The two intervention groups had similar characteristics at baseline. In the intention-to-treat analysis, the primary outcome occurred in 21 of 200 patients (10.5%) assigned to lung-protective ventilation, as compared with 55 of 200 (27.5%) assigned to nonprotective ventilation (relative risk, 0.40; 95% confidence interval [CI], 0.24 to 0.68; P = 0.001). Over the 7-day postoperative period, 10 patients (5.0%) assigned to lung-protective ventilation required noninvasive ventilation or intubation for acute respiratory failure, as compared with 34 (17.0%) assigned to nonprotective ventilation (relative risk, 0.29; 95% CI, 0.14 to 0.61; P = 0.001). The length of the hospital stay was shorter among patients receiving lung-protective ventilation than among those receiving nonprotective ventilation (mean difference, −2.45 days; 95% CI, −4.17 to −0.72; P = 0.006). CONCLUSIONS As compared with a practice of nonprotective mechanical ventilation, the use of a lung-protective ventilation strategy in intermediate-risk and high-risk patients undergoing major abdominal surgery was associated with improved clinical out comes and reduced health care utilization. (IMPROVE ClinicalTrials.gov number, NCT01282996.)

https://www.nejm.org/doi/pdf/10.1056/NEJMoa1301082

A trial of intraoperative low-tidal-volume ventilation in abdominal surgery.

Frequency-domain analyses of R-R intervals are used widely to estimate levels of autonomic neural traffic to the human heart. Because respiration modulates autonomic activity, we determined for nine healthy subjects the influence of breathing frequency and tidal volume on R-R interval power spectra (fast-Fourier transform method). We also surveyed published literature to determine current practices in this burgeoning field of scientific inquiry. Supine subjects breathed at rates of 6, 7.5, 10, 15, 17.1, 20, and 24 breaths/min and with nominal tidal volumes of 1,000 and 1,500 ml. R-R interval power at respiratory and low (0.06-0.14 Hz) frequencies declined significantly as breathing frequency increased. R-R interval power at respiratory frequencies was significantly greater at a tidal volume of 1,500 than 1,000 ml. Neither breathing frequency nor tidal volume influenced average R-R intervals significantly. Our review of studies reporting human R-R interval power spectra showed that 51% of the studies controlled respiratory rate, 11% controlled tidal volume, and 11% controlled both respiratory rate and tidal volume. The major implications of our analyses are that breathing parameters strongly influence low-frequency as well as respiratory frequency R-R interval power spectra and that this influence is largely ignored in published research.

Important influence of respiration on human R-R interval power spectra is largely ignored

THE present study was undertaken to determine if the pattern of ventilation, by itself, may influence oxygenation during anesthesia and surgery. The hypothesis was examined that progressive pulmona...

https://www.nejm.org/doi/pdf/10.1056/NEJM196311072691901?listPDF=true

Impaired oxygenation in surgical patients during general anesthesia with controlled ventilation. a concept of atelectasis.

ContextHypoxemia complicates the recovery of 30% to 50% of patients after abdominal
surgery; endotracheal intubation and mechanical ventilation may be required
in 8% to 10% of cases, increasing morbidity and mortality and prolonging intensive
care unit and hospital stay.ObjectiveTo determine the effectiveness of continuous positive airway pressure
compared with standard treatment in preventing the need for intubation and
mechanical ventilation in patients who develop acute hypoxemia after elective
major abdominal surgery.Design and SettingRandomized, controlled, unblinded study with concealed allocation conducted
between June 2002 and November 2003 at 15 intensive care units of the Piedmont
Intensive Care Units Network in Italy.PatientsConsecutive patients who developed severe hypoxemia after major elective
abdominal surgery. The trial was stopped for efficacy after 209 patients had
been enrolled.InterventionsPatients were randomly assigned to receive oxygen (n = 104)
or oxygen plus continuous positive airway pressure (n = 105).Main Outcome MeasuresThe primary end point was incidence of endotracheal intubation; secondary
end points were intensive care unit and hospital lengths of stay, incidence
of pneumonia, infection and sepsis, and hospital mortality.ResultsPatients who received oxygen plus continuous positive airway pressure
had a lower intubation rate (1% vs 10%; P = .005;
relative risk [RR], 0.099; 95% confidence interval [CI], 0.01-0.76) and had
a lower occurrence rate of pneumonia (2% vs 10%, RR, 0.19; 95% CI, 0.04-0.88; P = .02), infection (3% vs 10%, RR, 0.27; 95%
CI, 0.07-0.94; P = .03), and sepsis (2%
vs 9%; RR, 0.22; 95% CI, 0.04-0.99; P = .03)
than did patients treated with oxygen alone. Patients who received oxygen
plus continuous positive airway pressure also spent fewer mean (SD) days in
the intensive care unit (1.4 [1.6] vs 2.6 [4.2], P = .09)
than patients treated with oxygen alone. The treatments did not affect the
mean (SD) days that patients spent in the hospital (15 [13] vs 17 [15], respectively; P = .10). None of those treated with oxygen plus
continuous positive airway pressure died in the hospital while 3 deaths occurred
among those treated with oxygen alone (P = .12).ConclusionContinuous positive airway pressure may decrease the incidence of endotracheal
intubation and other severe complications in patients who develop hypoxemia
after elective major abdominal surgery.

https://jamanetwork.com/journals/jama/articlepdf/200264/jce40057.pdf

Continuous positive airway pressure for treatment of postoperative hypoxemia: a randomized controlled trial

Atelectasis occurs in the dependent parts of the lungs of most patients who are anesthetized. Development of atelectasis is associated with decreased lung compliance, impairment of oxygenation, increased pulmonary vascular resistance, and development of lung injury. The adverse effects of atelectasis persist into the postoperative period and can impact patient recovery. This review article focuses on the causes, nature, and diagnosis of atelectasis. The authors discuss the effects and implications of atelectasis in the perioperative period and illustrate how preventive measures may impact outcome. In addition, they examine the impact of atelectasis and its prevention in acute lung injury.

Pulmonary atelectasis: a pathogenic perioperative entity.

The ventilatory pattern at rest was examined in 28 healthy human volunteers by recording pneumograph tracings for a 1-hr period. The mean respiratory frequency was 19/min in females, 16/min in male...

Pattern of ventilation in young adults.

MARKED elevations of serum citrate have been reported to occur in man during multiple rapid transfusions of citrated blood.1 2 3 The possibility of harmful effects is well recognized but often discounted.2 , 4 In an attempt to separate the circulatory effects of citrate from many other potentially adverse effects of massive transfusion, we have studied the hemodynamic effects of intravenous infusions of sodium citrate in normal, lightly anesthetized man and in the dog. Methods Clinical Material Six patients, 5 females and 1 male, were studied. Their ages were thirty-one to forty-four, with an average of thirty-eight years. All were undergoing ligation and stripping . . .

Hemodynamic Effects of Intravenously Administered Sodium Citrate

Intermittent Deep Breaths and Compliance During Anesthesia in Man

The rate and magnitude of the effects of the pressure-volume history of the lungs on the degree of physiologic shunting (pulmonary venous admixture) were investigated in 20 dogs, anesthetized and curarized. Atelectasis was promoted by decreasing end-expiratory transpulmonary pressure. Ventilation was with 100% oxygen using a constant-volume pump at a frequency of 20 breaths/min. The rates of increase or decrease in the physiologic shunt and of the gradients between derived alveolar oxygen tension and directly measured arterial oxygen tension (A-aD) showed a variation controlled by the pressure-volume history of the lungs. The physiologic shunts produced varied between 0.5% and 80% of the cardiac output. The interrelationships of the components of the shunt equation were studied and their relative value in predicting atelectasis was discussed. The data obtained were related to other observations made in anesthetized man.

H. H. Bendixen

Papers

Impaired oxygenation in surgical patients during general anesthesia with controlled ventilation. a concept of atelectasis.

Pattern of ventilation in young adults.

Hemodynamic Effects of Intravenously Administered Sodium Citrate

Intermittent Deep Breaths and Compliance During Anesthesia in Man

Effect of changes in tidal ventilation on physiologic shunting.