"Open lung ventilation optimizes pulmonary function during lung surgery".

BACKGROUND: We evaluated an "open lung" ventilation (OV) strategy using low tidal volumes, low respiratory rate, low FiO2, and high continuous positive airway pressure in patients undergoing major lung resections. MATERIALS AND METHODS: In this phase I pilot study, twelve consecutive patients were anesthetized using conventional ventilator settings (CV) and then OV strategy during which oxygenation and lung compliance were noted. Subsequently, a lung resection was performed. Data were collected during both modes of ventilation in each patient, with each patient acting as his own control. The postoperative course was monitored for complications. RESULTS: Twelve patients underwent open thoracotomies for seven lobectomies and five segmentectomies. The OV strategy provided consistent one-lung anesthesia and improved static compliance (40 ± 7 versus 25 ± 4 mL/cm H2O, P = 0.002) with airway pressures similar to CV. Postresection oxygenation (SpO2/FiO2) was better during OV (433 ± 11 versus 386 ± 15, P = 0.008). All postoperative chest x-rays were free of atelectasis or infiltrates. No patient required supplemental oxygen at any time postoperatively or on discharge. The mean hospital stay was 4 ± 1 d. There were no complications or mortality. CONCLUSIONS: The OV strategy, previously shown to have benefits during mechanical ventilation of patients with respiratory failure, proved safe and effective in lung resection patients. Because postoperative pulmonary complications may be directly attributable to the anesthetic management, adopting an OV strategy that optimizes lung mechanics and gas exchange may help reduce postoperative problems and improve overall surgical results. A randomized trial is planned to ascertain whether this technique will reduce postoperative pulmonary complications.

Postoperative hypoxemia: common, undetected, and unsuspected after bariatric surgery.

BACKGROUND: Patients undergoing gastric bypass are at greater than ordinary risk for postoperative respiratory insufficiency, presumably related to obstructive sleep apnea (OSA) and patient-controlled analgesia (PCA). This study was proposed to quantify the magnitude of the problem. METHODS: Fifteen patients undergoing gastric bypass had oxygen saturation (SpO(2)) recorded continuously, but not displayed, for 24h postoperatively; eight also had arterial blood analysis every 4h. All received narcotic PCA. SpO(2)<90% lasting more than 10 s was reviewed. Results are mean+/-SEM. RESULTS: Mean age was 44+/-4 y, and mean BMI was 48+/-2kg/m(2); 77% had OSA. Every patient had more than one episode with SpO(2)<90% for longer than 30s undetected by routine monitoring; most had multiple episodes. Nadir SpO(2) averaged 75% +/- 8%. Mean longest duration of desaturation below 90% averaged 21+/-15min. Mean PaCO(2) was 37+/-3mm Hg; maximum PaCO(2) was 47mm Hg. CONCLUSIONS: Severe and prolonged episodes of hypoxemia were a consistent finding, despite aggressive preoperative diagnosis and treatment of OSA, including use of CPAP postoperatively. Although some postoperative hypoventilation was expected, the degree and frequency of desaturation were surprising. No patient exhibited arterial PaCO(2) evidence of hypoventilation. No patient experienced cardiopulmonary arrest/instability, in spite of severe, repeated episodes of hypoxemia. In no instance was a significant hypoxemic episode suspected or detected. Continuous pulse oximetry monitoring, with an audible alarm set for a saturation less than 90% for 10 s, would have alerted providers to 100% of significant hypoxemic episodes. Our recommendation is routinely monitoring (with alarm capability enabled) every bariatric surgical patient, to prevent such occurrence.

Proposal for Coronavirus Disease 2019 Management.

SETTING: The coronavirus disease 2019 pandemic has raised fear throughout the nation. Current news and social media predictions of ventilator, medication, and personnel shortages are rampant. PATIENTS: Patients with coronavirus disease 2019 are presenting with early respiratory distress and hypoxemia, but not hypercapnia. INTERVENTIONS: Patients who maintain adequate alveolar ventilation, normocapnia, and adequate oxygenation may avoid the need for tracheal intubation. Facemask continuous positive airway pressure has been used to treat patients with respiratory distress for decades, including those with severe acute respiratory syndrome. Of importance, protocols were successful in protecting caregivers from contracting the virus, obviating the need for tracheal intubation just to limit the spread of potentially infectious particles. CONCLUSIONS: During a pandemic, with limited resources, we should provide the safest and most effective care, while protecting caregivers. Continuous positive airway pressure titrated to an effective level and applied early with a facemask may spare ventilator usage. Allowing spontaneous ventilation will decrease the need for sedative and paralytic drugs and may decrease the need for highly skilled nurses and respiratory therapists. These goals can be accomplished with devices that are readily available and easier to obtain than mechanical ventilators, which then can be reserved for the sickest patients.

The Society for Translational Medicine: clinical practice guidelines for mechanical ventilation management for patients undergoing lobectomy.

Patients undergoing lobectomy are at significantly increased risk of lung injury. One-lung ventilation is the most commonly used technique to maintain ventilation and oxygenation during the operation. It is a challenge to choose an appropriate mechanical ventilation strategy to minimize the lung injury and other adverse clinical outcomes. In order to understand the available evidence, a systematic review was conducted including the following topics: (I) protective ventilation (PV); (II) mode of mechanical ventilation [e.g., volume controlled (VCV) versus pressure controlled (PCV)]; (III) use of therapeutic hypercapnia; (IV) use of alveolar recruitment (open-lung) strategy; (V) pre-and post-operative application of positive end expiratory pressure (PEEP); (VI) Inspired Oxygen concentration; (VII) Non-intubated thoracoscopic lobectomy; and (VIII) adjuvant pharmacologic options. The recommendations of class II are non-intubated thoracoscopic lobectomy may be an alternative to conventional one-lung ventilation in selected patients. The recommendations of class IIa are: (I) Therapeutic hypercapnia to maintain a partial pressure of carbon dioxide at 50-70 mmHg is reasonable for patients undergoing pulmonary lobectomy with one-lung ventilation; (II) PV with a tidal volume of 6 mL/kg and PEEP of 5 cmH2O are reasonable methods, based on current evidence; (III) alveolar recruitment [open lung ventilation (OLV)] may be beneficial in patients undergoing lobectomy with one-lung ventilation; (IV) PCV is recommended over VCV for patients undergoing lung resection; (V) pre- and post-operative CPAP can improve short-term oxygenation in patients undergoing lobectomy with one-lung ventilation; (VI) controlled mechanical ventilation with I:E ratio of 1:1 is reasonable in patients undergoing one-lung ventilation; (VII) use of lowest inspired oxygen concentration to maintain satisfactory arterial oxygen saturation is reasonable based on physiologic principles; (VIII) Adjuvant drugs such as nebulized budesonide, intravenous sivelestat and ulinastatin are reasonable and can be used to attenuate inflammatory response.

The Society for Translational Medicine: clinical practice guidelines for the postoperative management of chest tube for patients undergoing lobectomy.

The Society for Translational Medicine and The Chinese Society for Thoracic and Cardiovascular Surgery conducted a systematic review of the literature in an attempt to improve our understanding in the postoperative management of chest tubes of patients undergoing pulmonary lobectomy. Recommendations were produced and classified based on an internationally accepted GRADE system. The following recommendations were extracted in the present review: (I) chest tubes can be removed safely with daily pleural fluid of up to 450 mL (non-chylous and non-sanguinous), which may reduce chest tube duration and hospital length of stay (2B); (II) in rare instances, e.g., persistent abundant fluid production, the use of PrRP/B <0.5 when evaluating fluid output to determine chest tube removal might be beneficial (2B); (III) it is recommended that one chest tube is adequate following pulmonary lobectomy, except for hemorrhage and space problems (2A); (IV) chest tube clearance by milking and stripping is not recommended after lung resection (2B); (V) chest tube suction is not necessary for patients undergoing lobectomy after first postoperative day (2A); (VI) regulated chest tube suction [-11 (-1.08 kPa) to -20 (1.96 kPa) cmH2O depending upon the type of lobectomy] is not superior to regulated seal [-2 (0.196 kPa) cmH2O] when electronic drainage systems are used after lobectomy by thoracotomy (2B); (VII) chest tube removal recommended at the end of expiration and may be slightly superior to removal at the end of inspiration (2A); (VIII) electronic drainage systems are recommended in the management of chest tube in patients undergoing lobectomy (2B).

Supplemental oxygen impairs detection of hypoventilation by pulse oximetry.

STUDY OBJECTIVE: This two-part study was designed to determine the effect of supplemental oxygen on the detection of hypoventilation, evidenced by a decline in oxygen saturation (Spo(2)) with pulse oximetry. DESIGN: Phase 1 was a prospective, patient-controlled, clinical trial. Phase 2 was a prospective, randomized, clinical trial. SETTING: Phase 1 took place in the operating room. Phase 2 took place in the postanesthesia care unit (PACU). PATIENTS: In phase 1, 45 patients underwent abdominal, gynecologic, urologic, and lower-extremity vascular operations. In phase 2, 288 patients were recovering from anesthesia. INTERVENTIONS: In phase 1, modeling of deliberate hypoventilation entailed decreasing by 50% the minute ventilation of patients receiving general anesthesia. Patients breathing a fraction of inspired oxygen (Fio(2)) of 0.21 (n = 25) underwent hypoventilation for up to 5 min. Patients with an Fio(2) of 0.25 (n = 10) or 0.30 (n = 10) underwent hypoventilation for 10 min. In phase 2, spontaneously breathing patients were randomized to breathe room air (n = 155) or to receive supplemental oxygen (n = 133) on arrival in the PACU. MEASUREMENTS AND RESULTS: In phase 1, end-tidal carbon dioxide and Spo(2) were measured during deliberate hypoventilation. A decrease in Spo(2) occurred only in patients who breathed room air. No decline occurred in patients with Fio(2) levels of 0.25 and 0.30. In phase 2, Spo(2) was recorded every min for up to 40 min in the PACU. Arterial desaturation (Spo(2) < 90%) was fourfold higher in patients who breathed room air than in patients who breathed supplemental oxygen (9.0% vs 2.3%, p = 0.02). CONCLUSION: Hypoventilation can be detected reliably by pulse oximetry only when patients breathe room air. In patients with spontaneous ventilation, supplemental oxygen often masked the ability to detect abnormalities in respiratory function in the PACU. Without the need for capnography and arterial blood gas analysis, pulse oximetry is a useful tool to assess ventilatory abnormalities, but only in the absence of supplemental inspired oxygen.

Has oxygen administration delayed appropriate respiratory care? Fallacies regarding oxygen therapy.

Modern clinical use of supplemental oxygen supposes that: (1) exposure to F(IO)(2) < or = 60% is without adverse effects, (2) an individual at risk of developing arterial hypoxemia can be protected by administering high F(IO)(2), and (3) routine administration of supplemental oxygen is useful, harmless, and clinically indicated. There is now substantial evidence that none of those 3 suppositions are correct, and, on the contrary, supplemental oxygen is actually detrimental to many of the patients who receive it. Supplemental oxygen is much overused and its use should be limited to the few conditions and situations in which it is truly effective, useful, and non-detrimental.

Chest wall disruption with and without acute lung injury: effects of continuous positive airway pressure therapy on ventilation and perfusion relationships.

OBJECTIVE: We investigated the evolution of lung injury in an animal model with multiple rib fractures, both with and without acute lung injury, and the influence of spontaneous breathing with continuous positive airway pressure (CPAP) therapy on the relative distributions of alveolar ventilation ([OV0312]a) and perfusion ([OV0422]). DESIGN: Prospective, randomized laboratory investigation using an established porcine model with instrumentation for measurement of ventilation/perfusion distribution, pulmonary mechanics and gas exchange, and cardiovascular variables. SETTING: University experimental research laboratory. SUBJECTS: Twenty-nine domestic swine. INTERVENTIONS: Anesthetized pigs were assigned randomly to undergo chest wall dissection alone or chest wall dissection and bilateral fractures of ribs with or without oleic acid-induced acute lung injury. MEASUREMENTS AND MAIN RESULTS: Gas exchange was evaluated by blood gas analysis and multiple inert gas elimination technique. After baseline data were collected, subsequent data were collected at 60 and 120 mins after experimental injuries, and at 180 mins, which was 60 mins after titration of CPAP therapy. The range of CPAP was 4-22 cm H2O. Shunt ([OV0312]a/[OV0422] < 0.005), venous admixture [OV0312]a/[OV0422] < 0.1), and functional deadspace ([OV0312]a/[OV0422] > 10) before injury were similar among all animals and ranged from 3.4% to 4.5%, 4.2% to 5.0%, and 54.4% to 56.5%, respectively. There were no changes, throughout the study, in lung regions with low [OV0312]a/[OV0422] (0.005 < [OV0312]a/[OV0422]

Effect of low isoflurane concentrations on the ventilation-perfusion distribution in injured canine lungs.

BACKGROUND: Rapid recovery and weaning from ventilatory support and cardiovascular stability are suggested advantages of isoflurane inhalation, in concentrations ranging from 0.1 to 0.6 vol%, for long-term sedation in mechanical ventilated patients. This study was designed to determine whether isoflurane in low concentrations impairs pulmonary gas exchange by increasing ventilation and perfusion (V(A)/Q) mismatch during lung injury. METHODS: Fourteen anesthetized dogs received in random order 0, 0.25, or 0.5 vol% end-tidal isoflurane before and after induction of lung injury with oleic acid. Gas exchange was assessed by blood gas analysis and by estimating the V(A)/Q distributions using the multiple inert gas elimination technique. RESULTS: Administration of oleic acid produced a lung injury with severe V(A)/Q mismatch and 38 +/- 4% intrapulmonary shunting of blood. During lung injury, isoflurane accounted for a dose-related increase in blood flow to shunt units from 38 +/- 4 to 42 +/- 3 (0.25 vol%) and 48 +/- 4% (0.5 vol%) (P < 0.05), dispersion pulmonary blood flow distribution from 0.94 +/- 0.07 to 1.01 +/- 0.09 (0.25 vol%) and 1.11 +/- 0.11% (0.5 vol%) (P < 0.05), and a decrease in perfusion of normal V(A)/Q units from 58 +/- 5 to 55 +/- 4 (0.25 vol%) and 50 +/- 4% (0.5 vol%) (P < 0.05) (mean +/- SE). Isoflurane decreased arterial oxygen partial pressure from 72 +/- 4 to 62 +/- 4 mmHg (0.25 vol%) and 56 +/- 4 mmHg (0.5 vol%) (P < 0.05) and oxygen delivery from 573 +/- 21 to 529 +/- 19 ml. kg. min (0.25 vol%) and 505 +/- 22 ml. kg. min (0.5 vol%) (P < 0.05). Gas exchange, perfusion of shunt and normal V(A)/Q units, and pulmonary blood flow distribution was similar in absence of lung injury with and without isoflurane. Isoflurane 0.5 vol% lowered cardiac output during all conditions (P < 0.05). CONCLUSIONS Inhalation of low concentrations of isoflurane contributed to increased V(A)/Q mismatch and decreased systemic blood flow and oxygen delivery in mechanically ventilated animals with injured lungs.