This retrospective cohort trial demonstrates an association between hyperchloremia and poor postoperative outcome. Additional studies are required to demonstrate a causal relationship between these variables.

Reconstruction of circumferential pharyngeal defects following total pharyngolaryngectomy presents major challenges with respect to surgical morbidity and restoration of functional deficits, which are often made more demanding by the increasing trend to utilize primary chemoradiation protocols with surgery reserved for salvage cases. The present review evaluates the reconstructive techniques described in the literature, including historical techniques as well as more recent innovative methods. Each technique is critically appraised with particular reference to postoperative morbidity and functional rehabilitation. Treatment recommendations are made based on the available evidence.

Accurate measurements of arterial P CO 2 (P a,CO 2 ) currently require blood sampling because the end-tidal P CO 2 (P ET,CO 2 ) of the expired gas often does not accurately reflect the mean alveolar P CO 2 and P a,CO 2 . Differences between P ET,CO 2 and P a,CO 2 result from regional inhomogeneities in perfusion and gas exchange. We hypothesized that breathing via a sequential gas delivery circuit would reduce these inhomogeneities sufficiently to allow accurate prediction of P a,CO 2 from P ET,CO 2 . We tested this hypothesis in five healthy middle-aged men by comparing their P ET,CO 2 values with P a,CO 2 values at various combinations of P ET,CO 2 (between 35 and 50 mmHg), P O 2 (between 70 and 300 mmHg), and breathing frequencies (f ; between 6 and 24 breaths min −1 ). Once each individual was in a steady state, P a,CO 2 was collected in duplicate by consecutive blood samples to assess its repeatability. The difference between P ET,CO 2 and average P a,CO 2 was 0.5 ± 1.7 mmHg (P = 0.53; 95% CI −2.8, 3.8 mmHg) whereas the mean difference between the two measurements of P a,CO 2 was −0.1 ± 1.6 mmHg (95% CI −3.7, 2.6 mmHg). Repeated measures ANOVAs revealed no significant differences between P ET,CO 2 and P a,CO 2 over the ranges of P O 2 , f and target P ET,CO 2 . We conclude that when breathing via a sequential gas delivery circuit, P ET,CO 2 provides as accurate a measurement of P a,CO 2 as the actual analysis of arterial blood. Accurate measurement of arterial P CO 2 (P a,CO 2 ) is important for the clinical assessment of patients and, in physiological studies, for the assessment of control of breathing and cerebral blood flow. Currently, the reference standard for measuring P a,CO 2 is analysis of arterial blood via direct arterial puncture. This invasive approach has a number of disadvantages for both the subject (discomfort and potential arterial wall damage) and investigator (restricted mobility of the catheter insertion site, cost, time delay for blood analysis, and limited temporal resolution of changes in P a,CO 2 ). As a result, investigators have long sought a suitable non-invasive method to measure P a,CO 2 .Non-invasive methods of predicting P a,CO 2 from alveolar P CO 2 (P A,CO 2 ) consider the lung to be a tonometer in which CO 2 equilibrates between alveolar gas and capillary blood. In reality, however, the lung is not a single homogeneous time-invariant gas exchange compartment. Rather, P CO 2 varies in different regions of the lung as a result of differences in ventilation-to-perfusion matching (V A /Q ) throughout the lung and, in each lung region, throughout the respiratory cycle (Dubois et al. 1952;Lenfant, 1967). The contribution to the P a,CO 2 of blood passing each alveolus reflects the average P CO 2 in that alveolus during the respiratory cycle (Jones et al. 1979;Robbins et al. 1990). P a,CO 2 , then, reflects the timeand flow-weighted averages of all alveolar ventilatory fluctuations in allV A /Q regions throughout the lung, i.e. the mean P A,CO 2 (Lenfant, 1967). As a result, the r...