilized in infant ventilation have been found, with consequent estimation errors of the volume delivered. Experimental tests show that the correct value of the tidal volume actually delivered to the patient can be reliably estimated from measurements performed at the ventilator level if the circuit compliance is determined with the same flow rates that will be utilized in mechanical ventilation.

Animals↗

PubMed2002

Setting the frequency-tidal volume pattern.

Alveolar (and thus arterial) P(O2) and P(CO2) clearly depend on minute ventilation. However, we need to balance gas exchange goals against the risk of overstretching, especially of the healthier regions of the lung. The plateau pressure is probably the best easily-obtained marker of the risk of stretch in the lung, and a commonly quoted threshold is 30--35 cm H(2)O, the normal maximum transalveolar pressure at total lung capacity. In establishing the proper balance of stretch versus gas exchange, we need to address what levels of pH and P(aO2) we consider acceptable. There are no good data to guide us on the lowest tolerable pH, but 7.2 is commonly quoted in the literature, and 7.15 was the lower limit of acceptability in the ARDS (acute respiratory distress syndrome) Network trial. P(O2) levels as low as 55 mm Hg may be well tolerated, provided there is reasonable oxygen delivery. In distributing the desired minute volume between respiratory frequency and tidal volume (V(T)), a V(T) of 6 mL/kg ideal body weight has been shown to improve ARDS outcome, compared to 12 mL/kg. Thus, 6 mL/kg should be the "start point." Adjustments upward could be considered the plateau pressure is acceptable, in order to improve gas exchange or comfort. Conversely, downward adjustments should be considered if the plateau pressure is high and the gas exchange is acceptable. Frequency is adjusted for the desired minute ventilation. It must be recognized, however, that as frequency (and minute ventilation) increases, the risk of air trapping and intrinsic positive end-expiratory pressure (PEEP) increases. Just like applied PEEP, intrinsic PEEP increases the baseline pressure and stretch upon which the V(T) is delivered. The end-inspiratory stretch increases accordingly. The shape and duration of the flow pattern may affect gas mixing, recruitment, cardiac function, intrinsic PEEP buildup, and patient comfort. It is also conceivable that certain flow patterns can produce an acceleration injury. Although small clinical trials using physiologic end points espouse certain flow patterns, there are no good outcome data at present supporting any particular approach. Some authors suggest that high-frequency ventilation (HFV) might be considered an "ultimate" lung-protective strategy. HFV creates considerable intrinsic PEEP, which, when coupled with sustained inflation maneuvers, can provide substantial alveolar recruitment. In addition, the small V(T) of HFV prevents excessive end-inspiratory distention. Although considerable clinical data support the use of HFV in pediatric patients at risk for ventilator-induced lung injury, there are few data from adults. Whether HFV will prove valuable in well-designed open lung strategies in the adult population still has to be determined.

Carbon Dioxide↗

PubMed1994

Sustained inflations improve respiratory compliance during high-frequency oscillatory ventilation but not during large tidal volume positive-pressure ventilation in rabbits.

OBJECTIVE: To determine whether volume recruitment maneuvers that induce significant lung reexpansion during high-frequency oscillatory ventilation are also of value during conventional positive-pressure ventilation. DESIGN: Crossover comparison of volume recruitment maneuvers administered during high-frequency oscillatory ventilation and positive-pressure ventilation in normal and surfactant-deficient adult rabbits. SETTING: Laboratory. SUBJECTS: Nineteen adult New Zealand white rabbits (weight 2.3 to 3.3 kg). METHODS: Respiratory system compliance was measured plethysmographically before and after sustained inflations in six normal and five saline-lavaged anesthetized rabbits, using both ventilators over a range of mean and end-expiratory pressures. RESULTS: Under conditions where sustained inflations during high-frequency oscillatory ventilation at 15 Hz increased respiratory system compliance 50 +/- 28%, sustained inflations during conventional positive-pressure ventilation at a rate of 30 to 40 breaths/min and tidal volumes of 14 to 17 mL/kg did not change respiratory system compliance (mean change 3 +/- 9%). Sustained inflations during conventional positive-pressure ventilation could not be made effective by increasing the positive end-expiratory pressure level to equal the mean pressure during high-frequency oscillatory ventilation. Sustained inflations on conventional positive-pressure ventilation remained ineffective up to positive end-expiratory pressure levels of 17.5 cm H2O. In lavaged rabbits, sustained inflations increased respiratory system compliance 49 +/- 14% during high-frequency oscillatory ventilation and 0 +/- 3% during conventional positive-pressure ventilation. Sustained inflations increased compliance significantly during conventional positive-pressure ventilation only when ventilating with tidal volumes of 7 mL/kg and low end-expiratory pressure. CONCLUSIONS: Active recruitment of lung volume during high-frequency oscillatory ventilation appears necessary, because small pressure/volume cycles adequate to support high-frequency gas transport are not able to reexpand atelectatic lung units without the aid of a sustained inflation. We conclude that volume recruitment maneuvers improve respiratory system compliance substantially during high-frequency oscillatory ventilation at 15 Hz, but these maneuvers offer potential risk and no benefit during conventional positive-pressure ventilation with large tidal volumes or when using smaller tidal volumes and high levels of positive end-expiratory pressure.

Airway Resistance↗

PubMed2002

Tidal volume single-breath washin of SF6 and CH4 in transient microgravity.

We performed tidal volume single-breath washins (SBW) by using tracers of different diffusivity and varied the time spent in microgravity (microG) before the start of the tests to look for time-dependent effects. SF(6) and CH(4) phase III slopes decreased by 35 and 26%, respectively, in microG compared with 1 G (P < 0.05), and the slope difference between gases disappeared. There was no effect of time in microG, suggesting that neither the hypergravity period preceding microG nor the time spent in microG affected gas mixing at volumes near functional residual capacity. In previous studies using SF(6) and He (Lauzon A-M, Prisk GK, Elliott AR, Verbanck S, Paiva M, and West JB. J Appl Physiol 82: 859-865, 1997), the vital capacity SBW showed an increase in slope difference between gases in transient microG, the opposite of the decrease in sustained microG. In contrast, tidal volume SBW showed a decrease in slope difference in both microG conditions. Because it is only the behavior of the more diffusive gas that differed between maneuvers and microG conditions, we speculate that, in the previous vital capacity SBW, the hypergravity period preceding the test in transient microG provoked conformational changes at low lung volumes near the acinar entrance.

Adult↗

PubMed2003

One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure is injurious in the isolated rabbit lung model.

UNLABELLED: We tested the hypothesis that one-lung ventilation (OLV) with high tidal volumes (VT) and zero positive end-expiratory pressure (PEEP) may lead to ventilator-induced lung injury. In an isolated, perfused rabbit lung model, VT and PEEP were set to avoid lung collapse and overdistension in both lungs, resulting in a straight pressure-time (P-vs-t) curve during constant flow. Animals were randomized to (a) nonprotective OLV (left lung) (n = 6), with VT values as high as before randomization and zero PEEP; (b) protective OLV (left lung) (n = 6), with 50% reduction of VT and maintenance of PEEP as before randomization; and (c) control group (n = 6), with ventilation of two lungs as before randomization. The nonprotective OLV was associated with significantly smaller degrees of collapse and overdistension in the ventilated lung (P < 0.001). Peak inspiratory pressure values were higher in the nonprotective OLV group (P < 0.001) and increased progressively throughout the observation period (P < 0.01). The mean pulmonary artery pressure and lung weight gain values, as well as the concentration of thromboxane B(2), were comparatively higher in the nonprotective OLV group (P < 0.05). A ventilatory strategy with VT values as high as those used in the clinical setting and zero PEEP leads to ventilator-induced lung injury in this model of OLV, but this can be minimized with VT and PEEP values set to avoid lung overdistension and collapse. IMPLICATIONS: One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure (PEEP) is injurious in the isolated rabbit lung model. A ventilatory strategy with tidal volumes and PEEP set to avoid lung overdistension and collapse minimizes lung injury during one-lung ventilation in this model.

Airway Resistance↗

PubMed1996

Patient-triggered ventilation: a comparison of tidal volume and chestwall and abdominal motion as trigger signals.

Patient-triggered synchronized ventilation requires reliable and early detection of the infant's inspiratory effort. Several trigger methods have been developed that frequently lack the sensitivity to detect inspiration in small preterm infants (trigger failure), or show a high rate of breaths triggered by artifacts in the respiratory signal (autotrigger). The purpose of this study was to determine the effectiveness of the following trigger signals: abdominal movement sensed by a newly developed induction technique, chestwall motion detected by changes in transthoracic impedance, and tidal volume measured by anemometry at the endotracheal tube connector. Ten preterm infants (birth weight, 580-1,424 g; median weight, 943 g; study weight, 535-1,415 g; median weight, 838 g; gestation age, 26-32 weeks, median gestational age, 28 weeks, study age, 1-50 days, median study age, 11 days) were included in the study. A Sechrist SAVI ventilator was triggered by one of three signals: chestwall or abdominal movement, or tidal volume generated by the infants. Response time between beginning of inspiratory flow, the occurrence of the trigger signal (signal delay), and the onset of the triggered breath (trigger delay) were determined for each of the three signals. The signal response time was -13.5 msec (95% CI, -33 to -2 msec) for the abdominal movement signal, indicating that it started before inspiratory flow; 0.0 msec for the volume signal; and 44.0 msec (95% CI, 29-73 msec) for the chestwall signal (P < 0.002); this long delay was secondary to chestwall distortion and a subsequent delay in outward ribcage movement in many infants. The trigger delay for the abdominal signal was 90.0 msec (95% CI, 55-104 msec), 135.5 msec (95% CI: 82-186 msec) for the volume signal, and 176.5 msec (95% CI: 165-232 msec) for the chestwall signal, indicating that there was a difference in the rise time of signal voltage between the three methods (P < 0.01). The rate of autotriggered breaths was 3.2% (95% CI, 0.3-9.3%) when using the abdominal signal, 0.55% (95% CI, 0.0-2.1%) for the tidal volume signal, and 11.25% (95% CI, 0.5-27.8%) for the chestwall signal (P < 0.05). The incidence of trigger failure was low with all three signals and was not significantly different between the techniques. In summary, the chestwall signal had a long trigger delay and was highly susceptible to false triggering. It is, therefore, not a reliable trigger signal for synchronized mechanical ventilation in preterm infants. In contrast, tidal volume and abdominal movement signals had an acceptable trigger delay and a low rate of autotriggering, making them useful clinical trigger signals.

Confidence Intervals↗

PubMed1993

Oxygen cost of increasing tidal volume and diaphragm flattening in obstructive pulmonary disease.

Hypercapnia is associated with a shallow breathing pattern in patients with severe chronic obstructive pulmonary disease (COPD). We sought to determine the oxygen cost of increasing tidal volume and to relate this to hypercapnia [arterial PCO2 (PaCO2) > or = 45 Torr] and diaphragm flattening. We studied 3 normal subjects and 12 patients with stable but comparably severe COPD (forced expired volume in 1 s 1.01 +/- 0.09 liters) who had baseline PaCO2 ranging from 36 to 56 Torr. Oxygen consumption was measured during the subject's native breathing pattern and then while tidal volume was increased by 20%; minute ventilation was held constant by proportionately slowing frequency. There was a significant oxygen cost of increasing tidal volume for hypercapnic patients (235 +/- 23 to 260 +/- 25 ml O2/min; P = 0.002); no significant oxygen cost was observed in normal or eucapnic patients. This oxygen cost was positively correlated to baseline PaCO2 (r2 = 0.88, P < 0.001) and degree of diaphragm flattening assessed from chest radiographs (r2 = 0.74, P < 0.05). Although others have shown that force generation is preserved during chronic hyperinflation (G. A. Farkas and C. Roussos. J. Appl. Physiol. 54: 1635-1640, 1983; T. Similowski et al. N. Engl. J. Med. 325: 917-923, 1991), we conclude that diaphragm flattening produces mechanical inefficiency that may contribute to limiting the effective operating range of the respiratory muscles during tidal breathing.

Aged↗

PubMed1992

Effect of tidal volume on respiratory system elastance and resistance during anesthesia and paralysis.

Recent studies have shown that the mechanical properties of the respiratory system at normal breathing frequency in awake humans depend on tidal volume. Few measurements of respiratory system properties during anesthesia have accounted for this dependence. From measurements of airway pressure, flow and esophageal pressure, we calculated elastances and resistances of the total respiratory system (Ers and Rrs), chest wall (Ecw and Rcw), and lungs (El and Rl) in supine human volunteers during quasisinusoidal volume forcing in a normal range of breathing (250 to 800 ml) at normal breathing frequency (0.2 Hz). Measurements were made (1) with subjects awake and voluntarily relaxed; (2) after isoflurane-N2O anesthesia (end-tidal isoflurane concentration 0.3 to 0.5%); and (3) after complete muscle paralysis with vecuronium. In all conditions, Ers, Ecw, El, Rrs, and Rcw decreased at 800 ml tidal volume compared with 250 ml; Rl showed a similar decrease in awake measurements only. Compared with awake measurements, each elastance tended to increase after anesthesia, but only the increase in Ers was significant. Compared with anesthesia, there was no effect of paralysis on any measurement. We conclude that (1) tidal volume dependence of respiratory system properties in the normal range of breathing occurs in the absence of muscle activity; (2) anesthesia increases Ers and (3) respiratory muscle activity appears to be inhibited by isoflurane-N2O anesthesia at end-tidal isoflurane concentration of 0.3 to 0.5% during normocapnia.

Adult↗

PubMed1994

Reliability of respiratory inductive plethysmography for measuring tidal volume during exercise.

This study was designed to determine the reliability of measurements of respiratory volumes obtained with a respiratory inductive plethysmograph (RIP) during exercise. Tidal volumes (VT) from the RIP were compared with simultaneous flowmeter volumes in 8 healthy subjects at 5 incremental work rates of 60, 90, 120, 150, and 180 W during cycling and treadmill exercise. During cycling, average RIP and flowmeter values did not differ significantly at work rates below 180 W for 63% of the subjects. Average RIP and flowmeter VT were similar at work rates below 180 W for 50% of the subjects, and for 83% of the subjects at intensities below 150 W. The variability in these results may be attributed to several factors including RIP calibration errors and slippage of the RIP elastic bands containing the inductive coils. Correlations of breath-by-breath flowmeter and RIP VT were significant for subjects during cycling (R = 0.73, P < 0.05) and treadmill exercise (R = 0.78, P < 0.05). These findings suggest that the RIP should be considered a semi-quantitative method for measurements of tidal volume during exercise with and without respirator wear.

Adult↗

PubMed1988

Influence of controlled breathing with diminished tidal volume on hypoxic heart rate response in man.

In 12 normal healthy males, the effect of preventing augmentation in tidal volume (VT) on the heart rate (HR) was examined during isocapnic progressive hypoxia. The amount of diminished tidal volume (delta VT) was 0.61 +/- 0.36 liters from the maximal VT value attained in the free breathing hypoxia. Hypoxic HR response in terms of arterial oxygen saturation (SaO2)/HR response slope (delta HR/delta SaO2) was significantly decreased from the free to controlled breathing (p less than 0.05). The effective VT range for eliciting such a HR change appeared to be more than 1,000 ml as has been demonstrated in the Hering-Breuer reflex on ventilation in humans. However, the magnitude of delta HR/delta SaO2 decrement was not significantly correlated with delta VT, suggesting that the command signal from the higher nervous center interfered with the expected response. Contrary to the HR response, the hypoxic ventilatory and occlusion pressure responses were not significantly influenced by the controlled breathing. We conclude that the hypoxic HR response is significantly depressed by the diminished VT breathing.

Heart Rate↗

PubMed1989

Gas flow distribution and tidal volume during distal high frequency jet ventilation in dogs.

During distal high frequency jet ventilation (HFJV) in anaesthetized healthy dogs gas flows were recorded at the proximal end of the open tracheal jet tube. Spirometer measurements of minute volumes with and without entrainment were made. During the inspiratory or insufflation period, leakage of jet gas (bypass) could occur depending on the ventilator setting. From the gas flow recordings and the spirometer measurements, jet-, entrainment- and bypass minute volumes were determined. From these the effective minute volume, that is the minute volume of fresh gas entering the lungs, was calculated, as well as tidal volume. The results show that entrainment volumes are relatively small in an open system of distal HFJV and that at the same time bypass can (nearly) completely eliminate the effect of entrainment on tidal volume.

Animals↗

PubMed1982

Pulmonary oxygen exchange during endobronchial anesthesia: effect of tidal volume and PEEP.

To determine the effects of tidal volume (VT) and positive end-expiratory pressure (PEEP) on pulmonary oxygen exchange during endobronchial (one-lung) anesthesia, the authors studied the effects of VT at 8 and 16 per cent total lung capacity (TLC), at zero end-expiratory pressure (ZEEP), and at 10 cmH2O PEEP in 16 patients in the lateral position. Anesthesia was maintained with halothane and oxygen. During two-lung ventilation (FIO2 0.99), mean PaO2 and physiologic shunt (Qs/Qt) were 421 +/- 12 mmHg and 0.22 +/- 0.02, respectively. During one-lung ventilation, PaO2 decreased and venous admixture (or Qs/Qt) increased in every patient. The magnitude of this decrease correlated directly with preoperative forced expiratory volume in one second (FEV1) (r = 0.66, P less than 0.005). A VT of 16 per cent of TLC at ZEEP resulted in the highest mean PaO2 (210 +/- 30 mmHg) and lowest Qs/Qt (0.35 +/- 0.02), probably as a result of end-inspiratory alveolar recruitment with the least pulmonary blood flow redistribution. When 10 cmH2O PEEP was applied during 16 per cent TLC ventilation, mean PaO2 decreased from 210 +/- 35 to 162 +/- 25 mmHg (P less than 0.05). PEEP did not significantly affect PaO2 during 8 per cent TLC ventilation. At both levels of VT, PEEP reduced mean Qt by approximatley 10 per cent (P less than 0.01) and increased compliance (P less than 0.01). However, PEEP did not significantly affect mean Qs/Qt or mean arterial or pulmonary arterial pressures at either level of VT. There was considerable variation in PaO2 and Qs/Qt among patients.

Adult↗