Seth Manoach

Increasing ventilator surge capacity in disasters: ventilation of four adult-human-sized sheep on a single ventilator with a modified circuit.

OBJECTIVE Recent manmade and natural disasters have focused attention on the need to provide care to large groups of patients. Clinicians, ethicists, and public health officials have been particularly concerned about mechanical ventilator surge capacity and have suggested stock-piling ventilators, rationing, and providing manual ventilation. These possible solutions are complex and variously limited by legal, monetary, physical, and human capital restraints. We conducted a study to determine if a single mechanical ventilator can adequately ventilate four adult-human-sized sheep for 12h. METHODS We utilized a four-limbed ventilator circuit connected in parallel. Four 70-kg sheep were intubated, sedated, administered neuromuscular blockade and placed on a single ventilator for 12h. The initial ventilator settings were: synchronized intermittent mandatory ventilation with 100% oxygen at 16 breaths/min and tidal volume of 6 ml/kg combined sheep weight. Arterial blood gas, heart rate, and mean arterial pressure measurements were obtained from all four sheep at time zero and at pre-determined times over the course of 12h. RESULTS The ventilator and modified circuit successfully oxygenated and ventilated the four sheep for 12h. All sheep remained hemodynamically stable. CONCLUSION It is possible to ventilate four adult-human-sized sheep on a single ventilator for at least 12h. This technique has the potential to improve disaster preparedness by expanding local ventilator surge capacity until emergency supplies can be delivered from central stockpiles. Further research should be conducted on ventilating individuals with different lung compliances and on potential microbial cross-contamination.

Laryngoscopy force, visualization, and intubation failure in acute trauma: should we modify the practice of manual in-line stabilization?

CERVICAL spine stabilization during transport and general care reduced secondary neurologic injury from 10– 25% to 1–3%. This experience led airway managers to adopt manual in-line stabilization (MILS) during direct laryngoscopy (DL). Although MILS is intuitively appealing, there is, as Santoni et al. state in this issue of ANESTHESIOLOGY, “no objective evidence of benefit.” Substantial ethical and logistical hurdles stand in the way of a randomized controlled trial. The data presented by Santoni et al. combined with previously performed research suggest that no benefit would be found, even if a randomized controlled trial were performed. In contrast to transport and general care, DL mechanically displaces structures adjoining the cervical spine, which transfers force to the vertebrae. By fitting a size 3 Macintosh blade with miniature pressure transducers and employing a randomized crossover design, Santoni et al. demonstrate that MILS doubles the force that must be applied during intubation. That doubling of laryngoscopy force may be harmful is, like MILS, intuitively appealing. In fact, the cadaver study conducted by Lennarson et al. showed that application of MILS significantly increased subluxation at the site of complete ligamentous disruption, even though the intubators in that study obtained only “limited visualization . . . intended to produce the least cervical movement possible.” Santoni et al. provide a plausible explanation for the Lennarson group’s findings – the laryngoscopists in both studies needed to apply more pressure to overcome the effects of MILS, and the increased pressure caused greater subluxation in the cadaveric injury model. In practice, MILS probably has greater effects on the injury site than Lennarson’s group reported. Clinicians working under the trying circumstances of an acute trauma intubation are more likely than study participants to focus on successfully passing the tube and are less likely to focus on limiting the force they apply to the laryngoscope. Even with the important new data from Santoni et al., we doubt that clinicians will be eager to abandon or even modify MILS. During the past few decades, there have been few, if any, reliable reports of intubation causing secondary spinal cord injury, and MILS has been the standard of care. This record will not be easily dismissed because many clinicians share our concern that patients will be injured by any change in practice. The dilemma is ironic because the work of Santoni et al. and Lennarson et al. suggest that this fortunate history may be despite, and not because of, MILS. The paper by Santoni et al. raises another concern. As Nolan and Wilson and others have demonstrated, MILS degrades DL view. Santoni et al. observed this in six of nine patients who were successfully randomized. Although not designed to do so, the study illustrates how harmful view degradation can be. With MILS, anesthesiologists having an average of 19 yr experience could not intubate 3 of 10 fasted, stable patients screened to exclude predictors of difficult intubation. The first of these patients was not included in the study because the laryngoscopist obtained a grade four view with the modified Macintosh 3 blade and felt it necessary to use a size 4. One patient was esophageally intubated, and the third sustained a dental injury. These three incidents in this small study are remarkable because much trauma airway management is performed by clinicians with far less experience than the participating anesthesiologists. In addition, these intubation attempts were made under well-controlled circumstances, in contrast to many acute trauma intubations. Although trauma airway studies in academic centers demonstrate high success rates by anesthesia and emergency physicians, this work does not directly support MILS. These studies included penetrating trauma; although clinicians almost certainly used MILS in the blunt trauma cases, it is impossible to know how rigorously they applied the technique. One of these studies reported that 35% of the patients experienced complications, including hypoxia in 17%. The MILS-associated intubation failures observed by Santoni et al. probably explain a significant percentage of the hypoxic events. This is troubling because patients intubated with MILS are far more likely to have traumatic brain injury than unstable C-spine fractures, and SaO2 ! 90% predicts poor neurologic outcome. Technically, there are some important limitations to the work by Santoni et al. Because the group measured pressure directed against the anterior surface of a Macintosh blade, the intubators could not use external posteriorly directed pressure. Posterior pressure may improve view and increase intubation success in some patients, so this restriction could have resulted in the application This Editorial View accompanies the following article: Santoni BG, Hindman BJ, Puttlitz CM, Weeks JB, Johnson N, Maktabi MA, Todd MM: Manual in-line stabilization increases pressures applied by the laryngoscope blade during direct laryngoscopy and orotracheal intubation. ANESTHESIOLOGY 2008; 109:24–31. !

The Role of Transtracheal Jet Ventilation

Transcutaneous transtracheal jet ventilation (TTJV) is a minimally invasive ventilatory modality that uses a catheter to insufflate oxygen or air at high pressure (0.5–4.0 bar, or 8–60 psi) into the tracheal lumen. To perform TTJV, one can use an automatic jet ventilator or a manual trigger-activated device.