Transient effect of sudden mild hypoxia on respiration

Pulse oximetry as a fifth vital sign in emergency geriatric assessment

OBJECTIVE

To determine the utility of pulse oximetry as a routine fifth vital sign in emergency geriatric assessment.

METHODS

Prospective study using pulse oximetry to measure O2 saturation in geriatric patients presenting to ED triage. Saturation values were disclosed to clinicians only after they had completed medical evaluations and were ready to release or admit each patient. The authors measured changes in medical management and diagnoses initiated after the disclosure of pulse oximetry values. The study included 1,963 consecutive adults aged > or = 65 years presenting to triage at a university ED. Measurements included changes in select diagnostic tests: chest radiography, complete blood count (CBC), spirometry, arterial blood gases (ABGs), pulse oximetry, and ventilation-perfusion scans; treatments: antibiotics, beta-agonists, and supplemental O2; and hospital admission and final diagnoses that occurred after complete ED evaluation when physicians were informed of triage pulse oximetry values.

RESULTS

397 (20.2%) geriatric patients had triage pulse oximetry values <95%. Physicians ordered repeat oximetry for 51 patients, additional chest radiography for 23, CBC for 16, ABGs for 15, spirometry for 5, and ventilation-perfusion scans for none. Physicians ordered 49 new therapies for 44 patients, including antibiotics for 14, supplemental O2 for 29, and beta-agonists for 6. Nine patients initially scheduled for ED release were subsequently admitted to the hospital. Physicians changed or added diagnoses for 27 patients.

CONCLUSIONS

Using pulse oximetry as a routine fifth vital sign resulted in important changes in the diagnoses and treatments of a small proportion of emergency geriatric patients.

Pulse oximetry as a fifth pediatric vital sign

PURPOSE

To determine the utility of pulse oximetry as a routine fifth vital sign in acute pediatric assessment.

DESIGN

Prospective study using pulse oximetry to measure oxygen saturation in children presenting to emergency department triage. Saturation values were disclosed to clinicians only after they had completed medical evaluations and were ready to discharge or admit each child. We measured changes in medical treatment and diagnoses initiated after the disclosure of pulse oximetry values.

SETTING AND PARTICIPANTS

The study included 2127 consecutive children presenting to triage at a university emergency department.

MEASUREMENTS

Changes in select diagnostic tests: chest radiography, complete blood count, spirometry, arterial blood gases, pulse oximetry, and ventilation-perfusion scans; treatments: antibiotics, beta-agonists, supplemental oxygen; and hospital admission and final diagnoses that occurred after disclosure of triage pulse oximetry values.

RESULTS

Of 305 children having triage pulse oximetry values less than 95%, physicians ordered second oximetry for 49, additional chest radiography for 16, complete blood counts for 7, arterial blood gas measurements for 4, spirometry for 2, and ventilation-perfusion scans for 2. Physicians ordered 39 new therapies for 33 patients, including antibiotics for 15, supplemental oxygen for 11, and beta-agonists for 8. Five patients initially scheduled for hospital discharge were subsequently admitted. Physicians changed or added diagnoses in 25 patients.

CONCLUSIONS

Using pulse oximetry as a routine fifth vital sign resulted in important changes in the treatment of a small proportion of pediatric patients.

Effects of deep breaths on subsequent ventilation in man during rest and exercise

1. We examined the effects of twenty-four to thirty inspiratory capacity (IC), expiratory capacity (EC) and vital capacity (VC) breaths on subsequent breathing pattern in five normal subjects at rest. 2. During IC breaths and following EC and VC breaths at rest, end-tidal CO2 pressure (PET,CO2) fell by 7.5, 8.5 and 9.5 mmHg, respectively. In the group analysis significant inhibition of ventilation of 1.5 l min-1 was seen after the IC breath but not after EC or VC breaths. 3. We repeated the study with five normal subjects under conditions of higher ventilatory drive, namely 50 W exercise (one subject was common to both groups). 4. During exercise, the drop in PET,CO2 was smaller (4.0, 3.5 and 4.0 mmHg, respectively, with IC, EC and VC breaths) but ventilation was inhibited to a greater extent. Ventilatory undershoot was seen after all three types of deep breaths. 5. We propose that the expiration to residual volume in EC and VC breaths abolished the hypocapnic inhibition of ventilation at rest, possibly by a deflation reflex which was not sufficiently powerful to overcome the ventilatory undershoot during exercise. Our results also support the view that the slope of the CO2 response curve is steeper near the control point during exercise.

[The effect of halothane on blood gases and arterial acid-base equilibrium in intact rats and in chemo-denervated rats]

Halothane decreases the ventilatory response to hypoxia and the activity of peripheral arterial chemoreceptors, resulting in "chemical chemodenervation." In order to evaluate the role of this halothane-induced "chemical denervation" in acid-base and arterial blood gas changes, these values were measured in intact and chemodenervated rats, awake and under anaesthesia. Since the depth of anaesthesia could be modified by the anatomical chemodenervation, the ED50 of inspired halothane was determined in six rats before and after anatomical chemodenervation. To prevent haemodynamic changes due to halothane and/or anatomical chemodenervation from interfering with the results, systemic arterial blood pressure and heart rate were measured in six intact rats, awake and then anaesthetized, and in the same rats after chemodenervation, awake and then anaesthetized. In nine intact rats and in 19 chemodenervated rats, arterial pH, arterial bicarbonate concentration, and arterial blood gases (PaO2 and PaCO2) were measured before and after administration of halothane. Anatomical chemodenervation modified neither the inspired ED50 (1.1%), nor the mean arterial blood pressure or heart rate. The haemodynamic effects of halothane were comparable in intact and in chemodenervated rats. Changes in arterial blood gases and acid-base balance due to halothane in intact rats and due to chemodenervation in awake rats were not different, but there was a decrease in PaO2 and pHa, and an increase in PaCO2. In chemodenervated rats, halothane caused a further decrease in PaO2 and a further increase in PaCO2. The fact that halothane and anatomical chemodenervation have similar effects on arterial blood gases and acid-base balance favours a "chemical chemodenervating" action of halothane. However, the additional effects of halothane in the anatomically chemodenervated animal show that the action of halothane on blood gases and acid-base balance is the result of multiple sites of impact on the respiratory system.

Pattern of the ventilatory response to transient hypoxia in man: differences from transient hypercapnic test

The pattern of change in ventilatory variables after inhalation of pure N2 for two breaths was studied in normal children and adults. In six subjects the trends of change were compared to the ventilatory response to transient hypercapnia. We observed differences in the patterns of increasing ventilation with an initial abrupt increase of tidal volume for transient hypoxia and a progressive change for hypercapnia. In both cases respiratory frequency was progressively but unsystematically enhanced. A highly significant positive correlation was demonstrated between individual sensitivities to CO2 and O2, with a greater response to hypercapnia (5.6 time) than to hypoxia. Finally, a very short-latency decrease in expiratory duration occurred in the first breath after inhalation of hypercapnic mixture, supporting the recent data of Cunningham et al. (1977).

The control system regulating breathing in man

This review takes the regulation of breathing in man as an example of a highly developed and much studied control system in higher mammals.

Circulatory responses to graded stimulation of the carotid chemoreceptors in the dog

The vascular effects of graded stimulation of the carotid chemoreceptors were studied in 13 anesthetized and artificially ventilated dogs, and stimulus-response curves were defined. The carotid bifurcations were isolated and perfused at constant pressure, and the vagi were cut. Autologous blood collected in a reservoir was equilibrated at Po 2 varying from 104 to 34 mm Hg, Pco 2 from 39 to 81 mm Hg, and pH from 7.46 to 6.87 and was used to stimulate the carotid chemoreceptors. Systemic arterial Po 2 , Pco 2 , and pH were kept normal. Reflex increases in aortic blood pressure and in hind-limb perfusion pressure (constant-flow perfusion) were first seen with Po 2 of 70 mm Hg or Pco 2 > 39 mm Hg. The vascular responses increased linearly with lower Po 2 or higher Pco 2 , until tensions of 34 and 71 mm Hg, respectively, were reached. These stimuli caused a reflex dilatation of the perfused saphenous vein that was also proportional to the degree of stimulation. Increasing the pH of the blood perfusing the chemoreceptors decreased these changes by more than 50%; decreases in pH, with normal Po 2 and Pco 2 , caused marked vascular responses, indicating an important role of pH in the activation of the chemoreflex mechanism.