Lung aeration and pulmonary gas exchange during lumbar epidural anaesthesia and in the lithotomy position in elderly patients

Perioperative Pulmonary Atelectasis: Part II. Clinical Implications

The development of pulmonary atelectasis is common in the surgical patient. Pulmonary atelectasis can cause various degrees of gas exchange and respiratory mechanics impairment during and after surgery. In its most serious presentations, lung collapse could contribute to postoperative respiratory insufficiency, pneumonia, and worse overall clinical outcomes. A specific risk assessment is critical to allow clinicians to optimally choose the anesthetic technique, prepare appropriate monitoring, adapt the perioperative plan, and ensure the patient's safety. Bedside diagnosis and management have benefited from recent imaging advancements such as lung ultrasound and electrical impedance tomography, and monitoring such as esophageal manometry. Therapeutic management includes a broad range of interventions aimed at promoting lung recruitment. During general anesthesia, these strategies have consistently demonstrated their effectiveness in improving intraoperative oxygenation and respiratory compliance. Yet these same intraoperative strategies may fail to affect additional postoperative pulmonary outcomes. Specific attention to the postoperative period may be key for such outcome impact of lung expansion. Interventions such as noninvasive positive pressure ventilatory support may be beneficial in specific patients at high risk for pulmonary atelectasis (e.g., obese) or those with clinical presentations consistent with lung collapse (e.g., postoperative hypoxemia after abdominal and cardiothoracic surgeries). Preoperative interventions may open new opportunities to minimize perioperative lung collapse and prevent pulmonary complications. Knowledge of pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should provide the basis for current practice and help to stratify and match the intensity of selected interventions to clinical conditions.

[Hemodynamic and respiratory conditions of patients with obstetric fistulae operated under spinal anesthesia at the Regional Reference Hospital in Manakara, Madagascar]

L'objectif était d'évaluer les états hémodynamiques et respiratoires des opérées de fistules obstétricales et rapporter nos expériences sur la prise en charge de ces malades. Il s'agit d'une étude transversale descriptive effectuée au Bloc opératoire et Réanimation du CHRR Manakara allant du 20 au 30 aout 2013. Etaient incluses les patientes opérées de fistules obstétricales sous rachianesthésie. Nous avons exclu les patientes classées ASA >2 et celles ayant des tares cardio-vasculaires ou respiratoires. Après consultations préanesthésiques, et bilans préopératoires, nous avons administré chez les patientes 12,5mg de bupivacaïne adrénalinée 0,5% isobare en intrathécal. Elles étaient mises en position de Trendelenburg 5 minutes après l'injection du produit anesthésique et durant toute l'intervention. Le niveau sensitif, la pression artérielle, la fréquence cardiaque, la fréquence respiratoire et la saturation pulsée en oxygène (SpO2) étaient enregistrés pendant l'intervention. Nous avons retenues 57 malades. Le bloc sensitivomoteur était excellent pour toutes les malades. Un niveau métamérique supérieur à T6 était atteint chez 56,36% des malades. A part quelques épisodes d'hypertension artérielle et tachycardie, nous n'avons trouvé aucune difficulté respiratoire ni cardiovasculaire en rapport avec la position. Seuls, le niveau sensitif et la fréquence respiratoire présentaient une corrélation (p=0,01). Cette étude suggère que la position de Trendelenburg est réalisable au cours de la rachianesthésie en utilisant un produit anesthésique approprié, en faisant attention, notamment aux changements de position et en tenant compte de l'examen préanesthésique.

Mild loss of lung aeration augments stretch in healthy lung regions

Inspiratory stretch by mechanical ventilation worsens lung injury. However, it is not clear whether and how the ventilator damages lungs in the absence of preexisting injury. We hypothesized that subtle loss of lung aeration during general anesthesia regionally augments ventilation and distension of ventilated air spaces. In eight supine anesthetized and intubated rats, hyperpolarized gas MRI was performed after a recruitment maneuver following 1 h of volume-controlled ventilation with zero positive end-expiratory pressure (ZEEP), FiO2 0.5, and tidal volume 10 ml/kg, and after a second recruitment maneuver. Regional fractional ventilation (FV), apparent diffusion coefficient (ADC) of (3)He (a measurement of ventilated peripheral air space dimensions), and gas volume were measured in lung quadrants of ventral and dorsal regions of the lungs. In six additional rats, computed tomography (CT) images were obtained at each time point. Ventilation with ZEEP decreased total lung gas volume and increased both FV and ADC in all studied regions. Increases in FV were more evident in the dorsal slices. In each lung quadrant, higher ADC was predicted by lower gas volume and by increased mean values (and heterogeneity) of FV distribution. CT scans documented 10% loss of whole-lung aeration and increased density in the dorsal lung, but no macroscopic atelectasis. Loss of pulmonary gas at ZEEP increased fractional ventilation and inspiratory dimensions of ventilated peripheral air spaces. Such regional changes could help explain a propensity for mechanical ventilation to contribute to lung injury in previously uninjured lungs.

Effect of age on pulmonary gas exchange during laparoscopy in the Trendelenburg lithotomy position

BACKGROUND

Physiological changes in respiratory mechanics caused by aging may lead to a deterioration in pulmonary gas exchange, an increase in the alveolar-arterial oxygen gradient [(A-a)D(O2)] and a difference between the arterial carbon dioxide (CO(2)) tension (P(a)(CO(2))) and expired end-tidal CO(2) tension (P(ET)(CO(2))) [P((a-ET))(CO(2))] during laparoscopy in the Trendelenburg lithotomy position (TLP).

METHODS

The subjects were 51 gynecologic patients. Pressure-controlled ventilation was used to maintain P(ET)(CO(2)), measured by the side stream method, within the range 4-4.67 kPa. During laparoscopy with CO(2) insufflation in TLP, the tidal volume was increased to keep P(ET)(CO(2)) within +/- 20% of the pre-insufflation value. The subjects were divided into three groups by age: young group (< 45 years); middle-aged group (45-64 years); and elderly group ( > or = 65 years).

RESULTS

Before pneumoperitoneum (PPN), significant differences were found between the young and elderly groups in the arterial oxygen tension (P(a)(O(2))), (A-a)D(O(2)), P(a)(CO(2)) and P((a-ET))(CO(2)). In all groups, the peak inspiratory pressure and P(a)(CO(2)) increased progressively during PPN in TLP. P((a-ET))(CO(2)) increased gradually after starting CO(2) insufflation in TLP only in the elderly group.

CONCLUSIONS

An increase in P((a-ET))(CO(2)) was seen during PPN in TLP in the elderly group. With CO(2) insufflation in TLP, the setting of mechanical ventilation based on the value of P(ET)(CO(2)) (measured by the side stream method) should be determined with caution in elderly patients.

Non-invasive ventilation corrects alveolar hypoventilation during spinal anesthesia

PURPOSE

To document and explain the beneficial effects of non-invasive ventilation in correcting hypoxemia and hypoventilation in severe chronic obstructive pulmonary disease, during spinal anesthesia in the lithotomy position.

CLINICAL FEATURES

A morbidly obese patient with severe chronic obstructive pulmonary disease underwent prostate surgery in the lithotomy position under spinal anesthesia. Hypoxemia was encountered during surgery, and a profound decrease of forced vital capacity associated with alveolar hypoventilation and ventilation/perfusion mismatching were observed. In the operating room, an M-mode sonographic study of the right diaphragm was performed, which confirmed that after spinal anesthesia and assuming the lithotomy position, there was a large decrease (-30%) in diaphragmatic excursion. Hypoxemia and alveolar hypoventilation were successfully treated with non-invasive positive pressure ventilation.

CONCLUSIONS

Intraoperative application of non-invasive positive pressure ventilation improved diaphragmatic excursion and overall respiratory function, and reduced clinical discomfort in this patient.

Impact of spinal anaesthesia on peri-operative lung volumes in obese and morbidly obese female patients*

Although obesity predisposes to postoperative pulmonary complications, data on the relationship between body mass index (BMI) and peri-operative respiratory performance are limited. We prospectively studied the impact of spinal anaesthesia, obesity and vaginal surgery on lung volumes measured by spirometry in 28 patients with BMI 30-40 kg.m(-2) and in 13 patients with BMI > or = 40 kg.m(-2). Vital capacity, forced vital capacity, forced expiratory volume in 1 s, mid-expiratory and peak expiratory flows were measured during the pre-operative visit (baseline), after effective spinal anaesthesia with premedication, and after the operation at 20 min, 1 h, 2 h, and 3 h (after mobilisation). Spinal anaesthesia and premedication were associated with a significant decrease in spirometric parameters. Spinal anaesthesia and premedication were associated with a significant decrease in spirometric parameters; mean (SD) vital capacities were - 19% (6.4) in patients with BMI 30-40 kg.m(-2) and - 33% (9.0) in patients with BMI > 40 kg.m(-2). The decrease of lung volumes remained constant for 2 h, whereas 3 h after the operation and after mobilisation, spirometric parameters significantly improved in all patients. This study showed that both spinal anaesthesia and obesity significantly impaired peri-operative respiratory function.

Ventilation and metabolism during propofol anesthesia in rats

Many anesthetics are known to decrease ventilation (V(E)) and metabolic rate (MR). Because MR is known to contribute to the V(E) level, one would expect some parallelism between the changes in V(E) and MR during anesthesia. We tested this hypothesis in normoxia and hypoxia (12% O2) on male Wistar rats (n = 10; 221-288 g) by using a short-acting intravenous anesthetic, propofol. Propofol anesthesia was induced with a 7-7.5 mg kg(-1) (60-70 s) dose and maintained with a 20-22 mg kg(-1) h(-1) (<40 min) dose. In normoxia, propofol significantly decreased V(E) and MR and maintained the V(E)/MR ratio. In hypoxia, propofol decreased MR without a significant decrease in V(E), and the V(E)/MR ratio tended to increase. As a result, both in normoxia and hypoxia, propofol did not significantly increase the partial pressure of CO2 in arterial blood (PaCO2). Propofol was also associated with decreased body temperature and mean arterial pressure. The results suggest that during anesthesia, a large part of the drop in V(E) can be accounted for by the drop in MR, and that in both normoxia and hypoxia the V(E)/MR ratios and PaCO2values are maintained close to the levels of the conscious state.

Respiratory complications associated with anesthesia

Adverse pulmonary outcomes that follow anesthesia and surgery are often attributed to anesthesia care. PPCs are a significant concern for anesthesia caregivers because they use drugs and techniques that temporarily decrease lung volume, impair airway reflexes, limit immune function, and depress secretion mobilization. A significant component of perioperative risk derives from the surgical site, postoperative pain, and effects of pharmacologic pain management. Rapidly evolving surgical and anesthesia techniques and the introduction of newer pharmaceutical agents make it difficult to identify best practice from retrospective experience reported in the perioperative literature. Prospective studies that deal with specific patient populations, incomparable patient groups or techniques, and unique practice bias have limited validity of claims regarding several promising approaches to perioperative risk reduction. In the absence of clear scientific principles, a perioperative pulmonary risk management strategy for the early part of this century is based on the consensus practice of informed clinicians (Box 4).

Post-thoracotomy analgesia

Pain relief has come a long way in 20 years. Many aspects of the relief of pain of thoracic surgery must be rationalized and modernized to meet the demands placed on services and subject to new dynamics. To place the present state of practice and knowledge in the context of an anticipation that such attitudes will impact on and, ultimately, drive services for relief of pain, the key issues of safety, defining and measuring quality, and giving value for money must be addressed. Rationing is the impetus; the exercise to be conducted by those interested in the field of thoracic pain relief is to recognize that not all patients can have or require five-star services and gold standard techniques but are entitled to an equally high quality and measure of pain relief. Newer drugs, such as clonidine, ropivacaine, and modified local anesthetics, are on the horizon; old drugs, such as ketamine, are being revisited. Their place in the field will become apparent only if the ways that outcome measures are presented are more uniform and standard. Disaggregation analysis, pain profiling, a revisitiation of respiratory restoration factor, and optimization modeling are suggested ways forward to meet the clinical and organizationally holistic population forces being generated on the cusp of the third millennium. Increasingly, we live in a world defined by guidelines and protocols. The challenge is ensuring that these measure up to the watchwords--effective, safe, affordable.