Pulmonary mechanics during general anaesthesia. The influence of mechanical irritation on the airway

Comparing Clinical Features and Outcomes in Mechanically Ventilated Patients with COVID-19 and Acute Respiratory Distress Syndrome

Rationale: Patients with severe coronavirus disease (COVID-19) meet clinical criteria for the acute respiratory distress syndrome (ARDS), yet early reports suggested they differ physiologically and clinically from patients with non-COVID-19 ARDS, prompting treatment recommendations that deviate from standard evidence-based practices for ARDS. Objectives: To compare respiratory physiology, clinical outcomes, and extrapulmonary clinical features of severe COVID-19 with non-COVID-19 ARDS. Methods: We performed a retrospective cohort study, comparing 130 consecutive mechanically ventilated patients with severe COVID-19 with 382 consecutive mechanically ventilated patients with non-COVID-19 ARDS. Initial respiratory physiology and 28-day outcomes were compared. Extrapulmonary manifestations (inflammation, extrapulmonary organ injury, and coagulation) were compared in an exploratory analysis. Results: Comparison of patients with COVID-19 and non-COVID-19 ARDS suggested small differences in respiratory compliance, ventilatory efficiency, and oxygenation. The 28-day mortality was 30% in patients with COVID-19 and 38% in patients with non-COVID-19 ARDS. In adjusted analysis, point estimates of differences in time to breathing unassisted at 28 days (adjusted subdistributional hazards ratio, 0.98 [95% confidence interval (CI), 0.77-1.26]) and 28-day mortality (risk ratio, 1.01 [95% CI, 0.72-1.42]) were small for COVID-19 versus non-COVID-19 ARDS, although the confidence intervals for these estimates include moderate differences. Patients with COVID-19 had lower neutrophil counts but did not differ in lymphocyte count or other measures of systemic inflammation. Conclusions: In this single-center cohort, we found no evidence for large differences between COVID-19 and non-COVID-19 ARDS. Many key clinical features of severe COVID-19 were similar to those of non-COVID-19 ARDS, including respiratory physiology and clinical outcomes, although our sample size precludes definitive conclusions. Further studies are needed to define COVID-19-specific pathophysiology before a deviation from evidence-based treatment practices can be recommended.

Response to COVID-19 phenotyping correspondence

In their letter, R. Cherian and co-workers take issue with our interpretation of the respiratory physiology of coronavirus disease 2019 (COVID-19), arguing that it is based merely on “small cohort studies”, and instead declaring that “a high proportion of mechanically ventilated COVID-19 patients exhibit near-normal lung compliance”. Yet the low respiratory compliance of COVID-19 patients has now been extensively demonstrated by studies totalling more than 800 COVID-19 patients [1–7], including a direct comparison with non-COVID-19 acute respiratory distress syndrome (ARDS) patients that revealed no difference in respiratory compliance [7]. In contrast, the three case series cited by R. Cherian and co-workers in support of their claim comprise cohorts of, respectively, 16, 10 and 26 patients [8–10]. Furthermore, even these case series report average respiratory compliance in COVID-19 of 40–45 mL·cmH₂O⁻¹, which is in fact abnormal and far from “near-normal compliance” [11, 12].

Phenotyping of COVID-19-related ARDS should be done using careful, data-driven approacheshttps://bit.ly/3eX65Yu

Oral Pregabalin as Premedication on Anxiolysis and Stress Response to Laryngoscopy and Endotracheal Intubation in Patients Undergoing Laparoscopic Cholecystectomy: A Randomized Double-Blind Study

Background

Direct laryngoscopy and tracheal intubation lead to increase in heart rate and blood pressure. This can cause serious complications in patients with coronary artery disease, reactive airways, or intracranial neuropathology. Preoperative anxiety is associated with greater level of postoperative pain. Attenuation of anxiety and hemodynamic response to laryngoscopy and intubation are cornerstone of better anesthetic outcome. Gabapentinoids (gabapentin and pregabalin) have been known to possess anxiolytic, analgesic, and anticonvulsant properties.

Aim

The aim of this study is to determine the effects of oral pregabalin on anxiolysis and attenuation of stress response to laryngoscopy and endotracheal intubation.

Study Design

This was a prospective randomized double-blind placebo controlled study.

Materials and Methods

A total of 60 patients ASA physical status Class I and II, undergoing elective laparoscopic cholecystectomy, were randomly allocated into two groups receiving either oral placebo or oral pregabalin 150 mg, 60 min before induction of anesthesia. Visual analog scale (VAS) for anxiety was recorded before, and 60 min after giving the drug. Hemodynamic parameters (heart rate, systolic blood pressure, diastolic blood pressure, and mean arterial pressure) were recorded before, and 60 min after giving drug, during and 2, 4, 6, 8, and 10 min after intubation.

Results

During preinduction, pregabalin showed a decrease in VAS and attenuation of stress response to laryngoscopy and intubation compared to that of placebo. The premedicated patients were hemodynamically stable perioperatively without side effects.

Conclusion

Pregabalin is effective in attenuating preoperative anxiety and stress response to endotracheal intubation.

The effect on respiratory mechanics when using a Jackson surgical table in the prone position during spinal surgery

Background

Respiratory dynamics may be monitored and evaluated indirectly by measuring the peak inspiratory pressure and plateau pressure. In this study, the respiratory dynamics of patients undergoing spinal surgery using a Jackson surgical table were observed with a device after converting their position from supine to prone. The effects of the dynamic compliance and airway resistance were observed from the changes in peak inspiratory pressure and plateau.

Methods

Twenty five patients were selected as subjects scheduled to undergo lumbar spine surgery. After intubation, the patients were ventilated mechanically with a tidal volume of 10 ml/kg and a respiration rate of 10/min. Anesthesia was maintained with sevoflurane 1.5%, nitrous oxide 2 L/min and oxygen 2 L/min. The peak inspiratory pressure, plateau pressure, resistance, compliance, arterial oxygen tension, carbon dioxide tension, heart rate and arterial blood pressure were measured at 10 minutes after the induction of anesthesia. These parameters were measured again 10 minutes after placing the patient in the prone position.

Results

The prone position did not significantly affect the arterial oxygen tension, carbon dioxide tension, blood pressure and heart rate, but significantly increased the peak inspiratory pressure and resistance and decreased the dynamic compliance.

Conclusions

The peak inspiratory pressure was increased using a Jackson surgical table to minimize the abdominal pressure when converting from the supine to prone position. This might be due to a decrease in lung and chest compliance as well as an increase in airway resistance.

Chaotic dynamics of cardioventilatory coupling in humans: effects of ventilatory modes

Cardioventilatory coupling (CVC), a transient temporal alignment between the heartbeat and inspiratory activity, has been studied in animals and humans mainly during anesthesia. The origin of the coupling remains uncertain, whether or not ventilation is a main determinant in the CVC process and whether the coupling exhibits chaotic behavior. In this frame, we studied sedative-free, mechanically ventilated patients experiencing rapid sequential changes in breathing control during ventilator weaning during a switch from a machine-controlled assistance mode [assist-controlled ventilation (ACV)] to a patient-driven mode [inspiratory pressure support (IPS) and unsupported spontaneous breathing (USB)]. Time series were computed as R to start inspiration (RI) and R to the start of expiration (RE). Chaos was characterized with the noise titration method (noise limit), largest Lyapunov exponent (LLE) and correlation dimension (CD). All the RI and RE time series exhibit chaotic behavior. Specific coupling patterns were displayed in each ventilatory mode, and these patterns exhibited different linear and chaotic dynamics. When switching from ACV to IPS, partial inspiratory loading decreases the noise limit value, the LLE, and the correlation dimension of the RI and RE time series in parallel, whereas decreasing intrathoracic pressure from IPS to USB has the opposite effect. Coupling with expiration exhibits higher complexity than coupling with inspiration during mechanical ventilation either during ACV or IPS, probably due to active expiration. Only 33% of the cardiac time series (RR interval) exhibit complexity either during ACV, IPS, or USB making the contribution of the cardiac signal to the chaotic feature of the coupling minimal. We conclude that 1) CVC in unsedated humans exhibits a complex dynamic that can be chaotic, and 2) ventilatory mode has major effects on the linear and chaotic features of the coupling. Taken together these findings reinforce the role of ventilation in the CVC process.

Mechanical Insufflation-Exsufflation vs. Tracheal Suctioning via Tracheostomy Tubes for Patients with Amyotrophic Lateral Sclerosis

OBJECTIVE

To compare the effects of mechanical insufflation-exsufflation vs. suctioning via tracheostomy tubes on respiratory variables for six amyotrophic lateral sclerosis patients.

DESIGN

In this prospective crossover study, six consecutive patients with amyotrophic lateral sclerosis who required continuous mechanical ventilation via tracheostomy tubes and developed chest infections underwent measurement of pulse oxyhemoglobin saturation (SpO2), peak inspiratory pressure (PIP), mean airway pressure (Pawm), and work of breathing performed by the ventilator (WOBv) at baseline and 5 and 30 min after tracheal suctioning and 5 min after mechanical insufflation-exsufflation.

RESULTS

The baseline values were 93.50 +/- 2.26% for SpO2 in ambient air, 18.50 +/- 4.23 cm H2O for PIP, 4.67 +/- 1.37 cm H2O for Pawm, and 1.03 +/- 0.25 J/liters for WOBv. Only WOBv changed significantly, decreasing after tracheal suctioning (P < 0.05), whereas all variables improved significantly after mechanical insufflation-exsufflation.

CONCLUSION

For ventilator-dependent patients with amyotrophic lateral sclerosis, mechanical insufflation-exsufflation via a tracheostomy tube with an inflated cuff may be more effective in eliminating airway secretions than conventional tracheal suctioning.

Localized airway anesthesia with lidocaine partially suppresses cardiovascular responses To lung inflation

Lung inflation causes cardiovascular suppression via an increase in intrathoracic pressure and neural mechanisms. To examine the mechanisms involved, we mea-sured the heart rate (HR) and arterial blood pressure (AP) responses to lung inflation before and after spraying the bronchi with lidocaine to suppress airway reflex. Thirty women participated in the study. One group (n = 20, Group BT) had their tracheas intubated by using double-lumen tubes. The other group (n = 10, Group TT) received an ordinary endotracheal tube. They were all studied under general anesthesia by using nitrous oxide, isoflurane, and muscle relaxation after a thiopental induction. In each patient, airway pressure was increased for 3 s, and changes in HR and AP were measured. Lung inflation was repeated after 5 mL of 4% lidocaine had been sprayed into the main bronchi unilaterally in Group BT or bilaterally in Group TT. There were no significant differences in cardiovascular responses between left and right lung inflation with the pressure at 20 and 30 cm H(2)O. Both lungs inflated at 20 cm H(2)O caused an increase in HR with a significantly greater decrease in AP than with unilateral inflation. Anesthesia of the bronchi abolished the HR increase, but not the AP decrease. Lung inflation at 30 cm H(2)O caused significant decreases in HR and AP which were not affected with topical anesthesia. These results indicate that the cardiovascular responses elicited by lung inflation in anesthetized humans are predominantly the direct effect of the increase in intrathoracic pressure, although sympathetic afferent activity induced via stimulation of mechanoreceptors in the airways contributes.

IMPLICATIONS

Localized airway anesthesia with lidocaine is unlikely to suppress the cardiovascular responses to lung inflation. This suggests that a limited number of neurogenic mechanisms are involved in the cardiovascular responses to lung inflation in anesthetized humans.

Effects of tracheal suctioning on respiratory resistances in mechanically ventilated patients

OBJECTIVE

To evaluate the effects of tracheal suctioning (TS) on respiratory resistances in sedated critical care patients receiving mechanical ventilation (MV).

SETTING

Surgical ICU of Bichat Hospital, Paris.

PATIENTS AND PARTICIPANTS

Thirteen sedated critical care patients receiving MV for various conditions.

MEASUREMENTS AND RESULTS

Airway resistances (R1), airway and pulmonary resistances (R2), and intrinsic positive end-expiratory pressure (PEEPint) were measured according to the end-inspiratory and end-expiratory occlusion methods before and after TS. R1 and R2 increased by 49.1% and 46.3%, respectively, 0.5 min after TS (p<0.01) but returned to baseline values at 1 min without any change thereafter. PEEPint decreased progressively following TS to reach a significant level (-13.3%) at 10 min (p<0.05) and was persistently reduced at 30 min (p<0.01). Nine patients received 500 microg of inhaled albuterol before another suctioning procedure. R1 and R2 decreased by 11.5% and 9.9%, respectively, 20 min after inhalation (p<0.05), but the R1 and R2 initial increase following TS did not differ between the two suctioning procedures.

CONCLUSIONS

TS evokes only a transient bronchoconstrictor response, but thereafter, does not reduce respiratory resistances below presuctioning values. However, the decrease of PEEPint following TS suggests an increase of expiratory flow. Effective beta2-adrenergic receptor blockade fails to suppress the TS-induced bronchoconstrictor response.

The effect of changing end-expiratory pressure on respiratory system mechanics in open- and closed-chest anesthetized, paralyzed patients

The decrease in functional residual capacity (FRC) with anesthesia may cause lung volume to decrease below closing volume, thereby impairing oxygenation. Increasing end-expiratory pressure (EEP) reexpands atelectatic areas in anesthetized, ventilated patients, but its effect on pulmonary mechanics is less well understood. We studied the effect of varying EEP on the mechanical behavior of the respiratory system in patients undergoing either closed (Group 1) or open-chest (Group 2) surgical procedures. We measured airway opening pressure (PaO), flow (V), and esophageal pressure (Pes) (in Group 1 only) at EEPs of 0, 2.5, 5, and 10 cm H2O. Dynamic elastance (E) and resistance (R) for the respiratory system (RS), the lung (L), and the chest wall (CW) were estimated by fitting the equation P = RV + EV + K to the measured data by multiple linear regression where P was either Pao, Pes, or Pao-Pes. Group 1 EL decreased with increases in EEP to 5 cm H2O and then began to increase with EEP above this level. The same occurred in Group 2 before opening the chest. After opening the chest in Group 2, EL increased as EEP increased at all values above 0 cm H2O. The magnitudes of RRS and RL were similar in both groups of subjects and in each group these quantities decreased with increases in EEP. Dynamic EL responded differently to changes in EEP in subjects with open-chest and closed-chest procedures. We attribute this difference to overdistension of the remaining ventilable lung tissue at all levels of EEP in open-chest patients.

Effects of intravenous or endotracheal lidocaine on circulatory changes during Recovery from general anesthesia

Intravenous lidocaine (1.5 mg.kg(-1)) was not effective in attenuating the circulatory changes and the cough reflex induced by airway stimulation during recovery from general anesthesia, whereas endotracheal 4% lidocaine (3 ml) was effective. The arterial concentration of the intravenously administered-lidocaine peaked at a level of 9.52 +/- 0.81 microg.ml(-1) 0.5 min later. The arterial concentration of the endotracheally administered-lidocaine peaked at 1.44 +/- 0.13 microg.ml(-1) 15 min later. These findings indicate that the endotracheal administration of lidocaine may be superior to the intravenous administration for attenuating the circulatory changes and the cough reflex during recovery from general anesthesia, and that the arterial concentration of lidocaine did not correlate with the clinical efficacy for this purpose.