The effect of oxygen breathing on shunt and ventilation-perfusion ratios (VA/Q) in anesthetized rats was studied using a modification of the multiple inert gas elimination technique. Base-line analyses showed hypoxemia in some animals breathing room air (arterial O2 tensions 48-70 Torr) associated with intrapulmonary shunts ranging from 0 to 22%, and variable low VA/Q lung regions as determined by calculation of the inert gas arterial-alveolar difference curve. Of nine rats that breathed 100% oxygen for 30 min, three showed increases in shunt (0% leads to 19%, 1.5% leads to 16%, 11% leads to 40%). These three animals had larger preexisting low VA/Q regions than the six that developed no shunt (0.48 +/- 0.15 vs. 0.17 +/- 0.03 (mean +/- SD); P less than 0.05). These data are compatible with the theory of absorption atelectasis. This study documents the usefulness of the inert gas elimination technique for studying pulmonary gas exchange problems in small animals.

The oxygen dissociation curve and Bohr effect were measured in normal whole blood as a function of carboxyhemoglobin concentration [HbCO]. pH was changed by varying CO2 concentration (CO2 Bohr effect) or by addition of isotonic NaOH or HCl at constant PCO2 (fixed acid Bohr effect). As [HbCO] varied through the range of 2, 25, 50, and 75%, P50 was 26.3, 18.0, 11.6, and 6.5 mmHg, respectively. CO2 Bohr effect was highest at low oxygen saturations. This effect did not change as [HbCO] was increased. However, as [HbCO] was increased from 2 to 75%, the fixed acid Bohr factor increased in magnitude from -0.20 to -0.80 at very low oxygen saturations. The effect of molecular CO2 binding (carbamino) on oxygen affinity was eliminated at high [HbCO]. These results are consistent with the initial binding of O2 or CO to the alpha-chain of hemoglobin. The results also suggest that heme-heme interaction is different for oxygen than for carbon monoxide.

Introduction: Declining rates of operative vaginal deliveries and routine episiotomy in obstetric practice, along with rising cesarean section rates, have decreased OB/GYN resident experience with episiotomy repair and obstetric anal sphincter injuries (OASIS). Simulation models are valuable educational tools in procedural training. Several models have been reported, each with its own limitations and benefits. Methods: We developed a 1-hour workshop to teach novice OB/GYN residents perineal laceration repair skills on a modified beef tongue model. The model required 5-10 minutes to assemble following written and video instruction, and learners had 30-50 minutes to practice using learner instructions. Learners were evaluated using a procedure checklist and global objective structured assessment of technical skills. To evaluate the session, we surveyed current faculty and residents, as well as residency graduates. Results: Between 2008 and 2017, an estimated 82 OB/GYN residents participated in this activity, and 95 participants and facilitators received the survey. Forty-one (59%) respondents agreed that this model was similar to repairing OASIS in clinical practice. Our trainees reported that the optimal time for simulated OASIS repair was the R2 and R3 years; however, 90% of respondents felt residents should be offered this simulation yearly. Discussion: Based on our survey of trainees, graduates, and faculty, we created a realistic simulated OASIS repair training, despite the limitation that the model lacked a rectum. Learners reported an interest in repeating the simulation frequently during residency to augment their clinical experience and increase perceived competence in third-and fourth-degree laceration repair by their graduation.

No abstract