Activation procedures in the electroencephalograms of healthy and epileptic cats under propofol anaesthesia.

The current study evaluated the diagnostic value of electroencephalographic recordings (EEG) in cats with epilepsy under special consideration of photic stimulation and hyperventilation. EEGs in six healthy cats were recorded under light (mean dose of 0.23 mg/kg/min) and deep (mean dose of 0.7 mg/kg/min) propofol anaesthesia, whereas EEGs in 13 diseased cats were recorded under a propofol anaesthesia which was kept as light as possible (mean dose of 0.39 mg/kg/min). Paroxysmal discharges were detected in six of 13 cats suffering from seizures (two cats with idiopathic epilepsy and four cats with symptomatic epilepsy). Activation techniques did not enhance the diagnostic value of the EEGs. Photic driving was detected in one of six healthy cats under light, in five of six healthy cats under deep propofol anaesthesia and in 11 of 13 cats with seizures. Systematic use of activation techniques does not seem to increase the diagnostic yield of the recorded EEGs and should not be used in a clinical setting until future studies indicate value. Further investigations into the origin of photic driving under propofol anaesthesia are needed and could lead to the development of a reliable animal model to research into drug effects on the EEG.

Comparison of a sidestream capnograph and a mainstream capnograph in mechanically ventilated dogs.

OBJECTIVE: To compare the ability of a sidestream capnograph and a mainstream capnograph to measure end-tidal CO2 (ETCO2) and provide accurate estimates of PaCO2 in mechanically ventilated dogs. DESIGN: Randomized, double Latin square. ANIMALS: 6 healthy adult dogs. PROCEDURE: Anesthesia was induced and neuromuscular blockade achieved by IV administration of pancuronium bromide. Mechanical ventilation was used to induce conditions of standard ventilation, hyperventilation, and hypoventilation. While tidal volume was held constant, changes in minute volume ventilation and PaCO2 were made by changing the respiratory rate. Arterial blood gas analysis was performed and ETCO2 measurements were obtained by use of either a mainstream or a sidestream capnographic analyzer. RESULTS: A linear regression model and bias analysis were used to compare PaCO2 and ETCO2 measurements; ETCO2 measurements obtained by both capnographs correlated well with PaCO2. Compared with PaCO2, mainstream ETCO2 values differed by 3.15 +/- 4.89 mm Hg (mean bias +/- SD), whereas the bias observed with the sidestream ETCO2 system was significantly higher (5.65 +/- 5.57 mm Hg). Regardless of the device used to measure ETCO2, bias increased as PaCO2 exceeded 60 mm Hg. CONCLUSIONS AND CLINICAL RELEVANCE: RelevancehAlthough the mainstream cas slightly more accurate, both methods of ETCO2 measurement correlated well with PaCO2 and reflected changes in the ventilatory status. However, ETCO2 values > 45 mm Hg may inaccurately reflect the severity of hypoventilation as PaCO2 may be underestimated during conditions of hypercapnia (PaCO2 > 60 mm Hg).

Effect of instillation into lung of autologous blood on pulmonary function and tracheobronchial wash cytology.

This study aimed at measuring the functional consequences and the pulmonary cytology changes following a simulation of pulmonary haemorrhage. Pulmonary function tests including lobeline-induced hyperventilation, cytology of tracheo-bronchial wash (TBW) and thoracic radiographs were performed before, as well as 1, 7, 14 and 28 days after, the instillation of 300 ml of blood into the lungs of 4 horses deemed free of exercise-induced pulmonary haemorrhage (Group 1). Control data (Group 2) were obtained by instilling the same volume of saline into the lungs of the same horses in a crossover design (control). The instillation of blood or saline resulted in an increase in the number of neutrophils in the TBW. Thoracic radiographs showed increased opacity in the caudodorsal region of the lungs in 4/4 (Day 1) and 2/4 horses (Day 7), in Group 1, and in 2/4 (Day 1) and 0/4 horses (Day 7) in the control group. These changes were attributed to the instillation procedure rather than the nature of the instilled material. Breathing mechanics and arterial blood gases at rest were not affected in either Groups 1 or 2. However, the maximal expiratory peak flow recorded during lobeline-induced hyperventilation was significantly lower (P<0.05) and the total pulmonary resistance significantly higher (P<0.05) on Day 1 in Group 1, but not Group 2. These observations suggest that expiratory flows might be partly limited in bleeders when breathing at high airflow.

Hyperventilation and loss of hemolymph Na+ and Cl- in the freshwater amphipod Gammarus fossarum exposed to acid stress: a preliminary study.

The effect of acidification on the acid-sensitive species Gammarus fossarum was investigated in the laboratory. The results showed that as mortality increased, mean hemolymph chloride and sodium concentrations decreased rapidly. Concomitantly, organisms hyperventilated during the first 24 h and then started to hypoventilate. These results demonstrated that exposure to acid stress in the acid-sensitive species G. fossarum led to ion-regulatory and respiratory failure as previously reported in fish and crayfish exposed to acid stress.

Comparison of the performance of linear resistance and ultrasonic pneumotachometers at rest and during lobeline-induced hyperpnoea.

The performance of a Fleisch No. 5 pneumotachometer (F), and two commercial ultrasonic pneumotachometers, the BRDL (B) and the Spiroson (S) systems were compared in respect to their use for determination of ventilatory parameters at rest and during lobeline-induced hyperpnoea. Five clinically healthy Thoroughbred horses were tested with the three pneumotachometers in random order. Respiratory airflow, respired gas concentrations, oesophageal pressures, pressures within the mask systems and arterial blood gases were determined before and during lobeline-induced hyperpnoea. Because measured peak expiratory airflow rates exceeded the stated linear range of the Fleisch pneumotachometer ( approximately +/- 25 l s(-1)) differential pressure-flow curves were determined in vitro over the range of flows recorded in vivo. Expired flows greater than the linear range were corrected according to the derived regression equation. No differences in any of the measured variables among the three systems were present at rest. At peak ventilation of lobeline-induced hyperpnoea mask pressures [Delta P(mask)(mean (SEM)): F: 9.6 (2.8) cm H(2)O, B: 0.8 (0.4) cm H(2)O, S: 1.4 (0.8) cm H(2)O] and end tidal carbon dioxide [ ET CO(2)(mean (SEM)): F: 2. 6 (0.1)%, B: 2.1 (0.2)%, S: 2.1 (0.1)%] were significantly higher in system F. Despite a tendency for respiratory frequency and peak inspired and expired flows, to be lower with system F, no significant differences in the measurements of ventilatory mechanics were detected. In conclusion, the ultrasonic flowmeters pose significantly lower resistive loads onto the respiratory system during ventilation above resting levels than Fleisch No 5 pneumotachometers. However, at the flowrates achieved during lobeline-induced hyperpnoea an in vitro calibration of the differential pressure-flow relationship allows correction for expiratory alinearity in system F. In addition, the performance of the Spiroson flowmeter is accurate in determining ventilatory mechanics at rest and during lobeline-induced hyperpnoea.

Is there a significant gas exchange through the skin of the shrew Crocidura russula monacha?

Because of its small body mass, the shrew Crocidura russula monacha has a relatively high surface area to volume ratio, thin skin, and high thermal conductance compared with larger mammals. This study was aimed at examining the possibility that such a mammal may exhibit a significant skin gas exchange. Gas composition was measured in subcutaneous gas pockets. CO2 and O2 exchange through skin were measured both in vitro and in vivo. In 7-wk-old gas pockets, the steady-state PO2 and PCO2 values were 50 Torr (where 1 Torr = 133.322 Pa) and 35 Torr, respectively, compared with PO2 and Pco2 values of 73 Torr and 33 Torr, respectively, in 1-wk-old gas pockets. These changes are attributed to an increased capillary density and a decreased skin thickness after 7 wk. There was no significant gas exchange through skin during in vitro measurements. In vivo measurements indicated that O2 uptake was 0.5% and CO2 loss was 0.9% of total body metabolism at 20 degrees C. At 35 degrees C, skin O2 uptake and CO2 loss increased to 1.3% and 2.9%, respectively. These values are only part of the expected skin metabolism; thus, the rest must come from blood. Because gas exchange through the skin of this shrew is within the range of other mammals, the relatively low PCO2 and high PO2 in the gas pockets is better explained by the relative hyperventilation state exhibited by this shrew.

The effect of doxapram-induced hyperventilation on respiratory mechanics in horses.

To investigate the influence of increased respiratory frequency on respiratory mechanics in the horse, measurements were made in two groups of seven tracheostomized horses before and after the administration of doxapram. The horses in group I had normal base line values for respiratory mechanics, whereas the horses in group II had significantly lower values of dynamic compliance (Cdyn), higher respiratory resistance (R), and a higher total change in pleural pressure (delta P). The administration of 0.3 mg kg-1 doxapram intravenously resulted in a significant increase in respiratory frequency (fR), R, delta P, tidal volume (VT), and peak to peak respiratory flow (V), and a decrease in Cdyn in both groups of horses. The group II horses had significantly greater increases in R and delta P than the horses in group I.

[Non-invasive patient monitoring in veterinary medicine: pulse oximetry and capnography. II. Capnography]. / Nichtinvasive Patientenüberwachung in der Tiermedizin: Pulsoxymetrie und Kapnographie. Teil II: Kapnographie.

Capnography measures carbon dioxide concentration or partial pressure of the respiratory gas continuously and non-invasively. The endtidal value is of great diagnostic value, it corresponds approximately to the arterial value, except for ventilation-perfusion-mismatching (horse), shunting (horse), or increased dead-space-ventilation (panting in the dog). Capnography primarily serves for monitoring of spontaneous and artificial ventilation, it is a reliable method for detecting hypo- and hyperventilation. Because metabolism and circulation influence the amount of carbon dioxide eliminated in the lung, capnography monitors these functions too. The plotting of the carbon dioxide concentration as a carbon dioxide-time-diagram draws attention to malfunctions of the equipment. Technical problems of capnography depend on the design of the capnograph (main- or side-stream) used as well as on the weight of the patient. In the discussion the value of pulse oximetry and capnography in detection of critical events during anaesthesia is compared. Capnography is superior to pulse oximetry in the capability to detect critical events. But pulse oximetry complements capnography perfectly, both methods together give a good impression of the patient's state of health.

Effects of acute hyperventilation on serum potassium in the dog.

The effects of increasing respiratory rates on arterial pH, PaCO2, HCO3, and potassium (K) were measured in normal anesthetized dogs. Hyperventilation resulted in increased pH, decreased PaCO2, decreased HCO3, and decreased K compared with those parameters in spontaneously breathing dogs. The changes were related quantitatively: each 10 mmHg decrease in PaCO2 was associated with a pH increase of 0.1, a HCO3 decrease of 2.0 mEq/L, and a K decrease of 0.4 mEq/L. There were no cardiac arrhythmias or clinical signs of hypokalemia. After termination of hyperventilation, serum K was slower to return to control values than PaCO2. The ratio of the duration of hyperventilation to the time required for return of serum K to control was 0.67.

Atrio-ventricular block in a baboon (Papio ursinus).

Atrio-ventricular (A-V) block occurring in an anesthetized chacma baboon (Papio ursinus) is analysed. Hemodynamic, 12-lead electrocardiographical (ECG), hematological and biochemical parameters were monitored and data before and after block are compared. Though biochemical and other abnormal values were encountered, no conclusive evidence of the cause of the block was found.

Progesterone-induced hyperventilation in the guinea pig.

Progesterone-induced hyperventilation has thus far not been reported in animals other than humans. Accordingly we investigated the effects of chronic progesterone treatment on ventilation in guinea pigs. Virgin female guinea pigs were divided into those treated with cholesterol as controls (C), progesterone (P), or estrogen plus progesterone (E&P). All hormones were administered in silastic capsules placed subcutaneously for 28 days. On day 28 arterial blood gases and respiratory rates were determined. Arterial pH was elevated in P- and E&P-treated animals compared with controls (7.43 +/- 0.04 and 7.43 +/- 0.03 vs 7.39 +/- 0.05, respectively, P less than 0.05). Arterial PCO2 was reduced in both progesterone-treated groups compared to controls (33.9 +/- 5.8 (P), 33.1 +/- 2.8 (E&P), 38.0 +/- 4.3 (C)), and was correlated with systemic progesterone concentrations in animals receiving E&P (r = -0.85, P less than 0.01) but not in animals receiving P alone (r = -0.07, P = N.S.). Arterial [HCO-3], PO2 and respiratory rates were not different between groups. We conclude that chronic progesterone administration produces hyperventilation in guinea pigs, and that estrogen facilitates this action of progesterone.

Investigations of therapeutic measures for disophenol toxicosis in dogs.

Acute disophenol toxicosis, induced in 10 dogs by giving 33, 35, or 40 mg of disophenol/kg of body weight, was treated with the antipyretic dipyrone, lactated Ringer's infusions, or ice baths. Rectal temperature and estimates of hemoglobin concentration, packed cell volume, and total white blood cell count and differential count were recorded. Higher hemogram values were sometimes observed for dogs dying of the toxicosis. Toxicosis was induced in 5 other dogs which were not treated; 1 of these, given the low dose of disophenol, recovered. Two of 3 dogs (67%) treated with the antipyretic recovered, 0 of 2 (0%) given lactated Ringer's infusion recovered, and 2 of 5 dogs (40%) treated with ice baths recovered. One of the surviving dogs treated with antipyretic was given the low disophenol dose and all the other survivors were given the medium disophenol dosage level.